Baths, Finnish

Participants wore the GENEActiv watch on their nondominant wrist for 2 weeks. They were instructed to wear the watch day and night and only taking it off when going to the sauna or when playing a contact sport in which wearing a wristband is unsafe. They were also instructed to press the button on the device when going to sleep and when getting up. In this study, the accelerometer was set to sample at 30 Hz and raw actigraphy data were analyzed using an open source R package, GGIR (version 1.5–18, see Supporting Information for further details on the raw actigraphy data cleaning processing pipeline). Sleep was assessed as total sleep duration per night (in hh:mm) and sleep efficiency per night (%). CR was assessed by mid sleep on free days (MSF; clock time) and the relative amplitude (RA) between day‐time and night‐time activity per day. Physical activity was assessed as gross motor activity per day (milli‐gravity [mg], 1g = 9.81 m/s²) and minutes in moderate‐to‐vigorous PA per day (objective minutes in moderate‐to‐vigorous PA per day were defined as the sum of 1‐min epochs in which gross motor activity was larger than 125 mg, which has recently been used by others (Kim et al., 2017)). Average weekly estimates were derived for each participant. Actigraphy variables were chosen based on several reasons. First, the selected actigraphy variables are among the ones reported frequently in adult studies and have been previously linked to psychopathology (Burton et al., 2013; Hori et al., 2016; Luik et al., 2015; Lyall et al., 2018). Second, these measures cover the concepts often collected with self‐reported questionnaires allowing for a comparison on their association with depressive and anxiety disorders.

This study was approved by the Survey and Behavioural Research Ethics Committee of the Chinese University of Hong Kong. Written informed consent was obtained from all participants.
A questionnaire survey was conducted through face-to-face interviews at saunas frequented by MSM in Hong Kong, after venue-based sampling. To begin, mapping of saunas frequented by MSM was performed and an estimation of the number of potential MSM customers at each location and time made. Sauna operators were approached to secure their support in the administration of the surveys at the venues. Two experienced peer workers familiar with the MSM community were trained to conduct the survey at saunas with the permission of the operators. The interviews were conducted using a questionnaire form that had been field tested, with responses recorded on paper forms by peer workers at the site. Over a 7-week period, 32 visits were made to 9 saunas between 4 and 8 pm covering different days of the week. The number of visits (ranging from 1 to 8) for each sauna was determined after assessment by peer workers in conjunction with sauna operators on the number of clients, with the aim of recruiting all MSM above the age of 18 who agreed to participate in the study. Written informed consent was obtained from all participating MSM prior to the survey. An incentive, in the form of a HKD50 (USD1 = HKD7.8) cafeteria coupon, was offered on completion of each questionnaire.
Structurally, the questionnaire is divided into 3 main parts, with the first part covering demographics (age, ethnicity, employment, education level, residency in Hong Kong) and self-identified body appearance in accordance with the grouping of such characteristics proclaimed by MSM during field study – lean/lean toned; slim/slim/fit; sporty; muscular/macho; business suit; chubby; bear; feminine. Respondents were also divided into single type and mixed type appearance (table 1). In the second part, information about sex partners was profiled followed by a review on partner-sourcing channels. On partner characteristics, MSM were inquired about the number and types of sex partners, separated into steady partners or “lovers” (a term preferred by local respondents, denoting sex partner(s) that one considered to be emotionally attached); regular partners (those with sexual relationship without emotional attachment over extended period), casual partners (one-night-stand partners), and commercial partners (those exchanging sex for money or kind, also termed “money-boy”). Partner sourcing was defined as the networking of sex partners through specific channels; and respondents were asked if they had sourced partners at the following types of venues in the preceding 3 months – public toilet, bars, saunas, parties and/or sex parties and different frequency. They were also inquired if they had sourced partners through internet (chatroom, instant messaging and presence (IMP), bulletin board system (BBS) and smart-phone, the latter referring to special applications (Apps) for networking. In the last part, MSM were asked about the number of sex partners sourced through the various channels in the preceding 3 months. The frequency of condom use for anal and oral sex with the four types of partners was assessed for the preceding 3 month period. Condom use was ranked at 4 levels – never, sometimes (less than half of the occasions), frequently (more than half the occasions), and always (100%).
In the analysis, the means of sourcing sex partners of MSM was distinguished into physical venues and virtual channels, the latter further subdivided into internet with or without the use of smart-phone, again in the previous 3 months. Comparison was made between users of physical venues alone and concomitant users of physical and virtual channels, and then between smart-phone users and non-smart phone users on their association, if any, with sex partner profile as well as the practice of unprotected sex in the 3 month period before interview. MSM were classified as “high risk” if they sometimes (less than half of the occasions) or never used condom for anal intercourse with any of their partners (steady, regular or casual partners), whereas those frequently (more than half of the occasions) or always using condom were considered “low risk”. Comparison was made by bivariate logistic regression. Statistical significance was two-sided and a threshold of p<0.05 was considered to be significant for all analyses. PASW Statistics 18 was used in performing statistical analyses.

The effects of changes in the ambient temperature on the measurement accuracy of the prototype and commercial probes were studied in the following manner.
Referring to the study by Sawatari et al. [27 (link)], a domed sauna (KMC DOME SAUNA Professional, Kobe Medi-care Co., Ltd., Kobe, Japan) was used to raise the external temperature of the subjects below their necks. Seven healthy male adults (23 ± 2 years old) were involved in the following experiment in the supine position, wearing shorts and T-shirts, with their upper abdomen exposed.
A prototype probe and CTM-210 probe were placed side-by-side near the midline of the upper abdomen, and the values of T_Proto and T_CTM were sampled at the aforementioned time points. Another CTM-210 probe was attached to the forehead area to simultaneously measure CBT in the head (T_Head) as a reference value.
The ambient temperature T_Air was measured using a digital thermometer (CENTER 376, MK Scientific, Inc., Yokohama, Japan) with a dedicated sensor (Precision Pt100 Probe) fixed around the abdominal probe.
After each probe was secured, the subject was at rest in the supine position at room temperature (24 ± 1 °C) for 30–40 min (Phase A). In Phase B, a preheated domed sauna was placed over the subject’s body to raise their perimeter temperature from the feet to the neck up to 43 °C for 20 min. The sauna was then removed and the surrounding body temperature was allowed to return to room temperature for 20 min (Phase C).
The experiments were conducted with the approval of the Medical Ethics Committee of Kanazawa University (approval number: 2020-236 (087)).

To explore the potential economic impact of this practice, the participants were asked to report how much money they spent monthly to engage in SDU (<€50, €50–100, €100–200, >€200). We also asked participants who used drugs for sexual purposes to report how often (1 = never, 2 = sometimes, 3 = about half the time, 4 = very often, or 5 = always) they had used each drug in the previous 18 months; these substances included alcohol, hashish/cannabis, cocaine, poppers, ecstasy, erectile dysfunction drugs, MDMA, GHB/GBL, methamphetamine, mephedrone, ketamine, heroin, benzodiazepines, and other substances. We added the category “other substances” to include any drugs not listed in the provided options. Moreover, we asked participants whether alcohol use had led them to use other substances for SDU. Participants who chose intravenous administration as the route of consumption were asked how often they had engaged in slam sex in the previous 18 months (none, once, once a month or less, a few times a month, once a week, more than once a week, or daily) and whether they had shared injection equipment. Finally, the participants were asked to indicate where they usually engaged in SDU (e.g., saunas, sex clubs, private parties, own home, other’s home; see Table 1).