This is the first study investigating preferred (self-selected) step frequency (PSF) in relation to optimal step frequency (OSF) during running at different speeds outside the laboratory. OSF was defined as… Click to show full abstract
This is the first study investigating preferred (self-selected) step frequency (PSF) in relation to optimal step frequency (OSF) during running at different speeds outside the laboratory. OSF was defined as the SF at which heartrate (HR) showed a minimum during running at a constant speed. We aimed for a high ecological validity, which prohibits the direct measurement of oxygen consumption. HR was used as a proxy of energy cost, as has previously been validated. After a practice session, 21 experienced recreational runners (12 female) ran in an out-and-back manner on a straight flat tarmac lane in three main sessions: (1) 27 min at fixed comfortable speed with PSF, (2) at the same speed but with different imposed SFs (range 140-200 steps min-1) and at PSF and (3) similarly but at 15% higher speed. Runners were paced by a cyclist. Second order polynomials fitted the individual SF-HR relations well. At comfortable speed (3.04 ± 0.28 m s-1) mean r2 was 0.81 (range: 0.40-0.99) and PSF and OSF respectively were 165 ± 8 and 171 ± 8 steps min-1 (p < .05). Both increased (p < .05) by 3 steps min-1 at the 15% higher speed. SFs were negatively (-0.66 < r < -0.49, p < .05) related to body height. From the individual SF-HR relations we deduced that changing PSF to OSF would decrease median HR only by 0.5 beats min-1, but for two participants meaningful reductions (1-3 beats min-1) were predicted. Outdoors, experienced recreational runners ran at a PSF slightly below OSF, but for most of them, there was little to gain in terms of HR reductions by increasing their SF to OSF.
               
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