Abstract：This study investigated the effects of different muscle contraction modes on bench press training. Most studies have focused on concentric contraction and eccentric contraction for single-session movements, but fewer studies have focused on eccentric contraction training for multi-segment movements, and there are limited studies that utilize the combined velocity loss (VL) method to monitor the effectiveness of resistance training. Therefore, the purpose of this study was to compare the effects of concentric contraction, eccentric contraction, and concentric and eccentric contraction bench press training on upper extremity strength, endurance, muscle girth, and grip strength. A total of 40 adult males with at least one year of weight training experience were randomly divided into four groups: concentric contraction, eccentric contraction, concentric and eccentric contraction, and control group. Each underwent a five-week, twice-weekly bench press regimen with a grip spacing of 1.5 times the width of the shoulder. The intensity of the workout was gradually increased from 70% of 1RM (one-repetition maximum) to 90% of 1RM, and the VL was reduced from 25% to 15% between the first and second half of the training cycle, all with a training speed of 2 seconds. Body composition analysis, pectoralis major muscle circumference, grip strength test, maximal muscle strength (1RM), and muscular endurance (50% 1RM to failure) were performed before and after training. The results showed no significant differences between groups in body composition, muscle girth, grip strength, and maximal muscle strength tests, but only the eccentric contraction group showed a significant increase in the number of repetitions of the bench press in the muscular endurance test. This study concludes that the eccentric contraction group improves bench press endurance performance when fatigue is monitored in conjunction with VL during a five-week, high-intensity bench press training program, thus providing coaches or athletes with a different training method to improve upper extremity endurance performance even at higher intensities. (Full text)