hey man, yes I was boxing when I was at my leanest ever. The pics at 147 were taken while I was training for boxing. The pics at 155 were a few months after I had stopped boxing and was training for vert etc.
When I was boxing, I was eating like a monster. I didn't eat junk food very often, that's for sure, but tons of sandwhiches, pasta, rice & beans, steaks etc. The reason I had gotten so lean was simply due to my 2 workouts a day: boxing in the afternoon or morning, jump rope + road work + shadow boxing at night. Those night sessions were brutal, I was putting in serious jogging mileage every week (around 30+, combined with all of that other training). So, that's the #1 reason I was so lean during that period, I ate a ton more than I do now in comparison, but I do have more muscle mass now and I'm alot stronger.
I wouldn't recommend that activity level for vert/power though, that's for sure. I had some great endurance, my legs felt amazing, but I just had no power in my hips/legs.
peace!
