Johny Hendricks left hand

The Power Behind Johny Hendricks’ Left Hook
A look at the punch which could spell the end for GSP at UFC 167

1. Fast twitch muscle Fibres and strong/explosive core
You can build fast twitch muscle fibres to a certain extent, with exercises such as plyometrics and Olympic lifts; but someone like Johny Hendricks has no doubt been born with a high fast twitch to slow twitch ratio.  The muscles in his upper body are obviously pretty explosive but his core generates much of the power.
To emulate this kind of power you would ideally look to build a stable and flexible core first, with exercises such as pilates, yoga, and with stability ball work; before moving on to Olympic lifts and work with medicine balls and sledge hammers.

2. Elastic Recoil
By pivoting on his foot and rotating his hip first, and more specifically his shoulder, Hendricks produces a large amount of elastic energy around his chest.
Looking at the picture above you may be able to see how he rotates and moves his shoulder before his arm, completing flexing his chest, before he whips his arm and hand through to complete the punch.
By flexing his chest he ‘loads up’ this muscle, enabling him to powerfully contract it as he brings his hand forwards

3. Length of the lever – windmilling the arm
Imagine being hit by a hammer, on the chin. Not nice.
Now imagine being hit by a sledge hammer, on the chin. Even worse!
Even if both hammers weighed exactly the same, the sledge hammer would cause a lot more damage.
By extending his arm fully during the punching-movement, he generates more elastic and overall force by increasing the “length of lever” involved in the movement.
Extending the arm fully also enables him to flex and “open up his chest more”. Flexing his chest fully, enables him to contract it with more force as he punches (see point 2).

Remember, violence is stupid, unless it’s really technical, in which case it’s awesome