INFLUENCE OF PHYSICAL EXERCISE ON AGING RATS - III - LIFELONG EXERCISE MODIFIES THE AGING CHANGES OF THE MECHANICAL-PROPERTIES OF LIMB MUSCLE TENDONS

We have previously shown that long-term regular physical exercise has a systemic influence on the rat by slowing the aging of its connective tissues, measured as thermal stability and biomechanical properties o f tail tendons. This paper analyses whether the properties of limb mus cle tendons are influenced not only by the aging process and the syste mic effects of exercise but also from direct mechanical stimuli from l ong-term physical exercise. Male Sprague-Dawley rats were trained in a treadmill from the age of 5 to 23 months. The effects of training on muscle tendons were analyzed with respect to biomechanical properties. Also, the viscoelastic activation energies for interactions between c ollagen and the proteoglycan gel as well as between collagen fibrils w ere measured. Finally the asymptotes from the creep curves were calcul ated in order to estimate the magnitude of the viscoelastic creep. The effects of aging were analyzed with respect to the same parameters by comparing the group of 23-month-old sedentary rats with a 5-month-old baseline group. The biomechanical parameters did not change significa ntly with physical exercise. Neither did the activation energies chang e, but the asymptotes of the creep curves decreased, showing that ther e was less viscoelastic creep. Aging rendered the tendons significantl y stronger and stiffer, increased the energy-absorbing capacity and de creased the strain values. The activation energies did not change with aging, but the high creep curve asymptote for the flexor tendons decr eased.