Anatomical studies reported that human rectus femoris (RF) muscle is comprised of two different muscle-tendon units or neuromuscular compartments. Based on these anatomical characteristics, it can be assumed that the two regions within the RF muscle are controlled via different strategies by the central nervous system and play different functional roles. We are applying multi-channel surface electromyography technique to investigate regionspecific neuromuscular activation within the RF muscle. First, our study demonstrated that the proximal regions selectively activate during hip flexion while whole regions activate during knee extension (Watanabe et al. J Electromyogr Kinesiol 2012, Muscle Nerve 2014). This region-specific functional role was found during walking (Watanabe et al. J Biomech 2014) and pedaling (Watanabe et al. Muscle Nerve 2015). We also reported that regional neuromuscular regulation during walking is influenced by aging (Watanabe et al. J Biomech 2016). These studies suggest that regional neuromuscular regulation plays key role in human movements. Moreover, we showed that proximal regions are more fatigable than other regions (Watanabe et al. Muscle Nerve 2013). This may be explained by the potential of non-uniform arrangements of different types of motor units or muscle fibers along the muscle which was tested by electrical nerve stimulation (Watanabe et al. Eur J Appl Physiol 2014). From these studies, we concluded that the RF muscle is regulated by different strategies during human movements.
