In this study, we modeled the change in maximum muscle force when a skeletal muscle is subjected to a periodic workload. The model represents an increase or decrease in the maximum muscle force exerted. It was created to evaluate the effects of our power-assist technologies on skeletal muscle strength, and we think that it can be applied to sports science. The model equation is constituted by a formula of step responses of a first-order delay system. The model input has the following four constants: the target muscle impulse when exerting force during a day in daily life, the force impulse exerted in 1 day during a period in which the target muscle was under study, the target musclemaximal strength, and the subject-specific time constant that represents the ease of change in muscle force. The output is the change in maximal strength. We confirmed the validity of the model by fitting the model to measurements obtained from experimental subjects. For this, we applied a special filter to remove noise from muscle force measurements.