Atividade física e saúde óssea: princípios fundamentais da resposta a estímulos mecânicos / Physical activity and bone health: fundamental principles of the answer to mechanical loading

O papel-chave da atividade física no desenvolvimento e na manutenção da massa e da resistência ósseas é amplamente aceito. Este artigo revisa informações acerca das diferentes respostas do tecido ósseo aos estímulos mecânicos, através de consulta ao Portal de Periódicos CAPES, utilizando os unitermos “bone”, “exercise”, “mechanical loading”, “bone mass” e “osteogenic response” e incluindo artigos completos publicados entre 1980 e 2008. Os estudos analisados demonstram que: (1) o osso responde melhor a estímulos dinâmicos comparados a estímulos estáticos; (2) a resposta óssea é maior quando a taxa de aplicação da carga é alta; e (3) a resposta óssea satura rapidamente, sendo o intervalo entre as aplicações de carga é uma estratégia benéfica. Conhecer e aplicar informações como essas, além de assegurar que as rotinas de exercício proporcionem um estímulo suficiente para manter a densidade mineral óssea em um nível apropriado, são importantes para a prevenção de mecanismos de lesão osteomuscular.

The key role of physical activity in the development and maintenance of bone mass and resistance is widely accepted. This article reviews information about the different answers of bone tissue to mechanical loading, obtained through the “Portal de Periódicos CAPES” database, using the descriptors “bone”, “exercise”, “ mechanical loading”, “bone mass” and “osteogenic response”, and including full papers published in peer-reviewed journals from 1980 to 2008. The analyzed studies showed that: (1) the bone answers better to dynamic stimuli compared to static stimuli; (2) the bone response is better at higher loading rates; and (3) the bone response saturates quickly, and the insertion of rest intervals between the load applications could be a beneficial strategy. Knowing and using this information, beyond assuring that the exercise routines will provide a sufficient stimulus to maintain subject’s bone mineral density in a healthy level, could be very helpful to prevent mechanisms of musculoskeletal injuries.

EFFECT OF HIGH-IMPACT TRAINING AT DIFFERENT FREQUENCIES ON OSTEOGENIC RESPONSE IN RATS / 体力科学

Mechanical stress imposed by physical exercise is known to play an important role in increasing bone mass and preventing osteoporosis. As repetitional loadings may diminish mechano-sensitivity of bone cell, understanding shifts in mechano-sensitivity is important for making an effective training program for bones. The primary purpose of this study was to investigate bone responses when rats performed 400 repetitions of jump exercise in total using different training programs over 40 days. The secondary purpose was to clarify whether loading magnitude affects the results. This study comprised two experiments (EX1, EX2). In each experiment, 60 female Wistar rats (10-weeks-old) were divided into 1 sedentary group and 4 exercise groups. The 4 exercise groups were exercised with 10 jumps every day (10 jumps/day), 20 jumps every other day (20 jumps/2 days), 50 jumps every 5 days (50 jumps/5 days) or 100 jumps every 10 days (100 jumps/10 days). Jump height was set at 40 cm in EX1 and 30 cm in EX2. After 40 days, the 10 jumps/day, 20 jumps/2 days and 50 jumps/5 days groups in EX1 and EX2 showed significantly greater bone mass and strength compared to each sedentary group, although differences in training effects between these 3 groups were little. The 100 jumps/10 days group in EX1 also showed significantly greater bone mass and strength compared to the sedentary group, but the training effect was less. The 100 jumps/10 days group in EX2 did not show significantly greater bone mass and strength compared to the sedentary group. These results suggest that exercise everyday or every other day is not always necessary for bone development.