Exercise-related fatigue affects joint-driven resistance: comparison of flexor and extensor.

[Purpose] Muscle fatigue can affect the inherent properties of muscles. It is important to know how muscle stiffness changes with muscle fatigue and the different effects of the initial and terminal stages of exercise. Therefore, we aimed to examine the effects of bicep and tricep contraction tasks that lead to fatigue on joint-driven resistance of the elbow joint. [Participants and Methods] Twenty-five healthy men were included. Joint-driven resistance of the elbow joint was measured before and after the muscle contraction task. The slope of the regression line of the angle torque at the time of passive movement was calculated as an elastic coefficient and the entire movable range, proximal range, and distal range were compared. [Results] Owing to the muscular contraction of the biceps and triceps, the elastic coefficient increased in the elbow joint during both flexion and extension. The rate of change in the elastic coefficient was lower during the tricep contraction task than during the bicep contraction task. For both tasks, the change in the elastic coefficient varied depending on the range of exercise. [Conclusion] Resistance exercise increased the driven resistance of the joint during passive movement, and this effect was greater during terminal exercises.