If you pay for Strava you have access to high resolution global heatmap other wise it can be accessed in a lower resolution form limiting in how far you are able to zoom in. This heat map can be utilized as a custom layer in OSM the best way to get it as a custom layer is using this extension made by ezekielf that grabs a link that you can eaisly copy and paste into OSM. Before I found this extension I used to go into the websites code inspector and do this by hand and it was a real pain in the ass for someone who knows little to nothing about source code and how cookies work.

Here is an example of how the heatmap can be utilized to map trails in OSM

The different options for the heatmap

https://heatmap-external-{switch:a,b,c}.strava.com/tiles-auth/ACTIVITY/COLOR/{zoom}/{x}/{y}.png?Key-Pair-Id=MYVALUE&Policy=MYVALUE&Signature=MYVALUE

CloudFront-Key-Pair-Id
CloudFront-Policy
CloudFront-Signature

ACTIVITY:
    run
    ride
    both
    winter
    water
    all

COLOR:
    blue
    red
    bluered
    purple

when in Puerto Rico

https://wiki.openstreetmap.org/wiki/Puerto_Rico_Imagery

http://{switch:a,b,c}.tile.openstreetmap.us/usgs_large_scale/{zoom}/{x}/{y}.jpg