Training load quantifies the total physiological stress of your workouts — combining volume (duration) and intensity (RPE or heart rate zone) into a single number. The concept emerged from sports science research in the 1970s through Bannister's TRIMP (Training Impulse) model. For runners, tracking load week to week is the most evidence-based method for balancing fitness development against injury and overtraining risk.

This calculator uses the Session RPE method, developed by Carl Foster (University of Wisconsin, 2001). Session Load = Duration (minutes) × RPE (Borg CR-10 scale, 1–10). The simplicity is its strength — it captures perceived exertion across all session types (running, strength, cross-training) in a single number. The 7-day sum is your Acute Training Load (ATL, representing fatigue), while a 42-day average gives Chronic Training Load (CTL, representing fitness). The difference — Training Stress Balance (TSB = CTL − ATL) — indicates readiness and form.

Research consistently shows that a weekly load increase of more than 10% significantly raises injury risk, particularly for stress fractures, shin splints, and tendinopathy. The 10% rule, while debated in exact percentage, is supported by epidemiological studies and remains the most widely used training progression guideline. This calculator flags weeks where your ramp rate exceeds safe thresholds and provides recommendations based on your current ATL–CTL balance.