The objective of all training is to achieve the greatest level of adaptation, not to become the most tired. Lots of athletes train to get tired or to burn calories. Go ahead and burn calories if you want to work out and lose weight. That’s all well and good, but if you want to PERFORM, whether that is finishing your first sprint-distance race or trying to win on Kona, the best way to achieve your goal is to have an adaptive response to training, which results in improvement, not to simply do more training hard. You want training to have an effect. There are some consistent themes in the way the most successful athletes train, and that’s really about a polarization of effort – workouts should be extremely easy or extremely hard, with minimal training in the middle, and that’s the crux of my philosophy.
60- 75% of all training performed by the athletes who I work with is done at a fairly easy effort – what you might know as steady-state aerobic base pace, and I sometimes refer to as singing pace. Aerobic base and active recovery, or Zone 1 and Zone 2 training (see chart here), are going to make up the lion’s share of training, whereas most athletes spend too much time in Zone 2 and 3, thinking it is easy enough. Aerobic base workouts need to be performed at a low enough intensity that the athlete can recover from their high-intensity training and build a decent training volume base. The adaptations that we get from the low-intensity training, the steady-state aerobic base training etc, are an increase in economy and efficiency. We can then use more fat as fuel at any intensity level. Within the body you have two different fuels that are primarily used during endurance exercise: carbohydrates and fat. Protein is only used for energy production to about 5%, until extreme fatigue sets in. At lower-intensity exercise you’re going to have a more even mix of carbohydrate and fat used. As you work harder, there is a progressive shift to using more and more carbohydrates. Once an individual is near their threshold effort, the intensity they can do for one hour, they are using almost exclusively carbohydrate fuel. Carbohydrate can only be stored in limited quantities in the body: in muscle glycogen, liver glycogen and blood glucose. We also have a limited capacity to take in and process carbohydrate while we are exercising, and as intensity increases, the body can process less and less carbohydrate. When you run out of that precious carbohydrate fuel, intensity will drop. Fat calories stored within the body, even in a very fit individual, are essentially unlimited, so developing to utilise fat is critical to endurance performance because it spares precious glycogen stores needed to go fast.
When we train at low intensities, we develop an increased ability to use more fat at any given intensity. So, let’s just say that at 8min/mile pace an athlete with poor aerobic efficiency in terms of using fat may get 50% of all calories from carbohydrates and 50% from fat. With more aerobic base intensity training we could see that ratio shift over maybe a two- to three- to four-month period, so he’s burning 60 to 70% of those calories for that same running pace from fat and only 30 to 40% from carbohydrates.
An individual who has better aerobic efficiency – the ability to spare carbs and use more fat as a fuel at any given intensity – is going to be at an advantage versus somebody who uses more carbohydrate and has to eat more and then has to slow down to digest those carbohydrates. Low-intensity training allows athletes to eventually exercise at a higher intensity at the end of a long training session or a race because they spare glycogen.
Lactate threshold is the exercise intensity where the body starts producing more lactate than it is able to remove, so it begins to accumulate. Lactate itself is not a bad thing, it does not cause fatigue, but there is an association between the point that lactate levels elevate and creation of that burning sensation. When we train at an intensity just below our threshold, there is a very high influx of lactate being produced by the muscles and then being used as fuel. The main objectives of high-intensity training are both to increase the production of lactate and, more critically, increase your body’s ability to clear/use the lactate. Training just below lactate threshold is where we see the greatest increase in one’s ability to clear and re-use the lactate.
Given this, the majority of hard training is best done just below the lactate threshold to maximize the body’s ability to clear lactate. This training adaptation increases your maximum sustainable pace and power, which moves your lactate threshold level up to a faster speed.
Some athletes make the mistake of doing their steady-effort, hard workouts at an intensity too low to maximize lactate clearance; many people call it “tempo” training. In other words, many people spend too much time in Zone 3 during hard training (see below) instead of Zone 4. On the other hand, some individuals cross over and go above their threshold, into Zone 5, during long interval workouts instead of staying just below. Once you cross over your threshold you see a significant increase the in activation of your sympathetic nervous system, which is effectively activating the “fight or flight” response and signals that you’re under stress. That’s what will increase your levels of stress hormone, and will inhibit recovery from the workout, and you’ll see a pronounced increase in the percentage of carbohydrate used for energy when you cross over. A super-threshold effort (Zone 5) is far more strenuous on you than a sub-threshold effort, and a sub-threshold effort can be sustained much longer. You might be able to do workouts that are 3 x 15 minutes or 2 x 20 minutes of sub-threshold and not feel exhausted. Whereas if you did, say, 3 x 10 minutes or 4 x 8 minutes of above threshold, you’d be pretty shot. And you’d only have accumulated 30 to 32 minutes of super-threshold training versus 40 to 45 minutes of sub-threshold training, and you only need about 48 hours to get going again after the sub-threshold workout. Recovery from super-threshold intensity is going to take longer – closer to three days before you’re recovered and able to do another quality session – which reduces your overall training quality. That’s why doing hard efforts at lower, sub-threshold intensities increases the total amount of quality training time an athlete can accumulate.
Even though the majority of hard training is below race intensity, it conditions the body, when rested, to sustain super-threshold intensity on race day because the body is more able to clear lactate. When you look at what the best endurance athletes have done historically, you see a very high fraction of training done at slow and steady efforts, and they have always done more sub-threshold than super-threshold training. Mo Farah runs 120miles+ a week but the majority of that is at really low intensity (admittedly fast compared to us mortals!) so that he doesn’t get injured from his training load.
Our next intensity level is VO2max intervals, or intervals at Zone 6, which is another specific, critical training mode that many people don’t do enough. In other words, when athletes do intense sessions, they are typically doing these workouts in Zone 5 rather than Zone 6. VO2max running pace is all-out one-mile speed. Cycling VO2max power is the highest power an athlete can sustain for five minutes. Your heart rate at the end of a four to eight minute VO2max effort should yield your maximum sport-specific heart rate. You can only operate at a certain percentage of your threshold during an endurance race, so you need to bump up your threshold to increase your sustainable race pace. VO2max work pushes up the ceiling.
A set of 10 30-second efforts with 90-second recovery done during a moderately long session is a typical VO2max workout for an Ironman athlete, who is going to do significantly less VO2max-intensity work than a short-distance athlete, and when they do those intervals they’re going to be shorter duration with longer recovery.
Of course all this science tells us a lot about how the body reacts – and that the majority of athletes train in the wrong zones, at the wrong intensities to REALLY improve and make a difference. However, as most age group athletes, time is a luxury and if you’re on super tight schedules, the composition of your training might have to change accordingly. Personally, I’d still stay away from the zone 3 element, and go either harder or easier, depending on the time of year and the aim of the phase that you are working in.