I'm trying to get my splits; I'm well on my way, but I still have a long way to go. How often should I stretch to improve my flexibility at an optimal pace (and not injure myself)? Is flexibility like strength, in that I need rest days for my body to recover?
My source for flexibility is Stretching Scientifically, by Thomas Kurz:
Kurz has this to say:
Isometric stretches, to increase flexibility, should be done at least twice a week, but it all depends on your recovery. If your muscles are sore then no isometric stretching should be done as long as soreness is felt. Wallin et al. (1985) recommends isometric or contract-relax stretching from three to five times a week for increasing flexibility, and for maintaining it only once per week.
Kurz does not talk about the maximum number of times one can do relaxed stretching, but I imagine that it could be more frequent, though his warning about soreness would probably still apply.
Physiologically speaking, as I understand it, one can think of flexibility similarly to strength: the muscle needs to grow, and to grow it needs stimulus, fuel and rest.