LEWIS, M.G.C. ... et al., 2012. Are joint torque models limited by an assumption of monoarticularity? Journal of Applied Biomechanics, 28 (5), pp. 520 - 529.
This study determines whether maximal voluntary ankle plantar flexor torque could be more accurately
represented using a torque generator that is a function of both knee and ankle kinematics. Isovelocity and
isometric ankle plantar flexor torques were measured on a single participant for knee joint angles of 111°
to 169° (approximately full extension) using a Contrex MJ dynamometer. Maximal voluntary torque was
represented by a 19-parameter two-joint function of ankle and knee joint angles and angular velocities with
the parameters determined by minimizing a weighted root mean square difference between measured torques
and the two-joint function. The weighted root mean square difference between the two-joint function and
the measured torques was 10 N-m or 3% of maximum torque. The two-joint function was a more accurate
representation of maximal voluntary ankle plantar flexor torques than an existing single-joint function where
differences of 19% of maximum torque were found. It is concluded that when the knee is flexed by more than
40°, a two-joint representation is necessary.