You’re in the middle of a long gruelling workout. You’ve been giving it all your effort, but your thighs are already sore, and your energy is starting to wane. All of a sudden, a switch flips, and you forget you were just exhausted. It’s like the backup generator in your body kicked in, just as a storm was about to leave you depleted in the dark. In fitness circles, many people call this a “second wind.”
It’s a sudden burst of energy that hits you after you've been exercising for a a while. Researchers aren’t sure exactly why this happens – it’s hard to study, and there isn’t enough evidence backing the idea that this happens for physiological reasons.
There are some theories out there about why you get a second wind, though, according to a British Journal of Sports Medicine blog. One hypothesis is that your body is switching from burning carbohydrates to fat, but there are a few holes in the theory. Other experts think it could have to do with lactic acid and oxygen in your muscles. Research shows the chemical lactic acid requires less oxygen to power your muscles than other sources of fuel. When you have a build up of lactic acid in the muscles, you may be able to go harder and feel less pain as you do, explained sports medicine doctor and fitness expert Gabe Mirkin, M.D. in a blog post. "You tell everyone that you suddenly got your 'second wind,'" he writes. "But actually you started to use huge amounts of lactic acid, which requires less oxygen for energy, and your blood became less acidic so you were able to run faster again."
Most likely, second wind is a mental thing, having to do with your neurochemicals or psychology, scientists believe. The BMJ notes that “second wind” phenomenon is similar to the concept of a “runner’s high,” which has been researched throughout the years. Mayo Clinic notes that runner’s high may have to do with a physical activity triggering a release of endorphins, or your “brain’s feel-good neurotransmitters,” suppressing your perception of effort and pain. Another runner’s high theory is based on a 2015 study done on mice. It found that the rodents who’d been running on a wheel seemed to have activated their "endocannabinoid system,” as well as have increased their endorphin levels. So, your sudden burst of energy near the end of your cycling class may have to do with either or both of these things happening.
So, that’s the scientific side of this. Anecdotally, athletes and workout instructors believe a second wind can occur for all kinds of reasons.
Joey Foley, the cofounder of New York City’s Punch Pedal House and a former D1 Football player, says much of it has to do with being motivated by the environment you’re in. “In group fitness specifically, you have this energy aspect of being next to someone,” he says. “Being in a brick and mortar room with others pushes you a little bit more, and gives you energy to take it to the next level.” Foley himself has helped designed classes that will ideally help you hit a second wind and then a third wind with HIIT-like intervals bringing your heart rate up and back down as Foley's boxing and spinning classes progress. He adds that external factors can also help you get into a mental state where you can push through into a second wind. Those might include a particularly inspiring instructor, the lighting in the room you’re getting sweaty in, or even what you ate before your workout.
Jennifer Hicks, an instructor at 305 Fitness, adds that it can also have to do with a power playlist. “If I’m exhausted and ready to quit, but Whitney Houston comes on shuffle or the beat drops in a remix, I’m always inspired to get through a few more burpees,” Hicks says. “The effect music has on us is pretty amazing.”
Ultimately, although we still can't say for certain what scientifically is causing your second wind, you might be able to figure out what works for yourself on a personal level. Pay attention next time it happens, and think about what brought you to that breakthrough point. Like the weather, a second wind can be a fickle thing, but we can do our best to figure out what works for us.
“When I have no control over the music, I hit a second wind by hitting reset on my mind first and reminding myself why I’m there,” Hicks says. “I’m strong and I’ll only get stronger if I stay the course. Self encouragement goes a long way.”