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1.
J Sports Sci ; 20(5): 427-37, 2002 May.
Artigo em Inglês | MEDLINE | ID: mdl-12043832

RESUMO

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.


Assuntos
Creatina/farmacologia , Exercício Físico/fisiologia , Músculo Esquelético/efeitos dos fármacos , Fosfatos/metabolismo , Fosfocreatina/metabolismo , Adulto , Análise de Variância , Índice de Massa Corporal , Humanos , Concentração de Íons de Hidrogênio/efeitos dos fármacos , Espectroscopia de Ressonância Magnética , Masculino , Músculo Esquelético/metabolismo , Recuperação de Função Fisiológica/fisiologia
2.
Eur J Appl Physiol ; 82(1-2): 83-90, 2000 May.
Artigo em Inglês | MEDLINE | ID: mdl-10879447

RESUMO

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.


Assuntos
Envelhecimento/fisiologia , Sulfato de Desidroepiandrosterona/sangue , Fator de Crescimento Insulin-Like I/análise , Perna (Membro) , Músculo Esquelético/fisiologia , Testosterona/sangue , Idoso , Idoso de 80 Anos ou mais , Teste de Esforço , Feminino , Humanos , Hidrocortisona/sangue , Masculino , Aptidão Física , Análise de Regressão
3.
Med Sci Sports Exerc ; 32(4): 839-43, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10776904

RESUMO

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.


Assuntos
Ciclismo/fisiologia , Contração Muscular/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Adulto , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino
4.
Eur J Appl Physiol Occup Physiol ; 80(3): 192-9, 1999 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-10453920

RESUMO

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.


Assuntos
Perna (Membro)/fisiologia , Natação/fisiologia , Punho/fisiologia , Braço/fisiologia , Fenômenos Biomecânicos , Humanos , Masculino
5.
Eur J Appl Physiol Occup Physiol ; 77(1-2): 182-8, 1998.
Artigo em Inglês | MEDLINE | ID: mdl-9459540

RESUMO

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.


Assuntos
Envelhecimento/fisiologia , Músculo Esquelético/fisiologia , Consumo de Oxigênio , Adulto , Idoso , Idoso de 80 Anos ou mais , Anaerobiose , Ergometria , Feminino , Frequência Cardíaca , Humanos , Ácido Láctico/sangue , Masculino , Músculo Esquelético/anatomia & histologia , Análise de Regressão
6.
Artigo em Inglês | MEDLINE | ID: mdl-9243174

RESUMO

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.


Assuntos
Envelhecimento/fisiologia , Exercício Físico/fisiologia , Consumo de Oxigênio/fisiologia , Idoso , Índice de Massa Corporal , Feminino , Humanos , Inquéritos e Questionários
7.
Eur J Appl Physiol Occup Physiol ; 74(1-2): 100-6, 1996.
Artigo em Inglês | MEDLINE | ID: mdl-8891507

RESUMO

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.


Assuntos
Teste de Esforço/instrumentação , Exercício Físico/fisiologia , Músculo Esquelético/fisiologia , Aceleração , Adulto , Calibragem , Metabolismo Energético/fisiologia , Teste de Esforço/normas , Humanos , Masculino
8.
Eur J Appl Physiol Occup Physiol ; 74(1-2): 114-8, 1996.
Artigo em Inglês | MEDLINE | ID: mdl-8891509

RESUMO

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.


Assuntos
Ciclismo , Metabolismo Energético/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Músculo Esquelético/citologia , Músculo Esquelético/fisiologia , Adulto , Teste de Esforço , Feminino , Humanos , Masculino , Fibras Musculares de Contração Rápida/fisiologia
9.
J Appl Physiol (1985) ; 79(6): 2078-85, 1995 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-8847276

RESUMO

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.


Assuntos
Metabolismo Energético/fisiologia , Exercício Físico/fisiologia , Corrida/fisiologia , Adulto , Humanos , Cinética , Masculino , Contração Muscular/fisiologia
10.
Eur J Appl Physiol Occup Physiol ; 68(6): 508-13, 1994.
Artigo em Inglês | MEDLINE | ID: mdl-7957143

RESUMO

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.


Assuntos
Lactatos/sangue , Corrida/fisiologia , Adolescente , Adulto , Humanos , Ácido Láctico , Masculino , Fosfocreatina/sangue , Esforço Físico/fisiologia
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