Cycle training is widely performed as a major part of any exercise program seeking to improve aerobic capacity and cardiovascular health. However, the effect of cycle training on muscle size and strength gain still requires further insight, even though it is known that professional cyclists display larger muscle size compared to controls. Therefore, the purpose of this review is to discuss the effects of cycle training on muscle size and strength of the lower extremity and the possible mechanisms for increasing muscle size with cycle training. It is plausible that cycle training requires a longer period to significantly increase muscle size compared to typical resistance training due to a much slower hypertrophy rate. Cycle training induces muscle hypertrophy similarly between young and older age groups, while strength gain seems to favor older adults, which suggests that the probability for improving in muscle quality appears to be higher in older adults compared to young adults. For young adults, higher-intensity intermittent cycling may be required to achieve strength gains. It also appears that muscle hypertrophy induced by cycle training results from the positive changes in muscle protein net balance.Keywords: aerobic exercise, muscular adaptation, lower body, cycling, ergometer Endurance training is a major part of any exercise program seeking to improve aerobic capacity and cardiovascular health. Another major part of exercise programming is strength/ resistance training, which improves muscle morphology. Thus to improve muscular strength and cardiovascular fitness in young, middle-aged and older populations, the American College of Sports Medicine recommends combining training intensity, volume, and frequency to optimize muscle hypertrophy and strength gain as well as aerobic capacity (V O 2 max) (23). However, the vigorous training intensity and/or high training frequency might hinder some older adults from participating in this type of training program. Interestingly, recent studies have reported concurrent improvements in V O 2 max and muscle hypertrophy in young and older populations after single exercise training (27,62,64,65). These single exercise modes include ambulatory exercise (walking, jogging, and running), cycling, and swimming.