Internal training load and its longitudinal relationship with seasonal player wellness in elite professional soccer

- Weeks with two official matches revealed significantly greater values of DOMS and fatigue scores.
- Higher values of internal training load were found in weeks with one match.
- Significant negative small-to-moderate correlations in the weeks with 2 matches were found between ITL and HI scores.
- HI scores and ITL differed significantly from position to position

Monitoring internal training load has been extensively used and described within team sport environments, however when compared to internal physiological measures such as heart rate (HR) and rating of perceived exertion (RPE), the literature is sparse. The primary aim of this investigation study was to assess differences of playing position on ITL, session-RPE and wellness across two different training microcycles (1 vs. 2 competitive games), in addition with examining the relationship between ITL and Hooper's Index across an entire season. Thirty-five professional soccer players from the Portuguese premier league participated in the study (25.7 ± 5.0 years; 182.3 ± 6.4 cm; 79.1 ± 7.0 kg). Analysis of variance revealed higher values of DOMS (Means(M): 3.33 vs. 3.10; p = 0.001; effect Size (ES) = 0.087), fatigue (M: 3.18 vs. 2.99; p = 0.001; ES = 0.060) and HI (M: 11.85 vs. 11.56; p = 0.045; ES = 0.034) in 2-game weeks compared with 1-game weeks. Correlation between ITL and HI levels found significant negative correlations between ITL and DOMS (ρ = − 0.156), ITL and sleep (ρ = − 0.109), ITL and fatigue (ρ = − 0.225), ITL and stress (ρ = − 0.188), and ITL and HI (ρ = − 0.238) in 2-game weeks. Results from 1-game microcycle only highlighted negative correlations between ITL and stress (ρ = − 0.080). It was concluded from the study that greater fatigue potential, muscle soreness, stress and ITL was significantly more apparent within a 2-game microcycle. As a result, care should be taken when planning the lead into and out of a 2-game fixture microcycle highlighting key specific recovery strategies to damped the increased stress effect. Additionally, the potential utilization of squad rotation strategies may be a positive approach with aim of managing the fatigue effect.