Effect of creatine supplementation on phosphocreatine resynthesis, inorganic phosphate accumulation and pH during intermittent maximal exercise.

In this study, we examined the effect of creatine ingestion on muscle power output, muscle phosphocreatine resynthesis, inorganic phosphate and pH during repeated brief bouts of maximal exercise. Nine healthy males performed maximal plantar flexion before and after creatine ingestion (20 g x day(-1) for 6 days). The experimental protocol consisted of five 8 s bouts (bouts 1-5) interspersed with 30 s recovery, followed by bouts 6 (8 s) and 7 (16 s) separated by 1 and 2 min, respectively. Muscle phosphocreatine, inorganic phosphate and pH were estimated every 16 s by 31P magnetic resonance spectroscopy. After creatine ingestion, muscle power output increased by approximately 5% (P< 0.05) from bouts 3 to 7 and muscle phosphocreatine resynthesis increased (P< 0.05) during 10 min recovery. The higher phosphocreatine concentration observed after only 30 s of recovery was accompanied by lower inorganic phosphate accumulation and higher pH. Strong correlations were found between exercise power restoration and the corresponding pre-exercise phosphocreatine and inorganic phosphate concentrations and muscle pH after creatine ingestion. The better maintenance of muscle power output observed after creatine ingestion was attributed to a higher rate of phosphocreatine resynthesis, lower accumulation of inorganic phosphate and higher pH.

Leg extensor power and dehydroepiandrosterone sulfate, insulin-like growth factor-I and testosterone in healthy active elderly people.

We examined the association between quadriceps muscle function and serum levels of dehydroepiandrosterone sulphate (DHEAS), insulin-like growth factor I (IGF-I) and testosterone in a group of healthy elderly people. Fifty-three independent, community-dwelling elderly subjects (26 men and 27 women) aged from 66 to 84 years volunteered to participate in the study. Physical activity (PA) was evaluated by a questionnaire. Quadriceps maximal muscle power (Wmax) and optimal shortening velocity (v(opt)) were measured on a friction-loaded non-isokinetic cycle ergometer. The Wmax is expressed in relation to body mass (W(max/kg), W x kg(-1)), and in relation to the mass of the two quadriceps muscles (W(max/Quadr), W x kg(Quadr(-1))). In women, when adjusted for age, anthropometric measurements and PA indices, IGF-I correlated significantly with W(max/kg) (partial correlation: r = 0.59; P = 0.001), W(max/Quadr) (r = 0.58; P = 0.002) and v(opt) (r = 0.53; P = 0.004), whereas DHEAS was correlated significantly with W(max/kg) (r = 0.54; P = 0.003) and W(max/Quadr) (r = 0.58; P = 0.002). No such correlation was found in men. These findings indicate that in healthy elderly women lower values for quadriceps muscle Wmax and v(opt) are related, independently of age, anthropometric measurements and PA indices, to lower circulating levels of DHEAS and IGF-I.

Influence of fatigue on EMG/force ratio and cocontraction in cycling.

PURPOSE: The purpose of the present study was to observe force and power losses and electromyographic manifestations of fatigue during repeated sprints performed on a friction-loaded cycle ergometer. METHODS: Ten subjects performed 15 maximal 5-s sprints with 25-s rests between them. Power, velocity, and torque were measured during sprints 1 and 13 and during two submaximal constant-velocity (50 rpm) periods of cycling performed before and after the sprints. The EMG signals of five leg muscles were stored to determine the EMG/force ratio of power producer muscles and the coactivation of antagonist muscles. The power producer muscles were activated to the same level during sprints 1 and 13, despite a loss of force, whereas the vastus lateralis muscle was recruited more during the submaximal cycling period under fatigue conditions. RESULTS: This led to an increased EMG/force ratio for the power producer muscles, indicating the peripheral fatigue status of these muscles. Antagonist muscles were less activated during the sprints after fatigue; whereas they stayed unchanged during the last submaximal cycling period. CONCLUSIONS: This suggests that there is a decrease in coactivation as agonist force is lost. This decrease in coactivation under fatigue conditions has not been previously reported and is probably due to the training status of the subjects. Subjects may have learned to better use their antagonist muscles to efficiently transfer force and power to the rotating pedal. This coordination can be adapted to cope with fatigue of the power producer muscles.

Effect of hyperoxia on aerobic and anaerobic performances and muscle metabolism during maximal cycling exercise.

The hyperoxia-improved tolerance to maximal aerobic performance was studied in relation to exercising muscle metabolic state. Five students were submitted to four different tests on a cycle ergometer, each being conducted under normoxia and hyperoxia (60% FiO2) on separate days: Test 1, a progressive exercise until exhaustion to determine the maximal work load (Wmax) which was unchanged by hyperoxia; Test 2, an exercise at Wmax (287 +/- 12 W) until exhaustion to determine the performance time (texh) which was elevated by 38% under hyperoxia but exhaustion occurred at the same arterial proton and lactate concentrations; Test 3 (S-Exercise test) consisted of cycling at Wmax for 90% normoxic-texh (4.8 +/- 0.5 min under both O2 conditions) then followed by a 10-s sprint bout during which the total work output (Wtot) was determined; Wtot was elevated by 15% when exercising under hyperoxia; Test 4 (M-Exercise test) consisted also of cycling at Wmax for 4.8 +/- 0.5 min with blood and muscle samples taken at rest and at the end of the exercise to compare the level of different metabolites. During hyperoxic M-Exercise test, glycogen was twice more depleted whereas glucose-6-phosphate and lactate were less accumulated when compared with normoxia. No significant differences were observed for pyruvate, phosphocreatine and muscle/blood lactate ratio between the two conditions. Conversely to normoxia, levels of ATP, ADP and total NADH were maintained at their resting level under 60% FiO2. These data lead us to suppose a higher oxidation rate for pyruvate and NADH in mitochondria, thereby lowering the metabolic acidosis and allowing a better functioning of the glycolytic and contractile processes to delay the time to exhaustion.

Relative contribution of arms and legs in humans to propulsion in 25-m sprint front-crawl swimming.

Eight male subjects were asked to swim 25 m at maximal velocity while the use of the arm(s) and legs was alternately restricted. Four situations were examined using one arm (1A), two arms (2A), one arm and two legs (1A2L) and both arms and legs (2A2L, normal swim) for propulsion. A significant mean increase of 10% on maximal velocity was obtained in 1A2L and 2A2L compared to 1A and 2A. A non-significant 4% effect was obtained in 1A. This study focused on the actual contribution of leg kick in the 10% gain in maximal velocity. It was clear that the underwater trajectory of the wrist was modified by the action of the legs (most comparisons P < 0.001). Therefore it was thought that the legs enhanced the generated propulsive force by improving the propulsive action of the arm. The arm action was quantified by selecting typical phases from the filmed trajectory of the wrist, namely forward (F), downwards (D) and backwards (B). Although there was a tendency for individual changes in kinematic parameters (F, D and B) to occur with individual changes in velocity when 2A was compared to 2A2L, no relationship was found between the relative changes in F, D and B and relative changes in velocity. This was illustrated by describing the responses of three individuals who could represent three patterns of contribution by legs and arms to propulsion in high speed swimming.

Distribution of lung density after strenuous, prolonged exercise.

The postexercise alteration in pulmonary gas exchange in high-aerobically trained subjects depends on both the intensity and the duration of exercise (G. Manier, J. Moinard, and H. Stoïcheff. J. Appl. Physiol. 75: 2580-2585, 1993; G. Manier, J. Moinard, P. Techoueyres, N. Varène, and H. Guénard. Respir. Physiol. 83: 143-154, 1991). In a recent study that used lung computerized tomography (CT), evidence was found for accumulation of water within the lungs after exercise (C. Caillaud, O. Serre-Cousine, F. Anselme, X. Capdevilla, and C. Prefaut. J. Appl. Physiol. 79: 1226-1232, 1995). On representative slices of the lungs, mean lung density increased by 0.040 +/- 0.007 g/cm(3) (19%, P < 0.001) in athletes after a triathlon. To verify and quantify the mechanism, we determined the change in pulmonary density and mass after strenuous and prolonged exercise using another exercise protocol and methodology for CT scanning. Nine trained runners (age 30-46 yr) volunteered to participate in the study. Each subject ran for 2 h on a treadmill at a rate corresponding to 75% of maximum O(2) consumption. CT measurements were made before and immediately after the exercise test with the subject supine and holding his breath at a point close to functional residual capacity. The lungs were scanned from the apex to the diaphragm and reconstructed in 8-mm-thick slices. Attenuation values of X-rays in each part of the lung were expressed in Hounsfield units (HU), which are related to density (D): D = 1 + HU/1,000. No significant alteration in pulmonary density (0.37 +/- 0.04 vs. 0.35 +/- 0.03, not significant) was observed after the 2-h run test. Although lung volume slightly increased (change of 166 +/- 205 ml, P < 0.05), lung mass remained stable because of a change in density distribution. We failed to detect any changes in postexercise lung mass, suggesting that other mechanisms need to be considered to explain the observed alterations in pulmonary gas exchange after prolonged strenuous exercise.

Corticotroph axis sensitivity after exercise in endurance-trained athletes.

OBJECTIVE: The present study was conducted in order to describe human hypothalamo-pituitary adrenal (HPA) axis adaptation in a model of repeated physical stress (endurance training) that causes a moderate increase in cortisol levels. SUBJECTS: We performed the same stimulation tests (adrenal stimulation with ACTH or pituitary stimulation with combined CRH/LVP) in a population of 8 endurance-trained athletes in two distinct situations: resting (baseline cortisol values) and 2 h after the end of strenuous exercise (increased cortisol values) to evaluate the HPA axis sensitivity to endogenous sustained increases in cortisol concentrations. MEASUREMENTS: During these tests, saliva and plasma cortisol (Fs and Fp, respectively) were assessed and compared. RESULT: Cortisol values in both plasma and saliva at the end of 2 h of exercise were significantly higher than in rested controls: Fs 11.5 +/- 1.3 vs 6.5 +/- 0.8 nmol.l-1 and Fp 428 +/- 36 vs 279 +/- 27 nmol.l-1 (post exercise vs post rest sessions, respectively, P < 0.001 for both). After either hormone test (CRH/LVP or ACTH), cortisol levels in plasma and saliva increased similarly when rest was compared to post exercise. Saliva variations (delta %) under exogenous hormone stimulation were dramatically greater than plasma variations. For example, under ACTH stimulation, the relative increments in cortisol were on control day: delta Fs 980 +/- 139 vs delta Fp 218 +/- 43% (saliva vs plasma, respectively, P < 0.05) and on exercise day: delta Fs 605 +/- 89 vs delta Fp 102 +/- 14% (saliva vs plasma, respectively, P < 0.05). CONCLUSIONS: In endurance-trained athletes, displaying a moderate but sustained endogenous cortisol increase: (1) ACTH responses following pituitary stimulation are not blunted, (2) cortisol responses following maximal adrenal stimulation are not blunted. Our results favour the hypothesis of a decreased pituitary sensitivity to cortisol negative feedback whereas the hypothesis of a major decreased adrenal sensitivity to ACTH was discarded. The greater ability of saliva assays to detect a cortisol increase strongly supports its use in the study of HPA physiology, whether under basal or dynamic conditions.

Peak anaerobic power in elderly men.

The relationship of maximal anaerobic power (Pmax) of the quadriceps muscle and corresponding optimal shortening velocity (vopt) with age, habitual physical activity (PA) and maximal oxygen consumption (VO2max) were assessed in 37 healthy older [71.1 (SD 3.8) years] men and compared to those of 16 young [22.7 (SD 3.4) years] men. The PA was evaluated using a questionnaire. The Pmax and vopt were measured on a friction loaded non-isokinetic cycle ergometer. The Pmax was expressed relative to body mass - Pmax x kg(-1), and relative to the mass of the two quadriceps muscles - Pmax x kgquad(-1). The decline of Pmax x kg(-1) from youth to advanced age (8.3% per decade) was greater than the decrease in quadriceps muscle mass (3.8% per decade), in Pmax x kgquad(-1) (5.9% per decade) and in vopt (4.3% per decade). In the older men, a negative relationship of Pmax x kg(-1) (r = -0.33) and Pmax x kgquad(-1) (r = -0.44) with age was found. Ergometer measurements were not correlated with PA activity indices or VO2max, while VO2max was positively associated with PA. In a multiple stepwise regression analysis age was the only variable that contributed significantly to Pmax x kg(-1) and Pmax x kgquad(-1) variances. Our findings indicated that in these healthy elderly men, unlike the fall in VO2max, habitual PA did not attenuate the decline in Pmax of the quadriceps muscle with age. This finding was different from a previously described relationship in older women and would suggest sex differences in determining Pmax in healthy older subjects.

Habitual physical activity and peak anaerobic power in elderly women.

The aim of this study was to investigate the relationship between maximal anaerobic power (Pmax) and corresponding optimal velocity (Vopt) and habitual physical activity (PA) on the one hand and with maximal oxygen consumption (VO2max) on the other hand, in elderly women. Twenty-nine community dwelling, healthy women aged 66-82 years participated in the study. PA was evaluated using the Questionnaire d'Activite Physique Saint-Etienne (QAPSE) and expressed using two QAPSE activity indices: mean habitual daily energy expenditure (MHDEE) and daily energy expenditure corresponding to leisure time sports activities (sports activity). The subjects' Pmax and Vopt were measured while they cycled on a friction-loaded non-isokinetic cycle ergometer. Pmax was expressed relative to body mass [Pmax/kg(W.kg-1)], and relative to the mass of two quadriceps muscles [Pmax/Quadr(W.kg-1Quadr)]. A negative relationship between Pmax/kg (Spearman's r = -0.56; P < 0.01), Pmax/Quadr (r = -0.53; P < 0.01) and Vopt (r = -0.45; P < 0.05) and age was found. Pmax/kg was positively associated with MHDEE (r = 0.51; P < 0.01) and sports activity (r = 0.58; P < 0.01), as were Pmax/Quadr and Vopt (r = 0.55; P < 0.01 and r = 0.54; P < 0.01, respectively). Pmax/kg, Pmax/Quadr and Vopt correlated positively with VO2max. The positive relationship between ergometer measurements and PA indices was similar to that between VO2max and PA. Pmax/kg was, moreover, closely related to Vopt (r = 0.77; P < 0.001). When a multiple stepwise regression analysis was used to select the variables influencing ergometer measurements, MHDEE contributed significantly to Pmax/kg variance, whereas sports activity contributed to Pmax/Quadr and Vopt variances. In conclusion, the data from this cross-sectional study suggest that in healthy elderly women habitual PA, and especially leisure time PA, alleviates the decline of the Pmax of the quadriceps muscles.

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

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.

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

To determine whether power-velocity relationships 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 frequency 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 expressed 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 related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power. expressed 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 contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated 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.

Effect of vertical loading on energy cost and kinematics of running in trained male subjects.

This investigation examined, in a group of 10 trained male runners, the effect of vertical loading during level treadmill running at a velocity of 5 m/s. The net energy cost of running (Cr), the external work of the center of mass of the body (Wext; both expressed in J.kg-1.m-1), and the eccentric-to-concentric ratio (Ecc/Con) of integrated electromyographic activity for the vastus lateralis (VL) and gastrocnemius lateralis muscles were measured. It was observed that Wext and Ecc/Con for the VL could explain a large part of the interindividual variations in Cr. This result reinforces the hypothesis that Ecc/Con could be a good index of effectiveness in the stretch-shortening cycle. When the subjects ran with a vertical load of 9.3% of their body mass, Cr and Wext were significantly reduced (P < 0.01 and P < 0.05, respectively), whereas Ecc/Con for the VL and gastrocnemius lateralis remained unchanged. The variations in Cr and Wext due to vertical loading were significantly correlated (r = 0.75; P < 0.01). It was then concluded that the significant improvement of Cr observed with the added load was mainly due to the fact that Wext was significantly decreased.

Relationships between postcompetition blood lactate concentration and average running velocity over 100-m and 200-m races.

The relationships between anaerobic glycolysis and average velocity (v) sustained during sprint running were studied in 12 national level male sprinters. A blood sample was obtained within 3 min of the completion of semi-finals and finals in the 100-m and 200-m Cameroon national championships and blood lactate concentration ([la-]b) was measured. The 35-m times were video-recorded. The 100-m and 200-m [la-]b were 8.5 (SD 0.8) and 10.3 (SD 0.8) mmol.l-1, respectively. These were not correlated with the performances. Over 200 m [la-]b was correlated with the v sustained over the last 165 m (r = 0.65, P < 0.05). In the 9 athletes who participated in both the 100-m and 200-m races, the difference between the [la-]b measured at the end of the two races was negatively correlated to the difference in v sustained over the two races (r = 0.76, P > 0.02). Energy expenditure during sprint running was estimated from the [la-]b values. This estimate was mainly based on the assumption that a 1 mmol.l-1 increase in [la-]b corresponds to the energy produced by the utilization of 3.30 ml O2.kg-1. The energy cost of running was estimated at 0.275 (SD 0.02) ml O2.kg-1.m-1 over 200-m and 0.433 (SD 0.03) ml O2.kg-1.m-1 over 100-m races. These results would suggest that at the velocities studied anaerobic glycolysis contributes to at least 55% of the energy expenditure related to spring running. However, the influence of both mechanical factors and the contribution of other energy processes obscure the relationship between [la-]b and performance.

Assessment of running velocity at maximal oxygen uptake.

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