Introduction: It has been reported that endurance exercise training improves cardiorespiratory fitness levels (e.g., peak oxygen uptake: VO2peak) and mitochondrial function. On this matter, one study has shown that ventilation efficiency may be directly related to salivary mitochondrial DNA copy number (as an index of mitochondrial content) in healthy subjects with relatively low aerobic capacity (33 ml/kg/min VO2peak). However, the causal relationship for these indices in adolescent athletes is not yet clear. The purpose of this study was to clarify the relationship between ventilatory efficiency and salivary mitochondrial DNA copy number in aerobically active adolescent athletes.
Methods: Adolescent male and female athletes with similar fitness levels (Males; n=12, age: 15.2±1.6 years, VO2peak [peak oxygen uptake relative to fat free mass]: 77.2±9.8 ml/kg FFM/min; Females; n=11, age: 15.1±0.8 years, VO2peak: 72.3±5.7 ml/kg FFM/min [mean±SD]) were recruited as the participants. All participants executed an incremental cycling exercise until volitional exhaustion to measure ventilatory efficiency, including ventilatory threshold and peak oxygen uptake on an electromagnetically braked cycle ergometer. Each participant conducted a cycling exercise at an initial power output of 0 W for three minutes, which was increased by 25 W every 1 min until exhaustion. Pedaling frequency was 60 rpm. Expired gases and heart rate were continuously analyzed with using a respiratory monitor system and electrocardiograph. Ventilatory efficiency was assessed with the lowest minute ventilation per unit carbon dioxide production (VE/VCO2). Prior to maximal cycling exercise, salivary samples were collected for the later analysis of salivary mitochondrial DNA copy number quantified with real-time polymerase reaction. Correlation analyses were consequently performed to clarify the relationship between ventilatory efficiency and salivary mitochondrial copy number.
Results: No significant correlation was observed between ventilation equivalent and salivary mitochondrial DNA copy number in adolescent male (p=0.379) and female athletes (p=0.672).
Discussion: Previous investigation has shown that ventilatory efficiency may correlate with salivary mitochondrial DNA copy number in healthy people with relatively low aerobic fitness. On the other hand, the results of our study showed no significant differences between these indicators. This disparity may partially be due to the relatively higher aerobic fitness of the participants (VO2peak values: 55 ml/kg/min and 72 ml/kg FFM/min) in this study than in the previous study. In conclusion, the findings of this study suggest that there may be no direct link between ventilation efficiency and salivary mitochondrial DNA copy number in aerobically fit adolescent males and females.
Impact and application to the field: If a method of assessing fitness levels could be established using saliva, based on biomarkers of the mitochondrial function system, it could be a useful indicator for checking the physical condition of adolescent athletes.
We have no conflict of interest of relevance to the submission of this abstract.
