Cycling Fitness / Training Advice

Is there a trick to balancing decent intensity road biking, and running. I've been doing both in a high volume uber low intensity way for years. But when I turned things up a bit, I seem to develop niggleling injuries constantly.

Dont say rest days. :(

You do need to reduce volume when raising intensity, so yes more rest, but not just rest. You also need to factor in time for active recovery when doing more intensive workouts (recovery rides, stretching sessions etc. should be less than 60 mins, ideally 35-45).

Harder intensity work not only requires longer recovery times, but also it can highlight and/or exacerbate any physiological problems or injuries.