Whether physical activity is aerobic (with oxygen, Slow Twitch) or anaerobic (without oxygen, Fast Twitch) is determined by “effort.” An all out effort done in shorter bursts, like sprinting, high intensity training (HIT), burst training and high intensity interval training (HIIT) are anaerobic. While activities like sleeping, sitting, standing, walking and jogging are considered aerobic activity, with low power requirement and consequently little wellness value.
Although aerobic exercise is beneficial when compared to a sedentary lifestyle, it has minimal value on its own when compared to anaerobic training.
All energy for muscle contraction comes from molecules of adenosine triphosphate (ATP). In other words, ATP must be present for a muscle fiber contraction. ATP could be looked at as the refined fuel that works with both Type 1 (Slow Twitch) & Type 2 (Fast Twitch) muscle fibers.
There are two main energy systems for anaerobic work and one energy system for aerobic work that in a continuum produce the required ATP differently, but blend into each other as the activity progresses. They are the Maximum Power Level or ATP-PC System, the Moderate Power Level or Glycolytic System and the Low Power Level or Oxidative System.
Maximum Power Level or ATP-PC System
When rested, before any activity, a small reserve of adenosine triphosphate (ATP), together with phosphocreatine (PC) is available as ATP-PC for an immediate source of energy, to use any time instantly, without oxygen, good for a maximum of 11 to 13 seconds of all out “full effort”. During this short ATP-PC phase a person can produce 100% of potential power driven by the Fast Twitch muscle fibers.
Moderate Power Level or Glycolytic System
As the “full effort” continues past 11-13 seconds, more adenosine triphosphate (ATP) must be created to continue work. For that, the glycolytic system takes over and breaks down glucose circulating in the blood and glycogen stored in the muscles and the liver, to create adenosine triphosphate. This “fast glycolysis” goes on 30 seconds. Lactic acid accumulates and reduces power output down to 44%. With further accumulation of lactic acid the “fast glycolysis” shifts to “slow glycolysis” with further increase in lactic acid concentration and a decrease in power output, for another 50 seconds.
Low Power Level or Oxidative System
By the end of the “slow glycolysis”, the anaerobic system is exhausted and energy production shift to the oxidative system for Slow Twitch muscle fibers, which produce less than 27% of the power with the ATP-PC system activity. This oxidative system concerns the Slow Twitch muscle fibers and thus is of less interest here.
In aerobic activities like sleeping, sitting, standing, walking, jogging and working at a level that keeps the heart rate below 60-70% of the maximum, only the Slow Twitch muscle fibers participate. The Fast Twitch (Type 2) muscle fibers atrophy, unless anaerobic training is introduced!
In anaerobic activities, activities that cannot be maintained for more than 90 seconds, all muscle fiber types participate. In addition to the greater training effect, the Fast Twitch (Type 2) muscle fiber participation stimulates the production of human growth hormones, which happens only with the Fast Twitch muscle fiber participation.
Whether you train and achieve optimum training results, is determined by the level of your “effort”. An all out “effort” for any individual for 10 to 90 seconds will produce a significant training effect. Repeated short intense “efforts” will produce even greater results. The intensity of the “effort” is what counts. Your body will tell you with a burning sensation in your muscles when your “effort” is right. There is no escaping it. The more you burn, the more you gain, the better you feel!
Usain Bolt As a Live Example
A good example of an all out “effort” is Usain Bolt, the Olympic Gold medalist in the 100 & 200 meters and the world record holder with 9.58 seconds in the 100m., which fits nicely into the 11-13 second ATP-PC anaerobic phase. Running completely on the energy provided by the adenosine triphosphate (ATP), and phosphocreatine (PC) available instantly at the muscle fiber site. Usain did not have to breathe. Breathing would not have made the least bit of difference in his performance, because no oxygen could have been used at that “effort” level.
In the 200m., at 19.19s., Usain ran through the 11-13s., ATP-PC phase and into the “fast glycolysis” phase, urgently making more ATP from glycogen stored in the muscles and glucose circulating in the blood. To this point, with a 19.19s., “effort” oxygen is not and can not be used. Had Usain kept running with a full “effort” before 90 seconds were up, his anaerobic sources would be spent, and you and I could pass Usain Bolt, the fastest human! Complete exhaustion for Usain is a workout, though it is only 90 seconds. What is not surprising is that in training for the Olympics Usain used anaerobic training only.
Perhaps now is the perfect time to get serious and start anaerobic training or at least supplement whatever you are doing with a few minutes a week of intense interval training. If for no other reason than to feel better, look better, become healthier, stronger, more mentally alert, and even extend life expectancy. All while saving time. But it takes “effort”.
(from article by Dr. Juris Terauds, Professor Emeritus)