Publication:

Squat mechanics as predictors of countermovement jump performance in healthy young adults: a cross-sectional study

Background Squat depth and dynamic knee valgus (DKV) are widely discussed determinants of lower-limb performance and injury risk, yet their independent contribution to jump performance has rarely been examined together, particularly using accessible, application-based tools. This study examined whether squat depth and DKV predict countermovement jump (CMJ) performance in healthy young adults.

Methods In this cross-sectional study, 139 healthy young adults (71 men, 68 women; 18-25 years) underwent smartphone/tablet-based biomechanical assessment. Squat depth was quantified as trochanteric displacement normalised to femur length during a self-selected bodyweight squat; DKV was measured from frontal-plane video as peak medial knee displacement; CMJ, squat jump and horizontal jump performance were assessed using a validated flight-time application. Associations were examined using Spearman correlation, multiple linear regression (adjusted for age, sex and body mass index [BMI]), and squat-depth quartile comparison.

Results Squat depth correlated strongly with CMJ height (r=0.72), squat jump height (r=0.76) and horizontal jump length (r=0.61, all p<0.001), and remained an independent predictor of CMJ height after adjustment (β=6.79 cm per unit depth, p<0.001; model R²=0.879). DKV was not associated with squat depth (r=-0.12, p=0.152) and showed only a borderline association with CMJ height (β=-0.383, p=0.051). A squat-depth×sex interaction on DKV approached but did not reach significance (β=1.44, p=0.078).

Conclusions Squat depth, not DKV, was a strong, independent predictor of CMJ performance. Squat depth showed no meaningful relationship with knee valgus, suggesting the two are largely independent expressions of lower-limb function in healthy young adults.