Muscle fatigue and fatigue-related biomechanical changes during a cyclic lifting task

Area of Science:

• Biomechanics
• Human Movement Science
• Occupational Health

Background:

• Time-frequency analysis of electromyography (EMG) offers new insights into localized muscle fatigue during dynamic contractions.
• Understanding fatigue-related impairments is crucial for managing low back pain.

Purpose of the Study:

• To investigate the relationship between localized muscle fatigue and lifting biomechanics.
• To assess how fatigue modifies lifting strategies by analyzing EMG signals and kinematic/kinetic measures.

Main Methods:

• 14 healthy males performed cyclic lifting of a 13 kg box, with pre/post static lifting tests.
• Electromyographic signals from 14 muscle sites were analyzed using Instantaneous Median Frequency (IMF).
• Kinematic and kinetic data were collected using motion analysis systems.

Main Results:

• IMF significantly decreased in paravertebral muscles during cyclic lifting, correlating with self-reported fatigue and reduced trunk extension strength.
• Paravertebral IMF changes were influenced by the load relative to maximal lifting strength.
• Fatigue led to significant changes in joint kinematics (knee, hip, trunk, elbow) and increased L4-L5 vertebral forces.

Conclusions:

• Localized muscle fatigue is correlated with biomechanical adaptations during cyclic lifting.
• This analysis technique can inform research and clinical practice for repetitive work tasks, lifting ergonomics, and back school programs.
• Dynamic and static EMG assessments yield different muscle-specific results and should not be considered equivalent.