INSTRUMENTED START BLOCKS: A QUANTITATIVE COACHING AID

Abstract

To effect improvement in a skill such as the block start in sprinting, immediate quantitative feedback pertaining to the forces generated during the start is invaluable to both the coach and athlete. The purpose of the present study was to design a set of instrumented starting blocks, appropriate for use in the field, which would provide immediate feedback pertaining to the kinetics of a block start. Design considerations included: resolution of orthogonal force components for right and left foot pedals independently; adjustability to enable and athlete's normal foot and block placement; and adhering to standard international starting block design specifications in terms of dimensions and rigidity. The starting blocks consisted of two standard adjustable stadium starting block pedals suspended clear of the ground via two instrumented axles. The mild steel rod axles were milled to dimensions which allowed the axles to deflect minimally under expected loads. Each axle was attached laterally (and directed medially) from a 230 mm wide mild steel parallel flange channel. This base plate was firmly affixed to the synthetic track surface by six 12 mm commercial shoe spikes. Eight 3 mm student strain gauges were adhered to each axle with 4 gauges aligned to each orthogonal axis. The gauges were incorporated into a Wheatstone Bridge circuitry and arranged to measure the shear force on the axle by utilising the bending moment difference method. Using this bending moment difference method, the magnitude of the force signal recorded was unaffected by the position of force application across the block pedal. Each of the 4 orthogonal channels contained a separate amplifier to magnify the differential signal from the gauges. Calibration was accomplished via static loading of each axle in the orthogonal plane with known loads. The differential signal developed from the strain gauge circuitry under load was amplified and sampled (1000 Hz) by a personal computer using a WIN 30-D A-D converter card. From this data useful variables such as maximum horizontal and vertical force, impulse, block time, block velocity and block acceleration were quantified using custom software and were immediately available to the athlete and coach. Analysis of data obtained from the blocks for state level, national level and the current male 100 m world champion indicated the instrumented blocks were able to provide immediate relevant kinetic data for use by sprint coaches in the field.