This study used a randomised crossover design to analyse the effect of three different experimental interventions - i.e. standard conditions, music and verbal encouragement - on performance in an isometric endurance task, comparing results between untrained and trained individuals. The interval between each intervention was set at seven days. The outcome measures are muscle activity and fatigue, assessed by surface electromyography, and task duration.

Isometric endurance task requires participants to keep their arm flexed at a 90° angle while holding a dumbbell with a supine grip loaded to 80% of 1RM on the dominant side of the body. During execution, the back and head should remain in contact with a vertical wall, with the feet shoulder width apart and firmly planted on the floor. The bar is held with the dominant arm while the other arm remains in a neutral position close to the body. It is imperative to avoid any form of rocking or movement that would make it easier to maintain the position. The test officially begins when the bar is handed to the subject, who is already in the correct position, and ends as soon as the angle of the arm varies by more than five degrees from the starting position.

Inclusion Criteria:

To be included in the study, candidates had to be in good general health, with no medical conditions that could interfere with their ability to perform the test safely and effectively. In addition, to be considered trained, participants had to have performed 150 minutes per week of vigorous-intensity aerobic physical activity, in addition to muscle-strengthening activities, on at least two days per week. Those who did not meet this standard were considered untrained.

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Exclusion Criteria:

Exclusion criteria included a history of surgery to the arm, shoulder, or nearby areas that could limit the ability to perform the test. The use of medications that affect muscle function or pain perception was also a reason for exclusion, so that the test results could not be influenced by external factors.

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