Background

Multiple sclerosis (MS) is a chronic disease of the central nervous system, affecting approximately 2.5 million people worldwide. Although the exact cause of the disease is unknown, it is generally accepted that MS involves an abnormal immune response within the central nervous system. Depending on the severity of the disease, people with MS may experience varying limitations in, for example muscular strength and endurance, including in the muscles needed to breathe (respiratory muscles). Strength of the respiratory muscles is related to people’s ability to function and to exercise, and respiratory muscle weakness can lead to less effective coughing, which may result in aspiration pneumonia (when food, saliva or other liquids are breathed into airways instead of being swallowed) or even acute failure of respiratory function. These pulmonary complications are frequently reported causes of death in people with MS. Training of the respiratory muscles might improve breathing and cough effectiveness.

Study characteristics

We searched electronic databases for randomized controlled trials (where participants are assigned at random to either a treatment or a control arm) published up to 3 February 2017 that investigated respiratory muscle training in people with MS. In addition, we contacted experts in the field to identify additional studies.

Key results

We found six trials involving 195 participants with MS. Training consisted of two or three sets of 10 to 15 repetitions, twice a day for at least three days a week, and interventions lasted for six weeks to three months. Follow-up ranged from no follow-up to six months. Two of the included trials investigated inspiratory muscle training with a threshold device (i.e. a portable breathing device that increases airflow resistance while inhaling or exhaling). Three trials investigated expiratory muscle training with a threshold device, and one trial investigated breathing exercises. We found benefits with inspiratory muscle training for improving predicted maximal inspiratory pressure, but not for improving measured maximal inspiratory pressure. We did not find any effects for maximal expiratory pressure. Only one study measured quality of life, but it did not find any effects; two trials measured fatigue and also failed to find a difference between the treatment and control groups. Eighteen participants (~ 10%) dropped out, and no trials reported any serious adverse events.

Quality of the evidence

The six trials that were eligible for inclusion in this review were small, so statistical power was low, making analyses less precise. In addition, studies were heterogeneous in terms of the type of respiratory muscle training, dosing/intensity, and the severity of MS. In addition, we could not analyze the effects of training on, for example, cough efficacy, pneumonia, and quality of life, as the included trials did not report on these outcomes even though they are important for patients, caregivers and healthcare professionals. Altogether, this review provides low-quality evidence that resistive inspiratory muscle training improves predicted inspiratory muscle strength in people with MS. We did not find any effects for resistive expiratory muscle training. More high-quality research in respiratory muscle training in MS is needed.