Knee Joint Contact Force and Muscle Contributions in Back vs. Front Squats Across Different Loads

Kong, T, Kipp, K, and Kim, H. Knee joint contact force and muscle contributions in back vs. front squats across different loads. J Strength Cond Res XX(X): 000–000, 2026—Net joint moments (NJMs) are used to guide exercise prescription but are not enough to represent mechanical stress in a joint. This study aimed to compare joint contact forces (JCFs) and muscle contributions to JCFs between back and front squats performed at 3 loads. Ten female lacrosse athletes performed back and front squats at 40, 60, and 80% of front-squat 1 repetition maximum. Musculoskeletal simulations driven by motion capture and force plate data estimated muscle forces, muscle activations, JCFs, and muscle contributions to JCFs. Two-way repeated-measures analysis of variances (squat type × load) were used for analysis. A main effect of squat type was found for peak knee vertical JCF (vJCF) ( F [1,9] = 47.08, p < 0.001, = 0.83), with the back squat eliciting approximately 11.6% greater JCF than the front squat. The vasti were the primary contributors to knee vJCF in both exercises (>93% of vJCF). At peak vJCF, knee angles and NJMs did not differ between squat types. Vasti force was greater in the back squat ( p < 0.001, = 0.76). Knee vJCF was greater during back squats than front squats across load conditions. These greater knee joint loads were not explained by knee angle or NJMs at peak vJCF but simulations indicated that they were primarily attributable to greater vasti muscle forces. These findings suggest that the front squat may be considered when lower knee compressive loading is desired at a matched external load. However, the clinical relevance of the observed difference remains to be established.