Drop jump performance differences between ACL-injured and healthy semi-professional male soccer players

The purpose of this study was to examine differences in lower-body neuromuscular performance characteristics between ACL-injured athletes and their healthy counterparts, including peak take-off and landing force asymmetries. Forty-four semi-professional male soccer players volunteered to participate in the present investigation, from which 16 had previously undergone ACL reconstruction procedures and 28 were healthy controls. Following the warm-up completion, athletes performed three non-consecutive drop jumps (30 cm) with no arm swing while landing on a uni-axial force plate system sampling at 1,000 Hz. The injured athletes were screened nine months post-operative procedures and all athletes were active members of their respective soccer teams. The dependent variables included the force-time metrics within both the eccentric and concentric phases of the drop jump. Independent t-tests or Mann-Whitney U-tests were used to examine statistically significant (p < 0.05) differences in each variable (ACL-injured vs. healthy controls). The results revealed that ACL-injured athletes tend to display significantly lower jump heights (39.4%), shorter eccentric duration (21.1%), and greater peak drive-off force asymmetries (50.6%) when compared to their non-injured counterparts. Also, despite not reaching the level of statistical significance and being small-to-moderate in magnitude, ACL-injured participants attained shorter contact times (8.8%) and greater peak impact force asymmetry (16.1%).