Femur-bending properties as influenced by gravity: IV. Limits after high and low weight-bearing.

Gravity enhances femur growth as measured in terms of strength sigma u, but shows little or even a growth-retarding effecting in terms of "relative brittleness," defined as the inverse 1/epsilon u of ultimate or tolerable strain. Chronic weightlessness was simulated by harness suspension or by extrapolation of results from 3-G centrifugation. Experimental results from 45 male, white rats (34-520 d old) were compared to 72 control or baseline rats (28-520 d old) white correction for age and size differences. After suspension, the youngest rats showed subnormal epsilon u. Combined results, however, although predicting 19 +/- 1% below normal sigma u, after a week of weightlessness, predicted less effect (1 +/- 4%) for epsilon u.