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Updated: Jul 12, 2026
Lower Limb Biomechanical Analysis of Healthy Participants
Published on: April 15, 2020
Effect of prolonged walking with backpack loads on trunk muscle activity and fatigue in children
Youlian Hong1, Jing-Xian Li, Daniel Tik-Pui Fong
1Department of Sports Science and Physical Education, The Chinese University of Hong Kong, Hong Kong, China. youlianhong@cuhk.edu.hk
Insights
Carrying backpacks heavier than 15% body weight for 20 minutes can cause muscle fatigue in children. Researchers recommend limiting backpack loads to protect young muscles during walking activities.
Area of Science:
- Pediatric biomechanics
- Exercise physiology
- Occupational health
Background:
- Childhood backpack use is common, raising concerns about potential musculoskeletal strain.
- Understanding the impact of load carriage on young children's muscle activity and fatigue is crucial for developing safe guidelines.
Purpose of the Study:
- To investigate the effects of varying backpack loads (0-20% body weight) on muscle activity and fatigue during prolonged walking in 6-year-old boys.
- To establish safe backpack load limits for children to prevent muscle fatigue.
Main Methods:
- Fifteen 6-year-old boys walked on a treadmill for 20 minutes with backpack loads of 0%, 10%, 15%, and 20% body weight.
- Electromyography (EMG) measured muscle activity in the upper trapezius, lower trapezius, and rectus abdominis.
- Muscle fatigue was assessed using median power frequency (MPF) analysis of EMG signals.
Main Results:
- A 15% body weight load significantly increased lower trapezius muscle activity after 15 minutes.
- A 20% body weight load induced muscle activity from 5 minutes and fatigue from 15 minutes.
- Muscle fatigue was observed in the upper trapezius from 10 minutes, even without increased activity, while the rectus abdominis showed no significant changes.
Conclusions:
- Backpack loads for children should not exceed 15% of their body weight for walking durations up to 20 minutes.
- Prolonged load carriage can lead to muscle fatigue in specific muscle groups, particularly the trapezius.
- These findings support the need for stricter guidelines on backpack weight for school-aged children to mitigate risks of musculoskeletal issues.
Abstract:
This study investigated the effect of prolonged walking with load carriage on muscle activity and fatigue in children. Fifteen Chinese male children (age=6 years, height=120.0+/-5.4 cm, mass=22.9+/-2.6 kg) performed 20-min walking trials on treadmill (speed=1.1 ms(-1)) with different backpack loads (0%, 10%, 15% and 20% body weight). Electromyography (EMG) signals from upper trapezius (UT), lower trapezius (LT) and rectus abdominis (RA) were recorded at several time intervals (0, 5, 10, 15 and 20 min), and were normalized to the signals collected during maximum voluntary contraction. Integrated EMG signal (IEMG) was calculated to evaluate the muscle activity. Power spectral frequency analysis was applied to evaluate muscle fatigue by the shift of median power frequency (MPF). Results showed that a 15% body weight (BW) load significantly increased muscle activity at lower trapezius when the walking time reached 15 min. When a 20% BW load was being carried, increase in muscle activity was found from 5 min, and muscle fatigue was found from 15 min. In upper trapezius, increase of muscle activity was not found within the 20-min period, however, muscle fatigue was found from 10 min. No increased muscle activity or muscle fatigue was found in rectus abdominis. It is suggested that backpack loads for children should be restricted to no more than 15% body weight for walks of up to 20 min duration to avoid muscle fatigue.
