Riddle me this - Since I am pushing 70 - am starting to notice a decline in endurance and increased fatigue, which I would like to counter. Currently doing 4 days of Zone, 2 rest days and one HIIT. Would like to incorporate weight/strength/leg work. So how do I fit this in to my schedule? Do I need to drop one Z2 day, or do it on a rest day, which seems anti-rest?

How do you do it?