Different activated calf muscle groups measured simultaneously during plantar flexion exercise with multiple knee angles using multivoxel 31P-MRS.

The distribution of workload between GM and SOL during plantar flexion exercise is strongly linked to the knee angle. This work investigates the differences in muscle activation of GM and SOL during plantar flexion with multiple knee angles. Time series spectra of both muscle groups were acquired simultaneously with high time resolution using dynamic multi-voxel 31P MRS. A linear correlation was found between knee angle and 31P MRS parameters related to muscle activation (PCr depletion, pH, PCr recovery time), confirming predominant involvement of GM with a straight knee, and increasing contributions of SOL with a bent knee.