Bowfit is ok, I bought a couple different weight range models for my wife. Getting out and shooting your bow on a daily basis helps greatly. Both the Bowfit and shooting your bow is only strengthening one shoulder and puts your body out of balance. To have true balance and form you must strengthen both sides. You wouldn't just do arm curls with your right arm would you?
If you really want acheive then start free weight strength training. Military Press, shoulder shrugs, shoulder dumbell fly's, upright rows.....those are exercises that will work primarily your shoulders/traps, but you work your back when pulling back your bow as well, so you need to strengthen it too.
I recommend something to work all your major muscle groups.
1) Bench Press, works out your chest, shoulders, triceps
2) Seated Miltary Press, works out your shoulders, trapazoids
3) Bent over Rows, works out your back, shoulders, traps, biceps
4) Tricep curls, isolated work out for triceps
5) Squats, works out every major upper leg muscle
6) Deadlifts, works out every major upper leg, buttocks, upper/lower back & trap muscle
Any extra time add some bicep curls and any of the other shoulder exercises above.
Figure out what your 1 rep max is for the 6 lifts above and do 3-5 reps with 90% of your 1 rep max and then another set of 3-5 reps with 10% less than your first set. Do this 5 times a week with no more than 1 day rest in between workouts. Increase your weight weekly and you'll gain strength at an unbelieveable rate and soon be able to pull back high weight bows like they're toys.
I work 10-12hr days, with and hour drive there and an hour drive home, and still manage to strength lift an hour a day 5 times a week.....and I'm married with 4 kids.
