HuffPost blogger Tony Horton's blockbuster fitness DVD series, P90X has been popular for years. But now an independent analysis of the bootcamp-style fitness program confirms what fans have been saying all along: the workout improves cardio respiratory function.

The American Council on Exercise asked a panel of sports science and physical therapy researchers from the University of Wisconsin-La Crosse to analyze how people physiologically responded to the workout. They recruited 16 volunteers, between the ages of 19 and 26 -- all of whom were already physically fit. They had each participant perform four P90X workouts (Legs & Back, Plyometrics, Cardio X, and Chest, Shoulders & Triceps), with 48-hour rest periods between each workout, at a comfortable pace, duration and weight strength. The researchers then measured each participant's heart rate and VO2max -- a measure of maximum oxygen consumption that conveys aerobic power.

While performing the workout, the male participants used between 67 percent and 83 percent of their maximum heart rate, reported the Los Angeles Times. Women had to work slightly harder, maxing out at between 65 and 88 percent of total heart rate. Those ranges are well within the council's guidelines for a high-intensity workout. The team also found that each session burned between 441 calories to 699 calories for men and 302 calories to 544 calories for women.

"Our study results found P90X offers an effective workout, and, when combined with a sensible eating plan, we believe it can help many individuals achieve their weight-loss and fitness goals in the comfort of their homes," said the American Council on Exercise Chief Science Officer Cedric X. Bryant in a statement.