The Effects of Sprint Interval Training and Maturity Status on Metabolic and Neuromuscular Fatigue Thresholds in Adolescents

Purpose: To examine the maturity-related differences in the adaptations to systemic and localized fatigue thresholds (FTs) in response to sprint interval training (SIT) amongst adolescent male athletes. Methods: Twenty-seven adolescent male athletes, 11-17 years of age, completed pre-testing, six weeks of SIT, and post-testing. Participants were grouped according to their number of years from peak height velocity (PHV), an estimation of somatic maturity status, into PRE ( \u3c -1.5yr), PERI (between -1.5 to +1.5yr) and POST ( \u3e +1.5yr) PHV groups. Each testing session consisted of a ramp exercise protocol on a cycle ergometer. During the protocol, three systemic FTs, gas exchange threshold, ventilatory threshold, and respiratory compensation point were calculated from gas exchange and ventilatory parameters. Also, three localized FTs, neuromuscular fatigue threshold (NFT), deoxyhemoglobin breakpoint (HHbBP), and oxygenation deflection point (OxDP) were calculated from electromyography (NFT) and near-infrared spectroscopy signals (HHbBP and OxDP) from the vastus lateralis of both legs. Data were plotted versus oxygen consumption and 30-second moving averages were calculated. All FTs were determined using the maximal distance method. Localized FTs were averaged between the two legs. The six weeks of SIT consisted of repeated 20-second all-out sprints on a cycle ergometer against a load equivalent to 7.5% of body mass with 4-minute rest periods. Maturity-related differences to the adaptations to SIT were assessed with mixed-factorial ANOVA and magnitude-based inferences. Results: During training, POST and PERI completed significantly greater relative work (p=0.003 and p=0.002, respectfully) and peak power (p=0.025 and p=0.023, respectfully) per session than PRE. Furthermore, POST achieved significantly greater peak rotations per minute than PRE (p=0.001) and PERI (p=0.042) during the first training session. No significant group-time interactions existed for absolute V?O2max (p=0.386), relative VO2max (p=0.341) or maximum workload (p=0.593). However, there was a significant group-time interaction (p=0.030) for FTs, with POST having significantly greater changes than PRE (p=0.026) and PERI (p=0.023), and was the only group to experience a significant improvement in FTs from training (p \u3c 0.001). In addition, magnitude based inferences revealed that POST had Likely improvements in all measures of maximal aerobic performance, while PERI only had Likely improvements in maximum workload and PRE experienced Trivial changes. Furthermore, all measured FTs experienced Likely or Very Likely improvements amongst POST; however, PRE and PERI only had improvements in NFT and HHbBP. Conclusion: SIT improved maximal aerobic performance and FTs in POST, but had limited affects in PRE and PERI. The maturity-related differences in the adaptations to SIT may be due to the differences in performance during the training program or underlying physiological changes that occur with maturation