The overall take away from this article is that you don't need to kill yourself everyday on the bike, treadmill, or weight machines. The correct balance of exercise and physical activity should be slow and easy most of the time and then hard and fast for less of the time. This is how to achieve optimal health, fitness, and longevity benefits.
Zone 1 is 50-60% HRM (Heart Rate Max), Zone 2 is 60%-70% HRM, and Zone 5 is 90-100% HRM. You don't have to use a lactate meter to know you are doing Zone 2, a simple heart rate monitor or subjective check-in to your effort expenditure is plenty; the point is to go hard enough to where you feel like you need to increase breathing but not feel terrible burn or no burn at all; a pace you can sustain for a few hours, but with some effort. As for zone 5 training, don't worry about spending hours in this zone, more like seconds. The key is to push yourself hard every now and then, preferably keep these hard pushes under 1 minute with plenty of recovery time in-between; sprinting or some really hard exercise type either on land, bike, or in the water is what you are looking for here.
How do you calculate your HRM? A simple 220 minus your age is a great way to judge your HRM. This means Zone 1 for a 40 year old should be around 90BPM to 108, something you could achieve with some upbeat gardening or medium paced walking around the block.
What is Peter optimizing for with his exercise?
Everything Peter is talking about in terms of exercise is about optimizing for longevity
That is much different that optimizing for performance
For instance, if someone were to want to run the fastest 10k possible…
That means training at an energy system that is very demanding of the cardiovascular system.
It is pretty much maximum cardiac output just beneath VO2 max above functional threshold which is past the point of optimizing longevity returns and it actually comes at some cost to longevity relative to something more at a slightly lower energy system