Foam rollers are gaining in popularity -- and notoriety.

The rehabilitation staple used to treat injuries is becoming a more common sight in gyms and a go-to for CrossFit enthusiasts, marathoners, cyclists and casual athletes alike who are putting up with the pain for the gain.

"They're your best friend and worst enemy," said Lauren Blanda, General Merchandising Manager at sporting goods retailer City Sports, who's noticed more and more people looking to foam rollers to help release tension and tightness from a workout. "We've definitely seen growth and more developments in the last three or five years."

A foam roller looks innocuous enough. It's a flat, tubular piece of foam that you use to stretch and massage your muscles and tissue. In recent years, there have been more types of rollers too, from tubes with grooves to rollers you can freeze and then incorporate into cold therapy.

They're pretty straightforward to use, too, as all you essentially do is rock the area you want to target back and forth or side to side over the roller and then apply pressure for about 30 seconds. Overused or over-active muscles that are typically targeted include hamstrings, biceps, triceps, lower back muscles, gluteus maximus, hip flexors and quads. Foam rolling can also be used to help treat common running injuries, such as plantar fasciitis, or jogger's heel, and knee pain from a tight Iliotibial, or IT, band, the tissue that runs from your pelvis to your knee.

"The whole point of a foam roller is to mimic a deep-tissue massage," said Blanda. "Whether you're rolling your back, quads or hamstrings, it's breaking up the knots in the muscles."

How long you apply body weight to a tight muscle or sore tissue depends on your pain tolerance -- and gives the foam roller its infamous reputation.

"This is going to hurt," trainer Karen Nuccio says by way of introduction before "Grid Release," a 45-minute class at Crunch Gym that uses a short, grooved foam roller made by Trigger Point Performance to release tension while also working out your core.

"I'm teaching so long, that's the one class where I feel so sorry," said Nuccio, a trainer at Crunch since the late 1990s. "What the grid is doing is finding trigger points, whether it's scar tissue or muscle tension, and putting pressure on something that's knotted up."

In addition to being uncomfortable, foam rolling can look slightly ridiculous, especially if you're rolling out your groin. There's also an ongoing debate among trainers as to the benefits of foam rolling, particularly the IT band.

But if you can get past the groans and grimaces, discomfort and awkwardness, experts recommend foam rolling to improve flexibility and movement and work out overused muscles.

"Anybody who's really putting their muscles through a lot of wear and tear would get use out of them," said Blanda, a marathoner who uses foam rollers herself.

And though they're traditionally used in physical therapy to help treat an injury, foam rollers can also be incorporated into your workout to help prevent injuries from occurring in the first place.

"I recommend it to anybody that has been injured or doesn't want to be injured," said Nuccio. "At the end of the day, the pain will make you perform better."

IF YOU GET ONE

Looking to buy a foam roller but don't know where to start? City Sports general merchandising manager Lauren Blanda walked us through the three different types.