Corticospinal Excitability Is Lower During Eccentric Than Concentric Cycling in Men

Abstract

How corticospinal excitability changes during eccentric locomotor exercise is unknown. In the present study, 13 volunteers performed 30-min strenuous concentric and eccentric cycling bouts at the same power output (60% concentric peak power output). Transcranial magnetic and electrical femoral nerve stimulations were applied at exercise onset (3rd min) and end (25th min). Motor-evoked potentials (MEPs) amplitude was measured for the rectus femoris (RF) and vastus lateralis (VL) muscles with surface electromyography (EMG) and expressed as a percentage of maximal M-wave amplitude (M_MAX). EMG amplitude 100 ms prior to MEPs and the silent period duration were calculated. There was no change in any neural parameter during the exercises (all P > 0.24). VL and RF M_MAX were unaffected by exercise modality (all P > 0.38). VL MEP amplitude was greater (26 ± 11.4 vs. 15.2 ± 7.7% M_MAX; P = 0.008) during concentric than eccentric cycling whereas RF MEP amplitude was not different (24.4 ± 10.8 vs. 17.2 ± 9.8% M_MAX; P = 0.051). While VL EMG was higher during concentric than eccentric cycling (P = 0.03), RF EMG showed no significant difference (P = 0.07). Similar silent period durations were found (RF: 120 ± 30 ms; VL: 114 ± 27 ms; all P > 0.61), but the silent period/MEP ratio was higher during eccentric than concentric cycling for both muscles (all P < 0.02). In conclusion, corticospinal excitability to the knee extensors is lower and relative silent period longer during eccentric than concentric cycling, yet both remained unaltered with time.

Keywords: M-wave; knee extensor muscles; motor-evoked potential; silent period; transcranial magnetic stimulation.

FIGURE 1

Overview of the experimental protocol. In (A), a first session served to determine peak power output (PPO, W) during a concentric (CON) incremental cycling test before familiarizing participants with eccentric cycling (ECC). During the experimental sessions (2 and 3), maximal muscle action potential (M_MAX) and motor-evoked potential (MEP) were obtained using electrical stimulation of the femoral nerve and transcranial magnetic stimulation (TMS), respectively. Baseline measurements lasted about 10 min. M_MAX (plain arrows) and MEP (dashed arrows), were also measured at the 3rd and 25th min of the strenuous exercises. Heart rate and effort perception were assessed at the same time points. rpm: rotations per minute. The experimental set-up is illustrated in (B), with electromyographic electrodes on the vastus lateralis muscle (as well as the rectus femoris and vastus medialis, not represented in the figure) and reflective markers positioned directly on the skin on anatomical points chosen to calculate knee flexion angle. PNS: Peripheral nervous stimulation.

FIGURE 2

Knee flexion angle and neural drive across a pedaling cycle. (A,B) Illustrate knee flexion angle during concentric (CON) and eccentric (ECC) cycling, respectively. (C) (CON) and (D) (ECC) show vastus lateralis muscle EMG RMS and (E) (CON) and (F) (ECC) represent rectus femoris muscle EMG RMS. All data were obtained at the onset of the strenuous exercises, normalized to the amplitude of the maximal muscle compound (M_MAX) and are represented as mean ± standard error. Downward arrows indicate the moment of peripheral and transcranial stimulations.

FIGURE 3

Raw traces of the response to femoral nerve and transcranial stimulations for the vastus lateralis muscle. The figure shows motor-evoked potential (MEP) and maximal M-waves (M_MAX) during concentric (CON) and eccentric (ECC) cycling of a representative participant.

FIGURE 4

Corticospinal excitability and relative silent period. For each session (concentric—CON—or eccentric—ECC—cycling), this figure illustrates the average (mean of data from the onset and end of exercise) background EMG (A,B), motor-evoked potential (MEP) amplitude (C,D) and the average ratio between silent period duration and MEP amplitude (SP/MEP) (E,F) for the vastus lateralis and rectus femoris muscles. *Indicates a difference between CON and ECC; one sign means P < 0.05; ** means P < 0.01.