I use search in Training Log in the app often when I want to find past activities. However the search has one serious usability flaw in my opinion - when I search for multiple words it searches activities that match ANY of the words. It would be far more reasonable to search activities that combine ALL of the searched words.
For example, let's say I want to find my previous runs of Orcas 50K race. I had just a few of them in my long running history. If I type "Orcas" alone, I get a large number of runs that weren't the race or where I even mentioned Orcas in the description. That's too many results. However if I add "50K" to narrow the result, instead I get a bunch of other 50K races included, and everything that mentions any 50K. That doesn't make sense. Adding search terms should narrow the results, not expand them, at least when searching in your own activities.