Walking Cadence during Moderate-Intensity Physical Activity in Pregnant Women

Evidence has established that a cadence of 100 steps/min is indicative of the moderate intensity threshold of 3 metabolic equivalents (METs), but this has only been described in non-pregnant individuals. As metabolic alterations are well established during pregnancy, the purpose of this study was to determine if the walking cadence equivalent to 3 METs in pregnant women is similar to non-pregnant populations. Pregnant females (n = 29; age = 30.3 +/- 3.2 years, gestational age = 23.9 +/- 6.6 weeks) in their second or third trimester (>12 weeks gestation) completed three stages of treadmill walking for 5 min at different standardized walking speeds: 2.5, 3.0, and 3.5 miles per hour (mph). Oxygen consumption (VO2) and heart rate (HR) were measured each minute and METs were calculated for each stage. Real-time continuous monitoring of walking cadence was evaluated by an OptoGait gait analysis system. Following the three standardized speed stages, participants completed an additional stage walking at a speed that elicited 100 steps/min; VO2 and HR were also collected. A one-sample t-test was used to compare MET values at each stage to the heuristic 3 MET cutoff, and Pearson correlation coefficient was calculated to evaluate the relationship between cadence and METs. Mean cadence increased linearly across the three stages (2.5 mph = 103.7 +/- 4.5, 3.0 mph = 112.5 +/- 5.3, and 3.5 mph = 120.4 +/- 6.2 steps/min), as did METs (2.5 mph = 2.7 +/- 1.7, 3.0 mph = 3.2 +/- 0.8, and 3.5 mph = 4.3 +/- 1.8 METs) regardless of trimester. The average treadmill speed at which women walked at 100 steps/min was 2.4 +/- 0.4 mph which elicited an oxygen consumption of 9.5 mL center dot kg(-1)center dot min(-1), or 2.7 +/- 0.7 METs. There was no significant difference between METs at 3.0 mph and the conventional 3 MET cut point for moderate-intensity PA (p < 0.05). There was a moderate and significant relationship between METs and cadence (2nd trimester: r = 0.51; 3rd trimester: r = 0.42). Current data indicate for the first time that the traditionally used 3 MET cutoff for moderate-intensity activity is appropriate for pregnant women despite metabolic alterations associated with pregnancy. This may have important implications for exercise prescription in pregnant populations.