Disadvantages with aerobic training include spending longer and longer times training to increase metabolism once cardiovascular efficiency has been achieved and the relative increase of wear and tear on the joints with prolonged stress. Continued wear and tear on joints can lead to micro trauma, chronic inflammatory responses and pain, and potentially degenerative joint disease or arthritis. Steady state activities, such as running, take the variation out of exercise and eventually can compromise an individual’s adaptation to physical stress by recruiting only slow twitch, Type 1 muscle fibers. Fast twitch (Type 2a and Type 2b) fibers can begin to atrophy. In prolonged scenarios, the loss of fast twitch muscles can effect glycogen metabolism (the body’s source of energy) by promoting lack of insulin sensitivity. Insulin is a very important hormone in our bodies that regulates carbohydrate metabolism. Insulin resistance is a major problem in our country today with rampant increases in Type2 diabetes mellitus, mainly due to high carbohydrate diets and lack of exercise.
In contrast, interval training or high intensity interval training (HIIT) profoundly uses Type 2a and Type 2b muscle fibers due to the quickness, intensity and contractile nature of the exercise. The “burst-like” activity increases and shocks your body’s metabolism, burning more calories while performing the exercise and a continuance of calorie burn after exercise with the repair phases, just like other fast twitch muscle exercises, like lifting weights. This increase in metabolic rate causes an expansive amount of glycogen depletion in all of your muscles, leaving only some storage in your liver. This is a very important concept regarding HIIT. This type of training promotes insulin sensitivity vs. insulin resistance.
When there is no demand for fast twitch muscle activity, glycogen (energy storage form of glucose) stores are full, like lounging on the couch or sitting for 12 hours at work during the day. As your glucose intake continues to increase with meals high in refined carbohydrates, simple sugars, and high fructose corn syrup, a positive energy balance is established, causing fatty acid synthesis for triglyceride formation for energy storage. Over-consumption of glucose and constant stimulation of the potent hormone, insulin, from your pancreas causes insulin resistance leading toward diabetes. By using fast twitch muscle stimulation with HIIT and depleting glycogen stores, your body become insulin sensitive decreasing the need for insulin and preventing diabetes.
HIIT also has a tremendous influence on a very important hormone, human growth hormone or HGH. Unfortunately, as we age our levels of HGH decrease. After age 30, our levels of HGH drop precipitously leading to a condition called somatopause in both men and women. This is similar to menopause in women where aging leads to a drop in sex hormones and a host of conditions, like osteoporosis, loss of muscle mass, and depression. Further drops in HGH levels are also experienced by all of us in our daily lives, especially during periods of stress and cortisol production, loss or improper amount of sleep, and sedentary activity. Higher HGH levels help us with the retention and production of muscle cells, loss and breakdown of fats, anti-aging, and a decrease in insulin levels, promoting insulin sensitivity. HIIT causes a “fight or flight” reaction and an epinephrine release that significantly bolsters levels of HGH anywhere from 500-750%! This is a huge benefit! Growth hormone keeps us young, keeps our weight under control, prevents disease, increases muscle mass, and makes us healthier and stronger. Considering the shorter training times, the vast increases in HGH, and the promotion of insulin sensitivity, HIIT or anaerobic conditioning is a superior training technique.
See Part 3 of this series for an explanation on how to perform HIIT. Part 4 will recap all of the benefits of stimulating growth hormone for the best type of conditioning,