I have a 1hr commute each way, so I use a wrist squeeze device three times per week (M, W, Fri). Its low resistence, so I need to go high rep. I've worked up to 5 sets of 300 each way (3,000 per day, 9,000 per week). Since I started this routine, my forearms have developed a wicked "Cobra" shape with decent vascularity. I'm sure my regular workout (weighted pull ups, heavy shrugs, etc) have contributed to the overall mass.