High-intensity, short-duration interval workouts are a new frontier in fitness and sports training.
When you’re a sports fan, it doesn’t matter if you prefer the NBA, figure skating or the Olympics—you’re sure to admire the performances of athletes who work inconceivably hard to achieve greatness. It’s practically impossible to watch without feeling compelled to hit the gym and try some new training method, hoping to achieve your own gold-medal performance. So what’s the latest buzz in the training room?
It’s short-burst training (SBT), a variation of circuit training. SBT uses a series of high-intensity, short-duration exercises interspersed with brief periods of lower-intensity movement (www.exercisegoals.com). Clients go all-out for intervals of 30–60 seconds (depending on the intensity level and the equipment/apparatus used for training) before entering the recovery phase. This pattern repeats throughout the workout. The intent is to utilize the anaerobic energy system, long thought to be the exclusive realm of sprinters and court athletes whose movements are too brief and powerful to engage the oxygen pathways of the cardiovascular system (Smith 2002). During short-burst exercise, the body produces metabolic byproducts (hydrogen ions) that have been identified as the cause of acidosis (“the burn”). The cardiovascular exercise following the short burst of anaerobic exercise helps to neutralize or buffer this acidosis. The primary fuel used is carbohydrate (Smith 2002), with stored fat kicking in later.
By contrast, traditional endurance training keeps the body moving longer at more moderate intensity levels, with the aerobic system maintaining function. The primary energy sources are carbohydrate and fat (Smith 2002). There is abundant research verifying the physiological adaptations attributed to endurance training, especially improved exercise capacity—the body’s ability to “sustain a given sub-maximal workload for a longer period of time” (Gibala et al. 2006). For many exercisers, the rewards include improved cardiovascular function; decreased incidence of diabetes, high cholesterol and hypertension; weight loss; and reduction of body fat. And those training for competitive sports count on aerobic training to gain needed stamina.
In old-school thinking, accessing fat both stored and free-floating in the bloodstream required endurance-type “aerobic” training. Aerobic means “with oxygen,” and the physiological pathway initiated in the presence of oxygen utilizes fat for fuel, making it the superior choice. But recent research opens the door for a new theory—that high-intensity training is even more effective. One such study compared the effect of a 20-week endurance-training program with that of a 15-week high-intensity program in terms of body fat loss and muscle metabolism.
Researchers found a larger reduction in subcutaneous fat in the high-intensity group, despite noting that the total energy cost between the two groups indicated higher caloric expenditure for the endurance group. Furthermore, “when corrected for the energy cost . . . the reduction induced by the high-intensity program was nine-fold greater than the endurance program” (Smith 2002).
Another study, published in the Journal of Applied Physiology, measured skeletal muscle fuel content, fatty-acid transport proteins, and hormonal and other responses in women after a 2-week SBT program. Results indicated that “seven sessions of SBT over 2 weeks induced marked increases in whole body and skeletal muscle capacity for fatty acid oxidation during exercise in moderately active women” (Talanian 2006).
Traditional aerobic training is also praised for improving the body’s efficiency at burning stored fat once activity ceases, a phenomenon termed excess post-exercise oxygen consumption, or EPOC. But more and more studies are showing that the EPOC created by high-intensity training induces a response that renders the body even more efficient at burning fuel. For example, a 1996 study in Medicine & Science in Sports & Exercise comparing endurance- and interval-trained subjects showed that “the interval group burned more fat during exercise . . . [and] exhibited increased fat burning effects that persisted for 24 hours after the exercise had stopped” (Treuth, Hunter & Williams 1996).
In a 2001 study, researchers compared two groups, one exercising aerobically and the other using interval training. Both groups burned exactly 300 calories, but despite exercising longer, “the aerobic group lost less body fat” (King et al. 2001).
[Editor’s Note: See this month’s Making News column for more on post-exercise fat metabolism.]
Training in the “target zone” (65%–85% of one’s maximum heart rate) for an extended duration (20 minutes minimum) at least 3–5 times a week is an age-old exercise formula. However, that formula was challenged in 1995, when the Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine (ACSM) convened to re-evaluate physical activity recommendations for the general public. The panel determined that “every U.S. adult should accumulate 30 minutes or more of moderate-intensity physical activity” almost every day (Pate et al. 1995). This opened the door for beginners to add small increments of activity to their day and still improve their fitness levels. In line with this physical activity model, data now being accumulated with regard to short-burst training definitely support shorter bouts of intermittent activity.
Then there is a 2005 study published in the Journal of Applied Physiology. The subjects, who were not athletes, did a 2-week SBT program and were then retested. The result? Their endurance level, a direct measure of cardiorespiratory fitness, had actually doubled (Burgomaster et al. 2005).
In today’s world, time is precious. So if something can be accomplished faster, who wouldn’t do it? Traditional training is long, slow and time-consuming. SBT is not only effective, but markedly so in a significantly shorter period of time. Numerous studies demonstrate that, in terms of body fat, weight loss and fitness-related gains, subjects performing SBT for minimal time periods achieved more than endurance-trained subjects despite the overall training time being much less.
In a study by Gibala et al. (2006), six sessions of high-intensity, low-volume interval training and six of high-volume endurance training were compared for their effect on “muscle oxidative capacity, muscle buffering capacity and exercise performance.” Between the two groups, researchers noted significant differences in both training volume (approximately 90% less for the interval group) and time commitment (around 2.5 hours with intervals versus 10.5 hours with endurance training over 2 weeks), yet the resulting physiological changes were similar. While the authors cautioned that further research was needed, their findings suggest that “SBT is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance” (Gibala 2006).
Another study, published in Medicine & Science in Sports & Exercise, showed interval-trained groups achieving significant improvements in EPOC and calorie/ fat burning during exercise. And these benefits were achieved with an “exercise session that was a full 15 minutes shorter than the aerobic group” (Treuth, Hunter & Williams 1996).
With so much evidence favoring short-burst training, should we hang up our indoor cycling gear and list our stair-climbing machines on eBay? Not so fast. SBT has its perks, but the benefits of traditional training cannot be denied. Some people actually seek the solace and rhythm of long, slow, distance training—e.g., an hourlong aerobics class, precious reading time on the treadmill, an extended Sunday morning hill run. Studies may suggest that SBT gives superior results, but it’s all a matter of time: SBT garners much quicker results from significantly shorter training sessions, while traditional training effects take longer to achieve. Bottom line—are your clients in a hurry?
If you’re looking for a quick fix, athleticism or better competitive sports performance, SBT is a good choice. But if you’re training for a cross-country ski trip or long-distance bike race, traditional endurance training is still needed. As one researcher states, “The present data should not be interpreted to suggest that SBT is necessarily adequate for prolonged endurance type activities” (Gibala 2006). On the flip side, however, Mark Smith, PhD, an applied physiologist and the program director for X-iser Industries, in Southlake, Texas, reminds us that high-caliber endurance athletes do not train by distance alone: “Looking at elite endurance athletes like marathoners, people don’t realize that 50%, and sometimes as much as 75%, of their training is actually high-intensity intervals.”
What about exercise difficulty? As trainers, our job is motivating and educating our clientele, and they’ll usually work hard for their results. But there’s a fine line between time efficiency and movement quality. If a training technique is performed incorrectly or is so high in intensity that a person can’t keep up, results won’t come and injury potential will increase. Exercise science professor Stuart Biddle, PhD, of Loughborough University in Leicestershire, England, notes, “You have to strike a compromise between physiology and psychology. The harder you make it, the fewer people will actually do it” (BBC News 2006).
Smith disagrees: “When exercise clients are in control of their intensity, they tend to be self-limiting. A minute is the magic number for a human to go all-out. I tell clients, ‘Give me a good honest effort. If you need to stop short of our goal in terms of time, it’s okay.’’ With SBT, the higher the intensity is, the shorter the duration and the longer the recovery periods between intervals. So, in essence, the danger of injury from overuse may decrease compared with what can happen with continuous, repetitive exercises.
Getting in shape is a journey, not a destination. And the best journeys are ever-changing. Recreational exercisers should strive to achieve not only sleeker thighs, but also a long-term love of movement and activity, regardless of its form. The beauty of fitness and sports training is that there is no one “right way” to train. Keeping the workouts fresh leads to a constant renewal of your clients’ commitment to good health and well-being. And that, above all, is the key to success.