Neuromuscular impairment following backpack load carriage

Area of Science:

• Exercise Physiology
• Neuromuscular Function
• Biomechanics

Background:

• Load carriage, particularly with backpacks, is a common occupational and recreational activity.
• Understanding the neuromuscular consequences of load carriage is crucial for performance and injury prevention.

Purpose of the Study:

• To investigate the neuromuscular mechanisms underlying quadriceps femoris muscle function changes after load carriage.
• To differentiate the effects of load carriage from simple walking on neuromuscular parameters.

Main Methods:

• 10 male participants underwent treadmill walking for two hours under two conditions: level walking (LW) and level walking with a 25 kg backpack (LC).
• Measurements included voluntary and electrically stimulated isometric contractions before and after each condition.
• Key parameters assessed were maximal voluntary contraction force, voluntary activation, and doublet contraction properties.

Main Results:

• Maximal voluntary contraction force significantly decreased by 15% after LC, but not LW.
• Voluntary activation decreased in both conditions, indicating reduced central drive.
• The 20:50 Hz ratio decreased after LC, suggesting impaired calcium release during excitation-contraction coupling.

Conclusions:

• Two hours of 25 kg backpack load carriage induces significant neuromuscular impairment.
• This impairment involves reduced central drive and peripheral muscle fatigue or damage.
• The findings highlight potential reductions in physical performance and increased musculoskeletal injury risk.