I'm curious how to figure out how much extra work I'm doing pushing a jogging stroller while running? I have a 20 lb baby sitting in an otherwise empty Bob Evolution stroller.
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While drawing diagrams to calculate it would be fun, have you considered comparing your heart rate with and without the stroller?
That would be a much more reliable than trying to estimate the increased energy requirements. Here's why:
Regardless of all my points, what value does the answer have?
So you're still convinced you need to push a stroller and run at the same time? Like I said, simply compare your rate heart with or without on several runs (science requires multiple samples!) and see how the compare. To make sure you're not cheating, track your speed using GPS or an accelerometer and you get an idea of what the influence of the stroller is. Estimating it however, surely is not the way to go.
A very rough estimate could be obtained by looking up a METS score, in this case 8.0, and plugging it into following formula:
But to get an accurate figure you really need to sneak a labs worth of kit into the stroller, strap on a face mask and perform an Indirect calorimetry test, while out. Or slightly more sensibly estimate your VO2 intake through use of a heart rate strap, and convert the VO2 estimate to a MET number (MET = VO2 / 3.5) for the formula above (or just use one of the Phone app's). Alternatively you could weigh yourself and the stroller, try to estimate a few numbers, covering: VO2, fractional gradient, frontal surface area, surface type, wind speed, your speed.... and plug them in series into the Minetti, Pugh and Weir formula. As the gradient and surface will likely change over the run, as will the wind speed, you'll need to break the estimation down into a series of separate calculations, for each section, to later be combined, or just not bother.