I have to caution about heat treatments for PN....

Heat in general stimulates nerves. If you have nerve problems, then long heat treatments are in the LONG RUN going to make for more pain during the rest of the day.

My chiro explained this to me long ago. 10 minutes tops for any heat exposure (hot baths, heating pads, steam rooms).

Heat is primarily for deep muscle and joint pain. It will improve blood flow to deep areas. But for nerve pain, it is a stimulant...and will cause the pain nerves to fire more and basically irritate them.

For example, when I had IFc treatments with ultrasound following, the therapist put an ICE pack on the area that had the electrode pads. This deadened the pain from the treatment so I could tolerate higher voltages. When the ultrasound was done, she mixed Biofreeze with the lubricant so a higher level could be used to penetrate to my hip area where the tendons were injured.

The general rule is for PNers... to use cool or cold treatments sparingly to reduce nerve firing (pain). Too much cold is also bad, so use ice packs sparingly so as not to compromise circulation to a painful area.

CRPS (RSD) patients on the other hand prefer heat treatments.
So keep in mind that cold intolerance may be a clue to a diagnosis of CRPS.

Heat will help overworked muscles get rid of lactic acid build up. But more time than necessary will then irritate nerves in the area, which will cause pain, for all the other times the heat is missing.

To improve blood flow without heat, using the magnesium lotion is best.

I have MP in remission (lateral femoral nerve damage from a C-section surgery). If I go into a steam room or hot bath, it will wake up and zap me etc. So I avoid heat at all costs today.
I had it severely for over 10 yrs, until Lidoderms came out... and I used them for 2 weeks, and the nerve quieted down.
The steam room at the gym used to trigger me too. So now it is only lukewarm water for me!