Dumbbell curl is one of the most important strengthening exercises for the upper extremity. This exercise trains especially biceps brachii. Exercise load is increased to achieve more muscle strength for the biceps brachii. Researchers are usually focused on electromyography (EMG) in order to examine the effects of load increasing on muscle contraction. However, only the muscle force can be predicted with EMG measurement. Structural analysis of the muscles cannot be performed. In this study, the effects of load increasing on biceps brachii were investigated by mechanical analysis. The inverse dynamic model was simulated according to the motion analysis of dumbbell curl exercises performed with 6 kg and 10.7 kg. The muscle force of the biceps brachii was calculated from the elbow joint reaction moment. A simplified finite element model of biceps brachii was created and stress-strain response was examined. Although the muscle force increases by 78.3%, the rate of increase of elbow peak moment is 57.7% and the rate of increase of peak muscle force is 38.3%. Similarly, the rate of increase of maximum strain and maximum stress are 44.4% and 37.3%, respectively. According to these results, it is understood that increasing the dumbbell load does not increase the muscle force at the same rate.