Comparative analysis of the support phase during first two steps after leaving the starting blocks

BACKGROUND: Biomechanical analysis of accelerated running dynamics provide valuable information about movement execution. The key phase of the movement is the ground contact phase, in which force impulses applied on the human body are generated. OBJECTIVE: The main goal of the study was to analyze differences in the support phase during first and second ground contact off the blocks. METHODS: 10 male athletes (22.9 ± 4.6 years) took part in laboratory experiment. Force-plate Kistler 9281 EA (Winterthur, Switzerland) was used to determine the contact forces in both steps independently. Matlab Software (The MathWorks, Inc., Natick, USA) was used for calculations of the force impulse, produced velocities and average acceleration during the support phase. Matlab also provided the tool for statistical processing of the results (paired T-test and correlation analysis). RESULTS: Significant differences (α = 0.01) were identified between the first and second step's support phase in contact duration, produced horizontal velocity and average horizontal acceleration. Produced horizontal velocity achieved value 1.117 ± 0.081 ms-1 during first and 0.835 ± 0.074 ms-1 during second ground contact after blocks. Average acceleration showed negative correlation with the height of the athlete during the first ground contact off the blocks (r = -0.42). If braking force was present during first 20-40 ms of ground contact, it led to longer duration of support phase and was coupled with a smaller value of average acceleration. CONCLUSIONS: Braking phase during first steps after the blocks should be considered always as an imperfection of movement execution. Taller athletes seem to be disadvantaged during first ground contact after leaving the blocks. The first and second step's ground phases are significantly different.[VÝCHODISKA: Biomechanická analýza dynamiky akcelerovaného běhu poskytuje cennou informaci o exekuci pohybu. Klíčovou fází pohybu je fáze kontaktu s podložkou, při které dochází k aplikaci silových impulsů na lidské tělo. CÍLE: Cílem práce bylo analyzovat odchylky v dynamice oporové fáze při prvním a druhém kroku akcelerovaného běhu po výběhu z bloků. METODIKA: 10 mužů (22.9 ± 4.6 roku) se zúčastnilo laboratorního šetření. K detekci kontaktních sil během oporových fází v obou krocích byla použita dynamometrická deska (Kistler 9281 EA - Winterthur, Švýcarsko). Výpočty silových impulsů, produkce rychlosti a průměrného zrychlení byly provedeny v programu Matlab (The