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Theory is based on a lot of estimates so we don’t think SRM needs to worry just yet

Apple has applied for a US patent that could add a cycling power output function to its Apple Watch. The US brand says that measuring heart rate, position and orientation, velocity, altitude and riding position will allow it to estimate a cyclist's total power output.

Apple filed an application titled ‘Calculating an Estimate of Wind Resistance Experienced by a Cyclist’ in September last year.

Essentially – and we’re summarising a 6,800 word document here – Apple is looking at estimates for the various sources of resistance experienced by a cyclist, and thus at the total power output of the rider. 

“Estimates of the wind resistance experienced by a cyclist can be obtained through calibration of the effective resistance a cyclist experiences as a function of heading, and thereby separated from the effective resistance due to rolling resistance and grade,” says Apple. “Once such estimates are obtained, the user's total power output can be more accurately tracked throughout an activity.”

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Prepare yourself for repeated use of the phrase ‘wearable device’, possibly more than you’ve experienced in your life up until this point. What Apple has in mind is an Apple Watch. 

“The wearable device can include a heart rate sensor to provide a series of measurements of cyclist heart rate. The wearable device can also include motion sensors to collect data about the wearable device's position and orientation in space and to track changes to the wearable device's position and orientation over time. 

“Accelerometers in the device may track acceleration, including high frequency variation in acceleration, and use this to detect surface type. Because a cyclist can wear the wearable device, the orientation of the device can provide information about the cyclist's body position. 

“For example, when cycling, the cyclist's arms may be in a variety of positions, depending on the cyclist's style of riding and the type of handlebars on the bicycle. If the cyclist wears the wearable device on the cyclist's wrist, the wearable device may be able to infer the cyclist's hand position, and based on this hand position may be able to infer the cyclist's riding position and thereby provide an estimate of drag contributed by the cyclist's body.”

Alright, alright! There’s a lot going on there. As anyone with a conventional power meter knows, a higher heart rate doesn’t always mean a higher power output. And if your hands are on the drops your body is likely to be positioned in such a way that you’ll experience less air resistance than if your hands are on the hoods (see figures below), but not necessarily. 

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Anyway, we’re getting to the crux of the matter so you’d better concentrate.

“Combining these measurements of heart rate, position and orientation, velocity, altitude, and riding position, the cyclist's total power output and the contribution of each component of that power output may be estimated,” says Apple. “By estimating the relative contribution of each component to total power output, a less expensive and more power-efficient technique for providing accurate estimates of cyclist power output can be created.”

Okay, so that’s the theory, but how accurate is accurate? At this stage, we don’t think that SRM or PowerTap have too much to worry about because it certainly doesn’t sound to us as if Apple is going to end up with precise, consistent power figures using these estimates. But who knows? 

Will this power output function ever see the light of day? We just don’t know. Apple, like many other technology companies, applies for (and is granted) loads of patents that never actually make it out into the real world along with many that do, so we’ll all just have to wait and see.

It’s US Patent Application 20170074897 if you want to check it out yourself. Be warned, it’s heavy going in parts!

Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.