This study was performed to observe the influence of moderate treadmill run
ning on bone of middle-aged male rats. Seventy 15-month-old Wistar rats wer
e used. Ten initial controls (IC) were killed on day 0. Among the 60 others
, three groups of ten exercised rats (E) run 1 h/day, 6 days/week at 60% of
their maximum aerobic capacity. On days 30, 60 and 90 of the training peri
od, 20 rats, ten E and ten R (resting animals), were killed. Femoral failur
e stress never varied and was never different in E and R during the experim
ent. On day 90 whole body mineral content and mineral density were higher i
n E than R. Simultaneously, total, diaphyseal and metaphyseal femoral densi
ties were lower in R than IC or than in E. No difference was observed betwe
en IC and E. In resting rats, urinary deoxypyridinoline excretion (a marker
of bone resorption) increased between days 0 and 90, while it did not chan
ge in runners. These results indicate that in middle-aged rats, moderate ru
nning prevents decrease in bone mineral density, probably by inhibiting bon
e resorption. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.