Feasibility of a low cost and easy to use rowing ergometer for paraplegic individuals using surface stimulation of paralysed muscles: A pilot study

Investigators: Dr Prisca Eser, A/Prof Thomas Angeli, Prof Mary Galea

Patients with acute spinal cord injury (SCI) suffer from extensive bone loss in the paralysed extremities that is initiated shortly after injury. The disuse-associated bone loss is greatest within the first 2 to 5 years after injury and a new steady-state with regard to bone mass and geometry is reached after 3 to 8 years. Individuals with chronic SCI have a 40-75% mean deficit in bone mass of the paralysed legs compared to able-bodied individuals [1] . As a result, fractures of the paralysed extremities are a common complication in these individuals. Fractures often result from minor trauma, such as falls out of the wheelchair, and normally require hospitalisation for orthopaedic surgery. There is a high incidence of complications due to non-unions and infections.

In individuals with chronic SCI, muscle forces in the form of spasticity have been found to positively influence bone strength of the femur. Besides spasticity, muscle pull on the bones of the paralysed legs of SCI individuals can be reinstated by means of functional electrical stimulation (FES). Two previous studies have shown that FES in the form of cycling or knee extensions is not only successful at restoring muscle mass in the legs of individuals with chronic SCI, but also at restoring bone mass in the order of 10-30% within 6-12 months. FES-rowing is an easy to use exercise modality that combines FES training of the legs with volitional muscle training of the arms. Previous studies have shown its feasibility and efficacy as a cardiovascular training [8-11] . No studies have been performed to date that have assessed the effect of FES-rowing on bone strength.

This pilot study is a first step toward the main study that will assess the effects of FES-rowing on bone strength. The aim is to test the feasibility of a custom made rowing ergometer. An earlier rowing ergometer prototype, which was run with the same 8-channel stimulator, had already been used for a study at the Swiss Paraplegic Centre in Nottwil, Switzerland. The new prototype consists of a Concept 2 air-drum with handlebar, and a rail onto which the patient's own wheelchair is mounted (Fig. 1).

Figure 1 : Subject during a rowing stroke at the end of the extension phase. The air-drum and handle bar (including the chain) are adapted from a commercially available Concept 2 rowing ergometer. The rail securing the wheelchair and knee stabilisation system are custom built.

Four patients with a motor complete SCI (ASIA A and B) and a spastic paralysis sub C7 attending the Austin Health, Heidelberg, Victoria were recruited for this pilot study. Inclusion criteria were good health, at least 4 weeks and no longer than 12 months post trauma. Exclusion criteria were obesity, recent fractures of the appendicular skeleton, and pressure sores.

The rowing ergometer was custom made by the Department of Machine Engineering, Technical University Vienna, Austria. It partly consisted of a commercially available Concept 2 rowing ergometer (air-drum, handle bar, chain, and air-drum mount) and was adapted with a rail which secured the wheelchair to the ground. It was further fitted with a knee interface that constrained the leg movement to the sagittal plane. For the electrical stimulation, an 8-channel stimulator (Krauth+Timmermann, Hamburg, Germany) was used. Surface electrodes were applied to the proximal and distal ends of the muscle bellies of the following muscle groups: quadriceps, glutei, hamstring, and erector spinae. For the stroke phase, the subjects pressed a button with the right thumb on the handle bar of the rowing ergometer. The erector spinae muscles of both sides were stimulated first in order to stabilise the trunk. Quadriceps and gluteal muscles were stimulated together after a time lag of 0.5 s. The subjects released the button when the knees were fully extended and the stroke phase finished, this stopped the stimulation and the muscles relaxed. The subjects then pressed the button on the handlebar's left side, which triggered the stimulation of the hamstring muscles. Upon release of the button, the muscles relaxed.

Two subjects with a lesion level at C6/C7 and two at T4 were included in the present study. Without prior muscle conditioning they could all row between 5 and 15 minutes. Because of their relatively high lesion level, tight securing with a Velcro strap to the wheelchair's back rest was important in order to provide trunk stability. Although the back extensor muscles were stimulated in the extension phase, the trunk collapsed forward during recovery phase without back extensor stimulation. In one of the C6/C7 subjects hip extension with hamstring stimulation during recovery phase was a problem and better knee/hip flexion was achieved by stimulation of the peroneus reflex. Generally, propulsion force developed by the hamstring muscles is weaker than extension propulsion force developed by the quadriceps and gluteal muscles. This inequality was countered by a bungy system that supported the flexion phase while at the same time giving resistance to the extension phase. Also, greater adjustment range of the vertical level of the foot plate will allow an increase in hamstring muscle length and potentially improve force development capacity.

The tested new prototype of an FES-rowing ergometer that uses an SCI individual's own wheelchair mounted onto a rail proved to be suitable for a large scale intervention study. The vertical adjustment range of the foot plate will be increased to better accommodate subjects' individual muscle length optima.

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