Why a good endurance base is important for your season.
In previous blogs, we described the concept of periodization. Periodization is basically the build up of a season towards the moment of truth. For endurance sports, it’s often recommended to develop a solid base of endurance with long moderate-intensity rides during the off-season. But why should you start your off-season with these kind of rides and shouldn’t you just hit the road with some serious interval sessions from the start?
To explain this, we have to refer back to one of our previous blogs about the energy systems. Overall, cycling is an endurance sport (lasting for more than 2 minutes), which means that the aerobic or oxidative system is the major contributor to energy production. In other words: oxygen is used to make energy available out of carbohydrates and (mostly) fat during the major parts of your training or race.
The aerobic performance limiters
There are several factors that may limit an athlete in his or her aerobic performance. These limiters can broadly be divided in central and peripheral factors. The central factors may be described as the oxygen suppliers to the muscles. These include the cardiac output and the amount of blood-flow that is directed to the working muscles. The central factors are in particularly important for the aerobic power (VO2max).
The peripheral factors, on the other hand, may be described as the factors that contribute to the oxygen extraction in the muscles and the oxygen utilization by those muscles. These include the mitochondrial enzyme activity and the capillarization of the muscles. The peripheral factors are in particularly important for the aerobic capacity. The increase in aerobic capacity can be optimally utilized when it’s accompanied with an increase in oxygen delivery as well. Therefore, an endurance athlete should aim to improve both the central, as well as the peripheral factors.
Endurance training adaptations of central factors: a good endurance base.
The most important central training adaptations are an increase in the blood volume and an increase in the heart volume. The first is accompanied with an increase in red blood cell count. This can be trained by either a long-duration moderate intensity training, or a high intensity interval training. The increased heart volume consists of an increase in the ventricular chamber size and an increase in the ventricular wall thickness. This results in a greater filling-capacity of the heart, as well as a more forceful contraction of it. Both increase stroke volume and therefore cardiac output, which might increase VO2max.
One of the important training stimuli for the enlargement of the ventricular volume is the duration of the stretch of the heart walls during exercise. The amount of stretch increases with the exercise intensity up to 70-75% of VO2max. At even greater exercise intensities, the amount of stretch will increase further, but to a lesser extent. In addition, the intensity should be less than the lactate threshold intensity in order for someone to be able to get going for a longer time. For these reasons, training at higher intensities might affect the overall training stimulus that’s pursued. That’s why the most effective continuous training consists of exercising at an intensity of 70-75% of VO2max for extended durations. Of course, these ‘sessions with extended durations’ should be build-up gradually in your training program.
Endurance training adaptations of peripheral factors
The peripheral adaptations include increases in mitochondrial density, enzyme activity and number of capillaries near the muscle fibres. The increase in mitochondrial density and enzyme activity result in an increased oxidative reaction rate, a reduced lactate production and an increased lactate removal. The increase in capillaries around the muscle fibres results in a smaller distance between these tiny blood vessels and each of the muscle fibres. This makes oxygen extraction easier, as well as waste product removal.
The exact mechanisms behind the peripheral training adaptations aren’t completely clear yet. There are some possible mechanisms, but all seem to be dependent on exercise intensity. Training should therefore incorporate high intensity intervals. Since the peripheral training adaptations are also affected by the duration of the stimuli, the intervals (8-10, gradual build-up in your training program) should be 2-3 minutes long with intensities that approach 100% of VO2max. These intervals should be interspersed with recovery intervals of 2-3 minutes or longer when needed. By incorporating these rest intervals, one is capable of performing more work at the desired intensity. Intensities higher than 100% of VO2max might not be beneficial and may even lead to greater lactate build-up, which in turn reduces exercise duration.
These interval exercise sessions are quite stressful. Therefore, they should be performed every second day. When you do decide to perform such sessions on consecutive days, make sure you have a complete rest day afterwards!
The consequence for your training program
Back to our first question: why should you have a solid endurance base for your training? Based on the previous paragraphs, your endurance training program could be divided into two different main phases: the continuous training phase and the interval training phase. Each phase has a different goal. During the continuous training phase, the goal is to provide the body with a longer training stimulus needed for the central adaptations, whereas during the interval training phase, the goal is to provide the body with a high-intensity training stimulus required for the peripheral adaptations.
While the peripheral adaptations will be visible relatively quickly (after 1-2 weeks of training and a maximum after approximately 6 weeks), the central adaptations will not be apparent until after several months. In addition, peripheral adaptations will be lost relatively fast compared to the central adaptations. Therefore, endurance athletes should start their training program 5-6 months before the main competition. The first 3.5-4 months should be dedicated to maximizing central adaptations (continuous training). This phase should be followed by 6-8 weeks of high intensity training for the peripheral adaptations combined with training sessions to maintain central adaptations. Planning your training program the other way around might be possible, yet highly inefficient.
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Macdougall D, Sale D. The Physiology of Training for High Performance. Oxford: Oxford University Press; 2017.