Physical activity when young provides lifelong benefits to cortical bone size and strength in men

Abstract

The skeleton shows greatest plasticity to physical activity-related mechanical loads during youth but is more at risk for failure during aging. Do the skeletal benefits of physical activity during youth persist with aging? To address this question, we used a uniquely controlled cross-sectional study design in which we compared the throwing-to-nonthrowing arm differences in humeral diaphysis bone properties in professional baseball players at different stages of their careers (n = 103) with dominant-to-nondominant arm differences in controls (n = 94). Throwing-related physical activity introduced extreme loading to the humeral diaphysis and nearly doubled its strength. Once throwing activities ceased, the cortical bone mass, area, and thickness benefits of physical activity during youth were gradually lost because of greater medullary expansion and cortical trabecularization. However, half of the bone size (total cross-sectional area) and one-third of the bone strength (polar moment of inertia) benefits of throwing-related physical activity during youth were maintained lifelong. In players who continued throwing during aging, some cortical bone mass and more strength benefits of the physical activity during youth were maintained as a result of less medullary expansion and cortical trabecularization. These data indicate that the old adage of "use it or lose it" is not entirely applicable to the skeleton and that physical activity during youth should be encouraged for lifelong bone health, with the focus being optimization of bone size and strength rather than the current paradigm of increasing mass. The data also indicate that physical activity should be encouraged during aging to reduce skeletal structural decay.exercise | intracortical remodeling | osteoporosis | peak bone mass

Gradual decline in mobility with the adoption of food production in Europe

“…Studies of age-related changes in trabecular density or cortical bone relative thickness in Iron/Roman through early industrial European samples have produced mixed results, with some reporting less decline than in modern populations (64)(65)(66) and others finding no difference or even more negative trends in the earlier samples (67)(68)(69). The results of the present study suggest that only very vigorous exercise is a sufficient stimulus for increasing bone strength, as a possible protective mechanism for age-related bone loss (21,22).…”

“…Although skeletal morphology is determined by a complex interplay between various genetic and environmental factors (18,19), there is abundant evidence that mechanical loading during life has a strong influence on skeletal structure (20)(21)(22)(23). Earlier studies identified declines in skeletal robusticity (strength relative to body size) in Homo throughout the Pleistocene (24,25), but recent analyses suggest that the major decrease in robusticity occurred later, at the end of the Pleistocene, between early anatomically modern H. sapiens and Holocene populations (26,27).…”

Focal enhancement of the skeleton to exercise correlates to mesenchymal stem cell responsivity rather than peak external forces

“…A well-known example of focal adaptation to physical demand is the humeral hypertrophy of the playing arms of tennis players and baseball pitchers relative to their non-playing arms (Jones et al, 1977;Haapasalo et al, 2000;Warden et al, 2014). Implicitly, these athletes demonstrate the ability of bone to perceive and respond to biophysical signals in a sitespecific manner, perhaps to maintain an optimal mechanical environment to cells regulating the response (Rubin, 1984).…”

Bone Quality and Quantity are Mediated by Mechanical Stimuli

“…1 [8]. Similarly, the throwing arm of baseball players has been shown to have increased bone mass and improved structure as compared with the non-throwing arm [9]. Running [10][11][12], jumping [13], gymnastics [14,15], weight lifting [16], and swimming [17,18] have all been shown to increase bone mass as compared to sedentary controls.…”