Therefore, the purpose of this study was to determine the difference in the frequency Mdm2 inhibitor content of the impact shock and its subsequent attenuation between footfall patterns. It was hypothesized that RF running would result in greater peak tibial acceleration and signal power in the higher frequency range, representative of the vertical GRF impact peak, compared with FF running whereas tibial acceleration power in the lower frequency range, representative of the vertical GRF active peak, would be greater in FF than in RF running. Although RF running results in greater tibial acceleration than FF running,23 head acceleration may be similar because shock attenuation increases in response

to greater impact loads to maintain head stability for proper vestibular and visual function.14, 17, 22 and 26 Therefore, it was hypothesized that peak head acceleration and signal power in the lower and higher frequency ranges would not differ between footfall patterns. As a result of the previous observation that impact shock was greater with RF than FF running,23 it was hypothesized that RF running would result in greater shock attenuation of the higher range frequency

components than GSK2118436 price FF running. However, previous studies have indicated a reduced capacity for attenuation of lower frequency components,14 and 26 therefore it was hypothesized that no difference would be observed in the degree of attenuation of the lower frequency components between footfall patterns. Nineteen habitual RF runners and 19 habitual FF runners participated in this study (Table 1). Sample size estimation determined that 12 runners per group were required to achieve a power of 0.8 and an alpha level of 0.05. All participants were healthy, experienced runners and did

not have a history of cardiovascular or neurological problems. Inclusion criteria required that participants completed a minimum of 16 km/week at a minimum preferred running speed of 3.5 m/s and had not developed an injury to the lower extremity or back within the past year. Participants were divided into an RF group or an FF group based almost on the footfall pattern habitually performed when distance running. The participants’ habitual footfall pattern was determined by assessing the strike index, vertical GRF profile, and sagittal plane angle ankle at touchdown while the participants ran at his or her preferred speed over a force platform (OR6-5; AMTI, Watertown, MA, USA).42 Given that approximately 20%–25% of runners are either MF or FF runners, participants classified as either MF or FF were place in the FF group to ensure appropriate statistical power. All participants read and completed an informed consent document and questionnaires approved by the University Institutional Review Board.