How pros train nowdays?

Not really interesting, there could be many reasons they don't use weights.

1. They're ignorant of facts and think weights slow you down/cause injuries etc.
2. They don't need them.
3. They simply don't want to use them.
4. They're worried about using them for reasons spouted by ignorant old school coaches.
5. They don't know how.

Just a few reasons why they may not use weights.

I've seen so many people use the "Ali didn't use weights!" line, it's old and proves and disproves nothing.

Listening to a boxer talking about lifting weights is like listening to your bank manager for advice on your diet - more than likely it's an ignorant opinion.

 

Why would Mayweather be an authority in any way for weights in boxing? He's not in that field, he's a boxer. He doesn't have time for performing scientific experiments and getting them published in journals. His success is because he's been boxing since he was a kid in a boxing family, with a great work ethic. He could've done anything or nothing on top of boxing training and still been successful. If Mayweather regularly performed olympic weightlifting who is to say he wouldn't be a more explosive power puncher to compliment his skills? And I doubt Floyd knows much about what Bradley did or what the effects of what Bradley did would be.

 

Does long distance running have almost no advantages to cardio for boxers? What about swimming laps?

Also how much running is too much.
I personally run about 3-4 km, not just running forward though but also sideways and backwards. Would i really benefit that much more from sprints?

Oh and while we are at it, i've heard from a few youtube fitness gurus that front squats are much better for athletes than regular squats. Agree or disagree.

 

It depends on your training load, if you train boxing intensely 3+ days a week your 3-4km runs are probably a good break and allow some recovery if that's all you do on those days. So indirectly they'd help you due to the recovery factor, they wouldn't be doing much directly for your fitness though. Sprints will help you move faster and more efficiently, if you want to improve yourself athletically there's really nothing much better.
If I wanted to get fit for boxing my general preparation phase would consist mostly of sprints for conditioning as the energy system requirements of repeat sprints mimic that of boxing. You wouldn't want to be doing 3 sprint sessions a week and train boxing intensely 3 days a week, you'd burn out pretty quickly. So you need to plan your training and adjust as you get closer to the sports specific phase.

It depends how you squat, if you squat low bar powerlifting hips back style then they have little transfer to athletic movements, if you squat more upright like a weightlifter there will be more transfer to athletic movements like jumping. Front squats then by their nature have more transfer to athletic movements but you can lift more with back squats, so ideally you want to do both. The reason why front squats are so great for athletes is that they also help you out with the receiving position in the clean/power clean and variations, which help out an athlete more than any other weight room exercise. It's also important to do exercises like nordics and RDL's to keep your hamstrings strong for those sprints, when you squat more upright there is more emphasis on your quads so you need to balance it out.