Acute exercise can modulate the excitability of the non-exercised upper-limb representation in the primary motor cortex (M1). Accumulating evidence demonstrates acute exercise affects measures of M1 intracortical excitability, with some studies also showing altered corticospinal excitability. However, the influence of distinct M1 interneuron populations on the modulation of intracortical and corticospinal excitability following acute exercise is currently unknown. We assessed the impact of an acute bout of leg cycling exercise on unique M1 interneuron excitability of a non-exercised intrinsic hand muscle using transcranial magnetic stimulation (TMS) in young adults. Specifically, posterior-to-anterior (PA) and anterior-to-posterior (AP) TMS current directions were used to measure the excitability of distinct populations of interneurons before and after an acute bout of exercise or rest. Motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) were measured in the PA and AP current directions in M1 at two time points separated by 25 min of rest, as well as immediately and 30 min after a 25-minute bout of moderate-intensity cycling exercise. Thirty minutes after exercise, MEP amplitudes were significantly larger than other timepoints when measured with AP current, whereas MEP amplitudes derived from PA current did not show this effect. Similarly, SICI was significantly decreased immediately following acute exercise measured with AP but not PA current. Our findings suggest that the excitability of unique M1 interneurons are differentially modulated by acute exercise. These results indicate that M1 interneurons preferentially activated by AP current may play an important role in the exercise-induced modulation of intracortical and corticospinal excitability.

急性运动可以调节初级运动皮层 (M1) 中未运动的上肢表现的兴奋性。越来越多的证据表明，急性运动会影响 M1 皮质内兴奋性的测量，一些研究还显示皮质脊髓兴奋性改变。然而，不同的 M1 中间神经元群对急性运动后皮质内和皮质脊髓兴奋性的调节的影响目前尚不清楚。我们在年轻人中使用经颅磁刺激 (TMS) 评估了急性腿部自行车运动对非运动内在手部肌肉的独特 M1 中间神经元兴奋性的影响。具体来说，后到前 (PA) 和前到后 (AP) TMS 电流方向用于测量急性运动或休息前后不同的中间神经元群的兴奋性。运动诱发电位 (MEP) 和短间隔皮质内抑制 (SICI) 在 M1 的 PA 和 AP 电流方向上测量两个时间点，间隔 25 分钟休息，以及立即和 25 分钟回合后 30 分钟中等强度的自行车运动。运动后 30 分钟，当用 AP 电流测量时，MEP 幅度明显大于其他时间点，而来自 PA 电流的 MEP 幅度没有显示出这种影响。同样，在用 AP 而非 PA 电流测量的急性运动后，SICI 立即显着降低。我们的研究结果表明，独特的 M1 中间神经元的兴奋性受到急性运动的不同调节。这些结果表明，被 AP 电流优先激活的 M1 中间神经元可能在运动诱导的皮质内和皮质脊髓兴奋性调节中发挥重要作用。