Runners with mid-portion Achilles tendinopathy (AT) were recruited. Triceps surae endurance was measured as single leg heel raise (SLHR) to failure test. Short-interval intracortical inhibition (SICI) was assessed using paired-pulse transcranial magnetic stimulation.
Abstract Objective To investigate intracortical inhibitory mechanisms and muscle function in the Triceps surae of runners with mid-portion Achilles tendinopathy (AT). Design Cross-sectional study Methods Runners with (n=11) and without (n=13) AT were recruited. Plantar flexor isometric peak torque and rate of torque development (RTD) were measured using an isokinetic dynamometer. Triceps surae endurance was measured as single leg heel raise (SLHR) to failure test. Short-interval intracortical inhibition (SICI) was assessed using paired-pulse transcranial magnetic stimulation during a sustained contraction at 10% of plantar flexor isometric peak torque. Results AT presented 13.41% (95%CI:0.76 to 26.0) higher Triceps surae SICI, 68% inhibition (95%CI:58.5 to 76.4) compared to 55% inhibition in the control group (95%CI:45.1 to 63.0). AT performed 28%, -12.6 (95%CI:-19.4 to -5.7, p=0.001) fewer SLHR repetitions on the most symptomatic side, 27.5 (95%CI:20.7 to 34.3), compared to controls, 38.5 (95% CI:33.2 to 43.8) and 24%, -10.9 (95%CI:-18.4 to -3.3, p=0.008), fewer SLHR repetitions on the non-symptomatic, 29.0 (95%CI:19.4 to 38.6) compared to controls, 38.5 (95%CI:33.2 to 43.8). We found no between-groups differences in isometric peak torque or RTD. Conclusion Our data suggest greater intracortical inhibition for the Triceps surae muscles for the AT group ac-companied by reduced SLHR endurance, without deficits in isometric peak torque or RTD. The increased SICI observed in the AT group could be negatively influencing Triceps surae endurance; thus, rehabilitation aiming to reduce intracortical inhibition should be considered to improve patient outcomes. Furthermore, SLHR is a useful clinical tool to assess plantar flexor function in AT patients. Keywords: Achilles tendinopathy; SICI; sports physiotherapy; triceps surae endurance; single leg heel raise, runners