Response of the human triceps surae muscle to electrical stimulation during varying levels of blood flow restriction

The changes in muscle force associated with varying degrees of lower-limb ischaemia were investigated. Isometric torque production by the triceps surae muscle was measured during a 5-min continuous train of 2-Hz electrical stimulation in six healthy young adults under different thigh cuff occlusion pressures. The reproducibility of this protocol when performed under complete ischaemia (tested five times over a 2-week period) was assessed as having a coefficient of variation (CV) for fatigue (end/initial force) of [mean (SEM) 12 (1)%; n = 5]. This compares favourably with that obtained for maximum voluntary contraction torque [CV 9 (1)%]. In six subjects, triceps surae muscle fatigue was assessed under thigh cuff pressures of 0, 6.7 kPa (50 mmHg, venous occlusion) and 28 kPa (210 mmHg, complete ischaemia), as well as two intermediate levels of occlusion that were established by cuff pressures of 13.4 (0.5) and 20.3 (1.1) kPa [103 (4) and 152 (8) mmHg, respectively]. These corresponded to ankle-brachial pressure indices of 1.3 and 0.8, respectively when subjects were seated, or 0.8 and 0.36 when supine. With undisturbed lower-leg circulation, force potentiated steadily over the 5 min of stimulation such that the final force was 135 (8)% of the initial value. With complete ischaemia, force fell to 47 (2)% of the initial value. Stimulation under thigh occlusion pressures of 6.7, 13.4 and 20.3 kPa elicited intermediate levels of reduction in force, graded according to the increasing restriction of perfusion. The results show that low-force twitch contractions, which themselves do not occlude blood flow, are extremely sensitive to impaired perfusion and may represent a viable alternative to established methods of muscle performance assessment in patients with blood flow insufficiency.