I haven’t done scientific experiments but I think a MTB is still quite efficient on average. But a lot less than a road bike without suspension nor grip on a fl

I haven’t done scientific experiments but I think a MTB is still quite efficient on average. But a lot less than a road bike without suspension nor grip on a flat road. When going uphill on difficult terrain with my mountain bike, I sometimes get passed by trail runners. If we continue on the same path, I pass them back on flat and downhill sections so it may be worth it. I can also bike quite a bit longer than I can trail run. Sometimes I have to push or carry the bike and the efficiency isn’t great for sure but a mountain bike isn’t that heavy and you can use it as support too. But it’s slower than a hiker going uphill.