Kinetic Characteristics of Distance Running on Downhill Slope

Abstract

The purpose of this study was to investigate kinetic characteristics such as ground reaction forces (GRFs) and joint torques of the lower limb joints in downhill running for distance runners on overground. Six male distance runners were asked to run at three running speeds (3.3, 4.2, and 5.0 m/s) on the slopes of different grades (0, -3.2, -6.4, and -9.1 %) in which two force platforms were mounted. A two dimensional link model was used to calculate joint torques and joint powers of the lower limb joints. In spite that the downward velocity of the CG at the foot contact increased consistently as the grade increased, the impact peak of vertical GRF and the peak loading rate defi ned as maximum rate of change of the vertical GRF did not increase consistently as the grade increased. The runners on steep downhill conditions would be able to avoid excessive impact load by contacting with the ground in more extended hip position and increasing knee fl exion velocity after the foot contact. The negative power of the knee after the foot contact was larger for -9.1 % downhill than the level condition, which revealed the eccentric load on the knee extensors increased in the steep downhill condition. The hip extensors exerted negative power with hip fl exion just after the foot contact in -6.4 and -9.1 % downhill conditions so that the runners could absorb the impact force and mechanical energy.

Lower Limb Joint Kinetics During Moderately Sloped Running

“…Similarly, the increase in hip power generation during early stance in incline running indicates an increase in the rate of concentric loading. These results corroborate the findings of Yokozawa et al 27 with regard to power absorption during decline running as well as those of Swanson and Caldwell 28 and Roberts and Belliveau 29 with regard to increased hip power generation with incline running, albeit on a lower-grade slope. It should be noted that we held speed constant to standardize findings.…”

Muscle activities of the lower limb during level and uphill running

“…Increased ILP activity during UR would play an important role in faster and greater hip flexion in FRP. In SRP, greater muscle torques by GMAX, HAMS, and ADD during UR at the high speed increased the net hip extension torque and knee flexion torque, which would subsequently contribute to rapid backward swing of the leg before foot contact (Yokozawa et al, 2003). Contrary to our expectation, the knee extension torque by VAS in SP was significantly smaller during UR at all the speeds.…”

“…Heise et al (1996) reported that economical runners exhibited a greater amount of coactivation of RF and HAMS during SP when compared with noneconomical runners. In addition, the forward lean of the trunk is greater during UR throughout one running cycle (Paradisis and Cooke, 2001;Yokozawa et al, 2003). This indicates that the increased coactivation of RF and HAMS during UR in the present study would help to maintain the trunk in a forward-leaning position.…”

“…Yokozawa et al (2003) reported that the step frequency was greater during UR on a slope of 9.1% than during LR at 5.0 m/s despite the lack of any significant differences in the step length and step frequency between LR and UR at 4.2 and 3.3 m/s. Therefore, the increase in muscle activation during UR at high speed would facilitate an increase in the step frequency; however, the muscle activation did not increase during UR when compared with LR at medium and slow speeds because the runners used the same step length and step frequency as those used during LR.…”

“…5 and 6) contributed to faster and greater hip flexion in the recovery phase (Yokozawa et al, 2003). The finding that ILP contributed more than RF to the hip flexion torque during UR may be attributed to the fact that there was no significant difference in the net knee torque between LR and UR (Fig.…”