Mercola Peak Fitness: walking lunge with dumbbells

Nothing beats Ronnie Coleman's lunges...145lbs across the parking lot twice!

The second guys knees went a little past his feet when he did the lunge.

Instructor's first steps: 3rd step (his right leg) vivid example of the incorrect knee angle, way overpasses the tip of the toe; the 4th step (left leg) is an OK example of the correct knee angle. Doctor's knee angle is always wrong; because his legs are much longer than the instructor's, his steps should be a lot longer to allow a 90 degree angle when he bends the forward leg down; his back/ shoulders lean too forward.

Continuation from previous comment:
Correction:
sometimes the instructors bending leg knee over passes the line of the tip of the toe, too. and sometimes he does it right.
The knee can not be bent too forward beyond the line of the tip of the toe because at that point the tendon nor the muscle can retrieve it well and could snap causing severe damage, doing this over time with heavy weight could cause damage, too. The bending leg needs to always be at a 90 degree angle. Like a nice square.

the doctor's back pose starts good and then he begins to lean forward. His knee when he bend the front leg over passes the angle beyond the line of the tip of the toe. Instead of his bending leg being at a 90 degree angle straight down he over bend the knee and this can damage the joint.
Do it like the instructor.

This exercise IS a challenge to do correctly. Notice Dr Mercola's knee ends up frequently in front of his ankle, which is NOT correct technique. But it is nice to see a non-muscle bound "regular Joe" also demonstrate these exercises. (Lean back a little to get the knee back.)

cant you just take a step forward then go back to your starting position? i dont have room to walk around at my gym

These are my favorite for the lower body. I do 40 of these with 15 lbs DB.