I've spent a long time being keenly interested in combat sports, having competitively boxed for nearly a decade and having been a fan of all combat sports for over 25 years. In this time I've observed a slow evolution in the quality of these athletes movement. This change in movement styles has followed a change in training styles.
During my competitive years I would study footage of old fighters and in those videos I would notice a smoothness to the movement, a fluidity that I didn't see much in contemporary fighters. Boxers such as Ray Robinson, Pernell Whitaker, Muhammad Ali, Jersey Joe Walcott, and Willie Pep are great examples of this fluid movement. In contrast the contemporary fighters I was watching at the time tended to move in a more stiff and rigid manner. They're style was often more refined in many ways and they were still incredibly strong and skilled athletes, but there was a awkwardness to their movement that I couldn't stop seeing after comparing them to the older fighters.
After spending many years in a number a boxing and martial arts gyms I felt like I had discovered what happened. The older fighters would usually train with techniques like running, jump rope, heavy bag work, calisthenics and sparring. Occasionally you would see other modalities but they were a rarity. The benefit of all this basic training styles in that they are all full body athletic movements. Each one of them helps integrate the body and teach it to act as a single unit. In a sense they were performing athletically functional training regimens.
The more modern athletes, beginning in the 80's moving through to recently had altered the primary training techniques. While still utilizing the old techniques a lot of strength training had been added, and in particular body building style exercises. Body building style exercises do increase strength and they definitely gave the athletes a more muscled physique, but it also made them more stiff and less fluid.
Body building techniques often isolate muscles and teach the body to work in a disjointed manner, with the biceps learning to contract independently of the front delts and coracobrachialis muscles of the shoulders. While this will give you impressive looking arms, they will no longer move in sync with each other which is necessary for maximum power and peak athletic potential. Not to mention the increase in injury risk associated with this type of training.
However there has been a more recent evolution in the combat sports once again. Many of the strength training methods tried in the last decades have been sifted through and battle tested. New forms of strength training that incorporate the entire body such as kettlebells, steel mace and clubs, landmine training, and others have begun to gain wide acceptance. While old methods that yielded similar results such as calisthenics and gymnastics training have seen a resurgence. The result is a stronger athlete that is not athletically hindered by their strength training but instead enhanced by it.
Combat athletes are popping up left and right with strength, power, speed and yet exhibiting a grace of movement not seen in decades. Stand out athletes that come to mind include Fedor Emelianko, Floyd Mayweather, Roy Jones Jr, Conor McGregor, Jon Jones, Michael Venom Page, and Vasiliy Lomachenko. All of these athletes and many others have brought back graceful movement and added much more. They are at the pinnacle of the modern combat evolution and leave me excited for what's yet to come in the years ahead.
If your further interested in incorporating more functional training modalities into your combat or martial regimens, check out the book "Ultimate Conditioning for Martial Artists" by Loren Landow. It's chock full of interesting an unique training exercises divided by each individual martial art. Great resource for any martial artist.