Can we make Hiking a subcategory of Walking?

I get that, but does it really matter excepts for the walking challenges?

Then why have subcategories at all? And yes, it matters for walking challenges. If soeone creates a walking challenge, and I go for a harder form of walking, like hiking, ut doesn't count.  

The original reason is probably historic. In the beginning Garmin created a few main activities without any sub types. Hiking is one of the main types. Adding sub types to the main types is probably very easy, but moving a main type to a sub type is harder.

As someone in the database and IT world, I know there is a solution if they want to make the change. 

Example 1, assuming the primary categories are just category records with no "parent category ID":

1) Update the Hiking category record to have a new parent ID of "Walking"

2) All activities would now be classified as the Hiking subcategory of "Walking"

Example 2, assuming that primary categories are in a separate "primary category" metadata table:

1) Create a new Hiking subcategory under walking and deprecate the old one (probably the easiest). A simple insert statement for the new category.

2) Update (in batches) to move all "Hiking activities" to the new Hiking subcategory. Then delete the old primary category of "Hiking"

Jack said:

As someone in the database and IT world, I know there is a solution if they want to make the change. 

You might be our best hope - Garmin Careers  

Developers always love when people that don't know anything about the data model tell them how easy it is to make changes ;-)

Everything is of course possible to do. I work in software development. One big question is if it is worth doing the change.

Sure. Why are you opposed to the change?

I'm not really opposed to the change, but it means that there will be less to do in the challenges if there are both walking and hiking challenges at the same time. Shouldn't we do more exercising? 

If that is the argument, you should be asking why there are not "Casual Walking" challenges...  It's a "Walking" challenge.  Hiking is walking.  They don't disqualify "Mountain Biking" from "Cycling" challenges.  Be consistent. That is my request.  If you want a subcategory challenge, then make it a subcategory challenge.