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Task-Specific Rescue Loading Redistributes Lower Limb Joint Work During Simulated Sprinting Across Fatigue States in
Junqiang Zhang1, Xueyi Chen1, Min Chen2
1School of Physical Education, Shaanxi Normal University, Xi'an 710119, China.
Life (Basel, Switzerland)
|July 28, 2026
Summary
Firefighter fatigue and heavy loads alter how the body distributes mechanical work during sprints. This ankle-to-knee shift may increase knee stress, especially with whole-body fatigue.
Area of Science:
- Biomechanics
- Occupational Health
- Exercise Physiology
Background:
- Firefighters perform strenuous sprints with gear.
- The impact of fatigue and load on firefighter biomechanics is not well understood.
Purpose of the Study:
- To investigate how fatigue and rescue loads affect firefighter sprint mechanics.
- To analyze lower-limb joint work distribution and muscle activation.
Main Methods:
- Fifty-three male firefighters performed simulated rescue sprints.
- Tested unloaded and loaded (7-30 kg) conditions with varying fatigue levels.
- Collected kinematic, kinetic, and electromyographic data.
Main Results:
- Heavier loads reduced sprint speed and shifted mechanical work from ankle to knee.
- Mild local knee extensor fatigue maintained sprint speed, unlike whole-body or severe local fatigue.
- Global locomotor fatigue further influenced the ankle-to-knee work redistribution.
Conclusions:
- Firefighters redistribute mechanical work from ankle to knee under heavy loads.
- This adaptation may increase knee joint demand, particularly when fatigued.
- Understanding these biomechanical changes is crucial for injury prevention in firefighters.
