1. Power Production During Swim Starting D. Gordon E. Robertson, Ph.D. Vivian L. Stewart, M.Sc. Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA

2. Introduction theory holds that with explosive motions muscles are recruited sequentially from proximal to distal (CAC) vertical jumping research suggests simultaneous recruitment of leg moments (Robertson & Fleming, 1987) arm moments in running contribute little work to propulsion swim starters’ projectile angles are not optimized for maximum flight (< 10 deg)

3. Purpose determine determine whether changes in starting position increases projection angle determine recruitment ordering of moments power contributions of shoulder, elbow, hip, knee and ankle moments to swimming starts

4. Methods eight female varsity or club swimmers filmed at 50 frames/second force plate on starting platform synchronized to 50 Hz three starting positions: –declined platform with toes over edge –declined platform with toes flush with top –level platform with toes over edge flight phase distance calculated from fitting trajectory to least squares quadratic

5. Experimental Setup Forceplatform Cine-camera A/DconverterA/Dconverter ChargeamplifierChargeamplifier Computer

6. Results no significant differences in horizontal flight phase distances among three starting positions (mean distance was 2.0 m) level start produced significantly reduced takeoff velocity (4.9 vs. 6.0 and 6.3 m/s) toes-back start produced greater takeoff angles (mean 4.1 vs. 1.2 and 2.7 deg)

7. Stick-figures of Grab Start

8. Results - Moments greatest peak moments were hip extensors then hip flexors, then knee extensors and ankle plantar flexors and lastly shoulder, elbow and knee flexors

9. Averaged (n=8) Moments of Force Percentage of Thrust 0102030405060708090100 -300 -150 0 150 -150 0 150 Moments (N.m) Toes-over Shoulder Elbow Hip Knee Ankle Extensor Flexor Extensor Flexor

10. Results - Sequencing of Moments hip extensors recruited first later ankle extensors (plantar flexors) followed immediately by knee extensors hip flexors recruited to perform negative power synchronously with ankle/knee extensors

11. Variability of Moment Powers 0102030405060708090100 Percentage of Thrust -1000 0 1000 -1000 0 1000 0 2000 3000 4000 Powers (watts) Toes-over Hip Knee Ankle

12. Results - Powers greatest variability with hip powers, least with ankle powers largest positive work by hip extensors, then knee extensors and then ankle plantar flexors hip flexors perform negative work prior to takeoff

13. Averaged (n=8) Moment Powers Percentage of thrust -2000 -1000 0 1000 0 Powers (watts) 0102030405060708090100 Toes-over Shoulder Elbow Hip Knee Ankle

14. Discussion some evidence to support proximal to distal sequencing (i.e., hips preceded knee and ankle) knee and ankle extensors recruited simultaneously (like vertical jumping) hip moments dominated thrust negative work by hip flexors transfer energy from upper body to whole body (transfer of momentum)