Ability to train harder and avoid injuries. Therefore you can enter the ring fitter and with more training completed. Increased strength and stamina. There is a good reason why all the top fighters are on a concoction of medications. And the smart ones micro dose so they never fail a test.
Not just Boxers, but any athlete, and the answer is in any possible way you can think of. Helping improve performance all around, better recovery, better stamina, more power, more strength, hence more speed if they know what they are doing. They can help with fighter being more durable based on a lot. Just look at the Alistair Overeem before he was caught and ban for Peds, and after. And have in mind that he was 100% on PEDS after, but 100% on a lot lower dosage. I don't think he even cycle before he was caught, he was just full time on them. Full throtle.
Not just. In training as well. You can do a lot more volume, even with basic PEDS on low dosage. I can confirm this, as i was taking PEDS in the past. Your training in the gym and the volume you can go in, and not just in Boxing/Martial Arts, but in the Weight Room as well. It's not even comparable what you get compare to being clean. It's totally different ball game.
Depends on the PED's they take. Anabolic steroids will enhance strength and power as expected but also improve recovery which will allow them to train harder more frequently with less recovery. Then you have PED's designed to enhance endurance and stamina. Then you have PED's designed to help fighters make weight, so they can cut down to a lower division they normally couldn't make.