GASTROCNEMIUS AND SOLEUS MUSCLE LENGTH AND EMG RESPONSES TO CHANGES IN PEDALING CADENCE

Abstract

1806 Previous research has shown that gastrocnemius (GAST) activation increases systematically with increases in pedaling cadence, whereas soleus (SOL) shows little activation change (Marsh and Martin, MSSE, 1995). The purpose of this study was to examine GAST and SOL length and velocity changes as a function of pedaling cadence to consider mechanisms underlying GAST and SOL activation differences. Nine male and one female cyclists rode at 6 randomly assigned cadences (50, 65, 80, 95, 110 rpm and a preferred cadence) at a 200 W power output while EMG of the GAST and SOL and sagittal plane video was recorded. Joint coordinate data for the knee and ankle were used with equations of Grieve et al. (Biomechanics VI-A, 1978) to compute GAST and SOL lengths and velocity. Consistent with Marsh and Martin, the GAST displayed a significant (p<.05) increase in iEMG with increasing cadence, whereas cadence had no significant effect on iEMG of the SOL. The ankle became significantly (p<.05) more plantar flexed and reflected a reduced range of motion with increasing cadence while the knee became significantly (p<.05) less extended. Contrasting the SOL and GAST length changes showed that from 50 to 110 rpm SOL decreased its ROM (max-min) by 46% whereas GAST decreased its ROM by 8%. In contrast, SOL increased its velocity range (max-min) by 42% and GAST increased by 64%. These data show that with increased cadence GAST operates over a narrower range of operating lengths but at a higher range of shortening velocity than SOL. The higher range of velocity may have resulted in the need for a relatively higher activation, as indicated by the iEMG, as the muscle was working at a different range on its force-velocity curve.