Our general advice is to train to pace rather than heart rate. Additionally, training according to duration rather than distance is preferred.
The primary reason for our viewpoint is the lack of evidence and validity behind heart rate training methodologies. This becomes increasing true as a person becomes fitter, where the standard heart rate training zones will not allow an athlete to reach their true potential.
A primary issue of heart rate based training is that it is reliant on maximum heart rate (HRmax), and estimation of this is highly error-prone, with underestimation becoming greater with increasing age. Furthermore, each person's response to exercise is not determined by a simple fraction of their heart rate. For example, a untrained individual will experience great benefits at 50% of their HRmax, however highly trained individuals may require significantly higher intensities and more variety.
Furthermore there is the assumption that aspects of metabolism occur when running at a set percentage of heart rate. However, whilst these rules may hold quite well for highly trained athletes, they do not for the general population of runners. For example it is often stated that Lactate Threshold is around 90% of HRmax, yet it can be as low as 50% of maximum heart rate.
Additionally there is a natural day-to-day variation in your heart rate and many factors have a noticeable effect on this. For example dehydration, lack of sleep, caffeine, heat, humidity, altitude (even after acclimatisation), can alter your rate by as much as 20% - that could be 30 beats per minute!
Accuracy of heart rate monitors must also be considered. Overall chest straps would seem to be reliable, however optical (wrist worn) devices can often produce quite spurious and dubious values. The accuracy becoming an increasing concern as the level of activity rises from rest, with research illustrating errors by as much as +/- 40 beats.
This is not to say that pace-based training does not have its issues, which is why we would always advise people to 'never be a slave' to pace or heart rate. And at times, Subjective Pace may be your friend.
If you have specific concerns with regards to TrainAsONE's pace or heart rate specifications for your workouts, feel free to get in touch using the in-app question feature so we can investigate and advice.
References and Further Reading
Cooper, C.B. and Storer, T (2001) Exercise Testing and Interpretation, A Practical Approach. Cambridge: Cambridge University Press. Bouchard, C. (1982). Exercise and Sport Science Review. New York: Franklin Institute Press. p. 49-83. Gellish, R.L. et al. (2007) Longitudinal Modeling of the Relationship between Age and Maximal Heart Rate. Medicine & Science in Sports & Exercise, 39 (5), p. 822-829. Cadmus-Bertram L, Gangnon R, Wirkus EJ, Thraen-Borowski KM, Gorzelitz-Liebhauser J. The Accuracy of Heart Rate Monitoring by Some Wrist-Worn Activity Trackers. Ann Intern Med. 2017 Apr 18;166(8):610-612.