I have the power!

The blogs have lapsed recently due to uni, a new job and training/racing. However I’m thinking of taking a slightly different approach to these blogs now. I’ve spent several years racing, training and being coached in the process. Being about to enter the final year of my Sports and Exercise Sciences degree, I’ve also become a lot more interested in what goes into creating, maintaining and improving athletes. This has led me to start working for a coaching firm and also spend a lot more time reading into athlete physiology, biomechanics, nutrition and psychology. I don’t pretend to be an expert in these areas but feel I have some knowledge I could pass onto others and potentially help them. So here goes the first one of these, delving into power meters…

As soon as I started being coached I was recommended to get a power meter. Fortunately at the time I was able to get a loan of one but nowadays they are a lot more affordable. The reason for using power over metrics like Rate of Perceived Exertion (RPE) and Heart Rate (HR) is simple: it’s far more accurate. RPE is very hard to determine accurately due to too many factors to list, and using speed to gauge efforts is difficult with differing air pressures and winds on different days. HR is a good level up from that but still remains variable. A good/bad night’s sleep, caffeine and fatigue can all affect HR and how quickly it responds to changes in intensity. Say you were gauging an effort at threshold for 15 minutes, your HR would increase initially but then continue to do so; it’s very hard to pace effectively using solely HR. Additionally, if you are coming to the end of a large block of training your HR may be as much as 10-20 beats per minute (BPM) slower for the same given effort. This is another reason why using HR to track energy expenditure properly is notoriously difficult, but it can help (more on that later).

Wahoo KICKr Smart Trainer (power is measured at the hub)

Power meters are simply the gold standard for training (as long as they are calibrated correctly before each ride – additionally temperature changes can affect readings in some). You can find them in pedals, crank arms, crank spiders, smart trainers and wheels. Generally, the further away from the foot the lower the power reading will be. For example, my power is higher on my road bikes as they have 4iiii crank based power meters compared to my Wahoo KICKr smart trainer where power is taken at the hub. They traditionally work based on strain gauges recording torque and then using angular velocity to give you your Wattage (W). This is useful for so many applications in cycling.

Firstly, using a power meter is a great way to determine accurate training zones either by doing standalone threshold and critical power testing, or combining this with lab testing of expired gases and blood lactate to determine Lactate Thresholds (LT) and VO2max. Traditionally people do a 20 minute all out power test and multiply that by 0.95 to determine threshold power. Lab testing is a more accurate way to determine power/training Zones as LT and VO2max do not necessarily correlate; some people will have a high LT and low VO2max whereas others will be the opposite. Determining power zones allows you to train more effectively for whatever events you are targeting. Going for a 12 hour time trial, aim to work more Z2/Z3 which is the Zone you will predominantly working in. You can also use the power meter to make sure you don’t stray into the higher zones where your body will burn a higher percentage of carbohydrates (CHO) compared to fat, which is not sustainable for 12 hours. Targeting a 4 km pursuit, then it’s all about working your anaerobic capacity and VO2max. Road races (especially stage races) will be a mix of low intensity combined with very high intensity efforts, which is where the race is generally won or lost. Repeatability of efforts and resistance to fatigue are also highly important. There’s no point being an incredible sprinter when you’re fresh if you can’t replicate that effort at the end of a 3 hour road race full of on/off efforts. However, I’d recommend not looking at power during races as that really doesn’t matter, it’s about who crosses the line first (unless you’re pacing yourself up an alpine climb and trying to avoid going into the red). Analysing power data after races can be very useful though for determining where the race was won or lost, where you can improve and also looking at where you were strong. It’s always important to take in the positives, regardless of the result.

4iiii Podiiiium Dual sided crank based power meter

Another fantastic use of power meters is energy expenditure tracking. Some people will want to use this more than others, depending on how much you want to analyse (you can overanalyse!). Personally, I use this with every session. Using the wattage you’ve averaged for the duration of your ride, you can work out the kilojoule (KJ) expenditure (most computers will do this for you, I use a Wahoo Elemnt Bolt). Basically KJ = W * s / 1000, so 1 hour at 300 W equates to 300 * 3600 / 1000 or 300 * 3.6 = 1080 KJ. Using this you can then work out calorie burn fairly accurately as, by a fortunate fluke of nature, 1 KJ recorded at the power meter equates to ~1 kilocalorie (but we just refer to them as a calorie since a single calorie is such a tiny unit of energy) burned. Traditionally 1 calorie equals 4.184 KJ but thanks to humans not being entirely efficient, due to heat loss and other factors, a general rule of thumb can be used for 1 calorie = 1 KJ (although some people will be more or less efficient so this number is not entirely accurate for everyone, it is on the whole more accurate than HR or RPE though). So, if you ride at 300 W for 1 hour, you will burn around 1080 calories. Combining this with HR can also assist in working out Excess Post-exercise Oxygen Consumption (EPOC or afterburn) which is when your body’s metabolism is raised post exercise to compensate for oxygen debt and also to allow recovery and other metabolic processes to occur. This is particularly useful for working out if you need to eat more during a ride or race and for tracking energy expenditure for weight loss, gain or maintenance. I use it primarily to maintain body composition and ensure I remain in energy balance, therefore improving training and racing performance. It’s all well and good trying to get as lean as possible for racing and getting the best watts per kilogram (W/Kg) but, for some, it is possible to get too lean which will affect power, hormone balance and bone density. I’ve dipped into energy deficiency before and it was not at all pleasant. Fortunately using a power meter to track energy expenditure and ensure I’m in energy balance has resulted in me finding an ideal body composition for my optimum W/Kg without adversely affecting my health.

Wahoo ELMNT Bolt computer, easy way to keep track of your training during sessions and for recording data

So there we go, uses for a power meter explained fairly quickly and hopefully fairly simply. I personally think they’re a great addition for anyone training for any event or just fitness and for those looking to manage their body composition safely. Hope you enjoyed the read and if you’ve made it this far, thanks!

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