Stability depends on quality of sensory input

Motor control does not rely on strength alone. It relies on information.

Sensory input allows the system to estimate body position, direction of movement and distribution of load. This input originates from joints, muscles, ligaments, fascia, vestibular system and contact with the ground.

When sensory input is clear, effort matches task demand. When sensory input is reduced, the system may increase tone to create stability.

Reduced input increases effort

Reduced sensory clarity may not be consciously perceived, but it influences movement organization.

The system may choose solutions that provide stability but require more effort. Muscles activate more than necessary. Movement variability decreases. Ranges of motion become limited.

Effort may appear as persistent holding — perceived as heaviness, stiffness or reduced ease of movement.

Coordination reduces need for holding

When sensory input improves, effort can be more precisely regulated. Muscles act according to demand rather than beyond it.

When sensory input and motor response are coordinated, load distribution becomes more variable — reducing accumulation of strain.

Relationship to Parasitic Effort

When sensory input is insufficient, the system may generate Parasitic Effort — muscle activity that does not directly contribute to movement.

The relationship to stability beyond contraction explains why improving sensory clarity — not strength alone — reduces excess activation.

When sensory clarity improves, excess activation decreases. The change often occurs in organization rather than strength. Movement becomes more economical.

Conceptual schema