The posterior chain includes the hamstrings and lumbar muscles.
The lumbar muscles extend and stabilize the lumbar spine. Research suggests that the lumbar muscles are not adequately trained by multi-joint exercises like the deadlift and may require single-joint exercise for adequate training.1
Hamstrings have two functions:
Hip extension hamstrings exercises primarily activate the biceps femoris, the largest of the hamstrings. Leg flexion hamstrings exercises primarily activate the semitendinosis muscle of the hamstrings.
The Elastic Strength Program trains both functions for complete development of hamstring strength and mass.
The Elastic Strength program includes the back arch up on hyperextension bench to build lumbar extension and hamstring hip extension strength.
The back arch up (a.k.a. trunk extension) is chosen over all forms of deadlift because 1) it is safer than deadlifting, 2) it does not have the weak link (grip) of the deadlift, and 3) it produces the stronger contraction of the hamstrings and lumbar erectors.
Deadlifts are NOT as effective as back arch ups at loading the posterior chain (lower back and hamstrings). When you reach the top position of back arch ups the hamstrings and lumbar muscles are in their most contracted position and the load is directly opposed to their action. In contrast, when you reach the top position of a deadlift the load is compressing the spinal disks and borne by the leg bones, not significantly loading the lumbar and hamstring muscles. In fact, research has shown that deadlifting has little positive effect on the strength of the lumbar erectors, whereas lumbar extension isolation markedly improves lumbar strength.2
This is probably why Reg Park included hyperextensions in his routines.
Some people may need to include reverse leg lifts or barbell isolated lumbar extensions as auxiliary exercises for the lumbar erectors, although they are not included in the Elastic Strength program.
Low load Jefferson curl straight leg deadlifts are included in the Elastic Strength mobility program to improve pike mobility.
The best leg flexion hamstrings exercises is the standing band leg curl.
The standing band leg curl has a few of distinct advantages over other leg curls:
Therefore I recommend the standing band leg curl over the natural leg curl.
In the Elastic Strength program, you train the posterior chain by alternating back arch ups and standing leg curls from one lower body training session to the other. In this way you can build great posterior chain strength without risk of lumbar injury.
1. Gentil, P., Fisher, J., & Steele, J. (2016). A Review of the Acute Effects and Long-Term Adaptations of Single- and Multi-Joint Exercises during Resistance Training. Sports Medicine, 47(5), 843-855.
2. Fisher J, Bruce-Low S, Smith D. A randomized trial to consider the effect of Romanian deadlift exercise on the development of lumbar extension strength. Phys Ther in Sport 2013;14:139-145.