The word “sex” can to refer to gender, rather than sexual activity. Perhaps disappointingly, that seems to be the case in this medical study:
“The Effect of Sex on Heart Rate Variability at High Altitude,” Christopher John Boos [pictured here], Emma Vincent, Adrian Mellor, John O’Hara, Caroline Newman, Richard Cruttenden, Phylip Scott, Mark Cooke, Jamie Matu, and David Richard Woods, Medicine and Science in Sports and Exercise, epub July 20, 2017.
The authors, at Poole Hospital NHS Foundation trust, Poole; Bournemouth University, Bournemouth; Leeds Beckett University; Defence Medical Services, Lichfield; James Cook University Hospital, Middlesbrough; Wansbeck General and Royal Victoria Infirmary, Newcastle; and University of Newcastle; all in the UK, report (we added the bolding emphasis):
There is evidence to suggest that high altitude (HA) exposure leads to a fall in heart rate variability (HRV) that is linked to the development of acute mountain sickness (AMS). The effects of sex on changes in HRV at HA and its relationship to AMS are unknown.
METHODS: HRV (5-minute single lead ECG) was measured in 63 healthy adults (41 men and 22 women) aged 18-56 years at sea level (SL) and during a HA trek at 3619m, 4600m and 5140m respectively. The main effects of altitude (SL, 3619, 4600 and 5140m) and sex (men vs women) and their potential interaction were assessed…
This particular paper is distinguished by the advanced quality of the writing. The wording at the end of the paper’s abstract is so very concise that it approaches being poetry:
Conclusions: Increasing HA leads to a reduction in HRV. Significant differences between men and women emerge at HA. HRV was not predictive of AMS.
(Thanks to Adrian Smith for bringing this to our attention.)