Get stronger. It may sound obvious, but stronger muscles equals bigger muscles. CrossFit incorporates Olympic lifting and powerlifting-style movements but no arm isolation exercises. Still, you can build mass, according to 2011 and 2012 CrossFit Games champion Rich Froning. He adds that you can look like a bodybuilder when doing CrossFit, provided you work on increasing your strength.
Focus on movements that work your upper body. Most CrossFit workouts work the whole body, and while training your legs is important if upper-body training is your priority, there's no harm in performing more upper-body-specific workouts. These routines include chin-ups, pushups and handstand pushups, dips on gymnastic rings, overhead presses and jerks.
Get really good at kipping pull-ups. Kipping pull-ups are CrossFit's answer to the regular pull-up. Kipping pull-ups still involve hanging from a pull-up bar and moving your body up from a straight arm position until your chin is over the bar, but they permit the use of a lot more momentum. Start each rep by swinging your legs to build up some speed, then violently pull yourself up.
Add in one or two days of isolation arm exercises each week, advises Pedro Quiros, owner of CrossFit thump. To make sure you have energy for your regular CrossFit workouts, it makes more sense to train your arms on a different day. Your session could consist of dumbbell curls, barbell curls, cable push-downs and close-grip bench presses, each performed for three to four sets of 10 to 12 reps.
Up your protein intake and start packing in the calories. You need these calories and protein, along with healthy carbs and fats, to build muscle mass. CrossFit endorses the Paleo, or caveman diet, meaning you'll be eating lots of chicken, steak, salmon, eggs, fruits, sweet potatoes, nuts and coconut.