Blog
Why am I so tired after working out? Sleep, HRV and what three studies show
Why am I so tired after working out when the same session felt easy last week? What studies say about sleep loss, heart rate variability and why one morning number is not a verdict.
Sedentary lifestyle: what the WHO guidelines and accelerometer data say
What counts as a sedentary lifestyle by WHO numbers, why there is no hours-per-day limit for sitting, and what 36,383 people wearing accelerometers showed about activity and mortality.
Can exercise make you sick? Where the exercise and immunity debate stands
Can exercise make you sick? A marathon survey, the open window theory and a debate paper by both camps: what exercise and immunity research agrees on, and what is still unresolved.
Cycle syncing workouts: what two reviews found about training by menstrual phase
Cycle syncing workouts, planning training around menstrual phases, are popular. What a 78-study meta-analysis and an umbrella review found, and why the authors reject general rules.
Sleep and catching a cold: what the virus-challenge studies show
Healthy volunteers were given a cold virus on purpose; those who had slept less beforehand fell ill more often. What the studies measured, how uncertain the numbers are, what they did not test.
Sleep debt: how to actually think about it
Where 'sleep debt' comes from, what chronic sleep restriction research shows, why weekend catch-up sleep falls short, and why your own trend and regularity matter more than an hours-based number.
HRV explained: what heart rate variability is and why it matters
What heart rate variability actually measures, what makes it rise and fall, how accurately a wearable like Apple Watch estimates it, and why your own trend matters more than any single number.