Sex-specific morphological differences in the three main subsystems of the vocal apparatus—namely the respiratory, oscillatory, and resonatory systems—affect both the production and perception of the voice. These differences should be taken into account by anyone concerned with vocal function and health and are therefore here explored. Special attention is given to the female voice because sex steroid hormones (i.e., estrogens, progesterone and testosterone) seem to impact on voice function, and the variability in concentrations of these hormones across biological reproductive development is considerably greater in females as compared to males. Note that here, female/ male sex is referred to the sex at birth.

Taking the female voice as a reference and starting with the respiratory subsystem, males typically have larger lungs and, therefore, a greater lung volume (Sundberg, 1987). This greater volume affects the lung’s elastic recoil during exhalation, that is, the force needed to create a subglottal pressure that sets the vocal folds into vibration when they are adducted. In males, the elastic recoil of the lungs during exhalation tends to be greater than in females. As a result, females must use a higher initial percentage of their ribcage volume to generate sufficient exhalatory force to initiate vocal fold vibration (Stathopoulos and Sapienza, 1993). Other equally relevant sex-related specific characteristics are those observed in the oscillatory and resonatory subsystems. Males have longer vocal folds and vocal tracts as compared to females (Fitch and Giedd, 1999). In adult males, the vocal folds are about 6 mm and the vocal tract approximately 13 mm longer as compared to females (Roers, Mürbe and Sundberg, 2009). Moreover, in males, the vibrating part of the vocal folds is about 60% bigger. Being smaller, female vocal folds will have to vibrate faster than males’ vocal folds for the same duration of speech, resulting in more vibrating cycles per second or, in other words, in a bigger displacement in meters (Titze, Švec and Popolo, 2003). Also, the collision forces are higher in female vocal folds due to a smaller dissipating area (i.e., smaller contacting area) (Titze, 1989). In addition, male vocal folds have more hyaluronic acid and collagen fibers in their deeper layers, and generally a higher lubrification when compared to female vocal folds (Hammond, Gray and Butler, 2000; Butler, Hammond and Gray, 2001). Taking into account all these sex-specific voice characteristics, females seem to be at a disadvantage; they present a greater risk of developing vocal fatigue and vocal fold trauma (Dejonckere et al., 2001).

Besides this, female voices are more prone to be affected by sex steroid hormonal variations due to the complexity of their endocrine system (Hunter, Tanner and Smith, 2011). Besides puberty, concentrations in estrogens, progesterone and testosterone also occur during the menstrual cycle, pregnancy, breastfeeding and menopause. Thus, alterations of voice quality related to puberty, such as a drop in pitch – of about an octave in boys and a third in girls -, and voice timbre modifications (eg., roughness, hoarseness), may also be expected during subsequent stages of female reproductive development (Zamponi et al., 2021). This is partially because there are receptors for these hormones in several subunits of the vocal folds, namely the vocal ligament, macula flava, superficial lamina propria and epithelium (Kirgezen et al., 2017). Also, a similar histological response to variations in concentrations of sex steroid hormones have been found between the mucosae of the cervix and of the vocal folds (Perelló and Comas, 1959; Abitbol et al., 1989); this corroborates the assumption that female vocal folds are more prone to be affected by variations in these hormones, at least across the menstrual cycle.

During the pre-menstrual and menstrual phases of the menstrual cycle, female vocal folds may be swollen and possess small varices that interfere with their vibratory patterns (Higgins and Saxman, 1989; Amir and Biron-Shental, 2004; Rodney and Sataloff, 2016). Such condition, known as laryngopathia menstrualis (Van Gelder, 1974), leads to changes in voice quality and also promotes vocal fatigue (Abitbol et al., 1999). Laryngoscopic observations of the vocal folds revealed an increase in vascularity specially during the luteal or premenstrual phase of the menstrual, and this seems to be correlated with higher concentrations of progesterone (Shoffel-Havakuk et al., 2018). Similar vocal symptoms can be experienced during pregnancy, laryngopathia gravidarum (Van Gelder, 1974). Specially during the third trimester of pregnancy, the higher concentrations of estrogens and progesterone may lead to fluid retention and thus an increase in vocal fold mass, resulting in difficulties with singing, especially in the upper range, and impaired flexibility (Lã and Sundberg, 2012; Abitbol, 2019). In addition, during pregnancy, an increase in circumferential area of the thorax and the rise of the diaphragm in the trunk may result in a decrease in vital capacity (Gilroy et al., 1988; Weinberger et al., 1980), that is, the air in the lungs that is used to speak. This temporarily change results in a decrease in maximum phonation time and an increase in vocal fatigue (Hamdan et al., 2009).

During menopause, the considerably reduction in concentrations of sex hormones may result in a drop in the speaking tone and the ability to smoothly transition between regions of the whole singing voice (Lã & Ardura, 2020; Lã et al., 2023). Menopausal transition is the phase of reproductive aging that comprises perimenopause though the 12 consecutive months of cessation of the menstrual cycle (i.e., menopause). During this transition, sex steroid hormonal concentrations fluctuate and eventually decrease markedly at the time of the last period. This has implications in several aspects of voice production. In breathing, for example, a decline in lung function (based on spirometry) was observed in post as compared to premenopausal women (Campbell et al., 2017). Also, maximum phonation time seems to decrease while perturbations measures increase (Lã & Ardura, 2022). As to perceived symptoms, 35 to 46 % of women complain about vocal discomfort and vocal changes related to menopause (Schneirder et al., 2004). Such perceptions are important, especially when concerning impairment of voice-related ability to work; it also seems to decrease with menopause (Lã et al., 2022). Voice education and regular voice practice seem to be key factors when developing coping strategies for menopausal changes and may even prevent future voice injuries related to variations in sex hormones (Sataloff & Linville, 2005; Fiuza et al., 2022)

Although the mechanisms through which sex hormones impact vocal fold tissues are still poorly understood, it is evident that variations in concentrations of sex steroid hormonal concentrations impact on the voice. The presence of receptors for sex steroid hormones in the vocal folds may explain the sex-related differences in the respiratory, oscillatory and resonatory subsystems of the voice and changes in voice quality across female reproductive stages. These sex-related considerations are crucial when designing reproductive health policies for professional voice users and when making decisions on improving voice care measures and educational preventive strategies.

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