@hollyr.eth
My Road to 4×4s
Week 3, 2x4s HIIT on stationary bike. CoachClaude summary:
"That last 30-second struggle is the sweet spot — it means you're working hard enough to drive adaptation but not so hard you're dying. If it felt easy all the way through, you'd be undertraining. If you couldn't finish, you'd be overreaching.
What that sensation tells us physiologically:
• Your aerobic system is handling the first 90 seconds well — that's your base fitness from the 1×6 work paying off
• The last 30 seconds is where lactate starts accumulating faster than you can clear it — that burn is literally your body building new mitochondria in response
• The fact that you pushed through rather than backing off means you stayed in the adaptation zone the whole time
https://www.cnn.com/2026/04/15/health/vigorous-exercise-reduce-disease-risk-wellness