372Escamilla et al [ Physical Therapy ] T he core musculature includes both deep and superficial muscles of the lumbopelvic-hip complex: internal oblique, transversus abdominis, transversospinalis, quadratus lumborum, psoas major and minor, rectus abdominis, external oblique, erector spinae, latissimus dorsi, gluteus maximus and medius, hamstrings, and rectus femoris. 2,3,21,23 Although several studies have examined core muscle recruitment during the crunch and bent-knee sit-up exercises, 9,11,35,37 Background: Prone, supine, and side position exercises are employed to enhance core stability.