I took a grueling class at the first fitness club dedicated entirely to running - here's what it was like

As I entered one of the classrooms at New York City's Mile High Run Club, I saw nothing but wall-to-wall treadmills, 36 to be exact.

Black lights snaked along the ceiling, illuminating the white towels on every machine.

When the clock struck 6 a.m., instructor Laura Cozik cranked the music and the workout began.

Located at 28 E. 4th Street in Noho, Mile High Run Club is the first dedicated running studio where "everyone trains like an athlete, regardless of fitness level."

As a non-runner, I took the class to see how the average person might fare. I ran 4.76 miles and burned 465 calories.

I chose to brave the HIGH 45 class, the description of which warned that I'd be running between three and five plus miles over 45 minutes.

No Walking Allowed

Before class, Coznik said we'd be doing four-minute intervals - running uphill for one minute and flat for three minutes. Since the class follows a "build format," we started slow and accelerated with each interval.

I hate running uphill and I hate running fast, but thankfully, the treadmill I was assigned to was parked in the back of the room. I hopped on, deciphered the controls, and started walking until the class began.

As the music came on, Coznik told us to start warming up at a comfortable pace. But we weren't allowed to walk. Ever.

Each machine has a mini guide with suggested speeds for joggers (beginner and intermediate levels) and racers (advanced and elite).

I used the guide as a starting point but didn't end up following it. I listened more to my body and Coznik's instructions and descriptions about how we should feel.

I felt like I was entering hell.

Coznik loves motivating people to push themselves to the max. She walked around during class, telling us true stories about people overcoming challenges, distracting me almost enough to forget that I didn't like running on treadmills.

But then the intervals arrived. The lights turned red and Maroon 5's "This Summer's Gonna Hurt" blasted through the speakers. I felt like I was entering hell.

She told us to put the incline at 8.0 and jog at a "Level 2" speed; 60 seconds feels longer on a hill.

The Euphoria That Follows

After a minute, we immediately returned the incline to zero and ran our fastest speed of the class yet - but it wasn't a sprint. Then we did it all again at a faster speed. And then again at an even faster speed.

Thankfully, after each set we had a two-minute rest period to catch our breath while maintaining a "Level 1" pace.

After the intervals, the class was essentially over, except for the 30 second sprint. On Coznik's mark, I cranked the machine to 10.0 and prayed I wouldn't fly off and hit the wall.

I clutched the handlebars as I slowed to a steady 5.0 and let my heart rate drop from about-to-burst to normal.

Dripping in sweat with a strong runner's high, I'd survived - and actually enjoyed - HIGH 45.

Since it's broken down into intervals, the class doesn't feel like 45 minutes. You're too busy changing speeds and elevations to stare at the clock.

Add in the music (Coznik played upbeat pop and country) and changing lights, and your treadmill workout almost feels like a party.

A few hours after the class I felt like a baby giraffe attempting its first awkward steps, but I'd do it again.

According to Coznik, most beginners prefer to start with the DASH 28 class: a 45-minute workout that combines 28 minutes of treadmill intervals followed by 10 minutes of strength training with kettlebells.

And for those who live for running, there's The Distance class, which is a full hour of intervals, tempo, and hills. This one's recommended for cross-trainers, athletes, and elite runners.

When I first read about my class, I thought I was signing up for an early morning torture session. But, even for a non-runner like me, it was actually pretty manageable - enjoyable even.