Jin-Kyu Lee

Effect of the sagittal ankle angle at initial contact on energy dissipation in the lower extremity joints during a single-leg landing

BACKGROUNDnDuring landing, the ankle angle at initial contact (IC) exhibits relatively wide individual variation compared to the knee and hip angles. However, little is known about the effect of different IC ankle angles on energy dissipation.nnnRESEARCH QUESTIONnThe purpose of this study was to investigate the relationship between individual ankle angles at IC and energy dissipation in the lower extremity joints.nnnMETHODSnTwenty-seven adults performed single-leg landings from a 0.3-m height. Kinetics and kinematics of the lower extremity joints were measured. The relationship between ankle angles at IC and negative work, range of motion, the time to peak ground reaction force, and peak loading rate were analyzed.nnnRESULTSnThe ankle angle at IC was positively correlated with ankle negative work (ru202f=u202f0.80, R2u202f=u202f0.64, pu202f<u202f0.001) and the contribution of the ankle to total (ankle, knee and hip joint) negative work (ru202f=u202f0.84, R2u202f=u202f0.70, pu202f<u202f0.001), but the ankle angle was negatively correlated with hip negative work (ru202f=u202f-0.46, R2u202f=u202f0.21, pu202f=u202f0.01) and the contribution of the hip to total negative work (ru202f=u202f-0.61, R2u202f=u202f0.37, p <u202f0.001). The knee negative work and the contribution of the knee to total negative work were not correlated with the ankle angle at IC. The ankle angle at IC was positively correlated with total negative work (ru202f=u202f0.50, R2u202f=u202f0.25, pu202f<u202f0.01) and negatively correlated with the peak loading rate (ru202f=u202f-0.76, R2u202f=u202f0.57, pu202f<u202f0.001).nnnSIGNIFICANCEnThese results indicated that landing mechanics changed as the ankle angle at IC increased, such that the ankle energy dissipation increased and redistributed the energy dissipation in the ankle and hip joints. Further, these results suggest that increased ankle energy dissipation with a higher IC plantar flexion angle may be a potential landing technique for reducing the risk of injury to the anterior cruciate ligament and hip musculature.

Effects of mid-foot contact area ratio on lower body kinetics/kinematics in sagittal plane during stair descent in women

The mid-foot contact area relative to the total foot contact area can facilitate foot arch structure evaluation. A stair descent motion consistently provides initial fore-foot contact and utilizes the foot arch more actively for energy absorption. The purpose of this study was to compare ankle and knee joint angle, moment, and work in sagittal plane during stair descending between low and high Mid-Foot-Contact-Area (MFCA) ratio group. The twenty-two female subjects were tested and classified into two groups (high MFCA and low MFCA) using their static MFCA ratios. The ground reaction force (GRF) and kinematics of ankle and knee joints were measured while stair descending. During the period between initial contact and the first peak in vertical GRF (early absorption phase), ankle negative work for the low MFCA ratio group was 33% higher than that for the high MFCA ratio group (p<0.05). However, ankle negative work was not significantly different between the two groups during the period between initial contact and peak dorsiflexion angle (early absorption phase+late absorption phase). The peak ankle dorsiflexion angle was smaller in the low MFCA ratio group (p<0.05). Our results suggest that strategy of energy absorption at the ankle and foot differs depending upon foot arch types classified by MFCA. The low MFCA ratio group seemed to absorb more impact energy using strain in the planar fascia during early absorption phase, whereas the high MFCA ratio group absorbed more impact energy using increased dorsiflexion during late absorption phase.

Transition versus Continuous Slope Walking: Adaptation to Change Center of Mass Velocity in Young Men

During continuous uphill walking (UW) or downhill walking, human locomotion is modified to counteract the gravitational force, aiding or impeding the bodys forward momentum, respectively. This study aimed at investigating the center of mass (COM) and center of pressure (COP) velocities and their relative distance during the transition from uphill to downhill walking (UDW) to determine whether locomotor adjustments differ between UDW and UW. Fourteen participants walked on a triangular slope and a continuous upslope of 15°. The kinematics and COPs were obtained using a force plate and a motion capture system. The vertical velocity of the COM in the propulsion phase, the horizontal distance between the COM and COP at initial contact, and the duration of the subphases significantly differed between UDW and UW (all p < 0.05). Compared with the results of UW, longer durations and the deeper downward moving COM in the propulsion phase were observed during UDW (all p < 0.05). Additionally, a shorter horizontal distance between the COM and COP at initial contact was associated with a slower vertical COM velocity in the propulsion phase during UDW. The reduced velocity is likely a gait alteration to decrease the forward momentum of the body during UDW.