Chapter 29 Chapter 29 Physical Activity and Exercise in the Maintenance of the Adult Skeleton and the Prevention of Osteoporotic Fractures Copyright © 2013 Elsevier Inc. All rights reserved.

FIGURE 29.1 Age-related change in bone mass and bone size in men and women. The increase in cross- sectional area and diameter with age results in improved resistance to bending and compression, partially compensating for age- and menopause-related bone loss. Source: reprinted from Suominen (2006) [26], with permission from Editrice Kurtis s.r.l. 2

Copyright © 2013 Elsevier Inc. All rights reserved. FIGURE 29.2 Theoretical bone strength changes with varying mechanical usage patterns under conditions of normal hormone status and estrogen deficiency. Thresholds are defined by minimal effective strains (MES) for modeling, remodeling, and repair. With disuse osteoclast activity associated with remodeling increases and bone loss ensues while overload (above normal patterns) results in an increase in osteoblast activity and enhanced bone mass and strength. Estrogen withdrawal associated with menopause alters the mechanosensory set-point and dampens the response to increased mechanical usage. Source: reprinted from Suominen (2006) [26], with permission from Editrice Kurtis s.r.l. 3