Subjects took a 5 min break between bouts A handheld digital tachometer Shimpo

Subjects took a 5 min break between bouts a handheld

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USA, Waukesha, WI, USA). Subjects took a 5-min break between bouts. A handheld digital tachometer (Shimpo DT- 107A; Electromatic Equipment Inc., Cedarhurst, NY, USA) was used to verify all treadmill velocities. To allow famil- iarization, subjects breathed through an expired-gas analysis system (True One 2400; Parvo Medics, Salt Lake City, UT, USA) during this visit. Within 1 min after the completion of each 5-min trial, we obtained a ff nger-prick blood sample for blood [La] determination in duplicate (YSI 2300 lactate analyzer; YSI Incorporated, Yellow Springs, OH, USA). 2.2.3 Visits 2 and 3 Visits 2 and 3 were completed in random order, with at least 72 h between visits. Prior to their warm-up, subjects had their height, weight, and body composition reassessed. Subjects began running with a 15-min warm-up at their own selected speed ≤ 14 km·h −1 , in their own shoes. Fol- lowing the warm-up, all subjects completed 4 × 5-min bouts at 14 km·h −1 on a ffat Woodway ELG treadmill (Woodway USA) while wearing each of the shoe conditions in a ran- domized order. In-between bouts, subjects took an ~ 3-min break while they changed shoes. Note that runners mechani- cally adapt their biomechanics very quickly in response to changes in surface stiffness [ 18 ]. Subsequently, subjects completed another 4 × 5-min trial at 18 km·h −1 for men and 16 km·h −1 for women, as previously described. Throughout the running test, heart rate (Polar H7; Polar Electro, Kem- pele, Finland) was recorded at 5-s intervals and expired gases were continuously measured to determine VO 2 , carbon dioxide production (VCO 2 ), minute ventilation ( V E ), and res- piratory exchange ratio (RER). The mean VO 2 determined during the last 2 min of each running stage was expressed as running economy (ml·kg −1 ·min −1 ), gross oxygen cost of transport (O 2 COT; ml·kg −1 ·km −1 ), and energetic cost (W·kg −1 ) using the Peronnet and Massicotte equation [ 19 , 20 ]. In our laboratory, the typical error of measurement [ 21 ] of submaximal VO 2 was 1.9%. Rating of perceived exertion (RPE) was determined using a 1–10 Borg RPE scale upon completion of each interval [ 22 ]. Blood [La] was assessed at the completion of each running velocity interval series. Biomechanical measures (stride rate, stride length, con- tact time, and ffight time) were determined using high-speed video analysis (240 frames·s −1 ) while running at each veloc- ity and shoe condition [ 23 ]. The average of each biome- chanical parameter during the ff nal 30-s of each running speed and shoe condition was used for analysis. We also used the video recordings to determine the foot-strike pat- terns of the runners during all trials (rearfoot strike vs. mid/ forefoot strike). However, only 5 of the 24 subjects qualiff ed as mid/forefoot strikers, therefore our sample did not permit an evaluation of foot-strike pattern interaction on the ener- getic cost differences between shoes.
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