Maybe you've heard someone say, “Your muscles are like rubber bands,” or “Stretching will make you stronger.”
There are a lot of cliches about stretching, and people generally don’t think about them because stretching is treated almost as an afterthought — a garnish alongside the main courses that are weights and cardio.
But people should put more thought into stretching, because most of us aren’t doing it right, and don’t even understand how it works.
Flexibility Isn't What You Think It Is
Flexibility is commonly thought to work via three mechanisms.
1. Stretching makes your muscles, tendons, and ligaments longer.
2. It increases the elasticity of your muscles.
3. Stretching increases your neural stretch tolerance, or your pain tolerance.
The common thinking is that these are in order of importance. But in fact, it’s exactly the opposite.
According to one study, stretching elongates muscles via increases in viscoelasticity. And as the authors of that study point out, muscles don’t stretch like rubber bands, as commonly stated.
"Like solid materials, they demonstrate elasticity by resuming their original length once tensile force is removed. Yet, like liquids, they also behave viscously because their response to tensile force is rate and time dependent.”
Which makes sense, since muscles are, in fact, a mix of solid and liquid.
However, this lasts only tens of minutes. Long-term increases in flexibility are due to increases in neural stretch tolerance. As further evidence of this, stretching your lower body increases upper body flexibility, and vice versa.
As for muscle length, stretching doesn’t increase it. You wouldn’t necessarily want it to increase either, since this would also increase the minimum length of the muscle.
To recap, long-term increases in flexibility are purely neurological, while transient increases in flexibility are due to short-lived increases in muscle viscoelasticity.
Pre-Workout Stretching: Favor Dynamics
Stretching can be helpful as a warm-up, but more isn’t better. High-intensity static stretching (to the point of pain) before a workout can actually decrease strength and muscle growth. On the other hand, low-intensity static stretching — only to the point of mild discomfort — provides greater flexibility gains, apparently with less loss of strength.
And dynamic stretching seems not to impair strength the way static stretching does, at least if used in moderation.
Since it involves more movement, dynamic stretching also does more to get your blood flowing and your muscles warmed up. Thus, it should be favored over static stretching during warmups.
“Depending on the workout, there are specific warm-up recommendations," coach Sam Stauffer said. "Before a workout, you want a full-body dynamic stretch, followed by a dynamic warm-up that elevates the heart rate and prepares the body for what is to come.”
Granted, there are some cases where static stretching can be useful in a warmup, but that’s a subject so complicated that I can’t give you any hard and fast rules on when to do it.
Pre-Specific Exercise Stretching
Because increases in viscoelasticity are short-lived, you may actually want to stretch before a specific exercise, rather than just before the whole workout. There are several possible reasons for this.
1. You may need to increase your range of motion for the exercise.
In that case, do some light dynamic stretching of the main muscles used in that exercise.
2. You may need to increase the range of motion of a muscle that isn’t a prime mover for that exercise.
For instance, you may need to stretch your shoulders before a barbell squat to be able to hold the bar comfortably. For this purpose, you can stretch harder, and use static stretching — loss of strength isn’t much of an issue.
3. Because of the way muscles are mostly grouped into opposing pairs, you may want to weaken the antagonist muscle of an exercise (the muscle that would normally move your body in the opposite direction from the exercise you’re doing).
For instance, you may want to weaken your biceps before doing pushups, or your pectorals before doing rows. This is similar to the idea behind agonist-antagonist supersets. In this case, you could apply a brief static stretch to the antagonist muscle.
Post-workout, you no longer need to worry about losing strength, so you can stretch a bit harder. This is a better time to incorporate static stretching, which, aside from improving flexibility, can also be relaxing.
While you do want to stretch the muscles you used in order to ease any tension in them, remember how stretching works — you should be stretching your whole body, even if you didn’t use all your muscles in the workout.
More still isn’t better here. Post-workout stretching still shouldn’t be painful, and the whole process only needs to take five minutes or so.
Stretching also doesn’t need to be timed with workouts to build flexibility, although this can be convenient from a habit-building standpoint. To build flexibility faster, you could stretch for a few minutes several times a day. And, this is actually more productive than doing 20 or more minutes of stretching with your workouts.