Fatigue rate, central activation ratio, and EMG analysis in volunteers with quadriceps muscle inhibition following isokinetic quadriceps fatigue

Context. People with quadriceps muscle inhibition may be more susceptible to the effects of muscular fatigue due to a lower ability to activate their quadriceps muscle. If the quadriceps is less activated to begin with and the muscle becomes fatigued, the person may have a decreased ability to attenuate forces placed on their joints. Objective. To compare the ability of volunteers with quadriceps muscle inhibition following isokinetic quadriceps and hamstrings fatigue to attenuate forces in the thigh during a 60cm drop landing. Design. 2 x 2 factorial design. Setting. Exercise and Sport Injury Laboratory at the University of Virginia. Patients or other participants. Healthy, active volunteers with no history of lower extremity injury and a central activation ratio (CAR) of 0.94 or above served as controls. Recreationally active volunteers (exercise 3-5 times per week) with a history of knee pain/injury that had a CAR of 0.90 or less were placed in the muscle inhibition group. Interventions. Isokinetic quadriceps and hamstrings fatigue protocol until quadriceps force was reduced by 50%. Main outcome measures. Vertical force attenuation measured via an accelerometer at the tibial tuberosity minus the acceleration measured at the sacrum (expressed as a percent change in peak acceleration). Results. No differences were found in the ability to attenuate forces in subjects with and without quadriceps muscle inhibition (F1,22=0.019, P=0.892, eta 2=0.001, 1-beta=0.052). Conclusions. Recreationally active volunteers with mild muscle inhibition (mean CAR = 79.38) do not attenuate forces differently during a drop jump when compared to highly activated controls (mean CAR = 96.57).