External Workload Indicators of Muscle and Kidney Mechanical Injury in Endurance Trail Running

Muscle and kidney injury in endurance athletes is worrying for health, and its relationship with physical external workload (eWL) needs to be explored. This study aimed to analyze which eWL indexes have more influence on muscle and kidney injury biomarkers. 20 well-trained trail runners (age = 38.95 ± 9.99 years) ran ~35.27 km (thermal-index = 23.2 ± 1.8 °C, cumulative-ascend = 1815 m) wearing inertial measurement units (IMU) in six different spots (malleolus peroneus [MPleft/MPright], vastus lateralis [VLleft/VLright], lumbar [L1–L3], thoracic [T2–T4]) for eWL measuring using a special suit. Muscle and kidney injury serum biomarkers (creatin-kinase [sCK], creatinine (sCr), ureic-nitrogen (sBUN), albumin [sALB]) were assessed pre-, -post0h and post24h. A principal component (PC) analysis was performed in each IMU spot to extract the main variables that could explain eWL variance. After extraction, PC factors were inputted in multiple regression analysis to explain biomarkers delta change percentage (Δ%). sCK, sCr, sBUN, sALB presented large differences (p < 0.05) between measurements (pre < post24h < post0h). PC’s explained 77.5–86.5% of total eWL variance. sCK Δ% was predicted in 40 to 47% by L1–L3 and MPleft; sCr Δ% in 27% to 45% by L1–L3 and MPleft; and sBUN Δ% in 38%-40% by MPright and MPleft. These findings could lead to a better comprehension of how eWL (impacts, player load and approximated entropy) could predict acute kidney and muscle injury. These findings support the new hypothesis of mechanical kidney injury during trail running based on L1–L3 external workload data.