With the CDC reporting that over 70% of Americans are overweight, it's no wonder the top two new year's resolutions are staying fit/healthy and losing weight. Even if you're not shelling out for a gym membership or figuring out how much apple cider vinegar you need to drink each day, you can still get in on the fitness craze and its moneymaking potential.

Investors should consider four companies that cater to people focusing on their fitness: Planet Fitness (NYSE:PLNT), Mindbody (NASDAQ:MB), Fitbit (NYSE:FIT), and Under Armour (NYSE:UA) (NYSE:UAA).

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Planet Fitness welcomes everyone to the gym

Planet Fitness sets itself apart from other gyms by focusing on a "non-intimidating" environment where "everyone's welcome" at a value price of $10 per month. This approach has paid off for the company as 40% of members who joined in the last two years had never belonged to a gym before.

Planet Fitness has impressive unit financials with the average location clearing $1.8 million in revenue annually and 9.6% comps that contributed to 12% revenue growth last quarter. With only a $1.6 million start-up cost and a 40% EBITDA margin before franchise fees, it's easy to see why the company is looking to triple its current footprint of 1,367 stores. While the stock is at an all-time high as of this writing, the company has plenty of opportunity to sign up new members and add new locations in an environment where abandoned retail space can be snapped up on the cheap.

Three women in exercise clothing running on treadmills.

Image source: Getty Images.

Find a fitness class with Mindbody

Mindbody sells subscriptions to its cloud-based business software platform to businesses that provide boutique fitness, integrative health, and salon and spa services. Mindbody's platform allows small businesses to manage employees, collect payments, and facilitate online appointment bookings. With $170 million in revenue in the last 12 months, Mindbody is still incredibly small compared to the $9.5 billion global market for business management software in the wellness industry.

The company's growth has been impressive, with 32% revenue growth, 8% growth in high-value subscribers, and 23% growth in payments volume in the most recent quarter. Now the company is trying to help its customers win over millennials by playing to their tendency to make plans at the last minute with easy-to-book wellness appointments on its mobile app. I like this company's focus on wellness businesses and innovative approach to helping its customers grow. Even though the stock is up 40% over the last year, this company has plenty of opportunities.

Stepping up with Fitbit

Fitbit sells fitness trackers that aim to inspire, coach, and guide users on their health journey. It's the No. 1 fitness tracker brand and has the best-selling fitness tracker on the market. Recently, the company released its long-awaited smartwatch, but the company has run into some challenges with a reduced sales outlook, layoffs, and negative year-over-year revenue growth in the last four quarters.

My investment thesis is that Fitbit's can move beyond a consumer tech device and be known as a health company. The company has made steps in this direction and was recently selected as one of nine companies as part of the FDA's digital health precertification pilot program. With the company valued at 2.2 times cash, the market thinks that Fitbit will go the way of many other consumer tech companies, but I think it can grow beyond its fitness tracker beginnings.

Under Armour wicks away sweat

The idea of a performance T-shirt that wicks away sweat to keep athletes cool during workouts launched Under Armour as a global brand that competes head-to-head with Nike and Adidas. Once a Wall Street darling, the company's streak of 26 quarters of 20%-plus revenue growth came to a crashing halt in Q4 last year. Since then the company has struggled with revenue growth and posted its first ever revenue decline as a public company.

The main challenge for Under Armour is its heavy dependence on the North American market, where its revenue declined 12% last quarter. While the company's international and direct-to-consumer businesses grew a healthy 35% and 15% year-over-year, they are still too small to move the needle with the domestic business making up 77% of revenue. While the stock sits at a four-year low, the price-to-earnings ratio is at a nosebleed level of almost 50. This company may be a risky bet, but I think this high-tech apparel company has plenty of opportunity to be much bigger than it is today.

While there's no way to guarantee that these stocks will beat the market in the long term, each of these companies has a solid brand and growth plan. With Planet Fitness' low-cost model, Mindbody's focus on a niche market, Fitbit's opportunity to move beyond its devices, and Under Armour's global reach, they each should be poised to reward patient investors.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.