The effect of physical activity on fertility: a mini-review

Abstract

•Overweight and obese women with polycystic ovary syndrome should be encouraged to engage in vigorous aerobic exercise or resistance training to optimize their chances of conceiving.•In women undergoing assisted reproduction for other diagnoses, exercise likely has little to no impact on treatment outcomes. Individuals can therefore continue their regular exercise regimen throughout the treatment.•In healthy women who are trying to conceive, the potential for regular vigorous exercise to negatively impact fertility should be considered. The presence of anovulation and/or a luteal phase defect caused by vigorous exercise should be evaluated. Although lifestyle factors such as diet, cigarette smoking, and alcohol consumption are increasingly recognized as important contributors to the risk of subfertility, the role of exercise in fertility remains less clear. As such, it is challenging for healthcare providers to deliver clear, evidence-based recommendations to patients regarding the optimal frequency and intensity with which they should exercise to maximize their chances of conception. Therefore, this review provides a critical overview of the available research for various patient populations. Although lifestyle factors such as diet, cigarette smoking, and alcohol consumption are increasingly recognized as important contributors to the risk of subfertility, the role of exercise in fertility remains less clear. As such, it is challenging for healthcare providers to deliver clear, evidence-based recommendations to patients regarding the optimal frequency and intensity with which they should exercise to maximize their chances of conception. Therefore, this review provides a critical overview of the available research for various patient populations. The American Society for Reproductive Medicine provides clear guidance regarding the impact of smoking, alcohol consumption, and diet on conception, coupled with appropriate patient recommendations (1Practice Committee of the American Society for Reproductive MedicineDefinitions of infertility and recurrent pregnancy loss: a committee opinion.Fertil Steril. 2020; 113: 533-535Abstract Full Text Full Text PDF PubMed Scopus (206) Google Scholar). However, no such guidelines exist regarding patient engagement in physical activity (PA) and exercise, making it challenging for healthcare providers to deliver clear, evidence-based recommendations regarding the optimal frequency and intensity with which patients should exercise to maximize their chances of conception. This is particularly true given that appropriate recommendations may differ according to a patient’s baseline fitness level, health status, and infertility-related diagnosis. Thus, this review aims to provide an up-to-date overview of our current understanding of the impact of exercise on fertility, with particular consideration of patient characteristics that may warrant a modification of one’s specific recommendations. An electronic search of Ovid MEDLINE from inception until November 2022 was conducted. Key words included “exercise,” “physical activity,” “infertility,” “fertility,” “menstrual cycle,” “ovulation,” “assisted reproduction,” “in vitro fertilization,” and “polycystic ovary syndrome,” among others. Included studies could follow observational or experimental research designs. Participants could be male or female as long as they were attempting to conceive with or without medical intervention. In reviewing the research identified in the search, 3 main study populations were identified and discussed separately: healthy (presumed fertile) women attempting to conceive, women with diagnosed polycystic ovary syndrome (PCOS), and women undergoing assisted reproduction. To narrow the focus of this mini-review, it was decided that only studies measuring objective markers of fertility would be included. Such objective markers included pregnancy, ovulation, or levels of ovarian hormones (i.e., estradiol and progesterone) across the menstrual cycle. Thus, studies solely assessing self-reported menstrual regularity or surrogate markers of disease severity (e.g., acne or androgen levels in PCOS) were excluded. Physical activity (PA) encompasses all leisure and nonleisure bodily movements produced by skeletal muscle groups that raise energy expenditure over resting; exercise is a subcategory of PA that is structured, repetitive, and purposive toward maintaining or improving fitness levels. PA and exercise intensity can be measured using objective measures, such as heart rate or metabolic equivalents, a measure of energy expenditure (2American College of Sports MedicineACSM’s exercise testing and prescription. Lippincott Williams & Wilkins, 2017Google Scholar), or subjective measures, such as self-rated perceived exertion. Table 1 summarizes how exercise can be categorized into mild, moderate, and vigorous intensity using these various measures.Table 1Comparing exercise intensities using various methods of measurement.Exercise intensityMETsHRBorg rating of perceived exertion (RPE; 6–20 scale)Subjective experienceExamplesLight2.0–2.930%–39% HR reserveaHeart rate reserve is calculated by taking the theoretical maximum HR (208 − [0.7 × age]) and subtracting the resting HR (4). MET values refer to the energy expenditure, wherein 1 MET is at rest and 5 METs refer to expending 5 times the amount of energy a person would sitting at rest (2).57%–63% max HR9–11Movement that does not cause adults to sweat or breathe harder; easy to talkWalking slowly (2.0 METs)Housework while standing (2.0–2.5 METs)Moderate3.0–5.9 METs40%–59% HR reserve64%–76% max HR12–13Causes some sweating and shortness of breath; can only speak short sentencesBrisk walk: 5.0 METsBicycling (leisurely): 5.5–6.0 METsVigorous≥6.0 METs60%–89% HR reserve77%–955% max HR14–17Causes considerable sweating and shortness of breath; can only speak 1–2 wordsSwimming (leisurely): 6.0 METsRunning 9.65 km/h: 9.5–10 METsHR = heart rate; max = maximum; MET = metabolic equivalent; RPE = rating of perceived exertion.a Heart rate reserve is calculated by taking the theoretical maximum HR (208 − [0.7 × age]) and subtracting the resting HR (4Mottola M.F. Davenport M.H. Ruchat S.M. Davies G.A. Poitras V.J. Gray C.E. et al.2019 Canadian guideline for physical activity throughout pregnancy.Br J Sports Med. 2018; 52: 1339-1346Crossref PubMed Scopus (319) Google Scholar). MET values refer to the energy expenditure, wherein 1 MET is at rest and 5 METs refer to expending 5 times the amount of energy a person would sitting at rest (2American College of Sports MedicineACSM’s exercise testing and prescription. Lippincott Williams & Wilkins, 2017Google Scholar). Open table in a new tab HR = heart rate; max = maximum; MET = metabolic equivalent; RPE = rating of perceived exertion. In the general population, moderate-to-vigorous exercise is generally considered beneficial because it reduces the risk of multiple chronic illnesses, such as cardiovascular disease and cancer (3Warburton D.E.R. Bredin S.S.D. Health benefits of physical activity: a systematic review of current systematic reviews.Curr Opin Cardiol. 2017; 32: 541-556Crossref PubMed Scopus (1059) Google Scholar); during pregnancy, regular moderate-to-vigorous exercise is associated with improved maternal and fetal health outcomes (4Mottola M.F. Davenport M.H. Ruchat S.M. Davies G.A. Poitras V.J. Gray C.E. et al.2019 Canadian guideline for physical activity throughout pregnancy.Br J Sports Med. 2018; 52: 1339-1346Crossref PubMed Scopus (319) Google Scholar). From a mental health perspective, regular engagement in exercise has also been shown to have large beneficial effects on both depressive and anxious moods in the general population (5Saxena S. Van Ommeren M. Tang K.C. Armstrong T.P. Mental health benefits of physical activity.J Ment Health. 2005; 14: 445-451Crossref Scopus (122) Google Scholar) and, specifically, in women struggling with infertility (6Prémusz V. Makai A. Perjés B. Máté O. Hock M. Ács P. et al.Multicausal analysis on psychosocial and lifestyle factors among patients undergoing assisted reproductive therapy–with special regard to self-reported and objective measures of pre-treatment habitual physical activity.BMC Public Health. 2021; 21: 1480Crossref PubMed Scopus (5) Google Scholar, 7Rebar A.L. Stanton R. Geard D. Short C. Duncan M.J. Vandelanotte C. A meta-meta-analysis of the effect of physical activity on depression and anxiety in non-clinical adult populations.Health Psychol Rev. 2015; 9: 366-378Crossref PubMed Scopus (584) Google Scholar). However, what is less clear-cut is the impact of exercise of varying intensities on fertility among women either attempting and/or struggling to conceive. Therefore, this review considers the existing research examining the impact of exercise on indicators of fertility, specifically rates of ovulation and pregnancy as well as ovarian hormone levels, with specific consideration for 3 separate populations that have been of particular focus in this line of research: presumed healthy women attempting to conceive without medical intervention, women with diagnosed PCOS attempting to conceive without medical intervention, and women with diagnosed infertility pursuing assisted reproduction. A number of studies have examined the effects of PA on fertility in healthy women attempting to conceive (Table 2). For example, an early study by De Souza et al. (8De Souza M.J. Van Heest J. Demers L.M. Lasley B.L. Luteal phase deficiency in recreational runners: evidence for a hypometabolic state.J Clin Endocrinol Metab. 2003; 88: 337-346Crossref PubMed Scopus (78) Google Scholar) (2003) compared runners running a mean (±SD) of 32 km/wk with sedentary women, tracking hormonal markers and menstrual characteristics over 3 In this of regular runners were to menstrual anovulation and an luteal phase as a luteal phase of or a of for only of sedentary among the with a luteal luteal levels were among runners among sedentary were also to levels of a of in the an effect of exercise on Although the was not associated with of the the energy (i.e., using and activity that were categorized as were associated with a energy with other of However, by an luteal phase were to be associated with an energy to that of menstrual effects of physical activity in healthy and PA et al. De Souza M.J. of energy frequency not severity of menstrual associated with exercise and J Endocrinol Metab. 2015; PubMed Scopus Google Scholar), women with a all and all 3 of vigorous aerobic exercise 5 from and diet to 1 a exercise a exercise and 3 a exercise exercise regimen as groups without an energy of the and energy groups at 1 luteal phase defect in the 3 menstrual In only 1 in the and 1 in the toward rates of anovulation in and groups = to other groups Souza et al. (8De Souza M.J. Van Heest J. Demers L.M. Lasley B.L. Luteal phase deficiency in recreational runners: evidence for a hypometabolic state.J Clin Endocrinol Metab. 2003; 88: 337-346Crossref PubMed Scopus (78) Google Scholar), women and of sedentary women = and runners = running at of 32 the 3 menstrual of the running was of the sedentary In of the running a luteal phase or of the sedentary Luteal was in among runners sedentary et al. A study of physical activity and to Steril. Full Text Full Text PDF PubMed Scopus Google Scholar), women not of fertility the number of that they in PA during the and vigorous activity the number of of vigorous PA and the to pregnancy in women with to pregnancy was in in PA in all women who in vigorous et al. Physical activity and fertility in the Health PubMed Scopus Google Scholar), women and of PA were and the amount of PA was categorized as either moderate, or on the of at the and who were times likely to be women, and to was associated with times the of infertility compared with taking it for or was associated with of infertility compared to for = = not PA = physical Open table in a new tab = = not PA = physical The potential for vigorous exercise to negatively impact fertility in healthy women has been in large The is by et al. A study of physical activity and to Steril. Full Text Full Text PDF PubMed Scopus Google Scholar) which a the self-reported number of of vigorous exercise and to pregnancy in women with a in for and a number of health women in of vigorous exercise were less likely to be sedentary women over the women this number to less were associated with a in the chances of conception. In exercise the of for example, of activity the of pregnancy by The is a study by et al. Physical activity and fertility in the Health PubMed Scopus Google Scholar) that examined the impact of self-reported exercise in less the of et al. A study of physical activity and to Steril. Full Text Full Text PDF PubMed Scopus Google Scholar) the that women categorized as a PA a of PA frequency and were times likely to or compared with women with a PA However, a by Williams et al. 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S. A. R. A. et exercise training diet in obese polycystic ovary syndrome patients with a PubMed Scopus Google Scholar) the exercise the diet in of ovulation rates less This is also by the that in the large study by et al. D. M. G.A. et and PubMed Scopus Google Scholar), a vigorous exercise and a risk of infertility as a studies have examined the impact of resistance training on metabolic in women with PCOS only 1 of the studies in Table 3 the benefits of resistance training for are not the study by et al. M. The effect of a diet with and without exercise training on risk and reproductive in and obese women with polycystic ovary Clin Endocrinol Metab. 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Williams R. et physical and sedentary in to reproductive outcomes Full Text Full Text PDF PubMed Scopus Google Scholar) = was no effect of PA on patient was to this such that in moderate-to-vigorous PA was associated with an of among women not in recreational and PA were associated with the number of and pregnancy in a study by et al. (6Prémusz V. Makai A. Perjés B. Máté O. Hock M. Ács P. et al.Multicausal analysis on psychosocial and lifestyle factors among patients undergoing assisted reproductive therapy–with special regard to self-reported and objective measures of pre-treatment habitual physical activity.BMC Public Health. 2021; 21: 1480Crossref PubMed Scopus (5) Google Scholar) by et al. M. B. of energy expenditure and physical activity on the outcomes of assisted reproduction Full Text Full Text PDF PubMed Scopus Google Scholar) and et al. S. A. A. A. et chronic in women with polycystic ovary a Clin Endocrinol Metab. 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S. et physical activity and sedentary and during in vitro a study the with ovarian and pregnancy 2020; PubMed Scopus Google Scholar), women undergoing was measured for using during at and effect of PA or during on or et al. S. A. A. A. et chronic in women with polycystic ovary a Clin Endocrinol Metab. PubMed Scopus Google Scholar), obese women with PCOS undergoing or and frequency of PA using the PA in regular PA a pregnancy rate and rate compared with women who not et al. (6Prémusz V. Makai A. Perjés B. Máté O. Hock M. Ács P. et al.Multicausal analysis on psychosocial and lifestyle factors among patients undergoing assisted reproductive therapy–with special regard to self-reported and objective measures of pre-treatment habitual physical activity.BMC Public Health. 2021; 21: 1480Crossref PubMed Scopus (5) Google Scholar), women the of and and undergoing observational on the and frequency of PA using the PA using objective recreational PA was with = on PA PA was to pregnancy = = = in vitro PA = physical PCOS = polycystic ovary Open table in a new tab = = = in vitro PA = physical PCOS = polycystic ovary The only study to a effect of PA on outcomes was a large study of undergoing by et al. of exercise on the of in vitro PubMed Scopus Google Scholar) the were the was no PA and The of by both exercise as well as the number of during which the been in that In women who been in of PA for were less likely to pregnancy women who no However, this was not the for women who been in the regimen for a This is to and the of these of women in other important such as the infertility-related diagnosis. 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