Heart rate monitor and swimming

[GreatCanadian]

Hi folks. I have no idea what category to post this in, so I put it in everything else. I have a heart rate monitor that I wear when exercising. It is the Polar FT7. It is supposed to work underwater (swimming). As soon as I enter the water the watch loses communication from the transmitter (transmitter is on chest strap). I am wondering why this happens. Could it be because of the salt? I have not tried it in a non-salt pool so I do not have any basis for that assumption. If I stand in the pool so that the chest strap is above water, then raise the watch above water, communication is established again. Any ideas?

GC

 

[UnderWaterVanya]

Hi folks. I have no idea what category to post this in, so I put it in everything else. I have a heart rate monitor that I wear when exercising. It is the Polar FT7. It is supposed to work underwater (swimming). As soon as I enter the water the watch loses communication from the transmitter (transmitter is on chest strap). I am wondering why this happens. Could it be because of the salt? I have not tried it in a non-salt pool so I do not have any basis for that assumption. If I stand in the pool so that the chest strap is above water, then raise the watch above water, communication is established again. Any ideas?

Fill the bathtub and test it. That eliminates the salt and other chemicals.

 

[GreatCanadian]

Ok. I will do that. Never thought of it!!

 

[Durk]

From the Polar web site FT7 FAQ's:

Most Polar products can be worn when swimming. They are not, however, diving instruments. To maintain water resistance, do not press the buttons of the product under water. When measuring heart rate in water, you may experience interference for the following reasons:

Pool water with high chlorine content, and seawater are very conductive. The electrodes of the transmitter may short-circuit, preventing ECG signals from being detected by the transmitter.

I have a waterproof cordless phone. I can put it under water, and it survives, but it immediately drops any call in progress.

 

[GreatCanadian]

hmm..interesting. I wonder what they consider "high chlorine content". And is my saltwater pool at 4,000 ppm salt considered seawater? Thanks for that info.

GC

 

[benavidescj]

This was posted on Amazon by a user that bought the same FT7 unit:

"- Water Resistant. I have used this HRM in the pool and the monitoring is relatively accurate when it actually reads the transmitter. I believe the Polar website notes that in some highly chlorinated pools or seawater the transmitter will not be picked up underwater. The pool in my gym is very chlorinated and there were times when the HRM will not pick up my heart rate. But if I just sit still in the water for a minute or so the watch will pick up the signal again. Though this can get annoying if you are trying to swim laps for endurance. The watch still gives me a fair calculation of calories I have burned during my swim sessions. Though the calorie count is most likely lower since I'm not sure how long the watch is not reading my heart rate during times when I am swimming several laps nonstop. I also tried using this in a saltwater treated pool and the moment I went underwater the transmitter does not work at all. So I'm guessing that this HRM will not work if you are swimming in the ocean."

 

[UnderWaterVanya]

I guess you can try wrapping that part of your arm in plastic wrap to see if this helps.

 

[phonedave]

I guess you can try wrapping that part of your arm in plastic wrap to see if this helps.

My guess, and it is only a guess, is that it has to do with the tranmission of the radio waves between the HRM and the watch through a medium that has a lot of free ions in it (Salt water Na+ and Cl-, or just Cl-). Wrapping the watch and/or HRM is not going to help, you need to clear up the transmission path. I know people that when they are training for triathalons, and doing ocean swims, will put the watch under their swim cap. That way it is out of the water and can pick up the GPS singnals. However, if you did that, your HRM is still in the water.

Sorry - I really do not have a solution for you.


-dave

 

[benavidescj]

My guess, and it is only a guess, is that it has to do with the tranmission of the radio waves between the HRM and the watch through a medium that has a lot of free ions in it (Salt water Na+ and Cl-, or just Cl-). Wrapping the watch and/or HRM is not going to help, you need to clear up the transmission path. I know people that when they are training for triathalons, and doing ocean swims, will put the watch under their swim cap. That way it is out of the water and can pick up the GPS singnals. However, if you did that, your HRM is still in the water.

The problem is actually that the HRM shorts out in the salt environment due to the high conductivity of the water. The communication between the HRM and watch is possible since the transmission frequency of 5kHz is well within the range of radio wave transmission under saltwater. There are models of HRMs out there that are made for saltwater that deal with this issue.

 

[phonedave]

My guess, and it is only a guess, is that it has to do with the tranmission of the radio waves between the HRM and the watch through a medium that has a lot of free ions in it (Salt water Na+ and Cl-, or just Cl-). Wrapping the watch and/or HRM is not going to help, you need to clear up the transmission path. I know people that when they are training for triathalons, and doing ocean swims, will put the watch under their swim cap. That way it is out of the water and can pick up the GPS singnals. However, if you did that, your HRM is still in the water.

The problem is actually that the HRM shorts out in the salt environment due to the high conductivity of the water. The communication between the HRM and watch is possible since the transmission frequency of 5kHz is well within the range of radio wave transmission under saltwater. There are models of HRMs out there that are made for saltwater that deal with this issue.

If that is the case, then waterproofing the HRM should do the trick. Looking at mine, there are no exposed electrodes, so you should be able the pot it in something. That would make changing the battery a PIA of course.


-dave