Physical exercise may promote increases in bone mass, size, and strength that are retained to some degree throughout life, and these increases may be retained longer in those who continue to exercise as they age, according to a study. Bone mass, size, and strength increase in response to physical activity in youth, but whether these benefits of physical activity persist throughout adulthood is unclear. To investigate this question, Stuart J. Warden and colleagues compared humerus mass, size, and strength in the throwing and non-throwing arms of 103 professional baseball players during their careers and after retirement. The authors report that working baseball players displayed greater humerus mass, size, and strength in their throwing arms than in their non-throwing arms, with bone strength twice as high in the throwing arm. After retirement, players who stopped throwing eventually lost all of the bone mass benefits in their throwing arms as they aged. In contrast, retired players who remained active retained 28% of the bone mass benefit. Inactive players in their 80s retained 56% of the bone size and 34% of the bone strength benefits in their throwing arms that they had built when young, in spite of not throwing for more than 50 years. Bone strength benefit retention in active retirees rose to 50%. According to the authors, the results suggest that exercise at a young age increases bone mass, size, and strength, and that the improved bone size and strength are retained well into late adulthood, despite lack of exercise.

Article: “Physical activity when young provides lifelong benefits to cortical bone size and strength in men,” by Stuart J. Warden et al.