Fatigue influences the dynamic stability of the torso

[Guest guest]

Ergonomics. 2008 Aug;51(8):1258-71.

Fatigue influences the dynamic stability of the torso.

Granata KP, Gottipati P.

Department of Engineering Science & Mechanics, The P. Granata

Musculoskeletal Biomechanics Lab, Virginia Polytechnic Institute &

State University, Blacksburg, VA 24061, USA.

Fatigue in the extensor muscles of the torso affects neuromuscular

recruitment and control of the spine. The goal of this study was to

test whether fatigue influences stability of dynamic torso movements.

A controlled laboratory experiment measured the change in the maximum

finite-time Lyapunov exponent, lambda(max), before and after fatigue

of the extensor muscles. Non-linear analyses were used to compute

stability from the embedding dimension and Lyapunov exponent recorded

during repetitive dynamic trunk flexion tasks.

Torso extensor muscles were fatigued to 60% of their unfatigued

isometric maximum voluntary exertion force then stability was re-

measured. Independent variables included fatigue, task asymmetry and

lower-limb constraint. lambda(max) values increased with fatigue

suggesting poorer dynamic stability when fatigued. Embedding

dimension declined with fatigue indicating reduced dynamic complexity

when fatigued.

Fatigue-related changes in spinal stability may contribute to the

risk of low-back injury during fatiguing occupational lifting tasks.

The findings reported here indicate that one mechanism by which

fatigue contributes to low back disorders may be spinal instability.

This information may contribute to the development of ergonomic

countermeasures to help prevent low back disorders.