Abstract
Knee injuries in cyclists are often thought to result from an imbalance of load during the cycling motion as a consequence of inappropriate bike set-up. Recently, it has been postulated that incorrect foot positioning may be a significant factor in lower limb injury and poor cycling performance. The purpose of this study is to assess the effect of changing the foot position at the shoe-pedal interface on Vastus Medialis (VM) and Vastus Lateralis (VL) activity (mean and mean peak), knee angle and knee displacement.
Maximum power tests were completed on a first visit, with data collection on a second visit recorded at 60% of the subjects maximum. Video footage and surface electromyography (SEMG) from VM and VL muscles was obtained. Data was recorded over 10 crank cycles in 3 experimental conditions; neutral, 10 degrees inversion and 10 degrees eversion using Ethylene Vinyl Acetate (EVA) wedges fitted between the cyclists shoe and the shoe cleat. Raw data (mean SEMG, mean peak SEMG) was obtained using Noraxon and SiliconCOACH measured knee angle and knee displacement. Data was analyzed using Friedmans test with appropriate post hoc tests.
12 male subjects (range 26-45, mean 35.9 years) completed the study. Mean and mean peak SEMG data showed no significant differences between the 3 experimental conditions for VM and VL. VM:VL ratios from raw mean SEMG data demonstrated a decrease in synchronicity in inversion and eversion compared to neutral. Pronators demonstrated most synchronicity in inversion and least synchronicity in eversion. There were statistically significant differences in knee angle and knee displacement between neutral, inversion and eversion (p<0.05). Inversion promoted smaller knee valgus angles and greater knee displacement from the bike. Eversion promoted larger knee valgus angles and a smaller displacement from the bike.
By altering the foot position to either 10 degrees inversion or 10 degrees eversion, knee angle and knee displacement can be significantly influenced. Clinically, subjects who foot type is classified as pronating may benefit from some degree of forefoot inversion posting. Further research on subjects with knee pain needs to be undertaken.
