Immediate effects of isometric versus isotonic exercise on pain sensitivity and motor performance of ankle plantiflexor muscles

This study aimed to quantify the differences on pain sensitivity and motor performance ankle plantiflexor muscles after performing an isometric versus an isotonic exercise task. A parallel experimental trial was carried out at the European University of the Canary Islands. A total of 47 healthy volunteers were recruited and randomly assigned to a group receiving an isometric exercise (n = 23) and a group receiving an isotonic exercise (n = 24). Pain threshold to pressure was measured at four specific points of the triceps surae neurosensory territory in medial gastrocnemius, lateral gastrocnemius, Tendo Achilles osteotendinous unit and aponeurosis plantar insertion. Furthermore, the two-point discriminatory threshold of the osteotendinous junction of the Achilles tendon and maximum voluntary contraction for plantar flexion were assessed before and after the intervention. There were no statistically significant intergroup differences for any of the variables PPT-MG (U Mann Whitney = 25; [1.265-0.650], p = .527), PPT-LG (U Mann Whitney = 25; [1.325-0.945]; p = .527) y PPT-TA (U Mann Whitney = 25; [-1.465-0.405] p = .527), D2P (U Mann Whitney = 30.5, IC95% [-0.800-1.300], p = .630) and MVC-PF (U Mann Whitney = 26.5, IC95% [-8.400, 2.900], p = .386). Isometric exercise was the only one able to modify the PPT-AP before and after treatment in a statistically significant way. In contrast, isotonic exercise was the training that demonstrated clinically significant changes in 2PD and MVC-PF before and after treatment. No statistically significant changes were identified between both groups in any of the variables studied.