Changes in motor unit activity in the biceps brachii muscle under different intensities of isometric loading

Introduction: In patients with cancer, loss of muscle mass is observed in many cases and tumour types. This can lead to a drastic deterioration in the patient's quality of life, with the inability to support themselves. Nowadays, in addi-tion to primary treatment of the tumour, physical training of patients has become a priority in order to maintain their quality of life. One key to this is resistance training to prevent sudden muscle loss, which the patient can do alongside primary treatment, and isometric training may be one option.Objective: Our aim was to measure the activation frequency characteristics of the biceps brachii muscle in our subjects during a fatigue protocol while creating a constant controlled isometric tension in the muscle.Method: 19 healthy university students participated in our study. After determining the dominant side, the subjects' single repetition maximum was assessed using the GymAware RS tool and then 65% and 85% of this was calculated. We placed electrodes on the biceps brachii muscle and had them hold the weight at 65% and 85% until full fatigue. Immediately afterwards, subjects performed an isometric maximal contraction (Imax). The measured electromyogra-phy recordings were divided into 3 equal parts, then the first, middle and last 3 s (W1, W2, W3) were analyzed.Results: Our results show that, consistent with fatigue, at both 1RM 65% and 1RM 85% load, the activity of the low -frequency motor units increases, while the activation of the high-frequency motor units decreases.Discussion: The present study is consistent with our previous study.Conclusion: Our test protocol is not suitable for prolonged activation of high-frequency motor units because the activity of high-frequency motor units decreases over time.