Muscular Synergy of Trunk and Hip Segments in Carrying Hand Loads with Different Weights in Healthy Young People

Objectives: Designing one-handed carrying tasks based on biomechanical findings has a significant impact on preventing musculoskeletal injuries. The present study was conducted to investigate the muscle synergy of the trunk and pelvis in the manual carrying of loads with different weights in healthy young people. Methods: In this experimental study, 20 male volunteers performed the walking protocol without load, carrying different weights of 5%, 10%, and 15% of their own weight during unilateral manual load carrying. The electrical activity of the trunk and pelvis muscles while carrying loads of different weights was recorded using an electromyography device (Biovision). To evaluate the differences between different load-carrying conditions, a repeated measures test was used at a significance level of P≤0.05. Results: The results showed that in the performance of manual load carrying, there was a significant difference between muscle synergy (synergy size) in all walking protocols, including 5% and 10% of body weight and 5% and 15% of body weight and between 15% and 10% (P≤05). While in the performance of manual load carrying, a significant difference was found between muscle synergy (synergy direction) in 5% of body weight and 10% of body weight, this difference was not seen in manual load carrying with 5% of body weight and 15% of body weight and also between synergy of 15% and 10% (P≥0.05). Conclusion: It seems that the difference in muscle synergy in terms of size in unilateral manual load carrying can, with increasing load, create more tension in the back and pelvic muscles; however, the direction or angle does not change compared to the no-load state.