Showing papers in "European Journal of Applied Physiology in 1980"

Interference of strength development by simultaneously training for strength and endurance.

Abstract: The purpose of this study was to determine how individuals adapt to a combination of strength and endurance training as compared to the adaptations produced by either strength or endurance training separately. There were three exercise groups: a strength group (S) that exercised 30–40 min·day−1, 5 days·week−1, an endurance group (E) that exercised 40 min·day−1, 6 days·week−1; and an S and E group that performed the same daily exercise regimens as the S and E groups. After 10 weeks of training, VO2 max increased approx. 25% when measured during bicycle exercise and 20% when measured during treadmill exercise in both E, and S and E groups. No increase in VO2 max was observed in the S group. There was a consistent rate of development of leg-strength by the S group throughout the training, whereas the E group did not show any appreciable gains in strength. The rate of strength improvement by the S and E group was similar to the S group for the first 7 weeks of training, but subsequently leveled off and declined during the 9th and 10th weeks. These findings demonstrate that simultaneously training for S and E will result in a reduced capacity to develop strength, but will not affect the magnitude of increase in VO2 max.

Effects of strength training and immobilization on human muscle fibres.

Abstract: Seven healthy male subjects were studied under control conditions and following 5–6 months of heavy resistance training and 5–6 weeks of immobilization in elbow casts. Cross-sectional fibre areas and nuclei-to-fibre ratios were calculated from cryostat sections of needle biopsies taken from triceps brachii. Training resulted in a 98% increase in maximal elbow extension strength as measured by a Cybex dynamometer, while immobilization resulted in a 41% decrease in strength. Both fast twitch (FT) and slow twitch (ST) fibre areas increased significantly with training by 39% and 31%, respectively. Immobilization resulted in significant decreases in fibre area by 33% for FT and 25% for ST fibres. The observed nuclei-to-fibre ratio was 10% greater following the training programme. However, this change was non-significant. There was also a nonsignificant correlation between the magnitude of the changes in fibre size and the changes in maximal strength following either training or immobilization.

Influence of aging on the mechanical behavior of leg extensor muscles.

Abstract: Age dependence of the mechanical behavior of leg extensor muscle was investigated using vertical jumps with and without a stretch-shortening cycle on the force-platform. A total 226 subjects (113 females and 113 males) ranging in age from 4--73 years were examined. The results indicated in general that performance in males was better than that in females. This difference was reduced when body weight was taken into consideration. The peak performance of the various parameters, such as average force, height of rise of center of gravity, net impulse, and also the average power output, was reached in both sexes between the ages of 20 and 30 years. For example, the average vertical force in squatting had the following mean values in the various age groups of the male subjects: 114N (4--6 years), 402N (13--17), 618N (18--28), 508N (29--40), 435N (41--49), 320N (54--65), 315N (71--73 years). When the jumps were performed using the stretch-shortening cycle, the potential of the mechanical performance after prestretching was also sensitive to aging in a similar manner. The results suggest that it is not only the performance of pure concentric contraction that is influenced by the maturation and aging processes but, the that elastic behavior of muscle and reflex potentiation are also affected by the same processes.

Frequency analysis of the surface electromyogram during sustained isometric contractions

Abstract: Four male and four female volunteers served as subjects in these experiments to assess the frequency components of the surface EMG during and following brief (3 s) and sustained isometric contractions of the handgrip muscles. Two types of fatiguing contractions were performed. Contractions were either maintained to fatigue at a constant tension of up to 100% of their strength or were maintained as a sustained maximal effort in the unfatigued or previously fatigued muscle. The frequency components of the surface EMG were assessed by calculating the power spectra of 1.5 s samples of the EMG from a fundamental frequency of 4 Hz through the first 128 harmonics by Fourier analysis; the centre frequencies of the resultant power spectra were then used as an index of the mean frequency of the EMG. The results of these experiments showed that the centre frequency was independent of the tension exerted by the muscle during brief isometric contractions but decreased linearly with time throughout the duration of fatiguing isometric contractions at tensions between 25 and 100% MVC. During sustained maximal effort, the frequency initially decreased linearly with time. However, once the target tension could no longer be maintained, the centre frequency remained constant throughout the remainder of the contraction. The frequency was found to recover within 1 min following exercise at all tensions examined.

The influence of temperature on the amplitude and frequency components of the EMG during brief and sustained isometric contractions.

Abstract: The influence of temperature on the amplitude and frequency components of the EMG power spectra of the surface EMG recorded over the forearm muscles was examined in five male and five female subjects during brief and fatiguing isometric contractions of their handgrip muscles. Brief (3 s) isometric contractions were exerted at tensions ranging between 10 and 100% of each subject's maximum strength while fatiguing contractions were exerted at tensions of 25, 40, and 70% of their maximum strength. The temperature of the muscles during those contractions was varied by placing the forearms of the subjects in a controlled temperature water bath at temperatures of 10, 20, 30, and 40‡ C. The results of these experiments showed that the center frequency of the power spectra of the surface EMG was directly related to the temperature of the exercising muscles during brief isometric contractions. During fatiguing isometric contractions, the amplitude of the EMG increased while the center frequency of the EMG power spectra decreased for all tensions examined.

Isokinetic and static plantar flexion characteristics.

Abstract: Isokinetic and static maximum plantar flexion torques were measured in 135 adults with sedentary professions. Close associations between isokinetic and static peak torques were found. Between the ages 20–49 years strength did not differ. Thereafter strength declined as a function of age. Maximum strength was 35% lower in females than in males. The right plantar flexion strength was slightly lower than the left. Maximum plantar flexion strength was about 15% lower with flexed than with extended knees. A negative exponential model characterized the decline of strength as a function of increased isokinetic velocity of angular motion. Seventy per cent or more of the variations in maximum static and isokinetic strength could be explained by anthropometric variables and by age, and by the extent of physical activity in subjects younger than 50 years. Formulas for estimation of expected static and isokinetic strengths are given.

Plasma AVP, neurophysin, renin activity, and aldosterone during submaximal exercise performed until exhaustion in trained and untrained men.

Abstract: The effect of intense muscular work (80% of maximal oxygen uptake) on responses of plasma hormones involved in electrolyte and water balance were measured in 14 male subjects. They were divided into three groups according to their maximal oxygen uptake and the duration of exercise performed until exhaustion: well trained subjects (group I), trained subjects (group II), and untrained subjects (group III).

Towards an objective assessment of the "maximal voluntary contraction" component in routine muscle strength measurements.

Abstract: Routine measurements of muscle strength capabilities commonly use external dynamometers against which the subject exerts maximal voluntary contractions of muscles in static (isometric) tests. These tests require active cooperation of the subject, i.e., full motivation to “give the best”. At present, no practicable techniques exist that provide objective clues indicating that indeed a maximal effort is delivered, or if only a portion of the available strength is exerted. This paper describes experiments performed with 30 subjects which indicate that the rate of strength build-up in repeated exertions may provide objective criteria to judge whether or not a subject exerts full muscular strength in a routine test.

A contribution to the topography of temperature regulation in man.

Abstract: By means of climatic chamber studies the steady-state curves of body temperature and effector mechanisms of temperature regulation in man are determined for different areas of the body. Under cold conditions local temperature differences are considerable, whereas under warm conditions, the distribution of body heat is much more uniform. Evaporative heat loss, directly measured, and skin blood flow, recorded by the fluvographic method, show considerable local differences under the influence of environmental temperature. This should be the consequence of a "distributed parameter control strategy", which may be adapted to special requirements, such as exercise or partial thermal stress of the body. The experimental results form the basis for a mathematical model of human temperature regulation, and for further experimental studies which are devoted to clarifying the strategy of regulation with local distributed parameters.

Sex differences in the sympatho-adrenal response to isometric exercise.

Abstract: The effects on heart rate, blood pressure, and plasma catecholamines (epinephrine, norepinephrine, dopamine) of sustained isometric contraction (SIC) were studied in six women and nine men. Each subject held a tension equivalent to 30% of maximal handgrip strength until exhaustion. There were no significant differences between women and men in the duration of handgrip. Rise of heart rate and blood pressure were similar for women and men. Considering the absolute plasma levels of each catecholamine, no sex differences was observed at rest and at any time during SIC, except for epinephrine whose concentration was higher in men at first min of SIC. On the other hand, women and men exhibited different adrenergic patterns in response to SIC: in the first min of exercise the plasma level of the three catecholamines increased in men whereas for women plasma catecholamines levels were essentially unaffected. Thus, epinephrine seems to play a minor role in the regulation of heart rate and blood pressure during SIC for women. Another interesting result of our study is that SIC is able to induce an increase in dopamine plasma level for women as well as for men.

Effect of air resistance on the metabolic cost and performance of cycling

Abstract: The metabolic cost (VO2) of cycling against a range of wind velocities (V W) was studied in a wind tunnel of 15 male cyclists and the results compared with work on a stationary cycle ergometer, uphill cycling on a treadmill, and performance times in road racing competitions. The results showed that VO2 at constant treadmill speed was proportional to V W 2 and was a linear function of work rate, both on the stationary ergometer and during uphill cycling on a motor driven treadmill. Maximal values of 5.04 1×min−1 (69.3 ml×kg−1×min−1) and 482 W were observed. The mean force (F) acting on the cyclists during the experiments in the wind tunnel was found to be equal to 0.0175 V W 2 ×ms−1 (r=+0.98). The mean projected area (A P), drag areas (A D) and drag coefficient (C D) for the 15 cyclists were 0.50 m2, 0.280 m2, and 0.56 m2, respectively. During cycling out of doors on a calm day VO2 was calculated to be a curvilinear function of the cyclists' speed of progression (V). The best guide to the cyclists' maximal aerobic power output (VO2 max) was given by their 16.1 km (10 mile) time: $$\dot VO_{2\max } (1 \times \min ^{ - 1} ) = - 4.219 + 0.7727{\text{ }}V(ms^{ - 1} )r = + 0.89.$$ The results suggested that the relative aerobic power output (% VO2 max) which could be sustained for a given time by elite cyclists, is similar to that found previously for marathon athletes. However, due to the differences in the non-drag component of the work for given metabolic cost the cyclist will travel approx. 2 1/2 times the distance of an endurance athlete.

Force-, power-, and elasticity-velocity relationships in walking, running, and jumping

Abstract: Ground reaction forces and mechanical power were investigated when the subjects walked normally, while they were racing or running at four speeds, and when they performed the running long jump take-off. In addition, the apparent spring constants of the support leg in eccentric and concentric phases were investigated at the four running speeds, during the running long jump take-off, and in the triple jump. Six club level track and field athletes, four national level long jumpers, and six national level triple jumpers took part in the study. Cinematographic technique and a mathematical model of hopping (Alexander and Vernon 1975) were employed in the analysis. Force and power values were found to vary in the following order (from highest to lowest): long jump take-off, maximal running speed, submaximal running (80, 60, and 40% of maximum speed), racing gait, and normal gait. The data disclosed that the measured parameters had the highest values in the long jump take-off performed by the long jump athletes. Their peak values were: resultant ground reaction force 3270 +/- 74 N and mechanical power 160.1 +/- 10.5 J x kg-1 x s-1. For the track and field athletes the values were 2010 +/- 80 N and 126.0 +/0 12.6 J x kg-1 x s-1. The apparent spring constant values of the support leg in the national level jumper group were in eccentric phase 30.54 +/- 8.38 N x mm-1 x kg-1 and in concentric phase 0.129 +/- 0.012 N x mm-1 x kg-1. In the track and field athletes the values were 13.97 +/- 1.01 N x mm-1 x kg-1 and 0.093 +/- 0.003 N x mm-1 x kg-1, respectively. In general, the increase in force and mechanical power output was related to the value of the apparent spring constant of the support leg in the eccentric phase. The spring constant in the eccentric phase increased with the velocity of motion in running, the long jump take-off and the triple jump. This suggests that it may be possible to use this parameter as a measure of mechanical performance, as it may reflect the combined elasticity of muscles, tendons, and bones.

Influence of exposure to moderate altitude on the plasma concentraton of cortisol, aldosterone, renin, testosterone, and gonadotropins.

Abstract: The influence of 11 days at moderate altitude (2,000 m) combined with exercise on plasma concentration of testosterone, FSH (follicle-stimulating hormone), LH (luteinizing hormone), cortisol, aldosterone, and renin activity was studied in ten healthy subjects. Within 48 h of arrival at moderate altitude a significant increase in testosterone was found whereas FSH had decreased significantly and LH showed a tendency to decrease. Cortisol increased significantly at the beginning and reached a maximum at the end of altitude exposure. The plasma aldosterone level rose continuously and on the last day of altitude was significantly elevated. Plasma renin activity showed a tendency to decrease. On return to low land all measured parameters returned to base line values within 2 days. The findings of increases in plasma levels of aldosterone and testosterone (and serum T3 and T4, as reported by others) are in contrast to the previously found decrease of urinary excretion of all these hormones. This appears to be a distinct dissociation of serum levels of adrenal (and thyroid) hormones from their urinary excretion. The observed increase in plasma aldosterone is probably mediated through ACTH and the rise in plasma potassium, since plasma renin activity showed an opposite trend. The rise in plasma testosterone is probably of adrenal origin since plasma gonadotropins declined simultaneously. The increase of plasma levels of glucocorticoids, mineralocorticoids, and androgens after an ascent from 600 m to 2,000 m above sea level is compatible with an ACTH-mediated stimulation of the entire adrenal cortex and/or a diminished elimination of adrenal steroids: The concomitant fall of FSH, LH, and plasma renin would then be a consequence of a direct negative feedback inhibition of these hormones.

The relation of ventilation to metabolic rate during moderate exercise in man.

Abstract: To characterize more precisely the relationship between ventilation (VE) and CO2 output (VCO2) during incremental exercise, 35 healthy males were studied at rest and during upright cycle ergometry, with the work rate incremented every 4 min up to each subject's anaerobic threshold (Oan). Twenty-one subjects had arterial blood sampled at rest and in the steady state at each work rate to determine the relationship between physiological dead space ventilation (VD) and VCO2. At these work rates arterial PCO2 was regulated at the resting, control value. VE (BTPS) was linearly related to VCO2 from rest Oan with a slope of 24.6. However, the regression had a significant positive intercept of 3.2 L/min-1. This causes the ventilatory equivalent for CO2 (i.e., VE/VCO2) to decrease with increasing work rates. VD also increased linearly with increasing VCO2. However, this was consequent to increased breathing frequency as VD remained constant. Thus, the observed fall in VE/VCO2 with increasing work rates is due to the positive intercept but the inherent relationship between VE and VCO2, reflected by the linear regression slope, remains unchanged from rest through moderate exercise.

The synergy of elbow extensor muscles during dynamic work in man

Abstract: This study concerns the synergy of the elbow extensor muscles during voluntary elbow extension performed at various velocities against different inertia and in a horizontal plane

Altered hormonal response to short-term bicycle exercise in young men after prolonged physical strain, caloric deficit, and sleep deprivation

Abstract: The hormonal response to a standardized bicycle exercise test was studied in 11 male cadets exposed to a course of 107 h of continuous activity with less than 2 h sleep. The subjects expended about 8,600–11,000 kcal/24 h whereas their daily food intake contained only about 1,500 kcal. The exercise test was performed once 12 days before the course (control experiment) and on day 3 and day 5 during the course, always between 0700–0900 h.

Effect of Hidromeiosis on Sweat Drippage During Acclimation to Humid Heat

Abstract: Sweat rate and the rate of change in sweat drippage were studied during the acclimation of eight healthy male subject during exposure to heat during 10 consecutive days. During acclimation to hot humid conditions, the increase in total body sweat rate results in an increase in the rate of sweat drippage. We found, however, that on each day the drippage rate markedly decreased with time after the 1st h of heat exposure. This hidromeiosis was investigated as a function of the heat exposure time. No shortening of the onset time of hidromeiosis occurred with acclimation. With repeated heat exposures, the initial sweat rates in response to stress increased, and the subsequent decline became larger with higher sweat rates at the time of onset of hidromeiosis. Hidromeiosis appears to be a function of the degree of skin wettedness reached in the various local skin areas which determine the overall body skin wettedness upon which evaporative adjustments depend. Thus, the observed overshoot in total sweat rate as indicated by sweat drippage, and the subsequent hidromeiosis, result from initial oversweating in the poorly ventilated areas of skin. This sweat decline seems to be due to a reduction in output of the active sweat glands rather than to a reduction in active sweat gland number.

Transfer effects of endurance training to exercise with untrained limbs.

Abstract: There has been a controversy over whether the increases in maximal oxygen uptake ( $$\dot V$$ O2 max) and reductions in heart rate at a given submaximal workload after endurance training are limited to exercise with trained limbs or also may be observed during exercise with untrained limbs. In the present study five initially very sedentary young men trained by leg cycling (LT) and five by arm cranking (AT) 30 min per day on 4 days a week for 11 weeks at an intensity ≥75–80% $$\dot V$$ O2 max. Before and after training the subjects performed submaximal and maximal arm cranking and leg cycling tests. Leg cycling and arm cranking $$\dot V$$ O2 max increased 15% and 9% after LT and 12% and 35% after AT, respectively. Heart rate at a given submaximal workload was lower (p<0.05) during trained and untrained limb exercise following LT and AT. However, subjective ratings of perceived exertion (RPE) at a given submaximal workload were lower (p<0.01) only during exercise with trained limbs after LT and AT. In light of previous findings, the present increases in $$\dot V$$ O2 max and reductions in submaximal exercise heart rate with untrained limbs suggest that the initial fitness of the subjects as well as the intensity, frequency, and duration of training may be important factors in determining the extent to which transfer effects of endurance training can be observed. Although the present data suggest that reductions in RPE after endurance training may be the result of local changes in trained muscles, the possible contribution of central nervous adaptations cannot be excluded.

A comparison of various methods for the determination of VO2max

Abstract: Previous studies have shown that true maximal oxygen uptake (VO2max) obtained by means of cycle ergometer and step test are lower than the VO2max measured during uphill treadmill running. The predicted VO2max measured by ergometer was even lower. Four different methods for the determination of VO2max within the same group of examinees were compared: True VO2max by treadmill, ergometer, step test, and predicted VO2max (Astrand-Rhyming). This study was performed on 15 healthy non-professional sportsmen. They underwent progressive test protocols on alternating days and the results were as follows -- VO2max expressed in ml O2 kg BW/min (mean +/- SD): treadmill running 63.8 +/- 4.7; ergometer cycling 60.2 +/- 5.6; step test 59.6 +/-5.2 and predicted VO2max 59.9 +/- 6.9. The VO2max as determined by uphill treadmill running was significantly higher than with the other methods. No significant difference was found between true VO2max determined by the ergometer and step test. However, step test and properly executed Astrand-Rhyming test again proved to be reliable and deviate from the treadmill test by only 6%. Maximal heart rate was significantly higher in the treadmill and step tests than in the direct ergometer test.

Vibration-induced decrease in the muscle force in lumberjacks

Abstract: Isometric maximal hand grip force was measured with a strain gauge dynamometer in 91 lumberjacks and 31 controls during a 2-min compression-relaxation task. Measurements were carried out on both hands with and without simultaneous vibration exposure. The muscle forces of older subjects were smaller than those of younger men, independent of occupational vibration exposure. The fatigue curves of lumberjacks and control subjects had the same shape. During vibration exposure in the test, the forces diminished in the left hand significantly in the lumberjacks but not in the control subjects. The force level of fatigue curves of the lumberjacks with a history of diminished grip force was lower and decreased more during vibration exposure than in the lumberjacks with a history of normal grip force. The reduction in the hand grip force during vibration exposure in the lumberjacks seemed to be linked to lesions in the peripheral nerves and to activation of a tonic vibration reflex, but probably not to circulation disturbances. The fatigue mechanism seemed to be the same in lumberjacks and control subjects.

Physiological characteristics of young well-trained swimmers.

Abstract: The purpose of this study was to describe body composition, muscular strength, pulmonary function, and aerobic capacity of young swimmers, after 6 years of training. Twelve male members of a competitive swim team, ranging in age from 13 to 16 years, served as subjects. Each subject was measured on 2 separate days at approximately the same time of day on each occasion. On day one, body composition, muscular strength, TLC, FVC, FEV1.0, FRC, RV, and resting DLc0 were determined. On day 2, height, weight, \(\dot V\)E max Hr max, and \(\dot V\)O2 max were measured. Results indicated that children who train to swim competitively: (1) are lower than average in percent body fat (10.8%) as determined by hydrostatic weighing, (2) are muscularly fit as indicated by the Oregon Cable-Tension Strength Test, and (3) have cardiorespiratory capacities which are greater than one would expect to see in untrained youth of similar ages.

Skeletal muscle determinants of maximum aerobic power in man.

Abstract: The interrelationship between whole body maximum O2 uptake capacity (VO2max), skeletal muscle respiratory capacity, and muscle fiber type were examined in 20 physically active men. The capacity of homogenates of vastus lateralis muscle biopsy specimes to oxidize pyruvate was significantly related to VO2max (r = 0.81). Correlations of 0.75 and 0.74 were found between % slow twitch fibers (%ST) and VO2max, and between %ST fibers and muscle respiratory capacity, respectively (P less than 0.01). Multiple correlation analysis (R = 0.85) indicated that 72% (R2 = 0.72) of the variance in VO2max could be accounted for by the combined effect of muscle respiratory capacity and the %ST fibers. When the %ST fibers was correlated with VO2max, with the effect of respiratory capacity statistically removed, the relationship became insignificant (r = 0.38). These data suggest that muscle respiratory capacity plays an important role in determining VO2max, and that the relationship between %ST fibers and VO2max is due primarily to the high oxidative capacity of this muscle fiber type.

Thermic effect of food and exercise in obesity.

Abstract: The thermic effects of food and exercise were studied on groups of normally [10] weighted and obese [14] subjects using oxygen consumption as the criterion of energy expenditure. The results indicated that the increased resting metabolism resulting from the ingestion of a 4.200 kJ mixed content meal (thermic effect) was similar in the two groups (12–17%). But the further potentiation of this thermic effect resulting from exercise following a meal was virtually absent in the obese group (0.8%), while in the normally weighted controls it amounted to a further 17%. It is suggested that the absence of exercise-induced potentiation in the obese may help to explain their difficulty in regard to maintenance of “normal” weight and weight reduction.

Metabolic cost of exercise and physical performance in children with some observations on external loading

Abstract: The metabolic cost (VO2) of running was studied on a motor-driven treadmill in nine athletic boys, five athletic girls, and nine active boys aged 11–13 years and the results compared with their performance times during racing out of doors. On 15 of the children, additional observations of the effects of external loading on aerobic power output were made. The results showed that VO2 was proportional to body weight in children but when expressed in ml·kg−1·min−1, VO2 for a given speed of running was significantly higher in children than expected from previously collected data on adults. There were no significant differences between aerobic cost of running of the athletic boys, girls, or the active boys. The increased VO2 ml·kg−1·min−1 in children appeared to be independent of stride length and frequency but external loading equivalent to 5% of body weight reduced VO2 (ml·kg−1·min−1), particularly at the higher speeds. It was suggested in young active and athletic children due to their relatively light body weights and highly developed aerobic power outputs, that the required frequency of leg movement was not optimally matched to the force necessary to produce the most economic conversion of aerobic energy into mechanical work. Thus, in competitive events their performance times were related to their maximal aerobic power output (r=−0.75) but their times were always inferior to those which one might have expected from previous aerobic power weight data collected on adult male and female athletes.

Maximal isometric strength and fiber type composition in power and endurance athletes.

Abstract: The relationship between maximum isometric strength and muscle fiber type composition was examined in seven endurance and eight power trained athletes. Knee extension strength and ankle extension strength was assessed on 10 separate days and muscle biopsies were taken from the vastus lateralis and gastrocnemius muscles. The percent composition of slow twitch (ST) fibers and fast twitch (FT) fibers was determined from the biopsy samples. Correlation between maximal knee extension strength and percent ST fibers of the vastus lateralis was found to be 0.80 (n = 8,p less than 0.05) for the power group and 0.63 (n = 7,N.S.) for the endurance group. Corresponding correlation coefficients for the relationship between ankle extension strength and gastrocnemius percent ST fibers were -0.94 (p less than 0.01) and -0.19 (N.S.), respectively. The results suggest that the relationship to be expected between muscle fiber type composition and maximum isometric strength may well depend upon the muscle group under study as well as the type of athlete in terms of specific training adaptations.

Alterations in aerobic-anaerobic proportions of metabolism during work in heat

Abstract: With a view to investigating the aerobic and anaerobic proportions of oxygen supply during different grades of muscular activity in varying thermal stress, studies have been conducted on six young healthy Indians naturally acclimatized to heat. The subjects were given submaximal exercises of 400, 500, and 600 kgm/min (equivalent to 65.40, 81.75, and 98.10 W) for 6 min on a bicycle ergometer in three different simulated conditions, i.e., comfortable, hot humid, and very hot humid. Their O2 consumption (VO2), pulmonary ventilation (V E) and heart rate (HR) were measured during rest and throughout the exercise period (6 min) and for 30 min post exercise. Blood lactate level (LA) was measured during rest and recovery. From these, the total O2 cost with aerobic and anaerobic proportions were calculated. Results indicated a significant increase in the total O2 cost for each exercise with increasing thermal stress, along with a significant increase in the anaerobic fraction and a decrease in the aerobic fraction. The increase in anaerobic contribution to the energy supply processes was further confirmed by a significant increase in relative O2 debt (l/kg) and in blood lactate level at each work load. Thus, a highly significant correlation (P<0.001) was found between O2 debt contracted and increase in thermal stress. A significant fall in VO2 max was also observed in hot humid and very hot humid conditions as against comfortable temperature, with no change in HR max and V E max.

The blood pressure response during isometric exercise in fast and slow twitch skeletal muscle in the cat

Abstract: The blood pressure response during fatiguing isometric contractions was examined in a slow twitch muscle (the soleus) and a mixed muscle (the medial gastrocnemius) of the cat. The results of these experiments showed that electrical stimulation of the ventral roots of the spinal cord which carried the efferent innervation to the soleus muscle failed to result in a blood pressure response during isometric exercise. Further, although stimulation of the fast twitch motor units in the medial gastrocnemius muscle was associated with a potent pressor response to isometric exercise, stimulation of the slow twitch motor units was associated with a markedly reduced response throughout the duration of the exercise. These findings infer that the pressor response to isometric exercise may be a function of the fast twitch motor units in the muscle.

Effects of fatigue on the series elastic component of human muscle.

Abstract: The effects of fatigue on the muscular series elastic component were studied in man. The compliance-force relationship (K-F) of the fatigued muscle was compared with that of the unfatigued muscle. The K-F relationships were established under electromyographic control in two cases: 1. The F variation came from the decrease in maximum voluntary force appearing in fatigue which was produced by rhythmic flexions against an elastic resistance. The compliance was measured at regular intervals as fatigue developed. 2. The compliance was measured at different predetermined levels of force (maximal and submaximal) without the appearance of fatigue.

Metabolic changes in man during long-distance swimming

Abstract: Sixteen young adults were investigated before, immediately after and 24 h after swimming 5,200±618 m in 90 min. Mean pulse rate at the end of exercise was 151.3 min−1; skin and rectal temperature both slightly increased. Except for a marked leukocytosis, no changes were observed in other blood parameters (hematocrit, hemoglobin, erythrocytes). Serum enzyme activities showed (except for triosephosphate dehydrogenase) marked increases which in the case of creatine kinase and of malate dehydrogenase did not return to preexercise level on the next day. No hypoglycemia occurred in any of the subjects. Blood lactate increased to 4.2 mmol/l at the 15th min of exercise and at the end was still slightly above the resting value. Free fatty acids, free glycerol, 3-hydroxybutyrate, serum urea and uric acid rose markedly after swimming, whereas α-amino nitrogen, triglycerides, and serum magnesium significantly decreased. The electrical excitability of the two investigated muscles (M. vastus med. quadr. and M. deltoides) showed opposite changes, which was ascribed to their different involvement during swimming.

The effects of various warming up intensities and durations upon some physiological variables during an exercise corresponding to the WC170.

Abstract: Empirically, many procedures are used by sportsmen to warm up, such as massage, hot showers, or muscular exercise, although their objective effect on performance is still not evident. The present study investigates different warming up durations and intensities with or without a resting period between warming up and the criterion exercise, both performed on a bicycle ergometer. Heart rate, oxygen consumption, blood lactic acid level, and oxygen debt are measured. When the criterion exercise immediately follows warming up, heart rate, and oxygen consumption generally attain higher values during the criterion exercise but lactic acid level shows no important variation. When introducing a resting period between warming up and the criterion exercise, the heart rate and oxygen consumption values do not differ from those attained without warming up. The results do not conclusively show a positive effect of warming up before exercise.