Tuesday, December 15, 2015

Burning it up at the gym

A little while ago my sister asked me how many Calories I burned in my hour-long gym session. After a bit of totting up and estimating, I guessed around 600 kilocalories.

Recently Team Sky released power data for Chris Froome on the climb to La-Pierre-Saint-Martin, the decisive stage 10 of the 2015 Tour de France.
“It’s about a 15.3 km climb,” said Kerrison. “Around 41.30 [in duration]. Chris’s average for the whole climb was 414w,"
My '600 Calories over an hour' equates to 700 watts sustained. Gosh, I'm better than Chris Froome!


Time for a more accurate estimate. The aerobic machines give a semi-accurate account of Calories burned, but the resistance machines are more problematic. I spend 22 minutes aerobically exercising and around 28 minutes on the resistance machines and was assuming roughly equal energy expenditure.

But Lance Armstrong's former website begs to disagree:
"The exact number of calories burned during strength training workouts depends on intensity, time and your body composition. According to the Harvard Medical School, on average, caloric burn ranges from 90 calories per hour of moderate training by a 125-pound person to up to 266 calories per hour of vigorous effort by a 185-pound person."
I'm 70 kg = 154 pounds, and I think I'm doing vigorous exercise. On that basis, and scaling, I'm burning only 90 Calories on strength training.


So, putting it all together (and adding a minute recovery time after each hard exercise):
  • Cross-trainer: 80 Calories (five minutes: 2 x 90 secs hi-intensity)
  • Rowing machine: 68 Calories (five minutes: 3 x 60 secs hi-intensity)
  • Bike: 58 Calories (five minutes: 3 x 60 secs hi-intensity)
  • Treadmill: 44 Calories (4 minute warm-down at the end on 10%, ~6 km/hr).
My aerobic total = 250 Calories in 22 minutes - average power of 870 watts (no way!). *

About half the time on the first three machines is high-intensity but the average power overall seems way too high. Still, the Calorie estimate is not out of line with this LiveStrong estimate.

According to this website, averagely-fit people can produce sustained power at 3 watts/kg, which for me means 210 watts, with shorter-duration power 30% higher, say 280 watts (240 kcal/hr).

Perhaps I'm not burning as many Calories aerobically as I think I am!

Now add in the 90 Calories from resistance training (which over 28 minutes gives an average power of 200 watts - sounds about right).

So my grand total is at most 340 calories burned at the gym.

That's breakfast accounted for.


*  See this update.

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