TLDR;
Stretching does one thing; it increases the range of motion around a joint. Everything else you've been asking of it belongs somewhere else:
Stretching doesn’t lower injury risk: Warming up and activating your muscles does.
More flexibility might be a bad thing: A joint that travels further than your muscles can control is a problem, not an achievement.
Focus on range of motion under load: Strong muscles through a long range, not long muscles.
Foot up on a bench, hamstring pulled tight, thirty seconds a side, and off you go.
We’ve all been there (me included). The truth is… that's not a warm-up, it’s a stretch. And the two are doing completely different jobs.
Two words worth separating first, because most of the confusion lives in them:
Static stretching is pulling (stretching) the muscle beyond it’s normal length and staying there. E.g. the hamstring on the bench, the quad pulled up behind you.
Dynamic stretching is moving a joint through its range over and over without staying at the end position. E.g. leg swings front to back, or side to side.
So what does a stretch actually do?
The research
The primary purpose of stretching is to increase the range of motion around a joint. That's it. That's the job.
That' doesn’t mean it’s not important and should have a part in your fitness routine, but for the purpose of improving your running form or injury prevention it has no positive role.
To take it one step further, stretching might actually not only make you slower but increase your risk of injury. Here’s why:
Increased injury risk: When you stretch excessively you might become able to go beyond what your muscles can support. They’re stretchy, but not strong.
Worse performance: Think of a rubber band, when you stretch one beyond what its designed for and then let go you’ll notice it’s less snappy and not as elastic. The same thing can happen with your muscles, you want them to be strong with a wide range of motion, not just long.
Side note: if you want to improve your range of motion, practice dynamic low-weight high-rep exercises in the gym or speed drills. I can also help you with this in my 1:1 coaching.
Alright, so if stretching is a no no before a run. Then what should you do?
Get warm, not long
Raise your body temperature. Because a warmer muscle produces more force, moves through more range, and is less likely to cause pain.
And while a hot shower or sauna might work for some cases, ideally you want the heat to come from your own muscles working. Think of it like lubricating a hinge, that’s basically what we’re trying to achieve.
So movements like locked knees jumps on the spot, leg bends, and leg swings, are all great options. They’re not heavy, probably won’t make you feel out of breath, but they do oil the machinery.
And worth knowing is that you should be doing this while already out on the trail, as according to research the majority of benefits from warm-ups are gone after 15 minutes of no movement.
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Why and when flexibility matters
Some flexibility genuinely matters. If your hip flexors are tight enough that your hip can't extend properly, your lower back will hyperextend to make up the difference, and congrats, now you have a back problem.
But it runs out.
As mentioned earlier, your tendons behave like a rubber band. Stretch one inside its normal range and it stores energy and gives it back on the next step, which is free propulsion and a real part of how running works (look up the “spinal engine theory” for some more reading).
Take it past that range often enough and the structure of the tendon changes. It gets longer, and it stops snapping back the same way.
Which is why a very flexible runner with weak supporting muscles has a real problem; your joints will happily travel further than your muscles can control.
Personally as a running coach, I worry equally about someone who’s too tight as too flexible (looking at you yoga people).
And if something already hurts, stretching it is usually the wrong instinct:
Common causes for knee pain are tendonitis and tendinosis (-itis meaning inflammation and -osis meaning damage to the structural collagen of your tendons).
Stretching an area with tendonitis (inflamed) will likely just irritate it more and worsen the inflammation and extend the recovery period.
An area suffering from tendinosis (damaged tendon) will also likely just be damaged further from stretching. Imagine, it’s healing, attempting to rebuild itself, and suddenly you force it to stretch beyond what it’s used to. That’s not an ideal healing environment.
So as you might've noticed, the thing you're actually after isn't just range of motion. It's range of motion you can hold under load.
Take the muscle to the end of what it can do and then make it work there. A deep squat, deep single-leg ATG squats, or deep Bulgarian squats,
Because being flexible is not the same as being capable.
If any of this seemed confusing you’re more than welcome to book a 1:1 call with me, completely free, no strings attached.