El Mahdi
Muad'Dib of the Anauroch
Power come from mass. Not from little man with muscles. If he not have mass, he not have power.
Monks are umarmed combat martial-artists. Martial arts are less about mass-equals-power, as they are the proper and efficient application of that power. And Yes, a martial-artist with more strength/mass could do more damage than a weak/low mass martial artist. However, in this case, more damage is inconsequential because martial arts are also about "where" to hit, usually in areas where focusing even a few pounds of force will do significant damage (meaning strength is irrelevant).
Even a child, with the right training, can apply enough force to specific locations to cause significant damage or even death (real world examples: it only takes about 2-4 pounds of force to collapse a windpipe, resulting in suffocation and death; it only takes about 1 pound of pressure to completely close off the Jugular vein in the neck - hold for 10 seconds and the target passes out - hold for another 10 seconds and the target can die; a strike on the center of the chest with as little as 10 pounds of force, at the right time, can interupt the hearts beating and cause heart failure - a martial artist trained in the observation of pulse and respiration rythms, could possibly time such a strike to accomplish this - but in real life, even kids are accidentally killed by being hit in the chest with a thrown baseball, baseballs thrown by other kids).
Also, throws and flips use the attackers energy against them, which would also mean that the strength/mass of the martial artist is again irelevent. The martial artist simply becomes a fulcrum for the lever/attacker. A "throw" isn't about actually throwing anyone, but redirecting an attackers energy so they effectively throw themself.
If one also believes in the existence of Ki, the focusing and release of Ki also makes strength completely irrelevent, since the damage is actually the result of, or magnified by, released Ki energy. Although in real-life Ki has never been scientifically observed, measured or proven - martial artists do seem to be able to do things that defy physics. They explain this as the focusing of Ki. Whether or not Ki exists in the real-world, in a game-world it is real and therefore can explain "little man" injuring and defeating "big man" or "monster", even without having enough mass for the percieved application of "power".