Why did you decide to assess the effect of electrical stimulation plus voluntary strength training?

As a clinician working in the acute spinal cord injuries unit, I was interested in finding the best interventions to increase the strength of very weak muscles in people with spinal cord injury (SCI).

Electrical stimulation (ES) and strength training are very widely used in clinical settings and have been shown to be effective in stronger muscles (grade 3/5 and 4/5); however, weaker muscles (less than grade 3/5 strength) have not been investigated.

This randomised controlled trial looked at this question.

The research is part of my PhD and is supervised by Associate Professor Joanne Glinsky and Professor Lisa Harvey.

We had a team of collaborators from Royal North Shore Hospital and Royal Rehab in Sydney as well as the Centre for the Rehabilitation of the Paralysed in Bangladesh.

What was the regimen of the electrical stimulation and the voluntary strength training?

Participants in the treatment group performed three weekly sessions, each comprising six sets of 10 voluntary muscle contractions using ES—under the principles of progressive resistance training—followed by 60 ES-induced contractions.

ES was delivered at a standardised frequency of 50 hertz and a pulse width of 300 microseconds, with amplitude adjusted up to 100 milliamperes as required during the session.

Notably, this treatment was in addition to the care that they usually received at the units, which included functional training.

Those in the control group just received their usual care with no extra strength training for the target muscle group.

What outcomes were assessed in the study?

Our primary outcome was voluntary muscle strength of the target muscle group—measured using the 13-point manual muscle test.

The secondary outcomes were participants’ perceptions of changes in strength, function and ability to perform self-selected goals.

What effect did the combined regimen have on voluntary muscle strength?

After eight weeks, the mean between-group difference in voluntary strength (the primary outcome) was 0.7 out of 13 points, with
a confidence interval of –0.7 to 2.1.

The minimally worthwhile treatment effect was set at 1.0 prior to the start of the trial.

Therefore, our result indicates either no or very small effect.

This was a surprising result for a commonly administered physiotherapy intervention.

It challenges our long-held confidence in the ability of ES to strengthen very weak muscles effectively.

What about the secondary outcome measures?

The results of our secondary outcomes support the results of our primary outcome.

The participants’ perceptions of improvement in function and strength and their ability to perform self-selected goals did not differ between groups.

Given that this combined intervention appears ineffective, are there alternative interventions that could be tested on neurologically very weak muscles?

This is the second randomised controlled trial that our team has conducted investigating strengthening in very weak muscles.

The first trial showed that 10,000 isolated contractions of very weak muscles in people with SCI over eight weeks also have little to no effect on voluntary strength in people with SCI.

Further randomised controlled trials are needed to investigate the best way to strengthen very weak muscles in people with SCI.

These trials may investigate longer interventions, varying the dosage provided or combining the interventions with other types of training, such as motor training.

>>Lydia Chen is a clinical specialist physiotherapist at Royal North Shore Hospital in the spinal injuries unit and a PhD candidate at the University of Sydney. She has over 15 years of experience as a clinician working within the areas of neurology and spinal cord injuries.

Courses of interest:

Spinal Physiotherapy Part A (Cervical)