Force-velocity profiling in sled-resisted sprint running: Determining the optimal conditions for maximizing power (2016)

The measurement of power-velocity and force-velocity relationships offers valuable insight\ninto athletic capabilities. The qualities underlying maximum power (i.e. optimal loading\nconditions) are of particular interest in individualized training prescription and the enhanced\ndevelopment of explosive performance. While research has examined these themes using cycle\nergometers and specialized treadmills, the conditions for optimal loading during over-ground\nsprint running have not been quantified. This thesis aimed to assess whether force-velocitypower\nrelationships and optimal loading conditions could be profiled using a sled-resisted\nmultiple-trial method overground, if these characteristics differentiate between recreational\nathletes and highly-trained sprinters, and whether conditions for optimal loading could be\ndetermined from a single sprint. Consequently, this required understanding of the friction\ncharacteristics underlying sled-resisted sprint kinetics. Chapter 3 presents a method of\nassessing these characteristics by dragging an instrumented sled at varying velocities and\nmasses to find the conversion of normal force to friction force (coefficient of friction).\nMethods were reliable (intraclass correlation [ICC]>0.99; coefficient of variation\n[CV]<4.3%) and showed the coefficient of friction was dependent on sled towing velocity,\nrather than normal load. The ‘coefficient of friction-velocity’ relationship was plotted by a\n2nd order polynomial regression (R²=0.999; P<0.001), with the subsequent equation\npresented for application in sled-resisted sprinting. Chapter 4 implements these findings,\nusing multiple trials (6-7) of sled-resisted sprints to generate individual force-velocity and\npower-velocity relationships for recreational athletes (N=12) and sprinters (N=15). Data were\nvery well fitted with linear and quadratic equations, respectively (R²=0.977-0.997; P<0.001),\nwith all associated variables reliable (effect size [ES]=0.05-0.50; ICC=0.73-0.97; CV=1.0-\n5.4%). The normal loads that maximized power (mean±SD) were 78±6 and 82±8% of bodymass,\nrepresenting an optimal force of 279±46 and 283±32 N at 4.19±0.19 and 4.90±0.18\nm.s-1, for recreational and sprint athletes respectively. Sprinters demonstrated greater absolute\nand relative maximal power (17.2-26.5%; ES=0.97-2.13; P<0.02; likely), with much greater\nvelocity production (maximum theoretical velocity, 16.8%; ES=3.66; P<0.001; most likely).\nOptimal force and normal loading did not clearly differentiate between groups (unclear and\nlikely small differences; P>0.05), and sprinters developed maximal power at much higher\nvelocities (16.9%; ES=3.73; P<0.001; most likely). The optimal loading conditions for\nmaximizing power appear individualized (range=69-96% of body-mass), and represent much\ngreater resistance than current guidelines. Chapter 5 investigated the ability of a single sprint\nto predict optimal sled loading, using identical methods to Chapter 4 and a recently validated\nprofiling technique using a single unloaded sprint. Power and maximal force were strongly\ncorrelated (r=0.71-0.86), albeit with moderate to large error scores (standardized typical error\nestimate [TEE]=0.53-0.71). Similar trends were observed in relative and absolute optimal\nforce (r=0.50-0.72; TEE=0.71-0.88), with estimated optimal normal loading practically\nincomparable (bias=0.78-5.42 kg; r=0.70; TEE=0.73). However optimal velocity, and\nassociated maximal velocity, were well matched between the methods (r=0.99; bias=0.4-1.4%\nor 0.00-0.04 m.s-1; TEE=0.12); highlighting a single sprint could conceivably be used to\ncalculate the velocity for maximizing horizontal power in sled sprinting. Given the prevalence\nof resisted sprinting, practitioners and researchers should consider adopting these methods\nfor individualized prescription of training loads for improved horizontal power and\nsubsequent sprinting performance.