RESUMO
Athletes' ability to use motor imagery (MI) to predict the speed at which they could perform a motor sequence has received little attention. In this study, 21 alpine skiers and 16 equestrian riders performed MI based on a prediction of actual performance time (a) after the course inspection, (b) before the start, and (c) after the actual performance. MI and physical times were similar in expert skiers during each imagery session, while novice skiers and novice and expert riders underestimated the actual course duration. These findings provide evidence that the temporal accuracy of an imagery task prediction depends on the performer's expertise level and characteristics of the motor skill.
Assuntos
Desempenho Atlético/psicologia , Imaginação , Esqui/psicologia , Percepção do Tempo , Adolescente , Adulto , Análise de Variância , Animais , Feminino , Cavalos , Humanos , Masculino , Destreza Motora , Prática Psicológica , Adulto JovemRESUMO
Researchers realize that motor imagery (MI) duration is closely linked to actual motor action duration. In 2 experiments, the authors investigated the effect of changing MI speed on actual movement duration over a 3-week training period. Experiment 1 involved 2 series of body movements that 24 participants mentally performed faster or slower than their actual execution speeds. The fast MI group's actual times decreased on subsequent performance. Participants in Experiment 2 were 21 skilled athletes who increased (decreased) their well-rehearsed actual movement times after MI training at a slow (fast) speed. The effect was task-related, however: MI affected only self-initiated movement. The effect of MI on actual speed execution supports the ideomotor theory because anticipation of sensory consequences of actions is mentally represented.
Assuntos
Imaginação/fisiologia , Movimento/fisiologia , Prática Psicológica , Desempenho Psicomotor/fisiologia , Tempo de Reação/fisiologia , Adolescente , Adulto , Braço , Desempenho Atlético/fisiologia , Feminino , Humanos , Masculino , Artes Marciais/fisiologia , Valores de ReferênciaRESUMO
Dystrophic mice (mdx) and their controls (C57/Bl10) were fed for 1 month with a diet with or without creatine (Cr) enrichment. Cr supplementation reduced mass (by 19%, P < 0.01) and mean fiber surface (by 25%, P < 0.05) of fast-twitch mdx muscles. In both strains, tetanic tension increased slightly (9.2%) without reaching statistical significance (P = 0.08), and relaxation time increased by 16% (P < 0.001). However, Cr had no protective effect on the other hallmarks of dystrophy such as susceptibility to eccentric contractions; large numbers of centrally nucleated fibers in tibialis anterior; and elevated total calcium content, which increased by 85% (P = 0.008) in gastrocnemius mdx muscles. In conclusion, Cr may be a positive intervention for improving function of dystrophic muscle.
Assuntos
Creatina/uso terapêutico , Suplementos Nutricionais , Músculo Esquelético/efeitos dos fármacos , Distrofias Musculares/fisiopatologia , Animais , Creatina/administração & dosagem , Técnicas In Vitro , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos mdx , Contração Muscular/efeitos dos fármacos , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Distrofias Musculares/dietoterapiaRESUMO
Muscle hypertrophy during resistance training is reportedly increased by creatine supplementation. Having previously failed to find an anabolic effect on muscle protein turnover at rest, either fed or fasted, we have now examined the possibility of a stimulatory effect of creatine in conjunction with acute resistance exercise. Seven healthy men (body mass index, 23 +/- 2 kg/m2, 21 +/- 1 yr, means +/- SE) performed 20 x 10 repetitions of leg extension-flexion at 75% one-repetition maximum in one leg, on two occasions, 4 wk apart, before and after ingesting 21 g/day creatine for 5 days. The subjects ate approximately 21 g maltodextrin + 6 g protein/h for 3 h postexercise. We measured incorporation of [1-13C]leucine into quadriceps muscle proteins in the rested and exercised legs. Leg protein breakdown (as dilution of [2H5]phenylalanine) was also assessed in the exercised and rested leg postexercise. Creatine supplementation increased muscle total creatine by approximately 21% (P < 0.01). Exercise increased the synthetic rates of myofibrillar and sarcoplasmic proteins by two- to threefold (P < 0.05), and leg phenylalanine balance became more positive, but creatine was without any anabolic effect.
Assuntos
Creatina/administração & dosagem , Exercício Físico , Proteínas Musculares/biossíntese , Miofibrilas/metabolismo , Retículo Sarcoplasmático/metabolismo , Adulto , Biópsia , Velocidade do Fluxo Sanguíneo , Isótopos de Carbono , Creatina/análise , Deutério , Dieta , Proteínas Alimentares/administração & dosagem , Suplementos Nutricionais , Humanos , Cinética , Perna (Membro)/irrigação sanguínea , Leucina/metabolismo , Masculino , Músculo Esquelético/química , Miofibrilas/efeitos dos fármacos , Fenilalanina/metabolismo , Polissacarídeos/administração & dosagem , Retículo Sarcoplasmático/efeitos dos fármacosRESUMO
The effect of creatine (Cr) supplementation on muscle function and body composition of 12 boys with Duchenne muscular dystrophy and three with Becker dystrophy was evaluated by a randomized double-blind cross-over study (3 g Cr or maltodextrin daily for 3 months, with wash-out period of 2 months). After placebo, no change was observed in maximal voluntary contraction (MVC) and resistance to fatigue, whereas total joint stiffness (TJS) was increased by approximately 25% (P < 0.05). The patients receiving Cr did not show any change in TJS, improved MVC by 15% (P = 0.02), and almost doubled their resistance to fatigue (P < 0.001). In patients still independent of a wheelchair (n = 5), bone mineral density increased by 3% (P < 0.05), and urinary excretion of collagen type I cross-linking N-telopeptide declined to about one third (P < 0.001) after Cr. No adverse effect was observed. Thus, Cr may provide some symptomatic benefit in these patients.
Assuntos
Creatinina/administração & dosagem , Distrofia Muscular de Duchenne/tratamento farmacológico , Administração Oral , Adolescente , Densidade Óssea/efeitos dos fármacos , Criança , Creatinina/sangue , Creatinina/urina , Estudos Cross-Over , Método Duplo-Cego , Humanos , Espectroscopia de Ressonância Magnética , Masculino , Contração Muscular/efeitos dos fármacos , Músculo Esquelético/fisiologia , Isótopos de Fósforo , Resultado do TratamentoRESUMO
Dietary creatine supplementation is associated with increases in muscle mass, but the mechanism is unknown. We tested the hypothesis that creatine supplementation enhanced myofibrillar protein synthesis (MPS) and diminished muscle protein breakdown (MPB) in the fed state. Six healthy men (26 +/- 7 yr, body mass index 22 +/- 4 kg/m(2)) were studied twice, 2-4 wk apart, before and after ingestion of creatine (21 g/day, 5 days). We carried out two sets of measurements within 5.5 h of both MPS (by incorporation of [1-(13)C]leucine in quadriceps muscle) and MPB (as dilution of [1-(13)C]leucine or [(2)H(5)]phenylalanine across the forearm); for the first 3 h, the subjects were postabsorptive but thereafter were fed orally (0.3 g maltodextrin and 0.083 g protein. kg body wt(-1) x h(-1)). Creatine supplementation increased muscle total creatine by approximately 30% (P < 0.01). Feeding had significant effects, doubling MPS (P < 0.001) and depressing MPB by approximately 40% (P < 0.026), but creatine had no effect on turnover in the postabsorptive or fed states. Thus any increase in muscle mass accompanying creatine supplementation must be associated with increased physical activity.