Demetrio, which scientific approach are you referring to in combat sports, that you see absent in martial arts, specifically?
There are lots of studies about what affects performance in sports (food, biomechanics, training methodologies, psychology, metabolism, genetics...) combat sports included. Martial arts studies about performance are few and far between.
Try this for instance:
-Go to google scholar
-Search: judo performance training
-Search: aikido performance training