AGONIST/ANTAGONIST RELATIONSHIPS: RECIPROCAL INHIBITION

Hatha Yoga is the most popular form of yoga in the Western world. And although there are many styles, all derive from an ancient hygienic system for maintaining spiritual and physical health. The Sanskrit word hatha translates to mean sun/moon or yin/yang. This fits perfectly with how the body balances opposites through biomechanics and physiology.

FIGURE 1 Agonist/antagonist relationships and reciprocal inhibition illustrate such a balance. Agonist muscles contract to move a joint or appendage one way, and during this movement their antagonists stretch. When the brain signals an agonist muscle to contract, it simultaneously signals the antagonist muscle to relax. We can take advantage of this physiological combination when practicing forward bends and hip openers. For example, Kurmasana flexes the trunk forward, stretching the back extensors—the erector spinae and quadratus lumborum. You can use the arms and gravity to flex the trunk, but actively engaging the abdominals provides a more effective stretch. This produces reciprocal inhibition of the antagonist back extensors, causing them to relax.

FIGURE 2 In Paschimottanasana we flex the trunk and hips. A key agonist/antagonist relationship in this pose involves the psoas (which flexes the hips) and its antagonist, the gluteus maximus (which extends them). Activating the psoas produces reciprocal inhibition of the gluteus maximus, allowing it to relax into the stretch.

Krounchasana beautifully illustrates the agonist/antagonist relationship of the quadriceps and hamstrings. The raised-leg quadriceps activate to extend the knee while the hamstrings stretch. You can extend the knee with the arms, but consciously engaging the quadriceps produces reciprocal inhibition of the hamstrings, relaxing them into the stretch. You cannot achieve this effect using only the arms to straighten the knee.

Now, bring your attention to the bent knee. The quadriceps stretch in this position. If you use only your body weight to bend the knee, you will not obtain the physiological effect of reciprocal inhibition relaxing this muscle. Therefore, occasionally engage the agonist hamstring muscles to squeeze the lower leg against the thigh.

FIGURE 3 Upavistha Konasana illustrates the agonist/ antagonist relationship between the hip abductors (the gluteus medius and tensor fascia lata) and the adductor muscles that are stretching on the insides of the thighs. Press the heels into the mat and attempt to drag them away from the midline to contract the tensor fascia lata and gluteus medius. This produces reciprocal inhibition and signals the adductor muscles to relax.