When running heart rate jumps fro around 120 bpm to around 165. Drops after a few minutes. ( I do follow the guidance about how watch should be worn). Have done some runs with another watch and rate is constant, so am convinced problem is with watch not me. ( I am sure my perceived exertion would have noticed such big changes anyway). I wonder if it is confusing heart rate with cadence (steps per mile) or that could just be coincidence).
Would appreciate thoughts of others with similar experience. if it is just a problem with the watch, does anyone have experience of a more reliable watch?