Source: Planet Fitness.   

Planet Fitness (PLNT -0.40%) may not have been a scintillating IPO when it made its Wall Street debut last month, but it's sure been making up for lost time. Shares of the gym operator that prides itself on its low rate of $10 a month closed higher for eight straight trading days -- gaining 24% in the process -- before wrapping up Friday off by a mere penny.

Every good streak must end, but Planet Fitness has had its shares of ups and downs despite being on the market for less than five weeks. It raised $216 million by distributing 13.5 million shares at $16 on Aug. 6, only to open lower when the first trading crossed at $14.50. 

Planet Fitness began to bounce back in subsequent days, fetching as much as $19.40 two weeks after its IPO. It didn't stick, and the stock became a busted IPO as it slipped into the mid-teens a few days later. We're now wrapping up the second major recovery in a stock that's been on the market for all of a month, but don't let the volatility scare you away.

Gym operators have historically been poor investments. Beyond the seasonal nature of memberships where folks sign up with resolve in January only to cancel when reality sets in, individual chains can't seem to stay on top for too long. Could Planet Fitness buck the seasonal whims and fickle nature of gym popularity? Its model is intriguing. It charges just a $10 initiation fee and $10 a month, far less than rival operators. The low rate likely encourages members to stick around. Why cancel? 

It's working for now. Revenue has gone from $159.7 million in 2012 to $211 million in 2013 to $279.8 million last year. If the growth impresses you but the actual sums don't, keep in mind that more than 90% of what are now 1,000 gyms are franchisee-owned and operated. Systemwide revenue clocked in at $1.2 billion last year.

Expansion has played a big part in the growth, but the average unit continues to ring up more sales with every passing quarter. Planet Fitness has come through with 34 consecutive quarters of positive comps. That's a pretty buff stat in an industry where success often proves fleeting. 

Planet Fitness served up its first quarter as a public company last week. It was solid. Revenue climbed 26% since the prior year, and adjusted earnings soared 29% to $12.9 million or $0.13 a share. That was just ahead of where the pros were perched, an encouraging sign as it continues to prove that a ridiculously low subscription price can resonate with mainstream audiences.

It added 38 new stores to its growing empire of workout havens. It feels as if it's just getting started. Planet Fitness is targeting 4,000 eventual gyms, a figure that suggests that there's room to quadruple in size from where it is now. With a strong first quarter to kick off its publicly traded tenure and momentum in its corner, it's hard to deny the fitness of Planet Fitness.