Those who feel that mass hinders speed are losing out on a great deal, especially if they ignore strength training altogether. When it comes to mass and speed, the biggest cause of confusion stems from the misinterpretation of the terms power and strength.
From a physics standpoint, martial arts center around the concept of power.
What is power?
Power includes your ability to move a load (force) over a distance (point a to point b) within a certain time (one second).
In a high kick to the head, the force is your foot and your leg. The distance is from your foot to your opponent’s head. The time is how fast you can do it.
When you practice moving heavier loads over the same distance, your strength which is the ability to move weights increases.
When you practice moving heavier loads and do it faster, your power increases.
Adding wrist and ankle weights during practicing your punches and kicks is one way, not necessarily a safe way, to increase your strength and power.
Try to punch faster without the additional load and you limit how much your power increases.
Increasing power may or not add bulk as in muscle mass. Adding muscle mass requires a specific type of training that only in part is power-related.
Comprehensive martial arts training includes power training even when the motions of the art do not directly associate with the motions within the power training. Remember not to go too far in the way you power train and the way you fight. Practice the way you fight or compete.
For example, a grappler practices pulling power, and puncher practices plyo pushups.