What Fitness Actually Is: The 5 Systems Every Runner Trains (Plus Running in Wildfire Smoke)

What is fitness, really? VO2 max, lactate threshold, running economy, durability, and neuromuscular power — in this episode we break down the five distinct systems hiding inside that one word, how each one develops, which respond fastest to training, and which age best. If you've ever chased a watch number and wondered why your race results didn't follow, this framework explains why "getting fitter" is actually five separate questions — and how periodizing your training over years brings them together on race day.We also answer a timely listener question about running in wildfire smoke: what PM2.5 actually does to your lungs, how to use AQI (and its limits), CDC guardrails for exercising outside, when to move to the treadmill, and how to set your line in the sand before race day — including what to do if smoke rolls in mid-race.Plus Hot or Not: gravel running, Garmin's heat acclimation metric, photochromic lenses, and whether bells or eye patches actually deter mountain lions (spoiler: your voice works better).Send us your Hot or Nots and listener questions: microcosmcoaching@gmail.comCurious about coaching? Join the Foothills tier — $10/month for twice-monthly Ask-A-Coach calls and our Slack community of 200+ athletes. Use code FOOTHILLS10 at microcosm-coaching.com