A Case Study Of Muscle Activity In Giant Slalom Skiing

  • R. A. Hintermeister
  • C. L. Suplizio
  • C. J. Dillman
  • R. J. Steadman
Keywords: winter sports, muscle acticity, slalom, EMG

Abstract

Speed of movement respresents the ability essential for successful performance of a sportsman in many branches of sport. This is especially important in ski-jumping where the skier must develop optimum vertical velocity corresponding to the correct ski-jumping technique in extremely complex and demanding inertial environment. The objective of this investigation was to establish the size of the attained vertical velocity measured both in the field and laboratory conditions; its stability and relation to the jump length. The results of the investigation will be, above all, useful to experts in developing the take-off techniqueElectromyography (EMG) and video data from a single female US. Ski Team member were acquired during giant slalom (GS) skiing at Beaver Creek, Colorado. The purpose of the testing was to examine muscle activity relative to the skiing motion. Muscles on the right side of the body, consisting of the lower leg (anterior tibialis (AT) and lateral gastrocnemius (LG», thigh (vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), semitendinosus (ST), gracilis (Gr), and gluteus maximus (GM», and trunk (rectus abdominis . (RA), external oblique (EO), and erector spinae (ES» were monitored. Maximal voluntary contractions (MVC) were performed pre- and post-skiing to provide a relative reference for the amplitude of muscle activity (%MVC). EMG during skiing was monitored via a four channel telemetry unit. The eleven muscles were partitioned into three sets. Three skiing trials of a seven gate GS course were completed for each set. Peak amplitude (uv) and time measures (ms) were digitized and averaged across trials for each gate. In six of the eleven muscles, the peak activity occurred when the right leg was the outside leg in a turn (turns 1, 3, 5, 7). The exception to this pattern was for the ES muscles of the lower back. %MVC ranged from 27% (EO at gate 4) to 206% (Gr at gate 5). The coeffcients of variation (CV) ranged from 2.3 (VM at gate 4) to 130% (EO at gate 4), indicating a large amount of variation in arnplitude for several muscle groups. The mean duration of muscle activity across all three muscle sets was consistent, ranging from 1.08 to 1.56 s. Roughly two-thirds of the CV's were less than 14%, indicating that the timing was more consistent than the peak EMG. This case study of EMG activity in GS skiing revealed substantial muscle activity at large percentages of MVC with considerable variation. A large amount of cocontraction between opposing muscles and relatively long duration of muscle activity suggest a quasi static nature of muscle activity during a GS turn. These findings have implications for dryland training of GS skiers. of ski jumpers, and in building a model of performance in ski jumping.