Wheelchair Performance Outcomes: Absolute and Relative – Erik Kondo

Wheelchairs are like other personal mobility devices (PMDs) such that designers, manufacturers, and innovators are constantly attempting to make improvements in their performance. But wheelchairs are also unlike other PMDs in that the concept of “performance” is ambiguous.

A bicycle is a PMD. If someone claims to make a bicycle “perform better”, he or she would have to explain in what manner it performs better and for who? For example, claiming that an innovative wheel makes a bicycle perform better is meaningless. Does it make all bikes faster? Does it allow for regular people to ride their bikes further and with less effort, or does it allow for the creation of a new bicycle speed record? In the able-bodied world of bicycling and other PMDs, there are established performance metrics to compare against. This not the case for wheelchair performance.

Performance of PMDs can be divided into two categories of Absolute Performance and Relative Performance. Improving the Absolute Performance of a PMD means that its top-end capability has been exceeded. This means that an existing metric has been surpassed in terms of speed, distance, maneuverability, or some other measurable event. For example, assume the top speed of a human powered bicycle was 80 mph, the innovation of a new type of wheel enables a higher absolute bicycle top speed of 85 MPH, thus setting a new record.

Relative Performance refers to the improvement (or deterioration) of an individual user’s (or category of users) performance. In this case, the metric could be a personal best. For example, a new bike wheel allows many “regular” individuals to increase their top speed by 10%. For example, this means a personal best of 30 MPH now becomes 33 MPH. But this new wheel may not improve bicycling Absolute Performance. In fact, it could actually decrease Absolute Performance. Maybe, World Class bicycle racers who use the wheel incur top speed decreases. Maybe, the wheel becomes unstable at speeds over 50 MPH. World Class racers are a different category of bicyclist than regular riders. They have different skills and abilities. Therefore, the racers’ performance may differ when using the new wheel. Absolute Performance (AP) and Relative Performance (RP) are independent of each other. An increase (or decrease) in one may or may not affect the other. Therefore, an innovation to a PMD will have one of the following outcomes:

1. Record Breaker: AP improved, and RP decreased.

2. Gold Standard: AP improved, and RP improved.

3. Equalizer: AP decreased, and RP improved

4. Dud: AP decreased, and RP decreased.

Note. The outcome of no change is not shown as a possibility since it is unlikely that a modification will have zero effect. The effect may be negligible, but it will still exist.

An increase in universal performance is the result of both AP and RP improving (Gold Standard). This is the only time when an innovation can truly be described as increasing performance for everyone. An example of this type of innovation is an electrical power assist for a bicycle in terms of speed. In this case, electrical assists can help all bicyclists go faster. Racer and non-racer alike will benefit from the addition of some type of add-on motor. For this reason, their use is prohibited in traditional bicycling competitions. Another example is the use of light weight/strong/rugged materials in bicycle frame construction. All bicyclists benefit from the use of these modern materials in some manner. Illegal performance enhancing drugs seem to help everyone with their speed and endurance.

On the other hand, electrical assists for wheelchairs as currently designed, (Equalizer) do not improve the Absolute Performance of manual wheelchairs. They do not increase top-end speed or range for high performing manual wheelchair users. They decrease performance due to the increase in weight and their limited range. But they do increase the top-end speed and range of a category of manual wheelchair users who have difficulty with pushing their manual wheelchairs. As with bicycles, the use of modern lightweight/strong/rugged materials for wheelchair frames has created an improvement of universal performance for all wheelchair users (Gold Standard). Generally speaking, anti-tipping devices, when used on manual wheelchairs reduce the performance of high-skilled wheelchair users while increasing the performance of low-skilled wheelchair users (Equalizer). That being said, high performing wheelchair dancers, tennis, and basketball players use anti-tipping devices to enhance their movements during their activities (Record-Breaker). But they do not use them in their everyday lives. The performance outcome of using anti-tipping devices is situational.

When it comes to wheelchairs, the important point is to recognize that not all improvements in performance (or claims of such) are created equal. Most improvements are not universal. Without the standards and metrics that exist for PMDs in the able-bodied world, it is difficult to draw accurate conclusions on the effectiveness of an innovation to improve the performance of wheelchairs. Is it a Gold Standard, Record-Breaker, Equalizer, or a Dud?