Effects Of Cycling Cadence And Posture On Biomechanics Characteristics Of Human Lower Extremity At Constant Power Output

Effects of cadence,grade and posture on lower extremity joint kinetics in cycling have been widely studied,but few studies have analyzed them with respect to both magnitude change and phase shift in the time domain.On the other hand,whether the functional role of lower extremity joints changed with posture and level is still largely unknown.Purpose:The first purpose of this study was to investigate the effects of cadence on lower extremity joint kinetics and motion control in cycling.The second purpose was to investigate the interaction between cycling grade and posture on lower extremity joint kinetics and motion control in cycling.With changed cycling grade and posture,the functional role of joint would be changed.The third purpose was to investigate the effect of cycling posture on ankle joint stiffness curve.Methods:Sixteen participants cycled at 250 W power at level seated?LS?with two cadences?65 and 110 RPM?,level seated?LS?,uphill seated?US?and standing?ST?at 15%grade conditions,respectively.A motion analysis system and a custom instrumented pedal were used to collect ten cycles of kinematics and pedal reaction force data.The whole cycle was divided into eight phases according to crank angle?i.e.1st Phase range from 0°to 45°,2nd Phase range from 46°to 90°,etc.?.A two-factor mixed model repeated measures MANOVA was used to examine the effects of cadence,environment,task and phase on selected variables in the magnitude metrics.Cross-correlation analysis was used to examine the effects of cadence on selected variables in the time domain?p<.05?.Results:Phase and cadence interactions were observed on lower extremity joint and crank moment?p<.05?.The results revealed that cadence affects the functional role of hip?Phase 7?and ankle?Phases 1 and 2?joint moment?p<.05?.However,we did not observe a similar phenomenon in the knee.The cross correlation analysis showed significant shifts in the joint and crank moments objectively in the time domain(Joint_hip r?5°?=.97,Joint_knee r?13°?=.97,Joint_ankle r?47°?=.94 and crank r?4°?=.98).Cycling condition and phase interactions were observed on lower extremity joint and crank moment?p<.05?.The post-hoc ANOVA and pairwise comparison results revealed that posture affects the functional role of hip?Phase 8?,knee?Phase 3 and 6?,ankle?Phase 7 and 8?joint and crank?Phase 8?moment?p<.05?.However,we did not observe a similar phenomenon in lower extremity joint and crank moment between level and uphill seated cycling?p>.05?.We observed that cycling task influenced the ankle stiffness curve.Conclusion:The effect of cadence on lower extremity joint kinetics and functional role significantly.Hip as the leading source joint,it changed its functional role during phase 7^th with the changed cadence to supply extra energy.Ankle joint changed its functional role during phase 1^st and 2^nd to deliver energy to crank as much as possible with cadence increased.We did not observe a similar phenomenon on knee joint,due to the knee as the coordinate joint which obtained the energy from the hip and transferred to the ankle.Knee was in the role of source joint at the beginning of power phase.The cycling grade and posture effects on human lower extremity motion control from a biological perspective.Analyzing the joint moments with dividing into eight phases according to crank angle,which revealed whether the functional role of joint moments were statistically significant with changing cycling condition.The cycling task also effects on the ankle stiffness curve.We could not simply consider it was a quantitative change,it reflected the central nervous system did active adjustment according to different tasks.