Typically when working with a client we ALWAYS start training our larger muscles first unless working on full body, functional or athletic movements. If weight training we would spend the majority of the time training muscles originating from the shoulder/pectoral girdle, spine, and hips. Muscles of the arm and forearm would take a back seat and would only be used as secondary muscles. For example we would never train biceps with curls before performing chin-ups (basic compound back exercise). To gain lean mass and even use more calories we want to keep our attention and energy on our larger muscle groups, making them the priority.
New research gives us more reason to train BIG before small. Norwegian researchers found, when studying the effectiveness of our anabolic hormones (testosterone, growth hormone, IGF-1) on increasing muscle mass, that arm strength improved more so when the arms where trained after leg exercises than when arms trained alone. It seems that training the large muscles of legs maximized anabolic hormones thus helping the arms to grow themselves. Instead of isolation, muscles respond better to workouts emphasizing an increase in anabolic hormones of the body. (European Journal of Applied Physiology, Feb 16, 2011)
Put it to use: Here is an example of partnering smaller muscles with larger.
Push- Pair your triceps with both the shoulders and chest.
Pull- Pair your biceps while training the large muscles of the back
Legs- Be sure to train your legs consistently to improve lean muscle mass throughout the body.