Abstract
<title>Abstract</title> <p>PURPOSE To compare how derivatives of external training load (TL) metrics relate to perceptual and physiological internal TL in semi-professional soccer players. METHODS Thirty-five male semi-professional soccer players were monitored across two consecutive eight-week competitive seasons using 10-Hz GPS units with integrated heart-rate monitoring. External TL metrics, including total distance (TD), acceleration count (AccNumber), deceleration count (DeccNumber), and high-speed distance (HSD), were expressed as weekly accumulated volume (acc), training monotony (m), and week-to-week percent change (P_). Internal TL was assessed using weekly accumulated session rating of perceived exertion (accsRPE) and training impulse (accTRIMP). Linear mixed-effects models examined associations between standardized external TL derivatives and internal TL outcomes. RESULTS accTD was significantly associated with both accsRPE and accTRIMP (p < 0.001). accsRPE was associated with variability-related metrics, including mHSD (p < 0.01), mDeccNumber (p < 0.05), as well as P_TD (p < 0.01). accTRIMP was associated with accDeccNumber (p < 0.01) and mDeccNumber (p < 0.05), with no significant percent-change associations. CONCLUSION sRPE reflects both cumulative volume and monotony of mechanical demands, while TRIMP reflects accumulated distance and both the cumulative volume and within-week consistency of braking exposure. These findings highlight how distinct external load expressions relate to perceptual and physiological internal load.</p>