Showing papers in "European Journal of Applied Physiology in 2001"

Strenuous endurance training in humans reduces oxidative stress following exhausting exercise.

Abstract: The aim of this study was to evaluate whether high-intensity endurance training would alleviate exercise-induced oxidative stress. Nine untrained male subjects (aged 19–21 years) participated in a 12-week training programme, and performed an acute period of exhausting exercise on a cycle ergometer before and after training. The training programme consisted of running at 80% maximal exercise heart rate for 60 min · day−1, 5 days · week−1 for 12 weeks. Blood samples were collected at rest and immediately after exhausting exercise for measurements of indices of oxidative stress, and antioxidant enzyme activities [superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT)] in the erythrocytes. Maximal oxygen uptake (V˙O2max) increased significantly (P < 0.001) after training, indicating an improvement in aerobic capacity. A period of exhausting exercise caused an increase (P < 0.01) in the ability to produce neutrophil superoxide anion (O2•−) both before and after endurance training, but the magnitude of the increase was smaller after training (P < 0.05). There was a significant increase in lipid peroxidation in the erythrocyte membrane, but not in oxidative protein, after exhausting exercise, however training attenuated this effect. At rest, SOD and GPX activities were increased after training. However, there was no evidence that exhausting exercise enhanced the levels of any antioxidant enzyme activity. The CAT activity was unchanged either by training or by exhausting exercise. These results indicate that high-intensity endurance training can elevate antioxidant enzyme activities in erythrocytes, and decrease neutrophil O2•− production in response to exhausting exercise. Furthermore, this up-regulation in antioxidant defences was accompanied by a reduction in exercise-induced lipid peroxidation in erythrocyte membrane.

Non-invasive cardiac output evaluation during a maximal progressive exercise test, using a new impedance cardiograph device.

Abstract: One of the greatest challenges in exercise physiology is to develop a valid, reliable, non-invasive and affordable measurement of cardiac output (CO). The purpose of this study was to evaluate the reproducibility and accuracy of a new impedance cardiograph device, the Physio Flow, during a 1-min step incremental exercise test from rest to maximal peak effort. A group of 12 subjects was evaluated to determine the reproducibility of the method as follows: (1) each subject performed two comparable tests while their CO was measured by impedance cardiography using the new device (COImp1, COImp2), and (2) in a subgroup of 7 subjects CO was also determined by the direct Fick method (COFick) during the second test. The mean difference between the values obtained by impedance (i.e. COImp1-COImp2) was -0.009 l.min-1 (95% confidence interval: -4.2 l.min-1, 4.2 l.min-1), and CO ranged from 3.55 l.min-1 to 26.75 l.min-1 (n = 146). When expressed as a percentage, the difference (COImp1-COImp2) did not vary with increasing CO. The correlation coefficient between the values of COImp and COFick obtained during the second exercise test was r = 0.94 (P < 0.01, n = 50). The mean difference expressed as percentage was -2.78% (95% confidence interval: -27.44%, 21.78%). We conclude that COImp provides a clinically acceptable evaluation of CO in healthy subjects during an incremental exercise.

The expression of lactate transporters (MCT1 and MCT4) in heart and muscle.

Abstract: It is now known that lactate traverses the plasma membrane of many tissues, including heart and muscle, via a stereo-specific, pH-dependent monocarboxylate transport (MCT) system. In the past few years a family of MCTs (MCT1-MCT7) has been cloned. Transcripts of MCT1 and MCT4 are detectable in rat and human skeletal muscle and in the heart. However, only skeletal muscle expresses both the MCT1 and MCT4 proteins, whereas rat heart expresses the MCTI, but not the MCT4 protein. The kinetic activities of MCT1(Km=3.5 mM) and MCT4 (Km= 17-34 mM) are quite different. Among rat muscles, MCT1 expression is highly correlated with the oxidative fiber composition of the muscle, and other indices of oxidative metabolism. Lactate uptake from the circulation is also highly correlated with the MCT1 content of muscles. MCT4 is confined to fast-twitch (fast glycolytic and fast oxidative glycolytic) muscle fibers, in which MCT4 content is correlated with indices of anaerobic metabolism. Collectively, these data suggest that MCT1 and MCT4 are primarily responsible for lactate uptake from the circulation and lactate extrusion out of muscle, respectively. Exercise training can increase the expression of both MCT1 and MCT4 in human muscle, although the extent of this up-regulation may be related to the intensity of training. In the rat heart, MCT1 expression is induced more easily by exercise training than in rat skeletai muscle. It appears that MCT1 and MCT4 expression are regulated in a tissue-specific and isoform-specific manner. Therefore, skeletal muscle lactate concentrations are not only regulated by the rate of glycolysis, but also by the efficiency of trans-sarcolemmal lactate transport, a process that is regulated by the quantity of available MCT proteins.

Oxygen uptake during whole-body vibration exercise: comparison with squatting as a slow voluntary movement.

Abstract: In this study we investigated metabolic power during whole-body vibration exercise (VbX) compared to mild resistance exercise. Specific oxygen consumption ( % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $\dot V{\rm O}_{\rm 2} $ ) and subjectively perceived exertion (rating of perceived exertion, RPE; Borg scale) were assessed in 12 young healthy subjects (8 female and 4 male). The outcome parameters were assessed during the last minute of a 3-min exercise bout, which consisted of either (1) simple standing, (2) squatting in cycles of 6 s to 90° knee flexion, and (3) squatting as before with an additional load of 40% of the subject's body weight (35% in females). Exercise types 1–3 were performed with (VbX+) and without (VbX–) platform vibration at a frequency of 26 Hz and an amplitude of 6 mm. Compared to the VbX– condition, the specific % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $\dot V{\rm O}_{\rm 2} $ was increased with vibration by 4.5 ml·min–1·kg–1. Likewise, squatting and the additional load were factors that further increased % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $\dot V{\rm O}_{\rm 2} $ . Corresponding changes were observed in RPE. There was a correlation between VbX– and VbX+ values for exercise types 1–3 (r=0.90). The correlation coefficient between squat/no-squat values (r=0.70 without and r=0.71 with the additional load) was significantly lower than that for VbX–/VbX+. Variation in specific % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdAfawzaaca % Gaee4ta80aaSbaaSqaaiabbkdaYaqabaaaaa!386A! $\dot V{\rm O}_{\rm 2} $ was significantly higher in the squatting paradigm than with vibration. It is concluded that the increased metabolic power observed in association with VbX is due to muscular activity. It is likely that this muscular activity is easier to control between individuals than is simple squatting.

Markers of inflammation and myofibrillar proteins following eccentric exercise in humans.

Abstract: The purpose of this study was to examine the time-course and relationships of technetium-99m (99mTc) neutrophils in muscle, interleukin-6 (IL-6), myosin heavy chain fragments (MHC), eccentric torque, and delayed onset muscle soreness (DOMS) following eccentric exercise in humans. Twelve male subjects completed a pre-test DOMS questionnaire, performed a strength test and had 100 ml blood withdrawn for analysis of plasma IL-6 and MHC content. The neutrophils were separated, labelled with 99mTc, and re-infused into the subjects immediately before the exercise. Following 300 eccentric repetitions of the right quadriceps muscles on an isokinetic dynamometer, the subjects had 10 ml of blood withdrawn and repeated the eccentric torque exercise tests and DOMS questionnaire at 0, 2, 4, 6, 20, 24, 48, 72 h, and 6 and 9 days. Bilateral images of the quadriceps muscles were taken at 2, 4, and 6 h. Computer analysis of regions of interest was used to determine the average count per pixel. The 99mTc neutrophils and IL-6 increased up to 6 h post-exercise (P < 0.05). The neutrophils were greater in the exercised muscle than the non-exercised muscle (P < 0.01). The DOMS was increased from 0 to 48 h, eccentric torque decreased from 2 to 24 h, and MHC peaked at 72 h post-exercise (P < 0.001). Significant relationships were found between IL-6 at 2 h and DOMS at 24 h post-exercise (r=0.68) and assessment of the magnitude of change between IL-6 and MHC (r=0.66). These findings suggest a relationship between damage to the contractile proteins and inflammation, and that DOMS is associated with inflammation but not with muscle damage.

Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions

Abstract: The purpose of this study was to examine and describe the neuromuscular changes associated with fatigue using a self-paced cycling protocol of 60-min duration, under warm, humid conditions. Eleven subjects [mean (SE) age 21.8 (0.8) years; height 174.9 (3.0) cm; body mass 74.8 (2.7) kg; maximum oxygen consumption 50.3 (1.8) ml · kg · min−1] performed one 60-min self-paced cycling time trial punctuated with six 1-min “all out” sprints at 10-min intervals, while 4 subjects repeated the trial for the purpose of determining reproducibility. Power output, integrated electromyographic signal (IEMG), and mean percentile frequency shifts (MPFS) were recorded at the mid-point of each sprint. There were no differences between trials for EMG variables, distance cycled, mean heart rate, and subjective rating of perceived exertion for the subjects who repeated the trial (n=4). The results from the repeated trials suggest that neuromuscular responses to self-paced cycling are reproducible between trials. The mean heart rate for the 11 subjects was 163.6 (0.71) beats · min−1. Values for power output and IEMG expressed as a percentage of that recorded for the initial sprint decreased during sprints 2–5, with normalised values being 94%, 91%, 87% and 87%, respectively, and 71%, 71%, 73%, and 77%, respectively. However, during the final sprint normalised power output and IEMG increased to 94% and 90% of initial values, respectively. MPFS displayed an increase with time; however, this was not significant (P=0.06). The main finding of this investigation is the ability of subjects to return power output to near initial values during the final of six maximal effort sprints that were included as part of a self-paced cycling protocol. This appears to be due to a combination of changes in neuromuscular recruitment, central or peripheral control systems, or the EMG signal itself. Further investigations in which changes in multiple physiological systems are assessed systematically are required so that the underlying mechanisms related to the development of fatigue during normal dynamic movements such as cycling can be more clearly delineated.

The effect of endurance training on resting heart rate variability in sedentary adult males.

Abstract: Eleven previously sedentary adult males, serving as the experimental (EXP) group [mean (SE) age 36.6 (1.7) years, body mass 87.2 (4.3) kg, body mass index, BMI, 28.4 (1.5) kg·m–2] participated in a 16-week supervised exercise program (3 days·week–1, 30 min·day–1, at ≅80% of heart rate reserve) to determine the temporal effects of a moderate-to-vigorous-intensity exercise program on heart rate variability (HRV). Five sedentary males [mean (SD) age 36.6 (4.2 )years, body mass 83.8 (6.6) kg, BMI 22.8 (1.7) kg·m–2] served as non-exercising controls (CON). HRV was measured every 4 weeks from a resting electrocardiogram obtained while subjects paced their breathing at 10 breaths·min–1 (0.167 Hz). The time-domain measures of HRV recorded were the proportion of adjacent intervals differing by more than 50 ms (pNN50), the root mean square of successive differences (rMSSD), and the standard deviation of the resting interbeat interval. The frequency-domain measures recorded were high (HF) and low (LF) frequency oscillations, as determined using the fast Fourier transform technique. Aerobic capacity (i.e., peak oxygen uptake) increased by 13.8% in EXP (P<0.001), but did not change in CON. Resting heart rate did not change in either EXP or CON. In EXP, pNN50 at week 12 (P<0.01), rMSSD at weeks 12 (P<0.01) and 16 (P=0.05), and HF power at weeks 12 (P<0.01) and 16 (P=0.05) were elevated above baseline. Time- and frequency-domain measures of HRV remained unchanged in CON. It is concluded that a moderate-to-vigorous-intensity exercise program produces increases in time- and frequency-domain measures of HRV within 12 weeks.

Changes in muscle size, architecture, and neural activation after 20 days of bed rest with and without resistance exercise.

Abstract: Nine healthy men carried out head-down bed rest (BR) for 20 days Five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not Before and after BR, maximal isometric knee extension force was measured Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length) Decrease in mean muscle force after BR was greater in NT [−109 (SD 69)%, P < 005] than in TR [05 (SD 79)%, not significant] Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group The PCSA decreased in NT by −78 (SD 08)% (P < 005) while in TR PCSA showed only an insignificant tendency to decrease [−38 (SD 38)%] Changes in force were related more to changes in neural activation levels than to those in PCSA The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure

Preliminary results on mood state, salivary testosterone:cortisol ratio and team performance in a professional soccer team.

Abstract: Mood, as measured by the profile of mood states questionnaire (POMS), salivary cortisol (F) and testosterone (T) levels, and performance were examined in 17 male soccer players 4 times during a season. Soccer players provided three saliva samples when getting up (resting values, 8 a.m.), before breakfast (11.30 a.m.), and between 4.00p.m. and 6.00 p.m. The initial measures were performed 1 day following the start of season training (T1). They were then performed before and after a high-intensity training programme (T2 and T3, respectively) and 16 weeks after T3 (T4). Iceberg profiles of POMS were observed during T1, T2 and T3, which coincided with successful performance. Subsequent decreased performance between T3 and T4 coincided with a decrease in vigor and an increase in tension and depression. Indeed, when the normal nycthemeral rhythm for F was observed (i.e. a decrease from morning until evening at all times; T1–T4), there was seemingly a non-statistical elevation of F on the morning of T3, which only became statistically significant at 11.30 a.m. on T3. In spite of a post-high-intensity training programme (T3) increase in catabolism, the soccer players presented iceberg profiles together with a high percentage of winning. Our results could suggest that in team soccer, a decreased T:F ratio does not automatically lead to a decrease in team performance or a state of team overtraining. It appears that combined psychological and physiological changes during high-intensity training are primarily of interest when monitoring training stress in relation to performance.

Maximal voluntary force and rate of force development in humans--importance of instruction.

Abstract: The present investigation has been designed to confirm the effect of instruction (hard-and-fast instruction compared to fast instruction) upon maximal voluntary isometric force (MVF) and maximal rate of force development (MRFD) in muscle groups which differ with regards to muscle mass and usage. In addition, we took advantage of the force data collected during unilateral and bilateral leg extension, to compare the instruction effects on the indices of the bilateral deficits (BI, the differences between the data collected during bilateral extensions and the sum of the data collected during unilateral left and right extensions) with regard to MVF (BIMVF) and MRFD (BIMRFD). Force-time curves were recorded during maximal isometric contractions of the elbow flexors, the leg extensors of the take-off and lead legs and during bilateral leg extension in 26 healthy young male volunteers from the track-and-field national team of Tunisia. In the first protocol, the subjects were instructed to produce MFV as hard-and-fast as possible (instruction I). In the second protocol (instruction II) the subjects were instructed to provide MFRD, that is the most explosive force, by concentrating on the fastest contraction without concern for achieving maximal force. The present study confirmed the importance of an appropriate instruction for the measurement of MRDF. The MRFD (F=40.8, P<0.001) were significantly higher when measured after instruction II compared to instruction I. The effect of the instruction upon MRFD were similar for muscle groups with different volumes, cortical representations and uses. The same results (F=52.1; P<0.001) were observed when MRFD was related to MVF [MRFD%=(MRFD/MVF)×100]. On the other hand, MVF was similar following both instructions (ANOVA, F=0.562; P=0.454). Moreover, the results of the present study suggested that the effect of instruction was significantly larger for BIMRFD than forBIMVF.

The relationship between critical velocity, maximal lactate steady-state velocity and lactate turnpoint velocity in runners.

Abstract: In cycle exercise, it has been suggested that critical power, maximal lactate steady state, and lactate turnpoint all demarcate the transition between the heavy exercise domain (in which blood lactate is elevated above resting values but remains stable over time) and the very heavy exercise domain (in which blood lactate increases continuously throughout constant-intensity exercise). The purpose of the present study was to assess the level of agreement between critical velocity (CV), maximal lactate steady-state velocity (MLSSV), and lactate turnpoint velocity (LTPV) during treadmill running. Eight male subjects [mean (SD) age 28 (5) years, body mass 71.2 (8.0) kg, maximum oxygen uptake 54.9 (3.2) ml.kg(-1).min(-1)) performed an incremental treadmill test for the determination of LTPV (defined as a sudden and sustained increase in blood lactate concentration ([La]) at approximately equals 2.0-5.0 mM). The subjects returned to the laboratory on eight or nine occasions for the determination of CV and MLSSV. The CV was determined from four treadmill runs at velocities that were chosen to result in exhaustion within 2-12 min. The MLSSV was determined from four or five treadmill runs of up to 30 min duration and defined as the highest velocity at which blood [La] increased by no more than 1.0 mM after between 10 and 30 min of exercise. Analysis of variance revealed no significant differences between [mean (SD)] CV [14.4 (1.1) km.h(-1)], MLSSV [13.8 (1.1) km.h(-1)] and LTPV [13.7 (0.6) km.h(-1)]. However, the bias +/-95% limits of agreement for comparisons between CV and MLSSV [0.6 (2.2) km.h(-1)], CV and LTPV [0.7 (2.7) km.h(-1)], and MLSSV and LTPV [0.1 (1.8) km.h(-1)] suggest that the extent of disagreement is too great to allow one variable to be estimated accurately from another in individual subjects. Direct determination of MLSSV is necessary if precision is required in experimental studies.

Peak oxygen uptake in relation to growth and maturation in 11- to 17-year-old humans.

Abstract: This study used multilevel modelling to examine peak oxygen uptake (VO2peak) during growth and maturation. Body mass, stature, triceps and subscapular skinfold thicknesses, blood haemoglobin concentration, and VO2peak of boys and girls, [mean (SD)] aged 11.1 (0.4) years at the onset of the study, were measured at ages 11, 12, 13 and 17 years. Sexual maturation was assessed on the first three occasions and was assumed to be Tanner stage 5 at 17 years. The analysis was founded on 388 VO2peak determinations from 132 children. The initial model revealed mass, stature and age as significant explanatory variables of VO2peak with an additional positive effect for stage of maturity. Girls' values were significantly lower than those of boys and a significant age-by-sex interaction described a progressive divergence in boys' and girls' VO2peak. The introduction of skinfold thicknesses produced a model with an improvement in fit. The stature term was negated and the mass exponent almost doubled. The sex and age-by-sex terms were reduced but remained significant. Many of the observed maturity effects were explained with stage 5 becoming non-significant. Blood haemoglobin concentration was a nonsignificant parameter estimate in both models. Fat-free mass was the dominant influence on the growth of VO2peak but the multilevel regression models demonstrated that, with body size and fatness allowed for, VO2peak increased with age and maturation in both sexes.

Assessment of lower-back muscle fatigue using electromyography, mechanomyography, and near-infrared spectroscopy.

Abstract: We have investigated the etiology of lower-back muscle fatigue using simultaneous recordings of electromyography (EMG), mechanomyography (MMG), and near-infrared spectroscopy (NIRS) in an attempt to shed some light on the electrophysiological, mechanical, and metabolic characteristics, respectively. Eight male subjects performed isometric back extensions at an angle of 15° with reference to the horizontal plane, for a period of 60 s. Surface EMG, MMG and NIRS signals were recorded simultaneously from the center of the erector spinae at the level of L3. NIRS was measured to determine the level of muscle blood volume (BV) and oxygenation (Oxy-Hb). The root mean square amplitude value (RMS) of the EMG signal was significantly increased at the initial phase of contraction and then fell significantly, while mean power frequency (MPF) of the EMG signal decreased significantly and progressively as a function of time. There were also significant initial increases in RMS-MMG that were followed by progressive decreases at the end of fatiguing contractions. MPF-MMG remained unchanged. Muscle BV and Oxy-Hb decreased dramatically at the onset of the contraction and then remained almost constant throughout the rest of the contraction. These results, obtained by simultaneous recordings of EMG, MMG, and NIRS, demonstrate that the restriction of blood flow due to high intramuscular mechanical pressure is one of the most important factors in muscle fatigue in the lower-back muscles. In addition, the simultaneous recording system described here can be used to obtain more reliable information regarding the mechanism(s) of lower-back muscle fatigue.

The repeated bout effect of reduced-load eccentric exercise on elbow flexor muscle damage.

Abstract: In this study we investigated the extent to which an initial eccentric exercise consisting of two (2ECC) or six maximal eccentric actions (6ECC) of the elbow flexors would produce a similar effect to 24 maximal eccentric actions (24ECC), on a second bout of 24ECC performed 2 weeks later. Male students (n = 34) were assigned to one of three groups, and with their non-dominant arm performed either 2ECC (n = 12), 6ECC (n = 10), or 24ECC (n = 12) as a first bout of exercise. Two weeks later all groups performed 24ECC. Maximal isometric strength, range of motion, upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were assessed before, immediately after, and for 4 days after exercise. Changes in all variables were compared between the bouts and groups by a two-way repeated measures analysis of variance. All variables changed significantly (P< 0.05) after 2ECC, 6ECC, and 24ECC, but the amount of change after 2ECC and 6ECC was significantly smaller (P<0.05) than both 6ECC and 24ECC, and 24ECC, respectively. After the second bout, the 6ECC and 24ECC groups showed a profound repeated bout effect, and no significant differences were found between the groups. All variables except muscle soreness were significantly (P< 0.05) larger after the second bout for the 2ECC group, however the changes observed after 24ECC were significantly smaller (P < 0.01) than those observed after the first 24ECC of the 24ECC group. These results suggest that it is not necessary to conduct a high number of eccentric actions in the first bout to elicit a repeated bout effect in a subsequent bout performed some time later.

Force recovery after eccentric exercise in males and females

Abstract: In this study we investigated force loss and recovery after eccentric exercise, and further characterized profound losses in muscle function (n=192 subjects – 98 males, 94 females; population A). Maximal voluntary contractile force (MVC) was assessed before, immediately after, and at 36 and 132 h after eccentric exercise. Two groups were then established (A1 and A2). Group A1 demonstrated a >70% reduction in MVC immediately after exercise, but were recovering at 132 h after exercise. These subjects performed a follow-up MVC 26 days later (n=32). Group A2 demonstrated a >70% reduction in MVC immediately post-exercise, but still exhibited a >65% reduction in force at 132 h post-exercise; these subjects also performed a follow-up MVC every 7 days until full recovery was established (n=9). In population A, there was a 57% reduction in MVC immediately post-exercise and a 67% recovery by 132 h post-exercise (P 0.05). In group A1, although more females (two-thirds) showed large force losses after exercise, these females demonstrated greater %MVC recovery at 132 h post-exercise (59% vs 44%) and at 26 days post-exercise (93% vs 81%) compared to the males. In group A2, MVC recovery occurred between 33 and 47 days post-exercise. In conclusion, 21% of all subjects showed a delayed recovery in MVC after high-force eccentric exercise. Although there were no significant gender differences in force loss, a disproportionately larger number of females demonstrated force reductions of >70%. However, their recovery of force was more rapid than that observed for the males who also demonstrated a >70% force loss.

Human body surface area: measurement and prediction using three dimensional body scans.

Abstract: The development of three dimensional laser scanning technology and sophisticated graphics editing software have allowed an alternative and potentially more accurate determination of body surface area (BSA). Raw whole-body scans of 641 adults (395 men and 246 women) were obtained from the anthropometric data base of the Civilian American and European Surface Anthropometry Resource project. Following surface restoration of the scans (i.e. patching and smoothing), BSA was calculated. A representative subset of the entire sample population involving 12 men and 12 women (G24) was selected for detailed measurements of hand surface area (SAhand) and ratios of surface area to volume (SA/VOL) of various body segments. Regression equations involving wrist circumference and arm length were used to predict SAhand of the remaining population. The overall [mean (SD)] of BSA were 2.03 (0.19) and 1.73 (0.19) m2 for men and women, respectively. Various prediction equations were tested and although most predicted the measured BSA reasonably closely, residual analysis revealed an overprediction with increasing body size in most cases. Separate non-linear regressions for each sex yielded the following best-fit equations (with root mean square errors of about 1.3%): BSA (cm2) = 128.1 x m0.44 x h0.60 for men and BSA = 147.4 x m0.47 x h0.55 for women, where m, body mass, is in kilograms and h, height, is in centimetres. The SA/VOL ratios of the various body segments were higher for the women compared to the men of G24, significantly for the head plus neck (by 7%), torso (19%), upper arms (15%), forearms (20%), hands (18%), and feet (11%). The SA/VOL for both sexes ranged from approximately 12.m-1 for the pelvic region to 104-123.m-1 for the hands, and shape differences were a factor for the torso and lower leg.

Cyclic mechanical stretching modulates secretion pattern of growth factors in human tendon fibroblasts

Abstract: The objective of the study was to investigate whether the response profile of the growth factor of human tendon fibroblasts could be beneficially influenced through the application of mechanical stretch. It was considered that this would elucidate structural and functional problems, often seen after tendon and ligament healing. The secretion pattern of transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) was determined in mechanically stretched fibroblasts and compared to non-stretched controls. Human tendon fibroblasts were experimentally stretched for 15 and 60 mm at a frequency of 1 Hz and an amplitude of 5%. The secretion of TGF-beta PDGF and bFGF was measured by enzyme-linked immuno-sorbent assay. All the growth factors investigated were indeed secreted by human tendon fibroblasts both in stretched cells and controls. Mechanical stretch increased the secretion pattern of the growth factors. The increased concentrations of TGF-beta bFGF and PDGF after cyclical mechanical stretching may have a positive influence on tendon and ligament healing through stimulation of cell proliferation, differentiation and matrix formation.

Extreme human breath-hold diving

Abstract: In this paper, the respiratory, circulatory and metabolic adjustments to human extreme breath-hold diving are reviewed. A survey of the literature reveals that in extreme divers, adaptive mechanisms take place that allow prolongation of apnoea beyond the limits attained by non-diving subjects, and preservation of oxygen stores during the dives. The occurrence of a diving response, including peripheral vasoconstriction, increased arterial blood pressure, bradycardia and lowered cardiac output, is strongly implicated. Some peripheral regions may be excluded from perfusion, with consequent reliance on anaerobic metabolism. In addition, extreme breath-hold divers show a blunted ventilatory response to carbon dioxide breathing, possibly as a consequence of frequent exposure to high carbon dioxide partial pressures during the dives. These mechanisms allow the attainment of particularly low alveolar oxygen ( 50 mmHg) partial pressures at the end of maximal dry breath-holds, and reduce oxygen consumption during the dive at the expense of increased anaerobic glycolysis (rate of blood lactate accumulation > 0.04 mM.s-1). The current absolute world record for depth in breath-hold diving is 150 m. Its further improvement depends upon how far the equilibrium between starting oxygen stores, the overall rate of energy expenditure, the fraction of energy provided by anaerobic metabolism and the diving speed can be pushed, with consciousness upon emersion. The ultimate limit to breath-hold diving records may indeed be imposed by an energetic constraint.

Force/velocity and power/velocity relationships in squat exercise.

Abstract: The purpose of this study was to describe the force/velocity and power/velocity relationships obtained during squat exercise. The maximal force (F0) was extrapolated from the force/velocity relationship and compared to the isometric force directly measured with the aid of a force platform placed under the subject's feet. Fifteen international downhill skiers [mean (SD) age 22.4 (2.6) years, height 178 (6.34) cm and body mass 81.3 (7.70) kg] performed maximal dynamic and isometric squat exercises on a guided barbell. The dynamic squats were performed with masses ranging from 60 to 180 kg, which were placed on the shoulders. The force produced during the squat exercise was linearly related to the velocity in each subject (r2 = 0.83-0.98, P < 0.05-0.0001). The extrapolated F0 was 23% higher than the measured isometric force (P < 0.001), and the two measurements were not correlated. This may be attributed to the position of the subject, since the isometric force was obtained at a constant angle (90 degrees of knee flexion), whereas the dynamic forces were measured through a range of movements (from 90 degrees to 180 degrees). The power/velocity relationship was parabolic in shape for each subject (r2 = 0.94-0.99, P < 0.01-0.0001). However, the curve obtained exhibited only an ascending part. The highest power was produced against the lightest load (i.e., 60 kg). The maximal power (Wmax) and optimal velocity were never reached. The failure to observe the descending part of the power/velocity curve may be attributed to the upper limitation of the velocities studied. Nevertheless, the extrapolation of Wmax from the power/velocity equation showed that it would be reached for a load close to body mass, or even under unloaded conditions.

Post-exercise recovery of autonomic cardiovascular control: a study by spectrum and cross-spectrum analysis in humans.

Abstract: The recovery of the baseline autonomic control of cardiovascular activity after exercise has not been extensively studied. In 12 healthy subjects, we assessed the time-course of recovery by autoregressive spectrum and cross-spectrum analysis of heart period and systolic blood pressure during the 3 h after the end of 20 min of steady-state exercise at 50% (light workload, LW) and 80% (moderate workload, MW) of the individual's anaerobic threshold. The electrocardiogram and non-invasive blood pressure were simultaneously recorded during 10 min periods in the sitting position, at rest before exercise, and at 15, 60 and 180 min of recovery after exercise. At 15 min we observed a persistent tachycardia and relative hypotension; after MW, at 60 min heart rate was still slightly higher. Spectrum and cross-spectrum analysis showed, at 15 min, an increase in the low frequency component of systolic blood pressure, a reduction in the high frequency component of heart rate (larger in MW), and a decrease in baroreceptor sensitivity. After 60 and 180 min none of these parameters was significantly different from those at rest, although, in MW, some subjects still displayed signs of sympathetic activation after 1 h. We concluded that, after 15 min of recovery, the cardiovascular reflexes were blunted, that sympathetic nerve activity was still enhanced, and that the tone in the vagus had not fully recovered. Only the persistent vagal restraint seemed to be exercise intensity-dependent. For complete restoration of autonomic control after LW 1 h of rest was sufficient, and just enough after MW.

Respiratory muscle training increases cycling endurance without affecting cardiovascular responses to exercise.

Abstract: We tested whether the increased cycling endurance observed after respiratory muscle training (RMT) in healthy sedentary humans was associated with a training-induced increase in cardiac stroke volume (SV) during exercise, similar to the known effect of endurance training. Thirteen subjects underwent RMT by normocapnic hyperpnea, nine underwent aerobic endurance training (cycling and/or running) and fifteen served as non-training controls. Training comprised 40 sessions performed within 15 weeks, where each session lasted 30 min. RMT increased cycling endurance at 70% maximal aerobic power (\(\dot W_{{\rm max}} \) ) by 24% [mean (SD) 35.6 (11.9) min vs 44.2 (17.6) min, P<0.05], but SV at 60% \(\dot W_{{\rm max}} \) was unchanged [94 (21) ml vs 93 (20) ml]. Aerobic endurance training increased both SV [89 (24) ml vs 104 (32) ml, P<0.01] and cycling endurance [37.4 (12.8) min vs 52.6 (16.9) min, P<0.01]. In the control group, no changes were observed in any of these variables. It is concluded that the increased cycling endurance that is observed after RMT is not due to cardiovascular adaptations, and that the results provide evidence for the role of the respiratory system as an exercise-limitingfactor.

Chemokines are elevated in plasma after strenuous exercise in humans

Abstract: During the last few years much attention has been paid to the chemokines. Chemokine receptors are necessary to render a target permissive for infection by the human immunodeficiency virus (HIV) and high concentrations of chemokines have been shown to protect against the progression of HIV disease towards death. In the present study, we investigated the capability of strenuous exercise to induce elevated plasma concentrations of the chemokines interleukin (IL)-8, macrophage inflammatory protein (MIP)-1α and MIP-1β. Eight male athletes completed the Copenhagen Marathon 1997. Blood was sampled before, immediately after the run and every 30 min during a 4 h recovery period. Plasma chemokine concentrations were measured using enzyme-linked immunosorbent assays. The IL-8, MIP-1α and MIP-1β concentrations all peaked 0.5 h after the run when they were 6.7-fold, 3.5-fold and 4.1-fold increased, respectively. The elevated concentrations of chemokines in plasma after exercise could have implications for HIV-infected individuals; a possibility that needs further investigation.

Adaptation of the left heart, cerebral and femoral arteries, and jugular and femoral veins during short- and long-term head-down tilt and spaceflights

Abstract: The objective of this investigation was to identify the major cardiovascular changes induced by exposure to real or simulated 0g (spaceflights: 6, 14, 21 and 25 days, and 6 months; head down tilt, HDT: 10 h, 4, 5, 7, 30 and 42 days), with a minimum of countermeasures. The following cardiovascular data were measured by echocardiography and Doppler ultrasonography: left ventricle end-diastolic volume (LVDV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), middle cerebral artery flow velocity (\(\)\(\dot Q_{{\rm ca}} \) ), femoral artery flow velocity (\(\)\(\dot Q_{{\rm fa}} \) ), cerebral vascular resistance (Rca), femoral vascular resistance (Rfa), jugular vein cross-sectional area (Ajv), femoral vein cross-sectional area (Afv), heart rate (HR), and mean blood pressure (MBP). LVDV remained decreased compared to pre-HDT or pre-flight levels after 1 week of spaceflight or HDT (–8 to –13%, P<0.05), EF did not change. HR tended to increase (5–10%) during spaceflight and HDT, whereas MBP tended to decrease during flight, but did not change in HDT. These findings are consistent with the existence of a moderate and stable hypovolemia. \(\)\(\dot Q_{{\rm ca}} \) and Rca fluctuated between +10 and –10% from pre-HDT or pre-flight values, and always showed opposing variations. There was no significant decrease in cerebral perfusion. Lower-limb resistance (Rfa) remained decreased (–5% to –18%, P<0.05) throughout the flights or HDT after week 1. Ajv remained significantly enlarged (+40% P<0.05) after 1 week in spaceflight or in HDT. Afv was enlarged in spaceflight after week 1 (+15% to +35%, P<0.05), whereas it decreased after 4–5 days of HDT (–20% to –35%, P<0.05). The cardiovascular system reached a new and stable equilibrium during flight and HDT within less than 1 week. With the exception of the femoral vein, there was no significant difference in either the amplitude or the time course of the cardiovascular changes in both situations after 1 week.

Measurement and prediction of peak shivering intensity in humans.

Abstract: Prediction equations of shivering metabolism are critical to the development of models of thermoregulation during cold exposure. Although the intensity of maximal shivering has not yet been predicted, a peak shivering metabolic rate (Shivpeak) of five times the resting metabolic rate has been reported. A group of 15 subjects (including 4 women) [mean age 24.7 (SD 6) years, mean body mass 72.1 (SD 12) kg, mean height 1.76 (SD 0.1) m, mean body fat 22.3 (SD 7)% and mean maximal oxygen uptake (VO2max) 53.2 (SD 9) ml O2.kg-1.min-1] participated in the present study to measure and predict Shivpeak. The subjects were initially immersed in water at 8 degrees C for up to 70 min. Water temperature was then gradually increased at 0.8 degree C.min-1 to a value of 20 degrees C, which it was expected would increase shivering heat production based on the knowledge that peripheral cold receptors fire maximally at approximately this temperature. This, in combination with the relatively low core temperature at the time this water temperature was reached, was hypothesized would stimulate Shivpeak. Prior to warming the water from 8 to 20 degrees C, the oxygen consumption was 15.1 (SD 5.5) ml.kg-1.min-1 at core temperatures of approximately 35 degrees C. After the water temperature had risen to 20 degrees C, the observed Shivpeak was 22.1 (SD 4.2) ml O2.kg-1.min-1 at core and mean skin temperatures of 35.2 (SD 0.9) and 22.1 (SD 2.2) degrees C, respectively. The Shivpeak corresponded to 4.9 (SD 0.8) times the resting metabolism and 41.7 (SD 5.1)% of VO2max. The best fit equation predicting Shivpeak was Shivpeak (ml O2.kg-1.min-1) = 30.5 + 0.348 x VO2max (ml O2.kg-1.min-1) - 0.909 x body mass index (kg.m-2) - 0.233 x age (years); (P = 0.0001; r2 = 0.872).

Change in post-exercise vagal reactivation with exercise training and detraining in young men.

Abstract: We studied the effects of aerobic exercise training and detraining in humans on post-exercise vagal reactivation. Ten healthy untrained men trained for 8 weeks using a cycle ergometer [70% of initial maximal oxygen uptake (VO2max) for 1 h, 3-4 days.week-1] and then did not exercise for the next 4 weeks. Post-exercise vagal reactivation was evaluated as the time constant of the beat-by-beat decrease in heart rate during the 30 s (t30) immediately following 4 min exercise at 80% of ventilatory threshold (VT). The VO2max and the oxygen uptake at VT had significantly increased after the 8 weeks training programme (P < 0.0001, P < 0.001, respectively). The t30 had shortened after training, and values after 4 weeks and 8 weeks of training were significantly shorter than the initial t30 (P < 0.05, P < 0.01, respectively). The change in the t30 after 8 weeks of training closely and inversely correlated with the initial t30 (r = -0.965, P < 0.0001). The reduced t30 was prolonged significantly after 2 weeks of detraining, and had returned almost to the baseline level after a further 2 weeks of detraining. These results suggest that aerobic exercise training of moderate intensity accelerates post-exercise vagal reactivation, but that the accelerated function regresses within a few weeks of detraining.

Mechanomyogram and force relationship during voluntary isometric ramp contractions of the biceps brachii muscle

Abstract: The aim of the present study was to examine the non-stationary mechanomyogram (MMG) during voluntary isometric ramp contractions of the biceps brachii muscles using the short-time Fourier transform, and to obtain more detailed information on the motor unit (MU) activation strategy underlying in the continuous MMG/force relationship. The subjects were asked to exert ramp contractions from 5% to 80% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. The root mean squared (RMS) amplitude of the MMG began to increase slowly at low levels of force, then there was a slight reduction between 12% and 20% MVC. After that, a progressive increase was followed by a decrease beyond 60% MVC. As to the mean power frequency (MPF), a relatively rapid increase up to 30% MVC was followed by a period of slow increment between 30% and 50% MVC. Then temporary reduction at around 50% MVC and a further rapid increase above 60% MVC was observed. The interaction between amplitude and MPF of the MMG in relation to the MU activation strategy is discussed for five force regions defined on the basis of their inflection points in the RMS-amplitude/force and MPF/force relationships. It was found that the MMG during ramp contractions enables deeper insights into the MU activation strategy than those determined during traditional separate contractions. In addition, this contraction protocol is useful not only to ensure higher force resolution in the MMG/force relationship, but also to markedly shorten the time taken for data acquisition and to reduce the risk of fatigue.

Is passive stiffness in human muscles related to the elasticity of tendon structures

Abstract: The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles was measured during passive stretch from 90 degrees (anatomical position) to 65 degrees of dorsiflexion at a constant velocity of 5 degrees.s-1. The slope of the linear portion of the passive torque-angle curve during stretching was defined as the passive stiffness of the muscle. The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured using ultrasonography during ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force of MG and tendon elongation was fitted to a linear regression, the slope of which was defined as the stiffness of the tendon. In addition, the dynamic torques during maximal voluntary concentric plantar flexion with and without prior eccentric contraction were determined at a constant velocity of 120 degrees.s-1. There were no significant correlations between passive stiffness and either the tendon stiffness (r = 0.19, P > 0.05) or the relative increase in torque with prior eccentric contraction (r = -0.19, P > 0.05). However, tendon stiffness was negatively correlated to the relative increase in torque output (r = -0.42, P < 0.05). The present results suggested that passive stiffness was independent of the elasticity of tendon structures, and had no favourable effect on the muscle performance during stretch-shortening cycle exercise.

Adaptation to chronic eccentric exercise in humans: The influence of contraction velocity

Abstract: We compared changes in muscle fibre composition and muscle strength indices following a 10 week isokinetic resistance training programme consisting of fast (314 rads–1) or slow (052 rads–1) velocity eccentric muscle contractions A group of 20 non-resistance trained subjects were assigned to a FAST (n=7), SLOW (n=6) or non-training CONTROL (n=7) group A unilateral training protocol targeted the elbow flexor muscle group and consisted of 24 maximal eccentric isokinetic contractions (four sets of six repetitions) performed three times a week for 10 weeks Muscle biopsy samples were obtained from the belly of the biceps brachii Isometric torque and concentric and eccentric torque at 052 and 314 rads–1 were examined at 0, 5 and 10 weeks After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric [296 (64)%] and concentric torque [274 (73)%] at 314 rads–1, isometric torque [213 (43)%] and eccentric torque [252 (72)%] at 052 rads–1 The percentage of type I fibres in the FAST group decreased from [538 (66)% to 391 (44)%] while type IIb fibre percentage increased from [58 (19)% to 129 (33)%; P<005] In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque We conclude that neuromuscular adaptations to eccentric training stimuli may be influenced by differences in the ability to cope with chronic exposure to relatively fast and slow eccentric contraction velocities Possible mechanisms include greater cumulative damage to contractile tissues or stress induced by slow eccentric muscle contractions

The effect of heavy resistance exercise on the circadian rhythm of salivary testosterone in men.

Abstract: Circadian rhythms of serum testosterone concentrations in men have been shown, in general, to be highest in the morning and lowest in the evening. Thus, the purpose of this investigation was to determine the effects of acute resistance exercise upon the waking circadian rhythm of salivary testosterone over 2 days (with or without resistance exercise). The subjects included ten resistance-trained men (with at least 1 year of lifting experience) with the following characteristics [mean (SD)]: age 21.6 (1.1) years; height 177.8 (9.5) cm; body mass 80.5 (11.5) kg; percent body fat 7.9 (1.7)%. A matched, randomized, crossover study design was used such that each subject was tested under both the resistance exercise and control (no exercise) conditions. The resistance exercise protocol consisted of ten exercises performed for three sets of ten repetitions maximum with 2 min of rest between sets. Saliva sample 1 was collected at 0615 hours and resistance exercise began immediately afterwards at approximately 0620 hours, and sample 2 was collected at 0700 hours, which corresponded approximately to a mid-exercise (or control) time point. Saliva samples were then obtained every hour on the hour from 0800 hours until 2200 hours. No significant differences were observed between the exercise and resting conditions for salivary testosterone, with the exception of a significant decrease at 0700 hours during the resistance exercise protocol. The results of this investigation indicate that resistance exercise does not affect the circadian pattern of salivary testosterone secretion over a 16-h waking period in resistance-trained men.

Contraction-specific differences in maximal muscle power during stretch-shortening cycle movements in elderly males and females.

Abstract: Elderly people (age 75 years; n = 48 males and 34 females) were studied in order to elucidate gender differences in elderly subjects on the determinants of muscle power (force and velocity) during a stretch-shortening cycle. All subjects performed three maximal counter-movement vertical jumps using both legs, on a force platform (Kistler 9281 B). The eccentric (Ep) and concentric (Cp) phases of the jumps were analyzed. The Ep was further divided into an acceleration phase (Epacc: from the start of the downward movement to the maximal negative velocity) and deceleration phase (Epdec: from the maximal negative velocity to the end of the downward movement). Jump height for the men was higher than for the women (P < 0.001). During both Epacc and Epdec no significant differences were observed between males and females in force and power generation. However, the men had a higher peak muscle power during the Cp, which may be explained exclusively by the velocity determinant (P < 0.001). No specific gender-related strategy appeared to influence the motor pattern of the movement. The comparable eccentric force generation of the leg extensors in both genders suggests a similar ability to cope with eccentric muscle actions during everyday activities. In contrast, the marked lower capacity for concentric contractions in women may result in an impaired performance, especially in activities where intense and rapid movements are essential, for example when reversing a forward fall. This may be one reason why elderly women are more prone to falls than are elderly men.