A systematic review of velocity and accelerometer thresholds in soccer

Background: Velocity and acceleration have been highlighted as the most critical variables in soccer. However, there is a consensus gap in defining different levels of effort. Aim: The purpose of this systematic review is to identify if it is a consensus in those articles that proposed a threshold to establish (i) movement intensity at different velocities using tracking systems and (ii) accelerations using inertial measurement units, classifying the justification methods. Method: A systematic review of Cochrane Library, EBSCO, PubMed, Scielo, Scopus, SPORTDiscus, and Web of Science databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: Of the 1983 studies initially identified, 39 were thoroughly reviewed, and their outcome measures were extracted and analyzed. Conclusion: The 40-m maximal linear sprint and physical fitness tests are the most commonly used methods to generate speed and acceleration thresholds in soccer. However, there is substantial heterogeneity in locomotor test procedures and workload zones established from these performance data. Studies diverged when considering the use of individualized thresholds. The low sampling rate (≤ 10 Hz) in the publications calculating acceleration and deceleration demands should also be interpreted cautiously. The present study collected evidence to help professionals process and interpret external load data. More interventional work is needed to confirm the value of fitness-based individualizations.