1The purpose of this study was to examine the natural development of the mechanical 2 features of sprint performance in relation to maturation within a large cohort of boys. 3Three hundred and thirty-six boys (11-15 years) were assessed for sprint performance 4 and maturation. Maximal speed, stride length (SL), stride frequency (SF), flight time 5 (FT) and contact time (CT) were assessed during the sprint. Five maturation groups 6 (G1-5) were established based on age from peak height velocity (PHV). G1 were 7 early pre-PHV, G2 pre-PHV, G3 approaching-PHV, G4 around-PHV and G5 post-8PHV. There was no difference in maximal speed between G1-3 but those in G4 and 9 G5 were significantly faster (p<0.05) than G1-3. Significant increases (p<0.05) in SL 10 were observed across G1-3, but no significant (p>0.05) improvements in SL were 11 observed between boys G4-5. SF decreased whilst CT increased (both p<0.05) 12 between G1-2, but no changes were observed for either variable between boys in G3-13 5. While boys pre-PHV (G1-3) improved their SL concomitant decreases in SF and 14 increases in CT prevented them from improving maximal speed. Maximal sprint 15 speed appears to develop around and post-PHV as SF and CT begin to stabilize, with 16 improvements in maximal sprint speed in maturing boys underpinned by improving 17 SL.

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It has been suggested that agility is a key requirement for optimal performance in 2 sport (19). Research has highlighted the importance of agility for success in lacrosse 3 (11), basketball (9) and soccer (38), all of which are intermittent and multi-directional 4 sports in nature, requiring rapid changes of direction in response to a variety of 5 stimuli. Additionally, it has been established that agility is a fitness quality that can 6 distinguish between levels of playing ability in a range of different sports (37,14,17). 7Despite the significance of agility for sports performance, it was not prominent in 8 early long-term athlete development models, and has recently been highlighted as one 9 of the most under-researched fitness components within the paediatric literature (24). 10However, with the recent evolution of the Youth Physical Development (YPD) model 11 (24), the need for a structured and logical approach to developing agility throughout 12 childhood and adolescence has been highlighted.

Purpose:The purpose of the current study was to assess the reliability of a new protocol that examines different components of agility using commercially available timing gates.Methods:Seventeen physically active males completed four trials of a new protocol, which consisted of a number of 10-m sprints. Sprints were completed in a straight line or with a change of direction after 5 m. The change of direction was either planned or reactive, with participants reacting to a visual light stimulus.Results:There was no systematic bias in any of the measures, although random variation was reduced in the straight acceleration and planned agility when considering only the fnal pair of trials, with mean coefficients of variation (CV) of 1.6% (95%CI, 1.2% to 2.4%) and 1.1% (0.8% to 1.7%), respectively. Reliability of reactive agility remained consistent throughout with mean CVs of approximately 3%. Analyses revealed a high degree of common variance between acceleration times and both planned (r2 = .93) and reactive (r2 = .83) agility, as well as between the two agility protocols (r2 = .87).Conclusion:Both planned and reactive agility could be measured reliably. Protocol design and use of a light stimulus in the reactive test emphasize physical abilities comparable with other test measures. Therefore, inclusion of a reactive light stimulus does not appear to require any additional perceptual qualities.