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What REALLY Happens to Your Body When You Skip Your Post-Run Stretch

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. Not so fast. The fatigue and ravenous hunger that accompanies a long run make it difficult to talk yourself into a quick stretch, but it may be worth the extra ten 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, MS, 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: 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 very common for many runners. Thankfully, the accumulation of lactic acid isn't permanent and with proper stretching, can actually be flushed out of the body relatively quick, 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, which can ultimately be very tight and dense, thanks to a buildup of byproducts 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 which, over time, can result in muscle imbalances. This tightness increases the wear and tear on your joints and decreases 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 afterwards, says Metzelhe's seen this happen with some of his own patients. Although this doesn't occur with all runners, it's still a real (and very painful) reaction to the muscle shortening that occurs after a run.

Related: Your Guide to Muscle Spasms

Metzl says the 30 minutes directly 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 offset all the miles you've clocked, investing a little more time to loosen hard-working, powerful muscles, will set you up to be a better, pain-free runner over time.