By Lori Thein Brody and Paula Richley Geigle
The American College of Obstetrics and Gynecology and the American Society of Obstetrics and Gynecology recommend that healthy women maintain their exercise programs during pregnancy (Artal, Clapp, and Vigil 2000). Non-weight-bearing activities such as swimming and cycling and low-impact aerobics have well-known benefits on maternal fitness. Large increases in core body temperature, however, should be avoided during pregnancy. Proper hydration, appropriate modes of heat dissipation, and diligent monitoring can help mitigate significant increases in body temperature.
A study by McMurray, Katz, Bery, and Cefalo (1988) examined the effects of submerged cycling on 12 women at 15, 25, and 35 wk gestation. First, the researchers had the subjects pedal on land cycles at 50 rpm at increasing workloads (increased by 12 to 25 W every 3 min) to determine each person’s 60% maximal HR. Karvonen’s formula of 0.6 (220 – age – resting HR) + resting HR was used. The subjects then pedaled in xiphoid-level water for 20 min at their individual equivalent of 60% of their maximal HR as determined on the land cycle. Risch et al. (1978) selected this level of submersion (and vertical position) and reported that the same effect on the heart exists as in horizontal swimming. Subjects showed no significant difference in V.O2 or DBP. When subjects were cycling in the water, HR and SBP were lower than on land for a given workload. Overall, the cardiovascular response to cycling in the water followed the trends identified on land. The researchers stated that pregnant women could safely exercise in the water at a workload that corresponds to 60% of their maximal HR on land. In many clinical and recreational environments, testing workload may not be possible. If this is the case, the general recommendation for an aquatic target HR is to reduce the target HR on land by 15 bpm (when submerged to the xiphoid process). This level has been determined to be a safe zone for the pregnant female (McMurray, Katz, Berry and Cefalo 1988; Risch et al. 1978).
Of course, the status of the fetus is also a concern when a pregnant woman is exercising. Katz, McMurray, Goodwin, and Cefalo (1990) compared land and water cycling at 70% of maximal HR. As a result of discrepancies in using land target HR to monitor aquatic exercise, the researchers elected to standardize pedal frequency. On land, pedal frequency was recorded at 70% of maximal HR and V.O2. Subjects, submerged to the level of the xiphoid, pedaled for 20 min at the target pedal frequency. Maternal HR, fetal HR, SBP, DBP, and rectal temperature were all monitored. Maternal HR, SBP, and rectal temperature were higher during land cycling than during water cycling, whereas fetal HR and DBP were similar for the two conditions. The researchers concluded that 70% of maximal HR and V.O2 were acceptable limits of exercise for pregnant women. They further stated that with a lower HR and SBP, mothers and fetuses tolerated water exercise at 70% of maximal HR and V.O2 better than they did land exercise.
A study by Watson, Katz, Hackney, Ball, and McMurray (1991) looked at the effect of maximal swimming and cycling exercise at 25 and 35 wk gestation. BP, HR, fetal HR (FHR), and umbilical and uterine artery systolic–diastolic ratios were monitored. The swimming program used a pulley system to provide resistance while subjects swam a breaststroke. Subjects swam for 3 min bouts with 1 min rest periods. Weight was progressively added to the pulley at each bout until the subject could no longer propel herself forward. No difference was found in maximal HR, FHR, or umbilical and uterine artery systolic–diastolic ratios between cycling and swimming. But cycling caused a greater increase in maximal V.O2 and hematocrit and a greater decrease in plasma volume compared with swimming. The buoyancy effect and thermal conductivity of the water required less blood flow to the skin to dissipate the internal heat produced, therefore preserving blood flow to the uterus (Watson, Katz, Hackney, Ball, and McMurray 1991). Again, this research has demonstrated that aquatic exercises may be safer for the fetus than land-based exercises of comparable intensity.
This is an excerpt from Aquatic Exercise for Rehabilitation and Training.