Comparing the shoulder load using a wheelchair versus a handbike

What was the aim of this study?

On average, half of all people with spinal cord injury (SCI) are suffering from shoulder pain. Often it is unclear what exactly the reason is for the shoulder pain since it is influenced by various factors. The repetitive wheelchair propulsion movement is often named as one of the most frequent reasons for shoulder pain. Researchers therefore want to find out whether alternative forms of transport such as the handbike are more suitable to overcome longer distances. Since the study concentrated on situations of everyday life, the clip-on handbike was tested. This means of transportation consists of the person’s own wheelchair that is connected to an additional unit in front of the wheelchair to move around outside.

How did the researchers proceed?

Eight wheelchair users with paraplegia were invited to the movement laboratory of Swiss Paraplegic Research. On a treadmill they were using the wheelchair and the handbike on four performance levels reaching from easy everyday performance (25 watts) to a performance simulating an inclination of 4% (55 watts).
During the tests, the mode of propelling of the subjects was analysed:

• The applied forces were measured with sensors inside the handles of the handbike and the handrim of the wheelchair. This shows clearly which means of transport requires more power.
• The movement of arms, hands and upper body were recorded using reflective markers and then depicted three-dimensionally.

Figure 1: test setup

The results were combined in a mathematic model of the shoulder. This allowed calculating which force impacts the shoulder joint, i.e. with how much strength the humerus is pressing on the socket of the shoulder joint. Furthermore, it was analysed when which shoulder muscle is active and how much. Both these results reflect the load on the shoulder joint. This made it possible to compare the shoulder load when using a handbike compared to the shoulder load when using a wheelchair.

What did the researchers discover?

The results show that the shoulder load is higher when a wheelchair is used. The maximum joint force is twice as high when using a wheelchair compared with the handbike (see figure 2). The highest forces were measured in the middle of the propulsion phase when using the wheelchair, whereas the strongest forces when using the handbike were measured when lifting the crank. Also the average values of the forces measured throughout a complete cycle (one crank rotation on the handbike; propulsion and return phase on the wheelchair) are lower when using a handbike.

Figure 2: force on shoulder joint at a power of 55 watt

In addition to the joint forces, also the muscle forces are higher on the wheelchair. The biggest differences were determined for both the supraspinatus and infraspinatus muscles. These are both muscles of the rotator cuffs that are stabilizing the shoulder joint and thus protecting from injuries.

What do these findings mean?

Former studies have shown that strong and frequent forces on the shoulder joint can lead to injuries. Due to the short propulsion phase, the maximum forces when using a wheelchair are very high. Since the shoulder joint forces during the complete cycle are also higher than when using a handbike, there is a higher risk of shoulder injuries when using a wheelchair.
When using a wheelchair, the muscles of the rotator cuffs, which stabilize the shoulder joint, are more heavily used than when using the handbike. If the wheelchair is propelled for longer periods, the risk of overfatigue of these muscles is higher which may lower their ability to protect the shoulder joint optimally and make it prone to injury and pain.
The results of the study have shown that the handbike is not only more efficient but also that there is a smaller shoulder load. Therefore the handbike should be the preferred means of transportation for the outside and for training.

Who conducted and financed the study?

The study was carried out and financed by Swiss Paraplegic Research (Switzerland).