Showing papers in "European Journal of Applied Physiology in 1997"

Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive upper-body movements.

Abstract: Although explosive power in lower-body movements has been extensively studied, there is a paucity of research examining such movements in the upper body. This study aimed to investigate the influence of load and the stretch shortening cycle (SSC) on the kinematics, kinetics, and muscle activation that occurs during maximal effort throws. A total of 17 male subjects performed SSC and concentric only (CO) bench throws using loads of 15%, 30%, 45%, 60%, 75%, 90% and 100% of their previously determined one repetition maximum bench press. The displacement, velocity, acceleration, force and power output as well as the electromyogram (EMG) from pectoralis major, anterior deltoid, and triceps brachii were recorded for each throw. The results were compared using multivariate analysis of variance with repeated measures. A criterion alpha level of P < or = 0.05 was used. Similar force velocity power relationships were determined for this multijoint upper-body movement as has been found for isolated muscles, single joint movements, and vertical jumping. The highest power output was produced at the 30% [563 (104) W] and 45% [560 (86) W] loads during the SSC throws. Force output increased as a function of load; however, even the lighter loads resulted in considerable force due to the high accelerations produced. Average velocity, average and peak force, and average and peak power output were significantly higher for the SSC throws compared to the CO throws. However, peak velocity and height thrown were not potentiated by performing the pre-stretch because the duration and range of movement allowed the ability of the muscle to generate force at high shortening velocities to dominate the resulting throw. As such, explosive movements involving longer concentric actions than experienced during brief SSC movements may be limited by the ability of the muscle to produce force during fast contraction velocities.

Effects of maximal effort strength training with different loads on dynamic strength, cross-sectional area, load-power and load-velocity relationships.

Abstract: The effects of maximal effort strength training with different loads on maximal strength, muscle cross-sectional area, the load-power and load-velocity relationship were investigated in the elbow flexors Physical education students were matched into three groups; G90 (n = 9) trained with a load of 90%, G35 (n = 11) with 35%, and G15 (n = 10) with 15% of 1RM (1 repetition maximum) Training consisted of three to five sets, performed three times a week for 9 weeks Each set consisted of two, seven and ten repetitions in G90, G35 and G15, respectively Training was performed with the nondominant arm, and the dominant arm served as control The 1RM increased 152 (SD 45)% (P < 0001) in G90, 101 (SD 59)% (P < 0001) in G35 and 66 (SD 79)% (P < 005) in G15 The increase in G90 was significantly larger than for G15 (P < 005) In the untrained arm, 1RM also increased for G90 and G15 In contrast to G90, G15 showed a similar increase in 1RM in both arms Cross-sectional area of the elbow flexors did not change for G90 and G15, while G35 increased 28% (P < 005) Maximal power and velocity were tested at 25 kg and at 15%, 25%, 35%, 50%, 70% and 90% of pretraining 1RM Power increased for all tested loads in G90 and G35, and G15 showed an increase in power at 15%, 25% and 50% of 1RM No significant differences in increase in power could be found among the three groups at loads equal to or less than 50%, but at 70% and 90% of 1RM the increase was larger for G90 and G35 than for G15 (P < 005) The G35 showed a similar increase in power at all loads tested whereas G90 showed load specificity in the effect of the training There was a correlation between 1RM and maximal power (r = 093, P < 00001), and between 1RM and power at load 25␣kg (r = 073, P < 00001) In conclusion, training with loads of 15% and 35% of 1RM resulted in an increase in 1RM Although the increase in maximal power after training at 90% of 1RM showed some load specificity, it also increased maximal power at 15% of 1RM Training at loads near maximal power output would seem to increase power efficiently over a wide load range The high correlation between 1RM and maximal power at load 25 kg also would indicate that maximal strength is important for performance at light loads

Analysis of the tonic vibration reflex: influence of vibration variables on motor unit synchronization and fatigue

Abstract: The influence of vibration frequency (40, 80, 100, 120, 150, or 200 Hz) at selected displacement amplitudes (0.2, 0.3 mm) on tonic vibration reflex (TVR) characteristics was investigated. The degree of synchronization of motor unit activity with vibratory stimuli in ten humans was determined using the electromyographic (EMG) activity of the finger and wrist flexor muscles when vibration was applied to the distal tendons of the hand flexor muscles. The EMG spectral analysis indicates that harmonic and subharmonic motor unit synchronization mechanisms contribute to the modulation of the amplitude of the TVR as the vibration frequency increases. Harmonic synchronization decreases while subharmonic synchronization increases as vibration frequency increases. It is suggested that the synchronization process influences muscle fatigue, since it forces the driving of motor units, leading to a decrease in contraction efficiency. This phenomenon most probably results from an impairment of excitation-contraction coupling. High-frequency vibration (>150 Hz) tends to induce less motor unit synchronization in a frequency range beyond the known mechanical resonance of biological tissues. The findings of this study may be applied to the design of hand-held power tools, since their vibration triggers the TVR in active muscles.

Efficacy of tourniquet ischemia for strength training with low resistance

Abstract: To investigate the efficacy of ischemia in strength training with low mechanical stress, tourniquet ischemia was utilized in low-resistance training. Five untrained subjects conducted one-legged isometric knee extension training with one leg ischemic (I-leg) and the other non-ischemic (NI-leg). Repeated isometric contractions for 2 s with 3 s relaxation in between were continued for 3 min and conducted 3 days/week for 4 weeks as training. Training resistance was 40% of maximal voluntary contraction (MVC) of respective leg and tourniquet ischemia was applied during I-leg training. MVC in I-leg after 2 weeks (9% gain) and 4 weeks (26% gain) were significantly higher than pre-training value (p < 0.05). A significant increase in maximal rate of torque development in I-leg was observed after 4 weeks (p < 0.05). On the contrary, there was no significant changes in either of the parameters in NI-leg. As a consequence, the differences between legs for both parameters were significant after 2 and 4 weeks (p < 0.05 or p < 0.01). The substantial gain in strength and maximal rate of torque development in I-leg demonstrated the efficacy of tourniquet ischemia during low-resistance training of short duration, and suggested the importance of neuromuscular and/or metabolic activity, other than high mechanical stress, to the adapting responses to strength training.

Posture control after prolonged exercise

Abstract: The perturbations of equilibrium after prolonged exercise were investigated by dynamic posturography on nine well-trained subjects (four athletes and five triathletes). A sensory organization test, where the platform and visual surround were either stable or referenced to the subject's sway with eyes open or closed, was performed before and after a 25-km run (average time 1h 44 min) by the nine subjects. In addition, the same test was performed on the five triathletes only, before and after ergocycle exercise of identical duration (i.e. ergocycle time = running time). The results showed that the ability to maintain postural stability during conflicting sensory conditions decreased after exercise, with some differences depending on the kind of exercise. Sensory analysis revealed that the subjects made less effective use of vestibular inputs after running than after cycling (P < 0.05). Adaptation to prolonged stimulation of proprioceptive, vestibular and visual inputs had probably occurred in the integrating centres during exercise. This adaptation was maintained during the recovery period and could explain the postexercise balance disorders. Other mechanisms such as impairment of motor efferents or haemodynamic changes should not be excluded.

A comparison of strength and muscle mass increases during resistance training in young women.

Abstract: Strength gains with resistance training are due to muscle hypertrophy and nervous system adaptations. The contribution of either factor may be related to the complexity of the exercise task used during training. The purpose of this investigation was to measure the degree to which muscle hypertrophy contributes to gains in strength during exercises of varying complexity. Nineteen young women resistance trained twice a week for 20 weeks, performing exercises designed to provide whole-body training. The lean mass of the trunk, legs and arms was measured by dual energy x-ray absorptiometry and compared to strength gains (measured as the 1-repetition maximum) in bench press, leg press and arm curl exercises, pre-, mid- (10 weeks) and post-training. No changes were found in a control group of ten women. For the exercise group, increases in bench press, leg press and arm curl strength were significant from pre- to mid-, and from mid- to post-training (P < 0.05). In contrast, increases in the lean mass of the body segments used in these exercises followed a different pattern. Increases in the lean mass of the arms were significant from pre- to mid-training, while increases in the lean mass of the trunk and legs were delayed and significant from mid- to post-training only (P < 0.05). It is concluded that a more prolonged neural adaptation related to the more complex bench and leg press movements may have delayed hypertrophy in the trunk and legs. With the simpler arm curl exercise, early gains in strength were accompanied by muscle hypertrophy and, presumably, a faster neural adaptation.

Neuromuscular fatigue and recovery in maximal compared to explosive strength loading

Abstract: The purpose of this study was to examine acute neuromuscular fatigue and its recovery in men (n = 8) and women (n = 8). Two strenuous, but clearly different exercises were compared: maximal (MSL) versus explosive strength loading (ESL). The MSL included five sets of ten repetition maximum bilateral leg extensions. The same task and the same number of sets was performed in ESL but with 40% from the load used in MSL and performed as explosively as possible. Isometric force-time curves were measured during maximal voluntary bilateral isometric action of the leg extensors before the fatigue loading and after each set. The measurements were repeated after resting for 1 h, 2 h, 1 day and two days. Surface elecromyogram (EMG) activity was recorded from the vastus lateralis, vastus medialis and rectus femoris muscles. Blood samples from the fingertips were also taken throughout the experiment to determine blood lactate concentration. Marked changes took place in both sexes in force production during both MSL and ESL but the overall decreases were greater and the recovery was slower after MSL. Pronounced decreases occurred also in maximal integrated EMG (iEMG). In the men, the decrease in iEMG for the early contraction phase (0–100 ms) during ESL was greater (P < 0.05) than that of MSL, whereas the decrease in iEMG in the peak force phase (500–1500 ms) was similar. As expected, the increase in blood lactate concentration was greater during MSL in both sexes. It was concluded that heavy resistance loading may result in considerable acute fatigue of central and peripheral origin. The reduced electrical activity in the muscles accompanied by an accumulation of blood lactate led to marked decreases in strength. Explosive type loading, especially in men, appeared to lead primarily to central fatigue with less involvement of peripheral fatigue than MSL. The women seemed unable to fatigue themselves as much as the men, particularly in ESL.

Effect of short-term creatine supplementation on renal responses in men

Abstract: There is an increasing utilisation of oral creatine (Cr) supplementation among athletes who hope to enhance their performance but it is not known if this ingestion has any detrimental effect on the kidney. Five healthy men ingested either a placebo or 20 g of creatine monohydrate per day for 5 consecutive days. Blood samples and urine collections were analysed for Cr and creatinine (Crn) determination after each experimental session. Total protein and albumin urine excretion rates were also determined. Oral Cr supplementation had a significant incremental impact on arterial content (3.7 fold) and urine excretion rate (90 fold) of this compound. In contrast, arterial and urine Crn values were not affected by the Cr ingestion. The glomerular filtration rate (Crn clearance) and the total protein and albumin excretion rates remained within the normal range. In conclusion, this investigation showed that short-term oral Cr supplementation does not appear to have any detrimental effect on the renal responses of healthy men.

Changes in the mechanical properties of human and amphibian muscle after eccentric exercise

Abstract: Following a series of eccentric contractions, that is stretching of the muscle while generating active tension, the length-tension relationship of isolated amphibian muscle has been shown to shift towards longer muscle lengths (Katz 1939; Wood et al. 1993). Here we report observations of electrically stimulated ankle extensor muscles of nine human subjects, demonstrating a similar shift in optimum angle for torque generation [3.9 (1.5)°] following exercise on an inclined treadmill that involved eccentric contractions in one leg. (All values are means with the SEMs in parentheses.) The shift in the unexercised, control leg was significantly less [mean 0.4 (0.7)°P < 0.05]. Correlated with this shift was a drop in torque [25.1 (5.6)% for the experimental leg; 1.6 (0.7)% for the control leg, P < 0.002]. Optimum angles returned to pre-exercise values by 2 days post-exercise, while torque took a week to recover. A similar shift in optimum length [12 (1.3)% of rest length] was obtained for five toad (Bufo marinus) sartorius muscles subjected to 25 eccentric contractions. Isometrically contracted control muscles showed a smaller shift [3.5 (1.6)%, n = 5]. Accompanying the shift was a drop in tension of 46 (3)% after the eccentric contractions [control isometric, 23 (6)%, P < 0.0001]. By 5 h after the eccentric contractions the shift had returned to control values, while tension had not recovered. When viewed with an electron microscope, sartorius muscles fixed immediately after the eccentric contractions exhibited many small, and a few larger, regions of myofilament disruption. In muscles fixed 5 h after the contractions, no small regions of disruption were visible, and the number of large regions was no greater than in those muscles fixed immediately after the eccentric contractions. These disruptions are interpreted as the cause of the shift in length-tension relationship.

Subjective, physiological and biomechanical responses to prolonged manual work performed standing on hard and soft surfaces

Abstract: The aim of this laboratory study was to examine the subjective, physiological and biomechanical responses to prolonged light repetitive manual work during standing on soft (polyurethane standard mat) and hard (aluminum casting) surfaces. The subjects stood on the hard (10 subjects) and on the soft surfaces (11 subjects) for 2 h. Intensity of unpleasantness, shank circumference, electromyograph (EMG) activities from the right soleus and tibialis anterior muscles, mean amplitude and total angular displacement around the left and right ankle in the saggital plane, centre of pressure (CoP) displacement in the frontal and saggital planes, calf surface temperature, and pain intensity in experimentally induced muscle pain were recorded. Maximal voluntary contraction and fatigue tests were performed before and after the 2 h experiment. Standing on a soft surface caused a lower intensity of unpleasantness. During standing on a hard surface compared to a soft one the results showed an enhanced swelling of the shank, an increased EMG activity (right soleus muscle) of the lower leg, a greater amplitude and total angular displacement, and a larger CoP displacement in the frontal plane. Indications of more pronounced muscle fatigue while standing on the hard surface were also noticed. After 105 min, experimental muscle pain was elicited by injecting hypertonic saline. The intensity of the induced pain was lower when standing on the soft surface. Amplitude, angular distance and CoP displacement showed a tendency to be greater after injection of the hypertonic saline. It was found that the experimentally induced pain influenced postural activity, underlining central interactions between proprioceptors and nociceptors. The results highlighted a higher feeling of comfort when standing on the soft surface. In addition, postural activity was lower when standing on the soft surface, but the activity was sufficient to prevent swelling of the lower legs.

Metabolic and performance adaptations to interval training in endurance-trained cyclists

Abstract: This study examined the effects of sustained high-intensity interval training (HIT) on the athletic performances and fuel utilisation of eight male endurance-trained cyclists. Before HIT, each subject undertook three baseline peak power output Wpeak tests and two simulated 40-km time-trial cycling performance (TT40) tests, of which the variabilities were 1.5 (1.3)% and 1.0 (0.5)%, respectively [mean (SD)]. Over 6 weeks, the cyclists then replaced 15 (2)% of their 300 (66) km.week-1 endurance training with 12 HIT sessions, each consisting of six to nine 5-min rides at 80% of Wpeak, separated by a l-min recovery. HIT increased Wpeak from 404 (40) to 424 (53) W (P < 0.01) and improved TT40 speeds from 42.0 (3.6) to 43.0 (4.2) km.h-1 (P < 0.05). Faster TT40 performances were due to increases in both the absolute work rates from 291 (43) to 327 (51) W (P < 0.05) and the relative work rates from 72.6 (5.3)% of pre-HIT Wpeak to 78.1 (2.8)% of post-HIT Wpeak (P < 0.05). HIT decreased carbohydrate (CHO) oxidation, plasma lactate concentration and ventilation when the cyclists rode at the same absolute work rates of 60, 70 and 80% of pre-HIT Wpeak (P < 0.05), but not when they exercised at the same relative (% post-HIT Wpeak) work rates. Thus, the ability of the cyclists to sustain higher percentages of Wpeak in TT40 performances after HIT was not due to lower rates of CHO oxidation. Higher relative work rates in the TT40 rides following HIT increased the estimated rates of CHO oxidation from approximately 4.3 to approximately 5.1 g.min-1.

Indices of skeletal muscle damage and connective tissue breakdown following eccentric muscle contractions.

Abstract: Indirect indices of exercise-induced human skeletal muscle damage and connective tissue breakdown were studied following a single bout of voluntary eccentric muscle contractions. Subjects (six female, two male), mean (SD) age 22 (2) years performed a bout of 50 maximum voluntary eccentric contractions of the knee extensors of a single leg. The eccentric exercise protocol induced muscle soreness (P < 0.05 Wilcoxon test), chronic force loss, and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio [P < 0.01, repeated measures analysis of variance (ANOVA)]. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities were elevated (P < 0.01, repeated measures ANOVA) following the bout. The mean (SD) CK and LDH levels recorded 3 days post-exercise were 2815 (4144) IU.l-1 and 375 (198) IU.l-1, respectively. Serum alkaline phosphatase activity showed no changes throughout the study, and a non-significant increase (P = 0.058, repeated measures ANOVA) in pyridinoline was recorded following the bout. Urinary hydroxyproline (HP) and hydroxylysine (HL) excretion, expressed in terms of creatinine (Cr) concentration, increased after exercise (P < 0.05 and P < 0.01, respectively, repeated measures ANOVA). An increased HP:Cr was recorded 2 days post-exercise and HL:Cr was increased above baseline on days 2, 5, and 9 post-exercise. This indirect evidence of exercise-induced muscle damage suggests that myofibre disruption was caused by the eccentric muscle contractions. Elevated urine concentrations of indirect indices of collagen breakdown following eccentric muscle contractions suggests an increased breakdown of connective tissue, possibly due to a localised inflammatory response.

Time-of-day effects in maximal anaerobic leg exercise.

Abstract: Time of day variations in maximal anaerobic leg exercise were studied in 23 men mean age 23 (SD 3) years. All the subjects performed two anaerobic tests (force-velocity and multi-jump tests) and those familiar with sprinting ran an additional 50-m dash (n=16). The maximal anaerobic powers for cycling and jumping (Pcycling and Pjump) and maximal anaerobic velocity (\(\)peak) were performed consecutively in the same order for all tests. The force-velocity and force-power relationships were established to determine Pcycling. The flight time (tf) and the ground contact time (tc) were recorded from five consecutive jumps on a jump-ergometer to calculate Pjump. The \(\)peak was measured between the 35th and the 45th m during the dash-run. The test schedules were at 0900, 1400 and 1800 hours on separate days in random order. Rectal temperatures (Tre) and body mass (mb) were measured before each test. The Tre increased significantly from 0900 to 1800 hours (P 0.05). The Pcycling and Pjump were higher at 1400 and 1800 hours than at 0900 hours. The differences between the morning and the afternoon reached 3% (P<0.05) for Pcycling and 5%–7% for Pjump (P<0.01). The time-of-day effect was significant for tf (P<0.05) but not for tc. During the dash-run tests, the differences almost reached significance for \(\)peak between 0900 and 1800 hours (P=0.0544). No significant variations were observed between 1400 and 1800 hours for cycling, jumping and running tests. A time-of-day effect in the maximal anaerobic power of cycle and multi-jump tests existed. Such variations would have pronounced effects when expressed in competitions.

Hypoxemia increases serum interleukin-6 in humans.

Abstract: Serum concentrations of interleukin (IL) 1 beta, IL-1 receptor antagonist (IL-1ra), IL-6, tumor necrosis factor (TNF) alpha, and C-reactive protein (CRP) were determined in ten healthy men at sea level and during four days of altitude hypoxia (4350m above sea level). The mean (SD) arterial blood oxygen saturations were 78.6 (7.3)%, 82.4 (4.9)%, and 83.4 (5.3)% in the first, second, and third days at altitude, respectively. A symptom score of acute mountain sickness (AMS) revealed that the subjects had mostly light symptoms of AMS. Mean serum IL-6 increased from 1.36 (1.04) pg x ml(-1) at sea level to 3.10 (1.65), 4.71 (2.81), and 3,54 (2.17) pg x ml(-1) during the first three days at altitude, and to 9.96 (8.90) pg x ml(-1) on the fourth day at altitude (ANOVA p = 0.002). No changes occurred in serum concentrations of IL-1 beta, IL-1ra, TNF alpha, or CRP. The serum IL-6 were related to SaO2, (r = -0.45, p = 0.003), but not to heart rates or AMS scores. In conclusion, human serum concentrations of IL-6 increased during altitude hypoxia whereas the other proinflammatory cytokines remained unchanged. The major role of IL-6 during altitude hypoxia seem not to be mediation of inflammation, instead, the role of IL-6 could be to stimulate the erythropoiesis at altitude.

Psychomotor performance during prolonged exercise above and below the blood lactate threshold.

Abstract: Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La−]b, and plasma catecholamine [CA]pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La−]b, and [CA]pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La−]b, and [CA]pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = − 0.651) and noradrenaline concentrations (r = − 0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La−]b and [CA]pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT.

Effects of contract-relax stretching training on muscle performance in athletes.

Abstract: The effects of an 8-week unilateral contract-relax (CR) stretching training program (passive stretch after isometric contraction) on muscular performance were investigated in a group of 16 athletes. The flexibility, maximum torque and angular position as well as contraction work in movements of the knee joint were determined before training and after 4 and 8 weeks of training. The torque measurements were performed under isokinetic conditions, eccentrically at angular velocities of 60° · s−1 and 120° · s−1, isometrically at five different joint positions, and concentrically at angular velocities of 60, 120, 180 and 240° · s−1 using an isokinetic dynamometer. A surface electromyogram (EMG) of the thigh muscles (quadriceps and hamstrings) was recorded simultaneously. As compared to untrained control limbs, significant improvements in active and passive flexibility (up to 6.3° in range of motion), maximum torque (up to 21.6%) and work (up to 12.9%) were observed, and these were especially pronounced under eccentric load conditions. A comparison between integrated EMG recordings during eccentric and concentric loads, as well as the interpretation of the training-induced changes in the EMG, suggest that muscular activity under eccentric loads may be impaired by mental processes.

The effects of antagonist moment on the resultant knee joint moment during isokinetic testing of the knee extensors

Abstract: The purpose of this study was to examine the effects of moment of antagonistic muscle on the resultant joint moment during isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee extension and flexion efforts on a Biodex dynamometer at 0.52 rad · s−1 (30° · s−1). Electromyographic (EMG) activity of vastus medialis and biceps femoris (hamstrings) was also recorded. The antagonistic moment of the hamstrings was determined by recording the integrated EMG (iEMG)/moment relationship at different levels of muscle effort. The iEMG/moment curves were fitted using second-degree polynomials. The polynomials were then used to predict the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92 Nm and 28.97 Nm under concentric and eccentric conditions respectively; paired t-tests indicated that this was a significant difference (P < 0.05). These results indicate that the resultant joint moment of knee extensors is the result of both agonist and antagonist muscle activation. The greater antagonist muscle activity under concentric activation conditions may be partly responsible for the lower resultant joint concentric moment of knee extensors compared with the corresponding eccentric activation. The antagonist moment significantly affects comparisons between the isokinetic moments and agonist EMG and in vitro force measurements under different testing (muscle action and angular velocity) conditions.

Arterial blood pressure and forearm vascular conductance responses to sustained and rhythmic isometric exercise and arterial occlusion in trained rock climbers and untrained sedentary subjects

Abstract: Cardiovascular responses to sustained and rhythmic (5 s on, 2 s off) forearm isometric exercise to fatigue at 40% maximal voluntary contraction (MVC) and to a period of arterial occlusion were investigated in elite rock climbers (CLIMB) as a trained population compared to non-climbing sedentary subjects (SED). Blood pressure (BP), monitored continuously by Finapres, and forearm blood flow, by venous occlusion plethysmography, were measured and used to calculate vascular conductance. During sustained exercise, times to fatigue were not different between CLIMB and SED. However, peak increases in systolic (S) BP were significantly lower in CLIMB [25 (13) mmHg; (3.3 (1.7) kPa] than in SED [48 (17) mmHg; (6.4 (2.3) kPa] (P < 0.05), with a similar trend for increases in diastolic (D) BP. Immediately after sustained exercise, forearm conductance was higher in CLIMB than SED (P < 0.05) for up to 2 min. During rhythmic exercise, times to fatigue were two fold longer in CLIMB than SED [853 (76) vs 420 (69) s, P < 0.05]. Increases in SBP were not different between groups except during the last quarter of exercise when they fell in CLIMB. Conductance both during and after rhythmic exercise was higher in CLIMB than in SED. Following a 10-min arterial occlusion, peak vascular conductance was significantly greater in CLIMB than SED [0.597 (0.084) vs 0.431 (0.035) ml x min(-1) x 100 ml(-1) x mmHg(-1); P < 0.05]. The attenuated BP response to sustained isometric exercise could be due in part to enhanced forearm vasodilatory capacity, which also supports greater endurance during rhythmic exercise by permitting greater functional hyperaemia in between contraction phases. Such adaptations would all facilitate the ability of rock climbers to perform their task of making repetitive sustained contractions.

Muscle performance and electromyogram activity of the lower leg muscles with different levels of cold exposure

Abstract: The purpose of this study was to evaluate the relationship between different levels of body cooling and muscle performance decrement and to study the motor co-ordination of the working agonist–antagonist muscle pair of the lower leg. Eight volunteer male subjects dropped from a 40-cm bench on to a force plate and performed a maximal rebound jump (stretch–shortening cycle). The jumps were performed after 60-min exposures to 27°C, 20°C, 15°C and 10°C. In comparison to those at 27°C, all the exposures to lower temperatures decreased the flight time of the jump, average force production and take-off velocity in a dose-dependent manner. The changes in electromyogram (EMG) activity also behaved in a dose-dependent manner. During preactivity and stretch phases the integrated EMG (iEMG) activity of the agonist muscle (triceps surae) increased due to cooling (at 10°C, P < 0.05). In contrast, during the shortening phase iEMG of the agonist muscle decreased due to cooling (at 15°C and 10°C, P < 0.05). Moreover, the activity of the antagonist muscle (tibialis anterior) increased due to cooling (at 15°C and 10°C, P < 0.01). The mean power frequency of the agonist muscle during the shortening phase was shifted from 124 (SEM 12) Hz (at 27°C) to 82 (SEM 7) Hz (at 10°C, P < 0.01). We concluded that there was a dose-dependent response between the degree of cooling and the amount of decrease in muscle performance as well as EMG activity changes. A relatively low level of cooling was sufficient to decrease muscle performance significantly.

The influence of prior cycling on biomechanical and cardiorespiratory response profiles during running in triathletes.

Abstract: The aim of the present study was to determine the effects of 40 km of cycling on the biomechanical and cardiorespiratory responses measured during the running segment of a classic triathlon, with particular emphasis on the time course of these responses. Seven male triathletes underwent four successive laboratory trials: (1) 40 km of cycling followed by a 10-km triathlon run (TR), (2) a 10-km control run (CR) at the same speed as TR, (3) an incremental treadmill test, and (4) an incremental cycle test. The following ventilatory data were collected every minute using an automated breath-by-breath system: pulmonary ventilation VE, l x min[-1]), oxygen uptake (VO2, ml x min(-1) x kg[-1]), carbon dioxide output (ml x min[-1]), respiratory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2), respiratory exchange ratio (R) respiratory frequency (f, breaths x min[-1]), and tidal volume (ml). Heart rate (HR, beats x min[-1]) was monitored using a telemetric system. Biomechanical variables included stride length (SL) and stride frequency (SF) recorded on a video tape. The results showed that the following variables were significantly higher (analysis of variance, P < 0.05) for TR than for CR: VO2 [51.7 (3.4) vs 48.3 (3.9) ml x kg(-1) x min(-1), respectively], VE [100.4 (1.4) l x min(-1) vs 84.4 (7.0) l x min(-1)], VE/VO2 [24.2 (2.6) vs 21.5 (2.7)] VE/VCO2 [25.2 (2.6) vs 22.4 (2.6)], f[55.8 (11.6) vs 49.0 (12.4) breaths x min(-1)] and HR [175 (7) vs 168 (9) beats x min(-1)]. Moreover, the time needed to reach steady-state was shorter for HR and VO2 (1 min and 2 min, respectively) and longer for VE (7 min). In contrast, the biomechanical parameters, i.e. SL and SF, remained unchanged throughout TR versus CR. We conclude that the first minutes of the run segment after cycling in an experimental triathlon were specific in terms of VO2 and cardiorespiratory variables, and nonspecific in terms of biomechanical variables.

Back extensor and psoas muscle cross-sectional area, prior physical training, and trunk muscle strength--a longitudinal study in adolescent girls

Abstract: The association between physical training, low back extensor (erector spinae plus multifidus muscles) and psoas muscle cross-sectional areas (CSA) and strength characteristics of trunk extension and flexion were studied in adolescent girls. A group of athletes (n=49) (age range 13.7–16.3 years) consisting of gymnasts, figure skaters and ballet dancers was age-matched with non-athletes (n=17) who acted as a sedentary control group. The CSA of psoas muscles and multifidus plus erector spinae muscles were measured from lumbar axial images by magnetic resonance imaging. Maximal trunk extension and flexion forces were measured in a standing position using a dynamometer and trunk musculature endurance was evaluated using static holding tests. When CSA were adjusted with body mass, the athletes showed significantly greater CSA in both muscles studied (psoas P < 0.001; erector spinae plus multifidus P < 0.05) than the non-athletes. The athletes also had a greater absolute psoas muscle CSA (P < 0.01) and trunk flexion force (P < 0.01) compared to the controls. When the forces were expressed relative to body mass, the athletes were superior both in trunk flexion (P < 0.001) and extension (P < 0.001). There was a significant correlation between muscle CSA and strength parameters, but the force per muscle CSA did not differ significantly between the athletes and the non-athletes. In addition, the athletes showed a better body mass adjusted muscle endurance in trunk flexion (P < 0.05) than the non-athletes. Our study indicated that regular physical training enhances trunk musculature hypertrophy, force and endurance in adolescent girls, and that there is an association between muscle CSA and strength parameters.

The impact of heat exposure and repeated exercise on circulating stress hormones

Abstract: To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age = 27.1 (3.0) years; maximal oxygen consumption, V˙O2max = 47.6 (6.2) ml · kg · min−1; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral (23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min bouts at ≈50% V˙O2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3 h (CS and HS conditions). Blood samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E = 393 (199) pmol · l−1 (CEx) vs 174 (85) pmol · l−1 (CS), NE = 4593 (2640) pmol · l−1 (CEx) vs 1548 (505) pmol · l−1 (CS), and hGH = 274 (340) pmol · l−1 (CEx)vs 64 (112) pmol · l−1 (CS). At 40°C, bout 1: E = 596 (346) pmol · l−1 (HEx) vs 323 (181) pmol · l−1 (HS), NE = 7789 (5129) pmol · l−1 (HEx) vs 1527 (605) pmol · l−1 (HS), and hGH = 453 (494) pmol · l−1 (HEx) vs 172 (355) pmol · l−1 (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx = 364 (168) nmol · l−1 vs HS = 295 (114) nmol · l−1). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat (P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress, with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones to heat exposure and repeated moderate exercise.

Reduced performance of male and female athletes at 580 m altitude.

Abstract: This study examined the effect of mild hypobaria (MH) on the peak oxygen consumption ( O2peak) and performance of ten trained male athletes [ (SEM); O2peak = 72.4 (2.2) ml · kg−1 · min−1] and ten trained female athletes [ O2peak = 60.8 (2.1) ml · kg−1 · min−1]. Subjects performed 5-min maximal work tests on a cycle ergometer within a hypobaric chamber at both normobaria (N, 99.33 kPa) and at MH (92.66 kPa), using a counter-balanced design. MH was equivalent to 580 m altitude. O2peak at MH decreased significantly compared with N in both men [− 5.9 (0.9)%] and women [− 3.7 (1.0)%]. Performance (total kJ) at MH was also reduced significantly in men [− 3.6 (0.8)%] and women [− 3.8 (1.2)%]. Arterial oxyhaemoglobin saturation (SaO2) at O2peak was significantly lower at MH compared with N in both men [90.1 (0.6)% versus 92.0 (0.6)%] and women [89.7 (3.1)% versus 92.1 (3.0)%]. While SaO2 at O2peak was not different between men and women, it was concluded that relative, rather than absolute, O2peak may be a more appropriate predictor of exercise-induced hypoxaemia. For men and women, it was calculated that 67–76% of the decrease in O2peak could be accounted for by a decrease in O2 delivery, which indicates that reduced O2 tension at mild altitude (580 m) leads to impairment of exercise performance in a maximal work bout lasting ≈ 5 min.

Trained versus untrained men: different immediate post-exercise responses of pituitary adrenal axis A preliminary study

Abstract: The hypothalamo-pituitary-adrenal axis is involved throughout the exercise-recovery cycle. Nevertheless, differences in hormone responses during early recovery between sedentary and endurance trained subjects are not well known. The aim of this preliminary study was to monitor plasma cortisol and adrenocorticotropic hormone (ACTH) concentrations both during and after the end of running exercise performed by four endurance trained adults (marathon men) compared to four sedentary subjects. Two parameters, i.e. intensity and duration, were changed on 4 consecutive days. The 1st day (D0) was spent in the laboratory: all blood samples were obtained at rest to determine diurnal variations of each hormone. On the following days (D1-D4) the subjects exercised: D1 and D2 brief (20 min), light (50% maximal heart rate HRmax, D1) or strenuous (80% HRmax, D2), D3 and D4 prolonged (120 min), light (D3) or strenuous (D4). In both groups, neither brief (D1, D2) nor prolonged light exercise (D3) induced any significant variation in plasma ACTH or cortisol concentrations. Plasma ACTH and cortisol concentrations increased only if the exercise was intense and prolonged (D4). The training factor did not modify the intensity or duration thresholds for the activation of the pituitary-adrenocortical response to exercise in the conditions of our experiment. However, during immediate recovery from the four exercise regimens, the plasma ACTH concentrations of the marathon men were constantly above the values of the sedentary subjects, although plasma cortisol concentration remained similar in both groups. As an indirect means of evaluating the relationships between ACTH and cortisol we compared the areas under the cortisol and ACTH curves (AUC) from 0.5 to 3.5 h during recovery from D1 to D4 compared to D0 at the same time. Cortisol AUC were similar in the sedentary subjects and marathon men although the ACTH AUC were different in the sedentary subjects and marathon men, suggesting a change in the pituitary-adrenal relationship at some yet indeterminate level. During the immediate recovery from exercise whatever its intensity, the magnitude of the ACTH response was increased in the trained subjects but with a reduced effect upon its target, the adrenal glands. This phenomenon has not been described in the literature. Two non-exclusive phenomena may be involved, i.e. a decreased adrenal sensitivity to ACTH stimulation, and/or a decreased hypothalamo-pituitary axis sensitivity to cortisol negative feedback.

Lumbar paraspinal muscle fatigability in repetitive isoinertial loading: EMG spectral indices, Borg scale and endurance time

Abstract: The purpose of this study was to develop a submaximal repetitive isoinertial back muscle endurance test by defining the relationships between the power spectral indices of paraspinal muscle electromyographic (EMG) activities, endurance time and a subjective estimate of fatigue (Borg scale). Bilateral surface EMG recordings were obtained over the lumbar paraspinal muscles in ten individuals who were currently free from back pain. All subjects performed repetitive upper trunk extensions (25 degrees flexion and 5 degrees extension, 30 repetitions per min), while movement below the third lumbar vertebral body was mechanically restricted. The load level depended upon upper body mass, sex, and age. The tests continued for as long as the subjects were able to maintain the required repetition rate (endurance time). Median (MF) and mean power frequency (MPF) slopes were calculated by performing a fast Fourier transformation after confirmation of EMG stationarity by recurrence quantification analysis. MF and MPF correlations with endurance time/Borg scale were measured for the first 60 s (0.60-0.88/0.42-0.86), the first 90 s (0.62-0.89/0.52-0.90), the first 120 s (0.50-0.76/0.41-0.73), and the entire repetitive run (0.63-0.88/0.54-0.90). To test for the reproducibility of the spectral indices EMGs were recorded for 2 min during repetitive loading from the same subjects on two consecutive days. Corresponding spectral slopes of MF and MPF were correlated at 60 s (0.36-0.93), 90 s (0.58-0.92), and 120 s (0.70-0.94) at the L3-L4 and L5-S1 levels, indicating good reproducibility of results from alternate recording sessions at the L5-S1 level. It is concluded that paraspinal muscle spectral indices (MF and MPF) measured before the onset of total muscle fatigue are good predictors of endurance time and are closely related to the subjective perception of fatigue.

Abdominal and hip flexor muscle activation during various training exercises.

Abstract: The purpose of this study was to provide objective information on the involvement of different abdominal and hip flexor muscles during various types of common training exercises used in rehabilitation and sport. Six healthy male subjects performed altogether 38 different static and dynamic training exercises trunk and hip flexion sit-ups, with various combinations of leg position and support, and bi- and unilateral leg lifts. Myoelectric activity was recorded with surface electrodes from the rectus abdominis, obliquus externus, obliquus internus, rectus femoris, and sartorius muscles and with indwelling fine-wire electrodes from the iliacus muscle. The mean electromyogram amplitude, normalised to the highest observed value, was compared between static and dynamic exercises separately. The hip flexors were highly activated only in exercises involving hip flexion, either lifting the whole upper body or the legs. In contrast, the abdominal muscles showed marked activation both during trunk and hip flexion sit-ups. In hip flexion sit-ups, flexed and supported legs increased hip flexor activation, whereas such modifications did not generally alter the activation level of the abdominals. Bilateral, but not unilateral, leg lifts required activation of abdominal muscles. In trunk flexion sit-ups an increased activation of the abdominal muscles was observed with increased flexion angle, whereas the opposite was true for hip flexion sit-ups. Bilateral leg lifts resulted in higher activity levels than hip flexion sit-ups for the iliacus and sartorius muscles, while the opposite was true for rectus femoris muscles. These data could serve as a basis for improving the design and specificity of test and training exercises.

The effect of body temperature on the hunting response of the middle finger skin temperature.

Abstract: The relationship between body temperature and the hunting response (intermittent supply of warm blood to cold exposed extremities) was quantified for nine subjects by immersing one hand in 8 degree C water while their body was either warm, cool or comfortable. Core and skin temperatures were manipulated by exposing the subjects to different ambient temperatures (30, 22, or 15 degrees C), by adjusting their clothing insulation (moderate, light, or none), and by drinking beverages at different temperatures (43, 37 and 0 degrees C). The middle finger temperature (Tfi) response was recorded, together with ear canal (Tear), rectal (Tre), and mean skin temperature (Tsk). The induced mean Tear changes were -0.34 (0.08) and +0.29 (0.03) degrees C following consumption of the cold and hot beverage, respectively. Tsk ranged from 26.7 to 34.5 degrees C during the tests. In the warm environment after a hot drink, the initial finger temperature (T(fi,base)) was 35.3 (0.4) degrees C, the minimum finger temperature during immersion (T(fi,min)) was 11.3 (0.5) degrees C, and 2.6 (0.4) hunting waves occurred in the 30-min immersion period. In the neutral condition (thermoneutral room and beverage) T(fi,base) was 32.1 (1.0) degrees C, T(fi,min) was 9.6 (0.3) degrees C, and 1.6 (0.2) waves occurred. In the cold environment after a cold drink, these values were 19.3 (0.9) degrees C, 8.7 (0.2) degrees C, and 0.8 (0.2) waves, respectively. A colder body induced a decrease in the magnitude and frequency of the hunting response. The total heat transferred from the hand to the water, as estimated by the area under the middle finger temperature curve, was also dependent upon the induced increase or decrease in Tear and Tsk. We conclude that the characteristics of the hunting temperature response curve of the finger are in part determined by core temperature and Tsk. Both T(fi,min) and the maximal finger temperature during immersion were higher when the core temperature was elevated; Tsk seemed to be an important determinant of the onset time of the cold-induced vasodilation response.

Specificity of resistance training responses in neck muscle size and strength

Abstract: This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific neck exercise), or CON (no training). Groups RESX (n = 8) and RES (n = 6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal to the 3 x 10 repetition maximum (RM). Group CON (n = 8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which all muscles of interest were visible. The 3 x 10 RM for the head extension exercise increased for RESX after training [from 17.9 (1.0) to 23.9 (1.4) kg, P < 0.05] but not for RES [from 17.6 (1.4) to 17.7 (1.9) kg] or CON [from 10.1 (2.2) to 10.3 (2.1) kg]. RESX showed an increase in total neck muscle CSA after training [from 19.5 (3.0) to 22.0 (3.6) cm2, P < 0.05], but RES and CON did not [from 19.6 (2.9) to 19.7 (2.9) cm2 and 17.0 (2.5) to 17.0 (2.4) cm2, respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of generalized neck muscle hypertrophy in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by MRI, increased by 7 (1)% after this short-term training (P < 0.05). The results suggest that: (1) the splenius capitis, and semispinalis capitis and cervicis muscles are mainly responsible for head extension; (2) short-term resistance training does not provide a sufficient stimulus to evoke neck muscle hypertrophy unless specific neck exercises are performed; and (3) the postural role of head extensors provides modest loading in bipeds.

Anaerobic contribution to the time to exhaustion at the minimal exercise intensity at which maximal oxygen uptake occurs in elite cyclists, kayakists and swimmers.

Abstract: Using 23 elite male athletes (8 cyclists, 7 kayakists, and 8 swimmers), the contribution of the anaerobic energy system to the time to exhaustion (t(lim)) at the minimal exercise intensity (speed or power) at which maximal oxygen uptake (VO2max) occurs (IVO2max) was assessed by analysing the relationship between the t(lim) and the accumulated oxygen deficit (AOD). After 10-min warming up at 60% of VO2max, the exercise intensity was increased so that each subject reached his IVO2max in 30 s and then continued at that level until he was exhausted. Pre-tests included a continuous incremental test with 2 min steps for determining the IVO2max and a series of 5-min submaximal intensities to collect the data that would allow the estimation of the energy expenditure at IVO2max. The AOD for the t(lim) exercise was calculated as the difference between the above estimation and the accumulated oxygen uptake. The mean percentage value of energy expenditure covered by anaerobic metabolism was 15.2 [(SD 6)%, range 8.9-24.1] with significant differences between swimmers and kayakists (16.8% vs 11.5%, P < or = 0.05) and cyclists and kayakists (16.4% vs 11.5%, P < or = 0.05). Absolute AOD values ranged from 26.4 ml.kg-1 to 83.6 ml.kg-1 with a mean value of 45.9 (SD 18) ml.kg-1. Considering all the subjects, the t(lim) was found to have a positive and significant correlation with AOD (r = 0.62, P < or = 0.05), and a negative and significant correlation with VO2max (r = -0.46, P < or = 0.05). The data would suggest that the contribution of anaerobic processes during exercise performed at IVO2max should not be ignored when t(lim) is used as a supplementary parameter to evaluate specific adaptation of athletes.

Myoelectric evidence of peripheral muscle fatigue during exercise in severe hypoxia: some references to m. vastus lateralis myosin heavy chain composition

Abstract: Integrated electromyography (iEMG) of the m. vastus lateralis was analysed during cycle ergometry in male subjects (n = 8). Two work trials were conducted, one under normoxia (N), the other under environmental normobaric hypoxia (EH in which the oxygen fraction in inspired gas = 0.116), each trial lasting 10 min. The absolute power output (180 W) was the same for both trials and was equivalent to 77 (4)% of maximum heart rate in trial N. Maximal voluntary isometric contractions were performed after each trial to assess changes in force, muscle fibre conduction velocity (MFCV), electromechanical delay (EMD), median frequency of EMG (MF) and maximal iEMG (iEMGmax). Biopy samples of muscle were obtained from the m. vastus medialis before testing. Myosin heavy chain (MHC) differences were determined through sodium dodecyl-polyacrylamide gel electrophoresis followed by densitometric analysis. No differences in submaximal iEMG were observed between EH and N trials during the first minute of work. At the end of both work trials iEMG was significantly elevated compared with starting values, however the iEMG recorded in EH exceeded N values by 15%. At the end of the EH trials the following were observed: a decrease in isometric force, MFCV and MF with an increase in EMD and the iEMGmax/force ratio. The iEMGmax was unchanged. No differences in any of these variables were observed after the N trial. Mean (SD) lactate concentrations following EH and N trials were 9.2 (4.4) mmol · 1−1 and 3.5 (1.1) mmol · 1−1, respectively. Results indicate that an increased motor unit recruitment and rate coding was needed in EH to maintain the required power output. The increased motor unit recruitment and rate coding were associated with myoelectric evidence of “peripheral” muscle fatigue. Subjects with higher compositions of type II MHC accumulated more lactate and displayed greater reductions in MF and MFCV during fatigue.