Power cleans and deadlifts are quite similar.The two main differences are the end position of the bar and the speed of execution.In a deadlift, you basically just stand up with the bar at a moderate rate of speed.At the completion of the movement, the bar is resting across your thighs.A power clean is broken down into two parts.The first pull and the second pull.The first pull is done just like a deadlift.You pull the bar from the floor to about knee height at the same speed as a deadlift.This completes the first pull.To begin the second pull, you explode the bar up from the knees to about chest height by pushing through with the hips, dynamically shrugging the shoulders up and pulling with the arms.Once you have completed the second pull and the bar is at chest height, you must whip your elbows under the bar, dip at the knees and catch the bar at the shoulders, then stand up.
This is a very basic explanation of the power clean as it is a very complex exercise and I am sure that someone here could explain it better than I.When I was boxing on a regular basis, this movement was our core exercise and it really helped develop our punching power.
I hope this was of help in answering your question.
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matt toupalik