This DTube video is of me riding my Merida eONE-TWENTY 500 Electric Mountain bike on a steep climb near Lapstone in Australia.
Electric MTB like this one are pedal assist, they don't drive with a throttle like a motorcycle. They give assistance to make pedalling easier. This especially helps on steep climbs like this one, I wouldn't even attempt it on a regular MTB.
I have been able to build up my fitness from zero cycling fitness on this bike very well and I am now cycling 3-6 hours a week. I live in a hilly region and on a bicycle that makes it almost impossible to have easy riding days where you keep your heart rate low and save your legs for the hard days. This hard-easy principle is fundamental to training balance. On a regular mountain bike climbs of over 12% gradient tend to send your heart rate into the anaerobic lactic zone, but with the EMTB heart rates are able to be kept in the aerobic or aerobic threshold zone.
With an EMTB the battery assistance is limited to around 50km, so on longer rides part of the challenge is in extending the range by rationing the battery usage, this is done by riding on low assist as well as zero assist modes and saving high assistance only for when it is needed.
My max heart rate is around 165 in race mode and you can see in this video its close to that zone, so you certainly can get a solid workout on an Electric Mountain Bike.
Below is the DTube link
