A COMPARISON OF MUSCULAR MECHANICAL ENERGY-EXPENDITURE AND INTERNAL WORK IN CYCLING

The hypothesis that the sum of the absolute changes in mechanical ener gy (internal work) is correlated with the muscular mechanical energy e xpenditure (MMEE) was tested using two elliptical chainrings, one that reduced and one that increased the internal work (compared to circula r). Upper and lower bounds were put on the extra MMEE (work done by ne t joint torques in excess of the external work) with respect to the ef fect of intercompensation between joint torques due to biarticular mus cles. This was done by having two measures of MMEE, one that allowed n o intercompensation and one that allowed complete intercompensation be tween joints spanned by biarticular muscles. Energy analysis showed no correlation between internal work and the two measures of MMEE. When compared to circular, the chainring that reduced internal work increas ed MMEE, and phases of increased crank velocity associated with the el liptical shape resulted in increased power absorbed by the upstroke le g as it was accelerated against gravity. The resulting negative work n ecessitated additional positive work. Thus, the hypothesis that the in ternal work is correlated with MMEE was found to be invalid, and the t otal mechanical work done cannot be estimated by summing the internal and external work. Changes in the dynamics of cycling caused by a non- circular chainring may affect performance and must be considered durin g the non-circular chainring design process.