Muscle Imbalance, Altered Length-Tension, and Reciprocal Inhibition
Muscle Imbalance, Altered Length-Tension, and Reciprocal Inhibition
This domain tests the mechanisms behind compensation: why a muscle becomes tight or weak, how length affects force, and how the nervous system shuts down a muscle. Expect definitions and scenario questions that ask for the best explanation.
Core rules
- Length-tension relationship: muscle force depends on overlap of actin and myosin. A chronically shortened muscle may test tight and still be weak at end range; an over-lengthened muscle loses force production.
- Reciprocal inhibition: when an agonist contracts, the antagonist is inhibited. If the agonist is chronically overactive, the antagonist may become neurologically suppressed and weak.
- Synergistic dominance: a synergist takes over a prime mover's job. Example: hamstrings dominate a hip extension pattern when gluteus maximus is inhibited.
- Arthrokinematic inhibition: joint capsule or ligament irritation alters muscle recruitment around the joint.
- Altered reciprocal inhibition and altered length-tension often coexist. Pain, swelling, and fatigue amplify both.
- Imbalance types: tight/weak, tight/tight, and weak/weak. Test length and strength separately; do not assume tight means stretch first without screening.
Worked example
A client's hip bridge produces hamstring cramps and little glute sensation. Reasoning: the hamstrings are synergistically dominating hip extension because the glutes are inhibited. The fix is not more bridges. Inhibit hamstrings with foam rolling, lengthen if short, activate glutes in isolation, then integrate a bridge or hinge with cueing to keep the hamstrings quiet. Reassess.
Traps
- Equating tightness with strength.
- Stretching a muscle that is lengthened but weak.
- Forgetting that pain changes recruitment and needs referral or medical clearance.