Willpower is baffling. Especially when it comes to willpower for exercise. It seems to fall along a fluid spectrum with some amazingly disciplined, others boasting spurts of regular exercise, and some avoiding fitness much of their lives. Many of us slide back and forth varying points along the spectrum across our lifespan.

Science has much to say about willpower. Here are a two important willpower nuggets to ponder within a fitness framework:

• The brain has limited capacity for self-regulation. Research has shown exerting willpower in one area can potentially deplete the willpower bank -- meaning you may have less willpower for a second withdrawal in the near-term. People investing self-control to complete one task are not necessarily as persistent on a second, unrelated task.

Hmm ... makes me want to take off my Super Mom multi-tasking cape, it's like a Depression-era run on my personal Bank of Willpower. No wonder I feel I can't get anything done unless I focus on only one or two tasks. So if you're just starting a fitness program, remember willpower is finite. Don't simultaneously begin to tackle other serious tasks as they may undermine your original goal to get fit. Keep it simple! But once you've been hitting the cardio and weights for awhile, get this:

• Willpower is a muscle -- it grows stronger with use.

I love it! Consistently using your willpower is a compounding investment. Keep making deposits by visiting the gym and your fitness willpower will spill over to positively influence other areas of your life. One study showed people adhering to an exercise program for a mere two months reduced their impulsive spending, junk food consumption, alcohol use and smoking.