Understanding the Aerobic System By: Dave Lasnier Understanding energy systems and how they work in relation to one another is of utmost importance for any strength and conditioning coach in order to be able to give the most effective conditioning program to his athletes. The anaerobic system (alactic and lactic) has gotten a lot of attention in recent years because it is now understood that it is the way most team sports (hockey, soccer, basketball, lacrosse, etc) are played; short bursts of intense effort interspersed with periods of complete or active rest. Because of this "improved" understanding of the energy contributions to team sports, the aerobic system has gotten a pretty bad reputation. Aerobic system training, which is usually associated with slow steady-state activities, is now believed by a lot of strength and conditioning professionals to be detrimental for most athletes due to an unfavourable risk:reward ratio. Some of these stated risks include: negative hormonal response, affected gains in strength and power, overuse injuries, mobility restrictions, etc; while also stating that the benefits are minimum to nonexistent. But is training the aerobic system really that detrimental to an athlete's performance? I am far from being an endurance guy and I do believe in the importance of strength and in conditioning my athletes the way their sport is played. But the aerobic system still plays an important role in energy production in most team sports (maybe just not the way you think) and my goal here is to present aerobic training in a different perspective. Before going any further, some of the concepts I present in this article, as well as most aerobic training methods presented later in the article were inspired from Joel Jamieson's book Ultimate MMA Conditioning. It is an incredible resource that goes far beyond the sport of MMA; it goes into great detail about the energy systems and how to train each of them optimally to get the most out of your conditioning program, regardless of the sport you're involved with. It's a resource I would highly recommend to anyone. How Energy Systems Really Contribute to Energy Production The first and most important thing to know about the 3 different energy systems is that they're not as clearly defined as we may think from reading traditional textbooks.
Although this chart gives us a good idea of which system dominates energy production at what time during an effort, it's not totally accurate. There is not a clear cut separation between each of the systems when it comes down to their contribution during an effort. At 20 seconds, there is not a complete switch in the energy system that is being used, going from the alactic to lactic. The reality is that all systems are contributing to all movements to some degree, and there is a much smoother transition between the predominant system than typical charts display. One system never contributes to 100% of the energy production.
Another thing to take into account is that the intensity of the exercise will also dictate the energy systems' contribution. If you go for a jog and start slow, there won't be a high contribution of the alactic system like the one you see in the chart; your body won't need to rely as heavily on that system because the demands of the activity are low. What you should understand is that energy systems overlap, and the intensity of the exercise will also dictate which systems are used predominantly. So when doing high intensity interval training (HIIT), the energy production is not all anaerobic, especially if you do many repetitions with incomplete recovery. The anaerobic systems (lactic and alactic) need long periods to reach complete recovery (it is believed that it may take hours). As an example, what happens if you do 10 sprint intervals, sprinting for 20 seconds, and resting 40 seconds between each rep? Assuming you're going at near maximal intensity you'll have a big contribution of your lactic system, a little less of a contribution from your alactic system, and a fairly lower contribution of your aerobic system, for the first rep. Since your lactic system doesn't recovery completely in 40 seconds, your performance will drop, and your body will have to rely on your aerobic system more and more as the reps go by to produce the
necessary energy(1). And how does your body recover between each rep? By replenishing your energy stores using oxygen and the aerobic system (2). So you can see that even if you don't train your aerobic system directly, it still gets some contribution because it is an essential part of your body's energy production. The same thing happens when you play sports like hockey, soccer, lacrosse, football, etc. The longer the activity lasts, the bigger the contribution of the aerobic system. When you recover between shifts, plays, or bursts of activity, your body uses the aerobic system to replenish levels of ATP and muscle glycogen. But if there is such a big contribution of the aerobic system during anaerobic activities, what's the whole point of even training it directly? After all, as we've seen in the Tabata study(3), there is a significant increase in VO2max (a measure of aerobic capacity) when performing interval training for a short duration. As much as many coaches like to refer that study when stating that HIIT is all you need to improve your aerobic system, there are a couple subtleties about that study we may have failed to acknowledge. First, the group that was performing the Tabata protocol (the interval training), had a slightly lower VO2max than the steady-state group at the beginning of the study (~48ml/kg/min vs ~53ml/kg/min), which might suggest more room for improvement, but no conclusions were drawn in that regard. Also, a similar hypothesis could be drawn from the fact that the values (48 and 53ml/kg/min) represent what I would see as numbers at the lower end range for high level athletes. And lastly, the VO2max of the interval group improved pretty quickly in the first 3 weeks of this 6 weeks study, and then slowed down significantly as there were no major improvements noted in the last 3 weeks (3,4). This last piece of information can be quite confusing because the Tabata study (or at least the way we interpreted it) led us to believe that 4 minutes of HIIT was superior to "classic aerobic" activities to improve aerobic capacity. But what we could speculate from the results are the long term effects of HIIT on the aerobic system. From the data in this study, I would suspect that the long term benefits of HIIT on the VO2max of high-level athletes might not be as big as we thought it was; or at least, not as efficient over the long term. HIIT protocols are a good way to achieve results in less time, but keep in mind that it might not always be the most appropriate method, depending on what we're looking to improve. Benefits of Training the Aerobic System Directly
You can get benefits and improvement in aerobic fitness by using HIIT and other anaerobic training methods. But as we just saw, the rebound effect (the indirect benefits the aerobic system receives from anaerobic training methods) will only bring you so far. If you're dealing with highly detrained athletes, the benefits might carry over for a little longer, but if you're training well trained athletes with decent conditioning levels, the rebound effect of the aerobic system benefits from high intensity interval training probably won't last very long if you're using only anaerobic training methods. In other words, the improvements of the aerobic system could plateau pretty quickly. Therefore, it is important to address the aerobic system directly at some point in your training year. As I mentioned before, aerobic training is still not specific to most team sports, so it shouldn't be the focus of your conditioning programs year-round, but some direct work is appropriate. Below are some of the physiological benefits that will be attained through different aerobic system training methods: 1. Improved eccentric contraction of the cardiac muscle. This will increase the volume of blood in the left ventricular cavity prior to the ejection of the blood (concentric contraction) to the aorta, which divides in smaller arteries to send the blood out in the different tissues of the body. Basically, the more blood that accumulates in the left ventricular cavity during the eccentric contraction, the more blood that can be sent out to the muscles. Think of what happens if your heart has good concentric strength, but an eccentric contraction that's not as effective; no matter how hard your heart can pump the blood out towards the working muscles, the amount sent out to those muscles is always limited by the capacity of your left ventricular cavity to accumulate blood during the preceding eccentric contraction.
Improved eccentric contraction of the cardiac muscle occurs through low intensity, longer duration type of exercises, or what most people refer to as typical aerobic training (5). Although there can definitely be some downsides to performing slow, steady state cardio for long durations (mobility restrictions, overuse injuries, etc) when overdone, it's important to keep things in perspective. We're not asking for a hockey player to run 60 minutes, 5 times a week during his entire off-season training. You don't have to do an hour at a time to reach the benefits (30-40 minutes will usually be sufficient), and in most cases it'll only take 2-3 times per week of these methods for 4-6 weeks or less of the off-season to gain the desired adaptations. This could also be used sparingly during the season to aid with recovery, but the duration and the frequency would also be limited. Improved recovery will usually be one of the big benefits from using this method (6); it delivers a lot of fresh blood to the muscles and causes minimal fatigue. The important thing with this type of training is to keep the heart rate low (around 60% of your max heart rate). Going at high intensities won't allow the left ventricle to eccentrically contract, or inflate with blood, optimally because when the demands on the cardiac muscle
increase, your heart will just try to pump faster and faster (5). 2. Improved contractile strength of the cardiac muscle. This is the second part of the equation in sending more blood to the working muscles. The eccentric strength, which we just discussed, allows the left ventricle to fill with more blood. But you also need good contractile strength of your cardiac muscle fibres in order for that blood to be delivered optimally and quickly enough to your muscles. The increase in contractile strength of the cardiac muscle develops through higher intensities that push the heart rate as high as possible (5). Since it's impossible to maintain a near maximal heart rate for a long duration, this method is best achieved through medium-long duration intervals and incomplete rest periods (e.g. 2 minutes of work, alternated with 2-3 minutes of rest). Because of the duration of the effort, there will definitely be a contribution of the lactic system, but as we saw earlier, overlap is almost inevitable. Performing multiple repetitions will also increase the contribution of the aerobic system as the reps go on. 3. Higher anaerobic threshold. The anaerobic threshold can indeed be increased through aerobic training. By improving the efficiency of your aerobic system, you can increase its contribution during high intensity efforts (referring back to the overlap between the different energy systems in energy production). This can happen by pushing your anaerobic threshold higher. By doing this, you delay the point at which your body starts to produce energy predominantly through the anaerobic system, which is when your body starts accumulating fatigue at a much faster rate. In other words, by pushing your anaerobic threshold higher, you can have a bigger contribution of your aerobic system for an activity at any given intensity. Delaying, or minimizing, the anaerobic contributions to activity at any given level are important because the anaerobic system doesn't recover very fast, and results in a significant amount of fatigue to the nervous system and body in general. As powerful as the anaerobic system is, it is not so good at repeated efforts with incomplete rest. As a result, the larger the contribution of your aerobic system during an effort or an activity, the better. You'll be able to produce more energy aerobically, which is good because that system can produce a lot of energy, for infinitely longer, with much less fatigue accumulation. Training to specifically increase your anaerobic threshold requires you to work at a heart rate that is around or just below your anaerobic threshold for relatively long periods of time (about 5-10 minutes) for multiple reps (5). There are far more physiological responses to direct aerobic training that I have not even mentioned, such as improvements in mitochondrial density, enzymatic activity, muscle fiber composition, etc. The goal was not to give
you a full physiology lesson, but to highlight some the benefits of training the aerobic system directly. So by now you know that training the aerobic system directly will: - Increase recovery rate of the anaerobic system through the aerobic system and the use of oxygen (between shifts or bouts of intense activity) - Increase the aerobic system contribution during anaerobic activities - Delay fatigue during anaerobic activities Putting it All Together With all that said, what is appropriate when it comes down to training the aerobic system? How much should be done, how often, and at what time of a training year? Those are all questions that are dependent on the sport, team and individual player's situation. As we've seen, you don't need extremely high volumes of aerobic work year round, and it sure doesn't mean slow steady-state cardio is the only training method for training your aerobic system. It's about establishing a foundation for everything that's going to be trained in the following training phases, and getting the most out of your direct aerobic work. You'll get a better recovery out of your anaerobic intervals, and a bigger contribution of your aerobic system during high intensity activities, which will also help delay fatigue. Hopefully you now understand the aerobic system is not as evil as it is often presented to be, and like it or not, it greatly contributes to the energy production in most team sports. More than anything else, you can attain some great benefits by training the aerobic system directly, which will optimize conditioning levels, and make your athletes more dominant on the field, court, or ice. David Lasnier is a strength and conditioning coach at Endeavor Sports Performance in Sewell, New Jersey. He has been working with a wide range of athletes from different sports including baseball, hockey, soccer and football who play at different levels ranging from high school to professional for the past 8 years. David received his Bachelor of Science degree in Kinesiology from the Université de Sherbrooke in Quebec, Canada. You can reach David through is website athttp://davidlasnier.com. References (1) Glaister, M. (2005). Multiple Sprint Work : Physiological Responses, Mechanisms of Fatigue and the Influence of Aerobic Fitness. Sports Med,
35(9), 757-77. (2) Bogdanis GC, Nevill ME, Boobis LH, Lakomy HK. (1996). Contribution of Phosphocreatine and Aerobic Metabolism to Energy Supply During Repeated Sprint Exercise. Journal of Applied Physiology, 80(3), 876-84. (3) Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K. (1996). Effects of Moderate-Intensity Endurance and High- Intensity Intermittent Training on Anaerobic Capacity and VO2 max, Medicine & Science in Sports & Exercise, 28(10), 1327-30. (4) McDonald L. (2009). Research Review: Effects of Moderate-Intensity Endurance and High-Intensity Intermittent Training on Anaerobic Capacity and VO2 max, http://www.bodyrecomposition.com/research-review/effectsof-moderate-intensity-endurance-and-high-intensity-intermittent-trainingon-anaerobic-capacity-and-vo2-max.html (5) Jamieson J. (2009). Ultimate MMA Conditioning. (6) Tomlin DL, Wenger HA. (2001). The relationship Between Aerobic Fitness and Recovery from High Intensity Intermittent Exercise. Sports Med, 31(1), 1-11.