Heart rate strap issues

Spend the first mile of your run constantly adjusting it?

I actually had this same conversation the other week with some of the guys in my tri club. The common consensus is that it's either too lose and slides down, or too tight. There is no middle ground.

Something you _could_ try is athletic tape. Just put a piece over the strap on each of your sides to hold the strap in place.

Been using it for 4 years with no issues, just seemed to start doing this in the last 5 or 6 months.

^^^ This is exactly what I do.  I don't really have the issue for running and biking, but I always have it in the water.  So for races I just put two pieces of tape over it on each of my sides.  Works like a champ.

Good advice. I find mine slowly loosens up. every 5-10 runs, I have to stop, crank it down, and go on.

I was thinking to mark the spot and see if the band is stretching or the slider is sliding. If the latter, I would just sew it a bit to keep it in place. If the former, tape!

My husband had this problem due to the shape of his torso - no amount of tightening seemed to keep it on. I replaced the elastic with gripper elastic the same width as the original. (Gripper elastic is that sticky-backed stuff you see inside the hem of some cycling shorts.) Most fabric stores sell it, inless they specialize in quilting.

I used a size 14 ball-point needle. The only sewing issue was the fact that the elastic was sticky-side-up as I closed the loop, so I had to put a small piece of tissue paper between the presser foot and the elastic and sew through it.