Motor Dysfunction After Injury: Why the Body Stays Stuck
After an injury, the body does not simply “hurt.” It reorganizes. The nervous system triggers a cascade of protective responses — and if these are not understood and addressed in time, they can become fixed long after the tissues have fully healed. This is precisely why “it will sort itself out” does not always work — and why rehabilitation matters even after seemingly minor injuries.
What Changes Immediately After Injury
Injury is not only tissue damage. Simultaneous changes occur throughout the motor system: muscles weaken or, conversely, go into spasm; coordination and postural stability are disrupted. A psychological layer is added on top: a conscious sense of joint instability, avoidance of movement due to pain, and anxiety about loading the injured area. None of this is a character flaw — it is a physiological protection program.
Strategy One: Spasm and Fixation
When injury first occurs, the nervous system responds immediately by raising muscle tone around the damaged zone. The area becomes hypersensitive and muscles tighten. Co-contraction is activated — both the muscles that flex the joint and those that extend it contract simultaneously. The purpose is to immobilize the injured area and prevent movements that could cause further harm.
This is most clearly visible in acute torticollis or acute low back pain: the person literally “freezes” in one position, held there by continuous muscle contraction (Zedka et al., 1999). Muscle hypersensitivity even to the slightest change in joint angle is explained by irritation of nociceptors in the damaged tissues — they are essentially signaling to the nervous system: do not move (Solomonow et al., 1998).
Strategy Two: Weakness and “Switched-Off” Muscles
As acute pain subsides and tissues begin to heal, a second strategy engages — the opposite of the first. Motor neuron excitability decreases, muscles become sluggish and respond poorly to neural stimulation. This is functional weakness — not atrophy from disuse, but deliberate inhibition by the nervous system to prevent overloading a zone that has not yet fully recovered.
The classic example is quadriceps inhibition following knee injury: even a modest accumulation of fluid in the joint is sufficient for the nervous system to “switch off” the muscle (Hurley & Newham, 1993).
Both Strategies Can Coexist
Here is what is critical to understand: spasm and weakness are not mutually exclusive states. They can be present simultaneously in different muscle groups surrounding the same joint. Following an ankle sprain, for example, the gastrocnemius may be in hypertonia (spasm), while the peroneal muscles are in hypotonia (weakness). Both responses serve the same purpose: to prevent re-injury (Bullock-Saxton, 1994).
This means the therapist cannot apply a one-size-fits-all approach: some patients need inhibition and tone reduction, others need activation and restoration of motor control, and others need both simultaneously in different regions.
Why This Does Not Resolve on Its Own
In most cases following mild injury, the nervous system returns from “protection mode” to a normal functional pattern independently. But with more serious or prolonged injury, the protective response can become maladaptive: what began as a rational defense becomes an obstacle — the body continues to restrict movement even after tissues have fully healed (Tabor et al., 2018).
Van Uden et al. (2003) confirmed this with specific data: one year after ACL reconstruction, patients’ coordination during single-leg hopping remained impaired compared to healthy controls — despite complete anatomical recovery.
This is particularly evident in patients with chronic low back pain. In healthy individuals, the back muscles relax completely at end-range forward flexion — this is known as the flexion-relaxation phenomenon. In chronic pain patients, these muscles remain active even at full range — continuing to “guard” weakened ligaments and discs long after this protection is no longer necessary (Shirado et al., 1995; Kaigle et al., 1998). The brain has “decided” this is safer — and has reorganized accordingly.
This is precisely why such patients frequently sustain repeat injuries despite regular training: the muscles are active, but the motor pattern remains dysfunctional.
What to Do About It
Neuromuscular rehabilitation begins with a correct assessment of each muscle group: some require inhibition and reduced excitability, others require activation and restoration of normal motor control. The goal is not simply to “eliminate pain,” but to restore the nervous system’s correct movement program.
This requires conscious patient engagement, active techniques, feedback, and repetition — the same five elements of the adaptation code discussed in the article on motor learning. Passive massage and rest are insufficient here: the nervous system does not reorganize without the patient’s active participation.
References
Lederman E (2005) The Science & Practice of Manual Therapy. Elsevier
Zedka M, Prochazka A, Knight B et al. (1999) Voluntary and reflex control of human back muscles during induced pain. Journal of Physiology 520(Pt 2):591–604
Solomonow M, Zhou BH, Harris M et al. (1998) The ligamento-muscular stabilizing system of the spine. Spine 23(23):2552–2562
Shirado O, Ito T, Kaneda K, Strax TE (1995) Flexion-relaxation phenomenon in the back muscles. American Journal of Physical Medicine and Rehabilitation 74(2):139–144
Kaigle AM, Wessberg P, Hansson TH (1998) Muscular and kinematic behavior of the lumbar spine during flexion-extension. Journal of Spinal Disorders 11:163–174
Van Uden CJ, Bloo JK, Kooloos JG et al. (2003) Coordination and stability of one-legged hopping patterns in patients with ACL reconstruction. Clinical Biomechanics 18(1):84–87
Hurley MV, Newham DJ (1993) The influence of arthrogenous muscle inhibition on quadriceps rehabilitation. British Journal of Rheumatology 32(2):127–131
Bullock-Saxton JE (1994) Local sensation changes and altered hip muscle function following severe ankle sprain. Physical Therapy 74(1):17–28
