Force-length-velocity behavior and muscle-specific joint moment contributions during countermovement and squat jumps.

The countermovement (CMJ) and squat (SJ) jump are common tasks used to assess neuromuscular performance. While much is known about joint-level differences between both tasks, not much is known about differences in muscle-level biomechanics. The purpose of this study was to calculate the forces, force-length-velocity behavior, and muscle-specific contributions to net joint moments (NJM) during CMJ and SJ. Eight basketball players performed maximal CMJ and SJ while motion capture and ground reaction force (GRF) data were recorded. A musculoskeletal model and static optimization algorithm computed muscles forces and force generating abilities of the soleus (SOL), gastrocnemii (GAS), vastii (VAS), rectus femoris (RF), hamstring (HAM), and gluteus maximus (GMAX) muscles during CMJ and SJ. In addition, the moments created by each muscle were calculated and studied in relation to the respective NJMs. CMJ were characterized by longer movement duration, but similar GRFs and jump heights as SJ. VAS and GMAX exhibited greater muscle forces and force generating abilities during CMJ, likely because of more optimal force-velocity behavior. In contrast, the HAM exhibited more favorable force-length behavior during SJ. Muscle moments during CMJ and SJ were similar, except for the HAM, which produced greater hip extension and knee flexion muscle moments during CMJ. Although muscle forces and force generating abilities of the VAS and GMAX were greater during CMJ, more optimal force-length behavior and greater muscle moment contribution to knee NJM by the HAM during SJ appear to balance such that overall GRF and jump height remain similar regardless of jump task.