Intensity is 80-90% of the determinant of a muscle's adaptive response to load. If you plan to get somewhere near your genetic potential in strength and size, you will need to use rather high intensity to deeply fatigue ("inroad") the muscle. But you also have to not repeat that stimulus for days to a week, to allow recovery in people like us with middle of the bell curve genetics. The ideal profile for building strength is exercise that is intense, brief, and infrequent. Yes, it is unpleasant for a couple of minutes per muscle group, once or twice a week. So what? Do you enjoy brushing your teeth? Or do you just do it and get it over with? Note, this is for strength training. Skill building for sports, or general physical activity, is a different protocol, depending on the activity.

One of my favorite recent book titles is "If You Like Exercise ... Chances Are You're Doing It Wrong: Proper Strength Training for Maximum Results"[0], which is another book about the work of exercise genius Arthur Jones, inventor of Nautilus and MedX equipment.

[0] https://www.amazon.com/Exercise-Chances-Youre-Doing-Wrong/dp...

[1] https://www.youtube.com/watch?v=F7GB3h82tcQ

[2] https://www.amazon.com/Body-Science-Research-Strength-Traini...