Background <p>Monitoring training load is an important aspect of optimizing performance and preventing overuse injuries in runners. This is the first study comparing physiological, biomechanical and subjective load between typical outdoor training sessions, contributing to the transfer of methodologies from the gait laboratory to real-world conditions with the final goal of improving athlete monitoring.</p> Methods <p>Twelve experienced runners participated in distinct sessions: an endurance run, a submaximal effort, and interval training, which varied in perceived exertion. Using heart rate monitors, inertial measurement units and questionnaires, estimated cumulative load and its correlation with session Rate of Perceived Exertion (sRPE) and physiological load calculated via Training Impulse (TRIMP) were analysed.</p> Results <p>sRPE significantly distinguished between session types, while TRIMP and cumulative biomechanical load did not. Furthermore, correlations between the three training load metrics were weak to moderate (sRPE vs. TRIMP: <i>r</i> = 0.49; sRPE vs. weighted cumulative load: <i>r</i> = 0.25; weighted cumulative load vs. TRIMP: <i>r</i> = 0.35), where only sRPE and TRIMP correlated significantly (<i>p</i> &lt; 0.05). This suggests that the different measures capture different aspects of load or that the measures could be inadequate to capture load.</p> Conclusion <p>Objective physiological and biomechanical metrics alone may not adequately reflect athletes’ perceived exertion when training includes different session types. This highlights the importance of using a multifactorial approach to training load monitoring in running.</p>