Redditor noveltysin wore her Fitbit while she had sex, and shared the resulting graph of her heart rate with the world. Check out how well her graph matches the heart rates in Figure 1 of the classic 1956 paper Physiological Responses During Coitus.
She doesn’t include foreplay, so start your comparison at “period B” in the graphs. (She does include a bit more of the blow-by-blow detail than the older paper dared to.)
