Physical strain

Aim of this thesis was to study the effects of low-intensity wheelchair training on wheelchair-specific fitness, wheelchair skill performance, physical activity levels and propulsion technique in physically inactive people with long-term spinal cord injury (SCI). Chapter 1 provides the background of this thesis. Muscle paralysis and wheelchair dependence makes it difficult for many people with spinal cord injury to be physically active and fit. They are at risk of entering a vicious cycle of physical inactivity, low fitness and secondary health complications. People with long-term SCI are likely to enter this vicious cycle given age-related declines in physical activity and fitness levels, while also being at increased risk of developing secondary health complications. Negative effects of such a vicious cycle might be prevented or reduced by employing an aftercare system that includes interventions aimed at improving physical activity and fitness levels, while simultaneously reducing risk of secondary health complications. Given the lack of knowledge on this topic, research program ‘ALLRISC’ was developed. One of the studies in ALLRISC was a multicenter randomized controlled trial (RCT) on low-intensity wheelchair training in inactive people with long-term SCI. Previous research showed that people with SCI can improve fitness through wheelchair training at relatively vigorous intensities. However, it may lead to low adherence, dropout and musculoskeletal injury in inactive people with long-term SCI. The assumption in this thesis was that these problems do not occur in low-intensity wheelchair training, while still obtaining fitness improvements. Substantial fitness improvements have been found in able-bodied populations performing low-intensity training. However, effects had not yet been systematically investigated in inactive people with long-term SCI.

Chapter 2 presents a cross-sectional cohort study on the impact of physical activity and time since injury (TSI) on wheelchair-specific peak aerobic work capacity in people with SCI for at least 10 years (N=213). Participants used their own wheelchair in an incremental exercise test to determine peak power output and peak oxygen uptake. These parameters were negatively associated to longer TSI and less physical activity. This indicates that people with SCI need support in maintaining levels of physical activity and wheelchair-specific fitness over their lifespan. The test could not be performed by a third of the included participants (n=75). These non-participants seemed a negative selection of the cohort: they appeared to be older, have a longer TSI, lower activity levels and more upper-body pain than participants able to perform the peak test, while also more often having a tetraplegia. This finding shows the potential selection bias in research on fitness of people with long-term SCI.

Chapter 3 is a description of the design of the multicenter RCT on low-intensity wheelchair training. Inclusion criteria comprised TSI > 10 years, inactivity as defined by a reference score on a questionnaire, age ≤ 65 years, age at onset SCI ≥ 18 years and use of a manual wheelchair in daily life. Participants were randomly allocated to an exercise or control group. The exercise group followed a 16-week training in a rehabilitation center. The training consisted of wheelchair treadmill propulsion at 30-40% heart rate reserve or its equivalent in rate of perceived exertion, twice a week, 30 min per session. The control group was not offered any intervention. Measurements occurred at baseline as well as after eight, 16 and 42 weeks. One hypothesis was that the exercise group would increase fitness levels, and through that, improve wheelchair skill performance and physical activity levels. Another hypothesis was training effects in propulsion technique, leading to reduced risk of joint damage during daily wheelchair propulsion.

Since the RCT took place in rehabilitation centers, feasible tests were needed to study effects on wheelchair-specific fitness. For this purpose, a new test was developed: a 15 m-overground sprint test in a wheelchair equipped with a measurement wheel to determine power output. Chapter 4 is an evaluation on whether this test can be used to assess wheelchair-specific anaerobic work capacity. In a pilot study, an able-bodied group (N=19) performed the 15-m sprint test and a more established test of wheelchair-specific anaerobic work capacity (30-s sprint on a wheelchair ergometer using a Wingate-like protocol). A moderate association was found between peak power output over the 15-m test and mean power output over the Wingate-like test. Handrim velocities were significantly higher in the 15-m test. An explanation for these findings is that the 15-m test is more dependent on motor coordination than the Wingate-like test. When this is taken into account, peak power over the 15-m test seems acceptable for assessing wheelchair-specific anaerobic work capacity.

The group participating in baseline measurements in the RCT (N=29) performed several wheelchair-specific tests feasible for use in rehabilitation centers, including the 15-m sprint test, an isometric-push test and a peak wheelchair exercise test. Chapter 5 is a description of these results, which provide insight into wheelchair-specific anaerobic work capacity, isometric strength and peak aerobic work capacity of inactive people with long-term SCI. The majority of the group had relatively low levels in all fitness components. This implies that most inactive people with long-term SCI seem to require support in prevention or improvement of low wheelchair-specific fitness levels. The fitness components in the group were only weakly or moderately associated. This implies that separate tests should be used when assessing different components of wheelchair-specific fitness in rehabilitation centers.

Chapter 6 and 7 are evaluations of the training effects in the RCT. The low-intensity wheelchair training appeared to have little or no effect. This implies that substantial training effects require other forms or doses of exercise. Suggestions for more effective training than that used in the RCT are: more than twice-weekly low-intensity wheelchair exercise using a feasible training format; wheelchair training in which exercise intensity is gradually increased over a relatively long period; a combination of low-intensity wheelchair training and moderate-intensity handcycling; and moderate forms of resistance training. Another approach is to use programs aimed at stimulating an active lifestyle through exercise counseling and teaching self-management skills.

Chapter 8 is a discussion of main findings in this thesis. The impact of secondary health complications occurring over the lifespan with SCI may be an explanation for the negative associations among fitness, activity and TSI. These health complications may also explain the low fitness levels. Alternatively, it could be that were already present during inpatient rehabilitation, while these never improved after that. Longitudinal studies are required for inferences about causality of the relationships among physical activity, fitness and secondary health complications in people with long-term SCI. Such studies should include an evaluation of selection bias.

Future research on training interventions in people with long-term SCI should start with simpler study designs than an RCT. An RCT such as in this thesis often leads to inconclusive results due to insufficient sample size, high dropout rates and large heterogeneity in a study group with SCI. Another difficulty in an RCT is that the need for high internal validity can compromise ecological validity, challenging implementation in practice. These difficulties are less likely in studies based on non-randomized designs, cross-over designs or single-case designs that include multiple baseline measurements and mixed methods. Also recommended is to use study designs that allow analyses of interindividual differences, which can help to discern potential responders and non-responders to an intervention.

The 15-m test, isometric-push test and peak wheelchair exercise test used in this thesis seem to be exercise tests feasible for assessing wheelchair-specific fitness in rehabilitation centers. Widespread implementation of such tests is facilitated by: improving availability and affordability of test equipment; minimizing time and burden of test protocols; and providing more information about psychometric properties such as sensitivity of test outcomes to changes in individual participants.

The training in this thesis presumably has little or no effect on preventing or breaking a vicious cycle of physical inactivity, deconditioning and secondary health complications in people with long-term SCI. It seems challenging to find effective and feasible exercise interventions for the inactive population with long-term SCI. This implies that focus of health care in people with SCI should be on preventing physical inactivity and deconditioning. This may be supported by aftercare that covers the lifespan with SCI, including regular fitness screening as well as counseling on how to prevent secondary health complications and physical inactivity. In any approach, the focus should be on the individual needs of each person with SCI.

Contact address

Sonja de Groot / Lucas van der Woude

Center for Human Movement Sciences

University Medical Center Groningen

University of Groningen

Antonius Deusinglaan 1

9713AV Groningen,

The Netherlands

Summary