Novel Field Test To Identify Critical Velocity During Non-linear Running

Abstract

PURPOSE: Athletes and coaches have interest in identifying specific work rates and related physiology discriminating sustainable vs unsustainable exercise intensity. A threshold intensity for running, termed Critical Velocity (CV), is the boundary between stable metabolism and progressively disturbed metabolism (& ensuing fatigue). We aimed to develop a simple short duration field test (Critical Velocity Shuttle Test, CVST), to accurately and reliably identify CV during intermittent non-linear running. Further, we tested the hypothesis that CV during dynamic non-linear running is distinctly different (i.e. lower) than linear running. METHODS: Young healthy adults performed a custom designed 7 minute shuttle test consisting of intermittent dynamic non-linear sprint running. Each sprint covered 30 feet out and back, with rest time between maximal efforts of 15 secs for the first 3 mins, 10 secs for the next 2 mins and no rest for the final 2 mins. The CVST was performed twice over the course of 2 weeks to examine test reliability (N=6). In addition, two separate validation trials inclusive of 5% above or below shuttle test end velocity (EV; N=8) were conducted where blood lactate was measured every 4 mins until exhaustion. To compare CV during linear and non-linear running, 10 subjects completed 3 ‘linear’ time trial efforts (1.6, 2.4, 5KM) and the CVST. RESULTS: Average total distance and shuttle test EV were not significantly different between visits (visit 1 = 864±9 m and 3.23m/s± 0.05 vs visit 2 = 900±13 m and 3.21m/s±0.06, respectively). All subjects who ran 5% above shuttle test end velocity fatigued prior to 20 mins and displayed unstable blood lactate, whereas a stable lactate profile was observed for all running 5% below EV. Non-linear running CV obtained from the CVST was significantly lower than linear running CV ([INCREMENT]-17±2%), highlighting the importance of modality for threshold determination. CONCLUSIONS: Collectively, the CVST provides a repeatable and accurate estimate of critical work rate for dynamic intermittent non-linear running activity. Accordingly, the CVST could be employed by coaches and athletes to better understand the physiological impact and rate to fatigue of their chosen work rates during competition.