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From rehabilitation to performance

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Maintenance of fitness is vital for health and wellbeing, but how can patients with severe disability participate in exercise? The Institute for Rehabilitation and Performance Technology IRPT, together with clinical partner Reha Rheinfelden, has developed robotic systems for exercise testing and training.

Fig. 1: Treadmill max-test.

Performance testing in athletes
Within the field of high-performance sports, it is common practice to evaluate an athlete’s physical training status by carrying out a “max-test” on a treadmill or cycle ergometer. The aim is to take the athlete gradually to their limit of functional capacity, i.e. to exhaustion, over a short period of time. Cardiopulmonary exercise testing delivers two key outcomes which describe the functional status of the heart and lungs: the gold standard for describing the limit of aerobic capacity, which is obtained from a max-test, is the maximal oxygen uptake, referred to as “V-O-2-max” and denoted as V’O2-max; the maximal heart rate, HR-max, is also recorded.
When using a treadmill, the speed and slope are gradually increased with the aim of reaching maximal performance in around ten minutes (Fig. 1). The athlete has to run on the treadmill while the exercise intensity gradually increases, until he signals that he has reached his limit and can no longer continue – the test is then terminated.
V’O2-max is measured using a breath-by-breath spirometry system which involves the athlete wearing a face mask and a heart rate chest belt. The volumetric rate at which oxygen is taken up at the lungs (V’O2) and carbon dioxide is expelled (V’CO2) are directly measured. V’O2- max gives a direct indication of the body’s ability to extract oxygen from the air, and to transport it via blood circulation to the muscles doing the work during exercise: doing this well depends on the integrative capacity of both central and peripheral physiological systems, including the heart, lungs and muscles.
The reason measuring V’O2-max is important is that, because it reflects the efficiency of interactions between the cardiovascular, pulmonary and neuromuscular systems, it gives a very direct indication of the athlete’s overall fitness. This information can be used in two ways: to assess the effects of a training programme over time, by periodically re-evaluating V’O2-max; and to prescribe an appropriate level for training intensity, because this is often recommended to take place at a certain frequency and duration and at some percentage of V’O2-max or HR-max.

The rehabilitation context
Suppose now that we wish to measure the maximal cardiopulmonary performance of a patient with severe physical disability resulting from a stroke, a spinal cord injury, or some other neurological condition. The reasons for testing are the same as for athletes: to obtain crucial data on fitness and to allow the informed prescription of an exercise training programme. Because patients with serious impairments cannot use a normal system like a treadmill, the IRPT has focused its research programme on the development of robotic rehabilitation systems which facilitate exercise testing and training, and on the translation of assessment protocols from high-performance sports to this new and very challenging context.
The key is to adapt robotic systems so that the patient is able to perform an increasing amount of work over a short time by volitional activation of their available muscles. To do this, we provide patients with a biofeedback system which shows them a target level of exercise intensity together with a visualization of their own performance: the target intensity increases steadily over about ten minutes while the patient is instructed to exert themselves more and more to keep following the target. The test stops when it is clear that the patient has reached his limit.

Fig. 2: G-EO-System, end-effector robot for walking and stair climbing.

The scientific evidence
We have used this principle to adapt both the G-EOSystem (Reha Technology AG, Olten, CH), an end-effector robotic device for walking and stair climbing (Fig. 2, [1]), and the Lokomat (Hocoma AG, Volketswil, CH), an exoskeleton-based system for treadmill walking (Fig. 3, [2]). At the IRPT, and in collaboration with our clinical partners at the Reha Rheinfelden, we recently completed a breakthrough clinical study where a group of severely disabled stroke patients trained for four weeks using the augmented Lokomat system. Overall fitness was assessed using max-tests implemented on the Lokomat. We found that V’O2-max increased on average by 20% even though the four-week training period was relatively short and the training intensity was moderate [2]: this is a rapid and substantial improvement in cardiopulmonary fitness early after stroke. In comparison, other studies have shown that, without a guided training intervention and just following the normal rehabilitation programme, this magnitude of fitness improvement can take up to six months.

The clinical potential
These very promising new results represent the successful translation of methods and protocols from the field of high-performance sports to the context of neurological rehabilitation. These are important and necessary steps towards the clinical implementation of effective cardiopulmonary exercise training and accurate assessments in patients with severe impairments.

Fig. 3: Lokomat exoskeleton robot for treadmill walking.