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This story is part of a series on how getting fit and healthy can boost your bottom line.

Sticking with a fitness routine isn't always easy. Try focusing on the potential rewards: Heading to the gym at least three times a week has been linked to higher pay—7% more for men, 12% for women, according to Cleveland State associate professor Vasilios Kosteas. Improved energy levels, mental acuity, and mood may be fueling the boost.

Another recent study found that couch potato workers were at 20% to 34% higher risk of taking long-term sick leave than their more active peers.

And, of course, exercise also helps protect you from numerous costly ailments, from diabetes to stroke, with lasting, sometimes unexpected benefits. For instance, studies show that midlife fitness leads to lower medical costs in retirement.

The best free help

Fitness trends come and go (Tae Bo, anyone?), but the basic rule for how much exercise you need is simple: 150 minutes of moderate intensity or 75 minutes of intense physical activity a week (or a combo of both), and strength training at least two days a week, says the Centers for Disease Control and Prevention.

“If everyone did that, we’d be much more fit and healthy,” says Lisa Cadmus-Bertram, an assistant professor of kinesiology at the University of Wisconsin at Madison.

If you’re time-crunched and can take the discomfort, try high intensity interval training, which alternates short bursts of all-out exercise with recovery periods. But above all, find something you like—or at least tolerate—so you keep it up, says Anthony J. Wall, director of strategic partnerships at the American Council on Exercise.

Start your program at the office. According to a 2016 survey by the National Business Group on Health and Fidelity Investments, 84% of employers offer a physical activity program or challenge, while 71% have on-site fitness centers or classes. Even on your own, you don't need to spend a lot—think comfortable shoes and a place to walk or run.

Help worth paying for

There's no shortage of ways to spend money on working out, from gym memberships to high-tech shoes. Sometimes splurging pays off. A personal trainer can be worth it if he or she helps you establish and reach goals (you'll pay about $75 an hour, or $100 to $125 in major cities). "Some people benefit from the accountability," says Cadmus-Bertram.

Give yourself permission to pick up that Lululemon yoga gear— $48 sports bra, $64 tank top, $128 cropped tights, and $18 headband—or the pair of high-end sneakers you’ve been eyeing. “If buying a brand new outfit for $250 will put you in the mindset to be active over a long period of time, it’s the right choice for you,” says Wall.

What's not worth the money

Pass on the $3,000 universal gym. Kettlebells and a stability ball ($20 to $60-plus) and a TRX Suspension Trainer ($170) do the job fine. "Those things will never break down and don't take up a lot of space," says Nick Clayton, personal training program manager at the National Strength and Conditioning Association.

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Wearable devices can be helpful if they spark an exercise habit, says Kevin Volpp, director of the Center for Health Incentives and Behavioral Economics at the University of Pennsylvania. But, he says, “once the novelty wears off, many people stop using them.” So skip the fancy $250 models. A basic $60 Fitbit Zip or $50 Jawbone UP Move is all you need.

Or, if you can carry your smartphone while you work out, use a free app that will track your activity level, such as Moves or Health Mate. Volpp’s research suggests they’re similar in accuracy to wearable trackers.