During the course of Paul's attempt to take the 24 hour world record, we will be showing the data block appearing on the left hand side of this screen superimposed onto our webcast picture... but where does this data come from and what does it all mean?

Paul will be wearing a HR monitor transmitter around his chest and that will be broadcasting a signal to a receiver near his rowing machine. The receiver will be connected to a computer (in fact to one of the three computers that we will be using on the day to help us).

The HR monitor we use is incredibly accurate, recording the gap between each and every heart beat to the nearest 0.001 seconds. Why the need for such a degree of accuracy? We'll explain below why we need this precision and what it can tell us about how Paul is doing.

So what does all the information in the data block mean? Some of it is not entirely straightforward, but we will start with the easy parts.


"HR" (Heart Rate)

That's pretty straightforward - how often your heart beats each minute. The harder you exercise, the higher it will go, thereby pumping more oxygenated blood around the body (and in particular to the working muscles during exercise). 

Paul's maximum HR is 190 and his resting HR is about 37 (a bit lower in the racing season). We expect Paul's heart rate to settle at around 125 during hours 1 and 2 (a bit of excitement on the day might push it up at the beginning, but we can ignore this) . One would typically expect to see an upward drift over the first 6 hours, followed by a reverse drift back down between hours 6-12. We would get concerned if his heart rate was above 145 in the first 18 hours. 


"%HRmax" (Percentage of Maximum Heart Rate)

Everyone has different maximum heart rates, which can make it difficult to make comparisons as to how hard two people are exercising. Both athletes might be exercising at HR150, but if one has a maximum heart rate of 170 and the second has a maximum heart rate of 190, the first will be working relatively harder (being closer to their maximum). Accordingly %HRmax allows for easier comparison.

(The more physiologically aware might protest that percentage heart rate reserve would be more useful - we agreed, but the software does not show that but it does show %VO2max - see below)


Kcal (sum)

This is the total number of calories burned during the row. We can calculate this accurately because we know how much oxygen Paul can metabolise when he is working flat out, and we know how close (or not) he is to flat out at any time (see %VO2max below).

Due to the very large volume of training, Paul's body has become more metabolically efficient. His height also makes him mechanically efficient for rowing and so we are expecting him to burn no more than 750kcals/hr - that's 18,000 kcals over 24 hours. 


%VO2max

Whether you are sleeping or exercising, oxygen reaches the muscles as a result of you breathing it in. It passes across the surface of your lungs and binds to haemoglobin in your red blood cells. Your heart pumps the blood around your body. When the blood cells move into an area where there is relatively less oxygen (e.g. your exercising muscles), the oxygen is released into the muscle cells where it is used to burn fuel (typically glucose or fat), providing energy.

As the intensity of exercise increases, more oxygen is required. Everybody has a limit as to how much oxygen they can metabolise which is known as their "VO2max".

We can calculate at what percentage of his VO2max Paul is working at from moment to moment. We know Paul's resting HR and his maximum heart rate which is a good start to calculating %VO2max, but we can use something known as heart rate variability (HRV) to give us even more accurate information. HRV is explained below.

We are expecting Paul to be working at around 35-42% VO2max for at least the first 12 hours. Anything above 50% would be concerning until we are in the last 6 hours. In an event of this duration, there will be a separation of the relationship between HR and VO2, making it unsuitable to rely on HR alone to determine intensity.


EPOC (and HRV)

This is the most complicated bit. If you are sitting down with a heart rate of 60 bpm, the gap between each heart beat is not 1.000 seconds - it varies, hence "heart rate variability". Your heart rate is controlled by a number of inputs and the dominance of each input changes over time. The most easily identified change occurs when you breathe - as you inhale your heart rate marginally accelerates; as you exhale it slows. This is caused by different parts of your autonomic nervous system taking control. The size of these undulations provide valuable information about how your body is working. 

HRV is used to sharpen the accuracy of the VO2max figure above. It is also used to calculate something called "Excess Post-Exercise Oxygen Consumption" (EPOC). This is effectively the amount of extra oxygen that is needed to repair the body after exercise - it is the metabolic "cost" of the exercise. This too can be calculated from heart rate and HRV. It is measured in milliliters of oxygen per kilogram of body weight.

Paul typically records EPOC figures in the 45-90ml/kg range during distance rows in training (depending on the precise nature of the session) and up to around 280ml/kg in long time trials (30 to 60 minutes).

We need Paul's EPOC to be relatively low due to the duration of the row - even a moderate load per hour becomes enormous over 24 hours.  We are expecting it to sit below 15ml/kg for at least the first 12 hours. If it is higher than that later on in the row, we would not be too concerned provided it is fairly constant (and below 50ml/kg). We would become concerned if it started to steadily rise since this would indicate an increased degree of metabolic damage being caused by the row, potentially making the continuation of exercise impossible.  


EPOCpeak

This is simply the highest recorded EPOC in the course of the row.