I'm of the belief that the rest part is very important, or when the focus is not legs - don't do legs. Seems to me the bike is not the best tool for Zone 5+ training.
The thing I like so much about whole body stuff (swimming, stride ski, rowing) for zone 5 is it does not fatigue the legs so much. In a whole body exercise you can hammer your cardio without taxing your legs as much as you would using a bike. The same idea for zone 7 is to focus on muscles and rest the cardio. Use weights, so your cardio system rests a bit more than it might on the bike. I see the bike as the best tool for Z2,3 and maybe 4 as LT is mostly about leg LT that you get from cycling.
If you use the bike for everything, you may be using systems that need some rest. I feel that is less than ideal.
Just so the definitions are right using
Power Training Zones for Cycling | TrainingPeaks (pasted below).
[TABLE="width: 699"]
[TR]
[TD="class: small, align: center"]5[/TD]
[TD="class: small, width: 8%, align: center"]VO[SUB]2 [/SUB]Max[/TD]
[TD="class: small, width: 10%, align: center"]106-120%[/TD]
[TD="class: small, width: 9%, align: center"]>106%[/TD]
[TD="class: small, width: 9%, align: center"]6-7[/TD]
[TD="class: small alignLeft, width: 57%, align: left"]Typical intensity of longer (3-8 min) intervals intended to increase VO2max. Strong to severe sensations of leg effort/fatigue, such that completion of more than 30-40 min total training time is difficult at best. Conversation not possible due to often 'ragged' breathing. Should generally be attempted only when adequately recovered from prior training - consecutive days of level 5 work not necessarily desirable even if possible.
Note: At this level, the average heart rate may not be due to slowness of heart rate response and/or ceiling imposed by maximum heart rate)[/TD]
[/TR]
[TR]
[TD="class: small, width: 6%, align: center"]6[/TD]
[TD="class: small, width: 8%, align: center"]Anaerobic Capacity[/TD]
[TD="class: small, width: 10%, align: center"]>121%[/TD]
[TD="class: small, width: 9%, align: center"]N/A[/TD]
[TD="class: small, width: 9%, align: center"]>7[/TD]
[TD="class: small alignLeft, width: 57%, align: left"]Short (30 s to 3 min), high intensity intervals designed to increase anaerobic capacity. Heart rate generally not useful as guide to intensity due to non-steady-state nature of effort. Severe sensation of leg effort/fatigue, and conversation impossible. Consecutive days of extended level 6 training usually not attempted.[/TD]
[/TR]
[TR]
[TD="class: small, width: 6%, align: center"]7[/TD]
[TD="class: small, width: 8%, align: center"]Neuromuscular
Power[/TD]
[TD="class: small, width: 10%, align: center"]N/A[/TD]
[TD="class: small, width: 9%, align: center"]N/A[/TD]
[TD="class: small, width: 9%, align: center"]*
(Maximal)[/TD]
[TD="class: small alignLeft, width: 57%, align: left"]Very short, very high intensity efforts (e.g., jumps, standing starts, short sprints) that generally place greater stress on musculoskeletal rather than metabolic systems. Power useful as guide, but only in reference to prior similar efforts, not TT pace.[/TD]
[/TR]
[/TABLE]