24 Hour Heart Rate

The measurement of 24hr heart rate is one of the methods used to estimate 24hr energy expenditure. There is a good relationship between heart rate and energy expenditure, and during physical activity, where the heart rate is higher than 90 beats per minute, and lower than approximately 160 beats per minute, this relationship is almost linear. It is because of this relationship that heart rate may be used to estimate energy expenditure in a 24hr period. This method provides an easily executable method, that is not does not pose any discomfort to the person having their energy expenditure measured, unlike other methods of 24hr energy expenditure measurement that require that subjects either consume a dose of the stable isotope, heavy water (or Doubly labelled water) or live in a metabolic chamber for the 24 hours.

The subject having his energy expenditure measured over the 24hr period will wear a portable telemetric heart rate monitor and receiver. The heart rate monitor transmitter is in the form of a belt, worn around the subject’s chest and the receiver is in the form of a wristwatch. Data is collected and averaged to minute-by-minute intervals over the 24hrs, approximately 1440 minutes. At the end of the measurement period the heart rate data will be downloaded from the receiver, and this data in turn will be extrapolated into minute-by-minute energy expenditure.

It is known that in space there are cardiovascular changes, and as a result of the micro-gravity environment the heart does not have to work as hard as it does on Earth. On Earth, the heart must work against gravity to get the blood in the lower part of the body, legs, abdomen and pelvis, back up to the heart for re-circulation. In space, because there is a micro-gravity environment, the heart does not have to work as hard, as it is not working against gravity, and as a result the heart rate is on average about 10 beats per minute lower than that of Earth, during activities of moderate or little effort.

The heart rate monitoring technique for measuring energy expenditure relies on average minute-by-minute heart rate, and as a result this experiment is being conducted to investigate whether the heart rate monitoring technique will still be as accurate in the measurement of energy expenditure in space, as it is accurate on Earth.