I have two male clients who have informed me that they do not feel their hamstrings being worked on while performing a prone leg curl even under good form. Could it be that their hip extension mechanism is not firing in the right sequence?
First of all, my question to you is why are you having your client perform prone hamstring curls (i.e., what's the goal?)? Isolationist, uniplanar machine training can/will stimulate hypertrophy (assuming adequate intensity, nutrition, rest, etc.). However, in the long run, it may add virtually no benefit to "functional ability" or functional carry-over. The reason I ask this is because you made mention to hip extension and firing sequence. A prone leg curl (or any isolated leg curl machine, for that matter) teaches the body to isolate, when the body by nature actually only "knows" integration of muscle "synergies."
When training in an isolated, uniplanar, artificially stabilized environment the kinetic chain in not being prepared to deal with imposed demands of normal daily activities (walking up/down stairs, getting groceries out of the trunk, etc.). Training integrated, functional movement patterns targets synergistic muscles to produce force, reduce force and dynamically stabilize in all three planes of motion. This creates maximal motor unit recruitment, which facilitates a greater overall training response.
The nervous system is organized in such a way as to optimize the selection of muscle synergies and not the selection of the individual muscles. The nervous system thinks in terms of movement patterns and not isolated muscle function. Isolation and training individual muscles over prolonged periods of time creates artificial sensory feedback, faulty sensorimotor integration and abnormal forces throughout the kinetic chain. This ultimately acts to confuse the nervous system as muscles are being asked to perform a function that the nervous system does not understand. In essence, the muscles are re-programmed to perform:
- A different task. The hamstring performing knee flexion on a hamstring curl machine rather than decelerating knee extension, hip flexion and internal rotation of the tibia and femur.
- At a different speed. Consistently at slow controlled speeds rather than progressing to functionally applicable speeds (power training).
- With a different muscle action. Emphasizing concentric rather than eccentric muscle actions for the hamstrings or concentric rather than isometric (dynamic stabilization) for the hip abductors (outer thigh machines).
- In a different plane of motion. Working in the frontal plane (inner thigh machines) rather than sagittal and/or transverse planes for the adductors.
Now, if the goal IS ULTIMATELY HYPERTROPHY AND/OR REDUCED BODY COMPOSITION, it is important to realize that the above literature is stating that when the neuromuscular system is functioning optimally (i.e., optimal muscle synergy), the individual has a GREATER ABILITY TO MOVE HEAVIER LOAD(S) WITH THE APPENDAGES, THEREBY CREATING A GREATER OVER ALL TRAINING EFFECT (i.e., anabolic stimulation, fat burning, etc.) Hence, what you wind up with is a safe method of making the body strong and free of injury-causing compensation(s).
As far as the first part of your questionz: "...they do not feel their hamstrings being worked..." I would ask for other feedback, starting with:
- What DO you feel?
- What KIND OF FEELING does it take for these two gentlemen to qualify "work" (i.e., Do they need to feel a scorching burn?!?!)?
I would seriously suggest becoming familiar with the integrated training concepts I've mentioned above. To begin doing this, please refer to the "related articles" at right and below.
- Clark MA. "Integrated Training for the New Millennium." The National Academy of Sports Medicine. Thousand Oaks, CA 2001.