hi... judihui...
don't use these in-ears any more. with in-ear headphones, it depends on the shape of your inner ear. i've never had any problems so far. i've now bought the freebuds from huawei. and they fit me perfectly. thanks to a small vacuum, i can also do sports (freeletics, running). they stay in my ears.

but i bought them used. they wouldn't have stayed in my ears at all.

It's worth a try, because you can't hear anything except the music.

ahja... i don't have an iphone... I am a happy p30 owner...

hope i could help with the decision.

iPhone 4S: Sorry, I can't judge.
Running: No connection problems. Also: comes with earplugs of different sizes, a little trial and error to see which size fits, and they don't slip even when running for a long time.