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Joy's Adventures with a Power Meter 7: Physiological Measures at Beds Uni Human Performance Centre

Joy's Adventures with a Power Meter 7: Physiological Measures at Beds Uni Human Performance Centre


In my efforts to understand more about how to get faster and stronger on my bike, I have been using a power meter for targeted zone training. Now, I’m finding out more about how zones connect with my personal physiology through tests at the Human Performance Centre, University of Bedfordshire, Bedford.

I become a lab rat

 The door opens and I enter the testing lab. It’s a large room with a vinyl floor. Two walls are lined with floor and wall cabinets making it look like a fitted kitchen. But no cooker or microwave or kettle in sight. Instead the surfaces are covered in computer monitors and wires trail across to keyboards and printers and other machinery that is alien to me. It all looks very clean, almost clinical, with lots of wipe clean surfaces. In one corner is a treadmill. But my eyes are drawn to the middle of the room and the stationary bike. This is what I am here for.


Nervous anticipation

I’m not really sure what to expect. The guys in the shop who are members of the Flamme Rouge Cycle Team have had some testing done at the HPC. All I heard from them is how hard it was. And I have seen the picture of Jack collapsed in a heap on the testing room floor, face all red, hair dripping with sweat.

This is why I approach the centre with some trepidation. What is it going to be like?

Lactate profile measure

I have signed up to do two measurements, with sessions over two days.

Yes, blood is involved

The first is to measure my lactate profile. This involves taking regular blood samples from a pinprick in my finger while I cycle to exhaustion. I was a bit worried about the “cycle to exhaustion” bit. Surely this would take hours?

I meet the two guys conducting the tests, Shaun and Ryan. They are MSc students at the university and provide continual reassurance throughout the tests, reminding me that I can stop at any time.

Safety first

But first it’s a blood pressure measure. This is to make sure that it’s safe for me to go through with the testing today and critically for later in the week when I do the VO2 max measurement. This complements a health questionnaire I have already filled in.

My first measure is through the roof. Not surprising really, I’m nervous and anxious about what is to come. After five minutes it has gone down but not enough. Ryan gives me some advice: don’t cross my legs and take deep breaths. I chat to the guys about what the tests will show and I feel myself relax. My final blood pressure measurement is well down and I have the green light to go.

And so it begins

Ryan takes a resting blood sample, now all seriously attired in white coat and plastic gloves. He tells me I should only feel a small scratch in my finger. He’s right and I hardly feel it as he squeezes a dark red globe of blood out of my finger. He uses a small pipette to suck up the blood and rushes over to a magical machine in the corner which spits out results on a strip of paper within seconds.

The before picture

 It’s time to start the test proper. This involves cycling on the bike at a determined power setting. After a warm up, the power increases by 25 W, increasing again every 3 minutes. A blood sample is taken before the watts are ramped up each time. Once the test results show my lactate levels are increasing rapidly, the test stops. I wonder how long this will take and if I will manage to reach the end.

A quick check of the heart rate monitor I have strapped around my chest to ensure it’s connected properly and the test can start.

Shaun sets the bike up with the measurements of my own bike that I have brought. The pedals on the bike are single sided SPDs and I have not brought my own pedals. So I wear trainers and use the toe strap and cages fixed to the pedals. A few adjustments to ensure I’m comfortable. I grip the handlebars, the right one covered in clingfilm to catch escapee blood.

It’s easy! At first...

It starts off fine. The pedalling is easy and it feels great to be doing something I know how to do. What I find strange is that I can’t see any power readings. All I have in front of me is a readout of my cadence. I concentrate on keeping it at around 80 rpm. As the three minute countdown approaches, Ryan takes another blood sample, while Shaun shows me the chart for “rate of perceived exertion”. This starts at 6 with “very light” and goes to “very hard” at 20. It’s not something I’ve used before. I tell him it’s currently a 7.

The first few sets of three minutes are fine and I easily maintain my cadence of 80. Then it starts to get hard. In a workout, I’m used to pushing hard for a few minutes, then having a recovery period. But this test is relentless. There is no break and the watts I have to push out just keep going up. It starts to get hard. Really hard.

Not so easy now

The after picture, all red and sweaty


Sweat drips off me. My heart pounds. I’m breathing fast. My legs have lead weights attached.  Shaun encourages me to keep going. Every three minutes he asks if it’s okay for him to increase the power. He asks this very nicely. And I say “yes” very nicely. Though I’m not actually thinking nice thoughts.

After about 20 minutes, when I am starting to wonder when will it end, Ryan finally rushes over with the strip of paper from the machine that has been swallowing my blood. After confirmation from Shaun, he stops the test. “You’ve done it!” he says, “You’ve reached OBLA!” I have no idea what this means but I do hear that it’s now over. Rate of perceived exertion: 19.

VO2 max test

Only to do it all over again for the VO2 max test two days later.

At least this time I know a bit more about what to expect. No blood samples but I have a mask over my face. This feels strange and there is a slightly sweaty smell mixed with plastic as I breathe in. I thought the mask would restrict my breathing but a few practise breaths show me that I can still breathe quite normally through my nose and mouth.

The testing regime is slightly different this time. Instead of ramping up the power every three minutes, the power will increase by 25 W every minute. The good news is this means I will reach the end within 12-15 minutes.

I can do it, I know I can


It’s a test of will power. It’s really important I get to the point that I cannot push the pedals anymore. A lot of people fail to get their VO2 max at their first attempt because they don’t know what that endpoint feels like. I don’t either but I imagine it to be like the final sprint at the end of a TT where the end is in sight and you push yourself to the limit.

So it starts. The mask has a thick plastic tube which leads to a machine that continuously measures oxygen going in and coming out. As the exercise gets harder, my body will use more of the oxygen I am breathing in. Eventually, I will be using the maximum amount of oxygen my body can cope with and the amount of oxygen I breathe out will remain the same. At this point the test stops.

When will it all stop?

 Shaun, always smiling

 Every minute Shaun asks my permission to increase the watts. It’s an effort every time to say “Yes” which comes through the mask a bit muffled. Would he even notice if I said “NO!”? I focus on cadence and the magic number of 80. My heart is pounding loudly in my ears and my breathing is ragged, my mouth open wide to get as much air in as possible. Within just a few minutes it seems I am dropping to a cadence of 70 and below.

“Keep going! You can do it!” Shaun, my personal trainer and torturer. But I do. Keep going. And actually it doesn’t seem very long before Shaun is telling me I can stop in “15 seconds. 10 seconds, 5, 4, 3, 2, 1” and it’s all over. I slump over the handlebars but manage not to collapse on the floor.

Now I know why there are all those wipe clean surfaces in the testing room. It’s for the blood, sweat, and tears.

What did I learn?

What does the computer say?


Well, “cycling to exhaustion” wasn’t as bad as I had feared. It’s tough at the time but doesn’t last very long. And you don’t have to think about when to stop, the guys tell you when you’ve reached the end.

It does help to know what it feels like to reach the point of exhaustion. I was glad, if that’s the right word to use, that I had previously done an FTP test and also a few TTs so I know what it feels like to think you can’t do any more but you still keep going.

What about the numbers?

I get a report from Shaun a couple of days later.

VO2 max

This is the easier bit of data to get your head around. VO2 max is the highest rate at which your body can use oxygen to power exercise. There’s a lot involved in this: how big your lungs are, the volume of blood your heart can pump around in one beat, how many beats per minute, the efficiency of your blood circulation, and so on. Training affects these parameters resulting in an increase in VO2 max.

So what was my result? It was 42 mL per kg of bodyweight per min, at a heart rate of 184 bpm, and a power output of 275 W.

What does this mean? It’s not bad really. In fact, for a female of my advanced years, it’s excellent. The training is really paying off.

Lactate Profile

As part of our energy production systems, we produce lactate. At rest, the level of lactate in our blood stays pretty constant as the lactate that is produced is cleared away by the next steps in the pathway which require oxygen. As we start to exercise, lactate levels increase as we produce more energy, resulting in a rise in blood levels. This rise is gentle at first as the oxygen requiring parts of the system can still clear excess lactate. You just notice that you have to breathe a bit faster.

This first increase in lactate levels is sometimes called Lactate Threshold 1 and is taken to be the point at which blood lactate is 1 mmol/L (a measure of concentration) greater than the resting value.

As you continue to increase the intensity of the exercise, you produce more and more lactate. Eventually the levels start to accumulate exponentially as your oxidative systems are working flat out and can’t clear any more. The point at which your blood lactate accumulates at this really rapid rate is called the Onset of Blood Lactate Accumulation or OBLA. This is the point at which you hit the wall and cannot continue. It is also sometimes called Lactate Threshold 2. This occurs at lactate levels greater than 4.0 mmol/L. By this point you’re really gasping for breath, rib cage heaving, heart hammering loudly.

The advantage of a lactate profile is that you get the results for both thresholds. My results? I hit Lactate Threshold 1 at at a heart rate of 142 bpm, and a power of 125 W. Threshold 2 occurred at a heart rate of 180 bpm and a power of 225 W.

What do these results mean?

If my VO2 max is already excellent where do I go from here? With my VO2 max already being on the high side it is unlikely to change much. The figure I need to focus on here is the power I produce at VO2 max: training should result in me being able to produce greater power at my VO2 max.

The lactate profile measures can be used to set training zones. I already have power zones from doing an FTP test using a power meter. But the FTP test is a single measure and on the basis of this all the zones are set. In contrast, the lactate profile gives two measures: threshold 1 and threshold 2. This provides more detailed information to set low intensity (lactate threshold 1) and high intensity (lactate threshold 2) training zones.

I am happy with the power zones I have. But I have found that the heart rate zones do not match up. In TrainingPeaks particularly, I have found the boundaries for the HR zones are set too high. The values I get from the lactate profile are much more realistic for me personally.

There is the option to set custom heart rate zones on TrainingPeaks but with no other information it’s not easy to do this. Now I have my threshold measures, I can reset the heart rate zones to match with low and high intensity power zones.

Overall conclusion

The VO2 max and lactate profile measures are ways of setting baseline measures which can be reassessed to determine the effectiveness of training. The lactate profile is also a way of setting personalised zones for training if you have a heart rate monitor but do not have a power meter.

If you have a power meter, the lactate profile measure is useful for fine tuning training zones obtained via an FTP test, ensuring that zone boundaries are more personalised. A lactate profile measure is therefore a great complement to an FTP test.

And the tests are quite enjoyable. In the same way that cyclists think climbing mountains and doing time trials are fun.

Here’s the link for you to find out more: 


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