I was wondering if, assuming one gains lots of muscle while not stretching regularly, the process of stretching is more difficult or at least more painful after.
This isn't about the benefits of stretching, just the question if the calves, say, will be more difficult to stretch the same distance after muscle has build up.
Simply put, no it doesn't have to be. Unless you suffer a recent injury that stiffens the joints or muscles or just finished a significant lifting session in the past few hours, your current flexibility should be remain for awhile. Most studies reveal muscle can be gained and lost much faster than flexibility is gained and lost. Once you gain a lot of flexibility, it should last longer than muscle gains and fat loss if you were to stop exercising completely for awhile. If you continue stretching and improving your technique and length of sessions, muscle gains should not interfere with overall flexibility. A good rule of thumb is to never significantly stretch before or after weight lifting nor too much before cardio (however after cardio gives you an advantage to stretching if your post-cardio energy allows). Breathing very slow (4+ seconds in and out) along with slightly flexing stretched muscles for a few seconds and then releasing further into the stretch (Proprioceptive Neuromuscular Facilitation - PNF stretching) will also improve flexibility even further. Consistency and proper form, like any exercise, are the most important factors of maintaining results along with diet and rest.
I'd definitely need to read the whole article to be 100% this proves bigger muscles are more resistant to stretching, but judging only from the abstract of this review (http://www.clinbiomech.com/article/S0268-0033(00)00061-9/abstract) this seems to be the case:
"...passive extensibility is influenced by the size (mass) and length of muscle fibers...resistance to passive lengthening is influenced by the readily adaptable amount of muscle tissue..."
So it all depends on how often you are stretching during the time when you are upgrading your muscle mass. If you are consistent with your stretching routine you should have no problem stretching with the bigger muscle mass. If you have not been doing your regular stretching routine while upgrading your muscle mass you might feel like it is harder to stretch but that is not because of the bigger muscles its because you were not doing you regular stretching routine.
