Have to admit that today my legs felt fatigued (though it is windy) on my forth commute of the week.

I’ve booked in for next Tuesday but maybe it’s too early in the week to fry the legs when I have to commute by bike too.

OR maybe I’ll get used to it!

Spin is just very intense. Over half an hours spin class i’ll burn anywhere between 375 and upto 500 calories. I get nowhere near that when running (not a good runner to be fair) or on a proper outdoor bike ride. It’s the interval nature of it, constantly changing the speed and intensity.

Remember your HRM is generally a pretty rubbish way of measuring calorie output.

Get fitter, HR drops, power output goes up (along with calories), but HRM says you actually burn less.

Assuming a 30min spin is equivalent to about 20min at threshold, and you’re a “good for a weekend warrior” 250W at threshold, that’s 300kJ of work done, or 300 calories of food burnt (calories of food in : work output in kJ is 1:1 because the efficiency and conversion are about the same).

You can’t cheat the system and burn more calories than your threshold power allows over a half hour session, for every interval, you have a rest, so it averages out.

The exception that proves the rule is that high intensity intervals continue to burn calories for hours/days afterwards as muscles need repairing.

Interesting to compare what you quote as a pretty decent threshold power of 250W with the figure 420 that Chris Froome keeps up for half an hour …

My excuse for not being at Froome’s level is that I’m not doping a genetic freak who has trained all my life.

Broke the golden rule of spin last night. Shepherds pie before hand. Even though it was 2 hours before hand.

Thought I was going to burst, from both orifices.

Won’t make same mistake tonight…