The Effect of a Wheelchair Propulsion-induced Fatigue Protocol on Biomechanical and Neuromuscular Risk Factors of Shoulder Pain in Persons With a Spinal Cord Injury Living in Switzerland: a Cross-sectional Study With a Repeated Measures Within Subject Design

What are the implications of wheelchair propulsion-induced fatigue for the development of shoulder pain and how can this knowledge improve prevention programs?

With this project, the "Shoulder Health and Mobility group" of the Swiss Paraplegic Research in Nottwil (Switzerland) wants to investigate how fatigue during wheelchair propulsion affects risk factors for shoulder pain of persons with a spinal cord injury (SCI). The investigators want to find out how the handrim wheelchair propulsion technique changes with fatigue and want to define persons who are susceptible to fatigue.

Getting life back after a SCI will most likely occur with the help of a wheelchair, whether it is at the beginning of rehabilitation or throughout further life. Gaining back mobility and participation in social life is important, also because of the multiple positive effects of physical activity on person's health and self-esteem, preventing several chronic diseases. Therefore, it is needed to try to stay away from shoulder injuries. Since the shoulder is very mobile and thus unstable, the joint is at increased risk for injuries. This is reflected in the high amount of persons with a SCI having shoulder pain (between 30 to 70 %). Once pain or an injury occurred, it is hard to recover, as so far no effective treatment is available. Several factors as gender, weight, age, level and completeness of the SCI, movement patterns and muscle strength were found to be related with injury and pain. However, it is currently not well understood what exactly causes shoulder injuries.

Handrim wheelchair propulsion is an inefficient mode of propulsion and asks a lot of demands to the upper body. Because of the inefficient movement and the shoulder being prone to injuries, wheelchair propulsion has a high chance of inducing shoulder injuries and pain. Propelling with a technique minimizing the loads on the shoulders and improving the capacity to perform these movements (as increasing muscle strength) is of utmost importance as these factors can be modified by training. Previous intervention programs have learned wheelchair users to propel with long and smooth strokes aiming to reduce the loads. Although someone might be aware of the recommended techniques and can apply them, propulsion technique might change with fatigue and could become less optimal. A similar phenomena happens for example in landing strategies from a jump. In a fresh state, persons will try to have a stable landing reducing the impact on the lower limbs. With fatigue, however, there will be a tendency to forget about the proper landing technique which on its turn can increase the risk of injuries. This was suggested to be one of the reasons why there is an increased prevalence of injuries towards the end of a game. So far, it is unclear how fatigue alters propulsion technique and how these changes are related with an increased risk of shoulder pain.

Tis project aims to achieve the goals by investigating how very strenuous wheelchair propulsion (fatigue intervention) of 15 minutes alters the propulsion technique of 50 persons with a SCI. All participants will perform the fatigue protocol in the movement analysis lab at the Swiss Paraplegic Research. During the protocol, participants will be requested to perform as many 8 loops as possible with their wheelchairs, including starts, stops, and right and left turns. Before and after the protocol, movement patterns, muscle usage and loads during wheelchair propulsion and the characteristics of the shoulder muscle tendons during rest will be assessed. Furthermore, the person's characteristics, such as weight, age, gender, time since injury, injury level, health conditions, use of medication, muscle strength and activity levels will be assessed. All these factors might be associated with the susceptibility to fatigue.

To answer our questions, we will first compare the propulsion technique (movement patterns, loads, and muscle usage) before and after the protocol to investigate the direct effect of fatigue. Secondly, we will investigate the association of negative changes in tendon appearance (which has been related to injury) with the changes in the propulsion technique to investigate the implications of acute changes that might increase the risk of injury. Finally we will run a model including all variables to determine which person's characteristics are associated with an increased susceptibility to fatigue.

The results will be highly relevant as it will give answers about the content, the aims and the target population of prevention programs for shoulder injury, aiming to improve mobility, participation, and quality of life in persons with SCI.