See the picture below. Both of these sharp drops in VO2MAX happened after slow paced trail runs on very steep terrain (4000+ feet of elevation gain each) with fairly low average HR. Both of these were essentially a lot of Z1-Z2 hiking uphill followed by some very easy running downhill. Previously trail runs like that didn't affect VO2MAX - none of that indicative of my VO2MAX. I am sure my VO2MAX will pop right back tomorrow, but seeing those makes me want to disable Trail Running VO2MAX.