J Guin
A Gidley


J. Guin, A. Gidley

Brigham Young University – Idaho, Rexburg, ID

PURPOSE: To determine if the location of the placement of the foot on the ground relative to the center of mass explains the contradictory results of the metabolic cost of fore- and rear-foot running patterns found in the literature. METHODS: 10 trained runners, aged 17-49, initially ran on a treadmill with their normal heel-strike pattern (HS) at a preferred speed for four minutes. They then ran two, four minute trials at the same preferred speed, using two forefoot footfall patterns: (1) landing out in front of their body (FFOF), near where they landed heel-strike, or (2) landing under their center of mass (FFMID). The order of the forefoot landing patterns was alternated between participants. During each stage, oxygen consumption was collected and the fourth minute was averaged. During the last minute of each stage, 10 seconds of video (240 Hz) was collected, from which 10 consecutive strides were used to calculate kinematic and kinetic data. RESULTS: 3 runners interpreted the FFMID as an exaggerated vertical spring-like running style and were not included in main analysis. The natural running style had lower oxygen consumption (33.10 ± 3.85 ml/kg/min) than FFMID (36.15 ± 3.38) and FFOF (38.21± 3.35). FFOF oxygen consumption was significantly greater than the natural running mechanics (Tukey p-value = 0.037). Forefoot running, regardless of landing location, resulted in greater peak vertical ground reaction force (Fmax: HS: 3.12 BW, FFMID: 3.32 BW, FFOF: 3.28 BW, p > 0.05), shorter contact times (HS: 0.35s, FFMID: 0.31s, FFOF: 0.33s, p > 0.05), and stiffer legs (Kleg: HS: 7.07, FFMID: 8.04, FFOF: 8.10, p > 0.05). Larger Fmax and shorter contact times would mean greater muscle fiber recruitment, especially less economical type 2 fibers. Stiffening legs between running patterns is most likely due to coactivation of muscles about the hip, knee and ankle, thus increasing metabolic cost. The greater oxygen consumption of FFOF than FFMID is additionally explained by the necessary larger breaking force due to contacting the ground out in front of the body. Interestingly, the 3 who were more spring-like had even higher metabolic cost in their forefoot patterns (FFOF: 41.09±3.41; FFMID: 48.70 ± 7.62). Therefore, we conclude that metabolic cost of running is sensitive to the interpretation of foot placement with a novel footfall pattern.

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