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    Respiratory responses and isocapnic buffering phase in child and youth soccer players during an incremental exercise test
    (Frontiers Media SA, 2024) Korkmaz Eryılmaz, Selcen; Karakaş, Selçuk; Boyraz, Cumhur; Günaştı, Özgür; Kılcı, Abdullah; Özdemir, Çiğdem; Özgünen, Kerem; Koç, Muhammed; Adaş, Ümit; Kurdak, Sadi
    Purpose: This study investigated the respiratory response and isocapnic buffering (IB) phase during an incremental exercise test to exhaustion in 16 child soccer players (11.9±0.9 years) and 18 youth soccer players (18.2±2.9 years). Methods: The IB phase was calculated as the difference in oxygen uptake (VO2) between the respiratory compensation point (RCP) and metabolic threshold (MT) and expressed in either absolute or relative values. Results: The maximal oxygen uptake (VO2max) was higher in youth players than in child players. For youth players, VO2max was measured at 55.9 ± 3.6 mL min?1 kg?1 and 74.9 ± 4.8 mL min?1 kg?0.75, while for child players, VO2max was 50.8 ± 4.1 mL min?1 kg?1 and 67.2 ± 6.1 mL min?1 kg?0.75 (p < 0.001). MT and RCP occurred at 69.8 ± 6.7% and 90.9 ± 6.9% of VO2max in child players and at 73.9 ± 5.1% and 91.5 ± 4.5% of VO2max in youth players, respectively. The two groups had no significant difference (p > 0.05). Absolute IB (10.6 ± 2.8 vs 9.7 ± 3.1 mL min?1 kg?1), relative IB (23.1 ± 5.7 vs 19.1 ± 6.1), and the ratio of RCP VO2 to MT VO2 (1.3 ± 0.09 vs 1.24 ± 0.09) were similar in child and youth players (p > 0.05). There was no difference in minute ventilation (V?E, mL min?1 kg?1) and respiratory exchange ratio during exercise between the two groups (p > 0.05). During exercise, respiratory frequency, ventilatory equivalent for carbon dioxide (VE/VCO2) and oxygen (VE/VO2), VE/VCO2 slope, end-tidal O2 pressure were higher in child players than in youth players, while tidal volume (L kg?1), O2 pulse, and end-tidal CO2 pressure were lower (p < 0.05). Conclusion: Despite differences in aerobic capacity and ventilatory response to exercise, child players showed similar IB phase as youth players. Although child players have lower ventilation efficiency than youth players, the higher ventilation response for a given VCO2 may provide an advantage in regulating acid-base balance during intense exercise.
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    The relationship between lower limb stiffness and running economy in child soccer players
    (Sociedade Brasileira de Medicina do Esporte, 2023) Karakaş, Selçuk; Korkmaz Eryılmaz, Selcen; Boyraz, Cumhur; Kılcı, Abdullah; Günaştı, Özgür; Özdemir, Çiğdem; Özgünen, Kerem; Kurdak, Sadi
    Introduction: Lower limb stiffness has been shown to be associated with running economy (RE) in adults, but this relationship in children remains unclear. Objectives: The purpose of this study was to investigate the relationship between lower limb stiffness, RE, and repeated-sprint ability in child soccer players. Methods: Twenty-eight male child soccer players (mean age 11.8 +/- 0.9 years) participated in the study. RE was determined by measuring the steady-state oxygen uptake (ml/min/kg) at submaximal running speeds of 8 and 9 km/h. Vertical and leg stiffness were calculated from the flight and contact time data obtained during two submaximal running tests. Additionally, vertical stiffness was measured during the maximal and submaximal hopping tests. All participants performed the repeated sprint test consisting of 10 x 20-m all-out sprints interspersed with 20-s active recovery. Results: During both su bmaxima I running tests, vertical (r= -0.505 to -0.472) and leg stiffness (r= -0.484 to -0.459) were significantly correlated with RE (p< 0.05). Maximal (r= -0.450) and submaximal hopping stiffness (r= -0.404) were significantly correlated with RE at 8 km/h (p< 0.05). Maximal hopping stiffness was significantly correlated with the best sprint time (r= -0.439) and mean sprint time (r= -0.496) (p< 0.05). Vertical (r= -0.592 to -0.433) and leg stiffness (r= -0.612 to -0.429) at 8 and 9 km/h and submaximal hopping stiffness (r= -0.394) were significantly correlated with the fatigue index (p< 0.05). Conclusions: Current findings indicate that the lower limb stiffness may be an important determinant of both RE and repeated-sprint ability in child soccer players.