Metabolic Efficiency Testing and Heart Rate Training

Heart Rate Based Training

 It is the start of a new running season and people are starting to set themselves new goals for 2016. In order to get a clear picture of my own current fitness state and kick start my training I decided, at the tail end of last year, to undertake a VO2 Max (MET) Test.  This is a service I offer to my clients to help guide their training and is something I use myself to make sure I am training effectively.  Fortunately, at Physiologic - here on the Gold Coast - we have a fantastic VO2 Max testing facility so I didn't have far to travel.

​​VO2 Max is a measure of your maximal rate of oxygen consumption and is usually expressed relative to your bodyweight in ml/kg/min.  The people with the highest recorded VO2 Max are generally the most elite endurance athletes  with human values topping out around 90ml/kg/min (e.g. runner Kilian Jornet reportedly has a VO2 Max of 92ml/kg/min).  Although the general trend is for better athletes to record higher VO2 Max scores, the correlation to race performance is not as close as for other measures such as lactate threshold. What this means is that finding out your own VO2 Max is nice but is not really that useful in itself aside from bragging to your running mates about who has the highest score! So what is the purpose of doing the test if it isn't to find out your VO2 Max?

The main thing the VO2 Max test does really well is give you a very clear picture of your personal metabolic profile. How well do you burn fat?  At what heart rate do you start burning more carbohydrate than fat?  Which heart rate zones should you be training in to optimise your training? 

​My test started in the most relaxing way possible, with a 20 minute resting metabolic test. This measures what your metabolism does when you are not exercising and gives an idea of your fuel usage at rest (more about this later).  This is done by wearing a mask connected to an indirect calorimeter which analyses the make-up of your exhaled air. From this analysis it is possible to work out the percentage of fats and carbohydrates you are burning as fuel. 

​Next it was over to the treadmill.  At first I thought it would be awkward to run wearing a face mask but after a few minutes I got used to it and was able to concentrate on giving 100% during the test.  The exercise test is where the real fun begins.  Starting at walking pace, Tom, who ran my test, closely monitored what my heart rate registered (via a standard HRM chest strap linked to his laptop) and each time it stabilised he incrementally increased the gradient and the pace of the treadmill until I was running at my absolute limit.  The goal of the test is to run (or ride - it is just as easy to do the test on a stationary bike) until you reach RQ=1.  This is the point at which you are burning 100% carbohydrate as fuel and basically signals the end of your exercise session - it is impossible to hold this very high intensity for more than a few seconds.

Tom used an AIS testing protocol on me which took me from walking on the flat at 5km/h to running at 15km/h on a 15% gradient in increments lasting a few minutes each.  The whole test took about 25 minutes and I reached RQ=1 right at the point when I felt my legs turning to jelly and with my HR at 200bpm. 

A few days after the test, Mark Barrett, physio and metabolism expert sat down with me and went through all of my results.  His analysis showed some really interesting things that I was able to implement straight away into my training.

First up, my VO2 Max was 75.4 ml/kg/min, not as high as Kilian's but pretty good!  Better still was my ability to burn fat, even at relatively high heart rates.  All the way up to a heart rate of 186bpm (93% of max HR) I was able to burn more fat than carbohydrate.  This is a really good thing for someone doing long distance running as it means that I can preserve my limited carbohydrate reserves and use stored body fat as my main fuel.  Theoretically this means running further and faster without hitting the dreaded 'wall'. 

On the flip side, given my above-average ability to burn fat when exercising, my resting fat burning was quite poor - actually relying heavily on carbohydrates at rest.  Mark thinks this could be because I am not getting enough overall calories to fuel my training and am preserving my fat reserves.  It could also be an indicator of stress.
In addition to this my top end carbohydrate burning was quite poor.  This is seen in the graph where I almost struggle to get my carbohydrate burning fuel system going even at very high heart rates.  This top end is needed for shorter faster efforts, but more importantly for short bursts of strength within a longer event, such as a sudden uphill section in an otherwise flat run, or maintaining leg speed on a taxing technical downhill. This indicated to me that I need to incorporate more strength sessions into my training such as short and fast sprints, or lifting heavy weights.

So what does this mean for my training?  Well, I now have some actual numbers to work off for my heart rate zones.  For example to train in my aerobic zone, with carbohydrate use kept to a minimum I need to stay under 147bpm when running.  Estimating this figure from HR zone formulae would be highly inaccurate.

Many people will be familiar with age-based HR zone estimates such as 220-age=max HR. If I followed this formula I would have a max HR of 220-38= 182bpm. The VO2 Max test showed my actual max HR to be 200bpm.  This shows that the estimates can be wildly inaccurate and could lead to poor programming in your training.  

The test has also shown where my particular strengths and weaknesses lie and given some clear direction to my training.  Armed with this knowledge I can enter into my training for 2016 with confidence that I am training efficiently and not over (or under) stressing my system.

If you would like to learn more about VO2 Max testing or are interested in incorporating HR training into your training please visit these links.

TRAINING PROGRAMS - LEARN MORE

Metabolic Efficiency TEsting - learn more

​Huge thanks to Mark, Therese and Tom for the testing.  Happy Running :)