You just crushed your run (congrats on that extra mile!), and now you're ready to call it a day, jump into a much-needed shower, and just relax. Hold up: The fatigue and ravenous hunger that accompany a long run make it difficult to talk yourself into a quick stretch. But it may be worth the extra 10 minutes.
With stretching being a controversial topic in the running world, we went straight to the pros for definitive answers. Jordan Metzl, M.D., is a sports medicine physician and 34-time marathon runner. Jacque Crockford, CSCS, is an ACE fitness exercise physiologist and education specialist. Here, they share a quick play-by-play of what actually happens to your body post-run and sans stretch.
Step 1: Your muscles contract.
This may seem like a no-brainer, but without stretching, your muscles begin to contract and tighten after a long workout. "Sometimes, achy knees or painful hips are caused by muscular contractions surrounding the joint. Stretching loosens the muscle, which aids in a quick recovery and the prevention of pain," Metzl says.
Step 2: Lactic acid builds up.
The onslaught of lactic acid is every gym-goer's nightmare. Even if you never knew what it was called, we bet you know exactly how it feels. That burning sensation in your muscles is uncomfortable and unfortunately common for many runners. Thankfully, the accumulation of lactic acid isn't permanent. With proper stretching, it can actually be flushed out of the body relatively quickly, says Crockford. (Foam rolling has been shown to alleviate lactic acid accumulation.)
Step 3: Tissues become "dense."
When you skip a stretch after your run, the tissue remains in the position in which you left it. It can ultimately be very tight and dense, thanks to a buildup of by-products that weren't removed post-exercise. A foam roller would help with this, says Rockford.
Step 4: Muscles may become imbalanced.
Similar to the initial effect, the contracted muscles will remain in their shortened state if not sufficiently stretched. Certain movements within workouts keep specific muscles in a contracted state while others are kept in a lengthened position. This can result in muscle imbalances over time. This can increase the wear and tear on your joints and decrease your range of motion due to the reduced extensibility, making future injuries more likely.
Step 5: Minor spasms occur.
If you've never experienced a back spasm before, lucky you! Muscles in the lower back begin to spasm after a hard run if they're not adequately stretched out afterward, says Metzl. He's seen this happen with some of his own patients. Although this doesn't occur with all runners, it can be a very painful reaction to the muscle shortening that occurs after a run.
Related: Your Guide to Dealing with Muscle Spasms
Metzl says the 30 minutes immediately after your run are prime time to get the most out of your stretch—and ultimately see the most progress. So although skipping a stretch here and there won't negate all the miles you've clocked, investing a little more time to loosen hardworking muscles will set you up to be a better, pain-free runner over time.