If you think your workouts are tough, you should try Patience Cogar's.

Come Saturdays, you can find this Pilates instructor from New Orleans in full triathlon-training mode: cycling, running and swimming for hours at a time in the region's infamous heat and humidity. It's a workout that begs for a sports drink to hydrate and fuel the body. "Carbohydrates, carbohydrates, carbohydrates," said the 29-year-old Ms. Cogar, echoing the endurance athlete's traditional mantra.

Last year, though, intrigued by some research that has been causing a buzz among her training peers, she decided to add a little protein to her on-the-go intake - "just to see if it was going to help me or not." She now adds to her water bottles Endurox R4, a powder that contains a gram of protein for every four grams of carbohydrates. "I can go longer and stronger now," Ms. Cogar said.

For years, carbs have enjoyed a stranglehold on sports nutrition. Carbohydrates are in fact an ideal fuel for the body during and after exercise: they are digested easily and quickly, and they replenish the glycogen (a form of stored sugar) that powers muscles. Protein, long believed by physiologists to slow digestion and hydration, was until recently recommended only after a workout - to repair muscle damage.

But in the last year, studies have suggested that ingesting carbohydrates and protein in the proper ratio during exercise may provide surprising benefits, including increased endurance, enhanced hydration, and even faster muscle recovery after the workout. And although the jury is still out on the validity of the findings, the data are spurring many endurance athletes to switch sports drinks. "Recovery drinks" infused with protein are becoming the drink of choice for some of the world's fittest people, and, some experts predict, they may soon become the next generation of sports drinks for average exercisers.

Most sports drinks containing protein are the kind you can mix yourself with protein powders. Popular brands include Endurox R4, Cytomax Recovery, PowerBar Recovery and Spiz, a nutrient-heavy meal replacement used by some ultramarathoners - who race distances longer than the traditional 26.3 miles. All of those contain ingredients in high concentrations that can be difficult for the body to digest during exercise.

More recently, drink makers have pared down recipes to create products that are easier on the stomach during exercise. These include Hammer Nutrition's Sustained Energy, Champion Nutrition's Revenge Pro and PacificHealth's Accelerade.

The market is still small. Recovery drinks amount to about $10 million in sales each year, said Dr. Robert Portman, who founded PacificHealth Laboratories in Matawan, N.J. That is but a sliver of the sports-drink pie, which last year reached $3.9 billion in retail and vending-machine sales, according to Mintel International Group, a market research company. But sales of recovery drinks and other drinks with protein have seen significant revenue increases in recent years.

"If you were going to look at the next new opportunity in fitness beverages, protein would be a likely place to look," said Gary Hemphill, a managing director of Beverage Marketing Corporation, a research and consulting firm in New York. "Serious athletes really lay the groundwork for the development of the market."

Converts are spreading the word on Internet message boards. One cyclist wrote on Bikeforums.net in May that when he takes a bottle of Accelerade with him, "I'm good for three-plus hours of hard riding in the summer heat." And a marathoner, posting in the Runner's World forums last month, credited drinking Accelerade during long runs with faster recovery: "I have to say my after-run soreness has substantially decreased."

Lee Gardner, 33, a triathlete from New York, recently tried a number of protein-enriched beverages, finally settling on diluted Accelerade for workouts longer than an hour and Amino Vital for postworkout recovery. "I seem to be recovering these days quicker than I did before," he said.

The science justifying drinking protein during a workout may be preliminary but to some it is intriguing. Researchers from James Madison University looked at the effects of protein drinks on cyclists pedaling to exhaustion. Their study, published in May in the journal Medicine & Science in Sports & Exercise, found that a 4-to-1 carbohydrate-protein solution taken during exercise could decrease muscle damage.

A second study by the same scientists found that cyclists who drank Accelerade (a 4-to-1 carbohydrate to protein mix) could ride significantly longer than those who drank Gatorade. The extra endurance could not definitively be attributed to the extra protein, however, because the athletes who drank both carbohydrates and protein consumed more total calories than those who drank carbohydrates alone.

A recent study in Spain found that a 4-to-1 carbohydrate-protein solution is more quickly absorbed by the stomach during exercise than a carbohydrate-only beverage is. And research financed by PacificHealth (which makes Endurox R4 and Accelerade), found Accelerade to be 15 percent more effective than Gatorade and 40 percent more effective than plain water for the purpose of rehydrating athletes.

Many in the medical community remain skeptical. "I'm cautious," said Dr. Domenic Sica, an internist at the Virginia Commonwealth University Medical Center in Richmond, who works with the school's athletic department. "There are some data that exercising to the point of exhaustion can be improved upon by provision of protein. But it's just an observational phenomenon. Mechanistically it's not been proven yet."

Dr. Eugene Hong, the chief of sports medicine at Drexel University College of Medicine in Philadelphia, said, "The big problem with most of these studies is that a very small number of people is being studied."

Molly Kimball, a nutritionist with the Ochsner Clinic Foundation in New Orleans, is less skeptical. "Carbohydrates are our muscles' main source of energy, but protein seems to make the cells open up and accept that fuel more readily, so you're looking at more efficient entry," she said.

Ordinary exercisers may not benefit as much from drinking protein midworkout.

"Elite athletes are looking to maintain glycogen stores for as long as possible," Dr. Hong said. "For your average athlete that's less of a necessity." But that does not necessarily mean the average athlete will not want to try protein-laced recovery drinks. Gatorade, after all, started as a drink for elite athletes.

"Most of the people using Gatorade, the closest they come to being an athlete is drinking it on the couch watching football," Dr. Portman of PacificHealth said. "But by drinking it, they can call themselves an athlete. That took 30 years for Gatorade. We're trying to do it much sooner."

For now, most protein-bolstered drinks are available online or in specialty shops like GNC or Performance Bicycle. And most are still only sold as powders. Only Accelerade comes ready-to-drink (it is available at Rite-Aid stores). A spokesman for the drugstore chain said it has seen a "significant year-to-year increase" in Accelerade sales since it began selling it in 2002.

Armchair athletes, as we know from the Michael Jordan era, don't care nearly as much about the science of a drink as who is drinking it.

"Whether protein makes it into the next generation depends on who believes in it and puts it in their drink," said Darren Rovell, the author of "First in Thirst" (Amacom, 2005), a book about Gatorade. If famous professional athletes say they need protein in their drinks, their fans will want protein too, Mr. Rovell said.

Accelerade has won some professional converts, including the standout marathoner Meb Keflezighi; head trainers for the New York Rangers and Colorado Avalanche hockey teams; and a handful of professional football teams. (Though, Dr. Portman claims, the teams' agreements with Gatorade prohibit them from publicizing their use of Accelerade.)

Dr. Robert Murray, an exercise physiologist and the director of the Gatorade Sports Science Institute in Barrington, Ill., said protein won't be added to Gatorade drinks anytime soon. Some protein-enriched beverages feel clumpy on the tongue or taste odd, Dr. Murray said - problems that many endurance athletes already complain about.

"I only like the orange and the lemon-lime," Mr. Gardner, the New York triathlete, said of Accelerade. "The fruit punch flavor is disgusting."

Taste is only one roadblock to the acceptance of recovery drinks. "At the end of the day," Mr. Rovell said, "you're going to have to convince the mass consumer that protein belongs in a drink."