10 Longitudinal changes in muscle strength and rate of force development using HHD in the early phases of ACL rehabilitation

Introduction Understanding muscle strength and Rate of Force Development (RFD) changes after a cruciate ligament reconstruction rehabilitation is crucial for return to sport. The Limb Symmetry Index (LSI) offers a standardized measure to compare the injured limb’s function to the uninjured side. While force and RFD are commonly measured using an expensive isokinetic device, new research shows that a hand-held dynamometer (HHD) can be used to measure them reliably. Only a few studies have used HHD and described longitudinal changes of the force and RFD during early rehabilitation. Materials and Methods Using an HHD, 25 participants were assessed pre-surgery, two- and four-months post-surgery. We focused on peak force, early-phase RFD (100ms), and late-phase RFD (200ms). Effect sizes (ES) are reported to compare the injured and contralateral legs. Results Pre-surgery, the injured quadriceps peak force was 383±138 newtons with an LSI of 0.81±0.26%. Two months post-surgery, the participants’ force dwindled to 257±105 (ES -1.50; LSI 0.55±0.25). By the fourth month, it rebounded to 322±145 (ES -1.01; LSI 0.67±0.26). The hamstring’s peak force at pre-surgery was 225± 78.9. At two months post-surgery, the peak force was 162±75.2 (ES -1.52; LSI 0.59±0.29), which improved to 225±103 at four months (ES -1.02; LSI 0.72±0.27). The RFD metrics followed a similar trajectory.Conclusion Post-surgery, the injured limb’s muscle strength, and RFD decline, with some recovery by the fourth month, but as expected - still lower than the contralateral limb. Using an HHD can be valuable for clinicians as it offers insights outside the lab.