46 (−6.28 to 3.36) P = 0.55 −7.09 (−11.95 to −2.23) P = 0.004 0.76 (−5.32 to 6.85) P = 0.81 −2.09 (−8.22 to 4.05) P = 0.51 ToA (mm2) 1.24 (−1.29 to 3.78) P = 0.34 1.49 (−1.05 to 4.04) P = 0.25 0.10 (−2.72 to 2.92) P = 0.95 −0.49 (−3.34 to 2.35) P = 0.73 I max (mm4) 152.80 (−98.48

to 404.08) P = 0.23 124.07 (−129.3 to 377.46) P = 0.34 23.32 (−248.86 to 295.5) P = 0.87 −91.56 (−366.5 to 183.28) P = 0.51 CovBMD volumetric cortical bone mineral density, I max bone strength, ToA total area, BT balance and tone, RT1 resistance training once per week, RT2 resistance training twice per week There are several plausible explanations as to why there were no differences between groups in cortical bone over 12 months. First, our participants were very active Protease Inhibitor Library research buy prior to joining the study and outside of the intervention exercise classes over the course of the 12-month intervention. We previously reported [31], using accelerometry in a subset of participants (n = 77) from this study, find more no statistically significant between group differences for moderate to vigorous physical activity (MVPA) outside of the exercise classes and no seasonal differences at four measurement points over the year.

Further, for the combined groups, mean MVPA ranged from 24 to 27 min/day depending on the season. It may be that this group of highly motivated participants were already at their “optimum” bone health and had little room for improvement. Although there were increases in the muscle performance measures (one repetition max) in the RT groups over the study [21], there were no statistically significant differences in functional capacity (6MWT) at 6 or 12 months, and this may explain some of the observed statistically nonsignificant differences in bone outcomes. Frost [32, 33] theorized that older adults might not have the same ability to initiate the bone modeling cycle responsible for changes in cortical bone geometry such as increased total bone area due to periosteal apposition.

Erlotinib The Utah paradigm and the strain threshold theory suggest that older adults may not generate enough force or novel strains needed to stimulate bone formation. Thus, the role of physical activity in later life may be to sustain bone strength (by various means) in the aging skeleton [33]. It may also be that bone density is not a sensitive enough measure to assess the effect of RT or physical activity in general [34]. Further, current imaging techniques may not detect small changes in density at the midtibia whereas the distal tibia may be more responsive given its greater amounts of metabolically active trabecular bone. Exercise acts to stimulate osteoblasts to enhance bone formation, and the first phase includes osteoclastic activity, which removes older bone, followed by the creation of a new hypomineralized tissue.