Now, ask yourself this: how can anyone expect to improve his physique, or mental fortitude for that matter, in a gym that tries very hard to discourage its members from making any real effort? (fitnessandpower.com)
20 minutes on the battle ropes is indeed possible with mental fortitude. (onnit.com)
Those hills are hard and require mental fortitude as well as physical strength. (got2run4me.com)