Low-level intermittent quadriceps activity during transcranial direct current stimulation facilitates knee extensor force-generating capacity

•We tested the interference between motor practice and anodal tDCS on MVIC torque.•Knee extensor torque improved significantly when tDCS was paired with a motor task.•The increase in knee extensor MVIC torque was gradual and intensified with time.•This effect was isolated to the muscle group that was trained during tDCS.•These results offer new possibilities for tDCS-supplemented resistance training.

Anodal transcranial direct current stimulation (tDCS) is known to increase the force-generating capacity of the skeletal muscles. However, when tDCS is concurrently combined with a motor task, interference may occur that hinders tDCS effects. Here, we tested the interaction and time course of tDCS effects on force production when paired with a low-level force-matching task. Twenty-two subjects were randomized into two groups: tDCS-Matching and tDCS-Resting. Each group received tDCS and a sham stimulation, separated by one week. Maximal knee extensor and flexor torques were measured before and up to twenty-five minutes following the stimulation. The tDCS-Matching group produced greater knee extension torques relative to sham when compared with the tDCS-Resting group. There was no significant effect for knee flexion. This suggests that interference does not occur for force production tasks when tDCS is combined with a motor task. Rather, the task appears to aid and isolate the effects to the muscle groups involved in the task.