It is quite common for heart rate monitors to give false readings when used during exercise
Q My friend is 84 and has low blood pressure, usually 121/73 ish. Sometimes it drops to 80/50 and she has no energy. She will not go to her doctor because the next day she feels fine. Could there be an underlying problem?
A It is certainly possible that a blood pressure drop like this is causing your friend to feel tired. A little more detective work will be required to establish a definite connection; are the low blood pressures are always associated with low energy and do they coincide with any other symptoms? Time of day and any other particular circumstances can be relevant. Some older people develop low blood pressure when they stand after sitting or lying down for a while; this is called postural hypotension and can be measured by recording lying and standing pressures. Some drugs can cause low blood pressure and this effect might be more striking close to when the dose is taken. Heart disease and irregular pulse rates can also be responsible; usually the person will notice other symptoms such as breathlessness, chest pain or palpitations if this is the case. There are a wide range of other possibilities including losing weight, dehydration, anaemia and many others. I would suggest you try to persuade your friend to have some simple checks with her GP.
Q I am 60 and run 18 miles every week. I wear a heart rate monitor and noticed that the reading was between a third and half what I was expecting, 45 - 70 rather than around 135. After running up an incline and easing off, my heart rate sometimes drops as low as 32. On a recent half marathon, my lungs and legs were hurting but my heart rate was in the 60s for over two miles. Is this something I should boast about or worry about?
A If you are capable of this level of exercise and have not noticed any marked change in your exercise tolerance, there is nothing intrinsically wrong with your heart rate. The fault will lie with the recording device. Heart rates between 30 and 60 during endurance running are not compatible with normal aerobic capacity; you would be severely limited if it were really that low.
Most recording devices rely on picking up electrical signals from the heart which are transmitted through the skin, in the same way as an ECG which uses small pads on the skin surface. These signals are weak and their accuracy is heavily reliant on a good contact between the device and the skin. It is quite common for them to pick up only one in two or three beats, or fail altogether, particularly if the device is being used during exercise with the problems that sweating and body movement can cause. I have noticed similar phenomena when using a heart rate monitor myself.
Dr David Roche is a GP in Sussex and answers readers’ questions every month in Saga Magazine. He can only answers questions there or on the Saga health website; email your questions to email@example.com and he will answer as many as he can.