Purpose:
This study aimed to profile in-season training load management across different age categories in elite Brazilian male youth footballers, and to compare differences between playing positions (external defenders, central defenders, central midfielders, external midfielders, and forwards) and load structure relative to match-day.

Methods:
During the competitive season, data were collected from 43 players (175.8 ± 6.3 cm, 69.8 ± 8.1 kg) across three age groups (U15: n = 14; U17: n = 16; U20: n = 13), all from the same professional club. Positional data were collected using GPS devices during training sessions. A linear mixed model was used to compare age groups, training days, and positions, with ‘Athlete ID’ included as a random effect. Statistical significance was set at p < 0.05.

Results:
U15 and U20 players covered significantly greater total distances than U17 players (p = 0.01; t = 6.52, p < 0.01; t = 5.92, respectively), while U20s performed more decelerations than U15s (p < 0.02; t = 2.81). Total distances were higher on MD–4 and MD–3, and lowest on MD–1 and MD+2 (p < 0.05). High-speed running, sprinting, accelerations, and decelerations were greater on MD–4 and MD–2 across all age groups (p < 0.05).

Conclusions:
Training load variations across age groups largely reflect coaches’ activity choices, reflecting strategies to promote development while minimising pre-match fatigue. Concerning position-specific differences, external defenders demonstrated the greatest exposure to high-intensity actions and sprinting during the microcycles, regardless of the age category (p < 0.05). This greater external load is likely associated with position-specific demands, particularly overlapping runs and recovery sprints during both training sessions and matches.