As research continues to support regular exercise in low risk, healthy pregnancies, the number of pregnant women engaging in moderate intensity exercise remains below recommended levels for health benefits.

Current guidelines recommend that healthy pregnant and postpartum women, perform at least 150 minutes per week of moderate-intensity aerobic activity (i.e., equivalent to brisk walking) [1]. However, statistics show more than 50 percent of pregnant women do not achieve this due to multiple barriers to exercise such as lack of time, child care issues, as well as life and work commitments [2-4].

With this problem in mind, I teamed up with fellow researchers at The University of Western Australia’s School of Human Science to conduct a small pilot study in an attempt to find out whether continuous or interval typed aerobic training provided greater exercise enjoyment in pregnant women.

Why Exercise Enjoyment?

You might be wondering why we chose to look at enjoyment. Research suggests that exercise enjoyment is a major predictor of attendance and adherence to exercise [5], and we all know the importance of encouraging consistency in exercise, whether during pregnancy or not.

Since interval training is known to provide superior health benefits, and enhance exercise enjoyment and adherence compared with moderate intensity continuous exercise in a non-pregnant population [6-9], we were intrigued to find out if interval exercise had a similar effect in the pregnant population. This was of importance: if interval training was not well tolerated and enjoyed by pregnant women, it would be pointless to prescribe interval training to pregnant women and put them off exercise totally.

 

Stationary cycling was chosen as the mode of exercise as it is a recommended for pregnant women without obstetric complications [10]. This mode of exercise facilitates a higher self-paced intensity as it supports the increasing body mass of pregnant women. This  allowed women to expend more energy in the same amount of time compared to walking and thus a greater reduction in postprandial (post-meal) glucose concentration, which may have an implication to women with gestational diabetes [11].

 

Furthermore, a program of regular home-based stationary cycling also appears to have favorable effects on maternal fitness and glucose tolerance in previously inactive obese pregnant women [12]. Cycling on the stationary bike also encouraged adherence to the cycling training program as it can be performed indoors and not subjected to weather. Comparing the cost of exercise equipment, a stationary bike is also more affordable than most treadmills.

The Study

In our study published in BMC Pregnancy & Childbirth [13], twelve healthy pregnant women in their third trimesters visited the laboratory on two occasions within a two-week period and were scheduled at least two days apart to minimize any effects from the previous session. In a counterbalanced order, these women performed either:

• 30 minutes of continuous cycling exercise at an intensity of 65 percent of their age-predicted maximum heart rate, or
• An equivalent period of interval cycling consisting of continuous cycling at the same power output as continuous cycling, with the addition of six 15-second self-paced higher intensity efforts throughout, performed at regular intervals.

We measured the relevant physiological parameters (i.e., power output, oxygen consumption, heart rate and rate of perceived exertion) as well as assessed exercise enjoyment using the Physical Activity Enjoyment Scale (PACES) immediately following each trial [14]. The women were also ask to provided written responses to the questions such as:

• Did you prefer the continuous cycling session or the interval cycling session? Why?
• If you had to perform a cycling program for three months during pregnancy, would you choose continuous cycling or interval cycling? Why?

Interesting Findings

Mean cycling power output, heart rate, oxygen consumption and energy expenditure were higher during interval cycling compared with continuous cycling, but there was no difference in mean rate of perceived exertion between the two. This is surprising and exciting at the same time because:

• The mere addition of six 15-second (90 seconds in total) higher-intensity intervals to continuous moderate intensity exercise had effectively increased energy expenditure by 28 percent. In other words, women in the study worked hard during the interval cycling but found the overall rate of perceived exertion to be similar to continuous cycling.
• This potentially means that there is a possibility of creating exercise programs for pregnant women that maximises energy expenditure for a given time without making them feel like they are exerting more.
• Enjoyment of exercise was also higher with interval cycling compared to continuous cycling even though they expended more energy during interval cycling.

From the written responses provided by the participants, all women preferred the interval cycling over continuous cycling, citing it was “interesting,” “challenging,” provided a “better workout” and made time “go faster” because the exercise was “broken up” as the reasons of preference. One woman had “expected to prefer the continuous cycling” but found that interval cycling gave her a “sense of accomplishment and better understanding of her exercise capacity.”

When asked which type of exercise women would prefer if it was a three-month, thrice weekly cycling program, the majority preferred an interval cycling or mixture of both training types. A mixture of continuous and interval cycling may be ideal given that no two days are the same for a pregnant woman in terms of the physically symptoms she experiences daily.

This was a very promising finding for us, to see that interval cycling not only was allowing pregnant women in the third trimester to expend more energy without compromising and instead elevating enjoyment of exercise in the twelve participating women.

Important Note When Interpreting Research Findings

When we interpret research findings, it is imperative to be aware of each research studies’ limitations. Of note, the findings in this featured study are specific to recreationally active women, and do not make it a blanket clinical recommendation for all pregnant women.  While the outcome of this study prompts for more research more larger group of pregnant women, it is definitely not the end of this story.

But the implications of this small study do suggest the potential of using interval exercise, with caution, to promote exercise enjoyment in a group of women who may not have time or enjoy exercise.

Coaches’ Corner

When we are working with unconditioned and previously sedentary pregnant women, it might not be ideal to just put them on a program of continuous vigorous intensity as this level of exercise intensity would require more regular prenatal monitoring for maternal and fetal well-being [15]. However, the use of interval bouts of self-paced effort could be a way to incorporate some vigorous intensity into their exercise program as it allows for a higher intensity training stimulus with partial recovery between efforts, keeping the overall intensity of an exercise session within safe limits.

The addition of brief higher intensity intervals to continuous exercise at moderate intensity can also be an opportunity to safely optimize health and fitness benefits for pregnant women by increasing the energy expenditure of an exercise session, at the same time as maximising enjoyment.

Remember that it is highly advisable to work closely with your pregnant client’s obstetrician if you decided to utilize some interval cycling in her training and the extent of higher intensity should always be determined by the pregnant women and not the trainer.

As exercise professionals who work with pregnant women, the most important lesson to teach other clients is how to listen to their bodies and take their training to where their bodies and pregnancies want to go. Our physiology is very clever at sending us messages to reduce intensity or stop exercise during pregnancy. We just need educate our clients on how to pick up those messages.

References

1. Physical activity and exercise during pregnancy and the postpartum period. Committee Opinion No. 650. American College of Obstetricians and Gynecologists. Obstet Gynecol 2015;126:e135–42
2. de Jersey, S. J., Nicholson, J. M., Callaway, L. K., & Daniels, L. A. (2013). An observational study of nutrition and physical activity behaviours, knowledge, and advice in pregnancy. BMC Pregnancy and Childbirth, 13(1), 115.
3. Evenson, K. R., & Wen, F. (2010). National trends in self-reported physical activity and sedentary behaviors among pregnant women: NHANES 1999–2006. Preventive Medicine, 50(3), 123-128.
4. Evenson, K. R., Moos, M. K., Carrier, K., & Siega-Riz, A. M. (2009). Perceived barriers to physical activity among pregnant women. Maternal and Child Health Journal, 13(3), 364-375.
5. Ryan, R., Frederick, C., Lepes, D., Rubio, N., & Sheldon, K. (1997). Intrinsic motivation and exercise adherence. International Journal of Sport Psychology, 28(4), 335-354.
6. Helgerud, J., Hoydal, K., Wang, E., Karlsen, T., Berg, P., Bjerkaas, M., . . . Bach, R. (2007). Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine & Science in Sports & Exercise, 39(4), 665.
7. Little, J. P., Gillen, J. B., Percival, M. E., Safdar, A., Tarnopolsky, M. A., Punthakee, Z., . . . Gibala, M. J. (2011). Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Journal of Applied Physiology, 111(6), 1554-1560.
8. Wisløff, U., Støylen, A., Loennechen, J. P., Bruvold, M., Rognmo, Ø., Haram, P. M., . . . Lee, S. J. (2007). Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients a randomized study. Circulation, 115(24), 3086-3094.
9. Bartlett, J. D., Close, G. L., MacLaren, D. P., Gregson, W., Drust, B., & Morton, J. P. (2011). High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: implications for exercise adherence. Journal of Sports Sciences, 29(6), 547-553.
10. Artal, R., & O’Toole, M. (2003). Guidelines of the American College of Obstetricians and Gynecologists for exercise during pregnancy and the postpartum period. British Journal Of Sports Medicine, 37(1), 6-12.
11. Halse, R. E., Wallman, K. E., Newnham, J. P., & Guelfi, K. J. (2013). Pregnant women exercise at a higher intensity during 30min of self-paced cycling compared with walking during late gestation: implications for 2h postprandial glucose levels. Metabolism, 62(6), 801-807.
12. Ong, M., Guelfi, K., Hunter, T., Wallman, K., Fournier, P., & Newnham, J. (2009). Supervised home-based exercise may attenuate the decline of glucose tolerance in obese pregnant women. Diabetes & Metabolism, 35(5), 418-421.
13. Ong, M. J., Wallman, K. E., Fournier, P. A., Newnham, J. P., & Guelfi, K. J. (2016). Enhancing energy expenditure and enjoyment of exercise during pregnancy through the addition of brief higher intensity intervals to traditional continuous moderate intensity cycling. BMC pregnancy and childbirth, 16(1), 161. https://bmcpregnancychildbirth.biomedcentral.com/articles/10.1186/s12884-016-0947-3
14. Kendzierski, D., & DeCarlo, K. J. (1991). Physical Activity Enjoyment Scale: Two validation studies. Journal of Sport & Exercise Psychology, 13(1), 50-64.
15. Penney, D. S. (2008). The effect of vigorous exercise during pregnancy. Journal of Midwifery & Women’s Health, 53(2), 155-159.