Livestreamad disputation | Athletic Sprint Start Biomechanics: Investigations into the relationships between three dimensional starting technique, first step width and performance | Paul Sandamas, GIH, fredagen den 11 juni 2021

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Pรฅ fredag den 11 juni 2021 kl 13:00โ€“16:00 lรคgger Paul Sandamas fram sin avhandling i idrottsvetenskap vid Gymnastik- och idrottshรถgskolan GIH, Sprint start biomechanics: Investigations into the relationships between 3D lower body technique, first step width and performance. Se disputationen live (sรคndningen startar nรฅgra minuter innan).

Avhandlingsarbetet har bedrivits med stรถd av huvudhandledaren professor Toni Arndt, GIH, och bihandledaren professorย Elena M. Gutierrez-Farewik, KTH.

Aki Salo, chef vid KIHU Research Institute for Olympic Sports, รคr fakultetsopponent, och betygsnรคmnden utgรถrs av professor Mark King, Loughborough University; professor Anthony Blazevich, Edith Cowan University; och docent Elin Ekblom Bak, Gymnastik- och idrottshรถgskolan.

Avhandlingen รคr baserad pรฅ nedanstรฅende artiklar:

  1. Sandamas, P., Gutierrez-Farewik, E. M., & Arndt, A. (2018). The effect of a reduced first step width on starting block and first stance power and impulses during an athletic sprint start. Journal of Sports Sciences, 37(9), 1046โ€“1054.
  2. Martรญn de Azcรกrate, L., Sandamas, P., Arndt, A., Gutierrez-Farewik, E. M., & Wang, R. The effect of step width on muscle contributions to body mass center acceleration during the first stance of sprinting (Submitted).
  3. Sandamas, P., Gutierrez-Farewik, E. M., & Arndt, A. (2020). The relationships between pelvic range of motion, step width and performance during an athletic sprint start. Journal of Sports Sciences, 38 (19), 2200-2207.
  4. Sandamas, P., Gutierrez-Farewik, E. M., & Arndt, A. Angular momentum and external torque during the block and 1st stance phase of the sprint start (Submitted).

Avhandlingens kappa kan hรคmtas ned hรคr.


Abstract

The block and early acceleration phase plays a very important role in the overall outcome of athletic sprint events. During this part of the race it is commonly observed that sprinters use a lower-body technique that involves the swing leg crossing medially in front of the athlete followed by wide steps. These wide initial steps give the impression that the legs are flailing out to the side. Some coaches believe that this action could be inefficient and thus should be curtailed. However, there is limited knowledge about this movement pattern and its relation to performance.

Therefore, the overall aim of this thesis was to help elucidate from a biomechanical perspective a) the fundamental underlying kinematic and mechanical basis to this technique and b) how both performance and muscular contributions to propulsion would be affected when step width was restricted.

A cross sectional study design was used to examine specific kinematic and kinetic variables fromย 11 competitive sprinters (9 male, 2 female) performing maximum effort 15 m sprint starts. Three- dimensional kinematics, ground reaction force and electromyographical data were recorded from the block phase to the end of the 1st stance phase. Each athlete performed five trials with their natural technique and five trials inside a 0.3 m wide lane. A 15-segment, full-body model and a 37 degrees of freedom full-body musculoskeletal model were created and used to calculate relevant variables/ parameters. Normalised average horizontal external power was used as the performance measure.

A combination of pelvis list and rotation (but not hip adduction) was found to be coupled with the thigh of the swing leg moving medially during the single push phase. In the unrestricted width trials, pelvic list range of motion and medial impulses correlated positively with step width but step width was not found to be related to performance. When step width was restricted, a more forward pointing normalised average ground reaction force vector was seen but lower body muscular contributions to acceleration were reduced and no immediate improvement to performance was found.

The primary kinematic reason behind the lower body posture the sprinters adopt during the block phase whereby the swing leg moves medially in front of the body is caused by a combination of three dimensional pelvis rotations rather than simply hip internal rotation/or adduction of the swing leg. Trying to reduce pelvic range of motion or minimising the flailing leg motion is unlikely to lead to an improvement in performance. Therefore, the notion that this technique is inefficient, was not supported by this study.

Svensk sammanfattning

Lรถparens teknik under block- och den tidiga accelerationsfasen spelar en mycket viktig roll i sprintlopp. Under den fรถrsta delen av loppet anvรคnder sprinterlรถpare en speciell teknik som innebรคr att svรคngbenet rรถr sig medialt framfรถr kroppen fรถljt av breda inledande steg. Dessa breda steg samt tekniken som helhet ger intrycket att benen svรคnger mycket รฅt sidan. Nรฅgra trรคnare anser att dessa sidledsrรถrelser kan vara ineffektiva och bรถr dรคrfรถr begrรคnsas. Det finns dock en begrรคnsad kunskap kring dessa rรถrelsemรถnster och deras relation till sprintprestationen.

Det รถvergripande syftet med avhandlingen var att ur ett biomekaniskt perspektiv belysa a) grundlรคggande bakomliggande kinematiska och mekaniska orsaker fรถr tekniken och b) hur bรฅde prestation och muskulรคra bidrag till prestation pรฅverkas nรคr stegbredden begrรคnsades. Syftet med begrรคnsad stegbredd var att minska sidledsrรถrelser.

Specifika kinematiska och kinetiska variabler registrerades frรฅn 11 tรคvlingssprinters (nio mรคn, tvรฅ kvinnor) som utfรถrde 15 m sprintstarter. Tredimensionell kinematik, reaktionskraft och elektromyografiska data samlades frรฅn blockfasen till slutet av det fรถrsta steget. Varje sprinter utfรถrde fem fรถrsรถk med sin naturliga teknik och fem fรถrsรถk med stegbredden begrรคnsad till en 0,3 m bred lรถpbana. En helkroppsmodell med 15 segment och en muskelmodell skapades och anvรคndes fรถr att berรคkna relevanta parametrar. Normaliserad genomsnittlig horisontell extern effekt anvรคndes som prestationsmรฅtt.

En kombination av upprรคtt lutning och bรคckenrotation (men inte hรถftadduktion) var relaterad till en medial rรถrelse av svรคngbenets lรฅr under โ€single push phaseโ€. Nรคr stegbredd inte var begrรคnsad, korrelerade bรคckenets lutning och medialt riktade impulser med stegbredden, men stegbredd var inte relaterad till prestation. Nรคr stegbredden var begrรคnsad var den normaliserade genomsnittliga reaktionskraftvektorn mer framรฅtriktade, men bidraget av nedre extremiteternas muskler till accelerationen reducerades och ingen omedelbar prestationsfรถrbรคttring kunde pรฅvisas.

Den primรคra kinematiska orsaken bakom kroppshรฅllningen och rรถrelsemรถnstret som sprintarna antar under blockfasen, varigenom svรคngbenet rรถr sig medialt framfรถr kroppen orsakas av en kombination av tredimensionella bรคckenrotationer snarare รคn bara hรถftens internrotation eller adduktion av svรคngbenet. Att fรถrsรถka minska rรถrelseomfรฅnget i bรคckenet eller att minimera den svรคngande benrรถrelsen leder troligen inte till fรถrbรคttrad prestation. Uppfattningen att denna teknik รคr ineffektiv stรถddes dรคrfรถr inte av forskningen som presenterades i denna avhandling.

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