Resistance training performed with either low or high ratings of perceived exertion improves isometric torque steadiness during submaximal fatiguing contractions, with torque variability increasing significantly as fatigue progresses, but there is no difference in the rate of decline in torque steadiness between the low and high RIR training groups.

When muscles get tired from repeated use, the nervous system makes the smaller, already-active muscle fibers fire faster to keep the force steady. As those fibers weaken, the nervous system turns on larger, stronger muscle fibers to pick up the slack. This keeps the total force going, but makes the force output wobble more because the larger fibers are harder to control precisely.