Muscle disuse due to physical inactivity, ageing and many disease conditions results in muscle atrophy and reduced muscle functional capacity, which may impair activities of daily living. Strategies that may prevent or reverse these effects are of considerable functional significance to the individual. Recent evidence suggests that oral creatine supplementation is an effective intervention to prevent or reverse neuromuscular degeneration in humans.Since Harris and his co-workers (1992) 1. We investigated the effect of oral creatine supplementation during leg immobilization and rehabilitation on muscle volume and function, and on myogenic transcription factor expression in human subjects. A double-blind trial was performed in young healthy volunteers (n = 22).A cast was used to immobilize the right leg for 2 weeks. Thereafter the subjects participated in a knee-extension rehabilitation programme (3 sessions week _1 , 10 weeks). Half of the subjects received creatine monohydrate (CR; from 20 g down to 5 g daily), whilst the others ingested placebo (P; maltodextrin).3. Before and after immobilization, and after 3 and 10 weeks of rehabilitation training, the crosssectional area (CSA) of the quadriceps muscle was assessed by NMR imaging. In addition, an isokinetic dynamometer was used to measure maximal knee-extension power (W max ), and needle biopsy samples taken from the vastus lateralis muscle were examined to asses expression of the myogenic transcription factors MyoD, myogenin, Myf5, and MRF4, and muscle fibre diameters.4. Immobilization decreased quadriceps muscle CSA (~10 %) and W max (~25 %) by the same magnitude in both groups. During rehabilitation, CSA and W max recovered at a faster rate in CR than in P (P < 0.05 for both parameters). Immobilization changed myogenic factor protein expression in neither P nor CR. However, after rehabilitation myogenin protein expression was increased in P but not in CR (P < 0.05), whilst MRF4 protein expression was increased in CR but not in P (P < 0.05). In addition, the change in MRF4 expression was correlated with the change in mean muscle fibre diameter (r = 0.73, P < 0.05).5. It is concluded that oral creatine supplementation stimulates muscle hypertrophy during rehabilitative strength training. This effect may be mediated by a creatine-induced change in MRF4 and myogenin expression.

Background: Low levels of physical activity are characteristic in preschoolers. To effectively promote physical activity, it is necessary to understand factors that influence young children's physical activity. The present study aimed to investigate how physical activity levels are influenced by environmental factors during recess in preschool.

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effect of oral creatine supplementation (CR; 5 g/day) in conjunction with exercise training on physical fitness was investigated in men between 55 and 75 yr of age (n = 46). A double-blind randomized placebo-controlled (PL) trial was performed over a 6-mo period. Furthermore, a subgroup (n = 20) completed a 1-yr follow-up. The training program consisted of cardiorespiratory endurance training as well as moderate resistance training (2-3 sessions/wk). Endurance capacity was evaluated during a maximal incremental bicycle ergometer test, maximal isometric strength of the knee-extensor muscles was assessed by an isokinetic dynamometer, and body composition was assessed by hydrostatic weighing. Furthermore, in a subgroup (PL: n = 13; CR: n = 12) biopsies were taken from m. vastus lateralis to determine total creatine (TCr) content. In PL, 6 mo of training increased peak oxygen uptake rate (+16%; P < 0.05). Fat-free mass slightly increased (+0.3 kg; P < 0.05), whereas percent body fat slightly decreased (-1.2%; P < 0.05). The training intervention did not significantly change either maximal isometric strength or body weight. The responses were independent of CR. Still, compared with PL, TCr was increased by approximately 5% in CR, and this increase was closely correlated with initial muscle creatine content (r = -0.78; P < 0.05). After a 1-yr follow-up, muscle TCr was not higher in CR than in PL. Furthermore, the other measurements were not affected by CR. It is concluded that long-term creatine intake (5 g/day) in conjunction with exercise training does not beneficially impact physical fitness in men between 55 and 75 yr of age.

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