The first kilometre feels easy, so you speed up. Halfway through, maintaining that pace becomes the main task. A steady practice run offers a different lesson: learning to begin at an effort you can sustain.
Choose a familiar, reasonably flat route for an ordinary easy session. This is not a time trial or a reason to extend your usual distance. If you have health concerns or symptoms during exercise, get appropriate medical advice rather than using a pacing exercise to test your limits.
Compare sections that deserve comparison
A kilometre uphill into wind is not equivalent to a sheltered downhill kilometre. Note junctions, stops and changes in surface. When possible, use repeated laps or similar sections so the comparison is less dominated by the route.
Begin conservatively and let breathing settle. Look at the watch occasionally instead of chasing every momentary pace fluctuation. GPS estimates can jump, especially around buildings or trees; an average over a section is usually more useful for this exercise.
Read the pattern after the run
Write down whether the second half required noticeably more effort, whether you could maintain relaxed movement and what interrupted the rhythm. A slightly slower opening followed by stable sections may teach more than a quick start followed by repeated slowdowns.
For a fictional example, four comparable laps taking roughly similar times suggest a different pacing pattern from one very fast lap followed by three progressively slower ones. Neither pattern alone diagnoses fitness. Sleep, weather, terrain and the purpose of the session still matter.
Do not force identical splits on every run. Hills, intervals and recovery sessions have different goals. Keep this as an occasional observation exercise, then discuss it with your coach if you follow a plan.
On the next comparable outing, change only the opening effort. A calmer first section gives you a fairer chance to discover what sustainable pace feels like before you decide whether a faster finish belongs in the session.