Post-exercise stiffness is a part of any fitness regimen, but many treatments don’t address the underlying cause. Here’s what actually works.Maybe it was an intense spin class that put you over the edge, or reaching for a personal best in the squat. Perhaps it was dancing all night at a wedding reception, using muscles you haven’t worked in years. Whatever the cause, the next day you’re stiff, sore and moving a little slowly.The reasons the human body becomes sore are surprisingly mysterious, with various theories coming in and out of fashion. The cause of soreness is complex, according to said Gene Shirokobrod, a physical therapist and the chief executive of Recharge Health & Fitness in Maryland. “The answer is we still don’t know.”What we do know is that soreness is an inflammation response to damaged tissues. It generally doesn’t mean you’ve done something wrong, or that you’re getting fitter. In most cases, it’s just an unpleasant side effect of a hard workout, after which your body tends to recover on its own. But if you ignore a sore muscle and jump right back into hard training, you can be at risk for more serious injury.Finding ways to diminish muscle soreness is a multibillion-dollar industry that features compression recovery boots, massage guns and ice tubs. While many recovery tools do make you feel better, there’s a difference between relief and truly repairing the damaged tissues.Luckily, you don’t need expensive or elaborate gimmicks to get back on your feet. Simple techniques, along with thinking from the “inside out,” will help you prevent soreness, recover properly and avoid injury.Use your fascia.For more than a century, experts thought soreness was caused by lactic acid built up inside muscle cells during exercise, but that line of thinking was largely debunked in the 1980s.Today, there are two schools of thought on the mechanism of soreness. The theory of exercise-induced muscle damage says that soreness results from tiny tears in your muscular tissue. More recently, however, experts have suggested that soreness might be caused by irritated and inflamed fascia, said Jan Wilke, a professor of sports science at Alpen-Adria-Universität Klagenfurt in Austria, who is researching this theory.The pain of soreness is usually temporary, but it can signal deeper tissue damage that can make you prone to injury if you go right back to an intense workout. Justin J WeeAs such, he said, it’s helpful to take fascia into consideration during your warm up. A thick, supportive connective tissue, “fascia likes constant movement from multiple directions,” Dr. Wilke said. “So consider a dynamic warm-up that will make the tissue more resilient to the workout ahead.”Set yourself up for success.It’s important to be honest with yourself about your fitness level before you exercise, especially if you’re new to it or returning after a break. Too often, people jump into a fitness routine where they left off months or even years ago.“They’ve got the mentality of a time machine, thinking, ‘Five years ago I could lift 20 pounds, so I can still do that,’” Dr. Shirokobrod said.Instead, think about the minimum amount of exercise you need to become fitter in the beginning. If it helps, write it down, make a plan — or have a coach make a plan — and stick to it. If you do get sore, resist pushing through it during the next workout. Doing so prevents your muscles from recovering and increases your risk of injury. Also, progress is made when your muscles have time to recover.Eat and sleep well.Whether you’re new to fitness, returning after a break or a seasoned, consistent athlete, you’re going to face soreness now and again. Instead of attacking the pain from the outside, with massage guns or ointments, start from the inside. Studies point to both sufficient sleep and good nutrition as factors in injury prevention, including muscle soreness.At the first sign of soreness, or after a particularly taxing workout, “think about extra calories and protein, or some extra sleep,” Dr. Shirokobrod said. “They support your tissues and help you move forward.”Force yourself to get moving.While it’s not good to exercise hard while sore, low-intensity movement is helpful. Lighter duty exercise gets the blood flowing and helps move the recovery process along.Think easy walks, swimming some gentle laps or even performing a few sets of body-weight squats if your soreness came from weighted squats, for instance.“If I’m feeling sore and rundown from an intense workout, I’ll dial back and do a short, easy run the next day,” said Jamie Hershfang, 30, an ultrarunner from Chicago who set a record for the fastest time on the Chicago Lakefront Trail in 2020. “This always gets my muscles loosened up and feeling better.”Easing pain is not fixing muscle.Resist that urge to take ibuprofen, which some research suggests makes no difference or can even be detrimental. “The research shows that NSAIDs will reduce your feelings of soreness, but they will blunt the actual healing,” said Jason Sawyer, director of the exercise and movement science program at Bryant University.What about hot tubs, massages, Epsom salt baths or hot/cold contrast baths? They won’t cause any harm, and you might have the perception of feeling better, Dr. Shirokobrod said.But “understand that’s only sensory relief” and doesn’t affect the strained muscle or fascia itself, he added. You might emerge from these treatments feeling less stiff and sore, he said, but they cannot penetrate the tissue at a deeper level.Be aware if it’s more than just soreness.Some post-workout pain might actually be injury. One indicator is where you feel soreness. If the pain is global — felt in both legs, for instance — you’ve probably only overdone a workout. Injury, on the other hand, tends to be localized. In addition, injuries often cause immediate pain, while you usually don’t feel soreness until after.If you suspect an injury, dial back on the aggravating activity and see a medical practitioner.When it comes to beating soreness, simplicity rules the day. “Provide your body with the building blocks it needs to heal,” Dr. Sawyer said, “and it will do the rest.”Amanda Loudin is a freelance writer covering health and science.