Methods

During separate visits, 17 endurance-trained male participants performed 3 h of cycling and running at 105% of the gas exchange threshold. Neuromuscular assessments were taken are preexercise, midexercise, and postexercise, including knee extensor maximal voluntary contractions (MVC), voluntary activation (VA), high-and low-frequency doublets (Db100 and Db10, respectively), potentiated twitches (Qtw, pot), motor evoked potentials (MEP), and thoracic motor evoked potentials (TMEP).

Results

After exercise, MVC was similarly reduced by~ 25% after both running and cycling. However, reductions in VA were greater after running (-16%±10%) than cycling (-10%±5%; P< 0.05). Similarly, reductions in TMEP were greater after running (-78%±24%) than cycling (-15%±60%; P= 0.01). In contrast, reductions in Db100 (running vs cycling,-6%±21% vs-13%±6%) and Db10: 100 (running vs cycling,-6%±16% vs-19%±13%) were greater for cycling than running (P≤ 0.04).

Conclusions

Despite similar decrements in the knee extensor MVC after running and cycling, the mechanisms responsible for force loss differed. Running-based endurance exercise is associated with greater impairments in nervous system function, particularly at the spinal level, whereas cycling-based exercise elicits greater impairments in contractile function. Differences in the mechanical and metabolic demands imposed on the quadriceps could explain the disparate mechanisms of neuromuscular impairment after these two exercise modalities.