Maturity Related Differences in Systemic and Localized Fatigue Thresholds amongst Adolescent Male Athletes

Fatigue thresholds (FTs) can be determined via systemic pulmonary measurements such as oxygen consumption (VO 2 ), carbon dioxide production (VCO 2 ), and ventilation (VE) or through localized muscular measurements such as neuromuscular activation and oxygenation. Systemic and localized FT measures are non‐invasive techniques, which make them ideal tests for adolescents. During puberty, a gradual shift occurs in the metabolic response to exercise from predominantly aerobic metabolism to a balance between aerobic and anaerobic metabolic systems. However, limited research has examined the maturity related differences in systemic and localized FTs amongst adolescent male athletes. PURPOSE To examine the maturity related differences in systemic pulmonary and localized neuromuscular and oxygenation FTs amongst adolescent male athletes. METHODS Twenty‐six adolescent male athletes (age 11–17 yrs) volunteered with verbal assent and written parental consent to complete two incremental ramp exercise tests on a cycle ergometer separated by at least 48 hours. Three systemic FTs, gas exchange threshold (GET), ventilatory threshold (VT), and respiratory compensation point (RCP) were calculated from VCO 2 and VE. Three localized FTs, neuromuscular fatigue threshold (NFT), deoxyhemoglobin breakpoint (HHbBP), and oxygenation breakpoint (OxBP) were calculated from electromyography and near infrared spectroscopy signals from the right vastus lateralis. Data from the second test were plotted versus VO 2 and 30‐second moving averages were calculated. All FTs were determined using the maximal distance method and expressed relative to VO 2 max. All participants were separated according to the number of years from peak height velocity (PHV), an estimation of somatic maturity status, into PRE‐ (<−1yr), PERI‐ (between −1 to +1yr) and POST‐ (>+1yr) PHV groups. Differences between maturational groups were assessed with magnitude based inferences. RESULTS Group means and differences between groups are presented in Table 1. All systemic and localized FTs occurred at Very Likely or Likely greater relative intensities in PRE compared to POST. Only systemic FTs occurred at Very Likely or Likely greater relative intensities in PERI compared to POST, with Unclear differences for all localized FTs. When comparing PRE and PERI, only HHbBP and OxBP occurred at Likely greater relative intensities in PRE, with Unclear differences for all other FTs. CONCLUSIONS Systemic FTs occurred at lower relative intensities in POST when compared to PRE and PERI; while localized FTs were not different between PERI and POST. Furthermore, systemic FTs and NFT did not occur at different relative intensities in PRE and PERI; however, HHbBP and OxBP occurred at greater relative intensities in PRE. Therefore, maturity related differences in FTs do exist amongst adolescent males, which may represent the change in the metabolic response to exercise that occurs with maturation. The disparity in the maturity related differences between systemic and localized FTs may indicate that maturation affects the muscular response to exercise prior to affecting the pulmonary response. 1 Mean ± SD in fatigue thresholds (%VO 2 max) for each maturational group.Fatigue Threshold PRE PERI POSTSystemic Pulmonary GET 60.86 ± 5.43 * 61.25 ± 5.33 * 52.92 ± 5.73 VT 68.64 ± 1.59 * 68.05 ± 2.96 # 63.70 ± 5.86 RCP 82.33 ± 4.96 * 82.66 ± 4.12 * 76.11 ± 6.34 Localized Muscular NFT 80.26 ± 4.20 # 77.20 ± 5.68 74.61 ± 8.14 HHbBP 80.02 ± 6.83 # $ 72.89 ± 10.50 74.68 ± 7.97 OxBP 64.07 ± 10.55 # $ 55.54 ± 8.75 55.51 ± 10.73* Very Likely greater than POST; # Likely greater than POST; $ Likely greater than PERI