Yes, life stress could certainly be a factor for me…40 hour week job, wife, 3 kids, 3 grandkids, and 1 son-in-law. 
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listening to the latest podcast “Sweet Spot Polarized Training” and his point was consistent with he wrote on the forum. On this podcast the discussion starts around 20 minute mark. If you have flat terrain then z2 power is fine. But a lot of people ride in terrain where holding z2 power is a problem, and so he advocates z2 heart rate. Secondly he doesn’t want people chasing TSS and CTL. Then he says “slow the f*** down” in other words too many people don’t take it easy enough to set themselves up for success on the hard days. You know, going out for z2 and then pushing the pace and finding yourself at top of z2 and doing too much work in z3 and above.