# High-Intensity Interval Training Performed by Young Athletes: A Systematic Review and Meta-Analysis PMID: 30100881 Journal: Frontiers in physiology Published: 2018 Authors: Engel FA, Ackermann A, Chtourou H, Sperlich B ## Question What effects do HIIT and sprint-style interval training have on endurance, anaerobic, and sport performance outcomes in young and adolescent athletes compared with alternative training protocols? ## Summary This review of 24 controlled studies in young athletes found that HIIT was usually shorter than comparison training and may improve some aerobic and sprint-related performance measures. The overall effect sizes did not show clear superiority over alternative sport training, and the evidence applies mainly to already trained youth athletes. ## Population - Healthy young and adolescent athletes across 24 controlled training studies - Sample size: 577 - Age: 9-18 years; mean 15.5 +/- 2.2 years - Sex: Mixed and inconsistently reported across studies - Fitness level: Young athletes - Health status: Healthy athletes; clinical populations excluded ## Methodology - Systematic review and meta-analysis of controlled pre-post trials - Included interventions ranged from 5 days to 26 weeks - Published youth sport training studies - Controlled study design. ## Protocol - Youth athlete HIIT/SIT protocols. - Modality: Mostly running and sport-specific intervals. - Work intervals: Varied; repeated sprints around 3-7 seconds, SIT around 30 seconds, HIIT intervals under 45 seconds to 2-10 minutes. - Recovery: Varied; often short recoveries for repeated sprint training and 2-4 minutes for SIT. - Sets or repetitions: Varied across studies. - Intensity: Often 90-95% HRmax, 90-95% maximal running velocity, above threshold, or all-out. - Session duration: Mean 28 +/- 15 minutes. - Frequency: Mean 2.5 sessions/week. - Program length: Mean 7.5 weeks. - Progression: Varied. - Alternative youth training. - Modality: Small-sided games, continuous endurance training, fartlek, sport training, or other active training. - Intensity: Varied; included lower-intensity continuous training and sport-specific training. - Session duration: Mean 38 +/- 24 minutes. - Program length: Matched to included study designs. - Progression: Varied. ## Outcomes ### VO2peak Status: mixed HIIT showed only a small mean effect size for VO2peak versus alternative training, although average percent increase was larger with HIIT. Mean g=0.10 +/- 0.28; average VO2peak increase 7.2 +/- 6.9% with HIIT versus 4.3 +/- 6.9% with alternatives. ### Threshold performance Status: improved Running speed and oxygen consumption at lactate or ventilatory thresholds improved favorably with HIIT. Reported as large positive effects for threshold-based outcomes. ### Sprint performance Status: improved HIIT was associated with favorable effects on sprint running performance and repeated sprint ability. Sprint running mean g=0.85 +/- 5.95; repeated sprint ability mean g=0.35. ### Change of direction Status: worse/safety concern Change-of-direction ability showed a negative mean effect in the pooled analysis. Mean g=-1.51 +/- 3.8. ### Session time Status: improved HIIT sessions were shorter than alternative training sessions. 28 +/- 15 minutes versus 38 +/- 24 minutes. ## Practical Insights - For youth athletes, HIIT is best treated as a time-efficient conditioning option rather than a universally superior training method. - Sport-specific interval formats and small-sided games may be more relevant than generic shuttle or running HIIT for team-sport athletes. - The app should avoid applying youth-athlete performance findings to general users without clear age, training, and supervision boundaries. ## Limitations - Review-level evidence rather than a single reproducible protocol. - Large variation in interval duration, recovery, intensity, frequency, and sport mode. - No passive control groups in included studies. - Sex-specific and long-term adherence evidence was limited. ## Safety And Adherence - Adverse events were not pooled as a main outcome. - The review highlights overreaching and recovery-stress concerns for young athletes. - The authors recommend youth sport safeguards such as rest days, limited weekly progression, and off-season periods. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/30100881/) (pubmed) - [DOI](https://doi.org/10.3389/fphys.2018.01012) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6072873/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.