Ask Charles
I am confused about training the lower back. What is the difference between doing back extensions where in the end position you are parallel to the ground, and the end where in the end position, you are 45 degrees in relation to the ground?
The answer is simple:
there is a variation in motor unit recruitment of the posterior chain muscles.
If we take the case of the two benches given above, the 45 degree incline bench does not allow the erector spinae the level of stretch that you get from the flat version. However, they provide a greater percentage of recruitment of the hamstrings than the flat version. So, both of them recruit the posterior chain of erector spinae-glutes-hamstrings. These sets of muscles are part of a chain because of the anatomical feature of the sacro-spinal and sacro-tuberal ligaments.The point of overload is affected by the respective orientation of the body in relation to the strength curve. Therefore, for long term results, varying the points of overload every 4-6 workouts will ensure better balanced strength, faster growth in strength and hypertrophy, and protection from injuries. Or course, varying the position of the load such as dumbbell on chest vs barbell at arms length with a wide grip increases the number of permutations of the back extension exercise. Even varying the width of the grip on the barbell, or the hand position (supinated vs pronated) will in the end affect motor recruitment.