What it is: HydroTrack takes track training and translates it into no-impact water workouts, so runners can gain cardio and strength benefits with little risk of injury.

Who is it for: As with running, you go at your own pace, so it can be for anyone who wants an intense workout without the joint-jarring pounding of running. Many of the people in the class I took were training for marathons; a few were recovering from injuries.

Who it's not for: If you need blasting music to get revved up, this music-free class may not be for you.

Fun fact: Instructor Leslie Branham, a devoted runner, has completed almost 40 marathons as well as several 50- and 100-mile events. Branham, who's a running coach, wellness coach and kettlebell instructor, developed the HydroTrack class after suffering from severe plantar fasciitis that lasted for two years.

What's it like: The setup is easy. You strap a flotation belt around your waist and hop in the pool.

Branham then guides you through warmup "elevations," basically intervals of treading water. Then, you start full-out running in the water. During the session, she often leads the class in "ladders," running short distances, building to longer distances, then working back down to shorter ones.

"I coach on form, muscle recruitment and pacing," she said. "I want people to learn how their body feels at varying levels of intensity so they can pace correctly on land. I also want them to learn to push and challenge themselves in a safe, non-impacting environment."

Unlike swimming, where the focus is on moving efficiently through water, this exercise uses water as resistance. The idea is to forcefully move the water with your arms and legs while keeping your core steady and upright.

Focus on form: Branham keeps a sharp eye on the class and will shout out instructions from the side of the pool. Her favorites: "Keep your hips underneath you!" "Recruit your glutes!" "Move your legs an equal distance in front of and behind you!" From her vantage point on the pool's deck, she can see how effectively participants are moving the water, so there's no cheating.

Would I go again? Absolutely, even though I have no intention of ever running a marathon. HydroTrack provides a rigorous, high-quality interval workout that you can take at your own pace.

Details: A block of five classes costs $100. Sessions meet at the Oxford Pool in St. Paul on Sunday mornings. For information go to equiptfitness.com or e-mail Branham at leslie@equiptfitness.com.