Front and/or rear suspensions of bicycles become popular for the purpose of riding comfort especially for mountain bicycle. Suspension system include damper for shock absorbing and spring for rebounding. Therefore suspension systems would increase bicycle riding effort since damper dissipates energy. ADAMS®/LifeMOD® are proposed in this research to establish a Bicycle-Human Integrated Multibody Dynamic Model to investigate the impact of bicycle suspensions on cyclists leg muscle forces under various pedaling conditions. Muscles compared include adductor magnus, rectus femoris, vastus lateralis and semitendinosus. Pedaling conditions include riding on flat road, over a road bump, and climbing slope. The results indicate that suspension system increases the pedaling forces of vastus lateralis and semitendinosus. However suspension system decreases the pedaling forces of adductor magnus and rectus femoris. The integrated model built in this research may be used as reference for designing bicycle suspension systems. In addition, the results of this study can be used as the basis of leg weight training for long-distance off-road cyclists to strengthen certain muscles.