Power Meter Guide: Fueling, Cramping and Understanding the Metrics

Ride

October 23, 2023

How should you analyse the data you receive from your power meter, and how can you use it to improve all aspects of your performance (including how you feel on the bike)? Nik Cook explains the keys to understanding your power meter data.

Okay, five articles in and, by now, you should know your Functional Threshold Power (FTP), used it to set power training/pacing zones, set-up your head unit and ridden a few rides pacing with power. Hopefully you’ll already be noticing the benefit of this, seeing a positive impact on your ability to long pace a ride evenly.

In this article, we’ll start to touch on post-ride power data analysis, what the key power related metrics you’ll see on your Strava ride report mean and why you should be taking as much interest in these as in your performance of those segment leaderboards.

Before getting into that though, I just want to talk about another couple of key points as to why pacing well is so important – namely, how fueling and pacing are intrinsically linked and also why cramping is rarely linked to hydration/electrolyte level and is usually down to – guess what? Poor pacing.

The link between pacing and fueling

If you’ve ever suffered from gut or digestive issues on the bike or have simply run out of gas on a long ride, it’ll almost certainly be down to poor or overly ambitious pacing. If you’re pushing too hard, your body will divert blood away from your digestive system and to your working muscles. This effectively shuts the system down, meaning no more energy from the food you have put in and, if you try to eat more, it’ll just sit there causing you to feel bloated and nauseous.

Harder riding requires more fuel but….

This is the real kicker as, just like a car, if you’re pushing hard, you’ll require more fuel and, at these higher intensities, only carbohydrates will do. You have about 60-90 minutes worth of internal carb stores but, once you’re through those, you’re relying on carbs that you can take in and digest. If however you’ve shut your digestive system down, you’re going to come to a grinding halt.

Use a power meter to pace and fuel

Having established the link between pacing and fueling, the best way to pace a long ride is by riding to power zones as we discussed in my previous article.

Eat well when it’s easy

If you’re riding in Zone 1 to mid Zone 2 – the bulk of any well paced long ride, that’s the time to fuel up and you can take in a process “real food”. So, if you’re riding steady on the flat, sat in the wheels or have a long descent, reach for that panini, flapjack or similar.

Switch to easily digested when the pace picks up

Once you go above mid Zone 2 and up to mid Zone 3, you’re going to struggle to take on real food and should be questioning whether you need to be pushing that hard - especially on the flat.

However, on long climbs, Zone 3 isn’t super hard and, if you try sticking to Zone 2, your progress is going to be painfully slow. In these circumstances, especially on big HC cols where you could be easily be climbing for an hour or more, switching to gels and/or energy drinks, is the way to go.

If it gets any harder…

Above mid Zone 3 and into Zone 4, you’re treading that digestive shutdown tightrope. On a long ride, you should be looking to minimise and ideally avoid time spent pushing this hard as it’ll inevitably come back to bite you later on. Sometimes on brutally steep climbs it’s unavoidable though but, if you have punched this hard, give your system a bit of time at a steadier pace to settle down before trying to take fuel on.

Cramping is often also down to poor pacing

Many riders who have suffered cramp during a sportive or race blame poor hydration and a lack of electrolyte intake for their painful demise, but recent studies have indicated that this isn’t always the case. For such a common occurrence it might surprise you to know that the exact reason for cramping is still unknown.

FEEL THE POWER - THE SERIES: Check out other articles from Nik Cook

Many riders blame inadequate hydration or electrolyte levels and, although some studies have shown that consuming a 6% carbohydrate sports drink can help prevent them, other studies have failed to back this up and, recent work with Ironman triathletes found no link at all.

The main factor is usually an increase in exercise intensity or duration that you’re not conditioned to. So, if you suddenly ride harder or longer than you’re used to, you can expect to cramp. This tends to explain why you might not suffer from cramps on training rides but, come event day, when you push that bit harder or longer, the cramps bite.

The solution is to plan and build your training sensibly. Find a pacing strategy, ideally as previously described using personalised power pacing / training zones that you can sustain and, come event day, stick to it! Don’t expect a miraculous event day performance boost - even with a good taper and don’t let your ego write a cheque that your body can’t cash.

The metrics that matter

Let’s now take a look at those main metrics referring to this mountain bike ride I did.

Average Power

This is simply your average power over the whole ride – in this case 246W. This includes zero power periods of the ride such as when you’re freewheeling. Don’t make the mistake of thinking that if you were aiming to do a Zone 2 ride and your average power came out bang in the middle of Zone 2 then it’s job done, though. It’s possible, if it was a hilly ride, that you were in Zone 3/4 on the climbs, Zone 1 or zero on the descents and spent little or no time in your target zone. Make sure you focus on riding to that 3-second average (see previous article) and maximise the time spent in your target zone.

Weighted Average Power

As you can see from my ride, this was higher at 285w than my straight average. This is because weighted average power factors in jumps and spikes in power caused by the terrain, wind, race dynamics or even doing intervals. These variations in power all add to the physiological cost of the ride, Weighted Average Power takes this into account and provides an estimate of what your average power would have been if you’d ridden evenly for the whole ride.

As you’d expect from mountain biking, there was lots of variation so the fairly large disparity would be expected. For a flat time trial, I’d expect Average Power and Weighted Average Power to be really close.

Training Load

Training Load takes into account your FTP, Average Power and Weighted Average Power and uses this to calculate a tangible score for the load of a workout. This will feed into your Fitness, Fatigue and Form which we’ll look at in my next article. For now though it provides a good guide as to how long a ride will take to recover from

<125 - About 24 hours
125-250 - 36-48 hours
250-400 - 3 days
400+ - 5 days +

So, I should have been good to go after a day or so for my ride which was about right.

Intensity

Intensity compares Weighted Average Power to FTP and expresses it as a % to show how “intense” a ride was. So, for my ride, my Weighted Average Power was 285w, my FTP was 350w when I did the ride and so the Intensity was 81%. This correlates to a “tempo” style ride which is what I’d expect for a 2-hour MTB effort.

For comparison, an endurance ride would probably be around 65-70% and a punchy short race could easily be 105%+.

Work done/Calories burned

Expressed in kilojoules (kj), this is simply the sum of the watts generated during your ride – in this case 1640kj. This translates almost 1:1 with calories burned – 1584 kcals. It’s not a 100% accurate calories burn figure but reported calorie burn using a power meter is accurate to within about 5%. Compare this to using heart rate, which is typically 10-20%, and using time/distance/age/weight which range from 20-60%! So, if you are bothered about the calories your burning, it’s another reason to use a power meter.

In my next article, we look at your Power Curve and Fitness and Freshness.

Written by

Nikalas Cook

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