For the next few months I am currently experimenting with a long block of threshold training with the hope of improving my threshold and climbing. I have already trained up to a peak in May and been able to get in some good blocks of training over the last eight months avg. about 15hrs weekly. I can usually now only get in around 8-9hrs per week(if I'm lucky) with threshold workouts twice a week i.e. 2x20 & 3x12 under/overs etc. Also some tempo & SST sessions i.e. 3x20 and one long 5-6hr LSD xc or road ride per week. I race mtb xc marathons 60-100miles, most of my training is either trainer or road based.

I am currently training and planning another peak for a 100mile xc race in Sep.

However at the minute and for the next 2-3 weeks It looks like I wont be able to get in any long rides I've been able to get in some early back to back 90-120min SST trainer sessions over the weekend and plan on doing these whenever I can't fit in a LSD ride, this reduces my volume to about 7hrs weekly but with the slightly increased intensity the TSS is only slightly less.

Will I loose endurance and maybe start to de-train my aerobic base by missing the LSD rides? My limited time ensures that as a 42yo I get enough recovery between workouts ready to hit the next session but I don't want to throw in too much intensity into my week just yet as I like to include several VO2 sessions during the final build weeks before a race.

Any comments or thoughts on this?

I'd wager that if you maintain/sligtly increase the intensity you will most likely see beneficial gains rather than any reduction. At worst things will stay the same.

Just because you aren't plugging out 5hr rides doesn't mean that adaptions beneficial for aerobic power aren't occurring.

_________________
"Physiology is all just propaganda and lies... all waiting to be disproven by the next study."
"I'm not a real doctor; But I am a real worm; I am an actual worm." - TMBG

Thanks, I always try to extend my threshold sessions to include as much zone 2 time either side of the intervals but sometimes more often than most it is just a bear bones interval workout.

If you're intervals are suitably hard enough I wouldn't worry too much about trying to rack up some zone 2 work just to make up hours in zone.

The quality and consistency of the workout should be primary in these circumstances. Hence do the intervals as planned, cool off then stop.

_________________
"Physiology is all just propaganda and lies... all waiting to be disproven by the next study."
"I'm not a real doctor; But I am a real worm; I am an actual worm." - TMBG

Thank you, very helpful