I am coming off of an injury. And want to start slow with some easy base training. When training @ 70% of max rate is it nessecary to determine 70% in each discipline?
If you’re just coming off an injury then you shouldn’t do any max or LT HR tests in order to find your current ~70% value. Use old data and perceived exertion along with HR feedback to keep your workouts easy/aerobic for the time being. For example, if you know your max bike HR was 185 last season, keep training below 130 or so for a few weeks.