Maximal voluntary isometric contraction exercises: a methodological investigation in moderate knee osteoarthritis

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.