Recruitment plasticity of neuromuscular compartments in exercised tibialis anterior using echo-planar magnetic resonance imaging in humans.

We investigated the recruitment plasticity of the superficial tibialis anterior (TA-s) and deep tibialis anterior (TA-d) regions of neuromuscular compartments (NMCs) in the m. tibialis anterior (TA) during exercise using echo-planar imaging (EPI). Six healthy men performed dorsiflexion exercise at 60% of maximum voluntary contraction at a frequency of 10 contractions/min inside the magnetic resonance imaging. Transaxial EPIs of the right leg were acquired every 6 s at rest (0.5 min), during exercise (2.5 min) and recovery (5 min). In TA-s, significantly higher signal intensities (SIs) were shown than those in TA-d from immediately after starting the exercise to recovery. It has been demonstrated that SI reflects the degree of recruitment in the activated muscle, thus our result suggest that preferential firing of motor neurons in the superficial region of the NMC occurs during exercise in human TA muscle.