Showing papers in "European Journal of Applied Physiology in 1993"

Gender differences in strength and muscle fiber characteristics.

Abstract: Strength and muscle characteristics were examined in biceps brachii and vastus lateralis of eight men and eight women. Measurements included motor unit number, size and activation and voluntary strength of the elbow flexors and knee extensors. Fiber areas and type were determined from needle biopsies and muscle areas by computerized tomographical scanning. The women were approximately 52% and 66% as strong as the men in the upper and lower body respectively. The men were also stronger relative to lean body mass. A significant correlation was found between strength and muscle cross-sectional area (CSA; P≤0.05). The women had 45, 41, 30 and 25% smaller muscle CSAs for the biceps brachii, total elbow flexors, vastus lateralis and total knee extensors respectively. The men had significantly larger type I fiber areas (4597 vs 3483 μm2) and mean fiber areas (6632 vs 3963 μm2) than the women in biceps brachii and significantly larger type II fiber areas (7700 vs 4040 μm2) and mean fiber areas (7070 vs 4290 μm2) in vastus lateralis. No significant gender difference was found in the strength to CSA ratio for elbow flexion or knee extension, in biceps fiber number (180 620 in men vs 156 872 in women), muscle area to fiber area ratio in the vastus lateralis 451 468 vs 465 007) or any motor unit characteristics. Data suggest that the greater strength of the men was due primarily to larger fibers. The greater gender difference in upper body strength can probably be attributed to the fact that women tend to have a lower proportion of their lean tissue distributed in the upper body. It is difficult to determine the extent to which the larger fibers in men represent a true biological difference rather that a difference in physical activity, but these data suggest that it is largely an innate gender difference.

The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle

Abstract: The effect of electrode position on the upper trapezius muscle on the myo-electric signal amplitude was investigated with special reference to arm position and estimate of force output. Previously, a depression of the electromyogram (EMG) signal has been reported midway between the seventh cervical vertebrae (C7) and acromion (Veiersted 1991, Eur J Appl Physiol 62:91–98) although this electrode position has been recommended (Zipp 1982, Eur J Appl Physiol 50:41–54). Ten healthy subjects performed maximal shoulder elevations with the arm in vertical, abducted and flexed positions and they performed a dynamic movement test. The myo-electric signal was recorded along the length of the right upper trapezius muscle by a 16-channel bipolar array electrode and was integrated with a 0.2-s time resolution. A region just lateral to the midpoint between C7 and the lateral edge of acromion was found with high and stable amplitudes (% coefficient of variation equalled 5.6). At the midpoint a dip in the amplitude profile appeared which was slightly displaced by arm abduction or flexion probably due to sliding, of the skin relative to the muscle. A linear EMG-force relationship was found in the region with high signal amplitudes, whereas the more lateral and the dip region showed highly variable EMG-force relationships. Thus, it was found that when using bipolar surface electrodes with an interelectrode distance of 2 cm a centre position 2 cm lateral to the midpoint between C7 and acromion provided good repeatability and high signal yield.

Noninvasive measurement of human forearm oxygen consumption by near infrared spectroscopy

Abstract: This study reported on the application of near infrared spectroscopy (NIRS) to noninvasive measurements of forearm brachio-radial muscle oxygen consumption (\(\dot V\)O2) and recovery time (tr) in untrained volunteers. Seven healthy subjects were submitted to four consecutive protocols involving measurements made at rest, the induction of an ischaemia, and during a maximal increase of metabolic demand achieved with and without vascular occlusion. Two isometric maximal voluntary contractions (MVC) of 30-s duration were executed with and without vascular occlusion and a 50% MVC lasting 125 s was also performed. The protocols were repeated on 2 different days. The results showed that, during vascular occlusion at rest, the time to 95% of the final haemoglobin (Hb) + myoglobin (Mb) desaturation value was independent of \(\dot V\)O2. The MVC, performed during vascular occlusion, caused complete Hb + Mb desaturation in 15–20 s, which was not followed by any further desaturation when the second contraction was performed. No difference was found between \(\dot V\)O2during MVC with and without vascular occlusion. A consistent difference was seen between \(\dot V\)O2measured during occlusion at rest and \(\dot V\)O2measured during MVC with and without occlusion. During prolonged exercise (125 s) Hb + Mb desaturation was maintained for the whole contraction period. The results of this study show that \(\dot V\)O2can be measured noninvasively by NIRS. The \(\dot V\)O2during MVC was very similar both in the presence and absence of blood flow limitation in most of the subjects tested. This would suggest that muscle \(\dot V\)O2might be accurately evaluated dynamically without cuff occlusion.

H-reflexes are smaller in dancers from The Royal Danish Ballet than in well-trained athletes.

Abstract: The size of the maximalH-reflex (Hmax) was measured at rest and expressed as a percentage of the maximalM-response (Mmax) in 17 untrained subjects, 27 moderately trained subjects, 19 well-trained subjects and 7 dancers from the Royal Danish Ballet TheHmax/Mmax was significantly larger in the moderately and well-trained subjects than in the untrained subjects but smaller in the ballet dancers It is therefore suggested that both the amount and the type of habitual activity may influence the excitability of spinal reflexes

Motor unit recruitment during prolonged isometric contractions

Abstract: Motor unit recruitment patterns were studied during prolonged isometric contraction using fine wire electrodes. Single motor unit potentials were recorded from the brachial biceps muscle of eight male subjects, during isometric endurance experiments conducted at relative workloads corresponding to 10% and 40% of maximal voluntary contraction (MVC), respectively. The recordings from the 10% MVC experiment demonstrated a characteristic time-dependent recruitment. As the contraction progressed both the mean number of motor unit spikes counted and the mean amplitude of the spikes increased significantly (P < 0.01). This progressive increase in spike activity was the result of a discontinuous process with periods of increasing and decreasing activity. The phenomenon in which newly recruited motor units replace previously active units is termed "motor unit rotation" and appeared to be an important characteristic of motor control during a prolonged low level contraction. In contrast to the 10% MVC experiment, there was no indication of de novo recruitment in the 40% MVC experiment. Near the point of exhaustion a marked change in action potential shape and duration dominated the recordings. These findings demonstrate a conspicuous difference in the patterns of motor unit recruitment during a 10% and a 40% MVC sustained contraction. It is suggested that there is a close relationship between intrinsic muscle properties and central nervous system recruitment strategies which is entirely different in fatiguing high and low level isometric contractions.

Does critical swimming velocity represent exercise intensity at maximal lactate steady state

Abstract: The purpose of this investigation was to determine whether the critical swimming velocity (ν crit), which is employed in competitive swimming, corresponds to the exercise intensity at maximal lactate steady state.ν crit is defined as the swimming velocity which could theoretically be maintained forever without exhaustion and expression as the slope of a regression line between swimming distances covered and the corresponding times. A total of eight swimmers were instructed to swim two different distances (200 m and 400 m) at maximal effort and the time taken to swim each distance was measured. In the present study,ν crit is calculated as the slope of the line connecting the two times required to swim 200 m and 400 m. vcrit determined by this new simple method was correlated significantly with swimming velocity at 4 mmol · 1−1 of blood lactate concentration (r = 0.914,P < 0.01) and mean velocity in the 400m freestyle (r = 0.977,P < 0.01). In the maximal lactate steady-state test, the subjects were instructed to swim 1600 m (4 x 400 m) freestyle at three constant velocities (98010, 100% and 102070 ofν crit). At 100%ν crit blood lactate concentration showed a steady-state level of approximately 3.2 mmol · 1− from the first to the third stage and at 98% ofν crit lactate concentration had a tendency to decrease significantly at the fourth stage. On the other hand, at 102% ofν crit, blood lactate concentration increased progressively and those of the third and fourth stages were significantly higher than those at 100% ofν crit (P<0.05). These data suggest thatν crit, which can be calculated by performing two timed, maximal effort swimming tests, may correspond to the exercise intensity at maximal lactate steady state.

Ergometric and metabolic adaptation to a 5-s sprint training programme

Abstract: The effects of 7 weeks of sprint training (repeated 5-s all-out sprints) on maximal power output (Wν, max) determined during a force-velocity test and a 30-s Wingate test (Wpeak) were studied in ten students [22 (SD 2) years] exercising on a cycle ergometer. Before and after training, muscle biopsies were taken from vastus lateralis muscle at rest for the ten subjects and immediately after a training session for five of them. Sprint training induced an improvement both in peak performances by 25% (Wν, max and Wpeak) and in the 30-s total work by 16%. Before sprint training, the velocity reached with no load (ν0) was related to the resting muscle phosphocreatine (PCr) stores (r=0.87, P < 0.001). The training-induced changes in ν0 were observed only when these PCr stores were lowest. This pointed to a possible limiting role of low PCr concentrations in the ability to reach a high velocity. The improvement in performances was linked to an increase in the energy production from anaerobic glycolysis. This result was suggested in muscle by the increase in lactate production measured after a training session associated with the 20% higher activity of both phosphofructokinase and lactate dehydrogenase. The sprint training also increased the proportion of slow twitch fibres closely related to the decrease in fast twitch b fibres. This result would appear to demonstrate an appropriate adaptive reaction following high-intensity intermittent training for the slow twitch fibres which exhibit a greater oxidative capacity.

Effect of antioxidant vitamin supplementation on muscle function after eccentric exercise

Abstract: This study investigated the effects of antioxidant vitamin supplementation upon muscle contractile function following eccentric exercise and was performed double blind. Twenty-four physically active young subjects ingested either placebo (400 mg; n = 8), vitamin E (400 mg; n=8) or vitamin C (400 mg; n = 8) for 21 days prior to and for 7 days after performing 60 min of box-stepping exercise. Contractile function of the triceps surae was assessed by the measurement of maximal voluntary contraction (MVC) and the ratio of the force generated at 20 Hz and 50 Hz tetanic stimulation before and after eccentric exercise and for 7 days during recovery. Following eccentric exercise, MVC decreased to 75 (4) % [mean (SE); n = 24; P < 0.05] of the preexercise values and the 20/50 Hz ratio of tetanic tension from 0.76 (0.01) to 0.49 (0.03) [mean (SE); n = 24; P<0.05). Compared to the placebo group no significant changes in MVC were observed immediately post-exercise, though recovery of MVC in the first 24 h post-exercise was greater in the group supplemented with vitamin C. The decrease in 20/50 Hz ratio of tetanic tension was significantly less (P < 0.05) post-exercise and in the initial phase of recovery in subjects supplemented with vitamin C but not with vitamin E. These data suggest that prior vitamin C supplementation may exert a protective effect against eccentric exercise-induced muscle damage.

Decreased salivary immunoglobulin A secretion rate after intense interval exercise in elite kayakers

Abstract: Endurance athletes have been shown to suffer a high incidence of upper respiratory tract infection (URTI; e.g. colds, sore throat) during intense training and after competition. Previous studies have shown that concentrations of secretory immunoglobulin A (IgA), the major effector of host defense against micro-organisms causing URTI, decrease after intense endurance exercise. Many athletes perform intense interval exercise as part of their normal training. The purpose of this study was to determine whether salivary IgA concentrations also decrease after intense interval exercise during the normal training regime in elite athletes. Timed saliva samples were obtained from eight elite male kayakers immediately before and after three on-water training sessions during a 3-week period. The concentrations of IgA, IgG and IgM were determined separately by enzyme-linked immunosorbent assay, and secretion rates calculated for each Ig. The IgA secretion rate (micrograms.min-1) decreased 27%-38% after all three training sessions (P = 0.007); the largest decrease (38%) was noted after the most intense session at the end of an especially intense week of training. The IgA concentration relative to total protein (micrograms.mg protein-1) was significantly lower (P < 0.05) on this training day compared with the other 2 days. Concentrations and secretion rates of IgG and IgM did not change after exercise, indicating a specific effect on IgA. These data would suggest that, in elite athletes, IgA concentration and secretion rate are reduced by intense interval exercise, and that exercise-induced changes in IgA output may be one mechanism contributing to URTI in elite athletes.

Differences in activation patterns in elbow flexor muscles during isometric, concentric and eccentric contractions

Abstract: To investigate the relative activation of the synergistic muscles during three different types of muscle contraction, the electromyograms (EMG) of two elbow flexor muscles, the biceps brachii (BB) and the brachioradialis (BR), have been compared. To accomplish this eight healthy human subjects performed the following elbow flexions against the same load — concentric, eccentric and isometric contractions. The isometric contractions were performed at three elbow angles: 10, 45 and 90° (0° equal to full expension). The EMG were recorded by bipolar surface electrodes, and the relative activation between the two muscles was evaluated as the quotient of mean EMG activities (BR/BB). For the isotonic elbow flexions, BR/BB were calculated at three angle divisions: 0–30°, 30–60° and 60–90°. Results indicated that the relative activation of the BR during the concentric contractions was higher than that of the eccentric contraction, particularly at the extended elbow angles, i.e. the BR/BB of the concentric contractions for the elbow joint angles ranging from 0–30° and 30–60° were significantly greater (P<0.05) than those of the eccentric contractions. During the isometric and eccentric contractions, the BR/BB at the flexed joint angles tended to be greater than those at the extended angles. In contrast, there were no angle-dependent BR/BB variations during the concentric elbow flexions. Further, changing patterns in the EMG power spectra due to the type of contraction were different between BB and BR. These results indicated that the activation pattern in the two elbow flexor muscles varied with the muscle contraction pattern.

Relationship of middle cerebral artery blood flow velocity to intensity during dynamic exercise in normal subjects

Abstract: Cerebral blood flow has been reported to increase during dynamic exercise, but whether this occurs in proportion to the intensity remains unsettled. We measured middle cerebral artery blood flow velocity (vm) by transcranial Doppler ultrasound in 14 healthy young adults, at rest and during dynamic exercise performed on a cycle ergometer at a intensity progressively increasing, by 50 W every 4 min until exhaustion. Arterial blood pressure, heart rate, end-tidal, partial pressure of carbon dioxide (PETCO2), oxygen uptake (VO2) and carbon dioxide output were determined at exercise intensity. Mean vM increased from 53 (SEM 2) cm.s-1 at rest to a maximum of 75 (SEM 4) cm.s-1 at 57% of the maximal attained VO2 (VO2max), and thereafter progressively decreased to 59 (SEM 4) cm.s-1 at VO2max. The respiratory exchange ratio (R) was 0.97 (SEM 0.01) at 57% of VO2max and 1.10 (SEM 0.01) at VO2max. The PETCO2 increased from 5.9 (SEM 0.2) kPa at rest to 7.4 (SEM 0.2) kPa at 57% of VO2max, and thereafter decreased to 5.9 (SEM 0.2) kPa at VO2max. Mean arterial pressure increased from 98 (SEM 1) mmHg (13.1 kPa) at rest to 116 (SEM 1) mmHg (15.5 kPa) at 90% of VO2max, and decreased slightly to 108 (SEM 1) mmHg (14.4 kPa) at VO2max. In all the subjects, the maximal value of vm was recorded at the highest attained exercise intensity below the anaerobic threshold (defined by R greater than 1). We concluded that cerebral blood flow as evaluated by middle cerebral artery flow velocity increased during dynamic exercise as a function of exercise intensity below the anaerobic threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic and anaerobic indices contributing to track endurance cycling performance.

Abstract: A group of 18 male high performance track endurance and sprint cyclists were assessed to provide a descriptive training season specific physiological profile, to examine the relationship between selected physiological and anthropometric variables and cycling performance in a 4000-m individual pursuit (IP4000) and to propose a functional model for predicting success in the IP4000. Anthropometric characteristics, absolute and relative measurements of maximal oxygen uptake (VO2max), blood lactate transition thresholds (Thla- and Th(an),i), VO2 kinetics, cycling economy and maximal accumulated oxygen deficit (MAOD) were assessed, with cyclists also performing a IP4000 under competition conditions. Peak post-competition blood lactate concentrations and acid-base values were measured. Although all corresponding indices of Thla- and Th(an),i occurred at significantly different intensities there were high intercorrelations between them (0.51-0.85). There was no significant difference in MAOD when assessed using a 2 or 5 min protocol (61.4 vs 60.2 ml.kg-1, respectively). The highest significant correlations were found among IP4000 and the following: VO2max (ml.kg-2/3.min-1; r = -0.79), power output at lactate threshold (Wthla) (W; r = -0.86), half time of VO2 response whilst cycling at 115% VO2max (s; r = 0.48) and MAOD when assessed using the 5 min protocol (ml.kg-1; r = -0.50). A stepwise multiple regression yielded the following equation, which had an r of 0.86 and a standard error of estimate of 5.7 s: IP4000 (s) = 462.9 - 0.366 x (Wthla) - 0.306 x (MAOD) - 0.438 x (VO2max) where Wthla is in W, MAOD is in ml.kg-1 and VO2max is in ml.kg-1 x min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Myo-electric fatigue manifestations revisited: power spectrum, conduction velocity, and amplitude of human elbow flexor muscles during isolated and repetitive endurance contractions at 30% maximal voluntary contraction

Abstract: A brief survey of the literature on manifestations of myo-electric fatigue has disclosed a surprisingly sharp conflict between early studies, focusing on neuromotor regulatory mechanisms, and more recent studies which stress the determinant influence of local metabolism and skewed homeostasis Favoured explanations concerning changes in the electromyographic (EMG) spectrum were synchronization/grouping of motor unit (MU) firing and conduction velocity (CV) decreases of the action potential propagation The notion of mutual exclusivity interwoven with these theories prompted us to reinvestigate the EMG of moderate level, static endurance contraction Ten men in their twenties performed isometric elbow flexion (elbow angle 135°) at 30%6 maximal voluntary contraction (MVC), and the surface EMG of the brachioradialis (BR) and biceps brachii (BB) muscles was recorded Initially the CV — determined by cross-correlation — was 43 m · s−1 (BR) and 46 m · s−1 (BB) At exhaustion the CV of the BR muscle had declined by 33%, roughly twice the decrease of the BB CV Substantially larger relative median frequency (fm) reductions of 50% (BR) and 43% (BB) were found Simultaneously, the root-mean-square amplitudes grew by 150% (BR) and 120% (BB) All changes during contraction reached the same level of significance (P<0001, both muscles) From the largely uniform relative increases infm and CV during the last 4 min of a 5-min recovery period, variations in CV were suggested to produce equivalent shifts infm The gradually increasing discrepancies between relative decreases infm and CV during contraction presumably reflected centrally mediated regulation of MU firing patterns (notably synchronization) After the 5-min recovery another 11 endurance contractions at 30% MVC were executed, separated by 5-min intervals The series of contractions reduced the endurance time to one-third of the 153 s initially sustained, while the terminal CV recordings increased by 10 (BR) and 06 (BB) m · s−1, and the terminalfm increased by 24 (BR) and 14 (BB) Hz The relative CV decreased in direct proportion to the endurance time and thefm decreases varied with the CV; the findings did not support a causal link between CV decrease (signifying impaired fibre excitability) and the force failure of exhaustion

Twitch interpolation technique in testing of maximal muscle strength: influence of potentiation, force level, stimulus intensity and preload.

Abstract: The aim was to study the methodological aspects of the muscle twitch interpolation technique in estimating the maximal force of contraction in the quadriceps muscle utilizing commercial muscle testing equipment. Six healthy subjects participated in seven sets of experiments testing the effects on twitch size of potentiation, time lag after potentiation, magnitude of voluntary force, stimulus amplitude, stimulus duration, angle of the knee, and angle of the hip. In addition, the consequences of submaximal potentiation on the estimation of maximal force from twitch sizes were studied in five healthy subjects. We found an increase in twitch size with increasing levels of potentiation and twitch size decreased exponentially following potentiation. We found a curvilinear relationship between twitch size and voluntary force, and these properties were more obvious when the stimulation intensity of the preload was reduced. The relationship between twitch size and force was only linear, for force levels greater than 25% of maximum. It was concluded that to achieve an accurate estimate of true maximal force of muscle contraction, it would be necessary for the subject to be able to perform at least 75% of the true maximal force.

Influence of the menstrual cycle and oral contraceptives on thermoregulatory responses to exercise in young women.

Abstract: Thermoregulatory responses to exercise in relation to the phase of the menstrual cycle were studied in ten women taking oral contraceptives (P) and in ten women not taking oral contraceptives (NP). Each subject was tested for maximal aerobic capacity (VO2max) and for 50% VO2max exercise in the follicular (F) and luteal (L) phases of the menstrual cycle. Since the oral contraceptives would have prevented ovulation a quasi-follicular phase (q-F) and a quasi-luteal phase (q-L) of the menstrual cycle were assumed for P subjects. Exercise was performed on a cycle ergometer at an ambient temperature of 24 degrees C and relative air humidity of 50%. Rectal (Tre), mean skin (Tsk), mean body (Tb) temperatures and heart rate (fc) were measured. Sweat rate was estimated by the continuous measurement of relative humidity of air in a ventilated capsule placed on the chest, converted to absolute pressure (PH2Ochest). Gain for sweating was calculated as a ratio of increase in PH2Ochest to the appropriate increase in Tre for the whole period of sweating (G) and for unsteady-state (Gu) separately. The VO2max did not differ either between the groups of subjects or between the phases of the menstrual cycle. In P, rectal temperature threshold for sweating (Tre,td) was 37.85 degrees C in q-L and 37.60 degrees C in q-F (P < 0.01) and corresponded to a significant difference from Tre at rest. The Tre, Tsk, Tb and fc increased similarly during exercise in q-F and q-L. No menstrual phase-related differences were observed either in the dynamics of sweating or in G.(ABSTRACT TRUNCATED AT 250 WORDS)

Shoulder muscle load and muscle fatigue among industrial sewing-machine operators

Abstract: Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMGmax), while the average mean load was 15% EMGmax, and the average peak load was 23% EMGmax. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during. the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.

Effects of physical exercise on the elasticity and elastic components of the rat aorta.

Abstract: To evaluate the effects of exercise on aortic wall elasticity and elastic components, young male rats underwent various exercise regimes for 16 weeks. In the exercised rats, the aortic incremental elastic modulus decreased significantly when under physiological strain. The aortic content of elastin increased significantly and the calcium content of elastin decreased significantly in the exercised group. The accumulated data from the exercised and sedentary groups revealed that the elastin calcium content was related positively to the incremental elastic modulus. We concluded that physical exercise from an early age decreases the calcium deposit in aortic wall elastin and that this effect probably produced in the exercised rats a distensible aorta.

Ratings of perceived exertion and affect in hot and cool environments.

Abstract: The effects of hot and cool environments on perceptual and physiological responses during steady-state exercise were examined in men (n = 14) performing 30 min of constant exercise (cycle ergometry) at a perceived exertion of "somewhat hard" Subjects exercised at the same absolute exercise intensity in hot (40 degrees C), neutral (24 degrees C), and cool (8 degrees C) conditions Data were collected for differential ratings of perceived exertion (RPE), affect, thermal sensation, mean skin (Tsk) and rectal temperatures (Tre), and cardiac frequency (fc) The subjects completed the hot exposure with an average Tsk of 375 degrees C (SEM 011), while the neutral and cool conditions produced values of 338 (SEM 009) and 282 degrees C (SEM 030), respectively The Tsk was significantly higher in the hot than the neutral and cool conditions throughout exercise (P < 005) The fc was significantly lower in the cool than in the other conditions (P < 005), and the subjects completed the hot exposure with a mean fc more than 20 beatsmin-1 greater than observed in the other conditions The subjects felt worse (lower affect) in the heat throughout exercise (P < 005) Overall RPE was significantly lower in the cool than in the heat, while chest RPE scores for the cool and hot conditions were displaced vertically by approximately two points Subjects perceived work to be harder, felt worse, and experienced greater thermal sensation in the hot condition, compared with the neutral and cool conditions Changes in cutaneous vasomotor tone and heat-induced influences on the chest may have accounted for the RPE changes observed in the heat

Energy cost and efficiency of riding aerodynamic bicycles.

Abstract: Traction resistance (Rt) was determined by towing two cyclists in fully dropped posture on bicycles with an aerodynamic frame with lenticular wheels (AL), an aerodynamic frame with traditional wheels (AT), or a traditional frame with lenticular wheels (TL) in calm air on a flat wooden track at constant speed (8.6-14.6 m.s-1). Under all experimental conditions, Rt increased linearly with the square of air velocity (v2a); r2 equal to greater than 0.89. The constant k = delta Rt/delta v2a was about 15% lower for AL and AT (0.157 and 0.155 N.s2 x m-2) than for TL bicycles (0.184 N.s2 x m-2). These data show firstly, that in terms of mechanical energy savings, the role of lenticular wheels is negligible and, secondly, that for TL bicycles, the value of k was essentially equal to that found by others for bicycles with a traditional frame and traditional wheels (TT). The energy cost of cycling per unit distance (Cc, J.m-1) was also measured for AT and TT bicycles from the ratio of the O2 consumption above resting to speed, in the speed range from 4.7 to 11.1 m.s-1. The Cc also increased linearly with v2a, as described by: Cc = 30.8 + 0.558 v2a and Cc = 29.6 + 0.606 v2a for AT and TT bicycles. Thus from our study it would seem that AT bicycles are only about 5% more economical than TT at 12.5 m.s-1 the economy tending to increase slightly with the speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of intra-abdominal pressure and abdominal muscle activity during dynamic trunk loading in man

Abstract: The purpose of this study was to determine and compare interactions between the abdominal musculature and intea-abdominal pressure (IAP) during controlled dynamic and static trunk muscle loading. Myoelectric activity was recorded in six subjects from the rectus abdominis, obliquus externus, obliquus internus, transversus abdominis and erector spinae muscles using surface and intea-muscular fine-wire electrodes. The IAP was recorded intea-gastrically. Trunk flexions and extensions were performed lying on one side on a swivel table. An adjustable brake provided different friction loading conditions, while adding weights to an unbraked swivel table afforded various levels of inertial loading. During trunk extensions at all friction loads, IAP was elevated (1.8–7.2 kPa) with concomitant activity in transversus abdominis and obliquus internus muscles — little or no activity was seen from rectus abdomin is and obliquus externus muscles. For inertia loading during trunk extension, IAP levels were somewhat lower (1.8–5.6 kPa) and displayed a second peak when abdominal muscle activity occurred in the course of decelerating the movement. For single trunk flexions with friction loading, IAP was higher than that seen in extension conditions and increased with added resistance. For inertial loading during trunk flexion, IAP showed two peaks, the larger first peak matched peak forward acceleration and general abdominal muscle activation, while the second corresponded to peak deceleration and was accompanied by activity in transversus abdominis and erector spinae muscles. It was apparent that different loading strategies produced markedly different patterns of response in both trunk musculature and intea-abdominal pressure.

Trunk extensor endurance and its relationship to electromyogram parameters

Abstract: The present study was designed to investigate the relationship between muscle performance and electromyogram (EMG) parameters of the trunk extensor muscles in the development of fatigue. Nine subjects performed continuous isometric trunk extensions at 25% and 40% maximal voluntary contraction. The EMG signals of the longissimus thoracis, iliocostalis lumborum, multifidus and latissimus dorsi muscles were recorded. The EMG amplitude (RA-EMG) appeared to increase consistently during the contractions in all muscles, whereas the mean power frequency (MPF) showed a fairly consistent decrease during the contractions. The time constants of the exponential change of the RA-EMG and of the MPF were related to the endurance time. The prediction of endurance based on both EMG parameters appeared to yield better results than the prediction based on the relative force. In particular the time constants of the MPF changes of the multifidus and longissimus muscles appeared to be good predictors of endurance time. The consistency of the spectrum shift of EMG appeared to coincide with a reduced variability of the activation of the muscle involved.

A new method for the evaluation of anaerobic running power in athletes.

Abstract: A new maximal anaerobic running power (MARP) test was developed. It consisted of n.20-s runs on a treadmill with a 100-s recovery between the runs. During the first run the treadmill speed was 3.97 m.s-1 and the gradient 5 degrees. The speed of the treadmill was increased by 0.35 m.s-1 for each consecutive run until exhaustion. The height of counter-movement jumps and blood lactate concentration ([la-]b) were measured after each run. Submaximal ([la-]b = 3 mmol.l-1 and 10 mmol.l-1) and maximal speed and power (W3mmol, W10mmol and Wmax, respectively) were calculated and W was expressed in oxygen equivalents according to the American College of Sports Medicine equation. Thirteen male athletes whose times over 400 m ranged from 47.98 s to 54.70 s served as subjects. In the MARP-test the speed at exhaustion was 6.89 (SD 0.28) m.s-1 corresponding to a Wmax of 118 (SD 5) ml.kg-1 x min-1. The peak [la-]b after exhaustion was 17.0 (SD 1.6) mmol.l-1. A significant correlation (r = 0.89, P < 0.001) was observed between the Wmax and the average speed in the 400-m sprint. The maximal 20-m sprinting speed on a track and W10mmol correlated with both the Wmax and the 400-m speed. It was concluded that the new method allows the evaluation of several determinants of maximal anaerobic performance including changes in the force-generating capacity of leg muscles and [la-]b relative to the speed of the sprint running. the [la-]b at submaximal sprinting speed was suggested as describing the anaerobic sprinting economy.

Circadian variation in peripheral blood flow in relation to core temperature at rest.

Abstract: The aim of the present study was to examine the circadian variation in skin blood flow and its relationship to the rhythm of rectal temperature Eight young men were confined to continuous bed rest for 24 h in a thermoneutral environment Rectal temperature, oxygen consumption, and peripheral blood flow (laser-Doppler flowmetry and plethysmography) were measured at intervals of 2 h, except at 2400 hours and 0600 hours According to the cosinor-method, the mean rectal temperature displayed a statistically significant circadian variation with a minimum at 0400 hours A significant circadian rhythm was also observed in total finger blood flow, finger laser-Doppler flow, and forearm laser-Doppler flow, but not in total forearm blood flow and forehead laser-Doppler flow The rhythms of rectal temperature and extremity skin blood flow were phased differently, ie the decrease in rectal temperature was preceded by an increase in extremity skin blood flow with an average of 4-h time difference The results would support the idea that circadian rhythm of core temperature is, at least in part, regulated by variation in extremity skin blood flow

An investigation into the relevance of the pattern of temporal activation with respect to erector spinae muscle endurance

Abstract: The aim of the present study was to evaluate the viability of a relationship between the temporal activation pattern of parts of the erector spinae muscle and endurance. Seven subjects performed intermittent isometric contractions [4 s at 7007o maximal voluntary contraction (MVC), 2 s rest] until exhaustion, during which the electromyographical (EMG) activity of the multifidus, iliocostalis thoracis and longissimus muscle segments was recorded. Endurance was defined as the time until exhaustion. Subjects were divided into a high and a low endurance group. The high endurance group showed significantly more variability of EMG amplitude over succeeding contractions. This group demonstrated significantly more alternations of EMG activity between parts of the muscle also. Variability of the EMG amplitude within the contractions did not differ between the groups, nor did MVC. The results indicated that alternating activity between different parts of the erector spinae muscle may function to postpone exhaustion of this muscle as a whole.

Quantification of erector spinae muscle fatigue during prolonged, dynamic lifting tasks.

Abstract: A method was developed to quantify erector spinae fatigue resulting from repetitive dynamic lifting in the sagittal plane. This method was tested with the data from eight male subjects lifting inertial loads of 19 kg and 17 kg during sessions of 20 min and 2 h, respectively. Surface EMG electrodes were applied over sites representing the bilateral lumbar and thoracic erector spinae and external oblique muscles. Maximal and submaximal isometric trunk extensor contractions were performed at the start, intermittently throughout, and at the end of the dynamic lifting trials, within an apparatus designed to control spine posture in the upright standing position. These exertions were used to assess the decreases in strength, endurance and EMG mean power frequency (f w ) as well as the increases in EMG amplitude that have been shown to accompany muscle fatigue. The average of the group for extensor strength decreased 17% and 21% (P<0.05) and the endurance times decreased 60% and 62% (P<0.01) for the 2-h and the 20-min session, respectively. The average endurance time decreased at least 10% for each subject in each session. Strength decreased at least 10% in all but 2 of 16 cases (both in the 20-min session). The average decreases in f w were 12% (lumbar) and 17% (thoracic; P<0.05) in the 2-h sessions and 20% (lumbar; P<0.05) and 14% (thoracic) in the 20-min sessions. There was also a significant increase in EMG amplitude (P<0.05) for both muscle group in both sessions. In general, the measures used in this study appeared to be sensitive to the fatigue resulting from dynamic contractions. The main advantage of using a combination of myoelectric and mechanical indicators of fatigue was that it allowed for more informed decisions to be made concerning its existence and extent for each individual subject during each session. Often, the information provided by each variable was needed in confidently making these decisions.

Stimulation of the phagocytic function of neutrophils in sedentary men after acute moderate exercise

Abstract: All the different stages of phagocytic function in blood polymorphonuclear neutrophils of sedentary (untrained) young men before, immediately after, and 15 min after being subjected to submaximal acute moderate exercise (50% maximal oxygen uptake) on a cycle ergometer were studied. No statistically significant differences were found in adherence or microbicide capacity againstCandida albicans immediately after physical exercise. However, spontaneous mobility, chemotaxis and attachment and phagocytosis ofCandida albicans at 15 min of incubation were significantly stimulated. Fifteen minutes after exercise spontaneous mobility, chemotaxis, and attachment ofCandida albicans had returned to basal values, while phagocytosis ofCandida albicans remained higher than basal values. One can, therefore, conclude that acute moderate exercise stimulates the phagocytic capacity of neutrophils in sedentary young men. In addition, no differences were found in the plasma adrenocorticotropic hormone concentration after exercise. However, immediately after exercise there was a decrease in the serum cortisol concentration, which had returned to basal 15 min later.

Skeletal muscle damage during tourniquet-induced ischaemia. The initial step towards atrophy after orthopaedic surgery?

Abstract: Muscle biopsies from the vastus lateralis muscle of patients who had undergone anterior cruciate ligament surgery under conditions of tourniquet-induced ischaemia were examined under the electron microscope at different periods of time up to 90 min of ischaemia. The severity of the alterations in ultrastructure appeared to depend on the period of ischaemia. The pathological changes consisted of accumulation of lysosomes, persistent intrafibre oedema, and some extracellular oedema. Signs of fibre necrosis were found after 90 min of ischaemia. Capillary ultrastructure was only altered with regard to some swelling of the endothelium and marked thickening of the basement membrane. It was concluded that skeletal muscle could be severely affected even during relatively short periods of ischaemia, which might facilitate the development of muscle atrophy during immobilization after orthopaedic surgery.

The influence of exercise/rest schedule on the physiological and psychophysical response to isometric shoulder-neck exercise.

Abstract: Six female subjects, aged 24-34 years, performed shoulder-neck exercise for 1 h or until they were exhausted by holding out their arms horizontally at 60° to the sagittal plane. One continuous and six intermittent protocols were applied, all with a mean load corresponding to the torque of the arms, i.e. about 15% maximal voluntary contraction (MVC). The intermittent protocols varied according to cycle time (10 s, 60 s, 360 s) and duty cycle (0.33, 0.50, 0.67, 0.83). Electromyogram (EMG), mean arterial blood pressure ( $$\overline {BP}$$ a), heart rate (f c) and perceived fatigue were monitored at regular intervals during exercise. Blood concentrations of potassium, lactate and ammonia were determined in pre- and postexercise samples of venous blood. Before and up to 4 h after exercise, measurements were made of MVC, pressure pain threshold, proprioceptive performance, and of EMG, $$\overline {BP}$$ a and f c during 1-min arm-holding at 25% MVC. Endurance times ranged from about 10 min to more than 1 h, significantly relating to both cycle time and duty cycle. The $$\overline {BP}$$ a, f c EMG amplitude and perceived fatigue increased early during all protocols and continued to increase throughout the exercise period. Duty cycle influenced all of these variables, while only $$\overline {BP}$$ a and fatigue perception were related to cycle time. Cardiovascular and neuromuscular recovery was incomplete for hours after several of the protocols, as indicated for example by a sensitizised response to the 1-min armholding. The protocols differed substantially as regards the relationship between different responses. Thus, ranking of the protocols in terms of physiological strain was different, depending on the criterion variable. The result stresses the relevance of applying a comprehensive selection of variables when evaluating the responses to intermittent shoulder-neck exercise.

The influence of air temperature on the EMG/force relationship of the quadriceps.

Abstract: Surface electromyography (EMG) in the past has been used to estimate the intensity of muscle contraction. These estimates were derived from the EMG/force relationship measured at room temperature. How the surface EMG signal is influenced by varying air temperature as it relates to the EMG/force relationship has yet to be investigated. Thus, this study evaluated the influence of different air temperatures (10, 23 and 40 degrees C) on surface EMG during contractions of the quadriceps muscle. Ten subjects [mean (SD) age 29 (7) years and weight 78.3 (7.8) kg] performed a criterion task of five contractions ranging from 10 to 100% of a maximal voluntary contraction, five times over a 1.5-h period in all conditions. The EMG signals generated from the rectus femoris, and the forces associated with the contractions, were captured on FM tape and subsequently digitized at a sampling rate of 2000 Hz. The relationship between EMG and force was different under the different conditions; EMG was reduced at a given force as temperature increased, and the EMG increased in the 10 degrees C environment over time. The differences that occurred at the various temperatures were believed to be related to fluid distribution in the muscle, muscle conduction velocity and sweating. The data imply that the EMG/force relationship measured using surface electrodes is influenced by ambient temperature.

Physiological and subjective responses to maximal repetitive lifting employing stoop and squat technique.

Abstract: To establish safe levels for physical strain in occupational repetitive lifting, it is of interest to know the specific maximal working capacity. Power output, O2 consumption, heart rate and ventilation were measured in ten experienced forestry workers during maximal squat and stoop repetitive lifting. The two modes of repetitive lifting were also compared with maximal treadmill running. In addition, electromyogram (EMG) activity in four muscles was recorded and perceived central, local low-back and thigh exertion were assessed during the lifting modes. No significant difference was found in power output between the two lifting techniques. Despite this the mean O2 consumption was significantly greater during maximal squat lifting [38.7 (SD 5.8) ml·kg−1-·min−1] than maximal stoop lifting [32.9 (SD 5.7) ml·kg−1·min−1] (P<0.001). No significant correlation was found between O2 consumption (in millilitres per kilogram per minute) during maximal treadmill running and maximal stoop lifting, while O2 consumption during maximal squat lifting correlated highly with that of maximal treadmill running (r=0.928, P<0.001) and maximal stoop lifting (r=0.808, P<0.01). While maximal heart rates were significantly different among the three types of exercise, no such differences were found in the central rated perceived exertions. Perceived low-back exertion was rated significantly lower during squat lifting than during stoop lifting. The EMG recordings showed a higher activity for the vastus lateralis muscle and lower activity for the biceps femoris muscle during squat lifting than during stoop lifting. Related to the maximal voluntary contraction, the erector spinae muscle showed the highest activity irrespective of lifting technique.