Stand upright, feet together, and take a controlled step forward with your right leg, lowering your hips toward the floor by bending both knees to 90-degree angles. The back knee should point toward but not touch the ground, and your front knee should be directly over the ankle.
Press your right heel into the ground, and push off with your left foot to bring your left leg forward, stepping with control into a lunge on the other side.
This completes one rep. Do as many reps as you can for 30 seconds.
If you don't have enough room for walking lunges, try the alternating reverse lunge instead.