Study aim: Step aerobics is a form of aerobic power distinguished from other types of aerobic exercise by its use of an elevated platform. The purpose of this study was to examine how the aerobic exercise “knee up” affects kinematic and kinetic parameters and, above all, the length of the muscle contractions.

Material and methods: The study analysed ten female fitness instructors with at least six years of experience. The task consisted in the knee up move performed using a 15 cm step and music with the beat frequency of 148 BPM. Kinematic and kinetic parameters were recorded using the Vicon system synchronized with two Kistler force plates. OpenSim software was used for calculation of the length of involved muscles.

Results: Ranges in angles and torques suggest that the location that is the most prone to injuries and overtraining is the knee joint, followed by the hip and ankle joints. Greater values of the vertical component of ground reaction forces were observed during stepping down, which suggests greater load to the joints. The greatest work in the move analysed in this study was performed by the sartorius muscle and the tensor fasciae latae muscle.

Conclusions: Despite the benefits that have been demonstrated when step classes are structured correctly and adapted to the participants, further research is needed concerning biomechanical load, exercise prescription, and injury prevention.