Femur strength as influenced by growth, bone-length and gravity with the male rat.

Abstract Bending measurements with fresh, wet femurs from 76 normal male white rats indicate material strength σ u to increase with age t in proportion to the square L 2 of bone-length. For conditions of constant t , however, σ u is inversely proportional to L 4 . In studies where experimental treatment influences size, experimental values of σ u should, therefore, be compared neither to those from rats of the same age and differing size, nor to those from the same size but differing age. Comparison relative to the value of the quantity σ u L 4 × 10 55day ÷ t is proposed. This comparison was demonstrated by determining whether smaller size alone could account for the greater σ u of 26 rats reared during a week's centrifugation at 3 times normal gravity (3 g ). The experimental σ u was 40% greater than expected for control rats of comparable size and age.