Comparison of Position-Specific Internal and External Training Loads Within the Microcycle in Professional Football Players

This study aimed to examine position-specific differences in internal and external training load across microcycle training days in professional soccer players. Twenty-two players (4 full-backs (FB), 4 central defenders (CD), 6 central midfielders (CM), 4 wide midfielders (WM), and 4 forwards (FO)) were monitored over a 28-week competitive period using a 10-Hz GNSS-based Polar Team Pro system. Training days within the microcycle were classified relative to match day (MD) as MD-4, MD-3, and MD-2. Internal load variables were assessed using heart rate-based parameters, including average heart rate (HRavg), percentage of maximum heart rate (%HRmax), time spent in heart rate zones (Zones 1–5), and TRIMP. External load variables included total distance (TD), low-speed running (LSR), moderate-speed running (MSR), high-speed running (HSR), sprint running (SPR), maximum speed (Vmax), accelerations (ACC), and decelerations (DEC). One-way ANOVA revealed no significant positional differences in internal load variables. However, significant positional differences were observed in HSR, SPR, Vmax, ACC, and DEC (p < 0.05). FB, WM, and FO showed higher values in high-intensity activities than CD and CM. Additionally, FB recorded the highest external load values (except LSR), particularly on MD-3. In conclusion, while internal load variables reflect overall physiological stress, external load variables better reveal position-specific demands, particularly during high-intensity activities. Therefore, coaches should consider both internal and external load variables when planning training, particularly position-specific high-intensity demands.