Persistent quadriceps weakness in individuals with anterior cruciate ligament reconstruction (ACLR) has been attributed to arthrogenic muscle inhibition (AMI), which is partially due to the reciprocal inhibition of the quadriceps with the over-excitation of the hamstrings. The objective of this study was to investigate the effectiveness of the hamstrings fatigue immediately prior to quadriceps strength training on reducing AMI. Eight subjects with ACLR (time since injury: 46.5±23.6 months, age: 21.4±1.4 years) and eight healthy subjects (age: 22.5±2.7 years) with no previous history of knee injury participated. All subjects completed a single session of exercise intervention including 10-mins hamstrings vibration before performing three sets of 10 leg extensions (~20-30% 1-RM) with blood flow restriction through an inflated thigh blood pressure cuff. The central activation ratio (CAR) of the quadriceps, the normalized peak torque of knee extension at maximum voluntary isometric contraction (MVIC), and the co-contraction of the hamstrings during knee extension MVICs were measured by force load cell and Electromyography (EMG) before and after the exercise protocol.By using mixed ANOVA, the ACLR group showed significantly less quadriceps CAR (93±6% versus 98±1%, p=0.05) and higher co-contraction of the hamstrings (15±2% versus 7±2% , p=0.01) at the baseline, compared with the control group. The intervention exercise significantly increased quadriceps CAR ( 98±3%, p=0.001) and decreased hamstrings co-contraction (10±1%, p=0.006) in the ACLR group, but not the control group. Normalized peak torques of knee extension (p=0.3) at MVICs did not significantly change for both ACLR and control groups for a single session of exercise intervention.Therefore, vibration-induced hamstrings fatigue can be used to reduce the over-excitation of the hamstrings and disinhibit the quadriceps after ACLR. Future studies may investigate the effectiveness of a training program with multiple sessions of hamstrings fatigue in alleviating arthrogenic muscle inhibition and increasing the knee extension strength.

Date of publication

Spring 4-23-2019

Document Type




Persistent identifier


Committee members

X.Neil Dong,Yong Tai Wang, Benjamin Tseng


Masters in Health Sciences