Weight training out of season

That's a nice program, if you want to gain physical strength (not punching power) and a bodybuilder's physique. For a boxer to have that as sole training, it's terrible. You will bulk up, go up a few weight classes, with little gain in actual power, lesser stamina, and slower hands.. all the while fighting guys who are naturally bigger than you.

Mind you, it does take 6 months of doing this program (and this program only) before the mentioned effects will come into play. Depending on your diet, dedication and genetics, you may gain 10-20lbs of good looking but rather useless boxing muscle in half a year.

If you want to stay in boxing shape, then just run twice a week, do small weight training (many reps, stay fast and explosive) or none at all and just go for shadow boxing, some pushups, sitsup and cardio exercises.

 

Bulking up will depend on your training and diet.
If you do your regular cardio and boxing training, you won't grow that much as your body will not want to be any heavier. But you will get stronger from the strength training.
And obviously if you don't eat a lot you won't gain weight.
You won't get slower and worse stamina overnight, it would take a fair bit of work and diligently neglecting those areas for quite a while before anything happens.

If you have tendonitis, then you have to do the opposite movement of what caused that tendonitis. I would imagine if its in the elbow its too much extension. So 3 times a week do 50-100 reps of curls with some weight, can be the empty barbell or even some dumbells, but you need to do the opposite of what bothers you to flush blush to the area and bring balance to that area. tendonitis is usually just too much of one thing and not enough of the other. There are exceptions but shoulders/elbows are the most common as they are small weak joints to begin with, couple that with people boxing on these weak joints and extending the elbows and rotating their shoulders internally thousands of times a week, and you have a solid recipe for tendonitis and injury. Strength training to help a sport is probably more about injury prevention and strengthening the areas you don't think about, than it is gaining speed, physical strength and size.

 

In my experience, the most useful boxing exercises are ones that have your body or parts of it moving relatively fast: shadow boxing (general), heavy/speed bag/pad work (power/technique/general/coordination), roadwork (conditioning), rope skipping (coordination, conditioning), swimming/cycling (general conditioning), etc.

Low rep weight lifting can be good for general development if you feel you lack strength, but to have it as your sole exercise for a prelonged period (several months) can be detrimental, considering boxing has weight classes and depends largely on stamina, endurance and speed, and your power will not increase that much. Lifting weight will make you better at lifting weights, not at throwing punches.

If in your position, i'd focus on a lot of cardio exercises. If you can do light weight lifting, then you can also do light shadow boxing? At any rate, be careful and take the time to heal, while keeping your general conditioning on level.

 

I dont bother with weight lifting any more. Just do my own body weight excersises.