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Creep and fatigue development in the low back in static flexion
Gwanseob Shin1, Clive D'Souza, Yu-Hsun Liu
1Department of Industrial and Systems Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA. gshin@buffalo.edu
Spine
|August 1, 2009
Summary
Static deep back flexion can cause creep in spinal tissues and lead to muscle fatigue in back extensor muscles. This fatigue may increase the risk of low back pain due to reduced muscle capacity.
Area of Science:
- Biomechanical analysis of spinal posture and muscle function.
- Occupational biomechanics and ergonomics.
- Musculoskeletal disorder research.
Background:
- Static lumbar flexion is linked to low back disorders, with focus on passive spinal tissue changes.
- The role of extensor muscle fatigue in static flexion injury mechanisms remains under-explored.
Purpose of the Study:
- To investigate creep and muscle fatigue in the low back during prolonged static upper body deep flexion.
- To simulate an occupational posture resembling above-ground work.
Main Methods:
- In vivo measurements of trunk flexion posture and back extensor muscle activity (electromyography) in 20 asymptomatic subjects.
- Evaluated changes before, during, and after a 5-minute static flexion using isokinetic and isometric trunk extension tests.
Main Results:
- Significant increases in flexion-relaxation onset angle and EMG amplitude post-static flexion indicate spinal tissue creep.
- Reduced median power frequency of lumbar erector spinae EMG suggests muscle fatigue development.
- Observed low-level EMG and muscle spasms during static flexion.
Conclusions:
- Prolonged passive stretching during static flexion can induce low back extensor muscle fatigue.
- Fatigued muscles require increased force generation post-flexion to maintain spinal stability, compensating for tissue creep.
- Impaired muscle force capacity due to fatigue is a significant risk factor for low back pain.
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