Originally Posted by tetonrider

IME, as said a few months back when this came up, estimates of TSS for MTB (based on RPE or hrTSS) tend to be high vs actual power on the MTB.

i believe there is quite a bit of energy that goes into maintaining traction (core strength, balance) and even suspension (shock, but even fat tires at low pressure) that causes power to be lower than RPE might suggest.

definitely can vary based on local terrain, but the above is generally true.

it's just my opinion, but i disagree about the estimates being a better reflection of training load. as an analogy, if you pedal threshold for an hour in cool temps vs heat, the latter feels tougher, but does it really induce a better training effect and warrant over-estimation of load? so, too, for the mtb....might feel harder, but you're measuring power to the pedals. perhaps your answer is different than mine, and that's all good, but it is worth thinking about.

personally i feel like power on the MTB is nice to have as a record of what was done OR as a way to evaluate the demands of racing a MTB so they can be modeled in training -- but it's not so useful a tool DURING training or racing. at least that has been my experience in riding/racing with power on my MTBs.

also, your physiology may find high torque scenarios more difficult to deal with, or you may not deal as well with the generally more stochastic nature of pushing hard on the MTB vs road.