Right on i've been doing a lot of XC mtb training after my shoulder surgery so it's been mainly been just one modality of cardio for me. When you're switching between different types how does that work since you're building up slowly to more and more time in z2 endurance or intensity reps of intervals for anaerobic. So if you have worked your way up to say 4h z2 or 5x40 v02max in biking and decide you want to do some rowing to switch it up, wouldn't you injure yourself jumping into that same amount of work rowing and need to go back down to a small/easy amount when adding some rowing? So if you do multiple forms of cardio you'd need to keep track of the different progressions you're at?