Meeting Abstract
49.3 Saturday, Jan. 5 Independent Effects of Weight and Mass on Muscle Activity During Walking MCGOWAN, C.P.; University of Texas at Austin cpmcgowan@mail.utexas.edu
Most studies agree that both gastrocnemius (GAS) and soleus (SOL) contribute to weight support during walking in humans. However, there is no current consensus as to the relative contribution of GAS and SOL to forward progression. Experimental studies conclude that GAS provides propulsion, but SOL does not. Conversely, computer simulation studies conclude that both GAS and SOL accelerate the center of mass forward. Here we re-examine the relative contribution of the GAS and SOL to forward propulsion using independent manipulations of weight and mass. Our rationale is that if kinematics remain the same, muscles that provide forward propulsion will increase activity in the last part of stance during added weight and added mass conditions and activity will be similar to the control during weight support trials. Ten subjects walked on a dual-belt force-treadmill with combinations of added mass and/or weight support, while muscle activity was measured using surface EMG. In addition to a control trial, subjects walked with added trunk loads equal to 25 and 50% of body weight (BW), and with 25 and 50% weight support. Subjects also walked with simultaneous added load and weight support equal to 25 and 50% BW, effectively increasing mass without changing weight. Our results were consistent with the predictions made by computer modeling and simulations studies, and do not support previous experimental work. Added weight produced significant increases in muscle activity in both GAS and SOL, whereas added mass alone only produced significant increases in SOL. Further, during weight support trails, muscle activity decreased in GAS but not in SOL. Therefore, we conclude that the SOL plays a primary role in providing forward propulsion, whereas the GAS appears to play a less significant role. Determining the functional role of individual muscle during locomotion can provide valuable insight into musculoskeletal design.
