Can intermittent changes in trunk extensor muscle length delay muscle fatigue development?

Area of Science:

• Biomechanics and Ergonomics
• Exercise Physiology
• Musculoskeletal Research

Background:

• Prolonged static postures can lead to muscle fatigue and pain.
• Muscle length changes may mitigate fatigue by alternating muscle activity.
• Understanding interventions to reduce trunk extensor fatigue is crucial for preventing musculoskeletal disorders.

Purpose of the Study:

• To evaluate if intermittent trunk extensor muscle length changes (INTERMITTENT) delay fatigue during prolonged static bending.
• To compare the INTERMITTENT condition against a near-isometric (ISOMETRIC) and a voluntary variation (VOLUNTARY) condition.
• To assess the effectiveness of a postural intervention for reducing muscle fatigue.

Main Methods:

• Eleven healthy male participants performed prolonged static bending at 30° trunk inclination until exhaustion.
• Three conditions were tested: INTERMITTENT, ISOMETRIC, and VOLUNTARY.
• Conventional and high-density electromyography (convEMG and HDsEMG) measured trunk extensor muscle activity.

Main Results:

• Endurance time was 33.6% longer for INTERMITTENT vs. ISOMETRIC (p=0.027) and 29.4% longer for INTERMITTENT vs. VOLUNTARY (p=0.010).
• No significant difference in endurance time was found between ISOMETRIC and VOLUNTARY conditions.
• Higher variability in EMG amplitude (convEMG and HDsEMG) was observed in the INTERMITTENT condition, indicating alternating muscle activity.

Conclusions:

• Imposed intermittent trunk extensor muscle length changes effectively delay muscle fatigue during prolonged static bending.
• This intervention is superior to both near-isometric and voluntary muscle length variation for enhancing endurance.
• Alternating muscle activity, potentially detected by HDsEMG, is a key mechanism for fatigue reduction.