Table 3. Within-session reliability for PF and selected RFD across age categories. Variable Day Mean ± SD ICC (95% CI) ICC Interpretation CV (%) (95% CI) SEM (95% CI) PF (All) 1 1722.1 ± 716.1 0.97 (0.96-0.98) Excellent 4.6 (3.8-5.3) 17.94 (16.15-19.74) 2 1891.3 ± 706.7 0.98 (0.97-0.99) Excellent 4.3 (3.5-5.1) 12.46 (11.21-13.70) 3 1856.9 ± 730.3 0.97 (0.95-0.98) Excellent 4.9 (3.9-5.9) 22.97 (20.67-25.26) RFD50 (All) 1 1952.7 ± 2171.9 0.74 (0.63-0.82) Moderate 53.4 (47.5-59.3) 562.18 (505.96-618.39) 2 2455.0 ± 2039.2 0.55 (0.39-0.68) Moderate 49.6 (42.3-57.0) 921.58 (829.42-1013.73) 3 2714.5 ± 2162.0 0.35 (0.18-0.53) Poor 49.1 (41.8-56.4) 1403.20 (1262.88-1543.52) RFD250 (All) 1 2551.8 ± 1441.3 0.85 (0.78-0.90) Good 19.4 (15.3-23.4) 218.14 (196.33-239.96) 2 3075.9 ± 1551.8 0.86 (0.78-0.91) Good 17.4 (13.2-21.7) 221.53 (199.37-243.68) 3 3131.0 ± 1469.4 0.90 (0.85-0.94) Excellent 14.5 (11.3-17.6) 140.38 (126.34-154.42) PF (U12) 1 946.2 ± 176.5 0.96 (0.90-0.98) Excellent 3.5 (2.3-4.7) 7.65 (6.88-8.41) 2 1056.0 ± 191.7 0.85 (0.69-0.95) Good 5.4 (2.6-8.2) 27.73 (24.96-30.51) 3 994.7 ± 159.4 0.91 (0.79-0.97) Excellent 4.2 (2.7-5.8) 14.24 (12.82-15.67) RFD50 (U12) 1 1088.9 ± 673.8 0.41 (0.13-0.69) Poor 45.2 (36.9-53.5) 394.38 (354.94-433.82) 2 1381.8 ± 895.1 0.38 (0.06-0.70) Poor 46.3 (30.6-62.1) 551.17 (496.05-606.29) 3 1429.3 ± 868.9 0.15 (0.00-0.53) Poor 53.9 (38.9-68.9) 730.37 (657.33-803.41) RFD250 (U12) 1 1298.0 ± 510.4 0.75 (0.53-0.88) Moderate 18.0 (9.3-26.8) 128.49 (115.64-141.34) 2 1726.2 ± 544.2 0.55 (0.23-0.80) Moderate 17.7 (7.0-28.4) 242.08 (217.88-266.29) 3 1591.7 ± 540.6 0.65 (0.35-0.86) Moderate 20.5 (11.4-29.5) 187.04 (168.34-205.75) PF (U15) 1 1788.4 ± 430.6 0.93 (0.87-0.96) Excellent 4.7 (3.5-6.0) 29.71 (26.74-32.68) 2 1941.7 ± 504.9 0.98 (0.96-0.99) Excellent 3.4 (2.7-4.1) 11.68 (10.51-12.85) 3 1875.5 ± 501.6 0.95 (0.90-0.98) Excellent 5.2 (3.8-6.6) 27.25 (24.53-29.98) RFD50 (U15) 1 1624.4 ± 1417.3 0.49 (0.26-0.70) Poor 59.7 (51.1-68.3) 718.45 (646.61-790.30) 2 2462.0 ± 1790.3 0.40 (0.15-0.63) Poor 51.7 (41.1-62.4) 1069.01 (962.11-1175.91) 3 3107.3 ± 2260.6 0.31 (0.08-0.59) Poor 44.5 (34.5-54.4) 1570.90 (1413.81-1727.99) RFD250 (U15) 1 2491.3 ± 931.3 0.60 (0.39-0.77) Moderate 20.6 (14.6-26.6) 368.73 (331.85-405.60) 2 2954.5 ± 1129.4 0.69 (0.50-0.83) Moderate 18.6 (12.5-24.6) 345.41 (310.87-379.95) 3 3186.7 ± 1081.9 0.84 (0.70-0.92) Good 11.9 (7.9-15.8) 175.49 (157.94-193.04) PF (U18) 1 2591.7 ± 472.1 0.87 (0.73-0.95) Good 5.6 (3.8-7.4) 59.23 (53.31-65.15) 2 2632.8 ± 403.3 0.89 (0.75-0.96) Good 5.0 (4.0-6.0) 44.26 (39.83-48.69) 3 2626.8 ± 427.3 0.80 (0.59-0.92) Good 5.2 (2.5-7.9) 83.31 (74.97-91.64) RFD50 (U18) 1 3696.3 ± 3381.2 0.75 (0.50-0.90) Moderate 51.7 (35.2-68.1) 846.19 (761.57-930.81) 2 3515.4 ± 2679.1 0.54 (0.22-0.79) Moderate 49.0 (32.2-65.8) 1209.39 (1088.45-1330.33) 3 3262.5 ± 2381.9 0.22 (0.00-0.58) Poor 52.2 (34.5-70.0) 1846.93 (1662.24-2031.62) RFD250 (U18) 1 4280.6 ± 1322.5 0.66 (0.37-0.86) Moderate 18.8 (10.5-27.0) 441.83 (397.65-486.01) 2 4651.2 ± 1525.7 0.80 (0.58-0.92) Good 15.1 (7.1-23.1) 310.25 (279.22-341.27) 3 4468.7 ± 1241.8 0.78 (0.54-0.91) Good 13.2 (8.2-18.1) 269.80 (242.82-296.78) PF = peak force; RFD = rate of force development; SD = standard deviation; ICC = intraclass correlation coefficient; CI = confidence interval; CV = coefficient of variation; SEM = standard error of measurement.