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Alterations in grip strength during male sexual arousal

Abstract

Although it is known that alterations in grip strength occur under a number of conditions, little is known about relationships between grip strength and sexual arousal. This relationship was investigated in 30 healthy heterosexual males, who viewed both erotic and nonerotic videos. A questionnaire was used to assess the extent of sexual arousal. The grip strengths of both hands were measured with a five-position (P1–P5) dynamometer, before and after watching the videos. After watching the erotic video, there was a statistically significant reduction in grip strength for the P2 position, with nonsignificant overall reductions in grip strength for all other positions tested. No such effect was observed in control tests. The results indicate that during sexual arousal, the neural system is likely to reduce the output to muscles not directly related to sexual function, presumably to enhance the physiological responses of sexual arousal.

Introduction

Sexual arousal is an important precursor of sexual activity, and is a particular state of readiness, characterized by a series of adaptive physiological and behavioral changes.1 Many physiological responses to sexual arousal have been well documented, including cardiovascular, respiratory and genital responses, changes in hormone levels and the immune system as well as alterations of regional cerebral blood flow and neural activity.1, 2, 3, 4, 5, 6, 7 However, little is known about the muscular responses to sexual arousal, although some muscles have been found to facilitate sexual functions such as penile erection and pelvic floor contraction.8 Grip strength is a reliable and valid method of measuring upper limb muscle strength in clinical and physical procedures.9 The present study involves the use of a dynamometer to investigate changes in grip strength during sexual arousal. The aim of the study was to primarily develop an experimental paradigm for studying the relationship between sexual arousal and the muscles of the upper limbs by assessment of grip strength in response to exposure to both neutral and erotic visual stimuli. Based on the findings reported above, it was hypothesized that there would be significant alterations in grip strengths following sexual arousal evoked by visual stimulation.

Materials and methods

Subjects

In total, 30 male subjects (age 20–40 years, mean age 28 years, four subjects left hand dominant and the rest right hand dominant) volunteered for the study. The participants were recruited using advertisements displayed on the university campus. During a short interview prior to testing, the subjects were introduced to the study design, and all subjects read the participant information sheet and signed the consent form. The approval for this study was obtained from the Human Ethics Committee of University of Sydney. The inclusion criteria included good overall healthy, heterosexuality, and no history of upper limb injury in the past 6 months and no current pain in hands and arms.

Equipment

A standard, adjustable-handle Jamar hand dynamometer (JA Preston Corp., USA), which is widely employed for measurements of maximum isometric grip strengths, was used in the study. The Jamar dynamometer has a dial meter for displaying the strength scores and can be adjusted to five different spacing between two handles at spans of 1.0, 1.5, 2.0, 2.5 and 3.0 in, which are designated as positions 1, 2, 3, 4 and 5 (P1, P2, P3, P4, P5). As grip strengths are affected by grip span, the measurements for handgrip strength were tested at all spans.10 Maximal grip strength most commonly occurs in the second or third position.9 As posture can influence the static and dynamic aspects of upper limb muscle strengths, a standard posture was used. All subjects were seated with their shoulder adducted and neutrally rotated, and the elbow flexed at 90°.9

Audiovisual stimuli

Two types of visual material were used as stimuli: erotic video excerpts and nonerotic control video excerpts. The erotic video depicted sexual interactions between a man and a woman. The sexual activity involved four types of sexual coitus: fellatio, sexual intercourse with the female in the superior position, intercourse with the male in the superior position and rear entry intercourse. The content of the control video consisted of descriptive scenes of buildings and natural sites from a city documentary.

Testing procedure

All the experiments were conducted in the period from midday to late afternoon to avoid the possible influences of the circadian rhythms on grip strength. Some researchers have reported that the time of day can affect grip strength.11, 12, 13

The sexually aroused and control tests were carried out on separate afternoons to avoid the possible effects of fatigue during the testing procedure. Subjects were randomly allocated to the sexual arousal or control protocol for the first test.

A short questionnaire was used to measure the extent of sexual arousal after watching the erotic video. It included the following questions: (i) Did you enjoy watching the erotic video? (ii) Rate your enjoyment on the scale below (1 lowest, 5 highest enjoyment). (iii) When you watched the erotic video, did you have a penile erection? (iv) How many times did you have penile erection during the video session?

Initially, the use of the dynamometer was demonstrated to the subject and he was allowed to practice before the testing procedure began. After the subject was positioned comfortably in a chair and assumed the standard posture, the maximum isometric grip strengths of both left and right hands were measured over five width spans (P1–P5). This was done three times for each position. The mean score of three trials was used as the strength value for each span. It took 5–7 min to measure the strengths of both hands over five different spans.

Following this procedure, the subject was taken to a dim and quiet setting and watched the erotic or control video alone for 30 min. At the end of the session the subject completed the questionnaire (if they had watched the erotic video) and the grip strengths of both hands were retested using the same procedure. The subject then watched another erotic or control video for a further 30 min, and completed a second questionnaire (erotic group) before the grip strengths were measured again. The time schedule of experimental procedures is shown in Figure 1.

Figure 1
figure1

Time schedule of the experiment when watching the erotic video (EV) and the control video (CV) was shown above. The subject would randomly be allocated to one of either test periods for the first test. The measurement of grip strength (MGS) was carried out three times throughout the testing period: before watching the first erotic video (Bev) or the first control video (Bcv); After watching the first erotic video (Aev1) or the first control video (Acv1) and after the second erotic video session (Aev2) or the second control video session (Acv2).

Results

A paired design was used to analyze the results. Paired-sample t-tests (SPSS software) were used for statistical analysis. The data were collected at three time points: before watching the first video (Bev or Bcv), after watching the first video (Aev1 or Acv1) and after watching the video for the second period (Aev2 or Acv2). No significant difference was found in grip strength before watching the erotic video and control videos. Pooled results from all subjects (n=30) revealed that after watching the erotic video for 30 min, there was an overall decrease in the grip strengths of both hands at all the positions tested, compared with the strengths recorded before watching the erotic video (Figure 2). However, this reduction reached a statistically significant level only on P2 (left hand: t=5.481, DF=29, P<0.01; right hand: t=5.911, DF=29, P<0.01). The grip strengths measured after watching the erotic video in the second session were also significantly decreased at P2 (left hand: t=3.256, DF=29, P<0.01; right hand: t=4.564, DF=29, P<0.01), compared with values obtained before watching the erotic video. No significant difference was found between values obtained after the first and second erotic video sessions (Figure 2). In control experiments, no statistically significant difference was detected between measurements taken before and after watching the nonerotic video in either session (Figure 3).

Figure 2
figure2

Grip strengths measured at three time points: before watching the erotic video (Bev), after watching the erotic video for the first 30 min (Aev1) and after watching the erotic video for second 30 min (Aev2). The grip strengths for both left (L) and right (R) hands are shown for five grip positions (P1–P5) of the adjustable dynamometer. **Significant alterations of grip strengths.

Figure 3
figure3

Grip strengths measured before watching the control video (Bcv), after watching the control video for the first 30 min (Acv1) and after watching for the second 30 min (Acv2). The grip strengths for both left (L) and right (R) hands are shown for five grip positions (P1–P5) of the adjustable dynamometer. No significant changes were found.

P2 yielded the maximum grip strength for both hands in the majority of the subjects. The maximum grip strength of the subjects under the various test conditions is tabulated in Table 1. Pooled data from five positions revealed an overall bell-shaped curve in different test states (Figures 2 and 3).

Table 1 The maximum grip strengths of total number of subjects for each span position

The responses obtained from the questionnaires revealed that all subjects enjoyed the erotic video and the majority rated their enjoyment in the mild to high category during both sessions. Furthermore, all participants experienced penile erection at least once during both sessions (Table 2).

Table 2 Appreciation of the erotic video and penile erection

Discussion

The present study revealed an overall reduction in grip strengths of both hands following sexual arousal evoked by visual stimulation, although this effect was statistically significant only at P2. The results support the hypothesis that the grip strengths are altered during sexual arousal. Although the study involved a relatively small sample (n=30), it provides evidence that the contractile performance of skeletal muscles of upper limbs is influenced by sexual arousal. This study adds to the knowledge of physiological responses to sexual arousal.

A limitation of the study is associated with its lack of direct clinical relevance. All experiments were conducted on healthy heterosexual subjects and subjects with erectile dysfunction were not investigated. Although these results provide insight into physiological responses of muscles during sexual arousal, additional studies on subjects with nonorganic erectile dysfunction would further enhance the understanding of sexual physiology with possible clinical implications.

In relation to the mechanisms of the effects observed in this study, a number of factors, including hormonal changes and reduced sensory input may play a role. However, in view of similar studies in the literature, a role of the central nervous system in influencing physiological responses during sexual arousal appears more plausible.3, 4 Other studies which have demonstrated an increase in the activity of muscles associated with sexual function lend further support a mechanism influencing the central control of somatic musculature rather than one resulting from peripheral changes during arousal.8

A number of studies have shown that sexual arousal facilitates many muscular activities, such as the contraction of the ischiocavernous muscles in penile tumescence, and the musculature of the pelvic floor during sexual intercourse and semen ejaculation.8 However, the results of the present study reveal a negative effect on grip strength. Therefore, the effects of male sexual arousal appear to influence activity in different muscle groups in different ways. Although currently there is not sufficient evidence to explain the mechanism of this differential effect, parallels may be drawn with other physiological states. During pedaling a bicycle, the increased activity in the skeletal muscles of the legs induces an overriding local vasodilatation in those particular muscles. Consequently, the neural system increases blood to flow through the leg muscles, but not to the inactive arm muscles.14 There may be inhibition of the muscles not directly related to sexual function (e.g. muscles of the upper limbs) that coincides with activation of muscles that play a more direct role in sexual function (e.g. muscles of the pelvic floor).

Although there were reductions in strength at all grip positions of both hands after watching the erotic video, this effect reached a statistically significant level only at the P2 position. The observation that maximum grip strength was obtained at P2, and the bell-shaped test results are indicators of the reliability of the testing procedure.15

Erotic stimuli ranging in length from 21 s to 30 min have previously been used to examine the effects of sexual arousal.1, 16, 17, 18 The results of the present study suggest that subjects were sexually arousal after the first erotic video session. In this study, 30 min of stimulation was used. It is possible that varying the stimulus length may affect grip strength responses, but this was not assessed in this study.

In a recent ‘tentative model’ for sexual arousal, it has been suggested that visually evoked sexual arousal may comprise four components: cognitive, emotional, motivational and physiological.6 Although a number of physiological responses to sexual arousal have been well documented in the endocrine and cardiovascular systems, the body's complete functioning under sexual arousal is not fully understood.3, 4 This study provides additional insight into the neuromuscular responses during sexual arousal and more studies will be needed to fully understand the mechanisms of these alterations.

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Jiao, C., Turman, B., Weerakoon, P. et al. Alterations in grip strength during male sexual arousal. Int J Impot Res 18, 206–209 (2006). https://doi.org/10.1038/sj.ijir.3901399

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Keywords

  • grip strength
  • sexual arousal
  • audiovisual sexual stimulation

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