A SLIGHT CHANGE IN A BACKSTROKE START PRODUCES DISCRETE DIFFERENT SKILL DEMANDS
de Jesus, Karla, de Jesus, Kelly, Figueiredo, P., Gongalves, P., Pereira, S., Viler, S., Vilas-Boas, J. P., & Fernandes, R. J. (2011). Electromyographic analysis of the backstroke start with different feet positions. Medicine and Science in Sports and Exercise, 43(5). Supplement abstract 2309.
This study analyzed the electromyographic (EMG) activity of the propulsive and stabilizing muscles during backstroke starts performed with the feet submerged and with the feet above the water surface. High-level male swimmers (N = 4) performed two sets of six maximal repetitions using the two different feet positions over a distance of 15m. Surface EMG signals of deltoideus anterior, biceps brachii, triceps brachii, erector spinae longissimus, gluteus maximus, rectus femoris and gastrocnemius medialis were obtained. A qualitative video analysis was used to breakdown the backstroke start into five phases: hands-off, take-off, flight, entry, and glide.
During the hands-off phase EMG activity was higher for the biceps brachii and erector spinae longissimus with the feet above the water than when submerged. No differences between start variants were observed in the take-off phase. For the flight phase, EMG activity was higher for the deltoideus anterior, biceps brachii, and erector spinae longissimus when the feet were placed above the water. During the entry phase, the EMG value of erector spinae longissimus was higher when the feet were above the water. The EMG activity for biceps brachii and erector spinae longissimus in the last phase (the glide) was higher for the above water feet placement.
Implication. Placing the feet above the water level in the backstroke start requires greater activity in some propulsive and stabilizing muscles than when the feet are positioned below the surface. The placing of the feet in the backstroke start invokes different muscular activity in the start itself, indicating that forms of the start are different skills. One should not assume that both types of starts are variants or similar with regards to demands placed on a swimmer. Each would have to be practiced to produce high levels of skill.
Return to Table of Contents for Biomechanics of Swimming.