Physical training and connective tissues in young mice : physical properties of Achilles tendons and long bones

Abstract

The effect of physical training on the growth of Achilles tendons and long bones was studied in male mice of NMRI-strain. The mice to he trained and their controls were about 2 weeks old at the beginning of the training, which took place on a 5° inclined treadmill 5 days a week for 3 to 22 weeks. The duration of daily exercise was increased progressively over 3 weeks. The final daily exercise bouts were 50 and 80 minutes for moderate programs and 180 minutes for the intensive program at a speed of 30 cm/s. At the end of each experiment the Achilles tendons, the long hones of hind and fore limbs, the heart and a blood sample were taken for analyses. A transient increase in the dry weights of the Achilles tendons and the long bones was observed after 4 - 7 weeks' of moderate training. The intensive training increased the density and decreased the volume and length of long bones. Some programs tended to increase the breaking load of the femur. Moderate or intensive training continued to maturity brought about shorther femoral bones whereas the dry weight of the Achilles tendons and the long bones was not changed significantly. I conclude that the physical training of growing mice accelerates the maturation process, evokes permanent changes in the length of the femoral bones and causes transient changes in the dry weight, density, and volume of the long bones. The size of the effect depends on the age of the experimental animals as well as on the intensity and duration of the training program.