Landing from a jump is a commonly practiced athletic activity that frequently results in lower extremity injury. The biomechanics of landing have recently received increased attention in the literature; however, the differences between bilateral and unilateral landings have not been investigated. Athletes might have to land on one or both legs due to technique, the demands of the game or as a result of an external perturbation.
To investigate the effect of gender and jump type (bilateral vs. unilateral) on the biomechanics of landing from a jump.
Kinetic, kinematic and EMG data were collected for 32 recreational athletes (16 males) while performing three bilateral and three unilateral landings from a 40 cm platform. Knee flexion angle (maximum and at contact) and peak angle values for hip adduction, knee valgus, knee internal rotation, and foot orientation; peak vertical ground reaction force (VGRF); and peak EMG activity of the rectus, medial hamstrings, lateral hamstrings, and gastrocnemius muscles were recorded. A MANOVA test was performed with gender being the between subject factor and type of jump being the within subject factor.
Gender (p=0.001) and type of landing (p=0.000) had a significant effect on the dependent variables of the MANOVA test and no significant (p=0.599) interaction effect. Females landed with higher peak knee valgus angle [12.2° (7.5) vs. 6.15° (5.8), p=0.006] and VGRF [5.6 BW (0.92) vs. 3.9 BW (1.25), p=0.000] in both types of landing. Subjects landed in the unilateral jumps with the knee more extended at contact [15.1° (7.7) vs. 20.8° (8.0), p=0.000], less maximum knee flexion [72.2° (13.8) vs. 93.3° (12.2), p=0.000], decreased knee valgus angle [7.7° (6.2) vs. 10.62° (8.3), p=0.02], increased knee internal rotation [53.1°(13.7) vs. 49.6° (13.8), p=0.002], increased VGRF [4.99 BW (1.4) vs. 4.55 BW (1.4), p=0.013] and increased muscle activity for all four muscle groups (p<0.002).
A common compensatory strategy for unilateral landings involves landing with less knee extension and therefore achieve less maximum knee flexion. This strategy keeps the quadriceps closer to its resting length and prevents collapse. Subjects managed to maintain knee valgus angle in unilateral landings within a safer range when compared to bilateral landings but showed increased peak knee internal rotation that could potentially result to knee injury. As expected, when subjects landed on one leg they exhibited increased muscle activity. Neuromuscular injury prevention training programs should incorporate bilateral and unilateral landings.