In the United States, obesity is both a growing epidemic and a stigmatized condition. About two out of three adults are considered overweight or obese; and of those adults, over 60 percent of women fall into that category. In addition to the health issues that overweight women share with their male counterparts, they also have difficulty conceiving.
Overweight and obese women who go through assisted fertilization have pregnancy rates 30 to 75 percent lower than healthy weight women who seek the same assisted fertility care. Women who fall into abnormal weight ranges, whether over or under the healthy range, are at risk for infertility. Many reasons exist as to why, but one of the most prominent reasons is that abnormal weight conditions can cause hormone imbalances, which mean reproductive system issues like irregular periods and trouble ovulating.
However, researchers of a study published in the BMJ Open Sport & Exercise considered the effect that high-intensity interval training (HIT) could have on improving fertility in overweight women trying to conceive through assisted fertilization methods. In specific, they wondered what HIT could do to increase insulin sensitivity and, in turn, increase fertility. So would HIT before assisted fertilization boost pregnancy rates? Read to find out.
Below, we’ll address just some of the questions that might be weighing on your mind.
Body mass index (BMI) is calculated with a formula that considers your height and weight. Your BMI determines whether you’re overweight or obese. Physicians could tell you the normal weight range for someone your height, but online BMI calculators could also take your height and weight to make an estimation without a visit to the clinic.
Keep in mind that BMI ranges are approximations. Depending on your body type, race, and other physical factors, your healthy weight range may be different than what a calculator says.
The study’s participants were separated into a control group and a HIT group, which included ten and eight women respectively, equalling about 18 participants. They were separated before assisted fertilization and HIT for the cleanest results.
The idea behind high-intensity interval training is high levels of effort for brief amounts of time. These exercises work your muscles hard. Think heavy weights and fewer reps versus lighter weights and reps.
The HIT program implemented in the study required the women to come to training 3 times a week for 10 weeks. The program prescribed two 4x4 interval training sessions and one longer duration but lower intensity 10x1 interval training.
The researchers hypothesized that more successful pregnancies would come out of the HIT group after the experimental period, but other results such as insulin sensitivity, reproductive hormones, oxygen uptake, and body composition were also measured.
No, the aim of the study is not to make these women lose weight! Weight loss is a likely outcome because of the nature of HIT, but it isn’t the main goal-- increasing insulin sensitivity is. Exercise tends to improve fertility in overweight women and help them lose weight, but researchers suspected that weight loss might not be the main component affecting fertility. Instead, they suggested that increased insulin sensitivity may be more important.
HIT is one of the most common recommendations for improving insulin sensitivity because it works Type 2 (fast-twitch) muscle fibers, which will eat up blood glucose (sugar) for fuel.
Let’s take a mini biology lesson:
Your pancreas creates insulin. Insulin transports sugar from your blood into your cells for energy. That’s why people say carbs (they’re sugars!) give you energy.
Overweight and obese women typically have higher insulin resistance, which means that they need more insulin than average to mediate sugar levels in your blood. When your pancreas can’t create enough insulin for your body’s demands, then your blood sugar rises because all of it can’t be transferred into your cells fast enough. This is also part of the reason why overweight and obese women at more at risk for diabetes.
TL;DR: HIT helps manage those blood sugar levels by working your fast-twitch muscle fibers to eat up the excess sugar.
Out of the 18 women, about half from each group achieved pregnancy. Because the control and HIT group didn’t have a significant difference in successful conception outcomes, the study couldn’t tell whether increased insulin sensitivity, HIT, or something else was responsible.
However, the researchers did note an impressive increase in insulin sensitivity (measured as glucose infusion rate) from 264.1 mg/m2/min to a more standard 324.7 mg/m2/min. The women in the HIT group also lost belly fat and improved their cardiovascular fitness.
So whether or not HIT helped these women conceive, it did have a notable effect on their health.