The first wireless heart rate monitor was the Polar Sport Tester PE 2000, which was released in 1982. As you can imagine, a entire fitness tracking and wearables industry has significantly evolved since then.
For as long as human beings have participated in varying forms of fitness they have kept track of fitness statistics in an effort to both monitor and augment their performance. The resulting accumulation of data on heart rate, distance, speed, and more have given people the opportunity to take note of their fitness and improve it with regularity. That being said, fitness tracking is nothing like what it used to be — much has changed since it was done through handwritten logs.