Maximising Training Efficiency with Anaerobic Threshold Workouts

What is our Anaerobic Threshold? Very theoretically, it is the point where we find a rapid increase in blood lactate. Our body produces lactate when metabolising glycogen for fuel. At lower intensity levels our bodies utilise a higher percentage of fats in our fuel mix and therefore less lactate is produced. At easier intensities the body has more time to manage our lactate levels and actually uses the lactate to produce energy. So, training or racing at lower heart rates can be sustained for very long periods, pretty much as long as the muscles can repetitively perform the movements we are asking for.

As our intensity and heart rate rises, our fuel mix ratio moves from more fat towards more glycogen and more lactate is produced. This remains manageable for our bodies until we reach the theoretical Anaerobic Threshold, where the accumulation of lactate exceeds the body’s ability to manage it. The accumulation of lactate (and other by-products of exercise) eventually forces the body to reduce intensity and ease up. So, the anaerobic threshold (AnT) can be referred to as the maximum sustainable level of exertion.

VO2 is another term that refers to our ability to take in and utilise oxygen. It is largely genetically determined whereas AnT is very trainable. Very simply, the closer we can get our AnT to our VO2, the closer we are to our absolute potential as an runner.

How do we test or calculate our AnT in such a way that is useful for training? Fortunately this is simple. Running a 30-40 minute time trial or race as fast as we possibly can will produce a heart rate average that corresponds very closely to our anaerobic threshold HR.

There are two things that we are looking to achieve with regards to our AnT. Firstly, we want to push that AnT heart rate up. Increasing our maximum sustainable HR. The second thing we are trying to achieve is to improve the speed we can sustain at that HR. For more experienced, well-trained runners, speed at AnT will be the primary goal as AnT heart rate will be well developed and harder to improve.

So, that is all the theory. How do we make these improvements? Again, this is pretty simple, we need to train at intensity levels that stimulate the body to make the improvements we are looking for. Having determined our AnT heart rate in a 30-40 minute all out running effort will also have taught us how uncomfortable and difficult that level of intensity is. Spending a lot of time training at those levels is not palatable for all but the most masochistic runners. Fortunately, we don’t need to train right on AnT. Research has shown that training at heart rates 10-15% lower than AnT still produces the training effect that we are looking for. The advantage of this is that we can do more training at these levels as recovery is quicker and there is less chance of over-use and injury.

Anaerobic threshold training consists of longer intervals with short recoveries. We don’t want to allow the body enough time to deal with the lactate that we produce in each interval so that there is an accumulation through the set of intervals. The body will become better and better at dealing with lactate at high levels of exertion as a result. Our muscles will also become mechanically better at propelling us forward at these intensities and, over a block of training, our stride length and cadence will improve and our speed at AnT will be faster.

The key factor to remember when performing AnT focused interval sets is heart rate lag. Our heart rates rise gradually under load and the HR at the beginning of a longer interval will not correspond with the perceived effort. The biggest mistake made during these intervals is to start too hard and trying to force the HR up to our target levels too soon. For a well-trained runner, a HR of 85-90% of AnT should be achieved somewhere between a minute and a half and two minutes in a longer interval. So, we might not even reach our desired HR level in the first few intervals, depending on how long they are. We will see a gradual rise in HR throughout the set of intervals and we will reach our target HR earlier and earlier in each interval. Our HR will also not drop as low after each interval as a result of the shorter recoveries.

Remember, we are endurance athletes, not sprinters. Our interval sessions should be challenging but not excruciating. We should always be able to hold good running posture and form and always be in control, from the first interval to the last. Our bodies respond way more to this than they would taking them to their absolute limits and we will also recover quickly enough to repeat that sort of effort in only a few days. Over the medium to long term, we will avoid injury and over-training while seeing significant improvements. AnT work is by far the most ‘bang for our training buck’.