Background and Objective: 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 carrying manual loads of different weights .

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 , 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≤50). While in the performance of manual load carrying, although a significant difference was found between muscle synergy (synergy direction) in 5% of body weight and 10% of body weight, while 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; But the direction or angle does not change compared to the no-load state.