Yesterday, you enjoyed a long jog and your thighs are now feeling the burn. When do muscle aches and pains cross the line between soreness and a sports injury?

The American College of Sports Medicine (ACSM) defines soreness that occurs in the days following physical activity as delayed onset muscle soreness. This type of soreness can develop as early as 12 hours after your workout and may last for as long as three to five days. While the jury is out regarding the exact cause of delayed onset muscle soreness, it may be a byproduct of the process the body uses to repair muscle fibers damaged during exercise, according to the ACSM.

Delayed onset muscle soreness usually goes away without treatment. In many cases, noting the time symptoms begin can help you decipher between soreness and potential injuries, such as strains and sprains, according to Lindsey Dietrich, M.D., orthopedic surgeon on the medical staff at Texas Health Arlington Memorial Hospital and Sideline Orthopedics and Sports, a Texas Health Physicians Group practice.

“Signs of an acute injury include swelling, bruising or significant limping. If you experience any of these or your pain is getting worse rather than better, you may want to take a break and get things checked out,” said Dietrich.

Strains — injuries that occur when a muscle or tendon is torn or damaged — are most likely to occur during sudden changes in momentum. If you experience intense pain while starting or stopping during a run, for example, you may have a strain. In addition to pain, strains may cause muscle spasms and weakness, swelling and difficulty moving the muscle, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

“Most injuries to muscles will mend in a shorter period of time while tendon tears and ligament injuries can require a more prolonged recovery or even surgical repair,” Dietrich said. “Swelling, locking up, or feeling like a joint is unstable is a sure sign you should have one of our team evaluate your injury.”

Too Intense or Just Right?

Delayed onset muscle soreness typically strikes when people try a new workout or exercise for the first time after a long period of inactivity. Weight lifting, jogging, and walking or running up and down hills are among the most common activities that lead to delayed onset muscle soreness.

While some people judge the quality of their workout by the amount of soreness they experience the next day, living by the rule “no pain, no gain” can lead to injury. To protect your muscles and joints, Dietrich recommends people make time for a proper warm-up, stretch before and after their workout, and gradually increase the intensity of exercise over time. Alternating activities — for example, exercising your legs one day and your arms the next — is also important because it gives your muscles adequate time to recover. If you want to work through muscle soreness, low-impact cycling, swimming and using an elliptical machine can be beneficial recovery activities.

If you're experiencing a sports related injury, find a sports medicine specialist near you.