Alan Couzens (former Australian swim team coach) is a great follow on X for learning about athletic performance and the importance of exercise for longevity and health. A big thing he emphasizes is heart rate variability based training, and monitoring that as a signal of stress and adequate recovery.
Here are a few recent posts I loved.
https://x.com/Alan_Couzens/status/1726591761277943959 - Death zone health metrics to avoid and an aside demonstrating that an elite VO2max in the Mount Everest Death Zone is equivalent to a very old/unfit person teetering on the edge of death.
https://x.com/Alan_Couzens/status/1720437671623868878 - Decrease in all cause mortality directly correlated to MET-hours/week. MET-hours is effectively a measure of exercise level energy use you put your body through. It's also why people with a lower VO2max have to put in more hours to receive the same benefit, because a person with a high VO2max can do moderate exercise which would be an extreme effort for a less fit person, thus stacking MET-hours more quickly.
https://x.com/Alan_Couzens/status/1720437671623868878 - "50 and 50 goals"
His paid substack is also a wealth of valuable information.