Presenting the iWatch, I mean Apple Watch

The iWatch was unveiled on Tuesday to great anticipation. One surprise: it will be called Apple Watch, not iWatch. Another surprise was that the "smartwatch" did not contain as many health technology features as predicted despite its larger-than-expected size (Figure 1).

Figure 1. Apple Watch, perhaps a bit thicker than people expected.

In previous posts, I described the speculation around the activity and health tracking capabilities of the Apple Watch, and how the resulting data may be integrated with Apple's Health app as well as third-party apps via the HealthKit developer tool. There were rumors that Apple Watch would measure blood pressure, heart rate, blood glucose, and even hydration along with activity.

At the unveiling, health and fitness were indeed emphasized but the medical tracking functionality was limited to (1) an activity tracker and (2) a heart rate monitor.

Activity tracking was the main focus with some special hardware and software features. Interestingly Apple Watch contains both an accelerometer and a gyroscope. As described previously, an accelerometer is the centerpiece of any activity tracker and is used to monitor movement by "counting" the number of steps, which can be used to estimate the number of calories burned:

"Thus, your walking motion produces a repeated cycle of acceleration/deceleration that is transformed by the accelerometer into a cyclical pattern of electrical signals that is counted as steps. The number of steps can be converted into distance by determining the stride length. All that remains is the all-important number of calories consumed. There are estimates of the number of calories burned per pound per mile when walking at a certain speed i.e. 3 mph. In this manner, during the course of the day [the activity tracker] counts the total number of steps, which translates into the total distance traveled, and then finally an estimate of the total number of calories burned."

Of course not all activity is created equal. Running and walking the same distance may consume roughly the same number of calories, but they have different effects on cardiovascular fitness. The gyroscope is able to calculate the angular velocity from turning the wrist, arm or body. Together the information from the accelerometer and gyroscope can help the Apple Watch distinguish walking from running, cycling from swimming, and jumping jacks from climbing stairs. This allows for a more accurate classification of your activity over the course of the day.

From the software side, there will be an Activity app with three modes: Move, Stand, and Exercise. Each is represented by a ring that closes as you achieve your goals. In addition, the Apple Watch will possess a Workout app that divides your activities into specific groups such as Running, Cycling, or Cross Training, taking advantage of the ability to distinguish between different activities.

When you flip the Apple Watch over you can get a good look at the heart rate monitor (Figure 2):

"One of the most distinct elements of the new Apple Watch is a set of four rings built into its backside, but they're hardly there for style: inside those four rings are sensors that the Apple Watch uses to measure its wearer's pulse. The sensors include infrared and visible-light LEDS in addition to photosensors, which all work together to detect heart rate."

The general principle is the same as the heart rate monitor on the Samsung Galaxy S5. Light from the LEDs are directed toward a patch of skin, where it can penetrate the surface and get reflected by the blood underneath. Sensors next to the LEDs can detect the light signal from the blood (e.g. red glow when you shine a flashlight on your finger). The signal is stronger during the systolic phase of the heart beat (contraction) than the diastolic phase (relaxation).

A band on the wrist is probably a more convenient form-factor for measuring heart rate than placing your finger on the LED flash of your phone because it can track your heart rate in a less obtrusive fashion that does not require conscious effort.

Two big questions are how accurate is the heart rate monitor and how long can you monitor your heart rate. Given the battery limitations, I suspect it will not be continuous monitoring but rather for short periods of time like taking your pulse. Continuous monitoring would have interesting medical applications (e.g. signal a heart attack).

Interestingly, during the presentation, Apple highlighted a social rather than medical application of the heart rate monitor: you can send your heartbeat to another Apple Watch user. The watch senses your heartbeat, and sends the signal to another watch, which is converted into vibrational motion by the linear vibrating motor in the "taptic" feedback engine. Although possibly "romantic" ("It’s a simple and intimate way to tell someone how you feel"), this scenario is somewhat frivolous from a medical standpoint.

Overall, however, one should not be disappointed that Apple Watch is not laden with the most advanced medical technology doo-dads. This product represents version 1.0; I suspect future iterations will add more health-related sensors and software. Apple's foray into the health and fitness field is just beginning, and I will post more on this subject.

Figure 2. The LED lights and photosensors used to measure your heart rate on the back of Apple Watch.