Yes, definitely mix it up.
Waaaaay back in high school track our coach would make us do “fartleks” in this case 400m jog followed by insane sprints up this short, but very steep hill, over and over and over. Nowadays, I try to do the same on my road bike; 1 mile level ride with a sprint up a local hill….over and over. Works for me.
I also use the smith rack for squats at the gym, very low weights 135-185lb but 25-30 reps per set within a set time (which has gotten longer as I’ve gotten older).
I’m surprised you find cycling more difficult than swimming…..swimming just kills me, it’s a great workout, but it wipes me out.
Robert- Thanks for the advice, I will definitely try that. I have quite a bit of rolling hills around me (road) but a bit harder for me to get to the trails. I know it doesn’t exactly transfer over, but what’s your guys’ opinion on mostly road training for mountain bike prep?