Role of High Intensity Interval Training on Reproductive Health Among Women: A Narrative Review

Introduction

As per the prediction by Population Division of the Department of Economic and Social Affairs of the UN Secretariat (UNPD), China or India shows lowered fertility rate. Prediction was done from 2018 to 2100 for 195 countries and territories with the standard cohort component method of projection.¹ Most studies and articles mention infertility as failure to have child in spite of having regular sexual life for one year without any contraceptive measures.² It was noticed that infertility is one of the main issues faced by the youngsters.³ Looking into the statistics, (Figure 1) we can see that India leads in the rate of infertility. One of the study stated that currently the childlessness rate is 10 to 14% in India, which is maximum in urban areas. Every one out of six couples are affected. Primary infertility is noted in majority of the married couples. India stands second in population but increase in infertility rate of India, a drop in population is also noted.³ Incidence of infertility is seen in both the genders (Figure 2). Statistics reveal more harassment and violence faced by the women in the name of infertility. With this study, we are trying to bring forward the plan to support and to empower women facing such problems so that they can overcome the challenge by certain modifications in the existing lifestyle.

Causes of infertility

Below are the common causes for female infertility as suggested by WHO:⁴

• Tubal disorders - blocked fallopian tubes, due to untreated sexually transmitted infections (STIs) or complications of unsafe abortion, postpartum sepsis or abdominal/pelvic surgery

• Inflammatory disorders of uterus such as endometriosis, congenital such as septate uterus, or benign such as fibroids

• Disorders of the ovaries, like polycystic ovary syndrome (PCOS) and other follicular disorders

• Imbalance of reproductive hormones affecting endocrine system. An article published by the hormone foundation stated that age, sickle cell disease, HIV/AIDS, renal problems, smoking, alcohol, recreational drugs, medications such as antidepressants, tranquilizers, calcium channel blockers, narcotics, anti-cancer drugs, exposure to radiations, toxic fumes, pesticides, are also leading to infertility.⁵ Lifestyle factors resulting in infertility are modifiable.

An article published in the journal of Human Reproduction Update stated that lifestyle factors have a larger influence on reproductive ability. They are modifiable with exercise and diet.⁷ As per the survey conducted by Seyedeh Zahra Masoumi et al., in August 2015, one of the most common causes and foremost reason for infertility was due to disparity in hormones which in turn affects the ovulation.² As per American Society of Reproductive Medicine Practice Committee, infertility is defined as a sickness which fails to conceive even after twelve or extra months of trials of normal conception. They had mentioned this as one of the growing issues today.⁸ Main roles of the female gonads are the production of gametes, the oocytes, and sex hormones to control the secondary sexual characters in females and also support the pregnancy. These functions are wielded between adolescence and climacteric, and are controlled by endocrine and paracrine systems acting upon some of the ovarian cells.⁹ However, in addition to other pathological consequences, dysfunction or irregularity in any of these can directly or indirectly lead to infertility.¹⁰

Aim

• The purpose of this review was to investigate the role of hormonal imbalance and obesity in female infertility.

• This review further aimed to clarify and map out the efficacy of HIIT on infertility by managing the hormonal imbalance and obesity, and document the outcomes.

• In addition to this, this study also aimed to identify numerous protocols of HIIT which can be educated and practiced effortlessly, inculcating them in the clinical setup.

Hormonal imbalance and obesity

One of the most common causes of female infertility is changes in normal pattern of ovulation. Ovulation problems results due to imbalance in Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH), any injury to hypothalamus or pituitary gland, or overweight/ obesity.⁵ Insulin resistance and or compensatory hyperinsulinemia intensifies the availability of both circulating androgen and androgen production by the adrenal gland and ovary by reducing sex hormone binding globulin (SHBG).¹⁵

Obesity, is one of the major problems seen in women of reproductive age and is also one of the leading health issues in the world. There is an excess build-up of fat in obesity/overweight, which in turn can have harmful effects on the health of a person. As per World Health Organization, if Body mass index (BMI) equals to or is more than 25 kg/m2 , it is considered as overweight. If the BMI equals to or is more than 30 kg/m2 , then it is considered as obesity. One of the studies conducted in obese women reported that gonadotropin secretion is affected due to greater peripheral aromatization of androgens to estrogens. The insulin resistance/ hyperinsulinemia seen in obese women causes hyperandrogenaemia. There is decrease in sex hormonebinding globulin (SHBG), growth hormone (GH), and insulin-like growth factor binding proteins (IGFBP), while leptin levels are higher. This results in worsening of the neuroregulation of hypothalamic-pituitary-gonadal (HPG) axis.² All these can result in the impairment of normal ovulation, which in turn affects the reproductive capacity of the female. There are only minor chances of obese women giving birth to a healthy baby due to reduction in implantation and rate of pregnancy, increase miscarriage and high maternal and fetal problems in gravidity.¹³ As per the review conducted in 2016 on obesity and infertility, obesity plays the most important role in anovulation. Anovulation is found to be one of the common causes of infertility. Adipose tissue is the largest endocrine organ of the human body. It takes part in many processes, such as production of steroid, homeostasis of glucose, immunoregulation, haematopoiesis and reproduction. Adipose tissue also helps in conversion of androgens to estrogens, estradiol to estrone and dehydroepiandrosterone to androstenediol. Hence it plays one of the most important roles in the reproductive function of the body.¹⁴ Several studies found that one of the main reasons for PCOS is insulin resistance. Hypertension, obesity and increased abdominal fat will be present in such women. All these suggests that obesity is linked with several risks for the mother, embryo, as well as the foetus. Obesity is a changeable risk factor.¹⁵ With the relationship between overweight and increased risk for spontaneous abortion, weight loss could provide a better outcome of pregnancy; this however needs to be proved with further studies on women with infertility. Also, weight loss in obese patients results in improving the lipid and cardiovascular parameters. All these ideally directs us on recommending physical activity and exercise in obese women to improve their fertility parameter.

Exercising and female reproductive ability

Studies have stated that exercise program will have a positive impact on possible pregnancy. As per the study conducted to investigate the effects of physical exercise on the female reproductive system, exercise can have a great impact on maintaining an ideal body weight. It also mentioned that maintaining the ideal body weight can reduce risk of cardiovascular disease, diabetes mellitus, as well as reproductive health.¹² Vigorous activity will have an impact on adiposity and hence in the study, it was considered for reducing the risk of ovulatory infertility. The study mentioned that any physical activity can maintain the function of ovaries by increasing insulin sensitivity.¹¹ As per the previous studies, obesity is one of the key factors affecting the ovarian function via insulin resistance. Also, adiposity creates hormonal imbalances in female body reducing the reproductive ability. Since exercise has a positive impact on all these issues, it can be considered that these factors are modifiable, thereby can help the woman of reproductive age in increasing the fertility. Weight loss has proven to progress procreative results by bettering fertility, and also by bringing regularisation of ovulatory cycles. This helps in enhancing the chances of ovulation and natural way of conception in an anovulatory obese and overweight females.¹⁰ Research literature indicates that high chances of improving fertility are definite even with losing 5% - 10% of the body weight.²¹ Among men and women, if a balance is maintained between energy intake as well energy expenditure, increased chance of reproductive ability can be expected.²² Kirthika et al., in her study recommended education and creating awareness among women for early diagnosis of PCOS. Women should be educated regarding the importance of physical activity since obesity and PCOS are always related. A woman who is overweight or obese with PCOS will benefit from an exercise programme by losing the weight, thereby improving regular ovulation cycle and increasing the chances of pregnancy.²⁴ As per the research reported by numerous authors, it is clear that weight loss has positive impact on insulin sensitivity and extra androgen, thereby normalizing the ovulatory cycles and ensuing spontaneous pregnancies.

HIIT- High Intensity Interval Training

High intensity interval training is different from moderate intensity aerobic exercise. It consists of alternating short bouts of intense aerobic exercise with passive recovery periods.6 Typically, the work intervals lasts from 15 seconds to 4 minutes and approach 80% to 95% of Maximum Heart Rate (MHR). Recovery intervals are usually equivalent to or somewhat extended than the intense work interval. It consists of passive rest or mild activity at 40% to 50% of the MHR. The combined work/rest interval usually is repeated 6 to 10 times. The total HIIT exercise time ranges from 10 to 40 or more minutes depending on the actual duration of the work and rest periods.⁶ HIIT improves the athletic performance, as well several physiological adaptations in human body. American College of Sports Medicine (ASCM) recommends that everyone can perform HIIT programs. For people with health issues, precautions and supervision is required. HIIT has short bouts of high intensity exercise with in between intervals of light to moderate intensity activity; hence everyone can perform for longer duration without undue fatigue. Several studies are taking efforts to investigate the exact effects of HIIT. ACSM noticed some of the benefits as mentioned below:⁶

• Enhancement on aerobic and anaerobic fitness

• Better insulin sensitivity, glucose tolerance, and lipid profiles

• Reduced arterial stiffness and improved blood pressure

• Augmented skeletal muscle fat oxidation

• Improved postexercise metabolism

• Greater weight loss

• Decrease in abdominal and subcutaneous fat

• Improved exercise adherence

HIIT - Insulin sensitivity and obesity effects

Ida Almenning Kiel, Kari Magrethe Lundgren et al., (2018) conducted a study on the effects of highintensity interval training in women undergoing assisted conception. The programme consisted of three sessions per week and was conducted for 10 weeks. Intensity of the training was calculated based on the HRmax. Two sessions per week out of the three were four bouts of four minute high intensity training and at 85% - 95% of HRmax for each individual. Third session of the week was ten bouts of one minute high intensity training at maximum intensity in each bout of the exercise. Women in the experimental group conceived naturally. Experimental group observed results on obesity and insulin sensitivity post the session. Diet was not part of the session and all the participants were purely into intervention only. Hence the study could detail on the isolated effects of exercise. Certain limitations like smaller number of participants and blinding were mentioned.¹⁶ One of the articles published in molecular metabolism by Katarina Marcinko, Sarah R Sikkema et al., (2015) stated that HIIT improved insulin sensitivity by the initiation of adenosine monophosphate (AMP) – activated protein kinase supplying the skeletal muscle, liver and adipose tissue during the course of exercise.¹⁷ Samadi S et al., (2019) conducted a study with 12 week sessions of HIIT. Participants of the experimental group performed three sessions per week and each session extending for 30 minutes. It included warm-up for five minutes, therapeutic session of 20 minutes, ending with a five minute session of cool down. The HIIT part of it had four bouts each of four minutes. In each bout, there were eight rounds which had 20 second of maximal work intervals. Each 20 second work interval was followed by a 10 second rest interval with 80% - 95% of HRMax. There was one minute of rest with HRmax at 75% between each 4-minute sessions. Stretching and jogging were given during warm up. Cool down also had light stretching.²⁰ Leanne M Redman et al., (2011) conducted a study on obese women having PCOS to investigate the effects of aerobic exercise on insulin sensitivity of women as well as enhancing the reproductive health by improving the ovulatory cycle. In this study, author was not looking for the effect on weight loss. It was reported that regular exercise can regulate the metabolic activity, thereby improving the fertility.²⁵

Why HIIT?

Various studies were conducted on HIIT alone or on combination of interventions. In all the studies, observation were made that the participants never abandoned exercise in comparison to other interventions and diet.16 Kiel IA et al., (2020) conducted an Randomized controlled trial (RCT) to compare two different HIIT protocols. The programme was semisupervised including women having PCOS. They reported that supervised group sessions were always beneficial for the participants since they help in motivating and also facilitates interaction with others which helps in socializing and to complete the therapy with fun and enjoyment.18 In a study conducted by Bird SR et al., (2017), it was noted that faster exercise, especially HIIT had shown noteworthy improvements in average 24-hour blood sugar, fasting blood sugar, elevated postprandial blood glucose, blood glucose variability and hyperglycaemia time.¹⁹ Another RCT by Samadi C et al., (2019) also mentioned the effects of HIIT on patients with PCOS, irregular menstrual cycle, with BMI ≥30kg/m2 . Results had shown improvement by lessening the symptoms of PCOS as well as on BMI, fat mass, IR Homeostatic Model Assessment of Insulin Resistance (HOMA), free testosterone (FT), FSH and sex hormone binding globulin (SHBG), reducing hirsutism as well on menstrual cycle.²⁰ This suggests that HIIT can help to obtain satisfactory results by affecting the hormonal levels, insulin sensitivity, in turn having effect on fertility level of the female. A comparative study was conducted by Harrison et al., on the effect of HIIT over insulin resistance and overall fitness in overweight women with and without PCOS. The outcome of the study suggested that HIIT had a great impact on IR as compared to moderate intensity among the women. As per the study, both PCOS and non-PCOS women had an impact on IR; however the insulin sensitivity was lowered in women with PCOS. Hence, this study stated that it was beneficial for women with PCOS.²³ Kirthika et al., conducted a study to determine the effects of exercise on reproductive ability as well as on manging PCOS. The study included combination of Progressive Resisted Exercise (PRE), aerobics and diet management. In this study, an isolated effect of HIIT alone could not be established since PRE and diet management were also given for the experimental group. However, this study concluded that a combination of PRE along with aerobics and diet management for twenty-four weeks changed the body mass index and hormones and thus improved the quality of life.²⁴

Several outcome measures were used in various studies to determine the effectiveness of the programme. One of the studies had taken ongoing pregnancy as primary outcome. Secondary outcomes were insulin sensitivity, reproductive hormones, oxygen uptake and body composition.16 Another study had adopted the outcome measure as frequency of menstruation which included menstrual cycle and duration. Ultrasonography of ovarian morphology and questionnaires on pregnancies and fertility were also taken as the secondary outcome measures. Other outcome measures used were cardiorespiratory fitness, insulin sensitivity, composition of adipose tissue, physical activity, diet follow up, QOL questionnaires, anthropometry, BP, RHR, PACES and Borg’s scale.¹⁸ Samadi et al., in their study used PACER test, vaginal ultrasonography to identify the follicular phase, menstrual cycle frequency, visually identifying the features of hirsutism as outcome measures.¹⁷ As per different studies and reviews, body composition, peak oxygen intake, insulin sensitivity, frequency of menstrual cycles can be used as some of the measuring parameters for assessing the changes in metabolism and fertility after HIIT.

Discussion

Studies suggests that regular exercising/physical activity plays an important role in the management of infertility among women. At least 30 minutes of physical activity has to be performed which helps to enhance the procreation. Physical activity always helps in maintaining the balance between energy deficit and intake. Along with weight loss, exercise also helps in improving the insulin sensitivity which is beneficial for women with PCOS.²² In this review, it was noticed that among the various factors leading to infertility, the most common are obesity and hormonal imbalance. As per some authors, it was mentioned that ovulation irregularities are the most common reasons for infertility.^4,10,13 This irregularity is again related with hormonal imbalances as well as accumulation of fat in the adipose tissue.^13,15 Accumulation of fat in the adipose tissue in turn impairs its normal function affecting the reproductive ability.

We also reviewed certain articles stating that insulin resistance plays a key role in the reproductive ability. PCOS, one of the major health issue affecting the normal cycle of ovulation is due to the insulin resistance which results in hormonal irregularities.^10,11,15,22 We can find that there is a close relationship between PCOS and insulin resistance. Metabolic abnormalities are one of the most important factors seen in PCOS women with obesity resulting in anovulation.²⁶ All the factors pointing towards the anovulation and decreased reproductive ability are interlinked with each other, which is again related with one common factor i.e., obesity.

Most important treatment parameter for enhancing reproductive ability is by being physically active. Over exercising and under exercising are not recommended. Hence on review, we noted the best protocol to be given for women of reproductive age is the HIIT programme. Several studies had several protocol designs on HIIT which became successful. All the studies had one common feature on HIIT protocol, which suggest an aerobic exercise with high and low intensity cycles consecutively.^{16,17,18,19,20,25} HIIT helps in reducing the risk of obesity, heart health, Type 2 diabetes mellitus and thus improves the quality of life.

As per our reviews, we can find a very clear evidence that HIIT is one of the beneficial tool to augment the reproductive health in women who are obese and having hormonal imbalance.

Conclusion

All the above mentioned observations leads to the conclusion that one of the most common reasons for the global infertility is due to the changes in lifestyle of individuals. Especially the women of reproductive age need to be physically active which enhances the reproductive ability as well as chances for spontaneous pregnancy. HIIT has proven its benefits in several studies in improving the reproductive ability by effecting IR, obesity/overweight and also regulating the ovulatory cycle, which are all the common factors leading to infertility. Also, HIIT can help reducing the weight, thereby reducing the cardiovascular risk factors such as hyperlipidaemia, hypercholesterolemia and hyperinsulinemia.

Conflicts of interest

The authors do not have any conflict of interest to declare.