Every week, a new STACK Challenge gives you an opportunity to test your athletic ability and win a STACK T-shirt. Take the challenge and enter to win by tweeting your results with #STACKChallenge.

If you have access to a treadmill, you can test your speed, conditioning and endurance with this deceptively tough challenge.

Start by setting the treadmill to 8.5 mph at a 12-percent incline. Hop on for 20 seconds and step off for 10. Repeat until you can no longer keep up. If the challenge feels too easy in the beginning, don’t worry—you’ll really start to feel it around the fifth rep.

Stay safe throughout the challenge by taking a few precautions:

• When stepping on and off the treadmill, hold onto the rails and cycle your feet.
• If you feel like you can’t keep up in the middle of a set, immediately grab the rails and lift yourself off the treadmill.

The Challenge

Complete ten 20-second sprints at 8.5 mph and a 12-percent incline with 10-second rests in between.

How Do You STACK Up?

Rookie: 4 or fewer
Pro: 4-7
All-Star: 8-10

How to Win a STACK T-Shirt

1. Complete the Challenge by April 27
2. Follow STACK on Twitter (@stackmedia)
3. Tweet your results and include #STACKChallenge

Congratulations to @manomeadow, who earned a STACK T-Shirt for dominating the Towel Row Challenge!

Get Better

Not an All-Star yet? Get better by incorporating these exercises into your workout:

• Hill Sprints
• STACK Fitness Weekly: Interval Sprint Training
• Chris Legh 200-Meter Intervals