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Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles
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Can intermittent changes in trunk extensor muscle length delay muscle fatigue development?

Niels P Brouwer1, Idsart Kingma1, Wietse van Dijk2

  • 1Department of Human Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences, Amsterdam, the Netherlands.

Journal of Biomechanics
|December 4, 2023
PubMed
Summary

Intermittent trunk muscle length changes significantly delayed fatigue during prolonged static bending compared to isometric or voluntary variations. This postural intervention enhances muscle endurance by promoting alternating activity.

Keywords:
Back muscleErector spinaeLumbarLumbopelvic rhythmParaspinal muscles

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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.