Since I've called this month of training my Threshold Phase, I thought it might be a good idea to discuss the concept of a training threshold.

First of all let me point out that when I am training in this phase, most of it done on feel. I am far from concerned about exact heart rates, lactate values or specific speeds. With that said, there is a little bit of theory behind the concept.

What exactly is this threshold concept? The short answer is that it depends on who you ask. There are so many different definitions, slightly different names and different testing procedures to define the threshold. It is no wonder people get confused.

The list of names include: anaerobic threshold; lactate threshold; onset of blood lactate accumulation (OBLA), aerobic threshold; ventilatory threshold; aerobic threshold1 and or 2; maximal lactate steady state (MLSS); threshold 4.0; lactate turn point and plenty of others.

Basically I like to accept that there is an area of intensity at which the body's production of anaerobic byproducts (lactate) is greater than the body's ability to absorb these byproducts. The biggest problem with understanding this is that most people assume it is a set point to be defined as an exact heart rate or blood lactate reading. This is not the case. Lactate dynamics is a very complicated process in the body, is influences by blood supply to the working muscles, substrate availability, muscle fibre types recruited, fatigue levels, muscle buffering capacity, blood buffering capacity, ambient temperate, core temperate, hydration status, hormone levels, duration of exercise and many other factors.

But why do people get their lactate threshold tested in a lab? Because if you follow a standardised test each time it can be a good indicator of improvement. As long as you do the test under the same conditions every time. Different testing protocols can give different results so the test must be the same each time. These test will probably only be of value if do regular testing, to compare your training interventions. A one off will only provide some nice to know information that probably isn't that practical.

So what do I do in training? I accept that my threshold occurs somewhere in the range of 80-90%HRmax. It is roughly the pace you could for about 1 hour. It is often marked by a noticeable increase in breathing rate due to the increase in acidosis from increasing lactate levels. I should feel a very slight burn in the exercising muscle after working at this intensity for over 5 minutes and the effort should feel just above what I would call comfortably hard.

In each cycle of my Threshold phase I will include on bike-run set of 40-60min on the bike followed by a 20-40min run. I am able to achieve this extended time due to the change in disciplines. While most the set feel solid but doable, it does take all my concentration to complete towards the end. Also in each cycle I will include another set of 3-4x10min with 3-5min easy alternating between bike and run each week. Here I will usually aim for an intensity about 85-92%HRmax, but I will usually ignore the heart rate monitor during this.

How does this relate to the Half Ironman I have coming up in about 5-6 weeks? Well it is at an intensity slightly above race pace. Here I should further develop my specific strength endurance, overall core conditioning (be able to hold race form better), enhance efficiency at near race pace, improve substrate utilisation and hopefully when it comes to the day, the race pace will feel fairly comfortable for most the event.


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