Can complex contrast training interventions improve aerobic endurance, maximal strength, and repeated sprint ability in soccer players? A systematic review and meta-analysis

This systematic review and meta-analysis aimed to assess the effects of complex contrast training (CT) on aero- bic endurance, maximal strength, and repeated sprint ability (RSA) in soccer players. After an electronic search, nine peer-reviewed articles were considered, including soccer players from junior to professional-level (age 14 – 23 years). One study was conducted during the pre-season, seven studies during the in-season, and one study during the off-season period of a competitive schedule. The studies included were of moderate to high meth- odological quality (PEDro scale) and incorporated CT with soccer practice. Large significant improvements (ES = 1.30; 95% CI = 0.61 – 2.00; p < 0.001; I2 = 80.6%) for maximal strength, and small non-significant improve- ments for aerobic endurance (ES = 0.33; 95% CI = -0.19 – 0.85; p = 0.209; I2 = 0.0%) and RSA (ES = 0.32; 95% CI = -0.12 – 0.75; p = 0.156; I2 = 0.0%) were noted for CT groups when compared to active or specific-active control groups. Therefore, supplementing regular soccer training with CT induces adaptations to improve maximal strength. CT may be implemented during the pre-season and in-season to induce adaptations similar to tradi- tional strength training (e.g., maximal strength gains), although alternative training strategies may be needed to further improve aerobic endurance and RSA. The use of CT may be applicable during different periods of the season to achieve certain goals, e.g., pre- and in-season for maximal strength development, and off-season to attenuate the decline of strength or power.