FACTORS IN DAILY PHYSICAL-ACTIVITY RELATED TO CALCANEAL MINERAL DENSITY IN MEN

To determine the factors in daily physical activity that influence the mineral density of the calcaneus, we recorded walking steps and the t ype and duration of exercise in 43 healthy 26-to 51-yr-old men. Areal( g . cm(-2)) calcaneal bone mineral density (CBMD) was measured by sing le energy x-ray densitometry (SXA, Osteon, Inc., Wahiawa, HI). Subject s walked a mean (+/-SD) of 7902 (+/-2534) steps per day or approximate ly 3.9 (+/-1.2) miles daily. Eight subjects reported no exercise activ ities. The remaining 35 subjects spent 143 (2-772) (median and range) min . wk(-1) exercising. Twenty-eight men engaged in exercise activiti es that generate single leg peak Vertical ground reaction forces (GRF( z)) of 2 or more body weights (high loaders, HL), and 15 reported exer cise or daily activities that typically generate GRF(z) less than 1.5 body weights (low loaders, LL). CBMD was 12% higher in HL than LL (0.6 68 +/- 0.074 g . cm(-2) vs 0.597 +/- 0.062 g . cm(-2), P < 0.004). In the HL group, CBMD correlated to reported minutes of high load exercis e (r = 0.41, P < 0.03). CBMD was not related to the number of daily wa lking steps (N = 43, r = 0.03, NS). The results of this study support the concept that the dominant factor in daily physical activity relati ng to bone mineral density is the participation in site specific high loading activities, i.e., for the calcaneus, high calcaneal loads.