heavier bike + saddle time

[Eden]

I think that only works if they are completely equal in all other ways except for weight and they did the walk in the same amount of time. If she does the walk slower she will be getting less of a cardio workout and actually burning fewer calories.

I ran it through a calculator - numbers are round and low to keep it easy..
I'm assuming Bailey and his aunt weighed each 100 lbs, he put a 5 lb backpack on her and they walk the same distance.
if they walk the same speed she will obviously burn more calories. But if she goes slower she burns fewer calories even over the same distance

Him 100 lbs runs at 5.2 mph for 26 min, burns 187 calories and gets a higher level cardio workout, her 105 lbs walks at 3.5 mph for 38 min burns 128 calories. Both have covered the same distance, but he gets the better workout even though she has the extra weight.

Now the other way - say you are going he same speed, but doing less time - more low numbers for ease of use.
Assuming you weigh 100 lbs and your light bike weighs 20 lbs and you ride for 1/2 hour you would burn 230 calories if we assume the heavier bike is really twice as heavy for a total of 140 lbs and ride for 15 min you only burn 134 calories. The lighter bike with the longer workout still probably comes out to the better workout unless you up the amount of time you are spending on the heavier one.

How exactly the second example relates to cardio, I'm not entirely sure - you likely are getting a slightly better cardio workout for the time you are on the heavier bike (you'd have to monitor your hr to really find out), but because you are doing it much less the overall effect is probably diminished???