Kinetmatic characteristics of resisted sprinting
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In recent years, the adoption of resisted sprint training (RST) has surged as a method to enhance sprint performance (SP) in various athletic domains [1-3]. Given the central role of sprinting in optimising athletic performance, RST has gained prominence as a potential tool applicable to a wide range of athletes. Coaches seeking to improve SP typically target two primary aspects: enhancing force production and refining technical execution . The integration of external resistance into sprinting presents an opportunity to address both goals simultaneously, potentially offering a more 'sport-specific' form of resistance training. While the relationship between resisted sprints and SP has been explored in invasion-based team sports and track and field athletes, there remains a lack of clarity around how the addition of load influences running kinematics, what physical characteristics influence the kinematics adopted under loaded conditions, or how coaches interpret potential kinematic changes to inform load prescription during RST. The overarching aims that guided this research were: • To explore coaches' perceptions of how RST affects kinematics and their methodologies for prescribing RST. • To examine the reliability of an isotonic sprint device. • To examine the impact of load and sporting population on kinematics during RST. • To investigate if an athlete’s strength characteristics influences kinematic changes during RST. The main findings of this research were: 1) Coaches unanimously acknowledged the value of RST in enhancing SP, drawing from their practical experiences and insights from scientific literature. However, trends emerged: coaches often favoured the use of body mass (%BM) as a load indicator over velocity decrement (%Vdec) due to its simplicity. Additionally, modalities of RST were frequently chosen based on practicality and availability rather than strict adherence to scientific literature. 2) The Exer-Genie produces fair to good within-session reliability but revealed less reliable between-session measurements. 3) Loading introduced significant changes to hip, knee, ankle, and trunk angle for touch-down and toe-off for the acceleration and maximum velocity phase (p<0.05). Knee, hip, and ankle angles became more flexed with increasing load, for touch-down and toe-off, for all groups during the acceleration phase, and trunk lean increased with increasing loading conditions. Although there were minimal differences observed between groups, RSS resulted in xiii acute changes in sprint kinematics which differed based on the phase of the sprint and magnitude of the load. 4) Strength characteristics could explain the variance observed in athlete’s kinematics under loading conditions employed in study 3. Moreover, noteworthy negative correlations between strength metrics and changes in joint angles (hip, knee, and trunk) under different loading conditions were found. Several practical applications may be offered from the findings. There is an existing gap between scientific research and practical coaching application in the context of RST. Considering the linear and dependable relationship between load and velocity, coaches are encouraged to tailor sled loads individually. Rather than applying a uniform load as a fixed %BM to all athletes, this approach involves prescribing loads based on the specific desired decrement in velocity for each athlete. When employing isotonic sprint devices, coaches should be aware of its reliability characteristics. While it offers fair to good within-session reliability, its between session reliability is less dependable. This suggests that the Exer-Genie may be suitable for short-term training interventions but should be used cautiously for long term training programs. Coaches should recognise that loading in RST significantly alters sprinting kinematics, particularly in hip, knee, ankle, and trunk angles during both the acceleration and maximum velocity phases and an athlete’s strength characteristics have an influence on their kinematics during RST. These findings empower coaches and practitioners to design more effective and tailored training programs, advancing the realm of sprinting performance enhancement in both athletic and team sport contexts.
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