Kinematic analysis of the lower limbs and trunk of nonexercisers during forward lunges

Objective In this study, the lower limb and trunk kinematics of exercisers and nonexercisers during forward lunges were compared to determine the movement characteristics of nonexercisers. Methods Three-dimensional kinematic data were collected from 11 nonexercisers and 13 exercisers using a motion capture system (240 Hz) with 17 inertial measurement units. Joint angles at the hip, knee, and ankle joints as well as trunk inclination angles were calculated. Differences throughout the lunge cycle were compared using statistical parametric mapping. Results Compared with exercisers, nonexercisers had significantly shorter step length (p = 0.033) and lower peak center of mass velocity (forward: p = 0.005, backward: p = 0.016). Additionally, hip extension in the supporting leg was significantly smaller in nonexercisers than in exercisers (p < 0.001), accompanied by significantly smaller peak flexion angles in the leading leg’s hip (p = 0.022), knee (p = 0.036), and ankle (p = 0.001) joints. The trunk of nonexercisers exhibited significantly greater posterior tilt during the initiation phase (0%–16.3%, p = 0.040) and completion phase (92.5%–100%, p = 0.048) of the movement compared with that of exercisers. Conclusion The lunge movement in nonexercisers was characterized by restricted hip extension in the supporting leg, which may be associated with reduced forward progression and smaller flexion angles in the leading leg. Furthermore, the posterior trunk tilt observed during the initiation and completion phases may reflect compensatory movement patterns related to trunk control and balance demands, which may warrant attention in relation to potential injury-related concerns. For individuals without exercise habits, these findings suggest that upright trunk control during single-leg stance may be considered as one possible focus in early-stage exercise instruction.