Body Composition of Cold-Water Swimmers: The San Francisco Polar Bear Swim Study

ABSTRACT

To assess the body composition of recreational cold-water swimmers, to determine if cold-water swimmers have an increased % body fat when compared to average Americans, and to examine the relationships between body composition and total swim distance and time in the water per swim.

Following 3 months of swimming regularly in cold water in the San Francisco Bay (water temperature range: 9.6° C [49.3° F] to 12.6° C [54.7° F]) during the winter months, body mass index (BMI), % body fat (assessed by circumference technique), and surface/volume ratio were measured in 88 subjects (70 men and 18 women). The total cumulative swim distance was recorded by each subject and each subject estimated his or her average time in the water per swim.

For all subjects, averages were as follows: total swim distance in 3-month period (miles[km]): 50.3 [81.0] ± 17.6 [28.3] (range 40 [64.4] – 154 [247.8]), average estimated time in the water per swim (minutes): 32.5 ± 7.9 (range 17 -60), age (years): 52.3 ± 10.1 (range: 24-76), BMI (kg/ m2): 25.8 ± 3.4 (range:19.0-37.1), % body fat: 22.6 ± 6.7 (range: 6.9- 42.4), surface/volume ratio(m2/L): .0259 ± .0023 (range: .0200-.0311). Compared to corresponding American 50th percentile values, the % fat of men was modestly lower (Median of the difference =-1.6%; P=0.007); the % fat of women was modestly higher, but not statistically different (Median of the difference =1.7%; P<0.1). There was a marginal nonlinear correlation between % fat and average estimated time in the water per swim (Coef.=0.007; P=0.048). No body composition variable correlated with total swim distance (P>0.1 for all variables).

Our results suggest that recreational cold-water swimmers do not have an increased % body fat when compared to average Americans, and individuals with a wide variety of body types are able to swim recreationally in cold water. The marginal correlation between % fat and average estimated time in the water suggests that leaner swimmers voluntarily limit time in cold water.

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