Showing papers in "European Journal of Applied Physiology in 2002"

Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones.

Abstract: Thirty-two untrained men [mean (SD) age 22.5 (5.8) years, height 178.3 (7.2) cm, body mass 77.8 (11.9) kg] participated in an 8-week progressive resistance-training program to investigate the "strength–endurance continuum". Subjects were divided into four groups: a low repetition group (Low Rep, n=9) performing 3–5 repetitions maximum (RM) for four sets of each exercise with 3 min rest between sets and exercises, an intermediate repetition group (Int Rep, n=11) performing 9–11 RM for three sets with 2 min rest, a high repetition group (High Rep, n=7) performing 20–28 RM for two sets with 1 min rest, and a non-exercising control group (Con, n=5). Three exercises (leg press, squat, and knee extension) were performed 2 days/week for the first 4 weeks and 3 days/week for the final 4 weeks. Maximal strength [one repetition maximum, 1RM), local muscular endurance (maximal number of repetitions performed with 60% of 1RM), and various cardiorespiratory parameters (e.g., maximum oxygen consumption, pulmonary ventilation, maximal aerobic power, time to exhaustion) were assessed at the beginning and end of the study. In addition, pre- and post-training muscle biopsy samples were analyzed for fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarization. Maximal strength improved significantly more for the Low Rep group compared to the other training groups, and the maximal number of repetitions at 60% 1RM improved the most for the High Rep group. In addition, maximal aerobic power and time to exhaustion significantly increased at the end of the study for only the High Rep group. All three major fiber types (types I, IIA, and IIB) hypertrophied for the Low Rep and Int Rep groups, whereas no significant increases were demonstrated for either the High Rep or Con groups. However, the percentage of type IIB fibers decreased, with a concomitant increase in IIAB fibers for all three resistance-trained groups. These fiber-type conversions were supported by a significant decrease in MHCIIb accompanied by a significant increase in MHCIIa. No significant changes in fiber-type composition were found in the control samples. Although all three training regimens resulted in similar fiber-type transformations (IIB to IIA), the low to intermediate repetition resistance-training programs induced a greater hypertrophic effect compared to the high repetition regimen. The High Rep group, however, appeared better adapted for submaximal, prolonged contractions, with significant increases after training in aerobic power and time to exhaustion. Thus, low and intermediate RM training appears to induce similar muscular adaptations, at least after short-term training in previously untrained subjects. Overall, however, these data demonstrate that both physical performance and the associated physiological adaptations are linked to the intensity and number of repetitions performed, and thus lend support to the "strength–endurance continuum".

Considerations for use of the Hoffmann reflex in exercise studies.

Abstract: There continues to be great interest in evaluating the adaptive plasticity of the human nervous system in response to exercise training or other interventions. For various reasons, researchers have been interested in estimates of spinal reflex processing in intact human subjects before and after training. A reflex pathway that has been employed in this regard is the Hoffmann (H) reflex. This brief review describes the basic procedure for evoking the H reflex in different muscles. Other sections address methodological issues that affect interpretation of the H reflex. In particular, the role that presynaptic inhibition serves in the modification of the H reflex and how this precludes its use as an unambiguous measure of alpha-motoneuron excitability will be discussed. Applications of the H reflex to study adaptive plasticity in humans is also reviewed, and methodological requirements that should be maintained for accurate interpretation of H reflexes in exercise studies are presented.

Norms and correlates of bioimpedance phase angle in healthy human subjects, hospitalized patients, and patients with liver cirrhosis

Abstract: This study investigates whether bioimpedance indexes rather than derived body compartments would be adequate for nutritional assessment. Evidence is provided that the phase angle as determined by conventional tetrapolar whole body bioelectrical impedance analysis at 50 kHz (1) was largely determined by the arms and legs and not the trunk, (2) was higher in control subjects than in hospitalized patients [mean (SD) 6.6 degrees (0.6) degrees vs 4.9 degrees (1.2) degrees, P<0.001], (3) discriminated poorly between cirrhotic patients of different Child-Pugh class, and (4) was positively correlated with muscle mass ( r=0.53) and muscle strength ( r=0.53) in these patients (each P<0.01). In a prospective study of patients with liver cirrhosis Kaplan-Meier and log rank analyses of survival curves demonstrated that patients with phase angles equal to or less than 5.4 degrees had shorter survival times than patients with higher phase angles [6.6 degrees (1.4) degrees ] and that phase angles less than 4.4 degrees were associated with even shorter survival times ( P<0.01). The prognostic roles of the phase angle and standard nutritional parameters such as total body potassium, anthropometric measurements, and impedance derived fat free mass, body cell mass and fat mass were evaluated separately by Cox regression which eliminated all variables except the phase angle as predictors of patient survival time ( P<0.01). We concluded that for the clinical assessment of patients the phase angle may be superior to commonly used body composition information.

Effects of resistance exercise combined with vascular occlusion on muscle function in athletes

Abstract: The effects of resistance exercise combined with vascular occlusion on muscle function were investigated in highly trained athletes. Elite rugby players (n = 17) took part in an 8 week study of exercise training of the knee extensor muscles, in which low-intensity [about 50% of one repetition maximum] exercise combined with an occlusion pressure of about 200 mmHg (LIO, n = 6), low-intensity exercise without the occlusion (LI, n = 6), and no exercise training (untrained control, n = 5) were included. The exercise in the LI group was of the same intensity and amount as in the LIO group. The LIO group showed a significantly larger increase in isokinetic knee extension torque than that in the other two groups (P < 0.05) at all the velocities studied. On the other hand, no significant difference was seen between LI and the control group. In the LIO group, the cross-sectional area of knee extensors increased significantly (P < 0.01), suggesting that the increase in knee extension strength was mainly caused by muscle hypertrophy. The dynamic endurance of knee extensors estimated from the decreases in mechanical work production and peak force after 50 repeated concentric contractions was also improved after LIO, whereas no significant change was observed in the LI and control groups. The results indicated that low-intensity resistance exercise causes, in almost fully trained athletes, increases in muscle size, strength and endurance, when combined with vascular occlusion.

Effects of long-term training specificity on maximal strength and power of the upper and lower extremities in athletes from different sports.

Abstract: Maximal concentric one repetition maximum half-squat (1RM(HS)), bench-press (1RM(BP)), power-load curves during concentric actions with loads ranging from 30% to 100% of 1RM(HS) and 1RM(BP)were examined in 70 male subjects divided into five groups: weightlifters (WL, n=11), handball players (HP, n=19), amateur road cyclists (RC, n=18), middle-distance runners (MDR, n=10) and age-matched control subjects (C, n=12). The 1RM(HS)values in WL, HP and RC were 50%, 29% and 28% greater, respectively, ( P<0.001-0.01) than those recorded for MDR and C. The half-squat average power outputs at all loads examined (from 30% to 100%) in WL and HP ( P<0.001 at 45% and 60% with HP) were higher ( P<0.05-0.001) than those in MDR, RC and C. Average power output at the load of 30% of 1RM(HS) in RC was higher ( P<0.05) than that recorded in MDR and C. Maximal power output was produced at the load of 60% for HP, MDR and C, and at the load of 45% for WL and RC. The 1RM(BP) in WL was larger ( P<0.05) than those recorded in HP, RC, MDR and C. In the bench press, average muscle power outputs in WL and HP were higher ( P<0.05-0.001) than those in MDR, RC and C, and were maximized at a load of 30% of 1RM for WL and HP, and at 45% for RC, MDR and C. In addition, the velocities that elicited the maximal power in the lower extremities were lower ( approximately 0.75 m.s(-1)) than those occurring in the upper extremities ( approximately 1 m.s(-1)). The data suggest that the magnitude of the sport-related differences in strength and/or muscle power output may be explained in part by differences in muscle cross-sectional area, fibre type distribution and in the muscle mechanics of the upper and lower limbs as well as by training background.

How anaerobic is the Wingate Anaerobic Test for humans

Abstract: The Wingate Anaerobic Test (WAnT) is generally used to evaluate anaerobic cycling performance, but knowledge of the metabolic profile of WAnT is limited. Therefore the energetics of WAnT was analysed with respect to working efficiency and performance. A group of 11 male subjects [mean (SD), age 21.6 (3.8) years, height 178.6 (6.6) cm, body mass 82.2 (12.1) kg] performed a maximal incremental exercise test and a WAnT. Lactic and alactic anaerobic energy outputs were calculated from net lactate production and the fast component of the kinetics of post-exercise oxygen uptake. Aerobic metabolism was determined from oxygen uptake during exercise. The WAnT mean power of 683 (96.0) W resulted from a total energy output above the value at rest of 128.1 (23.2) kJ·30 s–1 [mean metabolic power=4.3 (0.8) kW] corresponding to a working efficiency of 16.2 (1.6)%. The WAnT working efficiency was lower (P<0.01) than the corresponding value of 24.1 (1.7)% at 362 (41) W at the end of an incremental exercise test. During WAnT the fractions of the energy from aerobic, anaerobic alactic and lactic acid metabolism were 18.6 (2.5)%, 31.1 (4.6)%, and 50.3 (5.1)%, respectively. Energy from metabolism of anaerobic lactic acid explained 83% and 81% of the variance of WAnT peak and mean power, respectively. The results indicate firstly that WAnT requires the use of more anaerobically derived energy than previously estimated, secondly that anaerobic metabolism is dominated by glycolysis, thirdly that WAnT mechanical efficiency is lower than that found in aerobic exercise tests, and fourthly that the latter finding partly explains discrepancies between previously published and the present data about the metabolic profile of WAnT.

Acute effects of stretching on the neuromechanical properties of the triceps surae muscle complex.

Abstract: Previous research has shown that an acute bout of passive muscle stretching can diminish performance in certain movements where success is a function of maximal force and/or power output. Two possible mechanisms that might account for such findings are a change in active musculotendinous stiffness and a depression of muscle activation. To investigate the likelihood of these two mechanisms contributing to a post-stretch reduction in performance, we examined the acute effects of stretching on the active stiffness and muscle activation of the triceps surae muscle group during maximal single-joint jumps with movement restricted to the ankle joint. Ten males performed both static (SJ) and countermovement (CMJ) jumps before and after passively stretching the triceps surae. Electrical activity of the triceps surae during each jump was determined by integrating electromyographic recordings (IEMG) over the course of the movement. Triceps surae musculotendinous stiffness was calculated before and after stretching using a technique developed by Cavagna (1970). Following stretching, a significant decrease [mean (SD) 7.4 (1.9)%; P 0.05) change in jump height was found. A small but significant decrease [2.8 (1.24)%; P 0.05). It appears that an acute bout of stretching can impact negatively upon the performance of a single-joint CMJ, but it is unlikely that the mechanism responsible is a depression of muscle activation or a change in musculotendinous stiffness.

Maximal lactate steady state, critical power and EMG during cycling.

Abstract: We hypothesised that: (1) the maximal lactate steady state (MLSS), critical power (CP) and electromyographic fatigue threshold (EMG(FT)) occur at the same power output in cycling exercise, and (2) exercise above the power output at MLSS (P-MLSS) results in continued increases in oxygen uptake (VO(2)), blood lactate concentration ([La]) and integrated electromyogram (iEMG) with time. Eight healthy subjects [mean (SD) age 25 (3) years, body mass 72.1 (8.2) kg] performed a series of laboratory tests for the determination of MLSS, CP and EMG(FT). The CP was determined from four exhaustive trials of between 2 and 15 min duration. The MLSS was determined as the highest power output at which the increase in blood [La] was less than 1.0 mM across the last 20 min of a series of 30-min trials. The EMG(FT) was determined from four trials of 2 min duration at different power outputs. The surface electromyogram was recorded continuously from the vastus lateralis muscle. The CP was significantly higher than the P-MLSS [242 (25) vs. 222 (23) W; P<0.05], although the two variables were strongly correlated (r=0.95; P<0.01). The EMG(FT) could not be determined in 50% of the subjects. Blood [La], VO(2) and minute ventilation all increased significantly with time for exercise at power outputs above the P-MLSS. In conclusion, the P-MLSS, and not the CP, represents the upper limit of the heavy exercise domain in cycling. During exercise above the P-MLSS, there is no association between changes in iEMG and increases in VO(2) and blood [La] with time.

Determinants of 2,000 m rowing ergometer performance in elite rowers

Abstract: This study examined the physiological determinants of performance during rowing over 2,000 m on an ergometer in finalists from World Championship rowing or sculling competitions from all categories of competion rowing (19 male and 13 female heavyweight, 4 male and 5 female lightweight). Discontinuous incremental rowing to exhaustion established the blood lactate threshold, maximum oxygen consumption (VO(2max)) and power at VO(2max); five maximal strokes assessed maximal force, maximal power and stroke length. These results were compared to maximal speed during a 2,000 m ergometer time trial. The strongest correlations were for power at VO(2max), maximal power and maximal force (r=0.95; P<0.001). Correlations were also observed for VO(2max) (r=0.88, P<0.001) and oxygen consumption (VO(2)) at the blood lactate threshold (r=0.87, P=0.001). The physiological variables were included in a stepwise regression analysis to predict performance speed (metres per second). The resultant model included power at VO(2max), VO(2) at the blood lactate threshold, power at the 4 mmol x l(-1) concentration of blood lactate and maximal power which together explained 98% of the variance in the rowing performance over 2,000 m on an ergometer. The model was validated in 18 elite rowers, producing limits of agreement from -0.006 to 0.098 m x s(-1) for speed of rowing over 2,000 m on the ergometer, equivalent to times of -1.5 to 6.9 s (-0.41% to 1.85%). Together, power at VO(2max), VO(2) at the blood lactate threshold, power at 4 mmol x l(-1) blood lactate concentration and maximal power could be used to predict rowing performance.

Validity and reliability of three commercially available breath-by-breath respiratory systems

Abstract: Information concerning the validity and reliability of commercial on-line gas analysis systems is limited. The aim of this study was to provide a comparison of the validity and reliability of three on-line systems (Oxycon Alpha, Oxycon Pro and Pulmolab EX670) with that of Douglas bags. Two separate studies were conducted. In study 1, the three gas analysis systems were compared with Douglas bags using a metabolic simulator over four increases in ventilation. In study 2, ten subjects were split into equal groups exercising at 100 W or 150 W for 85 min on three separate occasions. Each system was used twice per visit. Study 1 demonstrated that the Oxycon Alpha and Douglas bags produced similar respiratory values over all levels of ventilation. The Oxycon Pro tended to slightly overestimate mean expiratory flow (V(E) ), oxygen uptake ( VO2), carbon dioxide production (VCO2) and respiratory exchange ratio (RER) at the higher ventilations. The Pulmolab produced large overestimations at all ventilations for and RER (up to 26.3% away from expectations), whilst values for, and were slightly underestimated at higher ventilations (up to 7.5% from expectations). The results of study 2 support the findings of study 1, with the Oxycon Pro and Oxycon Alpha producing similar results compared to Douglas bags for, and RER. The coefficients of variation for and measured using Douglas bags, Oxycon Pro and Oxycon Alpha were 3.3-5.1%, 4.7-7.0% and 4.5-6.3%, respectively, whilst that for the Pulmolab was highly variable (26.8-45.8%). The exercise study showed the Oxycon Pro and Oxycon Alpha to be both valid and reliable on-line systems for the measurement of parameters of respiration, at least at workloads up to 150 W.

Interaction between pre-landing activities and stiffness regulation of the knee joint musculoskeletal system in the drop jump: implications to performance.

Abstract: The purpose of the present study was to investigate the interaction between the pre-landing activities and the stiffness regulation of the knee joint musculoskeletal system and the takeoff speed during a drop jump (DJ) Nine healthy male subjects performed a DJ test from the height of 50 cm The surface electromyographic (EMG) activity of the vastus lateralis (VL) muscle was recorded to evaluate both the pre-landing and post-landing muscle activation levels Simultaneous recording of the jumping motion and ground reaction force was performed by a high-speed video camera (100 frames·s–1), and a force platform was employed to allow joint moment analysis Joint stiffness was calculated by a linear regression of the knee joint moment/angle relationship Elasticity of the knee extensor muscle during DJ was estimated by means of a four-element muscle model consisting of a parallel elastic component, a series elastic component (SEC), a viscous damper, and a contractile element DJ performance correlated positively with the positive peak power of the knee joint (P<001) and with the moment of the knee joint at the end of stretch (P<001) However, there was no significant relationship between DJ performance and the positive peak power of the ankle joint The knee joint moment at the end of stretch correlated with the SEC stiffness during the transmission phase from the end of the initial impact to the onset of the concentric action (P<001) and with the maximum rate of isometric force development of the knee extensors (P<001) Multiple regression analysis showed that the SEC stiffness during the transmission phase of the knee joint can be explained by a combination of the pre-activity of the VL muscle and the knee joint angular velocity at touchdown (F=576, P<005) These results seem to emphasize the functional significance of the pre-programmed activity for controlling the subsequent stiffness regulation and then contributing to the performance in DJ Thus, it can be suggested that the centrally pre-programmed activity and the associated elastic behavior of the SEC in the knee extensor muscle in conjunction with the muscle contractile property play a major role in regulating the performance in DJ

Effect of moderate exercise on salivary immunoglobulin A and infection risk in humans.

Abstract: The incidence of upper respiratory tract infections (URTI) and salivary immunoglobulin A concentrations [IgA(s)] of nine individuals were examined during 12 weeks of moderate exercise training, and compared to ten sedentary controls. Changes in maximal oxygen uptake were assessed at initial, mid-point and final evaluations (T1-3), while changes in [IgA(s)] and salivary immunoglobulin concentration-salivary albumin concentration ratio ([IgA(s)]:[Alb(s)]) were monitored at T1 and T3. During the 12 week period, symptoms of URTI were self-recorded daily. During the period of training the level of fitness significantly increased ( P<0.05) in the exercise group. The number of days recording symptoms of influenza, but not of cold, and total light URTI symptoms was significantly reduced in the exercise group during the last weeks of training. A significant increase in [IgA(s)] and in [IgA(s)]:[Alb(s)] was found in the exercise group after training. Both [IgA(s)] and [IgA(s)]:[Alb(s)] were significantly related to the number of days showing symptoms of influenza ( P<0.01) and the total number of days of sickness ( P<0.05). These data provide quantitative support for the belief that regular, moderate exercise results in an increased [IgA(s)] at rest and [IgA(s)]:[Alb(s)], which may contribute to a decreased risk of infection.

Relationship between shock attenuation and stride length during running at different velocities

Abstract: The purpose of the study was to investigate the characteristics of shock attenuation during high-speed running. Maximal running speed was identified for each subject [n=8 males, 25 (SD 4.6) years; 80 (8.9) kg; 1.79 (0.06) m] as the highest speed that could be sustained for about 20 s on a treadmill. During testing, light-weight accelerometers were securely mounted to the surface of the distal antero-medial aspect of the leg and frontal aspect of the forehead. Subjects completed running conditions of 50, 60, 70, 80, 90, and 100% of their maximal speeds with each condition lasting about 20 s. Stride length, stride frequency, leg and head peak impact acceleration were recorded from the acceleration profiles. Shock attenuation was analyzed by extracting specific sections of the acceleration profiles and calculating the ratio of head to leg power spectral densities across the 10–20 Hz frequency range. Both stride length and stride frequency increased across speeds (P<0.05) and were correlated with running speed (stride length r=0.92, stride frequency r=0.89). Shock attenuation increased about 20% per m·s–1 across speeds (P<0.05), which was similar to the 17% increase in stride length per m·s–1. Additionally, shock attenuation was correlated with stride length (r=0.71) but only moderately correlated with stride frequency (r=0.40) across speeds. It was concluded that shock attenuation increased linearly with running speed and running kinematic changes were characterized primarily by stride length changes. Furthermore, the change in shock attenuation was due to increased leg not head peak impact acceleration across running speeds.

Cross Education of Muscular Strength During Unilateral Resistance Training and Detraining

Abstract: The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 days·week–1 for 6 weeks using 3 sets of 10–12 repetitions at 70–75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P<0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining.

Standardising surface electromyogram recordings for assessment of activity and fatigue in the human upper trapezius muscle.

Abstract: The objectives of this work were to determine optimal surface electromyogram (EMG) electrode locations, and inter-electrode distance (IED), when assessing activity and fatigue in the human upper trapezius muscle. Surface EMG signals were recorded from the upper trapezius muscle of 11 healthy male subjects using a linear array of 16 surface electrodes. Five arm positions were investigated (arms at the side of the body, 45° and 90° flexion, 45° and 90° abduction). Fatiguing (1 kg hand load held for 3 min) and non-fatiguing (no load, 0.5 kg and 1 kg hand load held for 3 s) contractions were made. The variabilities of the average rectified value, root mean square, mean and median power spectral frequency and slope over time of these parameters as functions of electrode location and IED (from 5 mm over a range of 35 mm in steps of 5 mm) were quantitatively evaluated. A criterion for selecting the optimal electrode position was applied. This criterion indicated an optimal location measured from the acromion (38% of the distance from the lateral edge of acromion to the spine of the seventh cervical vertebra) which was statistically the same for all the EMG descriptors, arm positions and IED investigated. Finally, it was found that both EMG variables and indexes of muscle fatigue depended on IED which should thus be properly standardised. On the basis of the sensitivity of the EMG descriptors to electrode location and cross-talk reduction, an IED of 20 mm is suggested when a global analysis of activity in the upper trapezius muscle is made using a single pair of electrodes. This study emphasises that a surface EMG analysis of the upper trapezius muscle, following a proper placement of the electrodes and selection of IED, can give reliable indications of muscle activity and fatigue. Data on the myoelectric manifestations of muscle fatigue of the upper trapezius muscle are provided for the optimal electrode location.

Maximal strength-training effects on force-velocity and force-power relationships explain increases in aerobic performance in humans.

Abstract: Maximal strength-training with an emphasis on maximal mobilization during cross-country skiing increases exercise economy when double-poling. The aim of this experiment was to investigate whether the mechanism of this increase is a change in the force-velocity relationship and the mechanical power output. A group of 19 cross-country skiers having an average peak oxygen uptake of 255 ml·kg–0.67 body mass·min–1 or 61 ml·kg–1·min–1 were randomly assigned to either a high resistance-training group (n=10) or a control group (n=9). Upper body endurance was tested on a ski ergometer. The high-resistance-training group trained for 15 min on three occasions a week for 9 weeks. Training consisted of three series of five repetitions using 85% of one repetition maximum (1RM), with emphasis on high velocity in the concentric part of the movement. Upper body exercise economy, 1RM and time to exhaustion increased significantly in the high resistance-training group, but was unchanged in the control group. Peak power and the velocities for a given load increased significantly, except for the two lowest loads. We conclude that the increased exercise economy after a period of upper body high resistance-training can be partly explained by a specific change in the force-velocity relationship and the mechanical power output.

Differences in leg muscle activity during running and cycling in humans.

Abstract: Delta (Δ) efficiency is defined as the ratio of an increment in the external mechanical power output to the increase in metabolic power required to produce it. The purpose of the present study was to investigate whether differences in leg muscle activity between running and cycling can explain the observed difference in Δ efficiency between the two activities. A group of 11 subjects performed incremental submaximal running and cycling tests on successive days. The Δ efficiencies during running and cycling were based on five exercise stages. Electromyograph (EMG) measurements were made of three leg muscles (gastrocnemius, vastus lateralis and biceps femoris). Kendall's correlation coefficients between the mean EMG activity and the load applied were calculated for each muscle, for both running and cycling. As expected, the mean Δ efficiency during running (42%) was significantly greater than that during cycling (25%). For cycling, all muscles showed a significant correlation between mean EMG activity and the load applied. For running, however, only the gastrocnemius muscle showed a significant, but low correlation (r=0.33). The correlation coefficients of the vastus lateralis and biceps femoris muscles were not significantly different from 0. The results were interpreted as follows. In contrast to cycling, which includes only concentric contractions, during running up inclines eccentric muscle actions play an important role. With steeper inclines, more concentric contractions must be produced to overcome the external force, whereas the amount of eccentric muscle actions decreases. This change in the relative contribution of concentric and eccentric muscle actions, in combination with the fact that eccentric muscle actions require much less metabolic energy than concentric contractions, can explain the difference between the running and cycling Δ efficiency.

Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: implications for body mass management

Abstract: Studies have shown metabolism to remain elevated for hours following resistance exercise, but none have gone beyond 16 h, nor have they followed a whole body, high intensity exercise protocol. To examine the duration of excess post-exercise oxygen consumption (EPOC) following a period of heavy resistance exercise, seven healthy men [mean (SD) age 22 (3) years, height 177 (8) cm, mass 83 (10) kg, percentage body fat 10.4 (4.2)%] engaged in a 31 min period of resistance exercise, consisting of four circuits of bench press, power cleans, and squats. Each set was performed using the subject's own predetermined ten-repetition maximum and continued until failure. Oxygen consumption ( $$ \dot V{\rm O}_{\rm 2} $$ ) measurements were obtained at consistent times (34 h pre-, 29 h pre-, 24 h pre-, 10 h pre-, 5 h pre-, immediately post-, 14 h post-, 19 h post-, 24 h post-, 38 h post-, 43 h post-, and 48 h post-exercise). Post-exercise $$ \dot V{\rm O}_{\rm 2} $$ measurements were compared to the baseline measurements made at the same time of day. The $$ \dot V{\rm O}_{\rm 2} $$ was significantly elevated (P<0.05) above baseline values at immediately post, 14, 19, and 38 h post-exercise. Mean daily $$ \dot V{\rm O}_{\rm 2} $$ values for both post-exercise days were also significantly elevated above the mean value for the baseline day. These results suggest that EPOC duration following resistance exercise extends well beyond the previously reported duration of 16 h. The duration and magnitude of the EPOC observed in this study indicates the importance of future research to examine a possible role for high intensity resistance training in a weight management program for various populations.

The role of FFM accumulation and skeletal muscle architecture in powerlifting performance.

Abstract: The purpose of this study was to determine the distribution and architectural characteristics of skeletal muscle in elite powerlifters, and to investigate their relationship to fat-free mat (FFM) accumulation and powerlifting performance. Twenty elite male powerlifters (including four world and three US national champions) volunteered for this study. FFM, skeletal muscle distribution (muscle thickness at 13 anatomical sites), and isolated muscle thickness and fascicle pennation angle (PAN) of the triceps long-head (TL), vastus lateralis, and gastrocnemius medialis (MG) muscles were measured with B-mode ultrasound. Fascicle length (FAL) was calculated. Best lifting performance in the bench press (BP), squat lift (SQT), and dead lift (DL) was recorded from competition performance. Significant correlations (P≤0.01) were observed between muscle distribution (individual muscle thickness from 13 sites) and performance of the SQT (r=0.79 to r=0.91), BP (r=0.63 to r=0.85) and DL (r=0.70 to r=0.90). Subscapular muscle thickness was the single best predictor of powerlifting performance in each lift. Performance of the SQT, BP, and DL was strongly correlated with FFM and FFM relative to standing height (r=0.86 to 0.95, P≤0.001). FAL of the triceps long head and vastus lateralis were significantly correlated with FFM (r=0.59, P≤0.01; 0.63, P≤0.01, respectively) and performance of the SQT (r=0.45; r=0.50, respectively; P≤0.05), BP (r=0.52; r=0.56, respectively; P≤0.05), and DL (r=0.56; r=0.54, respectively; P≤0.01). A significant positive correlation was observed between isolated muscle thickness and PAN for triceps long-head (r=0.64, P≤0.01) and gastrocnemius medialis (r=0.48, P≤0.05) muscles, but not for vastus lateralis (r=0.35). PAN was negatively correlated with powerlifting performance. Our results indicate that powerlifting performance is a function of FFM and, therefore, may be limited by the ability to accumulate FFM. Additionally, muscle architecture appears to play an important role in powerlifting performance in that greater fascicle lengths are associated with greater FFM accumulation and powerlifting performance.

Validity of ultrasonograph muscle thickness measurements for estimating muscle volume of knee extensors in humans.

Abstract: This study aimed to investigate the suitability of using ultrasonograph muscle thickness (MT) measurements to estimate the muscle volume (MV) of the quadriceps femoris as an alternative approach to magnetic resonance imaging (MRI). The subjects were 46 men aged from 20 to 70 years who were randomly allocated to either a validation or a cross-validation group. In the validation group, multiple and simple regression equations, which used a set of MT values determined at mid-thigh and thigh length (1) and the product of pi, (MT/2)2, and l [pi x (MT/2)2 x l], respectively, as independent variables, were derived to estimate the MV measured by MRI. Because the two equations were cross-validated, the data from the two groups were pooled to generate the final prediction equations: MV (cm3)=(MT x 311.732)+(l x 53.346) -2058.529 as the multiple regression equation and MV (cm3) = [pi x (MT/ 2)2 x l] x 1.1176+663.040 as the simple regression equation. In the multiple regression equation, MT explained 75% of the variation in the MV measured by MRI. The r2 and the standard error of the estimate (SEE) of the equations were 0.824 and 175.6 cm3 (10.6%), respectively, for the multiple regression equation and 0.829 and 173.7 cm3 (10.5%), respectively, for the simple regression equation. Thus, the present results indicate that ultrasonograph MT measurements at mid-thigh are useful for estimating the MV of knee extensors. However, the observed SEE values suggest that the prediction equation obtained in this study may be limited to population studies rather than individual assessments in longitudinal studies.

Influence of time pressure and verbal provocation on physiological and psychological reactions during work with a computer mouse.

Abstract: The overall aim of this study was to investigate whether time pressure and verbal provocation has any effect on physiological and psychological reactions during work with a computer mouse. It was hypothesised that physiological reactions other than muscle activity (i.e. wrist movements, forces applied to the computer mouse) would not be affected when working under stressful conditions. Fifteen subjects (8 men and 7 women) participated, performing a standardised text-editing task under stress and control conditions. Blood pressure, heart rate, heart rate variability, electromyography, a force-sensing computer mouse and electrogoniometry were used to assess the physiological reactions of the subjects. Mood ratings and ratings of perceived exertion were used to assess their psychological reactions. The time pressure and verbal provocation (stress situation) resulted in increased physiological and psychological reactions compared with the two control situations. Heart rate, blood pressure and muscle activity in the first dorsal interosseus, right extensor digitorum and right trapezius muscles were greater in the stress situation. The peak forces applied to the button of the computer mouse and wrist movements were also affected by condition. Whether the increases in the physiological reactions were due to stress or increased speed/productivity during the stress situation is discussed. In conclusion, work with a computer mouse under time pressure and verbal provocation (stress conditions) led to increased physiological and psychological reactions compared to control conditions.

Resistance exercise training attenuates exercise-induced lipid peroxidation in the elderly.

Abstract: This study examined the effects of 6 months of resistance exercise (RX) on basal and post-aerobic exercise lipid peroxidation (LIPOX). Men and women [n = 62, mean (SD) age 68.4 (6) years] were divided randomly into either a control (n = 16, CON), low-intensity training [LEX n = 24; 50% one-repetition maximum (1RM), 13 repetitions/exercise], or high-intensity training (HEX n = 22, 80% 1RM, 8 repetitions/exercise) group. Pre- and post-training, subjects performed a graded aerobic exercise test (GXT). Blood samples were collected prior to and 10 min following each GXT. Subjects trained 3 times per week for 6 months using 12 RX machines. LIPOX was determined by measuring levels of thiobarbituric reactive acid substances (TBARS) and lipid hydroperoxides (PEROX). RX had no effect on resting LIPOX. Post-training, post-GXT TBARS were lower in the LEX and HEX groups by 14% and 18%, respectively, compared to CON (P < 0.05). Post-GXT PEROX levels were lower (P < 0.05) in LEX and HEX compared to CON [CON 3.51 (0.56) nmol/ml, LEX 2.89 (0.80) nmol/ml, HEX 2.99 (0.63) nmol/ml]. Serum total and non-protein (glutathione) thiols were higher in the LEX and HEX groups following training compared to CON (P < 0.05). These data suggest that RX can (1) reduce serum LIPOX, (2) provide protection against oxidizing agents in vitro, and (3) provide a "cross-protection" against the oxidative stress generated by aerobic exercise, perhaps mediated by improvements in the thiol portion of the antioxidant defense.

Carbohydrate loading in human muscle: an improved 1 day protocol

Abstract: It is generally acknowledged that even without a glycogen-depleting period of exercise, trained athletes can store maximal amounts of muscle glycogen if fed a carbohydrate-rich diet for 3 days. What has never been examined is whether under these conditions this many days are necessary for the content of muscle glycogen to attain these high levels. To examine this issue, eight endurance-trained male athletes were asked to eat 10 g.day(-1).kg(-1) body mass of high-carbohydrate foods having a high glycaemic index over 3 days, while remaining physically inactive. Muscle biopsies were taken prior to carbohydrate loading and after 1 and 3 days of eating the carbohydrate-rich diet. Muscle glycogen content increased significantly ( P<0.05) from pre-loading levels of [mean (SE)] 95 (5) to 180 (15) mmol.kg(-1) wet mass after only 1 day, and remained stable afterwards despite another 2 days of carbohydrate-rich diet. Densitometric analyses of muscle sections stained with periodic acid-Schiff not only supported these findings, but also indicated that only 1 day of high carbohydrate intake was required for glycogen stores to reach maximal levels in types I, IIa, and IIb muscle fibres. In conclusion, these findings showed that combining physical inactivity with a high intake of carbohydrate enables trained athletes to attain maximal muscle glycogen contents within only 24 h.

Oxygen uptake kinetics during treadmill running across exercise intensity domains.

Abstract: The purpose of the present study was to examine comprehensively the kinetics of oxygen uptake ( % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ ) during treadmill running across the moderate, heavy and severe exercise intensity domains. Nine subjects [mean (SD age, 27 (7) years; mass, 69.8 (9.0) kg; maximum % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ , % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYiabb2gaTjabbggaHjabbIha4bqa % baaaaa!3C8B! $$\dot V{\rm O}_{{\rm 2max}} $$ , 4,137 (697) ml·min–1] performed a series of "square-wave" rest-to-exercise transitions of 6 min duration at running speeds equivalent to 80% and 100% of the % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ at lactate threshold (LT; moderate exercise); and at 20%, 40%, 60%, 80% and 100% of the difference between the % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ at LT and % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYiabb2gaTjabbggaHjabbIha4bqa % baaaaa!3C8B! $$\dot V{\rm O}_{{\rm 2max}} $$ (Δ, heavy and severe exercise). Critical velocity (CV) was also determined using four maximal treadmill runs designed to result in exhaustion in 2–15 min. The % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ response was modelled using non-linear regression techniques. As expected, the amplitude of the % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ primary component increased with exercise intensity [from 1,868 (136) ml·min–1 at 80% LT to 3,296 (218) ml·min–1 at 100% Δ, P<0.05]. However, there was a non-significant trend for the "gain" of the primary component to decrease as exercise intensity increased [181 (7) ml·kg–1·km–1 at 80% LT to 160 (6) ml·kg–1·km–1 at 100% Δ]. The time constant of the primary component was not different between supra-LT running speeds (mean value range = 17.9–19.1 s), but was significantly shorter during the 80% LT trial [12.7 (1.4) s, P<0.05]. The % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ slow component increased with exercise intensity from 139 (39) ml·min–1 at 20% Δ to 487 (57) ml·min–1 at 80% Δ (P<0.05), but decreased to 317 (84) ml·min–1 during the 100% Δ trial (P<0.05). During both the 80% Δ and 100% Δ trials, the % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ at the end of exercise reached % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYiabb2gaTjabbggaHjabbIha4bqa % baaaaa!3C8B! $$\dot V{\rm O}_{{\rm 2max}} $$ [4,152 (242) ml·min–1 and 4,154 (114) ml·min–1, respectively]. Our results suggest that the "gain" of the primary component is not constant as exercise intensity increases across the moderate, heavy and severe domains of treadmill running. These intensity-dependent changes in the amplitudes and kinetics of the % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $$\dot V{\rm O}_{\rm 2} $$ response profiles may be associated with the changing patterns of muscle fibre recruitment that occur as exercise intensity increases.

Physiological responses during exercise to exhaustion at critical power.

Abstract: Critical power (CP) is a theoretical construct derived from a series of constant load tests to failure. Many studies have examined the methodological limitations of deriving CP, but few studies have examined the responses to exercise at CP in well-trained individuals. The purpose of the present study was to examine the physiological responses to exercise at CP. Seven male subjects [mean (SD) body mass 75.6 (6.4) kg, maximum oxygen uptake 4.6 (0.7) l min(-1)] performed three constant load tests to derive CP. Subjects then exercised at CP until volitional exhaustion. Heart rate, oxygen consumption and blood lactate concentration were measured throughout. Repeated measures analysis of variance revealed significant differences over time in heart rate 118 (24) to 177(5) beats min(-1), oxygen consumption 3.7 (0.6) to 4.1 (0.5) l min(-1)and blood lactate concentration 4.3 (1.8) to 6.5 (2.0) mM. All seven subjects completed 20 min of exercise with the range of time to failure at CP from 20 min 1 s to 40 min 37 s. Time to failure and maximum oxygen consumption were significantly correlated (r = 0.779, P < 0.05). We conclude, therefore, that CP does not represent a sustainable steady-state intensity of exercise.

Prolonged exercise, lymphocyte apoptosis and F2-isoprostanes.

Abstract: Exercise induces a post-exercise decline in the number of circulating lymphocytes. The aim of the present study was to investigate whether strenuous exercise induces lymphocyte apoptosis and generation of reactive oxygen species. Eleven healthy male subjects exercised for 2.5 h on a treadmill. Apoptotic lymphocytes were defined by being annexin positive and 7-aminoactinomycin-D negative. Measurement of F2-isoprostanes was used as a marker of oxidant stress in vivo. An increase (60%, P<0.05) in the percentage of apoptotic circulating lymphocytes was found 2 h post-exercise, whereas the total number of apoptotic cells did not change in relation to exercise. The concentration of plasma F2-isoprostanes increased approximately 1.6-fold in response to exercise, but declined towards pre-exercise values within the 1st h of recovery. The plasma concentrations of adrenaline, noradrenaline and cortisol increased during exercise. In conclusion, the results of the present study demonstrate that even in a study design in which high levels of apoptosis-inducing factors are generated, such as cortisol and isoprostanes, lymphocyte apoptosis does not contribute to post-exercise lymphocytopenia.

Measurement of human muscle volume using ultrasonography.

Abstract: The volume of the human tibialis anterior (TA) muscle was estimated in vivo by ultrasonography (ULT) and by magnetic resonance imaging (MRI) in six subjects In both methods, 11 axial scans were taken along the muscle belly, and the cross-sectional area of the muscle in each scan was digitised Muscle volume was calculated by treating the muscle as a series of truncated cones To assess the reproducibility of the ULT method, all subjects were scanned twice A high test-retest reliability was found ( R(2)=099), with the two ULT measurements being significantly correlated with each other ( P<005) The ULT and MRI methods gave similar results [mean (SD) ULT: 1332 (20) cm(3); MRI: 1318 (18) cm(3)] Nevertheless, a systematic bias of 333 cm(3) and a random error of 353 cm(3) were found when using the ULT method compared with the MRI method, which results in an error of -015% to 517% We conclude that the ULT method is a reproducible and valid method for the estimation of human muscle volume

Repeatability of surface EMG variables in the sternocleidomastoid and anterior scalene muscles

Abstract: In this study we examined the repeatability and reliability of the surface electromyographic (sEMG) signal mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) measured for the sternocleidomastoid (SCM) and the anterior scalene (AS) muscles in nine healthy volunteers during 15-s isometric cervical flexion contractions at 50% of the maximal voluntary contraction level over 3 non-consecutive days. Repeatability and reliability estimates were obtained for the initial values and rates of change of each sEMG variable by using both the Intraclass Correlation Coefficient (ICC) and the normalised standard error of the mean (nSEM). Results from SCM indicated good levels of repeatability for the initial value and slope of ARV (ICC>65%). For the AS, high levels of repeatability were identified for the initial value of MNF (ICC>70%) and the slope of ARV (ICC>75%). Values of nSEM in the range 2.8-7.2% were obtained for the initial values of MNF and CV for both SCM and AS, indicating clinically acceptable measurement precision. The low value obtained for the nSEM of the initial value of MNF for the AS, in combination with the high ICC, indicates that of all of the variables examined, this variable could offer the best normative index to distinguish between subjects with and without neck pain, and represents the sEMG variable of choice for future evaluation purposes.

Using skin temperature gradients or skin heat flux measurements to determine thresholds of vasoconstriction and vasodilatation.

Abstract: Forearm–fingertip skin temperature differentials (T sk-diff) are used to indicate vasomotor tone, vasoconstriction defined as having occurred when T sk-diff≥4°C (Sessler et al. 1987, 1988a, b). This study was conducted to determine whether T sk-diff or finger pad heat flux (HF) can be used to predict when vasoconstriction and vasodilatation occur. Seven subjects (one female) sat in water at [mean (SD)] 40.7 (0.8)°C until their core temperature (T c) increased by 1°C, ensuring vasodilatation. The water was then cooled [at a rate of 0.6 (0.1)°C.min–1] until T c fell to 0.5°C below pretesting values, causing vasoconstriction. Subjects were then rewarmed in water [41.2 (1.0)°C]. Skin blood flow (SkBF) was measured using laser Doppler flowmetry (LDF) on the left second finger pad [immersed in water at 10.4 (1.4)°C as part of another experiment], and infrared plethysmography on the third finger pad of both hands. T sk-diff and HF were measured on the right upper limb, which remained in air. When vasodilated, the subjects had a stable T sk-diff and HF. During cooling, rapid-onset vasoconstriction occurred coincidental with large gradient changes in HF and T sk-diff (inflection points). In two subjects the original vasoconstriction definition (T sk-diff≥4°C) was not attained, in the other five this was achieved 31–51 min after vasoconstriction. During rewarming, the T sk-diff and HF inflection points less accurately reflected the onset of vasodilatation, although with one exception they were within 5 min of the LDF changes. We conclude that T sk-diff and HF inflection points predict vasoconstriction accurately, and better than T sk-diff≥4°C.

Development of muscle fatigue as assessed by electromyography and mechanomyography during continuous and intermittent low-force contractions: effects of the feedback mode

Abstract: The goal of the present study was to investigate the significance of low-force continuous or intermittent static contraction and feedback mode (visual or proprioceptive) on the development of muscle fatigue as assessed by electromyography (EMG) and mechanomyography (MMG). Visual (force control) and proprioceptive (displacement control) feedback was investigated during intermittent (6 s contraction, 4 s rest) and continuous static contractions at 10% and 30% of the maximum voluntary contraction (MVC). Mean force, force fluctuation, rating of perceived exertion and root mean square (RMS) and mean power frequency (MPF) of the EMG and MMG signals were analysed. The general pattern for MMG RMS and EMG RMS values and the rating of perceived exertion was an increase with contraction time, while the EMG MPF values decreased ( P<0.05). The increase in RMS values was generally more pronounced for the MMG compared with the EMG, while the decrease in MPF values was more consistent for the EMG compared with the MMG signal. During the intermittent contractions, the main effect was on MPF for both EMG and MMG. Lower force fluctuation and larger rating of perceived exertion ( P<0.05), greater slopes of EMG and MMG RMS and MPF values versus time were observed with proprioceptive feedback compared with visual feedback. The findings suggest that (1) the EMG and MMG signals give complementary information about localised muscle fatigue at low-level contraction: they responded differently in terms of changes in the time and frequency domain during continuous contraction, while they responded in concert in the frequency domain during intermittent contractions, and (2) the different centrally mediated motor control strategies used during fatiguing contraction may be dependent upon the feedback modality.