Does stretching muscles (both right after a workout but also very much throughout the day afterwards, when you still often feel they could do with a good stretch), actually play a role in helping to build them, (whether a direct positive effect on muscle fibre multiplication / growth, or an indirect effect such as fostering greater muscle health in general which in turn translates to more muscle / better growth - just like sleep plays a role in that way), or does it mostly just beneficial for preventing injury and muscle pulling etc.?
Strength training builds muscle. In other words, the forcible contraction of your muscles against resistance is what stimulates them to get stronger or more firm. While stretching has a role, it's not to build or tone muscle. NOTE: the amount of body fat you have can accentuate or hide muscularity, so a certain amount of "toning" is done in the kitchen.
A more complete picture is this:
- Strength training stimulus. When done with the proper intensity and effort, causes a hormonal chain of events that tells the body it needs to be stronger to meet the demands.
- Recovery. This is where your body actually does the work so that it can handle the next training stimulus.
When training you go in cycles of demanding more work of your muscles, and allowing the body to catch up.
So what good is stretching?
Stretching comes into play in one of two ways: you have a problem using full range of motion, or you need to get blood flowing through the muscle body to speed recovery.
When correcting mobility problems, typically there is a muscle group that is too tight, and an antagonist muscle group that is not properly activating. Fully correcting a range of motion problem requires learning how to activate and correct the malfunctioning muscles, as well as relieve the tightness that is pulling the joint out of it's normal functional range.
When using stretching to get blood moving, we are typically using dynamic stretching. This form usually works much better to loosen the body to better prepare to move. However, it also helps flush out general soreness as well.
Stretching doesn't build muscle. But it does have an important effect on your muscles that makes it useful both post workout and after any period of being still (sitting, sleeping, etc.).
The muscle spindles are accustomed being at a "resting length". Say, if you sit in a chair for hours on end, your hamstrings become accustomed to being shortened. The effects of this is that the shortened muscle will have a harder time relaxing or letting go of tension (hypertonic), and, the antagonistic muscles will become accustomed to being at a lengthened, or stretched out state (hypotonic). These things can produce slowed responses, muscle cramps, strains, joint instability and tendon issues if you need to do something active while the muscles are still in this state.
Part of it is that when you attempt to lengthen a muscle too fast compared to what it's accustomed to, it will attempt to lock up as a "braking" action - this is part of your body's method to prevent joint damage.
Stretching is the way you remind the muscles of their full length and reset muscle spindles.
After a solid workout, the muscles are primed to be set into new resting states, so failing to stretch, and say, going to sit for several hours, basically sets your muscles into those positions, instead of neutral ones. This is why people will feel a stiffness and tightness in the day or two after resistance training - the muscles have set into their new length resting state and going beyond/outside it takes a while.
The flip side is that the antagonist muscles which are left overextended, become weak relative to their actual muscle mass, simply because the muscle fibers are stretched in such a way that the chemical reaction that causes contraction can't operate efficiently.
This topic is still quite debatable and personally, I tend to gravitate more towards the "avoid injury and keep muscle oxigenated" school of thought but I recently read a publication by UT researchers J. Antonio and W. J. Gonyea called Muscle Hypertrophy vs Hyperplasia. They conducted some very interesting experiments with birds. An excerpt of this paper:
DOES STRETCH INDUCE FIBER HYPERPLASIA? This animal model was first used by Sola et al. (38) in 1973. In essence, you put a weight on one wing of a bird (usually a chicken or quail) and leave the other wing alone. By putting a weight on one wing (usually equal to 10% of the bird's weight), a weight-induced stretch is imposed on the back muscles. The muscle which is usually examined is the anterior latissimus dorsi or ALD (unlike humans, birds have an anterior and posterior latissimus dorsi). Besides the expected observation that the individual fibers grew under this stress, Sola et al. found that this method of overload resulted in a 16% increase in ALD muscle fiber number. Since the work of Sola, numerous investigators have used this model (1,2,4-8,10,19,26,28,32,43,44). For example, Alway et al. (1) showed that 30 days of chronic stretch (i.e., 30 days with the weight on with NO REST) resulted in a 172% increase in ALD muscle mass and a 52-75% increase in muscle fiber number! Imagine if humans could grow that fast! More recently, I performed a study using the same stretch model. In addition, I used a progressive overload scheme whereby the bird was initally loaded with a weight equal to 10% of the its weight followed by increments of 15%, 20%, 25%, and 35% of its weight (5). Each weight increment was interspersed with a 2 day rest. The total number of stretch days was 28. Using this approach produced the greatest gains in muscle mass EVER recorded in an animal or human model of tension-induced overload, up to a 334% increase in muscle mass with up to a 90% increase in fiber number (5,8)!
So, according to this experiment, yes. It most certainly does help with muscle growth. But who wants to tie weights to themselves for 30 days? :-)