If I run at the same pace in the morning compared to the evening my HR is usually 10bpm higher in the morning. Both runs feel the same, not any more out of breath in the morning. Will my run in the morning be more ‘intense’? Am I best off running in the evening? Or is HR just an outcome of your perceived intensity and to be ignored?
HR is impacted by many factors such a caffeine intake, stress, temperature, dehydration etc. It sounds like you have found this out through self monitoring. Your body is working a little harder from a HR standpoint in the morning – but this doesn’t not make this workout more intense per se. I would just keep that focus on your RPE and breathing to ensure you stay in the correct effort zones and run when it fits your daily schedule.
..or, switch to Pace as your primary measure of intensity. Leyla’s right on, HR is just an indicator, not an outcome or output like Pace and Power are. Pace is a superior primary measure of intensity for most athletes.