Showing papers in "European Journal of Applied Physiology in 1981"

The occurrence of brown adipose tissue in outdoor workers.

Abstract: Histochemical reactions and activities of mitochondrial enzymes in adipose tissue around the neck arteries and in pericardium were studied in men who had been outdoor workers in northern Finland. The purpose was to study the occurrence of brown fat in workers having been exposed to cool or cold ambient temperature. Indoor workers of the same age were used as controls.

Errors in the use of isokinetic dynamometers.

Abstract: The use of constant velocity dynamometers in functional testing and in exercise and therapy programs has been increasing in the past few years. For movements in the horizontal plane there are no gravitational errors. However, in vertical movements the limbs are not only working against the dynamometer but also are either aided or opposed by gravity. Far too often these gravitational forces have not been taken into account, and the error involved can be quite large. 1. A study on four subjects using knee extension (against gravity) and flexion (with gravity) showed the error in mechanical work to vary from 26–43% in extension and from 55–510% in flexion. 2. A relatively simple solution is offered to overcome the problem by compensating for the gravitational errors over the full range of movement. The time course of the error is such as to cause erroneous magnitudes of recorded moments which are a maximum at low level contractions and minimum at high level contractions. 3. The effect of gravitational and other acceleration errors are such as to cause false early peaks in the muscle moment curves resulting in erroneous conclusions about muscle function.

Effect of sleep deprivation on tolerance of prolonged exercise

Abstract: Acute loss of sleep produces few apparent physiological effects at rest. Nevertheless, many anecdotes suggest that adequate sleep is essential for optimum endurance athletic performance. To investigate this question, heavy exercise performance after 36 h without sleep was compared with that after normal sleep in eight subjects. During prolonged treadmill walking at about 80% of the VO2 max, sleep loss reduced work time to exhaustion by an average of 11% (p = 0.05). This decrease occurred despite doubling monetary incentives for subjects during work after sleeplessness. Subjects appeared to fall into "resistant" and "susceptible" categories: four showed less than a 5% change in performance after sleep loss, while four others showed decrements in exercise tolerance ranging from 15 to 40%. During the walk, sleep loss resulted in significantly greater perceived exertion (p less than 0.05), even though exercise heart rate and metabolic rate (VO2 and VCO2) were unchanged. Minute ventilation was significantly elevated during exercise after sleep loss ( p less than 0.05). Sleep loss failed to alter the continuous slow rises in VE and heart rate that occurred as work was prolonged. These findings suggest that the psychological effects of acute sleep loss may contribute to decreased tolerance of prolonged heavy exercise.

Metabolic types of muscle in the sheep: I. Myosin ATPase, glycolytic, and mitochondrial enzyme activities.

Abstract: The metabolic characteristics of 12 skeletal muscles of the sheep were studied. Glycolytic activities (hexokinase, glycogen synthetase I and D, phosphorylase a and b, phosphofructokinase) were measured. Myofibrillar ATPase activity was evaluated. Oxygen consumption, respiratory control and carnitine palmityl transferase, isocitrate dehydrogenase, succinate dehydrogenase and cytochrome oxidase activities were measured in isolated mitochondria. Three metabolic types could be distinguished; (1) essentially oxidative slow twitch muscles, typified by the supraspinatus and infraspinatus, having low ATPase activity, (2) fast twitch red muscles, typified by the longissimus dorsi and the semimembranosus, having a higher ATPase activity and both high oxidative and high glycolytic activity, and (3) essentially glycolytic fast twitch muscles, typified by the tensor fascia lata and the semitendinosus, having the highest ATPase activity.

The effects of a glycogen-loading regimen on the capacity to perform anaerobic exercise

Abstract: The effect of a pattern of exercise and dietary modifications, which was designed to produce alterations in the muscle glycogen content, on the capacity to perform anaerobic exercise was investigated. Six young male subjects worked to exhaustion on a bicycle ergometer at a supramaximal work load equivalent to 104±5% of \(\dot V\)O2 max after a normal diet, after a carbohydrate (CHO)-free diet following prolonged exhausting exersise, and after a high-CHO diet. This regimen has previously been shown to cause changes in the glycogen content of the working muscle. Mean work time for subjects on the first test was 4.87±1.07 min (mean ± SD). After the low-CHO diet, the time for which work could be maintained was reduced to 3.32±0.93 min, whereas administration of the high-CHO diet resulted in an increase to 6.65±1.39 min. The resting blood lactate concentration was lower than normal following the low-CHO diet and higher than normal following the high-CHO diet. Post exercise blood lactate concentrations reached a peak between 2 and 6 min after exhaustion and again were lower (8.60±1.58 mmol/l) after the low-CHO diet and higher (12.86±1.42 mmol/l) after the high-CHO diet than after performing the same intensity of work to exhaustion on a normal diet (11.66±1.16 mmol/l). The rate of lactate accumulation appeared to be approximately the same during exercise under all three dietary conditions. If this is the case, it suggests that the alterations in endurance capacity do not result from changes in the rate of anaerobic glycolytic energy production, but possibly from a change in the total capacity of the system.

Human motor unit activity during the onset of muscle fatigue in submaximal isometric isotonic contraction

Abstract: The onset of fatigue has been studied by relating motor unit activity and surface myoelectric activity during constant force isometric contraction in man.

Isokinetic contractile properties of the quadriceps with relation to fiber type

Abstract: Fifteen subjects were assigned to three groups on the basis of the proportion of fast-twitch fibers (%FT) in their vastus lateralis muscles. Torque production per unit of fat free thigh volume was then determined during knee extension on an isokinetic dynamometer at 60, 120, 180, 240, and 300‡·s−1. Maximal isometric force was also obtained at 65‡ from horizontal. Subjects with predominantly fast twitch muscle fibers demonstrated significantly greater peak power, rate of power production and work than subjects with predominantly slow twitch fibers at all but the lowest velocity of 60‡·s−1. Mean peak power for all subjects occurred at approximately 30% of maximal knee extension velocity (210‡·s−1) and 34% of maximal voluntary isometric contraction. When work, peak power and rate of power production were correlated with %FT fibers, then the highest correlations of 0.69, 0.57, and 0.73 respectively, all occurred at 180‡·−1. These observations suggest that: 1) the torque-velocity, power-velocity relationship of the quadriceps is similar to the force-velocity, power-velocity relationship found for excised muscle, 2) when using the knee extension exercise for the prediction of muscle fiber composition of the quadriceps the most appropriate speed for testing appears to be 180‡·s−1.

Changes in contractile properties of muscle after strength training in man.

Abstract: Thirty young male adults matched in two experimental groups (n=12) and a control group (n=6) were investigated before and after an 8-week strength training period. Group A trained with few repetitions and maximal loads, whereas group B had more repetitions with smaller loads. Both groups lifted the same total load during each training period, four times a week. Maximal voluntary strength (MVS) of a shot-put arm movement, muscular excitability and contractile properties (time to peak of contraction with threshold stimuli, half relaxation time) were measured in M. deltoideus and M. triceps brachii, C. longum, for two durations of stimulation. Increases of 14.8% (group A) and 12.2% (group B) in MVS were observed. Muscle excitability significantly increased in all types of training and both muscles. Significant shortening of the contraction time, dependent on the type of training, was observed in both studied muscles. It appears that the strength training in group A involved the fast fibers of both muscles, whereas in group B the training influence was less marked, and affected both fast and slow fiber types.

Frequency analysis of surface EMG to evaluation of muscle fatigue.

Abstract: A theory concerning the spectral density of surface electromyogram (EMG) in isometric contraction is described and herein, a conduction velocity measure, which was derived from a surface EMG model, is suggested. In order to confirm the validity of this measure, the spectral modification with respect to muscle fatigue is studied experimentally. The EMG signals were obtained from the biceps brachii and the rectus femoris in four subjects. The spectral modification shifted to a lower frequency as fatigue developed. The conduction velocity measure decreased linearly in both the biceps brachii and rectus femoris, but this tendency was more pronounced in the biceps. It is suggested that the spectral shift was concerned with conduction velocity of action potential along the muscle fibres. From these experimental results, we believe that we are justified in claiming that our conduction velocity measure is a useful index to estimate motor function.

Specificity of the anaerobic threshold in endurance trained cyclists and runners

Abstract: This study examined the specificity of maximum aerobic power and the anaerobic threshold (AT) in 10 endurance-trained cyclists and 10 endurance-trained runners who performed continuous progressive work tests on the bicycle ergometer and treadmill.

The energy cost of walking and running with and without a backpack load.

Abstract: The effect of a backpack load (20 kg) on oxygen consumption while walking and running at different speeds was investigated. Fifteen males walked and ran (with and without load) up a 5% sloped treadmill at 6.4, 7.2, 8.0, 9.6, and 11.2 km/h (4, 4.5, 5, 6, and 7 mph). While walking \(\dot V\)O2 rose at a rate of 0.6 (l/min)/(km/h) and while running 0.3 (l/min)/(km/h). The mean oxygen consumption at the various speeds was 28.65, 33.78, 40.64, 46.84, 54.48 ml O2/kg BW/min, respectively, for the whole group without load and 26.52, 32.26, 38.28, 44.26, 48.16, respectively, with load. The breaking point between walking and running was at about 8.2 km/h. Carrying the load increased \(\dot V\)O2 at a constant rate, and induced a breaking point between walking and running at a significantly lower speed for the smaller subjects than for the more robust ones. The results indicate that for certain tasks involving endurance and heavy load carriage, people should be selected according to criteria which integrate aerobic capacity and anthropometrical features.

Lactate after exercise in man: I. Evolution kinetics in arterial blood.

Abstract: Arterial and venous blood lactate concentrations were measured at 10 or 30 s time intervals before, during, and after several types of muscular exercise on an ergocycle in a sitting or supine position. Arterial blood lactate concentration curves over the recovery period were found to fit a biexponential time function including a rapidly increasing and a slowly decreasing component, even during active recovery at approximately 40% $$\dot V_{O_2 }$$ max exercise. The velocity constants were dependent on the exercise load. They were also linearly related to each other. The time of lactate disappearance during recovery increased with the work load.

Muscle strength and fatigue after selective glycogen depletion in human skeletal muscle fibers

Abstract: Two groups of male subjects were studied to examine the effects of different exercise protocols on performance of an isokinetic, short-time strength test, the performance of which is related to fast twitch (FT) muscle fiber recruitment The laboratory group (LG) (n=10) cycled (30 min, 70% VO2 max), ran (75 min), and performed repeated bouts of “sprint” cycling and rapid, maximal contractions of the quadriceps The marathon group (MG) (n=7) participated in and completed Stockholm's Marathon 1979 A strength test was performed before and within 1–2 h after completion of the group exercise protocol The m vastus lateralis was biopsied and muscle fibers classified as slow twitch (ST) or FT After periodic acid-Schiff staining fibers were qualitatively classified as to glycogen content In LG significant glycogen depletion occurred in both fiber types and in MG predominantly ST fibers were exhausted of glycogen after the exercise protocol The glycogen exhaustion from both fiber types in LG was associated with impaired maximal muscular strength produced during a single dynamic contraction, as well as with reduced muscle fatigue patterns When glycogen exhaustion was induced in ST muscle fibers only in the MG, no impairment was observed for maximal muscular strength but fatigue during 50 consecutive contractions was significantly increased

\(\dot VO_2 \) peak during free swimming using the backward extrapolation of the O2 recovery curve

Abstract: The purpose of this study was to evaluate the accuracy and feasibility of estimating oxygen consumption (\(\dot VO_2 \)) during maximal swimming by using the backward extrapolation (BE) of the\(\dot VO_2 \) recovery curve to time zero. Two series of experiments were conducted. In the first, the validity of the BE method was ascertained by comparing the\(\dot VO_2 \) peak values obtained during free swimming (Douglas bag technique) with those estimated by the BE method during recovery after the same tests. These results were also compared with\(\dot VO_2 \) peak measured during uphill treatmill running.\(\dot VO_2 \) peak measured during maximal free swimming and estimated by the BE method during the recovery period of that test, were not significantly different. No significant difference was found between\(\dot VO_2 \) peak uphill treadmill running and free swimming. In the second series of experiments,\(\dot VO_2 \) peak was measured in each of 28 swimmers during uphill running (conventional method) and during unimpeded swimming using the BE method. The mean value was significantly higher during swimming (\(\overline X \)3.37) than during running (\(\overline X \)3.23). Seventy-five percent of the subjects had higher\(\dot VO_2 \) peak during swimming. The swimming speed during maximal swimming effort was 10% higher when the BE method was used then when the same subjects were tested by the conventional Douglas bag technique. The BE method is a reliable and valid way to measure\(\dot VO_2 \) peak in maximal swimming and allows the swimmer to use his specifically trained musculature fully.

Estimation of myodynamic parameter values from observations on isometrically contracting muscle groups

Abstract: A new method is presented which makes it possible to estimate from a series of experimental observations of isometric maximum-effort muscle torque, a set of myodynamic parameter values for each of a number of muscles contributing collectively to the total torque output. The parameters that can be estimated are: the individual maximum isometric forces; the spreads of the length-tension curves; the relative maximum isometric tendon extensions; and the optimum muscle lengths; most of which parameters could not be estimated previously. The method is described for both penniform and fusiform muscles, and is demonstrated using the human triceps muscle as an example. The values obtained by this method are in general agreement with comparable values obtained by in vitro methods.

The validity of anaerobic threshold determination by a Douglas bag method compared with arterial blood lactate concentration

Abstract: Using an open circuit system (Douglas bag method), measurement of the anaerobic threshold (AT) was performed on ten healthy male college students during an incremental exercise test on a bicycle ergometer in an attempt to determine the validity of this method as compared with arterial blood lactate AT measurement.

Relation between pedalling- and breathing rhythm.

Abstract: The relationship between pedalling- and breathing rhythm was studied in 34 medical students (“non-cyclists”) and 10 racing cyclists on an electromagnetic bicycle-ergometer, the effective work load of which (50 W, 100 W, 150 W, 200 W) was independent of the pedalling rate. The criteria used were integer p/b ratios (pedalling rate being a multiple of breathing frequency) and phase coupling (the breathing phases starting preferentially at a certain angle of the pedalling cycle).

Plasma vasopressin, renin activity, and aldosterone: Effect of exercise and training

Abstract: The influence of endurance-training on hematocrit, plasma vasopressin, renin activity, and aldosterone changes at rest and at the end of an exercise performed until exhaustion at a given and constant relative work-load (87% of maximal oxygen uptake) has been studied in four untrained subjects submitted to a 5-month training. At the end of this period, maximal oxygen uptake increased of 15.2% (p<0.01). Hematocrit at rest slightly rose after training, and if exercise constantly induced increases in hematocrit before (p<0.001) and after training (p<0.005), the per cent increase after training was lower than before (p<0.05). Comparison between the importance of weight loss and hematocrit variation showed that when untrained subjects become trained the variation of hematocrit after exercise becomes smaller while weight loss is more important (p<0.01).

Relationship between force and integrated EMG activity during voluntary isometric anisotonic contraction.

Abstract: The surface electromyogram (EMG) was recorded for the extensor carpi radiales of normal human subjects during voluntary isometric anisotonic contractions as well as the force generated by the muscle. The relationship between force and instantaneous integrated EMG could not be fitted by a single linear function or a parabola. The muscle was then considered as a system (a) presenting a maximum force and (b) in which the EMG activity represented the input and the contraction force the output, that is F=f(iEMG) and not, as is usually done, iEMG=f(F). In addition the summed iEMG from the beginning of the contraction was used since the actual force depends on all preceding events. These findings led to testing for a non-linear and asymptotic function relating F to iEMG. A double exponential function: $$F = a[1 - \exp {\text{ (}} - b\sum \Delta iEMG)] + d[1 - \exp {\text{ }}( - c\sum \Delta iEMG)]$$ could account for the two mechanisms by which the force of a voluntary contraction is increased.

Einflu\ einer stufenweisen Laufbandergometrie bei Kindern und Erwachsenen auf die Plasmacatecholamine, die aerobe und anaerobe KapazitÄt

Abstract: Adrenalin, Noradrenalin, Lactat und Glucose im Blut sowie die Herzfrequenz und Sauerstoffaufnahme wurden wAhrend einer ansteigenden Laufbandergometrie bei acht Knaben (12,9±0,8 Jahre) und sieben Erwachsenen (27,8±2,9 Jahre) bestimmt. In Ruhe ist Noradrenalin bei den Erwachsenen signifikant hoher, Adrenalin, Lactat, Glucose, die Herzfrequenz und relative Sauerstoffaufnahme zeigen keine altersabhAngigen Unterschiede. Auf gleichen submaximalen Stufen sind Adrenalin (+90–180%), Noradrenalin (+28–77%) und die Herzfrequenz bei den Knaben, entsprechend der stArkeren Beanspruchung, signifikant hoher, Glucose, Lactat und die relative Sauerstoffaufnahme unterscheiden sich nicht. WAhrend maximaler Ergometerarbeit zeigen Adrenalin, die relative Sauerstoffaufnahme und der Glucosespiegel keinen Unterschied, Noradrenalin (−30%) und Lactat (−25%) sind bei den Knaben signifikant niedriger, die Herzfrequenz 4% hoher. Zwischen dem Lactat- und Catecholaminspiegel besteht ein gleichsinniges Verhalten (r=0,92 und 0,87), das keine altersabhAngige Anderung bis zur vierten Lebensdekade erfAhrt, jedoch bei hohergradigen „anaeroben” Beanspruchungen eine zunehmende UnschArfe erfAhrt. Die maximale Catecholamin- (Adrenalin und Noradrenalin) und Lactatkonzentration ist bei den Knaben 25% geringer; eine Bedeutung des verminderten maximalen sympathischen Antriebes fur die im gleichen Umfang verminderte anaerobe KapazitAt wird angenommen. Das wAhrend Korperarbeit konstante VerhAltnis Adrenalin zu Noradrenalin (r=0,90 und 0,85), das ebenfalls eine zunehmende UnschArfe bei sub- bis maximaler Belastung zeigt, Andert sich bei jungeren Erwachsenen (1∶5,5) gegenuber den Knaben (1∶3,5) (p<0.001) durch eine vermehrte Noradrenalinfrei-setzung in Ruhe, auf submaximalen Stufen und wAhrend maximaler Ergometerarbeit, die als Ursache eines altersabhAngigen negativ chronotropen Effektes angesehen wird.

The Anaerobic Threshold as Determined Before and During Lactic Acidosis

Abstract: During this study the relationships between venous lactate concentration and accociated changes in respiratory gas exchange were investigated. Five men performed two successive incremental exercise tests to exhaustion on an electronically braked cycle ergometer. These tests were separated by a 5 min rest period. During the initial test venous lactate concentrations showed a characteristic curvilinear increase and the anaerobic threshold (AT1) was determined conventionally. During the second test lactate concentrations were still decreasing at higher work rates than the AT1, and a second anaerobic threshold (AT2) was determined as the point where lactate concentrations again increased. The departure from linearity of the ventilatory response to both exercise tests occurred at a similar work rate, irrespective of whether venous lactate concentrations were increasing or decreasing. Carbon dioxide production was similar during the two exercise tests. The anaerobic thresholds as determined by respiratory gas analysis (ATR) were therefore similar for both tests. Results of this study indicate that changing venous lactate concentrations were not responsible for the ventilatory drive which occurred at the ATR. The venous lactate response to work at a constant rate determined within the range AT1-AT2 was also investigated. It was concluded that the lactate response to constant work rate will vary predictably at work rates falling within the AT1 to AT2 range. At AT1 no increase in venous lactate concentrations occurred, while at AT2 these increased progressively, and the test was terminated at varying times (12-15 min) due to subject exhaustion. At work rates determined from the ATR venous lactate concentrations varied according to the placement of the ATR within the AT1 AT2 range.

Maximum isokinetic ankle plantar and dorsal flexion torques in trained subjects.

Abstract: Isokinetic ankle plantar- and dorsal-flexion torques, IPF and IDF, respectively, were measured in twenty-five physically healthy athletes, fifteen males and ten females, with simultaneous recording of rectified, linearly enveloped surface electromyograms, and peak electromyographic tensions (PEMG). Angular delays from the start of motion to occurrence of peak torques were also registered. Manoeuvres were performed in two knee positions. For comparison of strength 30 non-athletic (untrained) controls were included. IPF, but not IDF, was greater in the trained than in the untrained subjects. Formulae for estimation of IPF at 30‡ differ between trained and untrained subjects. Smaller gender differences in maximum strength for trained than for untrained subjects suggest that habitual rather than genetic dissimilarities cause sex differences in strength. Slope differences in the negative exponential models which characterize IPF and IDF as functions of increasing velocity of angular motion may be caused by different structural properties of ankle flexors and extensors. A lower PEMG of them. gastrocnemius in the flexed than in the extended knee positions can explain the lower IPFs, suggesting that mechanical rather than supraspinal factors cause postural IPF differences. In contrast, greater IDF in the flexed than in the extended knee position may indicate that neurogenic mechanisms are involved.

Effects of sleep deprivation on the activity of selected metabolic enzymes in skeletal muscle.

Abstract: The effect of 120-h sleep deprivation on the activity of selected enzymes of energy metabolism in skeletal muscle was studied in seven healthy volunteers. The results showed a significant decrease in the activity of malate dehydrogenase, citrate synthase, glycerol-3-phosphate dehydrogenase and lactate dehydrogenase. Triosephosphate dehydrogenase, hexokinase, and hydroxyacyl-CoA-dehydrogenase activities showed an insignificant decrease. The findings are indicative of (1) decreased aerobic oxidation capacity; (2) reduced function of reducing-equivalent carriers from cytosol across the mitochondrial membrane; (3) relative accentuation of the non-aerobic glycolytic pathway; (4) a prediabetic type of muscle metabolism.

The effect of a high calory diet on hormonal changes in young men during prolonged physical strain and sleep deprivation.

Abstract: Major changes occur in the serum level of several hormones during 5 days of heavy and continuous physical activities, with less than a total of 2 h of sleep. The present investigation was designed to evaluate the importance of caloric deficiency, energy requirement being about 8,000–10,000 kcal/24 h. A comparison between well fed subjects and those with food deprivation revealed significantly higher levels of (T3) triiodothyronin, insulin and thyroid stimulating hormone (TSH) in the well-fed subjects, who also had lower levels of growth hormone (hGH) and cortisol, whereas no difference was found between the two groups for thyroxin (T4). Increased levels were found for T3 and T4 in both groups during the first day of activity, with a concomitant decrease in TSH and a subsequent decrease of T4 during the next 2 days. T3 decreased only in the low-calory group whereas increased levels were found in the iso-calory group throughout the course. The resting levels of insulin decreased during the course in the low-calory group whereas it increased in the iso-calory group. High levels were maintained throughout the course for hGH. Cortisol showed high levels just before the start of the course and then decreased from day 2 to day 4. No difference was found between the morning and evening levels for cortisol, indicating disappearance of the circadian rhythm. The present investigation has shown that energy deficiency during prolonged physical strain is responsible for the decreased serum levels of T3 and insulin and may contribute to the decrease in TSH and the increase in hGH and cortisol.

The role of the antigravity musculature during quiet standing in man.

Abstract: The view that postural regulation is achieved by controlling the destabilising effects of gravity through myotatic reflex activity was examined using surface electromyography. Forty seconds of recordings were made of myograms from eighteen muscles in each of a sample of nine young adults. It was observed that antigravity muscular activity in standing is generally low and often absent, and that the myograms from the muscles of the right and left sides of the body differed appreciably, the two sides rarely working together. Some sudden and united bursts of antigravity muscle activity could be observed. These might well have been stretch reflex induced, but they were transient and rare. It is concluded that the view that postural control in quiet standing is continuously mediated in a simple way by stretch reflex mechanisms is probably not valid, and that other mechanisms for controlling posture remain to be identified.

Anaerobic and aerobic power of top athletes

Abstract: In this study the alactic anaerobic and aerobic power of top level sprinters, long-distance runners, and untrained students were compared. Maximal oxygen uptake was measured during the progressive test on a treadmill. The anaerobic power was estimated according to a newly developed bicycle ergometer technique. As reported elsewhere, the maximal oxygen uptake is very high in twelve long-distance runners (77.6 +/- 2.7 ml/kg . min-1) whereas the maximal oxygen uptake of six sprinters amounts to 60.1 +/- 5.9 ml/kg . min-1. The average alactic anaerobic power of a control group of 32 students was 710 W or 10.1 +/- 1.2 W/kg. Significantly lower results were obtained by long-distance runners (551 W or 8.93 W/kg) whereas significantly higher results were obtained by sprinters (1,021 W or 14.16 W/kg). In top level athletes, but not in the control group, a negative relation was found between aerobic power and anaerobic power.

Lactate after exercise in Man: II. Mathematical model.

Abstract: A mathematical model of lactate kinetics after exercise has been constructed from the application of the mass conservation law and the following assumptions: 1. The total lactate distribution space is composed of two compartments, i.e., (M) the previously working muscles and (S) the remaining lactate space; 2. The rates of lactate release and utilization in (M) and (S) are proportional to the lactate contents of these compartments; 3. The post-exercise lactate production rates in (M) and (S) are constants; 4. Arterial lactate concentration can represent the average lactate concentration in (S).

Paradoxical influence of encouragement on muscle fatigue.

Abstract: A comparison between the fatigue developed during encouraged and non-encouraged maximum voluntary contractions (MVC) was carried out. Six subjects performed 150 isometric leg extension MVCs with the right and the left leg separately, and seven subjects performed 150 isometric MVCs with both legs simultaneously. Force and rectified smoothed electromyography (rsEMG) were followed during the contraction series. No significant difference was found in the initial force between the encouraged and the non-encouraged contraction series. Irrespective of the type of exercise performed, the relative strength in the encouraged contractions decreased more than the relative strength in the non-encouraged contractions. In all subjects a decrease in rsEMG was seen, and the ratio between rsEMG and strength remained constant throughout the 150 MVCs. The results suggest that part of the fatigue produced during repeated MVCs originates within the central nervous system, and is influenced by the presence and the encouragement given by the experimenters.

Physiological and muscle enzyme adaptations to two different intensities of swim training

Abstract: To test the hypothesis that a smaller quantity of high intensity (HI) as opposed to a larger quantity of moderate intensity (MI) swim training would result in adaptations more specific to the short performance times of swimming competitions, two groups of elite university swimmers were tested before and after 6.5 weeks of specific HI or MI intermittent swim training. In training, swimming times were faster and blood lactate concentrations were higher (10.2 vs. 7.5 mM) during HI compared to MI training. No significant differences were observed between the two groups for any of the variables measured, before or after training. However, significant increases with training were observed for the activities of hexokinase, phosphorylase, phosphofructokinase, succinate dehydrogenase, and 3-hydroxyacyl CoA dehydrogenase in the deltoid, but not the gastrocnemius muscles. Training resulted in significant increases in \(\dot V\)O2 max during treatmill running, but not during tethered swimming. It is concluded that a larger quantity of MI swim training results in physiological adaptations that are similar to those obtained with a smaller quantity of HI training, at least over a relatively short training period.

Metabolic types of muscle in the sheep: II. Lactate dehydrogenase activity and LDH isoenzyme distribution

Abstract: Lactate dehydrogenase activity and isoenzyme distribution were measured in fast-twitch red, slow-twitch red and fast-twitch white muscles in the sheep. Total enzyme activity is higher in fast-twitch muscles irrespective of their colour type. Isoenzymes M4 and H4 bear an inverse relationship, M4 being predominant in fast-twitch red and white muscles, and H4 in heart muscle and slow-twitch red muscles.