Multiple sclerosis does cause muscle atrophy, and it happens through more than one pathway. The disease damages nerve signals that activate muscles, but it also triggers a cascade of secondary effects, from chronic inflammation to reduced physical activity, that independently shrink muscle tissue. People with MS are nearly four times more likely to develop sarcopenia (clinically significant muscle loss) than the general population, based on data from over 1,700 MS patients in the UK Biobank.
How MS Leads to Muscle Loss
MS attacks the protective coating on nerve fibers in the brain and spinal cord. When those nerve pathways are damaged, the signals telling your muscles to contract become weaker, slower, or inconsistent. This disruption in nerve-to-muscle communication directly causes muscles to weaken and shrink over time. It’s what neurologists call neurogenic atrophy: muscle wasting driven by nerve damage rather than by anything wrong with the muscle itself.
But that’s only the first hit. The extreme fatigue and mobility limitations that come with MS often push people toward less active lifestyles, and muscles that aren’t regularly used begin to waste through simple deconditioning. Over time, underused muscles shift toward a smaller, weaker profile with less endurance capacity. This creates a reinforcing cycle: nerve damage reduces activity, reduced activity accelerates muscle loss, and muscle loss makes movement even harder.
Chronic inflammation adds a third layer. The inflammatory molecules circulating in MS promote the production of a protein called myostatin, which blocks muscle growth. At the same time, those same inflammatory signals ramp up the cellular machinery that breaks down muscle protein. So while nerve damage and inactivity are pulling muscle mass down from the outside, inflammation is degrading it from within.
Which Muscles Are Hit Hardest
The legs bear the brunt. Research consistently shows that MS disproportionately affects lower limb muscles, with the quadriceps (the large muscles on the front of the thigh) being a primary site of weakness and wasting. In one study comparing mildly affected MS patients to healthy controls, quadriceps strength was 22% lower in the MS group, even at early stages of the disease.
Muscle biopsies reveal that the damage isn’t uniform across all fiber types. Fast-twitch fibers, the ones responsible for quick, powerful movements like standing up from a chair or catching yourself during a stumble, show greater atrophy than slow-twitch endurance fibers. This selective loss of fast-twitch fibers helps explain why people with MS often struggle most with explosive movements and balance reactions, even when they can still walk at a steady pace. The legs also tend to accumulate more fat within and around the muscle tissue, further reducing functional strength relative to limb size.
Does MS Type Affect Severity?
Progressive forms of MS generally carry a higher burden of muscle atrophy than relapsing-remitting MS, though the relationship isn’t straightforward. Secondary progressive MS, which develops after an initial relapsing-remitting phase, tends to produce more severe spinal cord damage than primary progressive MS. Since the spinal cord is the main highway for motor signals to the limbs, greater spinal cord atrophy translates to more pronounced muscle wasting.
That said, muscle loss isn’t exclusive to advanced disease. Studies have documented reduced muscle fiber size and lower lean mass in patients with mild MS and minimal disability. The process starts early, which is one reason early intervention matters. People with MS are also more likely to develop presarcopenia (a preclinical stage of muscle loss) earlier in life compared to the general population: 14.1% of MS patients meet criteria for presarcopenia versus 7.2% in the general population.
Resistance Training Can Reverse Some Loss
The most effective tool for rebuilding muscle in MS is resistance training, and the evidence supports going heavier than many patients expect. A six-week program using loads at 70 to 80% of participants’ maximum lifting capacity, performed three times per week, produced measurable increases in muscle thickness, leg strength, and functional performance on tests like standing up from a chair and walking. Participants did three sets of eight to ten repetitions across seven exercises targeting all major muscle groups.
What made this finding particularly striking was that the same program also reduced blood levels of a marker associated with nerve fiber damage, suggesting that resistance exercise may protect nerve health in addition to building muscle. The key parameters appear to be intensity above 70% of your maximum, frequency of at least three sessions per week, and inclusion of exercises for all major muscle groups. Working with a physical therapist familiar with MS can help you find appropriate starting weights and manage fatigue.
The Role of Nutrition
Dietary protein provides the raw material muscles need to repair and grow, making adequate intake especially important when your body is already fighting muscle loss on multiple fronts. The National MS Society recommends choosing lean protein sources as part of an overall healthy diet. Amino acids from dietary protein have direct effects on both immune function and the brain, giving them a dual role in MS management.
While no MS-specific protein target has been established through clinical trials, the general recommendation for people at risk of muscle loss is higher than the standard daily guideline. Spreading protein intake across meals rather than concentrating it in one sitting helps maximize the body’s ability to use it for muscle repair. Combining adequate protein with regular resistance exercise creates the strongest stimulus for maintaining or rebuilding muscle tissue.