Heart Rate Index calculator

A heart rate-running speed index calculator over given (average) time span. The index reflexes the pace independent running performance; where a decrease means a performance increase. Optionally, the additional elevation effort can be include into the index equation to compensate for the pace reduction, or deduction when running downhill. As already found by Conconi, there is a linear correlation of HR and running speed below aerobe - anaerobe threshold (https://de.wikipedia.org/wiki/Conconi-Test#/media/File:Conconi-Diagr.jpg). The calculate index is the linear factor of the linear curve HR vs pace. The index is an individual factor as standing HR and aerobe - anaerobe threshold are individual for each person. As along the standing HR is not changed, a lower index means improve performance; you can run at same pace, but with lower HR. The HR Index is saved to FIT. Based on "Heart Rate - Running Speed–index May Be an Efficient Method of Monitoring Endurance Training Adaptation" (https://www.ncbi.nlm.nih.gov/pubmed/24345970). Optional elevation adjusted pace; constant 6x or GAP (Manetti et. al. | https://www.ncbi.nlm.nih.gov/pubmed/12183501). Note that GPS-calculated elevation may have major distortion and affecting the HR Index. Settings: In general: keep the defaults if you are not familiar with settings topic Averaging time interval of pace [s]: The time interval of paces to be averaged. Shorter time will give more updates, but with a greater chance of variation. Distance frequency [m]: The distance for the grade to be calculated. Shorter distances will give more updates, but with a greater chance of variation.

V 2.2: Upgrade to SDK 2.4.2 Added lap rate-running speed index Improved parsing of floats V 1.4: Averaging damping factor of gradients V 1.3: Use averaging of gradient and record to FIT. Using timer not elapsed time.