Lead arm/shoulder gets tired too quickly

[T.Horton]

To strength your shoulders and keep your hands up for defense better, shadowbox with 6-8 lb dumbells in your hands. No punches, just use footwork and defensive moves (parrys/blocks/upperbody movement). That'll work wonders for building strength for keeping your guard up.

my man! for the past few months i have been running with five pound weights and my speed and power difference is already noticeable.

[Walt Liquor]

my man! for the past few months i have been running with five pound weights and my speed and power difference is already noticeable.

those little weights do a lot for you, I'm looking for the thigh weights that you strap on your thigh and run with. I can't stand the vest.

[OG Van Persie]

You need to work on muscle endurance for your arms and shoulders. Do some light weights (about 40-60% of your 1 rep maximum). Do 14-20 reps, 5 sets with 45-60 seconds rest between each set.

Focus on your deltoids (medial, posterior and anterior), biceps and triceps.