After years of neglect, hotel fitness centers are finally getting into shape.

In the before picture, we see a wimpy gym housed in a claustrophobic, overheated room sparsely furnished with a garage sale assortment of equipment. With rusting parts and zero ventilation, the facility could be ruled a health risk. But the dawning of the age of health consciousness has sparked an evolution of fitness centers, sending subpar gyms the way of the bedside ashtray.

"I've seen a huge change," said Denise Austin, an established fitness expert who frequently finds herself working out in hotels. "Years ago, there was a small room that you opened with a card key. It would have a little treadmill, a few tiny weights, maybe a mat. And there would be one man in there. It was creepy. But now hotels are trying to make it a priority. They are building full-service fitness centers with spas and pools."

Today's fitness rooms are pumped up on adrenaline, replicating guests' hometown gyms with highly advanced cardio and strength-training machines, separate areas for yoga and stretching, and classes for muscle and mind. Some hotels have even devised services to address the unique challenges facing fitness-minded travelers, such as remembering to bring their sneakers. But mainly, the upgraded facilities advance a central goal: to help guests comfortably maintain their routine away from home, thus avoiding bringing home extra pounds of baggage.

"Over the course of 20 years, fitness centers have gone from optional to required," said John Sarver, director of design and development at Hotel Fitness Club, which creates hotel fitness centers and products. "The rooms weren't matching what consumers wanted."

Through surveys and studies, the industry has learned that travelers place a high priority on fitness centers and may pass on a property if it lacks one. Sarver says the presence or availability of a gym is one of the top three factors influencing booking decisions, after location and price, and is among the most desired amenities.

An April study conducted by D.K. Shifflet & Associates, a travel research and consulting firm, reveals the importance of exercise facilities: More than 25 percent of 405 business travelers said they would book a hotel if it offered a 24-hour fitness center. They won't have to look far: In the American Hotel & Lodging Association's 2010 Lodging Survey of 8,500 U.S. properties, 83 percent said that they have an exercise room/health/fitness facility, up from 79 percent in 2008, 75 percent in 2006 and 63 percent in 2004.

"For me, the gym is key. It's more important than the room," said Mark Holt, a Portland, Ore., guest who was using the gym at the Sheraton New York last month. "I go online, look at pictures and get an idea of what they have."

These days, it's easier to find a gym that matches your exercise goals. Many of the major chains are elevating their facilities while also standardizing them from property to property. Guests will find the same quality of equipment and programs no matter the Zip code. For example, in October, Sheraton rolled out its Sheraton Fitness Program by Core Performance in 100 hotels, with the goal of outfitting all its properties by year's end.

"It's a comprehensive approach," said Craig Friedman, director of the Performance Innovation Team of Core Performance, which helped create the Sheraton program, "that helps guests feel like they have the same tools on the road that they do at home."

The multi-pronged course, part of the company's $6 billion overhaul, completely reimagines the chain's approach to fitness. Among its renovations and innovations: upgrading the equipment; revamping the interior design of the fitness centers (the Sheraton New York, for example, features new linoleum floors that imitate blond wood); providing guests with sample workouts based on time and needs, available on its Web site ( www.sheratonfitness.com ) and in the gym; and stocking the front desk with gyms-in-a-bag for in-room sessions, complete with a half-hour fitness video.

For guests who tend to pack light or absent-mindedly (a.k.a. leaving one sneaker under the bed at home), the Westin, like Sheraton a Starwood property, has partnered with New Balance to create a free loaner program. (Fairmont has a similar arrangement with Adidas, available to its frequent-stay members.) Last year, 10 hotels started providing guests with a locker room's pile of apparel, such as running shoes with disposable insoles, shorts, shirts, socks, capri pants and sports bras. Despite the visceral ick response (sports bra swapping?), the hotel has received encouraging feedback from guests who slipped on the communal togs.