One of my fellow trainers has a degree in Kinesiology and a difference of opinion from me. A member was doing the leg press with her feet externally rotated and wide, in the mindset of stimulating more glute involvement. I argued that she was stimulating less glute, as well as encouraging poor anatomical alignment. He disagreed with me stating that she was affecting more muscle, that the position (externally rotated) was natural and gave the example of power lifter's externally rotating when deadlifting. Isn't the gluteus medius and maximus shortened in a externally rotated position, thereby limiting the contraction of the muscle? Any insight you can give me would be thoroughly appreciated.
In any leg press, the load has been "artificially" redirected to one of various angles (depending on the maker/model of the machine.) These artificially isolated and fixed machines allow for very little natural hip extension due the fact that the hips remain in a position of flexion throughout the entire ROM. What this equates to is a decrease in hip extension ROM and therefore a decrease in overall glute involvement, regardless of the degree of external rotation of the hips. Externally rotating the hip will begin to take the lower extremity out of the sagittal plane, approaching the frontal plane. This will "pre shorten" the external rotators of the hip (piriformis/rotators, posterior fibers of the glute medius, some glute max fibers...) as well as directing more force and stress into the SI joint.
Comparing a deadlift to a leg press is LITERALLY like comparing apples to oranges! The deadlift involves intense recruitment of the "inner unit" muscles (deep abdominal wall and spinal stabilizers) as they perform synergistically with the powerful muscles of the outer unit (upper and lower extremity) in order to complete the movement. Contrast this with the artificially fixed and isolated leg press, which requires comparatively little synergy between these two groups of muscles, possibly programming dysfunction into the body if performed with chronic regularity. This is because leg strength is ultimately increased drastically out of proportion to spinal strength.
- Purvis, T; Simon, M. (2001). Resistance Training Specialist.
- Kendal, McCreary, Provance. (1993). Muscles Testing and Function. (4th Ed.)
- Slavin, M. (2000). The Science and Physiology of Movement. (course manual)
- Integrated Training for the New Millenium. (NASM)
- Naumann, D. (2002). Kinesiology of the Musculoskeletal System.