Age-specific neuromuscular interaction during elderly habitual running

It has been reported that advancing age causes tendons to become more compliant and fascicles length shorter. This could then lead to enhancement of movement efficiency provided that the elderly adults can activate their muscles in the same way as the younger adults (YOUNG) during dynamic movements. This study was designed to examine the age-specific behaviour of the medial gastrocnemius (MG) fascicles and tendinous tissues together with lower-leg muscle activities when the well-trained elderly runners ran on the treadmill at preferred speeds.

The well-trained 11 elderly subjects (ELD) who have running experiences and 11 YOUNG were recruited as subjects. While ELD were running on the treadmill at their preferred speed, the lengths of the MG fascicles and tendinous tissues (Lfa and LTT respectively) were measured by ultrasonography together with kinematics and lower-leg muscle activities.

Although the behaviour of the MG muscle-tendon unit did not show any significant differences between both groups during the contact, our results showed significant differences in fascicle-tendinous tissue behaviour as well as muscle activities. The LTT during the entire contact phase was greater in ELD than in YOUNG (P < 0.001). Co-activation of lower-leg muscles from pre-activation to braking phases was higher in ELD than in YOUNG (P < 0.01). The changes of the Lfa during contact were less, and the LTT shortening was greater in ELD than in YOUNG (P < 0.001).

These results imply that ELD cannot activate their muscles similar to YOUNG during running, and those different activities may modify the Lfa to utilize the tendon elasticity effectively.