Thanks for the replies, it was mainly for training over the winter so I can come back stronger/faster in the summer. I specifically want to be able to sprint for longer yet still have the ability to go all day.
Sprinting power is very short term. Gym work on your sprint now will be of no effect in January let alone the Summer. Endurance and threshold power on the other hand lasts for months or years. That’s why roadies will be training now for next summer with long rides now, then threshold workouts in the spring, followed by tweaking their sprint just close enough to competition that they’re not knackered from overtraining on the day.
Spinning and Rowing will at least keep your cardio on form and the weight off over the winter if you can’t face similar workouts on the Turbo. IMO spinning is very comparable to MTB’ing form a cardio/leg perspective, especialy if combined with pump track/BMX over the winter to work on core strength.
Depends though, if you’re superfit now then just maintaining a base of the winter is fine. If youre not superfit now or never plan to be then there’s no point in long term planning, just go spinning and enter a winter XC series for motivation and you’ll still come out fitter for next summer.