ENERGETICS AND TIMING OF RELAY EXCHANGES IN SHORT TRACK SPEED SKATING 45

Abstract

Relays in short track speed skating (STSS) involve four skaters racing around a 111m oval for a total distance of 3000-5000m. Typically, exchanges occur every 1½-2 laps, with the skater on the oval (S1) pushing the next skater (S2) at the start of a straightaway. These exchanges offer an opportunity to gain time in an event usually decided by fractions of a second. The purpose of this study was to characterize the timing and energetics of relay exchanges in STSS, identify factors contributing to good and bad exchanges, and correlate these mechanical factors with subjective assessments made by the coach. We examined 12 relay exchanges between ten U.S. National Team members (6 men, 4 women) under simulated race conditions. A 60 Hz, 2-camera pan & tilt system was used to record skater motions. A mid-pelvic point on each skater was digitized, filtered (4th-order Butterworth) and used to compute 3D position, velocity and kinetic energy for each skater. Two factors appear critical for effective relay exchanges: 1. The time for S1 to contact S2 after exiting the turn (tcont), and 2. Energy exchange during skater contact. S1 suffers pre-contact velocity and energy losses averaging 11.7±5.2% which correlate with tcont (R2=0.79) and subjective rankings given by the coach (good, bad, average). During contact, energy is transferred between skaters with an efficiency of 66.8±17.8%. Energy exchange is largely independent of the amount of energy lost prior to contact (R2=0.22) and does not correlate with the coach's ranking or any time measure. Both factors combine to give an overall exchange efficiency (S2 kinetic energy gain/Total S1 kinetic energy loss) of 50.5±9.0%. Our findings suggest pre-contact losses and transfer efficiency combine to determine the overall exchange effectiveness. These factors are independent of each other; the former is visible to the coach and is well correlated with his perception of the exchange, the latter is not, and is influenced by the mechanics of the exchange.