It was subtle in the way they all got into it. The days following the end to their training as a whole they were left with their own devices more often then not. A well aged Splinter had offered they take up hobbies or take the time in learning another skill. They all took the latter to heart as Raph took up boxing in a professional way, studying their move sets and working out a regiment to better his skills in the chosen field. This change in combat style required him to learn from scratch, which as frustrating as that was it did have the positive effect of rewarding him with noticeable results. Results given the spotlight during his nights out fighting purple dragons.
Leo took up archery while not much of a combative activity it did offer him much a much needed way of calming himself in both brain and body simultaneously which he was much grateful for. While he was experienced with a bow and arrow he was no where near as proficient as he would of liked to be as such, he practiced. His first month had but anything but eventful seeing as starting from essentially a beginners position allowed for many angering mistakes. Splinters oldened age and deterioration mind allowed for little in way of learning personally from a mentor. His refusal to leave his brothers in search of one left him with no other choice but to learn by himself.
Years would pass before confidence in his abilities became realized as his form became near perfected and aim sharp with precision it was then he took his new learned skills on a testrun from his make shift training room to out into the field against the foot and he was met with little disappointment.
Donatello decided against learning new skills in the way of combat, instead he took up a more reserved activity to keep himself active, jogging. It wasn't anything life changing but it was something Don found himself prior to their training end always wishing he had more time for. Running was an unconscious action and it usually allowed him the ability to clear his mind or to think deep on a given subject. His usual pacing around the lair or his crowded workspace was no more as he instead gravitated more towards going topside or through the sewers. Time passed as his afternoon stretches was followed but long bouts of running. It was probably the main reason for his breakthroughs and it had the plus side of him becoming fastest of the four.
Mikeys chosen hobby was shunned the second it fell from his lips. Redirected to himself as Leo exclaimed that video games was not an activity he should be honing in on and focusing most his attention on. The backlash to the statement was monumental and emotional as this was something none of the brothers knew the younger was all that passionate about. Sure he played them alot and at times stressed about his level progression but that was just becuse it was for fun right? He wished to pursue gaming in a more professional fashion, he did have the best hand and eye coordination of four but Leo's stance stood tall as he rejected the extracurricular activities as noting but. It wouldn't be until later when the topic of gaming became such a controversial issue that Splinter decrepit and senile as he was gained some sense of his older-self and took control of the situation and in an understanding beyond Leo's own granted Mikey the allowance to pursue his gaming in a more professional manner. Down the line it was Mikey who with a smile so wide it dared to split the young adults features snarked at Leo with a smugness as he had managed to save their lives on more then one occation thanks to his faster than sin reflexes.
During this time they still trained in the ancient ways of ninjutsu starting every morning and before bed never ones to forget their origin.