Maximum likelihood factor analysis of the effects of chronic centrifugation on the structural development of the musculoskeletal system of the rat

Summary

At the age of 30 days female Sprague-Dawley rats were placed on a 3.66 m radius centrifuge and subsequently exposed almost continuously for 810 days to either 2.76 or 4.15 G. An age-matched control group of rats was raised near the centrifuge facility at earth gravity. Three further control groups of rats were obtained from the animal colony and sacrificed at the age of 34, 72 and 102 days. A total of 16 variables were simultaneously factor analyzed by a maximum-likelihood extraction routine and the factor loadings presented after rotation to simple structure by a varimax rotation routine. The variables include G-load, age, body mass, femoral length and cross-sectional area, inner and outer radii, density and strength at the midlength of the femur, dry weight of gluteus medius, semimenbranosus and triceps surae muscles.

Factor analyses on A) all controls, B) all controls and the 2.76 G group, and C) all controls and centrifuged animals, produced highly similar loading structures of three common factors which accounted for 74%, 68% and 68%, respectively, of the total variance. The 3 factors were interpreted as:

• 1. An age and size factor which stimulates the growth in length and diameter and increases the density and strength of the femur. This factor is positively correlated with G-load but is also active in the control animals living at earth gravity.

• 2. A growth inhibition factor which acts on body size, femoral length and on both the outer and inner radius at mid-length of the femur. This factor is intensified by centrifugation.

• 3. A muscle growth inhibition factor which is probably correlated with age and G-load but is also active at earth gravity.

A tentative biomechanical interpretation of these 3 factors has been ventured.