Step ups are great exercise for the lower body because they build the glutes, hamstrings and quads while placing minimal stress on the spine. A study from marquette University showed that different types of step ups have different effects on the lower body muscles. Researchers measured lower body muscle activation during a step up, crossover step up, diagonal step up and lateral step up. The crossover step up was best for loading the gluteus medius. The standard step up activated the gluteus medius during the eccentric phase (Going down) and the gluteus maximus and hamstrings during the concentric phase (going up) . Try doing a variety of step ups to maximize the load on the lower body muscles.
Source Fitness RX Magazine