Could massaging the psoas muscle to relax it, loosen the hamstrings?
Yes, it could. But it is not a guarantee. The psoas muscles and hamstring muscles are opposing muscles. The psoas muscles help with hip flexion (knee up) and the hamstring muscles help with hip extension and hyper-extension (knee down and backward). Opposing muscles (especially primary movers like these) are in constant communication and balance with each other. When one contracts or relaxes, the opposing muscle responds to balance the activity or inactivity of the other. For example, if you have a tight and shortened psoas muscle, you could have a reflexively tight and lengthened hamstring to go along with it. Only stretching the hamstring could possibly aggravate the situation. A properly delivered iliopsoas muscle release through manual therapy or stretching can work wonders on relieving tightness and even pain in the hamstring muscles. Improperly delivered techniques can either be ineffective or have the opposite effect.
