research indicates the immune system is lowered for a period after high intensity workout
Andy - I agree that one should do HIT when 'feeling well'. "Rested". Depends what you mean. Don't do two days in a row. How many is too many? 1 in 5 seems conservative. 2 in 5 perhaps. Depends what training effect you're seeking But, as I asked before,
could you share a link to the 'research'. I have looked (spurred on by your assertion) and, for example this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3920540/
suggests that HIT has much less effect on the whole range of proteins which modulate the immune system than "prolonged, continuous aerobic exercise " (90 mins + aerobic).
These guys are trying to sell stuff:
https://www.myxiser.com/hiit-training-boosts-your-immune-system/
I thought this was good:
https://foreverfitscience.com/exercise-science/physical-activity-and-the-immune-system/
"If you are performing extremely high intensity exercise for durations of
longer than 60 minutes, you see a different story. [Comment: You can't do HIT that long - impossible to keep the intensity high enough (varies between athletes obv)]
"The high stress environment created by extreme exercise conditions actually
downregulates these same immune cells that moderate intensity exercise
activates [and] you also see a huge spike in the secretion of stress hormones epinephrine and norepinephrine – both of which increase inflammation and further downregulate immune system function.
"[But] as you give your immune system time to bounce back after this type of session, it comes back stronger than ever – which may improve your resilience to disease and illness in the long run.
"[But] a problem
only arises when the immune system is not given time to recover appropriately after intense exercise.
after an extremely intense training session you should give your body enough time to adapt completely. This allows your immune cells to return to normal levels, while your body becomes better able to handle stress.
"Over time this would likely increase the function of your immune system further because it is forced to adapt to the high stress environment."