Active Voice: A Mechanism Underlying Preventive Effects of High-Intensity Training (HIIT) Against Colon Cancer
By Izumi Tabata, Ph.D., FACSM
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Izumi Tabata, Ph.D., FACSM, is a professor on the faculty of sport and health science, Ritsumeikan University in Japan. He recently has been a visiting professor at the University of Colorado, where he collaborated with Wendy M. Kohrt, Ph.D., FACSM. Dr. Tabata became a member of ACSM in 1990 and has published six papers in Medicine & Science in Sports & Exercise® (MSSE), including legacy papers that have stimulated development of contemporary fitness trends leading to various forms of High-Intensity Interval Training (HIIT) and which often are popularly identified as “Tabata protocols”. He also studied abroad in Oslo, Norway, with the late Dr. Lars Hermansen, and with John O. Holloszy, M.D., FACSM at Washington University in St. Louis, Missouri.
This commentary presents the author’s views on the topic of his research article, “A mechanism underlying preventive effect of high-intensity training on colon cancer,” which he and his colleagues had published in the September 2017 issue of MSSE.
Colon cancer is a prevalent disease in modernized countries. Epidemiological studies strongly suggest that physical activity/exercise is associated with the prevention of colon cancer. However, since epidemiological studies do not address mechanism(s), my colleagues and I over the past 10 years have sought to clarify biological pathways for the beneficial effects of physical activity/exercise on colon cancer.
This team first found, in animal experiments, that moderate-intensity prolonged run training reduces the number of chemically induced aberrant crypt foci (ACF) (see January 2007 MSSE).The appearance of ACF is the first step in colon cancer development, which has a "step by step" nature. Thus, it can be speculated that the reduced number of ACF after exercise training is linked to reduced polyp development and reduced risk of colon cancer.
Six years ago, our team found that exhaustive high-intensity intermittent swim training also reduced the number of ACF in the rat colon. However, since the mechanism was not certain at that time, we did not seek to publish those results. But, more recently, Aoi et al. (see June 2013 Gut) reported that secreted protein acidic and rich in cysteine (SPARC), a myokine produced and secreted from exercised skeletal muscle, had a preventive effect against colon cancer by inducing apoptosis of ACF. Based on other findings from our group (Terada et al. 2005), we hypothesized that, like other proteins in skeletal muscle (e.g., oxidative mitochondrial enzymes), SPARC expression may be induced by PGC1a, which is a transcriptional coactivator and known to be stimulated by exercise intensity-dependent AMPK activity. If true, SPARC expression and secretion also might be directly associated with exercise intensity. Other published evidence suggests that SPARC mRNA in isolated rat eiptrochlearis muscle increases after in vitro incubation with AICAR (AMPK activator) and that AMPK injection increased SPARC protein in the same muscle. Finally, our group has other published evidence that high intensity intermittent swim training may increase the serum concentration of SPARC in rats.
In humans, high intensity intermittent exercise (HIIE), consisting of 6 to 7 sets of 20 seconds of cycling at 170 percent of V(·)O2max with 10 sec rest intervals, has been shown to increase serum SPARC to the same level as 30 min of moderate intensity exercise. In addition, HIIE training significantly elevated mRNA of SPARC in human skeletal muscle. The enhanced mRNA of SPARC may increase the expression of SPARC in skeletal muscle and its secretion to blood, which may decrease the number of ACF. Because we believe that the interval required for the evolution of colon cancer from ACF is more than 20 years, colon cancer may be preventable if appropriate long-term prevention strategies are available.
Therefore, in addition to recommending low- to moderate-intensity exercise for the prevention of chronic diseases, high-intensity exercises and sports (e.g., soccer, rugby) can be recommended as primary colon cancer prevention tools for young and middle-aged adults, because such activities not only are enjoyable, but may result in better adherence for a longer lifespan.