Table 5. Study design and sample characteristics. Author (date) Country Study design Participants Intervention Maturity assessment N (sex) Age (years) Competitive Level Compared groups Type Duration Abbott et al. (2019) UK Repeated-measures crossover 25 M 12.7 ± 1.0 Soccer academy players BB vs. CA 11v11 4 x 20 min 2 matches (1 CA + 1 BB) Khamis–Roche (1994) method Arede et al. (2024) Portugal Repeated-measures crossover 116 M U13: 12.2±0.3 U14:13.2±0.4 Soccer academy players BB vs. CA 7v7 20 min 8 matches (4 CA + 4 BB) Khamis–Roche (1994) method Lüdin et al. (2022) Switzerland Randomized cross-over repeated 65 M 11.7-13.7 Elite youth soccer clubs players BB vs. CA 9v9 2 x 35 min 2 matches (1 CA + 1 BB) Mirwald et al. (2002) method Romann et al. (2020) Switzerland Repeated-measures crossover 60 M, 2 F U13: 12.2±0.3 U14: 13.2±0.4 Elite youth soccer clubs players BB vs. CA 9v9 20 min 8 matches (4 CA + 4 BB) Mirwald et al. (2002) method Towlson et al. (2021a) UK Repeated measures 32 M 12.9 ± 0.9 Soccer academy players BB vs. MM 4v4 SSGs 5 min, 96 matches (48 MM + 48 BB) Khamis–Roche (1994) method Towlson et al. (2021b) UK Repeated measures 72 M 11-14 Soccer academy players BB vs. MM 4v4 SSGs 5 min, 15 matches (5 MM + 10 BB) Khamis–Roche (1994) method; Fransen et al. (2018) method Towlson et al. (2022) UK Repeated measures 72 M 11-14 Soccer academy players BB vs. MM 4v4 SSGs 5 min 15 matches (5 MM + 10 BB) Khamis–Roche (1994) method; Fransen et al. (2018) method Salter et al. (2023) UK Repeated measures 55 M 13.8 ± 1.4 Soccer academy players BB vs. CA 6v6 SSGs, 5 min 30 matches (15 CA + 15 BB) Khamis–Roche (1994) method Salter et al. (2025) UK Repeated-measures crossover 139 M 12-16 Junior Premier League players BB vs. CA 11v11 20 min 6 matches (3 CA + 3 BB) Khamis–Roche (1994) method King et al. (2025) UK Cross-sectional repeated-measures 53 M 13.4 ± 0.9 Soccer academy players BB vs. MM 4v4, 5v5, and 6v6 SSGs 5 min 72 matches (36 MM + 36 BB) Fransen et al. (2018) method Robinson et al. (2025) UK Cross-sectional repeated-measures 118 M 13.7 ± 0.8 Junior Premier League players BB vs. CA 11v11 20 min 6 matches (3 CA + 3 BB) Khamis–Roche (1994) method De Macedo et al. (2025) Brazil Repeated measures 20 M 11.8 ± 1.15 Soccer academy players BB vs. CA 5v5 SSGs 4 x 5 min 6 matches (2 CA + 4 BB) Mirwald et al. (2002) method Barrett et al. (2022) UK Repeated measures 32 M 12.9 ± 0.9 Soccer academy players BB vs. MM 4v4 SSGs 5 min 12 matches (6 CA + 6 BB) Khamis–Roche (1994) method Abbreviations: N, number; M, male; F, female; BB, Bio-banded; CA, chronological age; MM, Mixed-maturity (surrogate control); SSGs, small-sided games.