Relationship Between Lower Limb Biomechanical Characteristics And Running Economy In Youth University Runners

Objective:Running Economy（RE）is recognized to reflect the level of oxygen consumption of runners during submaximal load exercise and is a crucial factor to further improve running endurance performance.Among them,running biomechanical factors have an important moderating effect on RE.However,previous studies on RE and biomechanics have focused more on runners at high training levels,and very limited research has been conducted on the relationship between RE and kinematic,kinetic and spatiotemporal gait characteristics in youth runners.Based on this,in this study,we aimed to investigate the relationship between RE and lower extremity hip,knee and ankle sagittal angles,ground reaction force,lower limb stiffness,contact/flight time and duty factor in youth university runners.To provide a theoretical basis for further clarifying the mechanism of running biomechanical factors regulating RE,and to provide new practical methods and means for youth runners to arrange training.Methods:Thirty male youth runners(age:21±1years,VO_2max:54.61±5.42ml·kg^-1·min^-1)from Shanghai University of Sport were recruited to perform three separate tests in the laboratory,with a 48h interval between the second and the third test.Before each test,subjects were asked to avoid vigorous exercise for 24h and to get enough sleep for at least 8h,with their bodies in a fatigue-free state to guarantee they had no muscle soreness or fatigue.In test 1,the subjects’body composition indicators were measured.In test 2,the subjects’physiological indicators such as RE and VO_2maxat 10 and 12 km·h^-1velocities were measured.In test 3,the subjects’hip,knee and ankle sagittal kinematic indicators,kinetic indicators such as ground reaction force,and spatiotemporal gait indicators such as contact/flight time and duty factor at 10 and 12 km·h^-1velocities were collected.Results:（1）RE at 10 km·h^-1running speed was moderately correlated with the corresponding contact time（r=-0.405,P=0.027）,flight time（r=0.405,P=0.027）and duty factor（r=-0.451,P=0.012）,and was not significantly correlated with the corresponding stride frequency,stride length and vertical oscillation of the centre of mass.The spatiotemporal gait parameters were not correlated with RE at 12 km·h^-1.（2）In the running contact phase,RE at 12 km·h^-1running speed was moderately correlated with the hip flexion angle at toe-off（r=0.374,P=0.042）,peak hip flexion（r=0.381,P=0.038）,knee flexion angle at toe-off（r=0.405,P=0.026）,and ankle dorsiflexion angle at the initial contact phase（r=0.423,P=0.020）were moderately correlated;RE at 10 and 12 km·h^-1running speed was moderately correlated with peak ankle dorsiflexion during the running contact phase（r=0.397,P=0.030;r=0.383,P=0.037）.（3）In the flight phase,RE at 10 km·h^-1running speed was moderately correlated with the peak knee flexion（r=0.457,P=0.011）and knee extension range of motion（r=0.439,P=0.015）;RE at 12 km·h^-1running speed was moderately correlated with the peak hip flexion（r=0.367,P=0.046）and knee peak hip flexion（r=0.367,P=0.046）,peak knee flexion（r=0.416,P=0.022）and peak ankle dorsiflexion（r=0.389,P=0.034）were moderately correlated.（4）During the running contact phase,RE at 10km·h^-1running speed was moderately correlated with the peak active force（r=0.434,P=0.017）,peak propulsive force（r=0.453,P=0.012）and peak braking force（r=-0.428,P=0.018）.RE at 12 km·h^-1running speed was moderately correlated with the peak impact force（r=0.429,P=0.018）and peak braking force（r=-0.496,P=0.005）were moderately correlated.RE at 10 km·h^-1running speed was moderately correlated with the vertical stiffness（r=-0.362,P=0.049）.Conclusion:（1）During the running stance phase,the ankle dorsiflexion angle at foot-strike,hip and knee flexion angle at toe-off,and hip and ankle maximum flexion/dorsiflexion angle were correlated with RE,and during the running swing phase,lower hip,knee and ankle maximum flexion/dorsiflexion angle and smaller knee extension range of motion correlate to better RE.（2）Higher vertical and horizontal ground reaction forces and smaller vertical stiffness may have a negative impact on RE.（3）Longer contact time at low speed and by increasing duty factor may be a new effective strategy for runners to achieve low energy expenditure.