By Matt Ballman, Ellen Dudzinski, Danny Livingston, Kathleen Wright
Recommended Further Reading:
Bio-electrical Impedance Analysis
Electrical Impedance Myography: Background, Current State, and Future Directions
What Does Bioelectrical Impedance Spectroscopy (BIS) Measure?
By Andrew Taylor and Kathleen Wright
Figure 1. Women participate in a HIIT class.
How many of us have said we would go to the gym, only to realize later that we don’t have the time? High-intensity interval training (HIIT) classes have increased in popularity over the last few years, partly because the sessions are shorter than traditional workouts. HIIT workouts alternate short (20 or 30 second) intervals of maximum exertion with periods of rest or low-intensity exercises. Elite athletes might take part in HIIT to improve their aerobic energy metabolism and performance. If you have ever played a demanding sport, you have probably been subjected to HIIT during the game or practice. The recent obsession with HIIT raises the question: is it just a fad, or will it stick around as an effective means of exercise?
HIIT can be defined as brief exercise that generates a VO2peak, or 90% of the maximum VO2 potential, commonly followed by a relaxation period. This study utilized the Wingate test: participants repeated 30 seconds all-out maximal cycling on a specialized ergometer, with 4 minutes of recovery in between, for a total of 2 to 3 minutes of intense exercise. The authors focused on specific markers in skeletal muscle metabolic control; they determined an increase in skeletal muscle oxidative capacity after 2 weeks of HIIT. They also found that changes in carbohydrate metabolism (Figure 2) were comparable to adaptations from endurance training. Although exercise performance improved, there was no measurable change in participants’ VO2peak after 2 weeks of HIIT. However, this study did not fully investigate how HIIT affects the cardiovascular and respiratory systems, or metabolic control in other organs.
Figure 2. Results depict the glycogen content, or resting carbohydrate dry weight, found in skeletal muscle during rest and 20 minutes after exercise, both before and after 2 weeks of HIIT.
Additional HIIT data concerning VO2peak and citrate synthase activity support the previous claim that HIIT provides similar benefits to endurance training. This review recognizes that Wingate-based training may not be tolerable for everyone, and instead tested low-volume HIIT. The authors found that their model was time-efficient and effective in producing cardiovascular and skeletal muscle adaptations. They reference the results of similar studies, saying that HIIT is superior to moderate-intensity continuous training (MICT) in increasing cardiorespiratory fitness and endothelial function. However, researchers still don’t know what intensity or training volume is required to be effective.
A study concerning overweight and obese adults found that HIIT had similar results to MICT, in terms of body composition measures, but HIIT required less training time. They concluded that HIIT may be a time-efficient way to manage weight. Meanwhile, this systematic review determined that MICT and HIIT provide similar benefits for body fat reduction, but HIIT was no more time-efficient than MICT.
The data from these studies indicate that HIIT is comparable to MICT, similar to the difference between traditional and functional workouts, as described previously in this post. High intensity workouts can be very demanding, as seen with the Wingate test, and may not be suitable for all individuals. HIIT should not be substituted for specialized athletic training, but can be beneficial for athletes who need to quickly use their bodily carbohydrates. Many HIIT studies are short-term, like the first study we mentioned, and further research needs to be conducted to determine the long-term effects of HIIT on cardiovascular and respiratory systems. Although HIIT attracts people with the allure of getting fit fast, there isn’t enough data currently to support that HIIT is actually more time-efficient than endurance training.
Questions to Consider:
Should HIIT workouts be recommended for the average person?
Why could an increase in glycogen dry weight be considered important for exercise?
How could your current workout routine benefit from HIIT?
What athletes do you feel would benefit most from HIIT?
Recommended Further Reading- Works Cited