Single twitch electrical stimulation technique has been used at submaximal and voluntary maximal muscle activation to evaluate lack of maximal activation of motor units. Patients with patellofemoral pain syndrome had a significantly lower knee extensor strength in the most symptomatic knee compared to controls and to the least symptomatic knee. The largest differences were found in eccentric activities and in range close to full extension.
Inhibition seems to be selective to knee angles and vastus medialis.
Comparing maximal knee torque in sitting and standing, the maximal voluntary isometric torque was lower in standing than in sitting, but with significant correlations between these measurements and no differences in that respect between patients and controls. The superimposed single twitch technique has also been used in other patient groups, as patients with fibromyalgia, rheumatoid arthritis, growth hormone deficiency and polio. In patients with primary fibromyalgia marked lack of voluntary maximal muscle activation was recorded at dynamometer measurements, but considerably better activation at diverted activities, such as stair climbing. The models for studying the stretch shortening cycle have been useful to evaluate the potentiating effect of the preceding muscle activation on the following concentric activation. There may be gender differences in that effect with larger effects in women, indicating better utilisation of elastic forces.