America’s Cup sailing: Biomechanics and conditioning for performance in grinding
Pearson, Simon Nathaniel
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Grinding is integral to tacking and gybing manoeuvres in America’s Cup sailing. Grinding is a standing position cyclic upper body task requiring manual arm cranking of winches, which control movement of the mast and sails. Limited information exists on biomechanical factors involved in grinding performance. This thesis determined technique and muscular performance characteristics of sailors related to grinding performance, and effects of a training intervention on grinding performance. Reliability of grinding ergometer performance testing was evaluated across direction, load and heel conditions. In all conditions relative performance between individuals was consistent (r = 0.84-0.99) and the grinding performance test differentiated well between individuals. External work had lower overall variation (1.6-3.9%) than peak power (1.3-5.4%), especially when grinding against greater loads. Grinding performance was less consistent in heeled conditions (4.6-6.9%) than on the flat, but grinding direction did not affect reliability. Performance changes over 4% could be interpreted with confidence. Peak torque occurred at 95° (77 N m) and 35° (69 N m) for forward and backward grinding respectively (0° = grinding crank vertically up). Torque of >50 N m was maintained through 72% of the cycle during forward grinding but only 47% for backward grinding. Differences were attributed to a greater spread of active muscles throughout the cycle for forward grinding, and contrasting movements contributing most to torque – upper body push for forward grinding and pull for backward grinding. Variant characteristics of the two grinding directions provide some explanation for the significant advantage (+8.0%, p<0.001) when grinding in pairs with an anterior-posterior heel compared to a medio-lateral heel. Movement characteristics did not readily explain why an anterior-posterior heel may be more advantageous under higher grinding loads (1.0%, p = 0.254), while medio-lateral heel is better at lower loads (2.0%, p = 0.017). Muscular performance of sailors, examined using an instrumented Smith machine, showed force and 1RM strength were greater in the bench press by ~17%. Velocity and power output were greater for the bench pull across the range of loads with the difference increasing exponentially as load increased to over 400% higher at 1RM load. Bench press 1RM and maximum force capability demonstrated strongest correlations with forward grinding performance (r = 0.88-0.99 and 0.87-0.99 respectively) with the relationship increasing with grinding load. There was a strong relationship for backward grinding with bench pull maximum power (r = 0.85-0.98) in addition to 1RM (r = 0.90-0.95) and maximum force (r = 0.87-0.95). Backward grinding performance showed greater improvements in the power-focussed training group than the control group for moderate (+1.8%) and heavy load (+6.0%) grinding in the intervention study. Changes in maximum power output and power at 1RM had large correlations (r = 0.56-0.61) with changes in both moderate and heavy load grinding performance. Time to peak force explained 70% of the change in heavy load grinding performance. Performance benefits from the training intervention were not entirely clear, but the likelihood of a detrimental effect was low (<5%), therefore further training intervention was recommended.