The American Heart Association (AHA) and the Center for Disease Control and Prevention (CDC) agree in their recommendations for the amount of physical activity that adults should obtain. These activity levels can help to prevent heart disease and stroke, the Nation's Number 1 and Number 5 causes of death each year. It is recommended for Adults to obtain important health benefits then they should obtain:
- At least 150 minutes of moderate intensity aerobic activity every week and strength training activities at least 2 days per week.
- 75 minutes of vigorous intensity aerobic activity each week and 2 days of muscle strengthening activities
The CDC also provides a guideline for Adolescents age 6-17:
- Aerobic activity should make up most of a child's 60 minutes or more of physical activity each day.
- With a recommendation to have at least 3 days of vigorous exercise.
- 3 days a week there should be some component of muscle strengthening activity, like gymnastics or push-ups.
Traditional endurance exercise training has been proven to improve performance in aerobic activities and to induce changes within muscle cells to make them work more efficiently and help burn fat. Studies have demonstrated that this type of exercise can increase the mitochondrial volume (the powerhouse of the cell), which can increase the body’s ability to utilize oxygen. Also, enzymes are induced (activated), that allow the muscle cells to utilize lipids (fats) as a source of energy. Although these changes that traditional endurance training can augment are beneficial to overall health, it is also a time consuming activity and many people state they do not have time to complete such workouts.
High-Intensity Interval Training (HIT) is a form of exercise that is gaining recognition as a form of exercise that can confer some of the same benefits as compared to traditional endurance training, but without requiring the same time commitment. HIT is generally described as physical exercise of repeated sessions of brief, intermittent bursts of maximal vigorous activity separated by periods of low-intensity exercise. Recent studies have be able to demonstrate noticeable changes in low-active individuals in as little as 8 weeks with periods of HIT times of about 20 minutes of training for 3 days a week.
In a study by Gibala, his team compared 6 weeks of HIT training with traditional endurance training. They were able to demonstrate similar training induced physiological changes in the muscles and the cardiovascular system. Endurance-like changes included an increased resting glycogen content (more stored energy in the muscles), and a reduced rate of glycogen utilization and lactate (an acid that can make your muscles sore) production; which may allow an athlete to exercise for longer periods of time. This was further evidenced by improved exercise performance, as athletes were able to increase their time-to-exhaustion values. The striking aspect was that these similar changes occurred despite the HIT group had about 90% less volume of training and about a 67% reduction in time spent training.
The effects of HIT have also been evaluated in the Adolescent population. In a study by Logan et al., they had low-active adolescents participate in HIT program where they would perform HIT sessions twice a week and have one day of resistance (weight) training, for a period of 8 weeks. They were able to demonstrate meaningful improvements in fitness and physique. Although the total amount of physical activity change from baseline in this study was not significantly significant, there was an improvement in maximal oxygen uptake and body composition. The former implies that the adolescents had improved their aerobic capacity and had improved their level of fitness. The latter consisted of improvements in their body fat percentage, lean tissue mass, and visceral fat; all which can help to contribute to improved cardiovascular health. This was an important study, as it was able to demonstrate that the principles of HIT can be applied to adolescents and delineated that it was indeed the HIT training and not other variables that contributed to the improved physiological changes.
With the results of various clinical trials and investigations into the cellular changes that occur with High-Intensity Interval Training, it appears that HIT is a viable alternative to traditional endurance training. It has been demonstrated that there are similar adaptations in cellular composition, energy substrate use and metabolism, and improvement in athletic performance. And for the individual with limited time, it was important to demonstrate that these similarities can arise even with reduced time spent training.
Chase King, MS-IV
David Carfagno, D.O., C.A.Q.S.M.
Gibala, Martin J., Jonathan P. Little, Maureen J. Macdonald, and John A. Hawley. "Physiological Adaptations to Low-volume, High-intensity Interval Training in Health and Disease." The Journal of Physiology 590.5 (2012): 1077-084. Web.
Gibala, Martin J., and Sean L. Mcgee. "Metabolic Adaptations to Short-term High-Intensity Interval Training." Exercise and Sport Sciences Reviews 36.2 (2008): 58-63. Web.
Gibala, Martin. "Molecular Responses to High-intensity Interval ExerciseThis Paper Is One of a Selection of Papers Published in This Special Issue, Entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and Has Undergone the Journal’s Usual Peer Review Process." Appl. Physiol. Nutr. Metab. Applied Physiology, Nutrition, and Metabolism 34.3 (2009): 428-32. Web.
Logan, Greig Robert Melrose, Nigel Harris, Scott Duncan, Lindsay D. Plank, Fabrice Merien, and Grant Schofield. "Low-Active Male Adolescents." Medicine & Science in Sports & Exercise 48.3 (2016): 481-90. Web.
Talanian, J. L., S. D. R. Galloway, G. J. F. Heigenhauser, A. Bonen, and L. L. Spriet. "Two Weeks of High-intensity Aerobic Interval Training Increases the Capacity for Fat Oxidation during Exercise in Women." Journal of Applied Physiology 102.4 (2006): 1439-447. Web.
Image 1 Credit: https://www.monash.edu/__data/assets/image/0020/402734/HIIT.jpg
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