Power output on flats versus hills

When riding on flat terrain I notice that I reach a power threshold whereby I am unable to produce any more power while my HR is nowhere near my max HR. I find that I just cant push any harder and my legs fail before my lungs do. Anyone else have these issues or thoughts? Is it purely a strength problem? When climbing I can easily elevate my HR and can seem to apply more power

2 posts were merged into an existing topic: RPE & Power on climbs vs flats