How can I have an app always on?

[dontgetit]

When I open an app the screen turns black after a few seconds; if I turn the wrist towards me within a few seconds it will show the app or the page I was looking at, but if I wait a minute or so it will go back to the time watch face.
What I'm trying to do is using an app called MotionX-GPS to track my current and max speed while wind-surfing without having to open the app everytime
How do I do that?

 

[melman101]

In your Apple Watch app on your iPhone -

Go to General | Wake Screen | On Wrist Raise - Resume Last Activity

 

[gsmornot]

You already have the correct answer but wanted to let you know that from the watch face, you can double click the crown to go back to the previous app.