We all know that staying physically active is key to good health, but that's only true if you don't get injured while exercising.

Some of the most common injuries — sprains and strains — account for 41 percent of sports- and recreation-related injuries, according to a November 2016 report from the U.S. Department of Health and Human Services.

The good news is that many common types of sprains and strains, including injuries to the hamstrings and knee, can be prevented by

hamstring injuries are probably the most common injuries across all sports. 
—Dr. Pablo Costa, associate professor, csu fullerton

focusing on stretching and flexibility, says Pablo Costa, Ph.D., an associate professor in the department of kinesiology at California State University, Fullerton. Dr. Costa has published several studies on the connection between strength, flexibility and balance and the risk for injury during exercise.

While every activity or sport tends to have a particular injury that's more common to it (think tennis elbow or runner's knee), "if we group everything together, hamstring injuries are probably the most common injuries across all sports," says Costa, who is chair-elect of the research committee for the National Strength and Conditioning Association.

Here's his best advice on how to stay safe and healthy while working out.

1. Focus on your hamstrings.

If hamstrings are the most injured body part, it makes sense to pay them special attention, right? "What we've been finding is that you want to strengthen the hamstrings, because that's going to help you not only prevent hamstring injuries, but also help you prevent knee-related injuries because of what the hamstrings do," explains Costa. These muscles at the back of the upper legs prevent the tibia, or shin bone, from going too far forward, he says. And hamstrings aren't just important in and of themselves — they also prevent serious knee-related injuries such as an ACL (anterior cruciate ligament) tear or sprain.

Costa says that hamstring curls and knee flexion exercises — in which you slowly straighten and bend your knee from a seated position — are particularly beneficial for strengthening the hamstrings.

2. Don't forget about balance.

One of the main causes of injury will come as little surprise: falling. If your balance is better, you're less likely to fall and wind up injured, of course, says Costa. "One of the things you can do to prevent injuries from falling is [to increase your] postural stability."

This means the ability to maintain balance using the muscles in your hips and legs. Lower-body (legs, glutes) resistance training, and balancing exercises such as standing on an unstable surface, like a stability ball, build strength and improve your ability to stay upright.

"Stretching has also been shown to be helpful to improve balance in the long term for both young people and older adults," notes Costa, "but try to do it after the activity."

3. Time your stretching wisely.

"Avoid stretching before exercise," Costa stresses, explaining that doing so creates muscle imbalance and may actually increase the risk for injury. Costa concedes that this view on pre-exercise stretching isn't shared by everyone. "Among the lay public this idea is still kind of new," he says.

"You want to stretch after you exercise, not before… or at a separate time of day."

In a recent study in the Journal of Sports Medicine and Physical Fitness, Costa and his team looked at the effect of stretching the hamstrings and fatigue on strength, muscle imbalance, injury risk and overall balance. "We basically found that stretching [before exercising] caused the negative effects, such as reduced hamstring strength or greater muscle imbalance, to happen earlier when there is fatigue involved," he notes. The study concluded that stretching the hamstrings immediately prior to long-duration activities, such as long-distance running, soccer or basketball, may increase the risk of injury.

Some trainers still recommend dynamic stretching — active muscle movements that aren't held, as opposed to static stretches held for 30 seconds or longer — as part of a warm-up. "But my 2014 study found that even with dynamic stretching [prior to exercise] you still have a decrease in strength, an increase in muscle imbalance, and you still increase your injury risk." That study concluded that strength and conditioning coaches, athletic trainers and physical therapists may want to avoid using static or dynamic stretching as a means of injury risk prevention immediately before an athletic activity.

4. Consider rolling with it.

So how do you warm up tight muscles if you can't do any kind of stretching? The answer could be foam rolling, a relatively recent fitness trend in which you use a large foam-based cylinder for self-massage.

In a 2018 study, Costa and his colleagues found that foam rolling can increase flexibility without some of the negative effects seen with stretching. One way it does this is by warming up muscles using the friction induced by the rolling motion. Foam rolling is also used as a post-workout practice to decrease muscle soreness.

When You're in Pain

If you pull a hamstring or tweak your knee, Costa recommends icing the injury right away; this will help reduce inflammation. Then take time to assess the pain, assuming it's a tissue or muscle-related injury.

"Is [the pain] in the muscle or near the joint? Is the pain sharp or more aching? That's going to determine whether it's something more serious or not," says Costa. "It shouldn't be terribly painful after you exercise." If the pain is sharp and/or in or near a joint, see a health care professional.


Campuses across the CSU offer study in kinesiology toward a variety of career paths, from physical therapy to professional conditioning coaching to personal training. Search CSU Degrees to find program options.