The objectives were, (i) to determine whether differences exist in relative activation amplitudes for participants with asymptomatic knees and participants with moderate medial compartment knee osteoarthritis during a series of maximal effort contractions and (ii) to determine whether maximum activations occurred on similar exercises for both groups.
Sixty-eight participants with asymptomatic knees and 68 participants with moderate medial compartment knee osteoarthritis completed eight standardized 3-s maximal voluntary isometric exercises. Maximal electromyographic amplitudes were identified for a 100 ms window from three quadriceps, two gastrocnemius and two hamstring muscle sites for each exercise. For each exercise, amplitudes were normalized to percent of the absolute maximum activation (%MVIC). Frequency counts for exercises eliciting absolute maximum amplitudes were recorded. Analysis of variance models determined exercise and group main effects and interactions in relative amplitudes (%MVIC) for each muscle.
The exercises produced similar relative activation amplitudes between groups. The highest relative amplitude occurred for gastrocnemius during standing plantarflexion (86-93%MVIC), for the vasti during knee extension (45°) and (15°) (81-86%MVIC), for rectus femoris during knee extension (15°) (89%MVIC) and for hamstring muscles during knee flexion (15°) and prone knee flexion (55°) (81-94%MVIC). No single exercise elicited absolute maximum activation for every participant for each muscle, supporting the value of using an exercise series for normalization purposes.