Effect of Different Sprint Start Techniques on Lower- limb Stiffness in Sprint Runners

Join angle of motion and muscle lever arms can be changed in different sprint start techniques. These changes could affect on leg and joint stiffness. The purpose of current study was to test the effect of three different sprint start techniques, (long, medium and short) on lower-limb stiffness. 15 runners (age of 24 ± 3 years; height of 170 ± 10.5 cm; weight of 75 ± 7.5 Kg) were selected in this study. A camera (200 Hz; SIMI) and a force plate (1000 Hz; Kistler) were used to collect marker coordination and ground reaction forces, respectively. Based on mass-spring model, leg stiffness was calculated dividing peak ground reaction force by the leg length. Joint stiffness was also estimated dividing the muscle moment of force by joint angular displacement. leg stiffness significantly different among three starting techniques (P< 0.001). Mean of leg stiffness in the long start technique was 16.8 % and 48% higher than medium and short, respectively. Ankle and knee joints stiffness were significantly higher in long starting technique in compared to two other techniques (p< 0.001). Lower limb stiffness could be altered by changing starting technique from long to short, in 100 meter sprint running. Therefore, stiffness could be an important factor in runner's record and should be considered in training program.