Compared with patients with MS who didn’t fall, those who did fall had worse neuromuscular function as evidenced by a reduced rate of force development.
“Our study suggests that instead of looking at reduced maximum muscle strength, perhaps we should start looking at reduced rate of force development when trying to identify potential fallers,” said Laurits Taul-Madsen, PhD student, Aarhus University, Denmark.
The study was presented at the annual meeting of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS).
Explosive strength
In contrast to maximal muscle strength, the rate of force development is a measure of explosive strength, or simply the amount of force that an individual can produce over a given time period. When a patient is about to fall, what’s most important is not how strong the person is, but how quickly they can produce enough force to counteract the balance perturbation, thus avoid falling, said Dr. Taul-Madsen.
“If a person is very slow to produce this force, [that person] will have fallen before he or she has produced enough force to counteract the balance perturbation that the person is experiencing,” he added.
Research has shown a reduced rate of force development (RFD) in patients with MS, compared with healthy controls. However, little is known about the impact of RFD on falls in those with MS.
To investigate, researchers studied 53 adults with MS: Twenty-four had no fall history in the prior year, 16 had one to two prior falls, and 13 had three or more falls. The two groups of fallers were both slightly older and had a slightly higher Expanded Disability Status Scale (EDSS) scores, “which may not be so surprising,” Dr. Taul-Madsen said.
Knee extensor neuromuscular function, including maximum muscle strength and RFD at 50 and 200 milliseconds, was assessed via isokinetic dynamometry.
A high RFD is “good and the non-fallers had the highest RFD at 50 ms.” On this measure, “we saw quite a big difference between the non-fallers and the two groups of fallers,” Dr. Taul-Madsen reported.
At 200 ms, the RFD was again highest in the group of non-fallers but the difference was somewhat smaller. Non-fallers also had greater maximum muscle strength than that of the fallers.
There was “good” correlation between these neuromuscular measurements and falls, Dr. Taul-Madsen said.
He noted that RFD, which can be improved with resistance training, “seems like a specialized and difficult measurement, but it doesn’t have to be. It can be measured with just a linear encoder and a chair to perform the sit-to-stand test, so in clinical practice, it’s quite easily measured.”
‘Highly promising’ approach
“There are some data on predictors of falls in persons with MS, but not yet on neuromuscular function, as has been done in other populations,” said Brian Sandroff, PhD, senior research scientist, Kessler Foundation, West Orange, N.J.
This study is “interesting in that recurrent fallers were distinguished based on having worse neuromuscular function,” said Dr. Sandroff, who was not part of the research team.
“Although this relationship is somewhat intuitive,” RFD provides a “potentially sensitive measure that can be addressed via specific resistance exercise programs as a highly promising approach for reducing fall risk and falls themselves in persons with MS,” Dr. Sandroff said.
More generally, he said this study provides “more evidence on the multisystemic benefits of exercise training and having better physical fitness in persons with MS.
“The evidence seems to be converging more and more on this, as research groups across countries and continents are reporting on similar themes,” said Dr. Sandroff.
The study had no specific funding. Dr. Taul-Madsen and Dr. Sandroff report no relevant financial relationships.
A version of this article first appeared on Medscape.com.