“…In gait analyses, the RF muscle has often been the subject of intense investigation, since it has been reported that an abnormality in regulation of neuromuscular activation of the RF muscle causes pathological gait in patients with upper motor neuron injuries such as stiff-legged (or -knee) gait (Chapman et al, 2008;Kerrigan et al, 1991;Reinbolt et al, 2008;Riley and Kerrigan, 1998;Sung and Bang, 2000). While numerous studies have investigated the neuromuscular activation pattern of the RF muscle during gait using electromyography (EMG) in able-bodied adults, children, the elderly, and patients (Annaswamy et al, 1999;Barr et al, 2010;Byrne et al, 2005;Chantraine et al, 2005;Di Nardo and Fioretti, 2013;Nene et al, 2004;Sung and Bang, 2000), little attention has been paid to the complicated anatomical characteristics of this muscle. It has been suggested that the RF muscle is comprised of two different muscle-tendon units or neuromuscular compartments, and this anatomical property is referred to as "muscle-withinmuscle" (Balius et al, 2009;Gyftopoulos et al, 2008;Hasselman et al, 1995).…”