Kinetics and Kinematics of the Free-Weight Back Squat and Loaded Jump Squat.

Thompson, SW, Lake, JP, Rogerson, D, Ruddock, A, and Barnes, A. Kinetics and kinematics of the free-weight back squat and loaded jump squat. J Strength Cond Res XX(X): 000-000, 2021-The aim of this study was to compare kinetics and kinematics of 2 lower-body free-weight exercises, calculated from concentric and propulsion subphases, across multiple loads. Sixteen strength-trained men performed back squat 1 repetition maximum (1RM) tests (visit 1), followed by 2 incremental back squat and jump squat protocols (visit 2) (loads = 0% and 30-60%, back squat 1RM). Concentric phase and propulsion phase force-time-displacement characteristics were derived from force plate data and compared using analysis of variance and Hedges' g effect sizes. Intrasession reliability was calculated using intraclass correlation coefficient (ICC) and coefficient of variation (CV). All dependent variables met acceptable reliability (ICC >0.7; CV < 10%). Statistically significant 3-way interactions (load x phase x exercise) and 2-way main effects (phase x exercise) were observed for mean force, velocity (30-60% 1RM), power, work, displacement, and duration (0%, 30-50% 1RM) (p < 0.05). A significant 2-way interaction (load x exercise) was observed for impulse (p < 0.001). Jump squat velocity (g = 0.94-3.80), impulse (g = 1.98-3.21), power (g = 0.84-2.93), and work (g = 1.09-3.56) were significantly larger across concentric and propulsion phases, as well as mean propulsion force (g = 0.30-1.06) performed over all loads (p < 0.001). No statistically significant differences were observed for mean concentric force. Statistically longer durations (g = 0.38-1.54) and larger displacements (g = 2.03-4.40) were evident for all loads and both subphases (p < 0.05). Ballistic, lower-body exercise produces greater kinetic and kinematic outputs than nonballistic equivalents, irrespective of phase determination. Practitioners should therefore use ballistic methods when prescribing or testing lower-body exercises to maximize athlete's force-time-displacement characteristics.