Background: A plateau in volume of oxygen consumption (VO2) is the primary indicator for determining if an individual has reached their maximal aerobic capacity. However, secondary criteria can also be used to identify maximal effort (i.e. lactate level, rating of perceived exertion [RPE], percent of age-predicted maximal heart rate [HR] and respiratory exchange ratio [RER]). Age and gender-specific secondary criteria have been developed for the general population, but no secondary criteria have been established for pregnant women. The primary purpose of this study was to analyze secondary endpoint criteria during VO2max testing among pregnant women. A secondary purpose was to identify emotional and physical barriers pregnant women have that may prevent them from reaching maximal effort.
Methods: Twenty-five pregnant women (age= 30.0±3.6 years; gestation age= 22.1±1.4 weeks, pre-pregnancy BMI= 23.68±4.04 kg/m2) participated. Each participant completed a Bruce protocol treadmill test and maximal HR, RER, lactate, and RPE were assessed and compared to standards. Barriers were assessed immediately postexercise via open-ended questions.
Results: The mean VO2max was 32.9±8.8 mL/kg/min. Mean RPEmax was 17.6±1.8 versus the standard of RPE≥17 (P=0.12). Percent of age-predicted HRmax was 88.0±6.8% versus the standard of ≥95% (P<0.001). Immediate postexercise lactate was 6.8±2.4mM versus the standard of ≥8 mM (P=0.03). Maximal RER was 1.2±0.2 versus the standard of RERmax ≥1.1 (P=0.08).
Conclusions: Our data provide preliminary evidence that secondary criteria may need to be adjusted for pregnant women. Additionally, physical and emotional barriers may be enhanced by pregnancy (e.g. pain, discomfort, anxiety, health concerns), and may limit the performance of pregnant women during maximal exercise.