The effects of immobilization on the mechanical properties of the patellar tendon in younger and older men.

BACKGROUND: It remains unknown if inactivity changes the mechanical properties of the human patellar tendon in younger and older healthy persons. The purpose was to examine the effects of short-term unilateral immobilization on the structural and mechanical properties of the patellar tendon in older men and younger men, in vivo. METHODS: Eight older men and eight younger men underwent 14 days of unilateral immobilization. All individuals were assessed on both sides before and after the intervention. MRI was used to assess whole patellar tendon dimensions. The mechanical properties of the patellar tendon were assessed using simultaneous force and ultrasonographic measurements during isometric ramp contractions. FINDINGS: In older men, tendon stiffness [Pre: mean 2949 (SD 799) vs. Post: mean 2366 (SD 774) N mm(-1), P<0.01] and Young's Modulus [Pre: mean 1.2 (SD 0.3) vs. Post: mean 1.0 (SD 0.3) GPa, P<0.05] declined with immobilization on the immobilized side. On the control side, tendon stiffness [Pre: mean 3340 (SD 1209) vs. Post: mean 2230 (SD 503), P<0.01] and Young's Modulus [Pre: mean 1.5 (SD 0.4) vs. Post: mean 0.9 (SD 0.3) GPa, P<0.05] also decreased with immobilization. In younger men, tendon stiffness [Pre: 3622 (SD 1760) vs. Post: mean 2910 (SD 1528) N mm(-1), P<0.01] and Young's Modulus [Pre: mean 1.7 (SD 1.1) vs. Post: mean 1.4 (SD 0.8) GPa, P<0.05] decreased only on the immobilized side. INTERPRETATION: Short-term immobilization led to impaired mechanical properties of the patellar tendon on the immobilized side in both younger men and older men, which can influence the function of the muscle-tendon complex.

Effects of aging on human skeletal muscle after immobilization and retraining.

Inactivity is a recognized compounding factor in sarcopenia and muscle weakness in old age. However, while the negative effects of unloading on skeletal muscle in young individuals are well elucidated, only little is known about the consequence of immobilization and the regenerative capacity in elderly individuals. Thus the aim of this study was to examine the effect of aging on changes in muscle contractile properties, specific force, and muscle mass characteristics in 9 old (61-74 yr) and 11 young men (21-27 yr) after 2 wk of immobilization and 4 wk of retraining. Both young and old experienced decreases in maximal muscle strength, resting twitch peak torque and twitch rate of force development, quadriceps muscle volume, pennation angle, and specific force after 2 wk of immobilization (P < 0.05). The decline in quadriceps volume and pennation angle was smaller in old compared with young (P < 0.05). In contrast, only old men experienced a decrease in quadriceps activation. After retraining, both young and old regained their initial muscle strength, but old had smaller gains in quadriceps volume compared with young, and pennation angle increased in young only (P < 0.05). The present study is the first to demonstrate that aging alters the neuromuscular response to short-term disuse and recovery in humans. Notably, immobilization had a greater impact on neuronal motor function in old individuals, while young individuals were more affected at the muscle level. In addition, old individuals showed an attenuated response to retraining after immobilization compared with young individuals.