The gymnast needs a costume not for training, but around her: the way to the gym, warm-up, waiting for her exit at the competitions, the opening parade. Hence the main requirement — it must be worn over a leotard and removed in ten seconds without touching the hairstyle.
Raise your hands up: the top should not go above the waist. Bend over: the bottom should not slide. The gymnast does these two movements in a suit dozens of times on the day of the competition. The zipper should walk with one hand — during the warm-up, the second hand is occupied with an object.
The kit is taken when the exact matching shade is important: the top and bottom come from the same batch of canvas. Separately — when the height and volume of the hips diverge in size, which happens all the time for growing girls.
For a hall with a normal temperature, medium-density knitwear is enough. For winter trips and cold halls, insulated models are used: warmed—up muscles cool down faster than it seems, and stretching after a break on cooled ligaments is a direct path to injury.