Saving money can lift your spirits and fill your wallet. After a while, though, pinching pennies may start to hurt.

Welcome to "frugal fatigue."

"It's a very real concern," says James E. Burroughs, a commerce professor at the University of Virginia in Charlottesville, who specializes in consumer behavior.

"I think it speaks to the challenge," he says. "It's very important for people to become habitual in their finances."

A budget and willpower can help you fight frugal fatigue. But it also never hurts to have a couple of proven tricks on your side.

"It's psychological jujitsu," says Douglas E. Hough, associate scientist, with the Johns Hopkins Bloomberg School of Public Health in Baltimore. "Instead of going up against the Force, you're using the Force to help you get there."

Here are six strategies to outwit frugal fatigue and treat yourself without breaking the bank or getting permanently off-track financially:

Strategy 1: Break your goal into small pieces -- and celebrate each step.

People are oriented to the present, a result of "hyperbolic discounting," says Hough. "That's a fancy term for saying we really like the present more than the future," he says.

Overriding that hard-wired programming can be difficult, but celebrating short-term milestones can help. For instance, if you want to save $50,000, break it down into smaller chunks. Maybe you can put aside $5,000 over the next six months, Hough suggests. When you get to $5,000, reward yourself, by taking a chunk of it -- say, $500 -- for yourself. "So you've got a real reward here," he says.

Strategy 2: Take charge, and frame it as a positive.

When fighting frugal fatigue, remember to remain upbeat. "Being optimistic can give you the psychological energy to counter that fatigue," Burroughs says. "When you see it in those terms, it becomes sustainable."

Need to save a pile of money to dig out from a mountain of debt? Think about what you will do, and how you will feel when you're debt-free. And give yourself kudos for taking the steps to make that happen.

Strategy 3: Make sure goals are reasonable.

Looking at a budget as a financial diet is a "very appropriate" metaphor, says Burroughs. People tend to set draconian goals that are not sustainable, he says.

Instead, Burroughs advises you to "set reasonable goals that let you balance living for now [with] living tomorrow." "When consumers go on the extreme financial diets, it's inevitably going to fall apart," says Burroughs. "You have to be careful about being so aggressive."

Strategy 4: Eliminate a few purchases entirely. 

How you spend your dollars can lessen the chances of frugal fatigue, says Chris Hydock, researcher at Georgetown University's Institute of Consumer Research in Washington, D.C.

"When you are experiencing a constricted budget, you tend to buy less variety," says Hydock. That's a good thing, he says. Recent studies have shown that buying less variety is a smart way to stay on budget. It is often less painful to eliminate a few items entirely than to try and buy all the items you typically purchase, only in smaller amounts, Hydock says.

Strategy 5: Beware your blood sugar.

Want to maintain a budget? Watch what you eat.

"Fluctuations in glucose levels can make us more impulsive when it comes to our financial decisions," says X.T. Wang, professor of psychology at the University of South Dakota in Vermillion. 

Experiments have shown big swings in blood sugar reduce self-control. Eliminating those peaks and valleys and "regulating the fluctuation is a good way to reduce these impulses," Wang says.

When you shop, reach for a snack that is low on the glycemic index, which measures the impact that foods have on blood sugar. Fruits such as peaches or strawberries, or nuts, are good choices.

Strategy 6: Look at buying decisions from another angle.

You have heard the old saying, "A dollar is a dollar is a dollar." Deep down, your brain believes differently.

Blame a concept known as "mental accounting," says Wang. Studies conducted by Nobel Prize winner Daniel Kahneman and his colleague Amos Tversky found that people act as though some buckets of money are worth more than others, even if they are equal in amount. 

For instance, if you lost a $30 concert ticket, would you replace it? The answer is "yes" about 50% of the time, depending on the individual, says Wang.

But tweak the question and you get a different answer. If you had not yet purchased the ticket and lost $30 out of your wallet, would you still buy the ticket? This time, about 90% of people will say "yes," he says.

In each case, it is the same person and the cost of the action is $30. But we segregate money into different piles in our heads, Wang says. And that $30 has different value depending on where it is placed.

So if you do make a mistake or fall off the budgeting wagon, keep it in perspective.

See related: How to stick with a frugal lifestyle, Finding fun while staying frugal