Classic endurance training has well-established benefits. Over time, engaging in submaximal training, at 65 to 75 percent VO2, yields improved work capacity due to increased delivery of oxygen to muscle, reduced glycogen and muscle glycogen utilization, and lower blood lactate levels.
Achieving further improvements in performance and physiological markers, however, typically requires the addition of a different training stimulus. And for nonathletes, including sedentary and moderately or recreationally active adults, it can take up to several years of endurance training to increase VO2 levels to reach those of highly trained athletes.
While not exactly new, high-intensity interval training (HIIT) is emerging as an effective and more time-efficient alternative to traditional endurance-based exercise programs. HIIT programs include short bursts of high-intensity activity performed at maximal effort (90 percent VO2 max), separated by short periods of low-intensity work that allow partial recovery. A typical HIIT session might include a three-minute warmup, four to six repetitions of a 30-second sprint followed by a 60-second active recovery, and a three-minute cool-down.
How HIIT works
HIIT causes physiological changes mirroring results of traditional endurance training, but through different pathways.
- Endurance training seems to operate through the calcium-calmodulin kinase (CaMK) path.
- HIIT seems to signal via the adenosine monophosphate kinase (AMPK) path.
- Both of these signaling pathways activate PGC-1alpha, a "master switch" in promoting the development of skeletal muscle functions.
The popularity of HIIT-based exercise programs in health clubs and elsewhere has brought this type of training renewed attention. According to Edward R. Laskowski, M.D., co-director of Mayo Clinic Sports Medicine Center in Rochester, Minnesota, multiple studies have shown that HIIT training can provide benefits for a broad range of patients.
"There's solid evidence that older, less active, overweight and obese individuals can benefit from HIIT training," explains Dr. Laskowski. "HIIT has also been shown to be very safe and effective in patients with heart disease and type 2 diabetes. In all of these populations, HIIT programs can produce significant benefit for the cardiovascular system and improved metabolic parameters. And people seem to like it better than traditional endurance exercise."
Dr. Laskowski notes that care must be taken in the design of HIIT programs to prevent injury and enhance adherence. Higher impact, ballistic HIIT activities are not appropriate for all patient populations, especially those with a musculoskeletal injury, a poor musculoskeletal foundation or improper movement patterns. But low-impact HIIT training options include bicycling, elliptical trainer or water running activities to provide an aerobic exercise challenge without significant joint or impact load. And the intensity, frequency and progression of each program can be tailored to a patient's diagnosis and abilities.
According to Dr. Laskowski, HIIT is a viable training modality that appears to be efficient and effective in diverse populations. "We are using HIIT in Mayo Clinic Sports Medicine performance programs and in our rehabilitation programs to maintain optimum conditioning during injury rehabilitation. Incorporating HIIT into a training program can enhance compliance and provide a time-efficient, enjoyable way for many of our patients to reach their goals."