First, lets consider the question from the age perspective before getting into the discussion from the gymnasts' perspective.
Should kids do yin yoga?
I have talked to this in a previous thread
. My philosophy is that kids, being in the yang stage of life, need to build strength, not mobility. Kids need to move! (Our culture’s penchant for forcing children to sit still for many hours a day while in a school classroom restricts the child’s normal behavior --- when a child can’t sit still, we label him hyperactive or ADD, but in reality he is the normal one. Kids who can passively sit for hours at a time are not normal.) Yin yoga can help build mobility, mindfulness, calm and centered awareness, but do children really need all that at this stage in life? I would much rather see kids out playing or doing Kid’s Yoga where they can move, than see them sitting still for an hour or more. Of course there are some children who really do benefit from Yin Yoga, but they are rare.
Now, the second part of your question – will yin yoga help gymnasts?
Gymnasts and dancers have always used yin yoga-like stretches to improve their range of motion. Restrictions to range of motion, when the restriction is due to tension, can come from several areas: the muscles, the fascia, the joint capsules, the ligaments and tendons. All of these can be remodeled through a yin yoga practice. Holding a pose near the edge of the range of motion for moderately long periods of time does increase range of motion, at least until the restriction to further movement is caused by compression. (Once compression is reached, no amount of yoga or stretching will increase range of motion.)
Many gymnastics and dance teachers include yin yoga postures in the basic training. Obviously, this does work to increase range of motion and so – yes, yin yoga could be beneficial to increasing a young student’s mobility.
The question still needs to be asked: should
the young student do yin yoga? It is worth consider the risks/rewards here. Some of the most broken bodies I have seen are retired gymnasts and dancers. Many gymnasts suffer lower back problems later in life because of extreme training they undertook as children and young teens. I have seen spondylothesis
caused by repetitive deep backbends done in a dynamic way: moving, deep back bends can push the spine beyond its limits causing one vertebra to slip backwards under its neighbour. The general literature on spondylothesis claims that 40~50% of gymnasts will develop it! (Not everyone
agrees with these statistics.)
If it were my child considering gymnastics and loves it, I would prefer her to work on strengthening her back and core musculature (yang yoga) rather than have her do yin yoga to enhance her range of motion. Her gymnastics training will give her the flexibility she needs, let her yoga practice develop the stability she needs too.