CRANK INERTIAL LOAD HAS LITTLE EFFECT ON STEADY-STATE PEDALING COORDINATION

Inertial load can affect the control of a dynamic system whenever part s of the system are accelerated or decelerated. During steady-state pe daling, because within-cycle variations in crank angular acceleration still exist, the amount of crank inertia present (which varies widely with road-riding gear ratio) may affect the within-cycle coordination of muscles. However, the effect of inertial load on steady-state pedal ing coordination is almost always assumed to be negligible, since the net mechanical energy per cycle developed by muscles only depends on t he constant cadence and workload. This study tests the hypothesis that under steady-state conditions, the net joint torques produced by musc les at the hip, knee, and ankle are unaffected by crank inertial load. To perform the investigation, we constructed a pedaling apparatus whi ch could emulate the low inertial load of a standard ergometer or the high inertial load of a road bicycle in high gear. Crank angle and bil ateral pedal force and angle data were collected from ten subjects ins tructed to pedal steadily (i.e. constant speed across cycles) and smoo thly (i.e. constant speed within a cycle) against both inertias at a c onstant workload. Virtually no statistically significant changes were found in the net hip and knee muscle joint torques calculated from an inverse dynamics analysis. Though the net ankle muscle joint torque, a s well as the one- and two-legged crank torque, showed statistically s ignificant increases at the higher inertia, the changes were small. In contrast, large statistically significant reductions were found in cr ank kinematic variability both within a cycle and between cycles (i.e. cadence), primarily because a larger inertial load means a slower cra nk dynamic response. Nonetheless, the reduction in cadence variability was somewhat attenuated by a large statistically significant increase in one-legged crank torque variability. We suggest, therefore, that m uscle coordination during steady-state pedaling is largely unaffected, though less well regulated, when crank inertial load is increased.