# High-Intensity Interval Training Combined with High-Load Strength Training Improves Aerobic Fitness, Match Goals and Match Result during the In-Season Period in Under-19 Soccer Players PMID: 38275981 Journal: Sports Published: 2023 Authors: Thomakos P, Spyrou K, Tsoukos A, Katsikas C, Bogdanis GC ## Question Does in-season high-load strength training combined with HIIT improve aerobic fitness and match outcomes more than a plyometric plus small-sided/tactical-game program in under-19 soccer players? ## Summary In two elite under-19 soccer teams, the team using weekly high-load strength plus running HIIT improved Yo-Yo IR2 performance, estimated VO2max, late-match scoring, and match results across the in-season period, while the comparison team using plyometrics and small-sided/tactical games did not show similar aerobic gains. The nonrandom two-team design limits causal certainty. ## Population - Elite under-19 male soccer field players from two Greek Super League teams - Sample size: 29 - Age: HIIT 17.8 +/- 0.6 years; SSG 18.0 +/- 0.6 years - Sex: Male - Fitness level: Elite youth soccer players - Health status: Field players without excluded injury-related absence; no medication or supplement use reported ## Methodology - Nonrandom two-team comparative training study - 11-12 weeks in-season - Elite under-19 Greek Super League soccer teams - Controlled study design. ## Protocol - High-load strength plus HIIT. - Modality: Gym strength training followed by running intervals. - Work intervals: 15 seconds at 110% vVO2max. - Recovery: 15 seconds passive recovery; 3 minutes between two 6-minute sets. - Sets or repetitions: Two 6-minute interval sets; strength exercises used 8, 6, 4, and 2 repetitions as load increased from 80% to 95% 1RM. - Intensity: Running at 110% vVO2max after high-load strength at 80-95% 1RM. - Session duration: Part of a 50-90 minute daily team training session; HIIT block about 15 minutes including between-set recovery. - Frequency: 1 session per week for the strength plus HIIT component. - Program length: In-season intervention across about 11-12 weeks. - Progression: Strength repetitions decreased as load increased; interval speed set from vVO2max. - Plyometric plus SSG/tactical games. - Modality: Plyometrics, small-sided games, and tactical games. - Work intervals: SSG and tactical games about 8 minutes each. - Recovery: 3 minutes recovery between small-sided and tactical games. - Sets or repetitions: Plyometrics plus 4v4-6v6 SSG and 7v7-10v10 tactical games. - Intensity: Team training intensity not directly matched to HIIT prescription. - Session duration: About 90 minutes on day 2 within normal 50-90 minute team training. - Frequency: 1 comparable weekly session within regular team training. - Program length: In-season intervention across about 11-12 weeks. - Progression: Tactical/game content followed team training plan. ## Outcomes ### Yo-Yo IR2 Status: improved The strength plus HIIT group improved Yo-Yo IR2 distance, while the SSG comparator did not. HIIT 902.5 +/- 147.5 to 1092.5 +/- 155.8 m, p=0.0002, d=1.25; post HIIT > SSG p<0.001. ### VO2max Status: improved Estimated VO2max and vVO2max improved only in the strength plus HIIT group. VO2max 57.6 +/- 2.0 to 60.2 +/- 2.1 mL/kg/min; vVO2max 17.4 +/- 0.5 to 18.1 +/- 0.5 km/h; post-group effects p<0.001. ### Goals Status: improved The HIIT team scored more late-match goals during the intervention period. Goals in last 30 minutes increased from 0.36 +/- 0.50 to 1.27 +/- 0.90, p=0.040, d=1.25. ### Match result Status: improved The HIIT team's match results improved during the intervention period. Wins increased from 5/11 before to 9/11 during intervention; league position improved from 7th to 3rd. ## Practical Insights - A weekly in-season session pairing high-load strength with short 15:15 intervals may improve high-intensity endurance in elite youth soccer. - Late-match scoring outcomes are promising but vulnerable to team, opponent, and tactical confounding. - Nonrandom team-level comparison should not be treated as proof that the protocol caused match results. ## Limitations - Nonrandom comparison of two different teams. - No GPS or external-load data. - No strength or power tests due coach constraints. - Match outcomes may be affected by tactics, opponents, technical factors, and randomness. - Only elite under-19 male players. ## Safety And Adherence - Players missing more than 20% of training days because of injuries were excluded; the NXML sections reviewed did not report intervention adverse events. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/38275981/) (pubmed) - [DOI](https://doi.org/10.3390/sports12010002) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10819200/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.