1 Purpose. The purposes of the present study were to examine: high-intensity running distance 2 during 6-a-side small-sided games (SSGs) and 11-a-side matches (11M) in youth soccer 3 players using speed and metabolic power approaches and; the magnitude of difference 4 between high-intensity running distance calculated with the two approaches. Method. Eleven 5 outfield players (age = 16.3 ± 0.6 years) performed SSGs with three pitch sizes (small SSG 6 (SSGS), medium SSG (SSGM) and large SSG

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... )) and 11M. A Global Positioning 7 System (15 Hz) was employed to calculate total distance covered, distance covered at a speed 8 ≥ 4.3 m•s -1 (TS) and metabolic power of ≥ 20 W·kg -1 (TP). Results. The total distance 9 covered increased from SSGS through to SSGL (P < 0.001) and was greater during 11M and 10 SSGL compared to other SSGs (P < 0.01). TS and TP increased from SSGS (TS vs. TP = 98 ± 11 55 vs. 547 ± 181 m) through to SSGL (538 ± 167 vs. 1050 ± 234 m, P < 0.001). TS and TP 12 during 11M (370 ± 122 vs. 869 ± 233 m) was greater than SSGS (P < 0.001 for both) and less 13 than SSGL (P < 0.05 for both). The magnitude of difference between TS and TP (%) reduced 14 with an increase in pitch size during SSGs and was greater in SSGS (615 ± 404%, P < 0.001) 15 and SSGM (195 ± 76%, P < 0.05) and smaller in SSGL (102 ± 33%, P < 0.01) compared to 16 11M (145 ± 53%). Conclusion. SSGs can replicate the high-intensity demands of 11M and 17 the speed approach underestimates high-intensity demands of SSGs and 11M compared to the 18 metabolic power approach. 19 20 21 22 23