Shortening your shoulders with a cross-body stretch
This is a stretch Little League coaches just love. But it can actually do more harm than good, says Jacob Boly, certified personal trainer for The Vitamin Shoppe. Every time you drive, eat, sit at a computer, and use your phone -- which is probably a LOT -- you're constantly rounding your shoulders in, leading to tight chest muscles, which can cause internal rotation. For those with internal rotation and a possible rounded upper back (cough, cough, anyone with a desk job), the cross-body shoulder stretch just takes an already-tight muscle and shortens it even more. Instead, Boly suggests a doorway stretch.
"Place your forearm and hand on a wall at 90 degrees parallel with the floor -- preferably on a doorway, or corner," Boly says. "While maintaining a neutral spine, or a normal standing position, lean forward and back to get a stretch -- without facilitating bad posture."
Stretching the wrong muscles
Choosing the best stretches and warm-ups depends on what the main movers are in the activity you’re about to perform, says Dyan Tsiumis, head instructor at SWERVE Fitness. "Think to yourself, 'What muscles are involved?’ and then focus on stretching those," Tsiumis advises.
For example, after a run or cycling session, you’ll want to focus on your lower body, whereas after a long day at your desk job you should stretch to open your hip flexors.
Doing seated spinal twists
Most people attempt this stretch to alleviate lower-back pain, but if you aren’t careful, seated spinal twists can actually aggravate the muscles in your lower back, says Nikki Warren, co-founder of Kaia FIT. "This stretch should only be performed with excellent posture," Warren explains.
Since most people, uh, don’t possess great posture, Warren recommends trying child's pose instead. "This passive stretch allows your lower back to release with zero pressure," Warren says. "Simply spread your knees as wide as possible while keeping your big toes together. Relax your glutes to heels -- place a towel under your hamstrings if you struggle to reach your heels -- and drop your forehead to the earth while walking your hands forward."
Only stretching what feels tight
"The most common stretching mistake I see time and time again is only stretching an area of the body that, 'feels tight,'" says Brooke Sheely, trainer at YG Studios. "For instance, doing a static, seated forward fold to eliminate hamstring tightness."
She suggests focusing on a larger area of your body, like the entire posterior chain. "Oftentimes if your hamstrings are tight, it’s due to muscular imbalances, tightness, and even weakness in your psoas, lower back, and calves," she says. "It’s important to stretch and foam-roll quadriceps as well: focus on the entire leg and posterior chain in stretches such as down dog, pigeon, and double pigeon."
Blindly attempting a scorpion stretch
You've probably attempted this stretch at one point or another, and odds are you did it wrong -- and may have harmed your back in the process. While the scorpion stretch (executed facedown with your arms spread wide, where one leg crosses your body to tap the opposite side) provides length to the anterior portion of the body, the risk to your lower back and spine is greater than the reward the stretch provides, says Maurice Christovale, personal trainer with Find Your Trainer.
Want an alternative? Christovale recommends the "Brettzel stretch" which is still pretzel-like but has fewer moving parts. "YouTube it. It’s a great way to increase thoracic mobility and glute, quad, and abdomen flexibility -- the whole nine yards," Christovale says.
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Erin Kelly is a writer, runner, and triathlete living in New York City. She needs about 500 more hours of yoga before she'll be able to touch her toes. Follow her on Twitter at @erinkellysays.