The Basics of “Optimal” heart rate zone training
One of our primary purposes of endurance training is to boost your body’s ability to use stored body fat for fuel instead of glycogen for optimal performance.
Your body’s stored reserves of glycogen (the stored for of carbohydrates) are extremely limited when compared to the supply of fat. Even the skinniest athlete has enough stored fuel in the form of fat to enable him to exercise continuously for days. In comparison, stored glycogen reserves will deplete after approximately 2 hours.
One of our main goals is to train our bodies to rely on a virtually endless supply of fat as our primary fuelling source.
All endurance-based training helps this happen, but our Optimal Heart Rate Zone Training is by far the most effective strategy for inducing this critical change.
Besides becoming better at using fat for fuel, you gain several other benefits by training at your Optimal Zone. This training relies almost exclusively on your slow twitch muscles fibres – your endurance muscles. This is where most of the beneficial changes take place. When you frequently train, your slow twitch muscle fibres adapt and develop more capillaries. In turn, this creates more delivery pathways for blood, oxygen and fuel. The fuel in this instance is fat.
Although the primary muscles used in this workout are slow twitch, a few fast twitch muscles are recruited to help out when fatigue sets in. These are the fast twitch that are most similar to slow twitches.
When these primarily power-related muscles are called upon to assist the fatiguing slow twitches, they become better at using oxygen to produce energy from fat. These fats twitches eventually super compensate by taking on the characteristics of your endurance muscles.
One more benefit is that solely as a result of our optimal training, all of the recruited muscles develop more aerobic enzymes. These enzymes are the chemical that help produce energy from oxygen and fat. As an added bonus of these workouts, your kidneys begin to create more of the Erythropoietin Hormone or EPO which stimulate the production of red blood cells. More red blood cells equates to more oxygen delivering capacity to your muscles.
What is aerobic base training?
Aerobic base training is specific training meant to increase your aerobic threshold and your ability to perform steady-state work for a long period of time. Base training workouts are simple: go at a pace just below your aerobic threshold and hold it. This will be the upper limit of Zone 2.
Your aerobic threshold is the exercise intensity at which blood lactate begins to increase substantially. Below your aerobic threshold (Zone 1 and Zone 2) the exercise intensity is quite low, and that’s why you can maintain these “easy” efforts for a long period of time. We will dive deeper into the blood lactate and training zones in the next section.
Research has shown that almost all elite endurance athletes us aerobic base training as part of their weekly routine. This includes sprint-distance triathletes, marathon runners and Tour de France cyclists. The reason is simple. Endurance events are typically longer than a few minutes, sometimes longer than a few hours and sometimes even longer than a week in events such as Grand Tours. These occurrences place physiological demands on the body for very long periods of time, testing the body’s ability to endure rather than it’s explosive energy output.
Training to increase your aerobic threshold, therefore, will allow you to sustain activity for longer periods of time so that you perform better on race day. Only in once off events lasting less than a minute, could you completely forgo aerobic endurance training. Think about powerlifters or javelin throwers, neither of which are endurance athletes.
Now that you know the why behind aerobic training, let’s get a bit deeper in to the science of it.
Aerobic Threshold and Anaerobic Threshold
In basic terms, aerobic refers to “with oxygen” while anaerobic refers to “without oxygen”. During an anaerobic effort, such as a 10-second sprint, your body is not using oxygen to fuel it’s main energy source.
In fact, there are three different energy systems in the human body that fuel muscle contraction. The Phosphagen System, Glycolytic System and the Oxidative System.
Phosphagen system (ATP-PCr system)
The Phosphagen System is used for short and explosive bursts of energy lasting less than one minute.
Glycolytic system
The Glycolytic Systems powers high intensity efforts lasting one to five minutes.
Oxidative System
The Oxidative System powers longer efforts lasting anywhere from a few minutes to multiple hours.
These systems use different amounts of oxygen to fuel exercise, with the least amount of oxygen used for sprints and the most amount used for long-duration endurance exercise.
Aerobic training utilizes your oxidative system and targets your aerobic threshold, which is the exercise intensity at which lactate starts to rise above resting levels (typically around 2mmol/L or millimole per litre). Blood lactate is directly associated with muscle fatigue and the degradation of endurance performance. This is why it is so important for endurance athletes to train their bodies to clear blood lactate.
As soon as your exercise intensity increases above aerobic threshold, your body isn’t able to clear blood lactate as quickly. This leads to quicker and earlier muscle fatigue. By raising you aerobic threshold, you will be able to go further and faster with less blood lactate build up, less fatigue and substantial exhaustion delay.
Anaerobic training on the other hand, targets your anaerobic threshold. This is when blood lactate begins to build up very quickly. Your muscles will quickly fatigue in this state and even the most highly trained athletes can only hold an anaerobic effort for a few minutes. Endurance athletes use their anaerobic systems during sprints and other high intensity efforts, but it is their ability to recover using their aerobic capacity that is more often the determinant of performance.
How to build an aerobic base for optimal performance
As we begin to look at training your aerobic base, we get to the term “Zone 2 Training”. Zone 2 is most often associated with aerobic threshold training because of the matching intensity between power output, heart rate and blood lactate concentration. Maintaining your power output in Zone 2, your optimal heart rate zone, will keep your blood lactate concentration below your aerobic threshold.
According to Dr. Inigo San Millan, Ph.D. Director of the Exercise Physiology and Human Performance Lab at the University of Colorado School of Medicine, the purpose of Zone 2 endurance training is to improve lactate clearance. This is done by increasing the number of MCT-1 and mLDH [lactate-specific transporters which transport lactate away from muscle fibres].
the key point is that lactate is cleared mainly by slow twitch muscle fibres and not fast twitch muscle fibres. Training at high intensity will not exactly improve your aerobic threshold or your body’s ability to clear lactate. High intensity exercise targets fast twitch muscle fibres. You need to train your slow twitch muscle fibres at low intensities in order to improve your aerobic threshold.
Summary
In this article we went over the endurance sport buzzwords “aerobic threshold training”. Unlike other fads, supplements and myths, aerobic training has decades of research behind it. Zone 2 training principles have stood the test of time. In the world of endurance sports, aerobic threshold might be the most underrated and underappreciated metric of all. FTP and VO2 max get all the love but it is more often your aerobic threshold that wins the race.
The aerobic threshold, or the upper limit of Zone 2, is the intensity at which blood lactate increases above resting levels. The best endurance athletes in the world are pushing 300w or running 6 minute miles below their aerobic threshold. That is what places them a step above the rest. Training your aerobic threshold is arguably more important than training your anaerobic threshold when it comes to endurance sport. With long Zone 2 rides, runs, swims or paddles, you are cultivating your body’s ability to maintain low blood lactate at a given intensity. The higher you raise the floor, the further and faster you will go as an endurance athlete.
The best way to improve your aerobic threshold is through a structured training plan with well timed periods of rest. As you increase your training volume, make sure to include one or two HIIT sessions per week and long Zone 2 training sessions to get the most out of your weekly training.
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