Let’s take a look at what’s going on…
Martial arts is about learning how to move your body efficiently. Efficiency in sport means that your movement economy allows you to maximize the output with minimal input. With sports mastery, technique takes over fitness, and your refined movement patterns have a lower energy cost than before. This means that to get the same feeling as the first time you ever performed 10 continuous kicks, you may now need 50. (Translation: less energy necessary for more work)
The law of diminishing returns (taken from economics) states that exercise will cause the body to adapt to a specific stimulus, and eventually, as the training stimulus continues to increase, the fitness gain will become smaller and smaller. This means that increasing to 20kicks from 10kicks may be a strong training stimulus, but when another 10kicks is added, the training stimulus won’t be as strong as the 10kick increase before. This will continue for every 10kicks, and eventually, there won’t be much difference between 120kicks and 80kicks. (Translation: more volume necessary for a gain in fitness)
So now that we need less energy for more work, and we have accommodated to a training stimulus, we now need more volume for a gain in fitness. This means your normal 60minute training session may need to increase to 120-180mins. Not everybody has the luxury of training for this amount every day (due to work, family and a social life for the few fighters who have one), and there is a chance of the athlete developing volume-induced overtraining (which should be avoided at all costs).