Typical rehabilitation strategies and performance tests after knee surgery are often based on peak lower extremity strength. However, people rarely generate maximal knee force in both daily and sports activities, which are characterized by brief periods of rapid muscle activation and relaxation. Thus, the ability to rapidly develop or modulate force may be more meaningful and more relevant to function. It is unclear how knee surgery influences the neuromuscular mechanisms controlling the ability to rapidly develop leg muscle force and produce power, or the functional relevance of these characterizations of muscle performance in relation to injury, surgery, and recovery.
The primary purpose of this collection of studies was to assess rapid quadriceps muscle activation and lower extremity force production in people undergoing arthroscopic knee surgery for meniscal debridement and anterior cruciate ligament (ACL) reconstruction.
People undergoing arthroscopic partial meniscectomy (APM) presented with significant deficits in knee extensor rate of torque development (RTD), leg press power, and rapid quadriceps muscle activation both prior to and in the initial month following surgery. Subjective knee function was significantly correlated with RTD variables but not with peak strength or quadriceps volume. Limitations in the ability to rapidly activate the involved quadriceps suggests that impaired centrally mediated neural function of the involved quadriceps may limit RTD and lower extremity power post-surgery.
Next, the speed and intensity of quadriceps exercise performed in the early post-surgical period of patients post-APM and the relationships between training parameters, strength, quadriceps RTD, and subjective knee function were investigated. Subjects performed high intensity quadriceps contractions 2-3x/week in the first month following surgery. All subjects increased quadriceps strength, but people who trained with greater RTD following APM demonstrated greater improvements in RTD and had better patient-based outcomes scores than those who trained with a slower rate of torque rise.
Finally, power and rate of force development (RFD) in people ≤ 1 year following ACL reconstruction were evaluated along with movement biomechanics, typical clinical measures of readiness to return to activity, and patient-based outcomes. Significant side-to-side asymmetries in quadriceps strength, RFD, leg press strength and power, and knee joint kinetics were noted. Deficits in voluntary quadriceps strength paralleled the deficits in early phase RFD, indicating that in this population RFD was limited by the intrinsic properties and force production capacity of the quadriceps, not the ability to rapidly activate the muscle. However, strong to very strong correlations were found between quadriceps RFD, movement biomechanics and subjective knee function, which were predominantly stronger than the correlations with peak quadriceps strength. Leg press strength, power, and acceleration were very strongly correlated with movement biomechanics and subjective knee function.
In summary, this series of studies provides important insight into the neuromuscular mechanisms related to rapid lower extremity force development and muscle activation in the context of knee joint injury and recovery after arthroscopic knee surgery. Collectively, this work suggests that the inability to quickly develop or modulate quadriceps force may have significant functional consequences, and that rehabilitation efforts following arthroscopic knee surgery to incorporate both specific dosage of and earlier performance of rapid leg muscle contractions should be explored.