Objective To develop a three-compartment kinetic fatigue model for the isometric muscle endurance of the hip, knee, and ankle joints at 50% IPT (isometric peak torque), so as to provide a theoretical basis for simulation-based assessments and load evaluations in biomechanics and sports science. Methods The IPT of the hip, knee, and ankle joints was measured in 40 male university students. Isometric endurance tests were then performed on all three joints at 50% IPT until exhaustion. Electromyography data and endurance time (ET) of major lower limb muscles were collected concurrently. The differences between ETs predicted by models based on previously recommended F and R parameters and actual ETs were analyzed. Subsequently, experimental ETs were used in a grid search to optimize F and R parameters, allowing for the development of an accurate three-compartment kinetic model. Results The ET of the hip and ankle joints was significantly longer than that of the knee joint (P<0.001). Models using previously recommended F and R parameters overestimated ET, with significantly higher predicted values than experimentally measured ET (P<0.001), as well as elevated root mean squared error (RMSE) and mean relatvie error (MRE) values. The grid search successfully identified F and R parameters for the three-compartment model in isometric endurance tests of lower limb joints , with no statistical difference between model-predicted ET and experimental ET (P>0.05). Conclusions The developed model in this study can serve as an indirect measurement tool for evaluating load in similar activities.