Today the US Patent & Trademark Office published a patent application from Apple that relates to the Apple Watch used in conjunction with a person in a wheelchair, especially for athletics. It's the patent behind Apple's Wheelchair Activity App.

Apple Watch has been heavily marketed as a health device for activity and now a heart study. Wheel Chair racing is another sport for the disabled and Apple's specialty teams have invented a way to assist these athletes using an Apple Watch supporting this activity. Below are just a few of the engineers who worked on this project:

Karthik Jayaraman Raghuram, Senior Engineering Manager at Apple: Responsible for overall fitness efforts as part of the Core Motion team. Working with and leading multiple teams that deliver the fundamental algorithmic components of our Fitness experience.

Adeeti Ullal, Scientist, Engineering Manager at Apple: Health/fitness algorithms, special projects. Adeeti led the team that designed and adapted fitness algorithms for wheelchair user.

Xing Tan, Senior Algorithm Research Engineer at Apple: Develop signal processing, machine learning and sensor fusion algorithm.

Apple's patent filing notes that various human activities, such as activities by a wheelchair user, involve repetitive motions of the arms. For example, pushing oneself in a wheelchair, rowing, push-ups and pull-ups, and assembly-line tasks may all involve repetition of a sequence of motions using the hands, arms, and wrists. A wearable device may be worn on the hand, wrist, or arm of the person performing the activity. It may be desirable to track activity by a wheelchair user for health, safety, or productivity reasons.

Apple's invention covers a method for tracking activity by a wheelchair user can include collecting motion data of a user device located on an appendage of the user, detecting by a processor circuit that one or more activities by the wheelchair user occurred based on the motion data, estimating by a processor circuit an energy expenditure by the user based on the one or more activities, and outputting the estimated energy expenditure by a processor circuit. In some embodiments, the motion sensor can include an accelerometer, a gyroscope, a magnetometer, or a combination thereof.

In one aspect, a method comprises collecting motion data of a user device located on an appendage of the user; detecting, by a processor circuit, that one or more activities by the wheelchair user occurred based on the motion data; calculating, by a processor circuit, an energy expenditure by the user based the one or more activities by the wheelchair user occurred; and outputting, by a processor circuit, the energy expenditure estimation.

Apple's method could include tracking pushes by the wheelchair user. In some embodiments, the method can include determining a pose angle and a calculated energy based on the motion data. In some embodiments, the method can include detecting a push occurred based on a determined pose angle and a calculated energy. In some embodiments, the method can include comparing by a processor circuit the determined pose angle with a pose angle threshold, comparing by a processor circuit the calculated energy with an energy threshold, and determining by a processor circuit a push occurred if the determined pose angle is below the pose angle threshold and the calculated energy is above the energy threshold.

In some embodiments, the method can include storing pose angles and calculated energies for the wheelchair user, updating by a processor circuit the pose angle threshold using the stored pose angle, and updating by a processor circuit the energy threshold using the stored calculated energies. In some embodiments, the method can include calculating by a processor circuit a current push rate for the user, determining by a processor circuit if the current push rate is consistent with previous push rates, and storing the determined pose angle and calculated energy if the current push rate is consistent with previous push rates.

Apple's Patent FIG. 1 illustrates an Apple Watch; Apple's patent FIGS. 4A to 4D illustrate four typical patterns of motion for a wheel chair user pushing their wheelchair.

Apple notes in their patent application that "manual wheelchair users propel their wheelchairs using a variety of different arm movements. These movements can typically be classified into four overall patterns--the arc, semi-circular, single loop, and double loop patterns. Each pattern consists of a "push" phase, during which the user is expending significant energy to move the chair, and a "return" phase, in which the arm is reset so that another push phase can begin. These patterns, in turn, correlate to various aspects of wheelchair user fitness such as energy expenditure, fitness level, mobility, stroke technique (which may then correlate to rehabilitation level), and other fitness metrics.

Apple's patent FIG. 28A noted above illustrates the directions of accelerometer forces for a wrist-worn device 2801 on the right wrist 2802 for user of wheelchair 2800. The X axis, as illustrated, is then the axis running horizontally across the display and roughly aligned with the direction of the forearm, with the positive X axis being towards the right elbow 2803 and right shoulder 2804. The Y axis, as illustrated, is the axis running vertically across the display, with the positive Y axis being generally away from the center of the body. FIG. 28B illustrates the directions of accelerometer forces for a wrist-worn device 2811 on the left wrist 2812. The X and Y axis are similarly oriented with respect to the device itself; however, because the device 2811 is located on the left wrist 2812 rather than the right wrist 2802, the sign of the X axis is inverted with respect to the body--the positive X axis is now oriented towards the left wrist 2812, rather than the left elbow 2813 and left shoulder 2814.

In patent FIGS. 34A-34C noted above we're able to see the results of using accelerometer-gyro sensor fusion to detect three dimensional paths. By measuring both acceleration and rotation using an accelerometer and gyroscopic sensors, a 6-degree of freedom measurement can be made providing an accurate path through 3-dimensional space. FIGS. 34A-34C illustrate the three-dimensional paths through space, with the axes of the graphic representing X, Y, and Z positions. In FIG. 34A, the lighter points represent a semicircular stroke path, while dark points illustrate an arc stroke path. In FIG. 34B, the lighter points represent a single loop stroke path, while dark points illustrate an arc stroke path. In FIG. 34C, the lighter points represent a double loop stroke path, while dark points illustrate an arc stroke path.

This path can then be classified to a stroke type by examining the actual path taken and determining which stroke type it most closely resembles (for example, by selecting the stroke type which has a minimum error between the measured path and the ideal for that stroke type, or by selecting the stroke type which has a minimum error between a distance-normalized measured path and a normalized ideal for each stroke type.) This provides an alternative method for identifying stroke type. To separate and classify these strokes, features of the 3D orbits are determined (e.g., angle of the stroke, pose angle or orientation of the device through the orbit, or circularity of motion). As gyro measurements tend to require significant battery consumption compared to accelerometer-only measurements, this method may also be used periodically to refine or correct accelerometer-only estimates or in other ways that are not constant, rather than being used on a stroke-by-stroke basis. Optionally, a magnetometer may be further incorporated to improve the 3D path accuracy.

Apple's patent application # 20170347885 was filed back in June 2017 with some original work having been done in August 2016. Another good article on the Apple Watch App for wheelchair athletes could be viewed here.

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