Comparison of knee biomechanical characteristics during exercise between pinnacle and step trainers

Background: A novel stair-climber called a pinnacle trainer (PT) provides both sagittal and frontal plane exercise, making it different from a step trainer (ST), which provides only sagittal plane exercise. Exercise with different trajectories may produce different biomechanical responses. There are currently no guidelines for choosing between a PT and a ST for different training or rehabilitation purposes. Research questions: Are there differences in the electromyographic patterns of lower extremity musculature and biomechanical responses of the knee joint during exercise between using a PT and a ST? Methods: This study utilizes a prospective observational study design. Eighteen healthy males participated in the study. A six-axis force and torque transducer embedded in the machine pedal synchronized with a three-dimensional motion capture system were utilized to measure kinematic and kinetic data of the right knee during the stepping movement. The activities of six lower extremity muscles of the same limb were captured with surface electromyography during exercise on the two trainer types. Results: The co-activation index of the vastus lateralis (VL) and the biceps femoris (BF) recorded during ST exercise was significantly greater than that for the PT exercise. Moreover, exercise using the ST produced a significantly greater knee downward force compared to that for the PT. Exercise with the PT produced a significantly greater internal knee varus moment compared to that for the ST. Significance: The ST provided greater co-activation of the BF and VL and a greater knee joint downward force, which may decrease the antero-posterior displacement of the tibia relative to the femur. Exercise with the PT produced a significant internal knee varus moment and a more balanced muscular activation on the vastus medialis and VL compared to that for the ST, which may decrease the maltracking of the patella.