Lately I've been feeling muscle fatigue when doing anything above z2 workouts. Legs feel tired and heavy but strangely enough my heart rate is really low. I hit my power targets during workouts for both vo2max, threshold and sweet spot so I'm where I'm supposed to be in terms of wattage week after week and improving but my RPE feels much higher than my heart rate indicates. My anaerobic thershold is at 183 bpm (205 max) and I can maybe hit 185 even when pushing all out until i'm almost dead. Been googling this issue for a couple of days now but can't seem to understand it. I would think i was fatigued if i couldn't hold my power targets but I have no problem doing that despite having a high RPE.
Background: This is my second year training with power. 73kg and 320W FTP currently so pretty happy with that but like everyone I want to get faster! Had the flu over xmas and had another cold a couple of weeks back but otherwise I've been training pretty well following TrainerRoads sweet spot base 1/2 training plans and some core workouts. Doing a build plan now with some more intensity but nothing crazy. I'm doing mostly 8 hours of training per week:
Tuesday VO2 (6x4 @ 115-120%)
Wednesday Recovery ride
Thursday 2x20 @ 95%
Sat 4x8 @ 105-110% give or take.
Sun recovery ride
Nothing extreme at all. Eating properly and sleeping properly. Not stressed at work.
Is this normal? Can there be differences between cardiovascular system and my muscles ability to actually use the oxygen being provided? If so how can i make my legs "catch up" faster as I feel like they are the ones holding me back? Longer distance rides or just have patience and keep pushing my current training plan until legs feel ok? Rest week?
Any ideas are welcome