The effect of anterior cruciate ligament reconstruction on hamstring and quadriceps muscle function outcome ratios in male athletes

Abstract

Introduction Maximal strength ratios such as the limb symmetry index (LSI) and hamstring-to-quadriceps ratio (HQ) may be considered the main outcome measures in the monitoring of recovery after anterior cruciate ligament (ACL) reconstruction. Although explosive strength is much more important than maximal strength, it is generally disregarded in the follow-up of muscle function recovery.

Objective The purpose of this study was to compare ratios between maximal (Fmax) and explosive strength (rate of force development – RFD) in individuals with ACL reconstruction.

Methods Fifteen male athletes were enrolled and had maximum voluntary isometric quadriceps and hamstring contractions tested (4.0 ± 0.1 months post reconstruction). In addition to Fmax, RFD was estimated (RFDmax, as well as RFD at 50, 100, and 200 ms from onset of contraction) and LSI and HQ ratios were calculated.

Results The involved leg demonstrated significant hamstring and quadriceps deficits compared to uninvolved leg (p < 0.01). Deficits were particularly significant in the involved quadriceps, causing higher HQ ratios (average 0.63), compared to the uninvolved leg (0.44). LSI was significantly lower for RFD variables (average 55%) than for Fmax (66%).

Conclusion The assessment of RFD may be considered an objective recovery parameter for one’s readiness to return to sports and should be an integral part of standard follow-up protocol for athletes after ACL reconstruction. Moreover, the combination of indices derived from maximal and explosive strength may provide better insight in muscle strength balance, as well as a clear picture of functional implications.

Keywords: anterior cruciate ligament (ACL); knee extensors; knee flexors; isometric