Showing papers in "European Journal of Applied Physiology in 1996"

Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists

Abstract: Skeletal muscle buffering capacity (βm), enzyme activities and exercise performance were measured before and after 4 weeks of high-intensity, sub maximal␣interval training (HIT) undertaken by six well-trained competitive cyclists [mean maximal oxygen consumption (\(\)O2max) = 66.2 ml · kg−1 · min−1]. HIT replaced a portion of habitual endurance training and consisted of six sessions, each of six to eight repetitions of 5 min duration at 80% of peak sustained power output (PPO) separated by 1 min of recovery. βm increased from 206.6 (17.9) to 240.4 (34.1) μmol H+ · g muscle dw−1 · pH−1 after HIT (P = 0.05). PPO, time to fatigue at 150% PPO (TF150) and 40-km cycle time trial performance (TT40) all significantly improved after HIT (P < 0.05). In contrast, there was no change in the activity of either phosphofructokinase or citrate synthase. In addition, βm correlated significantly with TT40 performance before HIT (r = −0.82, P < 0.05) and the relationship between change in βm and change in TT40 was close to significance (r = −0.74). βm did not correlate with TF150. These results indicate that βm may be an important determinant of relatively short-duration (< 60 min) endurance cycling activity and responds positively to just six sessions of high-intensity, submaximal interval training.

Some aspects of the acute phase response after a marathon race, and the effects of glutamine supplementation.

Abstract: Strenuous exercise may be associated with immune suppression. However, the underlying mechanism is not known. A decrease in the plasma level of glutamine, which is utilised at a high rate by cells of the immune system, and an increase in the plasma level of some cytokines may impair immune functions such as lymphocyte proliferation after prolonged, exhaustive exercise. In two separate studies of the Brussels marathon, using similar protocols, the time course of the changes in the plasma concentrations of some amino acids (glutamine, glutamate, alanine, tryptophan and branched chain amino acids), acute phase proteins and cytokines (interleukins IL-1 alpha, IL-2, IL-6, tumour necrosis factor type a) was measured in male athletes. The numbers of circulating leucocytes and lymphocytes were also measured. Amino acid and cytokine concentrations have not previously been measured concomitantly in marathon runners; the measurement of some of these parameters the morning after the marathon (16 h) is novel. Another novel feature is the provision of glutamine versus placebo to marathon runners participating in the second study. In both studies the plasma concentrations of glutamine, alanine and branched chain amino acids were decreased immediately after and 1 h after the marathon. Plasma concentrations of all amino acids returned to pre-exercise levels by 16 h after exercise. The plasma concentration of the complement anaphylotoxin C5a increased to abnormal levels after the marathon, presumably due to tissue damage activating the complement system. There was also an increase in plasma C-reactive protein 16 h after the marathon. The plasma levels of IL-1 alpha were unaffected by the exercise, while that of IL-2 was increased 16 h after exercise. Plasma IL-6 was increased markedly (approximately 45-fold) immediately after and at 1 h after exercise. Neopterine, a macrophage activation marker, was significantly increased post-exercise. There was a marked leucocytosis immediately after the marathon, which returned to normal 16 h later. At the same time there was a decrease in the number of T-lymphocytes, which was further reduced within 1 h to below pre-exercise levels. Glutamine supplementation, as administered in the second study, did not appear to have an effect upon lymphocyte distribution.

Does glutamine have a role in reducing infections in athletes

Abstract: There is an increased risk of infections in athletes undertaking prolonged, strenuous exercise. There is also some evidence that cells of the immune system are less able to mount a defence against infections after such exercise. The level of plasma glutamine, an important fuel for cells of the immune system, is decreased in athletes after endurance exercise: this may be partly responsible for the apparent immunosuppression which occurs in these individuals. We monitored levels of infection in more than 200 runners and rowers. The levels of infection were lowest in middle-distance runners, and highest in runners after a full or ultra-marathon and in elite rowers after intensive training. In the present study, athletes participating in different types of exercise consumed two drinks, containing either glutamine (Group G) or placebo (Group P) immediately after and 2 h after exercise. They subsequently completed questionnaires (n = 151) about the incidence of infections during the 7 days following the exercise. The percentage of athletes reporting no infections was considerably higher in Group G (81%,n= 72) than in Group P (49%,n = 79,p<0.001).

Mechanically corrected EMG for the continuous estimation of erector spinae muscle loading during repetitive lifting.

Abstract: Few studies have been carried out on the changes in biomechanical loading on low-back tissues during prolonged lifting. The purpose of this paper was to develop a model for continuously estimating erector spinae muscle loads during repetitive lifting and lowering tasks. The model was based on spine kinematics and bilateral lumbar and thoracic erector spinae electromyogram (EMG) signals and was developed with the data from eight male subjects. Each subject performed a series of isometric contractions to develop extensor moments about the low back. Maximum voluntary contractions (MVCs) were used to normalize all recorded EMG and moment time-histories. Ramp contractions were used to determine the non-linear relationship between extensor moments and EMG amplitudes. In addition, the most appropriate low-pass filter cut-off frequencies were calculated for matching the rectified EMG signals with the moment patterns. The mean low-pass cut-off frequency was 2.7 (0.4) Hz. The accuracy of the non-linear EMG-based estimates of isometric extensor moment were tested with data from a series of six rapid contractions by each subject. The mean error over the duration of these contractions was 9.2 (2.6)% MVC. During prolonged lifting sessions of 20 min and of 2 h, a model was used to calculate changes in muscle length based on monitored spine kinematics. EMG signals were first processed according to the parameters determined from the isometric contractions and then further processed to account for the effects of instantaneous muscle length and velocity. Simple EMG estimates were found to underestimate peak loading by 9.1 (4.0) and 25.7 (11.6)% MVC for eccentric and concentric phases of lifting respectively, when compared to load estimates based on the mechanically corrected EMG. To date, the model has been used to analyze over 5300 lifts.

Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans

Abstract: The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from −120 to 300°·s−1). The rms amplitude of each muscle was normalized with respect to its rms amplitude when acting as agonist at 15°·s−1. Whatever the angular velocity considered, peals torque and constant angular torque at 65° HS were significantly higher (P < 0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P < 0.05) than voluntary torque at −120, −90, −60 and −30°·s−1 angular velocities. For a given velocity, the rms amplitude of VL and VM were significantly lower (P < 0.05), during eccentric than during concentric actions, in S, but not in HS. However, whatever the angular velocity, ST co-activation in HS was significantly lower (P < 0.05) than in S. We concluded that co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric action in S, support the possibility of the presence of a tension-regulating mechanism in sedentary subjects.

Effects of active recovery on power output during repeated maximal sprint cycling

Abstract: The effects of active recovery on metabolic and cardiorespiratory responses and power output were examined during repeated sprints Male subjects (n = 13) performed two maximal 30-s cycle ergometer sprints, 4 min apart, on two separate occasions with either an active [cycling at 40 (1)% of maximal oxygen uptake; mean (SEM)] or passive recovery Active recovery resulted in a significantly higher mean power output ( $$\bar W$$ ) during sprint 2, compared with passive recovery [ $$\bar W$$ ] 603 (17) W and 589 (15) W, P < 005] This improvement was totally attributed to a 31 (10)% higher power generation during the initial 10 s of sprint 2 following the active recovery (P < 005), since power output during the last 20 s sprint 2 was the same after both recoveries Despite the higher power output during sprint 2 after active recovery, no differences were observed between conditions in venous blood lactate and pH, but peak plasma ammonia was significantly higher in the active recovery condition [205 (23) vs 170 (20) μmol · 1−1;P < 005] No differences were found between active and passive recovery in terms of changes in plasma volume or arterial blood pressure throughout the test However, heart rate between the two 30-s sprints and oxygen uptake during the second sprint were higher for the active compared with passive recovery [148 (3) vs 130 (4) beats · min−1;P < 001) and 33 (01) vs 28 (01) 1 · min−1;P < 001] These data suggest that recovery of power output during repeated sprint exercise is enhanced when low-intensity exercise is performed between sprints The beneficial effects of an active recovery are possibly mediated by an increased blood flow to the previously exercised muscle

Stretch shortening cycle fatigue: interactions among joint stiness, reflex, and muscle mechanical performance in the drop jump

Abstract: The purpose of the present study was to investigate the effect of strenuous stretch-shortening cycle exercise on the relationship between reflex and stiffness regulation during the drop jump. Ten healthy male subjects performed submaximal stretch-shortening cycle exercise on a special sledge apparatus. Exhaustion occurred on average within 3 min. A drop jump test from a 50-cm height was performed immediately before and after the sledge exercise, as well as 2 h, 2 days and 4 days later. The fatigue exercise showed relatively high blood lactate concentrations 12.5 (SD 2.6) mmol·l−1 and a 2-day delayed increase of serum cretaine kinase concentration. In drop jumps, the short latency M1 component of the vastus lateralis muscle electromyogram (EMG) response showed a continuous decline throughout the entire follow-up period after fatigue (NS), whereas the medium latency EMG component increased 2 days after the postfatigue sessions (P < 0.05). Immediately after the fatigue exercise a positive correlation (P < 0.05) was found between the changes in the short latency EMG response and in the amount of knee joint stiffness during the early post-landing phase of the drop jump. This suggests that the M1 response was closely related to the stiffness changes during the initial braking phase of the drop jump. Increase of creatine kinase concentration on the 2nd day correlated negatively with the changes in the drop jump performance (P < 0.05). Since the short latency EMG component has almost recovered on the 2nd day, impairment of the mechanical function of the muscle might have taken place. In conclusion, exhausting stretch-shortening cycle exercise induced local muscle impairment, which resulted in modulation of the reflex and stiffness interaction in the drop jump as well as compensation by central motor command.

Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition

Abstract: To determine whether power-velocity rela- tionships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling fre- quency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power (14.36 (SD 2.37)W" kg- 1) and velocity at maximal power (120 (SD 8) rpm) were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres ex- pressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be re- lated to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump perfor- mance was also related to cycling maximal power ex- pressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contri- bution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demon- strated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.

A comparison of prehension force control in young and elderly individuals

Abstract: Age-related changes were investigated in the control of precision grip force during the lifting and holding of objects with slippery (silk) and nonslippery (sandpaper) surface textures. Two groups of active elderly adults comprising individuals aged 69-79 years (n = 10), and 80-93 years (n = 10) together with a group of young adults aged 18-32 years (n = 10) participated in the study. Each subject lifted a free weight (3N) during which time gripping and lifting forces were monitored. The elderly subjects, especially the individuals in the 81-93 year group, had a larger number of fluctuations in the grip force rate curve and longer force application time than the younger subjects during lifting. The effect of prior experience with one surface on the following different surface was more pronounced in the younger subjects than the elderly subjects. These results suggest a decline in programmed force production capacity with increased age. The fingers of the elderly subjects were more slippery and they exhibited a greater safety margin of the grip force while holding the object than the younger adults. The overall results demonstrated that precision grip force control capacity declines with advancing age. It is suggested that this decline is due mainly to age-related changes in skin properties, and cutaneous sensibility functions, and in part to central nervous system function.

Restoration of fluid balance after exercise-induced dehydration: effects of food and fluid intake

Abstract: This study investigated the effects of post-exercise rehydration with fluid alone or with a meal plus fluid. Eight healthy volunteers (five men, three women) were dehydrated by a mean of 2.1 (SEM 0.0)% of body mass by intermittent cycle exercise in a warm [34 (SEM 0)°C], humid [55 (SEM 1)% relative humidity] environment. Over 60 min beginning 30 min after exercise, the subjects ingested a commercially-available sports drink (21 mmol · l−1 Na+, 3.4 mmol · l− K+, 12 mmol · l−1 Cl−1) on trials A and B; on trial C a standard meal [63 kJ · kg−1 body mass (53% CHO, 28%fat,19%protein; 0.118 mmol · kJ−1 Na+, 0.061 mmol · kJ−1 K+)] plus drink (1 mmol · l−1 Na+, 0.4 mmol · l−1 K+, 1 mmol · l−1 Cl−) were consumed. Water intake (in millilitres) was 150% of the mass loss (in grams). The trials took place after an overnight fast and were separated by 7 days. Blood and urine samples were collected at intervals throughout the study. Blood was analysed for haematocrit, haemoglobin concentration, serum osmolality, Na+, Ku+ and Cl− concentrations and plasma angiotensin II concentration. Urine volume, osmolality and electrolyte concentrations were measured. Dehydration resulted in a mean 5.2 (SEM 1.3)% reduction in plasma volume. With the exception of serum osmolality, which was higher on trial B than A at the end of the rehydration period, no differences were recorded for any of the measured parameters between trials A and B. Cumulative urine output following rehydration was lower (P < 0.01) on trial C [median 665 (range 396–1190) ml] than on trial B [median 934 (range 550–1403) ml] which was not different (P = 0.44) from trial A [median 954 (range 474–1501) ml]. Less urine was produced over the 1-h period ending 2 h after rehydration on trial C than on B (P = 0.01). On trials A and B the subjects were in net negative fluid balance by 337 (range 779-minus 306) ml and 373 (range 680-minus 173) ml, respectively (P < 0.01): on trial C the subjects were no different from their initial euhydrated state [median minus 29 (range minus 421−137) ml] 6 h after the end of rehydration (P = 1.00). A larger fraction of total water intake was retained when the standard meal plus drink was consumed. This may have been due to the larger quantities of Na+ and K+ ingested with the meal [mean 63 (SEM 4)mmol Na+, 21.3 (SEM 1.3)mmol K+] than with the drink [mean 42 (SEM 2) mmol Na+, 6.8 (SEM 0.4) mmol K+]. There was no difference between trials B and C in any of the measured blood parameters, but urinary Na+ and K+ excretion were both higher on trial C than B. These results suggest that post-exercise fluid replacement can be achieved by ingestion of water if consumed in sufficient volume together with a meal providing significant amounts of electrolytes.

Reduced stretch-reflex sensitivity after exhausting stretch-shortening cycle exercise

Abstract: The stretch-shortening cycle (SSC) is an effective and natural form of muscle function but, when repeated with sufficient intensity or duration, it may lead to muscle damage and functional defects. A reduced tolerance to impact has been reported, which may be partly attributed to a reduced stretch-reflex potentiation. The aim of the present study was to examine the influence of SSC-induced metabolic fatigue and muscle damage on the efficacy of stretch reflexes, as judged by the electromyograph (EMG) response of two shank muscles (lateral gastrocnemius LG, soleus SOL) to controlled ramp stretches. These EMG responses were recorded before and immediately after exhausting SSC-type leg exercise and 2 h, 2 days and 4 days later. Serum concentrations of creatine kinase ([CK]), myoglobin and lactate were measured repetitively along the protocol. Two maximal vertical drop jumps and counter-movement jumps were performed after each reflex test. The exhausting SSC-type exercise induced an immediate reduction (P < 0.05) with a delayed short-term recovery of the LG peak-to-peak reflex amplitude. This was not accompanied by significant changes in the reflex latency. The drop jump performance remained slightly but significantly reduced (P < 0.05) until the 2nd day postexercise. Peak [CK] appeared for all the subjects on the 2nd day, suggesting the presence of muscle damage. The increase in [CK] between the 2nd h and the 2nd day postexercise was found to be negatively related (P < 0.001) to the relative changes in the drop jump height. Furthermore, a significant relationship (P < 0.05) was found between recovery of the stretch reflex in LG and the decrease of [CK] between the 2nd and the 4th day. These findings support the hypothesis of a reduced stretch-reflex sensitivity. While the exact mechanisms of the reflex inhibition remain unclear, it is emphasized that the delayed recovery of the reflex sensitivity could have resulted from the progressive inflammation that develops in cases of muscle damage.

The specificity of strength training: the effect of posture.

Abstract: There is a paucity of research into the importance of performing strength training exercises in postures specific to the movements they are attempting to facilitate. In addressing this question, 27 previously trained subjects were randomly allocated into heavy weight training and control groups. The weight training group performed 4-6 sets of 6-10 repetitions of the squat and bench press lifts twice a week for 8 weeks. Prior to and after the training period the following tests were conducted: bench press throw at 30% of maximal load, vertical jump, maximal squat and bench press lifts, push-up test performed over a force platform, 40-m sprint, 6-s cycle, and isokinetic tests assessing upper and lower body musculature in varying actions. The results supported the concept that posture is important in training as those exercises conducted in similar postures to the training recorded the greatest improvement in performance. For example, after completion of the training the weight training subjects significantly increased by approximately 12% the maximal load lifted in the bench press exercise and the peak torque in the isokinetic bench press test. However, performance in the isokinetic horizontal arm adduction test was not significantly changed. We speculate that the phenomenon of posture specificity may, at least in part, be caused by the differing postures altering the neural input to the musculature. The results stress the importance of selecting exercises in which the posture closely resembles that of the movements they are attempting to facilitate.

Poor correlations between isometric tests and dynamic performance: relationship to muscle activation

Abstract: The purpose of this research was to perform isometric tests at two joint angles and examine their relationship to dynamic performance. In addition, electromyograph data were collected from the triceps brachii and pectoralis major muscles to compare underlying neural characteristics between the isometric tests and dynamic movement. A group of 24 healthy male subjects performed two isometric tests in a bench press position, at elbow angles of 90 and 120°. From these data, the maximal force and rate of force development were determined. In addition, each subject performed a seated medicine ball throw as a measure of dynamic upper body performance. Correlations showed that isometric measurements of force (r = 0.47–0.55) and rate of force development (r = 0.08–0.31) were poor predictors of dynamic performance. The angle of isometric assessment had little effect on the relationship between the tests and measurements of performance. The myo-electric data was processed in terms of the integrated electromyogram and the Fourier transformed frequency spectrum. These data demonstrated differences in the neural activation patterns of the musculature, between the isometric 90° test and the medicine ball throw. The poor relationship between isometric tests and medicine ball performance was consequently, at least partially, attributed to differing motor unit activation patterns between isometric and dynamic movement. The results of this research strongly suggest that isometric tests have limited value when assessing dynamic upper body performance.

The validity and reliability of a test of lower body musculotendinous stiffness.

Abstract: The aim of this study was to investigate the validity and reliability of an in vivo test of lower body musculotendinous stiffness. Male subjects (n = 23) with at least 12 months of weight training experience performed a series of quasi-static muscular actions in a supine leg press position during which a brief perturbation was applied. The resulting damped oscillations enabled each subject's maximal musculotendinous stiffness for the lower body musculature to be estimated. To assess the individual's capacity to benefit from active stretch, subjects also performed both a static jump and a countermovement jump. Statistical analysis revealed no significant different between day 1 and day 2 stiffness values (P < 0.01), an interday reliability ofr = 0.94 and a coefficient of variance of 8%. It was further demonstrated that maximal stiffness was significantly correlated to both isometric and concentric rate of force development (r = 0.50 andr = 0.54, respectively), and inversely related to the percentage difference between vertical jumps with and without prior stretch (r = − 0.54). Such results tend to suggest that the test is valid and are discussed with reference to the restitution of elastic strain energy, muscle potentiation and the interaction effects of elastic recoil on dynamic function. It was concluded that the assessment of stiffness of the lower body using the oscillation technique is a valid and reliable in vivo measure of musculotendinous stiffness.

Muscle function during brief maximal exercise : accurate measurements on a friction-loaded cycle ergometer

Abstract: A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N.kg-1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137-180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17-214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (vopt) and individual maximal power output (Pmax) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since vopt has been demonstrated to be related to human fibre type composition both vopt, Pmax and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.

Age-related changes in biomechanical properties of the Achilles tendon in rabbits

Abstract: We investigated age-related changes in the mechanical properties of rabbit Achilles tendon The animals used were immature (age 3 weeks, body mass 380 g), young adult (age 8–10 months, body mass 41 kg) and old (age 4–5 years, body mass 51 kg) rabbits The cross-sectional area of the tendon increased with growth and the tensile strength of the young adult [673 (SEM 42) MPa] and old [667 (SEM 38) MPa] tendon was significantly higher than that of the immature tendon [239 (SEM 38) MPa] However, there was no statistically significant difference in tensile strength between mature and old tendons These differences may be attributable to the change in body mass The gradient of the stress-strain curves, that is, the tangent modulus of the mature tendon [6180 (SEM 870) MPa], was higher than that of the immature [2810 (SEM 1046) MPa] and old [5305 (SEM 910) MPa] tendon, although the difference was not significant The elongation at failure was approximately 16% for all age groups These results would suggest that rabbit Achilles tendon is highly compliant during growth

Effects of exercise intensity and environmental stress on indices of oxidative stress and iron homeostasis during exercise in the horse

Abstract: The effects of prolonged variable-intensity and short-term high-intensity exercise on indices of oxidative stress and iron homeostasis were compared in six fit horses under cool [20°C, 40% relative humidity (RH)] or hot/humid (30°C, 80% RH) environmental conditions. The exercise protocols were designed to simulate equine competition, including racing (intense exercise) or the speed and endurance phase of a 3-day event (prolonged exercise). Increased plasma concentrations of lipid hydroperoxides and haemolysate concentrations of oxidised glutathione (GSSG) were measured within 30 min of the completion of exercise, indicating production of reactive oxygen species (ROS) and lipid membrane peroxidation. The horses were unable to complete the prolonged exercise protocol at high temperature and humidity. This coincided with higher maximal values of lipid hydroperoxides [138.2 (17.7) μM and GSSG [110.6 (18.2) μM], compared to high-intensity [105.2 (14.9) μM and 63.6 (8.6) μM, respectively] or prolonged [100.7 (18.7) μM and 86.2 (9.1) μM, respectively] exercise performed under cooler environmental conditions. Significant correlations were found between the duration of the final stage of exercise during hot/humid environmental conditions and increased levels of lipid hydroperoxides (r = 0.85), GSSG (r = 0.94), xanthine (r = 0.92) and uric acid (r = 0.96). Excerise also decreased the iron (Fe)-binding antioxidant activity of the plasma and increased the total plasma Fe levels, although this was only significant for prolonged exercise in ambient conditions. There was no detectable free Fe in the plasma at any stage of exercise. Other changes in biochemical parameters had returned to pre-exercise levels within 24 h after exercise. The results show that exercise can induce changes in biochemical parameters that are indicative of oxidative stress in the fit horse and that this was, exacerbated during exercise at high temperature and humidity.

Relationship between myoelectric and mechanical manifestations of fatigue in the quadriceps femoris muscle group.

Abstract: Fatigue is commonly defined as “the failure to maintain the required force”. As such, it may be argued that the use of electromyographic (EMG) power spectral statistics to monitor muscle fatigue is inappropriate, because, during the maintenance of a submaximal force of contraction, EMG changes are readily observable in the absence of any decline in the muscle's mechanical output. However, it is possible that the EMG changes reflect the changing metabolic status of the muscle and hence its inability to generate its normal maximal force. The present study sought to examine whether the decline in EMG median frequency, which occurs during the maintenance of a submaximal force, is correlated with a reduction in the muscle's maximum force-generating capacity. The maximum voluntary contraction (MVC) of the knee extensors in ten young, healthy subjects was determined. On five separate occasions, randomly assigned forces of 20, 30, 40, 50 and 60% MVC were held to the limit of endurance. At intervals throughout the sustained contractions, subjects were required to rapidly generate an MVC for 1–2 s, then return to the fixed submaxial target force. Surface EMG signals were recorded throughout the contractions from the rectus lemons and vastus lateralis muscles, from which the power spectrum median frequency was calculated. Regression analysis revealed highly significant relationships between the rate of decline in MF and the rate of decline in MVC, and between each of these parameters and endurance time to fatigue (P = 0.0001, in each case). It is concluded that the decline in MF can be used to monitor fatigue, where fatigue is defined as the inability to generate the maximum force that can be produced by the muscle in its fresh state.

Effects of low and moderate intensity treadmill walking on postprandial lipaemia in healthy young adults.

Abstract: We have previously shown that the lipaemic response to a fatty meal was reduced when prolonged (2 h) low intensity exercise was taken some hours before eating. The purpose of this study was to test the hypothesis that the effect is quantitatively greater after exercise of moderate intensity than after exercise at low intensity. Six men and six women, mean age 26.9 (SEM 1.5) years, took part in three trials, each conducted over 2 days; on the afternoon of day 1 of each of two exercise trials the subjects walked on a treadmill for 90 min at either 31 (SEM 1) % or 61 (SEM 1) % of maximal oxygen uptake, i.e. low and moderate intensity, respectively; on the control trial the subjects refrained from exercise on day 1. On the morning of day 2 of each trial they ingested a test meal (1.28 g fat, 1.44 g carbohydrate, 76 kJ energy · kg−1 body mass); blood samples were obtained in the fasted state and for 6 h after the meal. Fasting serum triacylglycerol concentration and the area under the postprandial triacylglycerol-time curve were lower than in the control trial (P < 0.05) after moderate intensity walking but not after low intensity walking. The results suggest that the mitigation of the lipaemic response to a meal high in fat and carbohydrate is related to the intensity and/or the energy expenditure of the preceding exercise.

Immune system of cold-exposed and cold-adapted humans.

Abstract: The aim of this study was to investigate whether or not the human immune system can be activated by a noninfectious stimulus, thereby improving the physiological status of the individual. The effect of a single cold water immersion (14° C for 1 h) on the immune system of athletic young men, monitored immediately after immersion, was minimal. With the continuation of the cold water immersions (three times a week for a duration of 6 weeks) a small, but significant, increase in the proportions of monocytes, lymphocytes with expressed IL2 receptors (CD25) and in plasma tumour necrosis factor alpha content was induced. An increase in the plasma concentrations of some acute phase proteins, such as haptoglobin and haemopexin, was also observed. After 6 weeks of repeated immersions a trend towards an increase in the plasma concentrations of IL6 and the amount of total T lymphocytes (CD3), T helper cells (CD4), T suppressor cells (CD8), activated T and B lymphocytes (HLA-DR) and a decrease in the plasma concentration of α1-antitrypsin was observed. Concentrations of IL1β, neopterin, C-reactive protein, orosomucoid, ceruloplasmin, macroglobulin, immunoglobulins (IgG, IgM, IgA) and C3, C4 components of the complement, as well as the total number of erythrocytes, leucocytes, granulocytes and neutrophils showed no significant changes after the repeated cold water immersions. It was concluded that the stress-inducing noninfectious stimuli, such as repeated cold water immersions, which increased metabolic rate due to shivering the elevated blood concentrations of catecholamines, activated the immune system to a slight extent. The biological significance of the changes observed remains to be elucidated.

Lactate kinetics during passive and partially active recovery in endurance and sprint athletes

Abstract: We investigated the effects of passive and partially active recovery on lactate removal after exhausting cycle ergometer exercise in endurance and sprint athletes. A group of 14 men, 7 endurance-trained (ET) and 7 sprint-trained (ST), performed two maximal incremental exercise tests followed by either passive recovery (20 min seated on cycle ergometer followed by 40 min more of seated rest) or partially active recovery [20 min of pedalling at 40% maximal oxygen uptake (\(\dot V\)O2max) followed by 40 min of seated rest]. Venous blood samples were drawn at 5 min and 1 min prior to exercise, at the end of exercise, and during recovery at 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 50, 60 min post-exercise. The time course of changes in lactate concentration during the recovery phases were fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (τ2) expressing the rate of blood lactate removal. The results showed that at the end of maximal exercise and during the 1st min of recovery, ET showed higher blood lactate concentrations than ST. Furthermore, ET reached significantly higher maximal exercise intensities [5.1 (SEM 0.5) W · kg−1 vs 4.0 (SEM 0.3) W · kg−1,P < 0.05] and \(\dot V\)O2max [68.4 (SEM 1.1) ml · kg−1 · min−1 vs 55.5 (SEM 5.1) ml · kg−1 · min−1,P < 0.01]. There was no significant difference between the two groups during passive recovery for τ2 During partially active recovery, τ2 was higher than during passive recovery for both groups (P < 0.001), but ET recovered faster and sooner than ST (P < 0.05). Compared to passive recovery, the τ2 measured during partially active recovery was increased threefold in ET and only 1.5-fold in ST. We concluded that partially active recovery potentiates the enhanced ability to remove blood lactate induced by endurance training.

Physical loading and performance as predictors of back pain in healthy adults A 5-year prospective study

Abstract: We investigated muscle strength, aerobic power, and occupational and leisure-time physical loading as predictors of back pain in a 5-year follow-up study. A cohort of 456 adults aged 25, 35, 45 and 55 years, free of back pain, participated in measurements of anthropometric characteristics, aerobic power and muscle strength characteristics at baseline. The subjects' levels and types of physical activity and occupational physical loading were also determined. At 5 years after the baseline examinations 356 of these subjects (78.1 %) were reached by mail, and 262 of them (73.6%) properly completed and returned a questionnaire including a detailed back pain history for the 5 years following the baseline measurements. Of this number 56 subjects (21 %) who reported back pain ( > 30 on a scale from 0 to 100) and functional impairment during the 5-year follow-up composed the marked back pain group. Other subjects (n = 71, 27%) noting lesser symptoms were included in the mild back pain group; 135 subjects (52%) reported having had no back pain. The subjects with marked back pain were on average taller than the subjects without back pain, while no such difference was found in body mass. Heavy occupational musculoskeletal loading (P = 0.005) and high general occupational physical demands (P = 0.036) predicted future back pain. Leisuretime physical activity, aerobic power or muscle strength characteristics were not predictive of future back pain.

Hip bone mineral density is improved by high-impact aerobic exercise in postmenopausal women and men over 50 years.

Abstract: Fifteen men and women (six men) between the ages of 50 and 73 years were recruited to begin keep-fit classes. They were matched for sex, age, menopausal status and mass to 15 non-exercising controls. The keep-fit classes were two to three times a week and included high-impact exercise, including step and jumping exercises specifically to load the proximal femur and spine. Proximal femur, lumbar spine and total body bone mineral density (BMD) were measured at 0 and 12 months. Urinary pyridinoline (Pyr) and deoxypyridinoline (dPyr) crosslinks were measured every 6 months to assess bone resorption. Quadriceps isometric strength was measured every 6 months. BMD increased non-significantly at the femoral neck [1.57 (0.8)%] and Wards triangle [1.97 (1.4)%], and significantly at the greater trochanter 2.21 (0.9)% (P = 0.02) in the exercise group. Femoral neck BMD decreased by -1.9(0.8)% (P = 0.049) in the control group, which was significantly different from the change in the exercise group (P = 0.009). BMD did not change at the Wards triangle or trochanter in the controls. Lumbar spine BMD did not change in either group. Total body BMD did not change in the exercise group, but decreased by -0.79 (0.3)% (P = 0.02) in the controls. Following 6 months of the exercise classes. Pyr and dPyr crosslinks were significantly reduced [-19.0 (7.2)%; P = 0.0019 and -20.0 (7.7)%; P = 0.021 respectively]. There was no significant change in crosslinks after 1 year, and no change at any time in the controls. Quadriceps strength changed by 5.4 (3.7)% in the exercise group and by -6.9 (2.5)% (P = 0.01) in the control group after 12 months, being significant between groups (P = 0.008). This study suggests that high-impact, aerobic exercise in postmenopausal women and men over 50 years old is feasible and effective at maintaining muscle strength and increasing proximal femur BMD but not spine or total body BMD.

Motor unit recruitment strategy changes with skill acquisition.

Abstract: The modifications of motor unit recruitment strategy due to skill acquisition was determined in the elbow flexor-extensor muscles of normal human subjects. The median frequency of the power density spectra of the electromyograms recorded from the biceps and triceps muscles during a 3-s linear increase in flexion force in the range of 0-100% maximal voluntary contraction (MVC) was calculated for each subject, every 2 weeks over a total 6-week period during which subjects practiced linear flexion force increase three times a week. Electromyograms were recorded with two pairs of electrodes of different size and electrode spacing. It was shown that skill acquisition due to the 360 practice trials over the 6-week period caused an increase in the initial motor unit recruitment phase of the agonist's force generation cycle from about 0-65% MVC to about 0-85% MVC. The increase in the recruitment range was gradual and statistically significant for the measurements made every 2 weeks. The recruitment range of the antagonist triceps demonstrated a minor, but statistically insignificant, decrease over the same training period. There was a minor, but statistically insignificant, advantage of using small electrodes and inter-electrode spacing. It was concluded that skill acquisition, due to repeated functional use of a muscle in the same contraction mode, results in a slower, prolonged recruitment of motor units in the initial segment of the force generation cycle, thereby allowing a more precise and accurate control of the increments of force increase. Such conclusions reinforce the concept advocating the plasticity of motor unit control according to the functional demands imposed on the muscle. The results have significant implications in the design of various athletic, occupational and rehabilitation training modalities for optimal performance of various movement functions.

Effects of fatigue and sprint training on electromechanical delay of knee extensor muscles

Abstract: Electromechanical delay (EMD) of knee extensors in isometric contraction was investigated in six healthy men before and after four periods of 30-s allout sprint cycling exercise, conducted pre and post a 7-week sprint cycling training programme. The EMD was lengthened from 40.4 (SEM 3.46) ms at rest to 63.4 (SEM 7.80) ms after the fatiguing exercise (P < or = 0.05) in the pre-training test. During maximal voluntary contractions (MVC) conducted after the fatiguing exercise, the peak contraction force (Fpeak) and peak rate of force development (RFDpeak) were reduced by 51%-56% and 38%-50%, respectively (both P < or = 0.05). The mechanisms of EMD lengthening during fatigue could have been due to the deterioration in muscle conductive, contractile or elastic properties and require further study. The training programme increased the total work performed during the four periods of sprint exercise (P < or = 0.05). However, no significant training effects were found in the resting or postexercise EMD, Fpeak and RFDpeak during isometric MVC. These unchanged isometric contraction variables but enhanced dynamic performance suggest that isometric tests of muscle are insensitive to the neuromuscular adaptations to sprint training.

Time and frequency domain analysis of electromyogram and sound myogram in the elderly

Abstract: The aim of this work was to evaluate the influence of the ageing process on the time and frequency domain properties of the surface electrical and mechanical activity of muscle. In 20 healthy elderly subjects (10 men and 10 women, age range 65–78 years) and in 20 young controls, during isometric contractions of the elbow flexors in the 20%–100% range of the maximal voluntary contraction (MVC), estimations were made of the root mean square (rms) and the mean frequency (MF) of the power density spectrum distribution, from the surface electromyogram (EMG) and sound myogram (0SMG) signals, detected at the belly of the biceps brachii muscle. Compared to the young controls, the MVC was lower in the elderly subjects (P < 0.05); at the same %MVC the rms and the MF of EMG and SMG were lower (P < 0.05) in elderly subjects; the rms and MF of the two signals increased as a function of the effort level in all groups. Only in the 80%–100% MVC range did the EMG-MF level off and the SMG-rms decrease; in contrast the young controls, at 80% MVC the high frequency peak in the SMG power spectrum density distribution was not present in the elderly subjects. The results for MVC and %MVC can be related to the reduction in the numbers of muscle fibres in aged subjects. In particular, the lack of fast twitch fibre motor units (MU), attaining high firing rates, might also explain the result at 80% MVC. In 80%–100% MVC range the two signals rms and MF behaviour may have been related to the end of the recruitment of larger MU with high conduction velocity, and to the further increment of MU firing rate in the biceps brachii muscle beyond 80% MVC, respectively. Thus, the coupled analysis of the EMG and SMG with force suggests that in the elderly subjects the reduction of the number of muscle fibres may have co-existed with a MU activation pattern similar to that of the young subjects.

Water balance during and after marathon running.

Abstract: To describe the time course of plasma volume alterations and the changes in the plasma concentrations of hormones regulating water balance in relation to a marathon race, six experienced marathon runners (five men, one women) aged 28 (SD 6) years were studied during and for the 3 days following a treadmill marathon run at 68 (SD 5)% of maximal oxygen consumption. Haematocrit, haemoglobin, plasma protein (Prot) and electrolyte (Na+, K+) concentration, osmolality (osm), plasma concentrations of renin (Ren), aldosterone (Ald) and atrial natriuretic peptide (ANP) were determined at rest in a sitting position (T−30), and then after 30 min in an upright posture (R0), while running a marathon at 10 km (R10), 30 km (R30) and 42.2 km (Rend), and after the marathon at 30 min (T30), 60 min (T60), 120 min (T120) and 24 h (TD+1), 48 h (TD+2) and 72 h (TD+3). The changes in plasma volume (PV), Prot, osm and Na+ observed during the race were nonsignificant. Significant increases in plasma concentration of K+ [4.8 (SD 0.6) vs 5.5 (SD 0.6) mmol·l−1; P < 0.01], Ren [38 (SD 57) vs 197 (SD 145) pmol·l−1; P < 0.02] and Ald [175 (SD 142) vs 1632 (SD 490) pmol·−1; P < 0.01] were observed at Rend. A significant increase of ANP (P < 0.05) was only found after R10. Body mass significantly decreased by 2.0 kg (P < 0.01) during the race in spite of the ingestion of 1.46 (SD 0.34) 1 of a 5% glucose solution. Urinary volume and Na+ excretion dropped significantly after the completion of the marathon in comparison with the day before [2600 vs 1452 ml·day−1 (P < 0.02) and 161.3 vs 97.1 mmol·l−1 (P < 0.05)]. At TD+1 and TD+2 a significant increase in PV was noted, compared to T−30. The lack of a decrease in PV during the marathon may have been due to the production of 402 g of metabolic water and by the release of 1280 g of water stored in glycogen complexes in muscle and liver. Thus, the hormone response during the marathon may have been due to the effects of the exercise itself and not to the effects of dehydration. The postmarathon PV expansion may be explained by a protein shift to the intravascular space and by renal sodium retention.

Regional differences in age-related decrements of the cutaneous vascular and sweating responses to passive heating.

Abstract: Ten older (aged 64–76 years) and ten younger (aged 20–24 years) healthy men were exposed to a standard heat stress [by placing the lower legs and feet in a water bath at 42°C while sitting in a controlled environment (ambient temperature 35°C and 45 % relative humidity) for 60 min]. During passive heating, the rectal temperature of the older men was significantly greater (P < 0.05) and mean skin temperature was lower (P < 0.001), compared to the younger men. Skin blood flow by laser Doppler flowmetry (LDF) was significantly lower on the chest and thigh for the older men (P < 0.001), but forehead LDF did not differ between the groups. The percentages of total LDF in the older men to total LDF in the younger men for the last 30 min were 99%, 58% and 50% on the forehead, chest and thigh, respectively. The age-related differences in LDF responses mirrored cutaneous vascular conductances (CVC), since no group and time effects were observed in mean arterial blood pressure during the test. During the last 30 min the local sweat rates (msw) on the back and thigh were significantly lower for the older men (P < 0.02), but not on forehead, chest and forearm, although the older men had lower msw during the first 30 min exposure regardless of site (P < 0.03). The percentages of total msw in the older men to total msw in the younger men during the last 30 min were 105%, 99%, 63%, 106% and 88% on the forehead, chest, thigh, forearm, and back, respectively. During the latter half of the exposure, the older men had similar LDF, CVC and msw on the forehead, lower LDF and CVC and a similar msw on the chest, and lower LDF, CVC and msw on the thigh, compared to the younger men. These results suggest firstly that regional differences exist in the age-related decrement of cutaneous vasodilatation as well as sweat gland function, secondly that the age-related decrement in cutaneous vascular function may precede a decrement in sweat gland function, and thirdly that the successive decrements may develop sequentially from the lower limbs to the upper body, and head.

Optic fibre as a transducer of tendomuscular forces

Abstract: Direct in vivo tendon force measurements open up new possibilities for understanding of muscletendon loads during natural locomotion. The present report presents a new optic fibre method for such applications. The method is based on light intensity modulation by mechanical modification of the geometric properties of the optic fibre. A special optic fibre with a plastic covering buffer and with a total diameter of either 265 μm or 500 μm was carefully prepared at both ends for receiving and transmitting light. The fibre was inserted through the rabbit common calcaneal tendon with a 20 gauge needle. By removing the needle the optic fibre remained in situ. Static loading demonstrated that the voltage output of the optic fibre transducer showed a good linear fit of r =.999 with added loads. In dynamic loading conditions the optic fibre followed well the response of a strain gauge transducer, which was also attached to the tendon. The optic fibre method seems suitable for many applications for tensile and possibly ligament force measurements.

Increase in energy cost of running at the end of a triathlon

Abstract: The purpose of the present study was to verify the increase in energy cost of running at the end of a triathlon. A group 11 trained male subjects performed a triathlon (15-km swimming, 40-km cycling, 10-km running). At least 1 week later the subjects ran 10-km as a control at the same pace as the triathlon. Oxygen uptake (VO2), ventilation (VE) and heart rate (HR) were measured during both 10-km runs with a portable telemetry system. Blood samples were taken prior to the start of the triathlon and control run, after swimming, cycling, triathlon run and control run. Compared to the control values the results demonstrated that triathlon running elicited a significantly higher (P < 0.005) mean VO2 [51.2 (SEM 0.4) vs 47.8 (SEM 0.4) ml.min-1.kg-1] VE [86 (SEM 4.2) vs 74 (SEM 5.3) l.min-1], and HR [162 (SEM 2) vs 156 (SEM 1.9) beats.min-1)]. The triathlon run induced a greater loss in body mass than the control run [2 (SEM 0.2) vs 0.6 (SEM 0.2) kg], and a greater decrease in plasma volume [14.4% (SEM 1.5) vs 6.7% (SEM 0.9)]. The lactate concentrations observed at the end of both 10-km runs did not differ [2.9 (SEM 0.2) vs 2.5 (SEM 0.2) m.mol.l-1]. Plasma free fatty acids concentrations were higher (P < 0.01) after the triathlon than after the control run [1.53 (SEM 0.2) to 0.51 (SEM 0.07) mmol.l-1]. Plasma creatine kinase concentrations rose under both conditions from 58 (SEM 12) to 112 (SEM 14) UI.l-1 after the triathlon, and from 61 (SEM 7) to 80 (SEM 6) UI.l-1 after the control run. This outdoor study of running economy at the end of an Olympic distance triathlon demonstrated a decrease in running efficiency.