15 YO is 5'10" and 120 lbs. Arms seem to hang down to his knees. Very skinny but can throw in the upper 70's/80. Almost seems to fast for his body type/maturity. He has never lifted weights but has become very interested in doing so. Would it be best to build some bulk first?

Correction: He has been lifting for about 2-3 months now. He is in 8TH grade and therefore can't play high school ball in Ohio. He has been doing bench press, chest flys, bicep curls, tricep curls, lat pull-downs, front pull-downs, bent over rowing, sit-ups, wrist curls and baseball throwing. He has some definition but has not added a great deal of body weight. I know these lifts are not baseball specific. Should he continue witn these lifts to add body weight or switch to more baseball specific lifts?

Please clarify some things:
Tricep curls - do you mean tricep extensions with the weight behind the head and the arms are then extended to above the head? If so these are hard on the elbows in the long run
lat pull-downs, front pull-downs - are the lat pull-downs to the back of the neck? hard on the shoulders, pull-downs should be to the chest. If he can chin (to the front) that would be better.
bent over rowing - Barbell or dumbbell? Barbell can be hard on the low back with heavier weights depending on form.
Now - You need to add squats, deadlifts or power cleans and drop the bench press (especially if getting to heavy weights) and chest flyes (hard on the deltoids). Weighted push-up would be better. Oh and add running - start with a mile 5X a week and work up to 2. Then begin to add sprints and work up in these to 10-20 3X a week.
Just remember that mass and strength do not necessarily equal velocity - ask Roy Oswalt. You are throwing 5 oz., how strong do you need to be?
Do some searches of stuff by Jon Doyle as he has many good ideas also.
Hope this helps

Tim Robertson

Start buy building a base. If he is very weak you can start with machines. If he is very weak. However, once he gets stronger, machines will actually start to hinder his performance. It will actually make you worse. I suggest at that point that you go here and http://www.baseballtrainingsecrets.com

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Agreed, he should do all compound movements. 80-90% of his lifting should be compound lifts and only 10-20% isolation work.