Record enough to make the next decision
A running log should connect what you intended, what you completed and how you responded. Distance alone cannot explain heat, hills, poor sleep or an unusually hard effort. A notebook or spreadsheet is enough if you review it consistently.
Review the week
Check completed frequency and duration, the cost of the longest or hardest sessions, and whether ordinary easy running stayed comfortable. Compare similar conditions across several weeks rather than interpreting every pace fluctuation as progress or decline.
For example, a slower run in heat with normal conversation and recovery does not automatically justify lowering all training paces. Repeatedly high effort on familiar easy routes, especially with persistent symptoms or poor recovery, deserves a different response: hold or reduce training and investigate the cause.
Heart rate, sleep estimates and other wearable measures are optional context. Keep a metric only if you understand its limitations and it changes a useful decision. Logging cannot diagnose an injury or guarantee that one will be prevented.
Use the adaptive-plan guide for missed sessions and the fueling planner to check long-run intake arithmetic. Seek appropriate care for persistent symptoms or pain that changes movement.