[Michael Bruno recently finished his undergraduate degree at West Chester University of Pennsylvania. He is currently in the Coaching Mentorship Program at Athletic Lab]
The fitness industry is a fickle one with fallacies that continue long after the truth is uncovered. One fallacy I’ve found in the fitness community is that energy systems of the body are thought of as timed switches. Traditional thought has been during the onset of activity it’s the anaerobic alactic for 15 sec, followed by the anaerobic lactic up to 1:30 and anything over two minutes would be the aerobic system. And that depending upon time demands of your sport you should train the appropriate system exclusively. On the contrary, the systems are not independent of each other, but more so dependent upon each other. The ceiling of the next system depends on the development of subsequent system development starting with the aerobic system then lactic, and finally alactic system. If you think of the energy systems as a pyramid the aerobic system would be the base. The bigger the base the larger the alactic and lactic energy systems can be.
The more I read the research I feel as though the aerobic system has gotten the worst reputation possible, the ugly duckling of the energy systems. When people think of the aerobic system, they think long distance runs, fragile, non-explosive athletes. If you were to tell me that the aerobic system although produces the most amount of ATP per substrate but does so at the expense of time, I would say that it would be of no benefit of any field sport athlete. But interesting enough if you’re a team sport athlete this is the most important system and is the only system that if not properly developed or its development is shorted to work on the more sport specific energy system this will limit the potential on subsequent energy system development. In the following paragraphs, I will explain why long slow distance is great for ball sport athletes, anaerobic threshold is malleable, and recovery from exercise can all be improved substantially by the aerobic system.
I think when people hear the word aerobic they immediately think long slow distance (LSD) runs. I would like to go on record as saying I’m 100% in favor of LSD style training. If you keep heart rate between 130-150bpm for 30-90 minutes, it has two main adaptations on the body: increases eccentric cardiac hypertrophy and increases peripheral vascular network. Eccentric cardiac hypertrophy is the increase of left ventricle cavity of the heart. An easier way to think about is If you think of the heart as a balloon and constantly filled with water, it increases in size of the left ventricle allowing for larger blood volume. This increase allows for a lower resting heart rate because the heart has less work to put out the same volume of blood. This increase in heart efficiency at resting allows higher efficiency when operating during a sport. The increase in the peripheral vascular network allows for increased oxygen throughout skeletal muscles, increase metabolic byproduct clearing, and transport deoxygenated blood away from muscles. The increasing capillarization of muscle tissue also allows for an increase in vasodilation, which helps to decrease heat out of the system. This type of training doesn’t have to involve running long distances but could be broken up in bodyweight exercises circuits, sport skill technical work, and anything else pertaining to the sport if the beats per minute are kept under 150 bpm. Anything over 150 bpm, the blood moves too fast through the ventricles to stretch them. Unfortunately, the blood moves too fast to stretch out the ventricles, but not fast enough out of the heart to develop concentric hypertrophy, which in turn increases contractility of the heart. Increasing the efficiency of the heart and vascular network can be seen as step one in the success of any conditioning program, it allows for other styles of training to push anaerobic threshold.
Although the aerobic system is known as the workhorse of the energy system because of its huge capacity for energy production and can last for hours. It is largely underrated in the potential improvement in the rate of energy production and how trainable that rate can be. Higher levels of aerobic fitness allow for that system to be more of a contributor of ATP by giving more oxygen to exercising muscles allowing for a higher level of exercise intensity before the anaerobic threshold is reached. The anaerobic threshold is a representation of the outer limits of aerobic contribution to energy production although the aerobic system is always contributing to energy supply the contribution varies depending upon the rate at which supply is needed. The anaerobic threshold is usually marked by heart rate. Anaerobic threshold reflects the peripheral aerobic training adaptations. This threshold has been associated with increased capillary density, and an increased capacity to transport lactate and hydrogen ions away from the muscle. All of which have been proposed to induce fatigue in athletes. Repeat sprint ability (RSA) or the ability to continue to perform sprints at or with minimal deformation of performance is something that team sport athletes need to be successful at sport. Repeat sprint activity (RSA) has been proposed to be largely determined by biochemical changes in muscle fibers or peripheral training adaptations. By increasing anaerobic threshold, it allows for an increase in RSA, which makes sense considering the strong correlation between RSA and anaerobic threshold because of increase in peripheral adaptations in the body. The anaerobic threshold is one of the many trainable components of the aerobic system allowing for its huge potential to contribute to athletic performance. But it doesn’t matter how hard you train unless you can recover and adapt from it which the aerobic system plays a huge role in.
Having a robust aerobic system allows for a higher amount of work that the athlete can perform and can recover and adapt from allowing for a higher ceiling for performance. The ability to perform maximally on repeated exercise bouts is influenced by nature of both exercise and recovery periods. Generally, the more that exercise disrupts homeostasis, the greater the effect on recovery metabolism. The more complete these restorative processes, the greater the ability to generate force or maintain power on subsequent work intervals. Recovery is biphasic in the body with the first phase being the initial rapid phase of recovery lasting from 10s to a few minutes. The second slower phase ranges from a few minutes to hours. In the fast phase, which is marked by declining VO2 and heart rate. Having heart rate which declines very quickly post exercise is a trait of a very efficient cardiac system. The tissue stores of oxygen are replenished and ATP and PCr are restored to 70% within 30 seconds and 100% at 3-5 minutes. This process depends upon how much work you put into your aerobic system. Recovery from high-intensity exercise or sprinting is thought to be an oxidative process stemming from studies done limiting blood flow to conditioned areas and seeing decreased phosphocreatine recovery rates. One of the benefits of having a developed aerobic system allows for increased capillary density, which allows for decreased diffusion distances making the movement of oxygen and nutrients to muscles as well as clearing metabolic byproducts such as lactate and hydrogen ions from the muscle. Also, an added bonus of having a large vascular network allows for vasodilation to decrease heat, which is also a byproduct of the anaerobic energy systems. The peripheral network in the body is only as good as the system that dictates its influence. The autonomic nervous system makes up part of your nervous system. The autonomic nervous system is broken up into two systems. The sympathetic nervous system is known for fight or flight tasked with preparing the body to defend itself, whereas the parasympathetic is known for activating rest, recovery and digestion. The two systems have a tug of war style relationship depending upon the task at hand. If the body is chronically in a state of sympathetic tone, it can wreak havoc on your body. Heart rate variability is a non-invasive tool that allows the user to understand what is happening. If HRV is at high frequencies, it reflects cardiac parasympathetic modulations and lower frequencies reflect sympathetic and parasympathetic influences of the heart. The increase in aerobic capacity allows for an increase in autonomic regulation, which allows for increase parasympathetic tone and to allow the body to focus on recovering and adapting to the training stimuli.
In conclusion, the aerobic system is the Swiss army knife of the energy systems. If developed correctly, it lays a solid foundation for not only anaerobic systems to build on but for increased efficiency of the cardiorespiratory system. This system can increase the rate at which it produces ATP and can do so without the expense of the metabolic byproducts that the anaerobic systems do. It also allows for increased recovery by clearing byproducts with an extensive peripheral vascular network as well as increasing autonomic regulation leading to faster parasympathetic tone after exercise.
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