I have done both week long MTB touring off road with about 20kg of gear plus the bike. And 12 day off trail hikes through river gorges and crossing some steep ranges starting with about 24kg on my back.
On the MTB I got more fatigued each day due to the pace we were riding at. This meant we were burning glycogen most of the time. When you run out of glycogen you really struggle to keep pace.
On the hike the pace is usually at a level that allows effecient fat burning. Finding palatable food that has a high enough energy density and protein content to weight is a challenge.
If we rode slower then I would have been less fatigued each day.
Both types of activity are tiring but in different ways. The biggest difference though will come from the pace you set.
On the MTB I got more fatigued each day due to the pace we were riding at. This meant we were burning glycogen most of the time. When you run out of glycogen you really struggle to keep pace.
On the hike the pace is usually at a level that allows effecient fat burning. Finding palatable food that has a high enough energy density and protein content to weight is a challenge.
If we rode slower then I would have been less fatigued each day.
Both types of activity are tiring but in different ways. The biggest difference though will come from the pace you set.