re: I quit doing cardio

I don’t consider walking 8k steps a day to be cardio unless they are with increased effort (with resultant increase in heart rate) for a meaningful duration (all 8k steps in one session). If those steps are taken without increased effort I don’t think it’s making anyone more fit.

In all these studies we have know there is significant confounding, which I’ll define for those who might not know (not you) as factors other than the one being measured that affect the outcomes. The sedentary people likely had less healthy lifestyles in other ways as well (overnourishment, diabetes, htn, smoking, drinking) that weren’t measured that affected the results.

That study showed a 16% benefit to 8k steps. The VO2 max study I cited, showed at minimum a 40% benefit when going from low average to above average and up to a 500% benefit when going from low to elite. So 2.5x to 30x higher mortality benefit. Confounding significantly affects these results. To show this, we have to make assumptions. Let’s assume that 10% of all excess deaths are due to a confounder not measured, which I think k is conservative (the number could easily be 16%, erasing all of the benefit to walking 8k steps). When you factor in confounding, the effect of the study variable changes a lot in the 8k steps group, now 6% benefit, and very little in the Vo2 max groups, now 30-490% benefit, with VO2 now 5-81 times more beneficial than 8k steps.

Regarding sprinting vs endurance training. That article seems more like hypotheses rather than measurements of hard outcomes, but I think the hypotheses are reasonable. However, I think the benefits of sprint training listed can be more effectively reached with strength training.