Is it not kinectic energy = half mass x speed squared?
this is basically true, but actual deliverable power is realised through intertia - which is the inclination for any object to stay in its current frame of reference..or more accurately (from Mirriam-Webster)
a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force
The "external force" would be whatever u r hitting. Now, the inclination of an object to maintain its velocity relates to its mass - the heavier an object, the longer it will maintain its velocity; forces of acceleration (in this case the attempt to reduce the velocity of ur fist/foot) have less effect on the velocity of heavier objects...which is why a coal train moving at 20mph will hit a brick wall and keep moving at close to 20mph, while a car moving at 30mph will hit the wall and stop.
so while force=mass x velocity(2), slower heavier objects will deliver more force due to their inclination to keep moving.... which is why big slow guys generally hit "harder" than smaller faster guys. Its not that they generate more force, but more gets delivered. Look at Butterbean....he is huge, slow, and his hand speed sucks...but he delivers A LOT of power.
Sorry about that. Didnt mean to give a physics lesson. but i went through the same thing when i was 15..i was 6'0' and 140 lbs (yes, that skinny) and wanted to develop more power. More speed does generate more power, but doesnt deliver all that power. More mass generates power at a lower rate, but delivers more of it.
The most important thing i learnt while fencing is that "Speed will come with technique". When u get ur techniques right, your muscle memory will only fire the muscles you need to perform the necessary movement. This delivers more speed because the thing that slows u down is tension in anterior muscles.
And Yari is right, timing delivers more power, becuase u are using the opponents energy against him....which is why a well timed left hook delivers more knockouts than a freight-train style over-hand right.
my 0.02c