Showing papers in "European Journal of Applied Physiology in 1991"

Muscle activation during maximal voluntary eccentric and concentric knee extension

Abstract: The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360 degrees.s-1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30 degrees-70 degrees) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%-146%, P less than 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%-31%, P less than 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P greater than 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P less than 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.

Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids.

Abstract: Previous studies have shown that sustained exercise in human subjects causes an increase in the plasma concentration ratio of free tryptophan: other large neutral amino acids [including the branched-chain amino acids (BCAA)]. This should favour the transport of tryptophan into the brain and also the synthesis of 5-hydroxytryptamine, which is thought to contribute to fatigue during prolonged exercise. A mixture of the three BCAA was given to subjects during a 30-km cross-country race or a marathon (42.2 km) and the effects on mental and physical performances were measured. The mental performance, measured as the performance in the Stroop Colour and Word Test (CWT), was improved after, as compared to before the 30-km cross-country race when a BCAA supplement was given during the race, whereas the CWT scores were similar before and after in the placebo group. The running performance in the marathon was improved for the “slower” runners (3.05 h–3.30 h) when BCAA was taken during the race; however, there was no significant effect on the performance in the “faster” runners (<3.05 h). The results showed that both mental and physical performance was improved by an intake of BCAA during exercise. In addition, the effects of exercise on the plasma concentration of the aromatic amino acids were altered when a BCAA supplement was given during the marathon.

Time course of muscle adaptation after high force eccentric exercise.

Abstract: The repeated bout effect on changes in muscle damage indicators was examined in two groups of subjects following two bouts of 70 maximal eccentric actions of the forearm flexors. Fourteen college age female subjects were placed into two groups. The two bouts were separated by 6 weeks (n = 6), and 10 weeks (n = 8). The subjects performed the same amount of work for the bouts. The muscle damage indicators were isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness ratings (SOR), and plasma creatine kinase activity (CK). These measures were obtained pre-exercise and 5 days following each bout. The first bout showed significant changes in all measures over time for both groups (P less than 0.01). For the 6-week group, significantly smaller changes in RANG (P less than 0.01), SOR (P less than 0.05), and CK (P less than 0.01), as well as significantly faster recoveries (P less than 0.05) for STR and FANG were produced in the second bout. For the 10-week group, significantly smaller changes in RANG (P less than 0.05) and CK (P less than 0.01) were demonstrated by the second bout, but not significant difference was found for STR, FANG, and SOR between bouts 1 and 2. Changes in CK were still significantly smaller than that of the first bout when 6 subjects (3 subjects from each group) performed the same exercise 6 months after the second bout, but no difference in other measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Uniqueness of interval and continuous training at the same maintained exercise intensity.

Abstract: The present study sought to evaluate the inconsistencies previously observed regarding the predominance of continuous or interval training for improving fitness. The experimental design initially equated and subsequently maintained the same relative exercise intensity by both groups throughout the program. Twelve subjects were equally divided into continuous (CT, exercise at 50% maximal work) or interval (IT, 30 s work, 30 s rest at 100% maximal work) training groups that cycled 30 min day−1, 3 days week−1, for 8 weeks. Following training, aerobic power (VO2max), exercising work rates, and peak power output were all higher (9–16%) after IT than after CT (5–7%). Vastus lateralis muscle citrate synthase activity increased 25% after CT but not after IT. A consistent increase in adenylate kinase activity (25%) was observed only after IT. During continuous cycling testing the CT group had reduced blood lactate (1ab) levels and respiratory quotient at both the same absolute and relative (70% VO2max) work rates after training, while the IT group displayed similar changes only at the same absolute work rates. By contrast, both groups responded similarly during intermittent cycling testing with lower 1ab concentrations seen only at absolute work rates. These results show that, of the two types of training programs currently employed, IT produces higher increases in VO2max and in maximal exercise capacity. Nevertheless, CT is more effective at increasing muscle oxidative capacity and delaying the accumulation of 1ab during continuous exercise.

Muscle cross-sectional area, force production and relaxation characteristics in women at different ages.

Abstract: Thirty women, divided among three different age groups, i.e. 30 years (range 26–35;n = 10), 50 years (range 46–55;n = 10) and 70 years (range 66–75;n = 10) volunteered as subjects for examination of the characteristics of the muscle cross-sectional area (CSA), maximal voluntary isometric force, isometric force-time and relaxation-time of their leg extensor muscles. The CSA of the quadriceps femoris muscle in the youngest age group was slightly larger (NS) than in the middle-aged group and much larger (P<0.41) than in the oldest age group whose CSA was markedly smaller (P<0.01) than the middle-aged group. Maximal force in the youngest group was slightly greater (NS) than in the middle-aged group and much greater (P<0.01) than in the oldest group whose values were markedly smaller (P<0.05) than the middle-aged group. The individual values in CSA correlated with maximal force both in the total subject sample (r=0.82;P<0.001) and in the three age groups separately (r=0.72;P<0.01;r=0.86;P<0.01 andr=0.67;P<0.05, respectively). When the force values were related to the CSA of the muscle, the mean values of 45.4N·cm−2, SD 5.6, 47.6 N·cm−2, SD 5.0 and 46.8 N· cm−2, SD 7.0 for the three groups did not differ significantly from each other. The isometric force-time curves differed among the groups, so that the times to produce the same absolute as well as relative force levels were shorter in the 30-year age group (P<0.05) than in the 70-year age group. The times of relaxation did not differ significantly among the groups. The present results suggested that the decline in maximal force in females with age could well be related to the decline in the cross-sectional area of the muscle. However, the time taken in the production of explosive force may worsen even more than maximal strength especially at older ages. This indicated that atrophying effects of aging may be greater on fast than on slow twitch muscle fibres and/or that the rate of neural activation of the muscles could also be influenced by aging.

Static and dynamic assessment of the Biodex dynamometer.

Abstract: The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r = 0.998 and r greater than 0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450 degrees.s-1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400 degrees.s-1) identified possible errors associated with reporting knee extension torques at 30 degrees of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be exercised when interpreting and ascribing torques and angular velocities to the limb producing motion.

Electromechanical response times and muscle elasticity in men and women.

Abstract: The purpose of this study was to compare the delay in performance attributable to muscle elasticity in men and women. A group of 11 active young men age (mean, SE) 21.9, 0.7 years, stature 1.780, 0.020 m, body mass 76.4, 3.2 kg and 11 women age 20.9, 0.4 years, stature 1.670, 0.020 m and body mass 61.9, 2.6 kg provided written informed consent and were recruited to the study. In response to an acoustic signal delivered via headphones, the subjects performed a plantar flexion movement of the preferred leg as quickly as possible. A seated position ensured that the knee of the subject was flexed at a right angle and that the shank was vertical. The ball of the foot was on a force platform which was used detect the onset of muscle tension and the heel rested on a pressure pad which was used to identify movement. Surface electrodes sensed electromyographic activity (EMG) in the soleus muscle. Force platform output was captured by a digital storage oscilloscope and recorded via a y-t pen recorder for subsequent analysis. A separate timer was used to determine total reaction time (TRT). Premotor time (EMGT) was taken to be the time interval from the delivery of the signal to change in EMG. Electromechanical delay (EMD) was the time interval between the change in EMG and movement and was subdivided into force time (FT) i.e. the time interval between EMG and the onset of muscle tension and elastic charge time (CT) i.e. the time interval between the onset of muscle tension and movement. The subjects performed ten trials and in most cases the mean of ten readings was used to determine TRT, EMGT, EMD, FT and CT. There were no differences between men and women in TRT (163.3, 5.6 ms vs 176.2, 6.3 ms; P=0.149), EMGT (123.6, 6.0 ms vs 131.8, 6.4 ms; P=0.359) and FT (9.5, 1.1 ms vs 10.9, 1.2 ms; P=0.400) whereas there were differences in EMD (39.6, 1.2 ms vs 44.9, 2.0 ms; P=0.037) and CT (30.2, 1.3 ms vs 34.1, 1.3 ms; P=0.044). The results suggest that there are sex-linked differences in musculotendinous elasticity and these might in part account for observed performance differences.

The peak oxygen uptake of British children with reference to age, sex and sexual maturity.

Abstract: The purposes of this study were to provide baseline data on the peak oxygen consumption (VO2) of British children, aged 11–16 years and to examine the peakVO2 of children in relation to their pubertal stage of development. The peakVO2 of 226 boys and 194 girls was determined during either treadmill running or cycle ergometry. The sexual maturity of 320 of the children was estimated using Tanner's indices. PeakVO2 increased with chronological age in both sexes and from about the age of 12 years boys exhibited significantly higher (P<0.05) values than girls. Boys' peakVO2 in relation to body mass was consistent over the age range studied and was superior (P<0.05) to girls' values at all ages. It appears that mass-related peakVO2 is independent of sexual maturity in both sexes. The more mature boys demonstrated a significantly higher (P<0.05) peakVO2 (l·min−1) than the less mature boys on both ergometers. The more mature girls demonstrated significantly higher (P<0.05) peakVO2 (l·min−1) than the less mature girls only on the cycle ergometer. On both ergometers the differences between the peakVO2 of the girls and boys were more pronounced in the mature children whether expressed in relation to body mass or not. Comparison of the results with earlier data drawn from smaller samples failed to provide evidence to suggest that British children's peakVO2 has declined in recent years. No study with which to compare our maturity peakVO2 data appears to be available.

Assessment of running velocity at maximal oxygen uptake.

Abstract: To investigate the different ways of assessing the running velocity at which maximal oxygen uptake (VO2max) occurs, or maximal aerobic velocity (vamax), 32 well-trained runners (8 female and 24 male) were studied. The vamax and the running velocity corresponding to a blood lactate concentration of 4 mmol.l-1 (vla4) were measured during a progressive treadmill session. Within the week preceding or following the treadmill measurement the subjects completed a Universite de Montreal Track-Test (UMTT). The velocity corresponding to the last stage of this test (vUMTT) was slightly higher than vamax: 6.08 m.s-1, SD 0.41, vs 6.01 m.s-1, SD 0.44 (P less than 0.03) but these two velocities were strongly correlated (r = 0.92, P less than 0.001). The heart rate values corresponding to these velocities were similar and well correlated (r = 0.79, P less than 0.01); the corresponding blood lactate values had similar mean values: 10.5 mmol.l-1, SD 2.7 vs 11.8 mmol.l-1, SD 2.5, but were not correlated. Both vamax and vUMTT correlated well with the best performance sustained over 1500 m during the season. These results suggest that the UMTT provides a value of vamax as accurately as a treadmill measurement and that either could be used to measure the running velocity corresponding to VO2max. The v1a4 was 86.6%, SD 2.6 of vamax; these two velocities correlated strongly. Thus, in well trained runners, v1a4, when measured with a well-defined procedure, corresponds to a constant fraction of vamax and depends then on VO2max and the energy cost of running.

Significance of skin temperature changes in surface electromyography.

Abstract: Differing results have been reported concerning the direction and quantity of the electromyogram (EMG) amplitude response to changes in tissue temperature. The EMG signals from the soleus muscle of six healthy human subjects were therefore recorded during dynamic exercise (concentric contractions) at ambient temperatures of 30 degrees C and 14 degrees C. The mean skin temperature (Tsk) above the muscle investigated was 32.9 degrees C and 21.7 degrees C, respectively. The core temperature, estimated by rectal temperature, was unchanged. The cooling of the superficial tissues caused approximately a doubling of the EMG amplitude. For the probability level 0.9 in the amplitude probability distribution function, the average signal level increased from 73 microV to 135 microV (P = 0.02). The average mean power frequency of the EMG signal was reduced from 142 Hz to 83 Hz (P = 0.004). The amplitude increase was not due to shivering but other possible explanations are presented. As the changes in Tsk investigated were within the range which may occur normally during the working hours, it was concluded that Tsk should be carefully controlled in vocational EMG studies.

Effects of sleep disturbances on subsequent physical performance.

Abstract: The purpose of the study was to compare the cardiovascular, respiratory and metabolic responses to exercise of highly endurance trained subjects after 3 different nights i.e. a baseline night, a partial sleep deprivation of 3 h in the middle of the night and a 0.25-mg triazolam-induced sleep. Sleep-waking chronobiology and endurance performance capacity were taken into account in the choice of the subjects. Seven subjects exercised on a cycle ergometer for a 10-min warmup, then for 20 min at a steady exercise intensity (equal to the intensity corresponding to 75% of the predetermined maximal oxygen consumption) followed by an increased intensity until exhaustion. The night with 3 h sleep loss was accompanied by a greater number of periods of wakefulness (P<0.01) and fewer periods of stage 2 sleep (P<0.05) compared with the results recorded during the baseline night. Triazolam-induced sleep led to an increase in stage 2 sleep (P<0.05), a decrease in wakefulness (P<0.05) and in stage 3 sleep (P<0.05) After partial sleep deprivation, there were statistically significant increases in heart rate (P<0.05) and ventilation (P<0.05) at submaximal exercise compared with results obtained after the baseline night. Both variables were also significantly enhanced at maximal exercise, while the peak oxygen consumption (VO2) dropped (P<0.05) even though the maximal sustained exercise intensity was not different. Lactate accumulation was altered by sleep loss, undergoing an upward drift from the 9th min of steady power output [4.92 (SEM 0.44) mmol·1−1 vs control (CT) 3.91 (SEM 0.27) mmol·1−1, P<0.05] until maximal effort [10.92 (SEM 0.83) mmol·1−1 vs CT 9.26 (SEM 0.79) mmol·1−1, P<0.05]. After triazolam-induced sleep, heart rate, ventilation, (VO2) and blood lactates were not significantly different during steady power output from the values observed after the baseline night. However the maximal sustained exercise intensity was greater [380 (SEM 13.1) W vs CT 361.4 (SEM 13) W, P<0.01], which led to an increase in ventilation (P<0.01) without any change in heart rate, (VO2) or lactate concentration. These results suggested that partial sleep loss may have contributed to the change in athletic performance and that triazolam did not impair the physiological responses to exercise during the following afternoon.

Influence of the bicarbonate pool and on the occurrence of 13CO2 in exhaled air

Abstract: In 13C02 breath tests, based on 13C:12C ratio measurements, the appearance of 13C in exhaled C02 was monitored after the administration of a 13C-la-belled compound. Independently of the substrate used, the existence of a bicarbonate pool into which the C02 produced enters before being exhaled, imposes a delay on the appearance of changes in the 13C:12C ratio. To estimate the nature and magnitude of this delay, we applied a two-compartment model to describe the kinetics of the body bicarbonate pool and we evaluated the 13C:12C ratio of C02 entering that pool from the measured 13C:12C ratio in the exhaled C02 after an oral intake of “naturally labelled” 13C-glucose. Our results demonstrated that discrepancies between total and exogenous glucose oxidation in relation to the peak occurrence time, as well as the absolute quantities, could be adequately explained by the interference of the bicarbonate stores.

The effects of caffeine on graded exercise performance in caffeine naive versus habituated subjects.

Abstract: The physiological effects of caffeine on subjects habituated to caffeine is relatively unstudied compared to those of caffeine naive subjects during graded exercise. Thus, the purpose of this investigation was to determine the effects of caffeine on maximal oxygen consumption (VO2max) and the anaerobic threshold in these two populations. Seventeen moderately trained males were classified according to caffeine usage: (1) caffeine consumption 25 mg·day−1 or less (CN) (n=8) or (2) caffeine consumption above 300 mg·day−1 (CH) (n=9). The subjects were tested post-absorptive on the same cycle ergometer on three occasions with 7 days separating the tests. One hour before each test the subject ingested either a gelatin capsule (C); 3 mg·kg−1 body weight of caffeine (C3); or 5 mg·kg−1 body weight of caffeine (C5). The subject then performed an incrementalVO2max test beginning at 50 W and the work rate was increased 30 W every 2 min until the subject could not maintain the power output. Serial venous blood samples were drawn over 30 s at the end of each stage. The CN group significantly increased resting heart rate (fc) and expired ventilation volume (VE) after C3 and C5 andVO2 after C5. No significant differences were found for exerciseVE,VO2, respiratory excharge ratio,fc or time to exhaustion. There were no significant differences (P < 0.05) in the lactate threshold or the ventilatory threshold between treatment in either group. The CH subjects showed a significant increase (P<0.05) in resting plasma free fatty acid (FFA) concentration only during the C3 and C5 treatments. Plasma FFA levels were significantly increased (P < 0.05) at all times during C3 and C5 treatment in the CN subjects when compared to the control values. These data indicate that caffeine has no effect onVO2max or the anaerobic threshold seen during incremental, graded exercise. However, resting metabolism and ventilation, and both resting and exercise plasma FFA are increased in CN subjects.

The energy cost of running increases with the distance covered.

Abstract: The net energy cost of running per unit of body mass and distance (Cr, ml O2.kg-1.km-1) was determined on ten amateur runners before and immediately after running 15, 32 or 42 km on an indoor track at a constant speed. The Cr was determined on a treadmill at the same speed and each run was performed twice. The average value of Cr, as determined before the runs, amounted to 174.9 ml O2.kg-1.km-1, SD 13.7. After 15 km, Cr was not significantly different, whereas it had increased significantly after 32 or 42 km, the increase ranging from 0.20 to 0.31 ml O2.kg-1.km-1 per km of distance (D). However, Cr before the runs decreased, albeit at a progressively smaller rate, with the number of trials (N), indicating an habituation effect (H) to treadmill running. The effects of D alone were determined assuming that Cr increased linearly with D, whereas H decreased exponentially with increasing N, i.e. Cr = Cr0 + a D + He-bN. The Cr0, the "true" energy cost of running in nonfatigued subjects accustomed to treadmill running, was assumed to be equal to the average value of Cr before the run for N equal to or greater than 7 (171.1 ml O2.kg-1.km-1, SD 12.7; n = 30).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of exercise intensity and duration on salivary immunoglobulin A

Abstract: Two experiments were performed to examine salivary immunoglobulin A (s-IgA) responses to varying levels of exercise intensity and duration. For experiment 1, 9 college men (mean age, SD=23.56, 1.64 years) completed treadmill runs of 15, 30, and 45 min at approximately 60% of maximum oxygen consumption (VO2max). For experiment 2, 9 other college men (mean age, SD=23.67, 2.0 years) ran for 20 min at approximately 50, 65 and 80% of VO2max. Unstimulated salivary samples were collected before, and immediately, 1 and 2 h after the exercise. Samples were assayed for s-IgA using an enzyme-linked immunosorbent assay. Mean s-IgA levels did not change significantly (P>0.05) at any of the post-exercise collection times when compared to pre-exercise levels. The results of this investigation indicated that running at intensities of 50–80% of VO2max and for durations of 15–45 min did not affect s-IgA levels.

Changes in conduction velocity, median frequency, and root mean square-amplitude of the electromyogram during 25% maximal voluntary contraction of the triceps brachii muscle, to limit of endurance.

Abstract: The objective of the present study was to investigate whether isometric contraction of the right triceps brachii muscle, of maximal duration and at 25% of the maximal voluntary contraction (MVC), would reduce mean fibre conduction velocity (CV) for the active motor units (MU). In addition to the cross-correlation of surface electromyograms (EMG) for CV determination, median frequency (fm) and root-mean-square amplitude (rms-amplitude) were calculated. The initial 5 min of the recovery of the three parameters was also investigated. The MVC were performed before and after the sustained contraction. Seven males — six in their twenties and one aged 43 - participated in the investigation. Mean CV for the unfatigued muscle was 4.5 m·s−1, SD 0.38. On average, CV decreased less than 10% during the sustained contraction (P<0.05). Thefm decreased almost linearly (46%) during the endurance time, while three quarters of the 250% increase in rms-amplitude took place during the last 50% of the contraction (P<0.001, both parameters). The MVC was reduced by 39% immediately after exhaustion (P<0.05). During the 1st min of recovery the rms-amplitude decreased by 50%, and the fm increased from 54% to 82% of the initial value (bothP<0.05. No measurable simultaneous CV restitution occurred. A parallel 15% increase infm and CV took place during the last 4 min of recovery (bothP<0.001), while the amplitude remained constant. Since mean CV was essentially unchanged during the last 50% of the endurance time where large changes infm and rms-amplitude occurred, factors supplementary to CV probably caused the striking changes in fatigue EMG, notably —MU recruitment, synchronization of MU activity, and lowering of MU firing frequencies. Nevertheless, during the last 4 min of recovery the entire increase infm could be accounted for by the simultaneous increase in CV.

Sex difference in the pattern of lower limb movement during treadmill walking.

Abstract: To evaluate the characteristics of stereotyped movement of the lower limb during treadmill walking, the step length and duration of 200 steps were monitored consecutively and calculated by means of a computerized system, consisting of a position sensor, shoes with foot switches and a minicomputer. Eleven male and 10 female subjects walked at various constant speeds ranging from 60–130 m · min−1. Mean, standard deviation (SD) and coefficient of variation (CV) of the time-distance component at each speed were utilized for the assessment of stereotyped movement. When compared with males, females had a tendency to increase their speed by increasing their cadence. The difference of the walking pattern was specifically related to their height. The SD and CV of the time-distance component at a given speed were significantly greater in females than in males. Regression analyses revealed that in the relationship between the walking speeds and the SDs or CVs of the time-distance component, the significant quadratic equations could be fitted. The speed, at which the SD of step length was minimum, was estimated to be about 90 m · min−1 in both males and females. This was regarded as the free walking speed or as the walking speed resulting from a mechanically efficient step length which suited the subject's body size.

Biphasic changes in leukocytes induced by strenuous exercise.

Abstract: Seven healthy male volunteers participated in short- (STR, 1.7 km), middle- (MTR, 4.8 km) and long- (LTR, 10.5 km) term runs at a speed close to their maximum. A prompt mobilization of white cells, and lymphocytes in particular, appeared following the exercise. The initial increase in the number of lymphocytes was succeeded by a significant decrease [(P < 0.03) lymphopenia), which on average was 32%–39% of the pre-exercise values in all groups. A close correlation was found between the initial increase in plasma cortisol concentration after exercise and the subsequent lymphopenia. A modest enhancement in the number of granulocytes immediately after the exercise was accompanied by a comprehensive increase in polymorphonuclear (PMN) elastase concentration accounting for 78.6%, SEM 16.3%, 140.7%, SEM 31.8% and 241.3%, SEM 48.1% in the STR, MTR and LTR groups. No correlation was found between granulocyte number and the plasma PMN elastase concentration. A delayed granulocytosis was noted in all subjects, reaching a peak between 2 and 4 h after the exercise. The magnitude of the granulocytosis varied among subjects and peak values of the number of circulating granulocytes were found to be 5.7 × 109 cells · 1−1, SEM 0.5, 6.7 × 109 cells · 1−1, SEM 0.6 and 8.8 × 109 cells · 1−1, SEM 0.5 in STR, MTR and LTR respectively, whereas the mean baseline value was 3.6 × 109 cells · 1−1, SEM 0.4. The neutrophilic granulocytosis was not accompanied by a corresponding enhancement in PMN elastase concentration. The plasma cortisol concentration reached a peak 30 min after exercise and declined below the control level in 4 h. Neither the initial increase, nor the subsequent decrease in plasma cortisol concentration were found to be essential for the magnitude of the delayed leukocytosis.

The reproducibility of test contractions for calibration of electromyographic measurements.

Abstract: The main purpose of this study was to evaluate the reproducibility of electromyographic (EMG) measurements and specifically to test a calibration procedure with submaximal test contractions. Bipolar surface electrodes (20 mm fixed distance) were repositioned by a tracing sheet on both trapezius muscles, halfway between acromion and processus prominens. Submaximal test contractions were performed by keeping both arms straight abducted 90° and forward flexed 10° for 15-s periods. The arm position could be precisely reproduced in the frontal plane, but deviated forwards by 4° in the horizontal plane, where the sensitivity of the EMG response to arm position was lowest. The electrodes were repositioned within a radius of 3 mm with a probability of 90%. Large deviations in the EMG response were found within this radius and a significant depression of the EMG response was recorded over the middle part of the muscle (the innervation zone?). This change in sensitivity of the EMG response with electrode position occurred in parallel for the test and maximal contractions. The total coefficient of variation was estimated to be 23% for recurrent EMG measurements using the calibration procedure described.

Peak anaerobic power in master athletes

Abstract: The age-related decline in maximal physical performance of healthy subjects may be attributed both to the aging process per se and/or to a progressive reduction in physical activity. In two groups of master athletes, power (P) or endurance (E) trained (n = 115; aged 40–78 years), the degree and rate of the age-related deterioration of the maximal instantaneous muscle power (peak power,Wpeak, and the relative contribution ofquantitative (muscle mass) andqualitative factors possibly underlying such deterioration were determined. Two groups of young athletes (n = 20; 17–26 years) and healthy untrained subjects (U,n = 37; 22–67 years) were also tested for comparison. The following two variables were assessed, firstly the lower limb muscle plus bone volume (LMV) by anthropometry, and secondlyWpeak, by means of a standardized vertical jump off both feet, performed on a force platform. The results obtained were that LMV of E and P, as well as of U, was about the same between age 20 and 45 years, whereas at older ages a progressive reduction was observed; the LMV values were higher in P than in E and U. TheWpeak, expressed in W and in W·kg−1 body mass, both in E and P, decreased linearly as a function of age, being at age 75 years about 50% of the value measured at age 20 years (corresponding to a reduction of about 1%year−1); whenWpeak was expressed per kg of LMV, the percentage reduction between athletes aged 20 and 45 years was the same as that observed forWpeak, in W and W·kg−1 body mass, whereas between age 45 and 75 years the difference was almost halved; in all age-groups (with the exception of the oldest)Wpeak was higher in P than in E and in U. It was concluded that at 75 yearsWpeak was reduced, both in absolute units and per kg body mass, to about 50% of the value measured at age 20 years; up to about age 45 years such deterioration was mainly attributable toqualitative factors, whereas after that agequantitative (muscle mass) factors were also involved.

Physiological responses to prolonged treadmill walking with external loads.

Abstract: Limited information is available regarding the physiological responses to prolonged load carriage. This study determined the energy cost of prolonged treadmill walking (fixed distance of 12 km) at speeds of 1.10 m·s−1, 1.35 m·s−1, and 1.60 m·s−1, unloaded (clothing mass 5.2 kg) and with external loads of 31.5 and 49.4 kg. Fifteen male subjects performed nine trials in random order over a 6-week period. Oxygen uptake (VO2) was determined at the end of the first 10 min and every 20 min thereafter. A 10-min rest period was allowed following each 50 min of walking. No changes occurred in VO2 over time in the unloaded condition at any speed. The 31.5 and 49.4 kg loads, however, produced significant increases (ranging from 10 to 18%) at the two fastest and at all three speeds, respectively, even at initial exercise intensities less than 30% VO2max. In addition, the 49.4 kg load elicited a significantly higher (P<0.05) VO2 than did the 31.5 kg load at all speeds. The measured values of metabolic cost were also compared to those predicted using the formula of Pandolf et al. In trials where VO2 increased significantly over time, predicted values underestimated the actual metabolic cost during the final minute by 10–16%. It is concluded that energy cost during prolonged load carriage is not constant but increases significantly over time even at low relative exercise intensities. It is further concluded that applying the prediction model which estimates energy expenditure from short-term load carriage efforts to prolonged load carriage can result in significant underestimations of the actual energy cost.

The effect of a 5-month endurance-training programme on physical activity: evidence for a sex-difference in the metabolic response to exercise.

Abstract: The effect of a 5-month endurance training programme on physical activity and average daily metabolic rate (ADMR) was studied. Subjects were 16 males and 16 females preparing for a half marathon. Total physical activity, measured using an accelerometer, had increased by 62% and 63% after 20 weeks in males and females, respectively. Physical activity during the non-exercise part of the day did not change although in males it tended to increase (15%, NS). The ADMR had increased significantly in males after 8 and 20 weeks (+2.3 and +3.3 MJ.day-1, respectively, P less than 0.05) and exceeded the net energy expenditure for endurance-training three to four times. In females no significant increase in ADMR was found (+1.5 and +1.3 MJ.day-1, after 8 and 20 weeks, respectively). In females the change in ADMR could be largely attributed to the net cost of running itself and a small increase (10%) in resting metabolic rate during the time of day they were awake. In males a discrepancy was observed between the increase of ADMR and the expenditure due to exercise and non-exercise activities. We suggest exercise stimulates habitual physical activity and diet-induced thermogenesis in males but not in females.

Bio-energetic profile in 144 boys aged from 6 to 15 years with special reference to sexual maturation.

Abstract: The effects of growth and pubertal development on bio-energetic characteristics were studied in boys aged 6–15 years (n = 144; transverse study). Maximal oxygen consumption (VO2max, direct method), mechanical power at (VO2max ( $${\text{P}}_{\dot V{\text{O}}_{{\text{2max}}} } $$ ), maximal anaerobic power (Pmax; force-velocity test), mean power in 30-s sprint (P 30s; Wingate test) were evaluated and the ratios between Pmax,P 30s and $${\text{P}}_{\dot V{\text{O}}_{{\text{2max}}} } $$ were calculated. Sexual maturation was determined using salivary testosterone as an objective indicator. Normalized for body massVO2max remained constant from 6 to 15 years (49 ml· min−1 · kg−1, SD 6), whilst Pmax andP 30s increased from 6–8 to 14–15 years, from 6.2 W · kg−1, SD 1.1 to 10.8 W · kg−1, SD 1.4 and from 4.7 W · kg−1, SD 1.0 to 7.6 W · kg−1, SD 1.0, respectively, (P < 0.001). The ratio Pmax: $${\text{P}}_{\dot V{\text{O}}_{{\text{2max}}} } $$ was 1.7 SD 3.0 at 6–8 years and reached 2.8 SD 0.5 at 14–15 years and the ratioP 30s: $${\text{P}}_{\dot V{\text{O}}_{{\text{2max}}} } $$ changed similarly from 1.3 SD 0.3 to 1.9 SD 0.3. In contrast, the ratio Pmax:P 30s remained unchanged (1.4 SD 0.2). Significant relationships (P < 0.001) were observed between Pmax (W · kg−1),P 30s (W · kg−1), blood lactate concentrations after the Wingate test, and age, height, mass and salivary testosterone concentration. This indicates that growth and maturation have together an important role in the development of anaerobic metabolism.

Muscle ATP loss and lactate accumulation at different work intensities in the exercising Thoroughbred horse

Abstract: The effect of 2 min treadmill exercise, at speeds of 6-12 m.s-1 on an incline of 5 degrees, upon muscle adenine nucleotide loss and lactate accumulation was studied in six Thoroughbred horses. Minimal change occurred in the adenosine triphosphate (ATP) content of the middle gluteal muscle at speeds of 10 m.s-1 or less, but significant loss (up to 47%) had occurred in all horses by 12 m.s-1. The decline in ATP significantly correlated with the accumulation of muscle lactate, beginning shortly after the accumulation of 40 mmol.kg-1 dry muscle lactate. Decline in muscle ATP was mirrored closely by the appearance of ammonia, and to a lesser extent, hypoxanthine and uric acid in plasma. The results suggest that peak accumulation of any of these, or simply the concentration at a specified recovery time, may be used as a measure of ATP loss in the musculature as a whole. This was not so in the case of xanthine, which may also be formed from the degradation of guanidine nucleotides. An In-In plot of plasma ammonia against treadmill speed indicated a break point in accumulation between 8 and 9 m.s-1. The kinetics of ammonia accumulation with speed differed from those of lactate.

Measurement of anterior tibial muscle size using real-time ultrasound imaging

Abstract: Cross-sectional images of the anterior tibial muscle group were obtained using real-time ultrasound scanning in 17 normal women. From photographs taken of the images, the cross-sectional area (CSA) and two linear measurements of muscle cross-section were determined. A measurement of the shortest distance of the muscle depth was termed DS, and a measurement of the longest distance through the muscle group was termed DL. Both linear dimensions showed a positive correlation with CSA and the best correlations were obtained when the dimensions were squared or combined (DS × DL). The correlation values were: CSA vs DS2, r=0.9; CSA vs DL2, r=0.75 and CSA vs DS × DL, r=0.88. An approximate value for CSA could be calculated from DS2 by the equation 2 × DS2 + 1. A shape ratio, obtained by dividing DL by DS, was consistent within the group [mean 2.1 (SD 0.2)] and characterised the muscle geometrically. The CSA of repeated scans was assessed for repeatability between-days and between-scans by analysis of variance and the coefficient of variation (CV) calculated. Areas were repeatable between-days (CV 6.5%) and between-scans (CV 3.6%). Linear dimensions of the anterior tibial muscle group reflected CSA and their potential for assessing changes in muscle size with atrophy and hypertrophy have yet to be established.

Recovery of the human biceps electromyogram after heavy eccentric, concentric or isometric exercise.

Abstract: Five men performed submaximal isometric, concentric or eccentric contractions until exhaustion with the left arm elbow flexors at respectively 50%, 40% and 40% of the prefatigued maximal voluntary contraction force (MVC). Subsequently, and at regular intervals, the surface electromyogram (EMG) during 30-s isometric test contractions at 40% of the prefatigued MVC and the muscle performance parameters (MVC and the endurance time of an isometric endurance test at 40% prefatigued MVC) were recorded. Large differences in the surface EMG response were found after isometric or concentric exercise on the one hand and eccentric exercise on the other. Eccentric exercise evoked in two of the three EMG parameters [the EMG amplitude (root mean square) and the rate of shift of the EMG mean power frequency (MPF)] the greatest (P less than 0.001) and longest lasting (up to 7 days) response. The EMG response after isometric or concentric exercise was smaller and of shorter duration (1-2 days). The third EMG parameter, the initial MPF, had already returned to its prefatigued value at the time of the first measurement, 0.75 h after exercise. The responses of EMG amplitude and of rate of MPF shift were similar to the responses observed in the muscle performance parameters (MVC and the endurance time). Complaints of muscle soreness were most frequent and severe after the eccentric contractions. Thus, eccentric exercise evoked the greatest and longest lasting response both in the surface EMG signal and in the muscle performance parameters.

Basketball exercise and secretory immunoglobulin A.

Abstract: This study examined saliva levels of immunoglobulin A (IgA) before and after three games and three practice sessions during the basketball season. Saliva was collected from 27 prepubescent boys (10-12 years) in a small Fry league and 23 postpubescent boys (16-18 years) on a high school varsity team. Saliva samples were frozen for later assay using a standard enzyme-linked immunosorbent assay technique. IgA levels were significantly increased after games 1 and 3 in both age groups and after practice 3 in the high school athletes. Over the 2 months of saliva collections the pre-exercise IgA increased significantly with games 2 and 3 higher than game 1, and practice 3 higher than practices 1 and 2, in both age groups. These results indicate that basketball exercise can increase saliva IgA levels and that chronic exercise over the basketball season may increase the resting levels of IgA. These changes may give athletes more protection against respiratory infections both after exercise and in the resting state later in the season.

Serum hormones in male strength athletes during intensive short term strength training

Abstract: Training-induced adaptations in the endocrine system and strength development were investigated in nine male strength athletes during two separate 3-week intensive strength training periods. The overall amount of training in the periods was maintained at the same level. In both cases the training in the first 2 weeks was very intensive: this was followed by a 3rd week when the overall amount of training was greatly decreased. The two training periods differed only in that training period I included one daily session, while during the first 2 weeks of period II the same amount of training was divided between two daily sessions. In general, only slight and statistically insignificant changes occurred during training period I in mean concentrations of serum hormones examined or sex hormone-binding globulin as well as in maximal isometric leg extensor force. However, during training period II after 2 weeks of intensive strength training a significant decrease (P<0.05) was observed in serum free testosterone concentration [from 98.4 (SD 24.5) to 83.8 (SD 14.7) pmol · l−1] during the subsequent week of reduced training. No change in the concentration of total testosterone was observed. This training phase was also accompanied by significant increases (P<0.05) in serum luteinizing hormone (LH) and cortisol concentrations. After 2 successive days of rest serum free testosterone and LH returned to (P<0.05) their basal concentrations. Training period II led also to a significant increase (P<0.05) [from 3942 (SD 767) to 4151 (SD 926) N] in maximal force. These findings suggest that in male strength athletes dividing the amount of training into smaller units may create more effective training stimuli leading to further strength development.

Influence of prolonged physical exercise on the erythropoietin concentration in blood.

Abstract: Erythropoietin (EPO) and red blood cells were studied in 15 well-trained men before and several times after a marathon run. Changes in red blood cells reflected changes of plasma volume. Immediately after the run, red blood cells were increased due to haemoconcentration, whereas 31 h later the values were decreased due to haemodilution. The EPO concentration was increased 3 h, and more impressive 31 h, after the run. This long-lasting increase in EPO concentration after the marathon run would seem to be responsible for the increased red blood cell mass in long distance runners.

EMG power spectra of elbow extensors during ramp and step isometric contractions.

Abstract: The goal of the present study was to compare electromyogram (EMG) power spectra obtained from step (constant force level) and ramp (progressive increase in the force level) isometric contractions. Data windows of different durations were also analysed for the step contractions, in order to evaluate the stability of EMG power spectrum statistics. Fourteen normal subjects performed (1) five ramp elbow extensions ranging from 0 to 100% of the maximum voluntary contraction (MVC) and (2) three stepwise elbow extensions maintained at five different levels of MVC. Spectral analysis of surface EMG signals obtained from triceps brachii and anconeus was performed. The mean power frequency (MPF) and the median frequency (MF) of each power spectrum were obtained from 256-ms windows taken at 10, 20, 40, 60 and 80% MVC for each type of contraction and in addition on 512-, 1024-and 2048-ms windows for the step contractions. No significant differences (P>0.05) were found in the values of both spectral statistics between the different window lengths. Even though no significant differences (P>0.05) were found between the ramp and the step contractions, significant interactions (P<0.05) between these two types of contraction and the force level were found for both the MPF and the MF data. These interactions point out the existence of different behaviours for both the MPF and the MF across force levels between the two types of contraction.