Effects Of 12-week Cadence Retraining On Impact Force And Lower Limb Biomechanics

Purpose With the development of nationwide fitness,running has become one of the most popular sports in China.However,corresponding to such a large-scale running boom,it is the high incidence of running injuries.High impact loads at initial contact during running were considered to be one of the risk factors for running-related injuries such as stress fractures.Studies found that running impact(impact peak,loading rate,etc.)could be reduced by acutely increasing the step frequency.However,currently there are few studies on increasing step frequency as a retraining method for long-term retraining,and the previous studies have shortcomings such as insufficient number of subjects,short training time,and lack of evaluation parameters.Therefore,the purpose of this study was to explore the effects of cadence retraining on running impact,kinematics and kinetics of the lower extremity,namely hip,knee,and ankle,through 12-week cadence retraining,expecting to reduce the running impact and the risk of running injuries.Methods Thirty healthy male recreational runners were recruited and randomly divided into a cadence retraining group(CAD)and a control group(CON),with 15 in each group.All subjects participated in a 12-week cadence retraining protocol,3 times a week,with 5 to 48 minutes for each training(increasing with the number of weeks).The CAD group run at preferred speed with 7.5% increase in step frequency,while the CON group run at preferred speed and step frequency.Before and after the 12-week training,participants were required to run across a 10-meter runway at 3.33 m/s and preferred step frequency,with 10 Vicon infrared cameras(sampling frequency: 100Hz)and 2 Kistler 3D force plates(sampling frequency: 1000Hz)to simultaneously collect the ground reaction force and the trajectory of mark point.A repeated measures twoway ANOVA was used to compare the effects of time factors(before and after training)and group factors(CAD and CON)on impact mechanics,kinematics,and kinetics.Results 1)The preferred step frequency of the CAD group increased significantly by 5.7% after retraining(p < 0.05),and the step length significantly decreased(p < 0.05).No significant differences were observed for the CON group.In addition,after retraining,the step length of the CAD group was significantly reduced by 5% compared with the CON group(p < 0.05).2)The impact peak,average loading rate,and maximum loading rate of the CAD group were significantly reduced after training(p < 0.05),and there were no significant differences in the CON group.Moreover,the impact peak of the CAD group after retraining was significantly reduced by 12% compared to the CON group(p < 0.05);3)The vertical velocity of center of gravity,the angle between the foot and the ground,the ankle angular velocity,and the sagittal distance between the ankle and hip joints were significantly reduced at initial contact(p < 0.05).During stance,the vertical excursion of center of gravity,the peak knee flexion angle,and the knee joint range of motion were also significantly decreased in the CAD group after training(p < 0.05).No significant differences were obtained for the CON group.In addition,after retraining,the vertical excursion of center of gravity of the CAD group was significantly reduced by 10.3% compared with the CON group(p < 0.05);4)The impact impulse,braking impulse,and vertical momentum at initial contact of the CAD group were significantly decreased after training(p < 0.05),and significant increase of leg stiffness was observed in the CAD group(p < 0.05).However,there were no significant changes in the CON group.Conclusion The results of this study showed that the 12-week cadence retraining significantly increased the cadence of the CAD group by 5.7%,and effectively reduced the impact force.The significant decrease in impact peak,loading rate,and other factors after training suggested that increasing the step frequency as a retraining method could reduce the risk of running injuries.In addition,after training,the foot became more flat at initial contact and the strike position was closer to center of gravity.Moreover,the decrease in peak knee flexion angle and the vertical excursion of center of gravity during stance resulted in an increase in leg stiffness.Which indicated that cadence retraining could cause biomechanical adaptive changes during running.