Facial immersion bradycardia in teenagers and adults accustomed to swimming

We compared heart rate and breath-hold duration during facial immersion in teenagers, 11–14 years (N=6), 15–18 years (N=6) and adults, 33–48 years (N=11). The subjects were members of a competitive swimming club, and were familiar with facial immersion. In contrast to the results of a previous study (J. Appl. Physiol. 63 (1987) 665) in which naïve subjects were used, the 11–14 group were able to breath-hold as long as adults (mean±SE, 47±6 vs. 46±4 s). This allowed time for the full development of bradycardia. Pre-immersion heart rate was significantly higher in young teens than in adults (100±4 vs. 78±3 b.p.m.). Heart rate after 30 s of head immersion was statistically identical (young teens, 65±5 b.p.m.; adults, 64±3 b.p.m.). Therefore, both the percentage reduction from pre-immersion rate and rate of fall in heart rate were greater in 11–14-year-olds than in adults. Oxygen loading increased breath-hold time in all groups, and slowed the onset of bradycardia in adults and older teens, but not in the 11–14-year-old group, during the first 10 s after immersion. We conclude that breath-hold time in teenagers is influenced by familiarity with underwater breath-holding. The resulting cardiovascular adjustments in 11–14-year-olds are intrinsically at least as intense as those in adults and seem to have a faster onset.