With regular endurance training the body experiences a number of physical adaptations that can lead to improved performance including:

Changes in heart function (notably an increase in how much blood is pumped per stroke)
An increase in the oxygen carrying capacity of the blood (through both increased blood volume and increased haematocrit)
An increase in capillarisation around skeletal muscle
Increases in both mitochondrial number and density
Increases in levels of enzymes involved in energy production
Increased buffering/utilisation of acid
Increased fatigue resistance and contractile potential in the muscle
Improved inter and intra muscular co-ordination

When we exercise the body starts producing lactate as a by-product of energy metabolism. The level of lactate increases as exercise intensity increases. Lactate is measured in the blood in either a lab setting or using a portable hand held device. When lactate accumulation remains under 2mmol we can usually sustain the work load for many hours. When lactate increases beyond 2mmol and up to 4mmol the body has more difficulty clearing it from the system and our ability to sustain workload starts to reduce. These two lactate measurement points are extremely important when considering workout duration and intensity.

Typically the following terms have been used as indicators of these parameters:

The 2mmol point is often referred to as our 'Aerobic Threshold'. This should be thought of as the maximal pace you can maintain comfortably at over 2-3 hours of exercise. It is the point where lactate production is matched by the rate of lactate clearance in the body. It’s also called ‘easy to steady effort’ training. It is definitely not hard and you can exercise for hours at this level.
The 4mmol point is often referred to as the 'Anaerobic Threshold'. This should be thought of as a pace able to be maintained for 30-60 minutes and reflects the point where lactate begins to accumulate faster than the rate of clearance. This intensity is ‘moderately hard to very hard’ – a pace you can sustain for 45-60 minutes but not much more.

Why are these two thresholds important? Because building a training plan around your individual thresholds will go a long way to developing your endurance and speed as an athlete.

The size of your aerobic engine plays the biggest role in endurance performance, so building this should be where you focus the majority of your training. This engine can be most significantly improved by working in and around the intensity that produces 2mmol of lactate. In other words as much as 80% or more of your training should involve exercise at ‘easy to steady effort’. It's the intensity that elicits most improvements in maximal endurance performance.

Depending on your sport and its' specific demands it is recommended that approximately 1-3 sessions per week, or between 60-90 minutes of total work per week, should be performed at anaerobic intensity. If this seems like a ratio that may improve endurance but not speed then consider this…

Here's an analysis of the training of the 2000 Olympics German Track Cycling team competing in the 4km Teams Pursuit. Now this is an event lasting roughly 4 minutes and yet the great majority of the team’s training is described as ‘easy aerobic (circa 2mmol lactate) work' to the tune of 29,000-35,000 km/year! That’s approximately 600km per week at an exercise intensity that produces around 2mmol of lactate when, during the actual race, they will be working at levels well above 4mmol of lactate. So lots and lots of easy aerobic training at intensity well below race intensity for an event lasting only 4 minutes!

For completeness, this was supplemented with some road races for variety and brief bouts of high intensity along with specific race interval training in the 10 days prior to competition to maximise things like lactate buffering and speed. Please read that again, for an event lasting 4 minutes, interval training and some speed work was done for about 10 days immediately prior to competition.

Other sports use similar volumes, running volumes of 160-180km per week are fairly common at the highest levels. Current rowing training incorporates masses of aerobic training; swimming has always used pretty much the same high volumes with most of their races being over in a couple of minutes max.

To determine ‘easy aerobic’ intensity the German Track Cycling Team set intensity to heart rate at individual anaerobic threshold (IAT) minus 30-50 beats. So for someone with an IAT at around 175 that’s a heart rate of 125-145. With an IAT of 180, that’s 130-150.

It barely feels like you’re doing anything at all but the stimulus comes from the volume (and frequency) of training being done.

Understanding these training concepts and also determining your threshold values will go a long way towards helping formulate an accurate training plan. An exercise lab is able to perform a VO2/Lactate Test which can give you your personal data points; however a coach is always useful for putting this information into practice. You may also find that, like ourselves, coaches have there own hand held portable lactate testing units for immediate results in the field.

Bevan McKinnon

Endurance Training and Individual Thresholds