Showing papers in "European Journal of Applied Physiology in 1979"

Electromechanical delay in human skeletal muscle under concentric and eccentric contractions.

Abstract: In contraction of skeletal muscle a delay exists between the onset of electrical activity and measurable tension. This delay in electromechanical coupling has been stated to be between 30 and 100 ms. Thus, in rapid movements it may be possible for electromyographic (EMG) activity to have terminated before force can be detected. This study was designed to determine the dependence of the EMG-tension delay upon selected initial conditions at the time of muscle activation. The right forearms of 14 subjects were passively oscillated by a motor-driven dynamometer through flexion-extension cycles of 135 deg at an angular velocity of approximately equal to 0.5 rad/s. Upon presentation of a visual stimulus the subjects maximally contracted the relaxed elbow flexors during flexion, extension, and under isometric conditions. The muscle length at the time of the stimulus was the same in all three conditions. An on-line computer monitoring surface EMG (Biceps and Brachioradialis) and force calculated the electromechanical delay. The mean value for the delay under eccentric condition, 49.5 ms, was significantly different (p less than 0.05) from the delays during isometric (53.9 ms) and concentric activity (55.5 ms). It is suggested that the time required to stretch the series elastic component (SEC) represents the major portion of the measured delay and that during eccentric muscle activity the SEC is in a more favorable condition for rapid force development.

The significance of the aerobic-anaerobic transition for the determination of work load intensities during endurance training

Abstract: Anaerobic and aerobic-anaerobic threshold (4 mmol/l lactate), as well as maximal capacity, were determined in seven cross country skiers of national level. All of them ran in a treadmill exercise for at least 30 min at constant heart rates as well as at constant running speed, both as previously determined for the aerobic-anaerobic threshold. During the exercise performed with a constant speed, lactate concentration initially rose to values of nearly 4 mmol/l and then remained essentially constant during the rest of the exercise. Heart rate displayed a slight but permanent increase and was on the average above 170 beats/min. A new arrangement of concepts for the anaerobic and aerobic-anaerobic threshold (as derived from energy metabolism) is suggested, that will make possible the determination of optimal work load intensities during endurance training by regulating heart rate.

EMG frequency spectrum, muscle structure, and fatigue during dynamic contractions in man

Abstract: Fatigue of the vastus lateralis muscle was studied in healthy well-conditioned students, who differed considerably regarding their muscle fibre type distribution. Muscle force decline during repeated maximum voluntary knee extensions at a constant angular velocity (180‡×s−1 or π rad×s−1), using isokinetic equipment, was taken as the criterion for the degree of fatigue. In an attempt to study quantitative as well as qualitative changes in the EMG pattern, integrated EMG (IEMG) and the frequency of the mean power (MPF), computed from the power spectral density function (PSDF), were analysed. It was found that individuals with muscles made up of a high proportion of fast twitch (FT) muscle fibres demonstrated higher peak knee extension torque, and a greater susceptibility to fatigue than did individuals with muscles mainly composed of slow twitch (ST) muscle fibres. An IEMG decline (p<0.01) was demonstrated during 100 contractions in individuals rich in FT fibres. Only a slight, but not significant, reduction in IEMG occurred in individuals with a high percentage of ST fibres. Concomitantly, MPF decreased (p<0.001) in individuals with a high percentage of FT fibres, while their opposites demonstrated only a slight decrease (non-significant). It is suggested that muscle contraction failure might also be related to qualitative changes in the motor unit recruitment pattern, and that these changes occur more rapidly in muscles composed of a high proportion of FT muscle fibres than in muscles composed of a high proportion of ST fibres.

Frequency and amplitude analysis of the EMG during exercise on the bicycle ergometer

Abstract: The surface EMG was recorded from above the quadriceps muscle in 3 male subjects during bicycle ergometry at work loads between 20 and 100% of the VO2 max to measure the EMG amplitude (RMS) and frequency (assessed from the center frequency of the power spectra) during this type of work During brief (3 min) bouts of work the RMS amplitude of the EMG was linearly related to the work load; the center frequency of the EMG power spectra was the same at all work loads examined In contrast, during sustained bouts of work maintained for 80 min at 20 and 40% of the VO2 max, the RMS amplitude of the EMG remained constant while the center frequency initially increased for the first 20 min of work and then progressively decreased as the work continued When work loads of 60, 80, and 100% of the VO2 max were sustained to fatigue, the RMS amplitude continually increased while the EMG frequency decreased from the beginning to the end of the work periods The results of this study showed that the EMG is a complex waveform, being influenced not only by fatigue, but to even a larger extent in many cases, the temperature of the exercising muscles Therefore, although muscular fatigue caused an increase in the RMS amplitude and decrease in the center frequency, the increase in muscle temperature associated with the work opposed these changes by causing a reduction in the RMS amplitude and an increase in the center frequency

Mechanical characteristics and fiber composition of human leg extensor muscles.

Abstract: To investigate the influence of skeletal muscle fiber composition on the mechanical performance of human skeletal muscle under dynamic conditions, 34 physical education students with differing muscle fiber composition (M vastus lateralis) were used as subjects to perform maximal vertical jumps on the force-platform Two kinds of jumps were performed: one from a static starting position (SJ), the other with a preliminary counter-movement (CMJ) The calculated mechanical parameters included height of rise of center of gravity (h), average force (F), net impulse (NI) and average mechanical power (W) It was observed that the percentage of fast twitch fibers was significantly related (p less than 005--001) to these variables in SJ condition and also to h and NI of the positive work phase in CMJ It is concluded that skeletal muscle fiber composition also determines performance in a multijoint movement The result is explainable through the differences in the mechanical characteristics of the motor units and their respective muscle fibers

Aerobic performance of female marathon and male ultramarathon athletes.

Abstract: The aerobic performance of thirteen male ultramarathon and nine female marathon runners were studied in the laboratory and their results were related to their times in events ranging in distance from 5 km to 84.64 km. The mean maximal aerobic power output (VO2 max) of the men was 72.5 ml/kg·min compared with 58.2 ml/kg·min (p<0.001) in the women but the O2 cost (VO2) for a given speed or distance of running was the same in both sexes. The 5 km time of the male athletes was closely related to their VO2 max (r=−0.85) during uphill running but was independent of relative power output (%VO2 max). However, with increasing distance the association of VO2 max with male athletic performance diminished (but nevertheless remained significant even at 84.64 km), and the relationship between VO2 max and time increased. Thus, using multiple regression analysis of the form: $$\begin{gathered} 42.2 km (marathon) time (h) = 7.445 - 0.0338 \dot V{\text{O}}_{{\text{2 max}}} ({\text{ml/kg }} \cdot {\text{ min}}) \hfill \\ - 0.0303\% \dot V{\text{O}}_{{\text{2 max}}} (r = 0.993) \hfill \\ \end{gathered} $$ and $$\begin{gathered} 84.64 {\text{km (London}} - {\text{Brighton) time (h) = 16}}{\text{.998 }} - {\text{ 0}}{\text{.0735 }}\dot V{\text{O}}_{{\text{2 max}}} \hfill \\ ({\text{ml/kg }} \cdot \min ) - 0.0844\% \dot V{\text{O}}_{{\text{2 max}}} (r = 0.996) \hfill \\ \end{gathered} $$ approximately 98% of the total variance of performance times could be accounted for in the marathon and ultramarathon events. This suggests that other factors such as footwear, clothing, and running technique (Costill, 1972) play a relatively minor role in this group of male distance runners. In the female athletes the intermediate times were not available and they did not compete beyond 42.2 km (marathon) distance but for this event a similar association though less in magnitude was found with VO2 max (r=−0.43) and %VO2 max (= −0.49). The male athletes were able to sustain 82% VO2 max (range 80–87%) in 42.2 km and 67% VO2 max (range 53–76%) in 84.64 km event. The comparable figure for the girls in the marathon was 79% VO2 max (ranges 68–86%). Our data suggests that success at the marathon and ultramarathon distances is crucially and (possibly) solely dependent on the development and utilisation of a large VO2 max.

The effect of weight-lifting exercise related to muscle fiber composition and muscle cross-sectional area in humans

Abstract: Isometric and dynamic strength and endurance of knee extensors were tested in 18 young males. The relative composition of slow (ST) and fast twitch (FT) fibers in the vastus lateralis muscle was registered from needle biopsies. Thigh muscle volume was evaluated from ultrasonic measurements. Six subjects served as controls, six trained with 50%, and six with 80% dynamic strength three times per week for 7 weeks with 20 and 12 repetitions per session, respectively. The training load was adjusted to the increases in strength observed during training. Dynamic strength increased by 42.3% in the 80% group (p less than 0.01). In the control group and 50% group no significant increases were observed. Dynamic endurance: Controls showed no change. There was an over-all increase in the 50% group, while the 80% group only increased dynamic endurance for heavier loads. Isometric strength and endurance and fiber composition did not change in any group. In the 50% group the area of FT-realtive to ST-fibers increased 12.4% (p greater than 0.05). Dynamic strength relative to muscle cross section increased by 30% in the 80% group (p less than 0.01) positively correlated to relative content of FT fibers. The present results confirm the specificity of training and indicate that a high content of FT fibers is a prerequisite for a successful strength training.

Biochemical changes in a 100 km run: free amino acids, urea, and creatinine.

Abstract: Free amino acids, urea, and creatinine were analyzed in venous blood and urine of 11 trained (28--81 years old) male subjects before, immediately after, and 1 day after a 100 km running competition. The urinary excretion per minute of all amino acids was lowered after the contest. The renal clearance of creatinine was reduced from 116 to 60 ml/min and the clearance of most amino acids was reduced to a similar extent. However, for the amino acids with a resting clearance under 1 ml/min (x), a high relative clearance ratio (y in % of x) was seen post-exercise: y = -92.3 (log10 x) +23.1, r = -0.83, showing that their high reabsorption capacity had been impaired. Serum concentrations of most free amino acids, including the branched-chain amino acids and alanine, were reduced to 35--85% of the pre-race values. The sulfur amino acids were elevated either at the end of (cystine, to 180%) or 24 h after (methionine, to 155%) the race. Urea production increased by 44% while creatinine production tended to decrease. The production of 3-methylhistidine remained unchanged. These findings are compatible with a stimulation of gluconegenesis at the expense of the amino acid pool without induction of muscle protein catabolism.

Capillary supply and mitochondrial content of different skeletal muscle fiber types in untrained and endurance-trained men. A histochemical and ultrastructural study.

Abstract: The number of capillaries per fiber, per mm2, around each fiber type and relative to fiber area was determined in six untrained subjects (UT) and six elite cross-country skiers (ET). Average values for maximal oxygen uptake were 49.8 ml . kg-1 . min-1 (UT) and 77.9 ml . kg-1 . min-1 (ET). Type I fibers constituted 39.2% (UT) and 68.6% (ET), type II A fibers 39.6% (UT) and 19.2% (ET), while 12.8% (UT) and 6.6% (ET) of the fibers were type II B. The mean fiber area for the type II A fibers was significantly greater (p less than 0.01) than the areas for type I and II B in the untrained group. The average numbers of capillaries around each fiber type (CA) were 4.76-4.84-2.94 (UT) and 7.79-6.63-4.5 (ET) for type I, II A, and II B, respectively. There was a significant difference (p less than 0.01) in the CA values relative to fiber area for all fiber types in both groups, being highest for type I and lowest for type II B. The CA increased linearly with increasing size of the fibers for all fiber types in both groups. The mitochondrial content was determined semiquantitatively for each fiber type. The differences in capillary supply between the fiber types are accompanied by similar differences in mitochondrial content. The results indicate that endurance training increases the capillary supply of all fiber types in the human quadriceps muscle. The fact that light microscopical studies have given lower capillarization values than those obtained with the electron microscope is discussed.

Effects of exercise on the serum concentrations of FSH, LH, progesterone, and estradiol.

Abstract: The effects of 30 min of exercise (74.1±3.0% (VO2), on the responses of progesterone (P), estradiol (E2), follicle stimulating hormone (FSH), and luteinizing hormone (LH) were investigated in 10 women. With such exercise significant increments occurred in P (37.6±9.5%) and E2 (13.5±7.5%) (p 0.05). Exercise in the luteal phase and during menses provoked similar changes in P, but E2 concentrations remained unchanged when exercise occurred during menses (p>0.05). With 8–11 weeks of training the menstrual cycles were quite irregular and retesting of subjects in the same phase of the cycle was not possible. Yet, when subjects were retested after training, no changes occurred in P, E2 or LH (p>0.05) but a decrement did occur in FSH (p<0.10). Thus, heavy exercise in untrained subjects provokes significant increments in ovarian hormones, whereas no such increments are observed in trained subjects exercising at the same absolute workload.

Fiber composition, fiber size and enzyme activities in vastus lateralis of elite athletes involved in high intensity exercise.

Abstract: In order to determine the influence of an extensive history of participation in high intensity activity on muscle fiber type, fiber size, and metabolic profile, elite ice hockey players were selected for investigation from three different leagues. Biopsy samples from the vastus lateralis muscle were obtained from different groups of players prior to and following the season and compared with control subjects. No significant differences were found in the percentage (49.6 vs. 43.8%) or the size of the ST fibers between the elite athletes and the control group, nor was there any significant alteration following the season of play in these variables. For the FT fiber subgroups, a reduction in the FTb (12.2 vs. 3.9%) and an increase in FTa (38.0 to 45.2%) fiber populations occurred over the season. Similarly, increases in fiber area were observed for both FT subgroups pre to post season. Of the enzymes studied only 3-hydroxyacyl CoA dehydrogenase was elevated in the post season measures, while total phosphorylase and phosphofructokinase were significantly lower. The metabolic pattern exhibited does not appear to be substantially different from what would be expected from an untrained group of similar fiber distribution.

Thermoregulation during exercise in relation to sex and age.

Abstract: The thermoregulatory responses to 1 h exercise of 14 male (age range 18--65 year) and 7 female (age range 18--46 year) athletes and 4 (3 male and 1 female) non-athletic subjects have been investigated in a moderate environment (Tdb = 21 degrees C, Twb = 15 degrees C and rh less than 50%) and analysed in relation to age, sex, and maximum aerobic power output (VO2max). The maximal sweat loss (Msw max) under the given conditions was closely related (r = + 0.90) to VO2max and for a given relative work load (%VO2max), rectal (Tre) and mean skin (Tsk) temperatures was the same in all subjects. Sweat loss (Msw) was linearly related to total heat production (H) and to peripheral tissue heat conductance (K) and if expressed in relative terms (%Mswmax) was linearly related to Tre. For a given Tre relative sweat rate was identical in the groups studied. From these results it would seem that during exercise Tre rises to meet the requirements of heat dissipation by establishing a thermal gradient from core to skin and stimulating sweating in proportion to maximal capacity of the system. Thus provided the thermal responses to work were standardised using the appropriate physiological variables, there was no evidence to be found for differences in thermoregulatory function which could be ascribed to sex or age.

Mechanical power and segmental contribution to force impulses in long jump take-off.

Abstract: Changes in total mechanical work, its partitioning into different energy states, mechanical power, force-time characteristics, force impulses of body segments and mass center's pathway characteristics during long jump take-off were investigated on four national and six ordinary level athletes. Both cinematographic and force-platform techniques were used. The data showed that the national level jumpers had higher run-up and higher take-off (release) velocities in horizontal and vertical directions. In addition, they were able to utilize efficiently the elastic energy stored in the leg extensor muscles at take-off impact. This was seen in high support leg eccentric and concentric forces, which were produced in short contact times. The ordinary level athletes had greater variability in the investigated attributes, and they reached their maximum length of jumps in many different ways. Cinematically the greatest difference between the subject groups was observed in the timing of the various body segment movements. In better athletes all the body parts (arms, trunk, and legs) had decelerating horizontal impulses, but in all ordinary level athletes the horizontal impulse of the swing leg was accelerating during take-off.

The effect of unilateral isokinetic strength training on local adipose and muscle tissue morphology, thickness, and enzymes

Abstract: One-leg exercise of 5 weeks duration in 10 healthy middleaged women resulted in a significant increment of muscle force in the exercising leg and in a less, but at some angular velocities also significant, increase in the nonexercising leg. The thickness of subcutaneous tissue measured by ultrasound and skinfold caliper decreased, while muslce thickness increased in the exercising leg only. The increased thickness of muscle tissue was associated with an increase in the relative number and relative fiber area of type II fibers in the exercising leg. The mean fiber area of type IIB fibers increased significantly as well as the activity of lactate dehydrogenase and myokinase. The decrease of thickness of subcutaneous adipose tissue was not associated with a significant decrease in fat cell size and was probably due to geometrical factors secondary to hypertrophy of the underlying muscle. It is concluded that the relationship between lean and fat components of the human thigh is significantly influenced by changes in the activity of the thigh skeletal muscles, but a local dynamic strength training program can hardly be used for local emptying of the fat depot over the exercising muscles.

The amplitude distribution of surface EMG in static and intermittent static muscular performance

Abstract: A measure of the variation of load on individual muscles or parts of muscles may be obtained by estimating the amplitude probability distribution function (APDF) of the myoelectric signal. In a study of elbow flexor muscular performance in static and intermittent static low level muscular contractions, the APDF was computed from the surface EMG obtained from the belly of the brachial biceps muscle. The APDF was also computed from the simultaneously recorded force signal. The APDF of the myoelectric signal and of the force signal were similar, indicating that the APDF of the myoelectric signal closely reflects the muscular load in non-fatiguing muscular contractions. The effect of the time constant in lowpass filtering when processing the surface EMG-signals was also studied. A suitable time constant appears to be in the range of 50-100 ms.

Effects of active, passive or no warm-up on the physiological response to heavy exercise.

Abstract: Six endurance-trained young men were subjected to a 4 min maximal aerobic treadmill run (100% of VO2 max), after active or passive warm-up or rest on separate days. The increase in body temperature during the active and passive warm-up was controlled, so that the temperature reached the same level, before the subject was exposed to the maximal exercise. On average the rectal temperature rose to 38.3 degrees C (range 38.1-38.6 degrees C). The standard work resulted in a significant higher oxygen uptake, lower lactate concentration and higher blood pH when the work was preceded by active warm-up as compared with passive or no warm-up. The difference in total oxygen uptake during the run between the active and passive warm-up procedure was 0.8 1. No significant difference in minute volume of expired air or respiratory quotient was found. It is concluded that the physiological effects of a thorough active warm-up may be of substantial benefit to athletic performance.

Resting heart rate in apparently healthy middle-aged men.

Abstract: Resting heart rate (fcrest) was measured by a standardized technique in 2,014 men aged 40–59 years during a cardiovascular survey. All men were thought to be healthy prior to the survey examination. According to the survey findings, the material was subdivided into 5 clinical subgroups, according to survey findings of coronary heart disease (CHD), or suspect symptoms, or signs. Coronary angiography was performed in 105 subjects with particularly strong suspicions of CHD. Fcrest varied between 61–63 among the 5 groups (p>0.10). In 1832/2014 defined as “normals” the following findings were made: 1. Mean fcrest 61 (SD 9.7), and almost identical values obtained by auscultation and from resting ECGs in the same persons. 2. Linear drop in fcrest by age (−0.126 beats/year, p<0.001). 3. Increase in fcrest with increasing systolic blood pressure.

Biochemical changes in a 100 km run: Proteins in serum and urine

Abstract: Eleven male subjects took part in a 100 km running competition. Alterations in the total plasma protein and in ten individual plasma protein concentrations in blood and urine were measured prior to the run, immediately after and after 1 day of recovery. Five individual proteins showed a 7–10%, and lysozyme a 40%, increase in the plasma after the run. On the contrary, the haptoglobin concentration fell to 40% of its pre-race level. None of these variations were correlated with the plasma volume change. The present data showed a moderate hemolysis, as evidenced by plasma lysozyme and hemoglobin-haptoglobin binding. The urinary excretion of plasma proteins was slightly increased, especially albumin and α 1-acid-glycoprotein. The renal clearance of plasma proteins revealed that the 100 km run induced a moderate increase of glomerular permeability without any significant change in the tubular reabsorption process.

Perception of effort in isometric and dynamic muscular contraction.

Abstract: The perception of muscular effort was studied using estimation and production methods in the adductor pollicis and quadriceps. A psychometric scale (percentage magnitude) was used. Static contractions were studied in the adductor pollicis, and both dynamic (isokinetic) and static contractions were studied in quadriceps. Linear and logarithmic equations were fitted for the perceived effort as a percentage of the maximum in relation to the produced percentage maximal force or torque. The logarithmic exponent was around or above 1.0. No significant difference was found between mean exponent and intercept values for the adductor pollicis and the quadriceps, or when estimated or produced values for the two muscles were compared. There was no difference in the same subjects between the equations for static and dynamic contractions with low angular velocity of the quadriceps.

Optimal hematocrit for canine skeletal muscle during rhythmic isotonic exercise.

Abstract: Contractile power, blood flow, O2-uptake. and O2-extraction during isotonic, rhythmic exercise were determined in the isolated canine gastrocnemius muscle during perfusion with blood with hematocrits between 0.21 and 0.81. The results obtained in 36 measurements on nine muscles showed that maximal O2-delivery to the muscle is found at hematocrits between 0.5 and 0.6. Both in the range of hemodilution, and in the range of extreme hemoconcentration, O2-delivery decreases significantly. O2-consumption and contractile power of the muscles are almost unaffected in the hematocrit range between 0.4 and 0.7; beyond and below this hematocrit range both parameters decrease. O2-extraction is virtually constant in the hematocrit range between 0.3 and 0.6, but increases both below and above these hematocrit levels.

Modifications du reflexe de Hoffmann en fonktion de l'entraÎnement chez le sportif

Abstract: Nous avons mesure les valeurs du reflexe de Hoffmann et principalement du rapport reponse reflexe maximale sur reponse motrice directe maximale (H max/M max), et nous avons suivi son evolution. Il s'agissait de sportifs orientes soit vers des activites de type aerobie, soit vers des activites de type anaerobie. Six groupes ont ete constitues (nageurs — footballeurs — tennismen — athletes de sprint — athletes de demi-fond et fond — divers sportifs).

Factors influencing quantified surface EMGs

Abstract: Isometric flexions of the elbow are studied in man. For the three joint angles studied, the torque, the surface EMG of the biceps brachii muscle, and the quantified EMG are recorded. The EMGs are picked up by means of bipolar electrodes located in such a way as to vary the interelectrode orientation, the interelectrode distance and the position on the muscle.

Cardiovascular response to interval and continuous training in women.

Abstract: Three groups of five women (age = 18--25 years) participated in a 12-week training program. Cardiovascular responses up to 85% VO2 max to interval (ITG) and continuous (CTG) training were studied in two groups, before training and after 4, 8, and 12 weeks of training four times per week. A control group was assessed before and after 6 and 12 weeks. Both exercise groups demonstrated significant increases in Cao2--Cvo2 after 8 weeks with only slight further increases after 12 weeks (CTG = 8.9%, ITG = 20.0% at 85% VO2 max). No significant changes were noted in either group in SV (+ 5 ml ITG, + 9 ml CTG) or in their Qc. These results indicated that, in response to high intensity training, women may demonstrate similar cardiovascular adaptations to training as have been observed for men.

Physical training under the influence of beta blockade in rats: Effect on adrenergic responses

Abstract: Rats were trained by daily swimming or running exercises with and without daily propranolol injections. Both training methods resulted in cardiac enlargement, but only swimming exercise caused hypertrophy of the brown adipose tissue. These changes were antagonized by beta blockade. The size of the adrenals reflected the stress of the treatments, but other known stress parameters, such as the size of the thymus or sexual organs dit not. Only swimming training without beta blockade sensitized the rats to the calorigenic action of noradrenaline. The cooling rate of the rats in water, when taking into account the insulative capacity of the body, was decreased in swimming-trained as well as in propranolol-treated rats but increased in running-trained rats. The latter two changes may be due to circulatory alterations, while the delayed body cooling in swimming-trained rats probably results from increased heat production capacity. Training-induced resting bradycardia and enhanced tachycardic response to isoprenaline were observable only in the animal groups trained without beta blockade. The pressor response to noradrenaline tended to be higher in the trained groups and the propranolol-treated group than in the controls and was smaller in the animal groups trained under the influence of beta blockade. On the other hand, the hypotonic response to isoprenaline was smaller in the propranolol-treated and running-trained animals. The results emphasize the importance of the sympathetic nervous system in the adaptation of an organism to physical training.

Quantitative study of free amino acids in human eccrine sweat excreted from the forearms of healthy trained and untrained men during exercise

Abstract: The free amino acids in eccrine sweat collected from the forearms of 20 healthy trained and 20 healthy untrained men during controlled exercise were determined quantitatively using ion exchange column chromatography. Sweat was deproteinized by adding an equal volume of 5% sulphosalicylic acid. The amino acid concentrations showed a constant qualitative pattern in sweat and large individual differences. Essential amino acids, such as isoleucine, leucine, lysine, methionine, phenylalanine, and valine were excreted in relatively small amounts. As compared to the trained men, untrained men showed statistically significantly higher concentrations in sweat for the following amino acids: Alanine, arginine, glycine, histidine, isoleucine, leucine, lysine, ornithine, phenylalanine, serine, taurine, threonine, tyrosine, and valine. No significant differences were found for citrulline, cystine, ethanolamine, and methionine. The comparison of the amino acid excretions in sweat obtained under controlled exercise and in urine showed that the amounts of amino acids excreted in sweat under controlled exercise were comparable to the losses of amino acids in urine.

The physiological cost of carrying light and heavy loads

Abstract: Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.

Metabolic adaptation to prolonged exercise.

Abstract: A study was undertaken to evaluate and to examine the role of substrate supply in 50 healthy subjects after long distance events, such as 10 km, 25 km, and marathon races. The metabolic, variables of carbohydrate metabolism were greatest in 10-km runners, with the highest increase in glucose, lactate, and pyruvate, while in marathon runners only moderate changes were observed. Marathon competitors gave the greatest decrease in insulin concentration whereas glucagon and cortisol showed a contrary tendency. As for lipid concentrations, the most remarkable point was that after the marathon competition the best runners had the highest increase in free fatty acids; the longer the race, the higher were the Β-hydroxybutyrate and acetoacetate levels after the competition. It is important to emphasize that the limiting factor up to 90 min duration is the competitor's ability to deplete the stores of glycogen. Beyond 90 min (or 25 km) the decrease in insulin, the rise in cortisol and the higher concentration of ketnne bodies found indicate a change in metabnlic response.

The perception of effort: an inductive approach.

Abstract: A theoretical model has been proposed relating physical effort to perceived exertion. The model has been applied to a comparative investigation of the perception of various forces exerted by the adductor pollicis muscle and the quadriceps in five male subjects. The increase in perception of effort with increasing applied force in both muscle groups has been shown to increase exponentially. A force constant, defined in the paper, as the applied force at which perception of effort approximates two-thirds of maximum seems to discriminate effectively between the muscle groups concerned. The description of psychophysical data in this concise quantifiable manner may offer better insight into physiological processes contributing to the appreciation of effort.

Specificity of maximal aerobic power.

Abstract: Several types of work tasks are used to assess maximal aerobic power (MAP) in humans. Although it is well established that these work tasks may yield different absolute MAP values, little is known about the extent of the specificity of each MAP work task. 30 moderately active young men were tested at random for MAP with five commonly used work tasks: cycling supine, cycling sitting, alternate arm cranking standing, walking on a treadmill, and stepping on a bench. Statistical analyses show that these five tests do not give equal MAP means, equal variances or equal covariances. Various correlation techniques indicate, furthermore, that the common variance between the five aerobic power measurements is at best moderate. It was estimated that the overall common variance for Max ml O2 . kg-1 . min-1 reached about 50% of the total variance. The most efficient linear loading of each test in the first principal component could account only for 75% of the observed variance in MAP. It is concluded that these five work tasks do not yield parallel test forms, that the practice of transforming one MAP value into another should be abandoned, and that the practice of generalizing from one MAP value to a theoretical general MAP of the human body is not justified.

Post-competition blood lactate concentrations in collegiate swimmers.

Abstract: The purpose of this investigation was to quantitate post-competition lactate (LA) concentrations of swimmers during a competitive collegiate meet. Blood LA was measured by an enzymatic method on 23 subjects 5 min after each race event. The largest mean LA concentration of 25.7 mM/L was observed in swimmers after competing in the 200-yd individual medley. Swimmers in the 200-yd butterfly, back, breast and freestyle races had similar mean blood LA concentrations (ranging from 16.4 to 20.6 mM/L). Swimmers in the two longest events, the 500-yd and 1,000-yd free style races, had mean LA concentrations of 15.6 and 10.0 mM/L, respectively. To account for the effects of motivation, LA concentrations were measured following maximal effort noncompetitive 100 and 200-yd swims. LA concentrations were slightly greater in conjunction with faster performances for the competitive as compared to the noncompetitive 100 and 200-yd swims.