Short-term fatigue is typically exercise-related; disease, immobility, or aging can lead to chronic muscle fatigue ,possible explanation for this could be that continuous gripping exerts a constant load on the muscles, leading to a quicker buildup of fatigue.It's also worth considering that the initial higher fatigue rate in 
continuous gripping might decrease as the muscles adapt to the 
sustained activity, while in repetitive gripping, the muscles might not 
fully recover during the short breaks, leading to a cumulative fatigue 
effect over time.