If you set aside the stylized form of the reverse punch demonstrated in kata and look at how boxers and karateka actually fight in a full-contact environment, the karate reverse punch and the boxing straight right start to resemble each other to the point where there is as much of a difference between two individual fighters than there is between the two styles.
Well that is a different subject than what i was addressing.
1..we have to agree on what a reverse punch is
for me it is the traditional, typical shotokan style, hand chambered next to the ribs, palm up position. the arm extends outward keeping the elbow pulled in tight next to the ribs, fist turns palm down at the end of travel. usually thrown with the right hand having the right foot back, left foot forward.
if you compare this reverse punch to a text book boxers straight right . the over all bio mechanics of the body are very different. the major difference is in the orientation of the elbow and the rotation of the shoulder.
(again i like to put in the disclaimer this is only my experience and the way i do things, other people may be different)
in the reverse punch the palm is up and elbow is kept tight to the body. as the arm is extended the hand,elbow and shoulder is kept inline with the force vector that runs parallel with the shoulder (the force vector plane is horizontal) .
in a boxers punch the arm is in a "guard" position to start and the palm position is irrelivant but usually facing the throwers centerline or rotated slightly outwards to the target. as the arm extends the hand is rotated palm down at the begining of the punch which rotates the elbow outward away from the body creating a force vector on a vertical plane. the hand ,elbow and shoulder are now in allignment in a vertical vector plane and extend towards the target.
in a reverse punch (looking at the punch from the throwers right side) the shoulder rotates in a back, down then forward to the target this is counter clockwise rotation.
a boxers punch has the shoulder rotate down, backward , upward then forward to the target. this is clockwise rotation.
my discriptions may be very hard to visualize and without a video clip i dont think i can really get the idea across.