This is the first systematic review investigating the physical demands of sexual intercourse. It included a total of 18 studies. The main findings were that all the studies analyzed either the physiological demands or the kinematics of sexual intercourse, but no studies combined both analyses. Sexual intercourse can elicit an energy expenditure of ~ 100 kcal (or ~ 6 METs) per activity, mean heart rates between ~ 90 and ~ 130 bpm, and peak heart rates up to ~ 170 bpm. Therefore, sexual intercourse may be a significant contributor to physical health, and it can be considered as a form of physical activity. However, these physical demands may vary depending on health status, intercourse position, activity duration, intercourse phase, lubrication, erections, and sex differences. Furthermore, although little information is available concerning the kinematics of sexual intercourse, it is suggested that some positions (e.g., the cowgirl, scorpion, missionary, or superman) may not be recommended for individuals with low back pain, hip pathologies, or shoulder injuries. More high-quality studies are required to gain a better understanding of the physical demands of this activity.
Characteristics of Included Studies
These studies analyzed kinematic and physiological parameters independently. Based on the definition of physical activity as being any musculoskeletal movement that results in energy expenditure (Caspersen et al., 1985), the possibility of making conclusions may be limited—for instance, in terms of energy expenditure during sexual intercourse—without knowing the kinematic parameters such as range of motion, speed of movement, or the specific energetic cost of getting and maintaining an erection, orgasm, and ejaculation. In consequence, sex tracking technologies (e.g., smart condoms or wearable sensors synchronized with physiological monitors) may be a productive alternative for future research on this topic (Kreitmair, 2018; Oliva-Lozano et al., 2020).
In addition, there are significant concerns regarding the context for testing the physical demands of sexual intercourse. For example, some studies collected data in laboratory settings. However, this suggests that psychological artifacts may have been introduced into the natural intercourse situation, even if only minimally, and therefore such artifacts cannot be absolutely eliminated (Fox & Fox, 1969). Moreover, the data were collected both from real and simulated intercourse. Although participants were encouraged to move as naturally as possible during simulated intercourse, there was no actual intercourse, and this is its main limitation. Nonetheless, these data also have their own limitations—many studies did not mention or control what type of sexual activity the participants engaged in, requiring only that it culminated in intercourse and male orgasm (Palmeri et al., 2007). Moreover, some participants got paid (Bohlen et al., 1984)—a recent study considered that paying participants to have sex as part of a scientific study might be controversial (Zavorsky et al., 2019).
In addition, there were no studies of high quality, and this limits the generalization of the results, which are not amenable to meta-analysis because there is a potentially high risk of bias. Only 6 studies have been published within the last 10 years, which is difficult to explain given current technological advances. However, this might be interpreted in various ways. Perhaps in recent decades, sexologists have become wiser about all the dependent variables that exist, and have come to recognize how difficult it is to carry out properly controlled, high-quality research on the demands of sexual intercourse. Although we do not assume that newer studies would be better, this systematic review highlights the lack of high-quality studies, which hopefully will be published in future.
Physical Demands Examined Through the Energetic System’s Physiological Response
Two studies reported that sexual intercourse elicited an energy expenditure of between 100 and 130 kcal in healthy adults (Frappier et al., 2013; Zavorsky et al., 2019). In addition, the mean intensity was ~ 6 METs (Frappier et al., 2013), which can be categorized as moderate intensity physical activity (Garber et al., 2011; Haskell et al., 2007). Examples of activities performed at this intensity include jogging (speed: 6 km/h), swimming leisurely (not lap swimming), or stationary rowing (Ainsworth et al., 2011). However, these studies did not analyze the energetic cost of different positions.
One research study analyzed energetic demands based on VO2 in different positions during the activity (Bohlen et al., 1984). VO2 is a measure used when reporting data on energetic demands and it is considered more accurate than absolute measures (e.g., METs or kcal) (Ainsworth et al., 1993; Garber et al., 2011). However, only one study reported the energetic requirements in participants with cardiovascular disease, with the VO2 ranging from ~ 12 to ~ 16 mL/min//kg (Hellerstein, 1970), which suggests that they also performed the activity at moderate intensity (Ainsworth et al., 1993; Garber et al., 2011; Haskell et al., 2007). Nonetheless, these studies did not analyze the energetic requirements for different positions during sexual intercourse in unhealthy participants. Future research could investigate the effect of different positions on energy expenditure during sexual intercourse in order to estimate which are the most or least demanding for men and women. Moreover, these studies might use perceived effort questionnaires and dispense with collecting any energy expenditure data in the laboratory as previous researchers have (Frappier et al., 2013).
Physical Demands Examined Through the Heart Rate Physiological Response
Healthy participants reached peak heart rates between ~ 145 bpm (Zavorsky et al., 2019) and ~ 170 bpm (Bartlett, 1956). Nevertheless, it is not known how much of that is related to hip thrusts, the orgasmic experience, erection, or ejaculation. Within the context of sexual intercourse, it is important to note that this heart rate response is not only a consequence of the activity’s physical demands but also depends on emotional components, especially those characterized by the orgasmic experience (Bohlen et al., 1984; Falk, 2001; Xue-Rui et al., 2008). This may explain why the heart rate progressively increases from the foreplay to the orgasm phase (Bohlen et al., 1984; Xue-Rui et al., 2008). However, differences were observed between the heart rate response in men and in women (men: ~ 96 bpm; women: 90 bpm) (Xue-Rui et al., 2008). This might be because men are the more active partner in sexual intercourse when in specific positions (e.g., the missionary or the man-on-top) (Bohlen et al., 1984; Levin, 2007). Nonetheless, understanding the heart rate response to any physical activity is not all about sex differences. Indeed, it is estimated that both sedentary and trained women exhibit greater maximum heart rate (bpm) than men. However, it is important to mention that the heart rate response may vary depending on other factors such as age or cardiorespiratory fitness (Whyte et al., 2008).
In contrast to the above findings, the heart rate reached by participants with cardiovascular diseases was ~ 139 bpm in women and ~ 121 bpm in men (Mann et al., 1982). Although the data on women’s sexual physiology are limited, these differences might be explained by the facts that a marked increase in heart rate accompanying the orgasm may be observed (Bartlett, 1956; Xue-Rui et al., 2008) and that women may experience multiple orgasms within the same period of sexual intercourse (Gérard et al., 2021). However, women do not reach orgasm from penetration alone and these differences may be a result of sympathetic contributions to arousal in women (Lorenz et al., 2012; Meston, 2000).
Another interesting finding of this systematic review was that following a regular exercise program for 16 weeks decreased the mean heart rate (from ~ 127 bpm to ~ 120 bpm) during sexual intercourse in patients with cardiovascular diseases (Stein, 1977). Given that regular exercise may have such a protective effect for these patients, physicians could advise patients to participate in these programs before engaging in sexual activities (Kumagai et al., 2020; Stanton et al., 2018; Stein, 1977).
Physical Demands Examined Through the Blood Pressure Physiological Response
All the studies observed that systolic blood pressure (Fox & Fox, 1969; Nemec et al., 1976; Palmeri et al., 2007; Xue-Rui et al., 2008) and diastolic (Nemec et al., 1976; Xue-Rui et al., 2008) blood pressure were greater in healthy men than in healthy women. This difference was also observed in patients with cardiovascular diseases, but with higher blood pressure values in both men and women (Mann et al., 1982). In this regard, it is worth mentioning that sex differences play a significant role in regulating blood pressure (e.g., men typically have higher blood pressure than women at similar ages) (Maranon & Reckelhoff, 2013; Reckelhoff, 2001). Furthermore, although blood pressure increases in other physical activities (Hedberg et al., 2009; Laukkanen & Kurl, 2012), what stands out about sexual intercourse is how the isometric and dynamic positions (e.g., men in the missionary positions or women in the quadruped positions) increase blood pressure (Mann et al., 1982).
Physical Demands Examined Through the Perceived Exertion Response
Even though there were only two studies measuring the perceived exertion of the participants during sexual intercourse, both agreed that sexual intercourse elicited moderate-intensity (Garber et al., 2011) physical demands (Frappier et al., 2013; Palmeri et al., 2007). These studies used self-designed questionnaires to measure perceived effort (Frappier et al., 2013; Palmeri et al., 2007). This suggests that future research should apply valid and reliable tools since criterion-related validity and reliability represent the empirical relationship between perceived effort and physiological measures, which best describe exercise intensity (Chen et al., 2002). Indeed, specific tools need to be designed for the sexual intercourse context because the strength of the relationship between perceived effort and physiological response may vary based on the characteristics of the activity, which implies that a lot of contextual variables need to be considered (Chen et al., 2002; Garber et al., 2011).
Physical Demands Examined Through the Duration of the Sexual Intercourse
When considering the studies that analyzed the duration of sexual intercourse (Table 1), the results suggest that the sexual intercourse duration is highly dependent on the couple themselves; this may be related, among other factors, to the age of the participants (e.g., duration of foreplay, experimental environment), since a negative correlation was found between age and the sexual intercourse duration (Palmeri et al., 2007). It was also observed that the duration of the activity was not always controlled. For instance, researchers from a previous study mentioned that they did not control what type of sexual activity the participants engaged in as long as they acknowledged it concluded with sexual intercourse and male orgasm (Palmeri et al., 2007). From a physical activity perspective, the duration of the exercise does not necessarily imply greater health benefits (Garber et al., 2011); rather, it is the intensity that greatly determines the energetic demands (i.e., the amount of energy required to perform any activity) and, therefore, the possible health outcomes (Garber et al., 2011).
Physical Demands Examined Through the Kinematics
The scarcity of studies on the kinematics of sexual intercourse may be explained by the difficulties associated with doing high-quality research in this area. Some positions might not be recommended for individuals with low back pain as they have a restricted range of motion in the lumbar spine (i.e., flexion-intolerant or extension-intolerant) (Sidorkewicz & McGill, 2014, 2015), perhaps due to the combination of kinematic position and kinetic force on the lumbar spine (Saraceni et al., 2020). For example, there are positions that may demand high lumbar spine flexion for men (e.g., side-lying) and women (e.g., missionary) (Sidorkewicz & McGill, 2014, 2015). However, a previous systematic review reported that using parameters other than range of motion, such as angular velocity or acceleration, was recommended by the included studies when assessing low back patients (Papi et al., 2018). Given the current developments in wearable sensors, these could be used in future studies to collect such information during sexual intercourse (Ciuti et al., 2014; Oliva-Lozano et al., 2020).
Only one study collected data on the pace of the intercourse based on the penetration cycle speed (Sidorkewicz & McGill, 2014). These results suggest that positions such as the quadruped, which elicited greater speed, and therefore greater intensity, may increase the energy required (i.e., kcal, METs, or VO2) (Garber et al., 2011). However, as the speed increases, the risk of hip dislocation may increase as well (Charbonnier et al., 2014; Dahm et al., 2004; Harmsen et al., 2018).
To the best of the authors’ knowledge, scant information is available concerning hip range of motion (Charbonnier et al., 2014). The main limitation was that the data were collected from a limited sample size (one man and one woman); nonetheless, the sexual intercourse simulation required high levels of hip flexion and abduction, with mainly external rotation in the woman, whereas the man was exposed to less hip range of motion but pronounced external rotation (Charbonnier et al., 2014). Consequently, certain positions might not be recommended for people (particularly women) suffering from hip pathologies (e.g., hip arthritis, total hip arthroplasty surgery) (Charbonnier et al., 2014) because the risk of total hip arthroplasty dislocation exists (Dahm et al., 2004). Based on the results from a survey conducted by hip surgeons, whose aim was to report a set of specified guidelines for resuming safe sexual intercourse after total hip arthroplasty, 51 of the surgeons reported at least one case of patients with total hip arthroplasty dislocation during sexual intercourse (Dahm et al., 2004). Also, it was observed that 43.5% of the patients, who expected to be sexually active after surgery, perceived this expectation as unfulfilled (Harmsen et al., 2018).
In this regard, a recent study concluded that intercourse positions such as the scorpion, missionary, or superman may cause rotator cuff degeneration because of friction on the undersurface of the acromion (Lädermann et al., 2018). This is due to the reduced or minimal subacromial space height (Lädermann et al., 2018). However, it is not only subacromial impingement that might lead to rotator cuff degeneration but also the scapular morphology (Moor et al., 2014).
The present systematic review has its own limitations, the main one being that scant methodologically solid research has been carried out on the physical demands existing during sexual intercourse; this weakens the interpretation of the results obtained to date and the potential of this review. For example, future studies of the kinematics of sexual intercourse need to consider many more parameters than just range of motion or penetration cycle. This is of interest if we know all the variables associated with greater (or lesser) range of motion or thrusting sequence timing. To obtain such data, far greater sample sizes are required that consider a wider range of variables. However, this objective may be easily stymied by the implicit biases involved in who volunteers as subjects for such studies. There are also contextual variables, like the size and body mass of the couple, the penis dimension, the penis angle during erections, the amounts of lubrication, or the couple’s dyadic quality, that were not controlled in previous studies but might affect the demands of sexual intercourse. Moreover, most of the studies mainly analyzed the physical demands on men, while little is known about the physical demands on women. Furthermore, the lack of diversity in the literature should be recognized given that scant data exist on sexual activity in same-sex couples or non-penetrative sexual activity. Consequently, future studies should consider all the variables that previous authors failed to define or qualify.
This is the first systematic literature review on physical demands during sexual activity. It comprised a total of 18 studies, all of which analyzed either the physiological demands or kinematics of sexual intercourse, although none of the studies combined both analyses. Sexual intercourse can elicit moderate physical demands, which may vary depending on the participants’ health status, the intercourse position, the activity’s duration, the intercourse phase, and the sex of the participant. However, there are contextual variables (e.g., cardiorespiratory fitness, orgasmic experience, amounts of lubrication, or the couple’s dyadic quality) that are difficult to control but might influence the demands of sexual intercourse. Furthermore, only four studies, which were conducted on healthy adults, analyzed the kinematics of sexual intercourse in different positions. The movement pattern was cyclic, with the greatest flexion demands on the lumbar spine in women being observed in the missionary positions; in contrast, for men, the missionary 1 and side-lying positions elicited the greatest lumbar flexion movement. Regarding hip joint movement during sexual intercourse, flexion, abduction, and mainly external rotation characterized the women’s movement, while external rotation characterized the hip joint movement in men. Therefore, some intercourse positions may increase the risk of low back pain and hip or shoulder injury. Consequently, a kinematic analysis of pelvic rotation in the sagittal plane would be helpful. Although the lumbar flexion in specific intercourse positions (e.g., missionary) may help rotate the woman’s pubis in a way that increases physical contact between the clitoris and the penis, sexologists might wonder if the rate of orgasm for women in these positions relates to insufficient pelvis rotation for achieving adequate clitoral stimulation.