How should I monitor my exercise?

Up until the last decade or so, monitoring activity was limited to a watch and possibly writing in a diary or calendar to keep track of your sessions. If you wanted to know how far your regular walking or running route was, you got in your car and drove it. Nowadays there is a whole host of products you can use to monitor your activity, from simple pedometers to sophisticated phone apps and devices to measure your heart rate, speed, and more.

Which one will work for you? Some of that depends on the type of activities you want to monitor and your goals. Here are a few things to consider when you’re choosing a device.

Pedometers are simple devices (no more than one square inch) that are usually attached to your pant belt just in front of your hip. Their main function is to measure the number of steps (using a mechanical swing arm). Some pedometers attach to other areas of the body but they tend not to be as accurate. The use of pedometers has been demonstrated to motivate people to be physically active. However they can’t measure the intensity of your activity; they are only good for stepping activities (walking, running) and the mechanics break down with frequent use.

Accelerometers are more sophisticated devices that can measure movement in multiple planes (not just moving forward) and can be used to determine intensity, distinguishing between running and walking. In the world of research, accelerometers are worn around the waist and are accurate for assessing walking/running movements but are limited in their ability to properly measure upper body activities. Some accelerometers are worn on the wrist and can measure more diverse activities. However, there are few studies to determine how accurate many of the commercial devices are. Like pedometers, accelerometers cannot measure activities like cycling and are generally not waterproof.

Heart rate monitors measure your heart rate and provide an indication of how hard you’re working. There are two main types, those that include a chest strap and those that do not. Chest straps directly measure heart rate while devices on other parts of the body measure pulse. The two are not exactly the same, as indicated here, and for people with heart conditions, it may be important to measure heart rate with a chest strap. .

GPS trackers measure distances and speeds, which can be quite useful for runners and cyclists. This is especially valuable when you’re starting out or trying a new route. After using a GPS tracker once or twice on each route, however, the value diminishes since you are not gaining any additional information (your exercise time will indicate whether you have done the route faster or slower). In addition, there is very limited value in GPS tracking for people who do activities like tennis, team sports and water sports (the GPS signal can’t transmit through water).

Calorie counters attempt to give you the number of calories you use during an exercise session; this may be attractive if you’re counting calories for weight management. Knowing calories can also give a sense of how activities compare in volume and intensity. For example, a long walk may be equivalent to a short run in terms of calories. The problem is that none of the devices determine calories directly and most are grossly inaccurate. The simplest devices use equations based on data of external work (like most fitness machines), which themselves have error in them. The more accurate devices will ask the user to input individualized information like age, sex and weight, among other things, but are still not great. Until the accuracy improves, it may not be worth using these devices.

When deciding on which device to use, it usually isn’t an either/or of the features listed above as many devices nowadays combine a number, if not all, of these features along with others such as an online diary. Yet not all devices measure each feature with the same accuracy. For example, many devices have some sort of heart rate function along with GPS tracking and accelerometry, but if measuring heart rate is important, you may want to get one using a chest strap. The bottom line is to get a device that offers the best and most accurate measurements for the type of activities you commonly do.

Dr. Scott Lear is a leading researcher in the prevention and management of heart disease. He holds the Pfizer/Heart and Stroke Foundation Chair in Cardiovascular Prevention Research at St. Paul’s Hospital in Vancouver, and he is a professor in the faculty of health sciences and the department of biomedical physiology and kinesiology at Simon Fraser University. Dr. Lear also lives with heart disease himself. Follow his blog at drscottlear.com.