Few hand-strengthening devices are simpler or more effective than the GRIPPRO TRAINER ($7.95, gripprotrainer.com), heavy-duty rubber donuts available in three resistance levels: 30, 40, and 50 pounds. I was able to work the 30-pound GripPro for 45-plus reps before getting a burn, whereas a mere 30 squeezes on the 50-pounder had me grimacing. (Worth noting: I’m a big guy with big hands — the 50 might further challenge small folks.) The light and medium trainers are great for pre-climb warmups, road trips, or at-the-desk angst relief; then you can go heavy when looking for a serious workout. The Trainers are also indestructible, affordable, and handy — it’s nice to own the whole set.