Effect of Puberty on Gas Exchange Threshold in Untrained Boys and Girls

Abstract

Trained boys increase absolute, relative, and gas exchange threshold (GET) as a percent of VO2max (GET%VO2max) following puberty. Also, trained girls increase absolute GET, but not GET%VO2max. It is unknown if these changes exist in untrained boys and girls pre- to post-puberty. PURPOSE: The purpose of this longitudinal study was to determine if differences exist in GET pre- to post-puberty in untrained subjects. A secondary purpose was to determine if sex differences were present. We hypothesized that following puberty 1) absolute and relative GET would increase and 2) no sex differences would be present in absolute or relative GET in untrained subjects. METHODS: 17 untrained subjects (B: 8; G: 9) were recruited pre- (9.8 ± 0.8 yrs) and post-puberty (14.8 ± 1.0 yrs) from a previously published study (Swain, et al. 2010). Subjects performed an incremental exercise test to exhaustion using a cycle ergometer to determine VO2max. Subjects then rested for 15 minutes and performed a constant load exercise bout at 105% VO2max to exhaustion to validate VO2max. GET was determined using the V-Slope method. Maturation was determined via Tanner stages. RESULTS: Maturation status increased for boys and girls following puberty (p<0.05); however there were no differences (p>0.05) between boys and girls post-puberty (B: 4.1 ± 0.6 stage; G: 3.8 ± 0.7 stage). Absolute GET increased pre- to post-puberty (p<0.05). Absolute GET was higher in boys than girls pre-puberty (B: 0.85 ± 0.10 L/min; G: 0.61 ± 0.13L/min) and post-puberty (B: 1.78 ± 0.41 L/min; G: 1.20 ± 0.24L/min); however change in absolute GET was not different (p>0.05) between boys and girls. Relative GET was not different (p>0.05) pre- to post-puberty. Relative GET was higher in boys than girls pre-puberty (B: 26.9 ± 5.6 ml/kg/min; G: 18.6 ± 3.5 ml/kg/min) and post puberty (B: 28.4 ± 4.5 ml/kg/min; G: 20.5 ± 5.2 ml/kg/min). There were no differences (p>0.05) in GET%VO2max pre- to post-puberty between sexes. DISCUSSION: These data suggest absolute GET increases with increasing body weight during puberty; however, relative GET and GET%VO2max do not change in untrained subjects. At pre- and post-puberty, untrained boys have a higher absolute and relative GET than untrained girls; however, no sex differences existed in the change in GET during puberty.