I've got a fitbit heart rate monitor. It lets me know when I'm in calorie burn mode or higher intensity. Seems like the harder I work and the more I sweat, the lower the calorie burn. Riding motorized it's easy to stay in the calorie burn zone. However, the easy spinning which reduces calories does not seem to help build muscle at all. Riding motorless I see a difference in my abs, butt, and thighs regardless of
what the scale says; it tones my parts up. Riding motorized I can drop numbers on the scale but there is less toning and muscle definition.
So I do both now on a regular basis, short high intensity spurts without the motor and sustained spinning with the motor.
Unfortunately, with shelter in place and most things closed, I've been baking a LOT. That has completely messed with the benefits of
my bike, haha.