The squat may be one of the most effective exercises of all time. When done correctly, it trains a lot of muscles, particularly big ones like your quadriceps, glutes, and hamstrings. In fact, it burns more calories per rep than almost any other exercise.

Now, you can instantly enhance the benefits of a squat with this weekend's challenge from Todd Durkin, C.S.C.S., trainer of some of the biggest names in pro sports and author of The IMPACT! Body Plan. The test: How long can you perform the wall sit?

The wall sit adds resistance to the most difficult portion of the squat—the very bottom. Bracing your back against a wall, you'll slide down until your thighs are parallel to the floor. Then, you'll hold this position for as long as possible. Maintaining this fixed position increases the time your muscles are under tension. As a result, you'll strengthen weak spots and stimulate new muscle growth.

Ready to give it a shot? Grab a stopwatch and check out the video below to see Durkin perform the Wall Sit Weekend Challenge. He held the wall sit for 3 minutes and 37 seconds. What was your time? Let us know in the comments below.

preview for Wall Sit Weekend Challenge