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The Official Journal of the Korean Academy of Kinesiology 2010;12(4):81-94.
Published online October 30, 2010.
The Study of Optimal Bending Stiffness of Marathon Shoe Sole by using Energy Return(Joint Power Method) in Lower Extremity Joint
Chang-Soo Kwak, Chung-Il Lee, Chung-Il Lee, Oh-Bok Kwon, Oh-Bok Kwon
Hallym University
SungKyunKwan University
Correspondence:  Chang-Soo Kwak,
Email: cskwak@hallym.ac.kr
Received: 2 September 2010   • Accepted: 8 October 2010
Abstract

INTRODUCTION
The purposes of this study were to determine optimal bending stiffness of a marathon shoe which increased bending stiffness, rearfoot control and impact force absorption of marathon shoe sole, and to compare usual methodology with energy return method(joint power method) for determining optimal midsole hardness.
METHOD
The subjects employed for this study were 13 college students who did not have lower extremity injuries for the last one year and whose running pattern was rearfoot striker of normal foot. The shoes used in this study had 4 different midsole hardness of shoe A 40, shore A 50, Shore A 60, Shore A 70 and bending stiffness was 0.05 N.m/deg - 0.4 N.m/deg. The lower leg motion during at the speed of 4m/sec were measured using a force platform and motion analysis system.
RESULT
The findings of the study were as follows : 1. It was appeared that total contact time of each phase was decreased as the increment of marathon shoe midsole hardness. 2. Maximal impact force and maximal impact force loading rate increased except shore A 40 as the midsole hardness increased. It was shown that Shore A 40 and Shore A 70 were not fitted for a marathon shoe. 3. Initial achilles tendon angle of each midsole hardness was shown similar results, and a maximal achilles tendon angle and a angular displacement of achilles tendon angle was the largest at shore A 40 and the smallest at shore A 50. 4. Initial rearfoot angle was the smallest at shore A 60 and the largest at shore A 70. A minimum rearfoot angle and the displacement of rearfoot angle was the largest at shore A 50 and the smallest at shore A 60. 5. Maximal power in 1st contact contact phase was not shown any particular tendency, but in 2nd contact phase maximal power was increased as midsole hardness was increased and distal joint. 6. The energy in 1st phase was produced at hip joint and absorbed at knee joint and ankle joint, in 2nd contact phase the energy was largest at knee joint and increased as midsole hardness was increased.
CONCLUSION
The study confirmed the previous findings that the midsole hardness of marathon shoe did influence on impact force absorption, rearfoot stability and joint energy. The optimal midsole hardness of marathon shoe was most fitted at shore A 50 and the next shore A 60 by usual shoe methodology study. It was proved that shore A 40 and shore A 70 were not fitted for marathon shoe sole. Also it was appeared that shore A 50 was the most fitted for marathon shoe sole by new attempted joint power method results that the joint energy was largely generated as midsole hardness was most flexible or hard. However, the study suggests that the similar studies like energy return were performed verified optimal bending stiffness because these conclusions were based only on tendencies of current results.
Keywords: Marathon shoe, Energy return, Midsole hardness


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