Study ties weaker muscles in old age to faulty nerve-to-muscle signals

Scientists have long argued about why muscles get weaker as people age. A new study adds a third suspect to the usual two (shrinking muscles and dying nerve cells). It points to the tiny gap where a nerve passes its signal to a muscle. The research, published in The Journal of Clinical Investigation, reports that this hand-off fails in weak older adults. It also reports that the failure is worse in people who are weaker.¹ In old rodents, an experimental drug approach made muscles respond better to nerve signals and improved their function.¹ That approach comes from a Danish biotech whose lead drug of the same kind is already being tested in people with rare nerve and muscle diseases.¹

What happened

The paper is titled “Neuromuscular junction failure in sarcopenia is linked to NaV1.4 loss and reversed by ClC-1 inhibition.”² Sarcopenia is the medical name for age-related loss of muscle strength and mass. A University of Missouri report says it affects nearly half of adults 80 and older.² The neuromuscular junction is the point where a nerve communicates with a muscle to make it contract.²

The work was led by W. David Arnold, executive director of the NextGen Precision Health Initiative and a professor of physical medicine and rehabilitation at the University of Missouri.¹ He leads an international team of scientists and clinicians from Denmark, Scotland, Saudi Arabia and India.² Co-authors include Hiroshi Nishimune, a researcher who studies the neuromuscular junction.² The company NMD Pharma, based in Aarhus, Denmark, announced the publication in July 2026.¹ The University of Missouri described the work in September.²

The evidence so far

The study combined two kinds of work. First, the team took electrical measurements of nerve-to-muscle signaling in older adults with clear muscle weakness. Second, it ran experiments in old rodents to look at how the problem arises and whether it could be reversed.¹ The sources read for this article do not say how many people or animals were studied.

In the older adults, the researchers found that signals at the junction were failing, and that worse failure went along with worse weakness.¹ Arnold’s team linked this weaker communication to reduced levels of a protein called NaV1.4.² The sources do not say whether NaV1.4 levels were measured in people, in animals, or both.

Arnold said the result challenges an older view of the field:

“A long-held assumption in the field was that the neuromuscular junction remains reliable during aging, and some even suggested it may get better with aging,” Arnold said. “The significance of this new study is we are showing, in both humans and animal models, that the neuromuscular junction is failing with aging.”

²

The team then tested a small-molecule drug (a chemical compound, as opposed to a gene or antibody treatment) that partly blocks ClC-1, an ion channel found only in skeletal muscle.¹ In old rodents that had nerve-signal problems similar to those seen in weak older adults, blocking ClC-1 made muscles more electrically excitable. It improved the signal hand-off and increased muscle function.¹ Arnold summed up the idea in the company’s announcement: “Aging muscle may not simply receive a weaker nerve signal—it can become less able to reliably translate that signal into muscle activation.”¹

What it does not show yet

The drug result comes from animals. No source describes a test of a ClC-1 blocker in older adults with age-related weakness. Arnold called the animal result “a potential path toward eventually testing this approach in older adults.”² Results in rodents often do not carry over to people. So this does not yet show that the approach would make older people stronger, or that it would be safe for them over years of use.

The measurements in older adults show a link between failing signals and weakness. On their own, links like this cannot prove which comes first. The authors describe signal failure as “a key, reversible contributor” to sarcopenia, not the only cause.¹ Muscle loss and the loss of nerve cells, the two older explanations, are still part of the picture.²

The study’s size, the ages of the volunteers and the details of the animal experiments are not given in the sources read here. The full paper would be needed to judge them.

Who is behind it

The study was a collaboration with NMD Pharma, which developed the ClC-1 approach used in the animal experiments.² NMD Pharma describes itself as a clinical-stage biotech developing therapies to restore skeletal muscle health.¹ Arnold has also worked with the company on its drug in people. He was an investigator in a multicenter trial of its drug ignaseclant in Charcot-Marie-Tooth disease.² The company has a direct business interest in the findings. It said the paper “further strengthens” its long-term strategy.¹ The sources read for this article do not describe who funded the study.

NMD Pharma’s chief executive, Thomas Holm Pedersen, said the company’s goal is to restore muscle function in people whose daily lives are limited by weakness.¹ He added that the idea that a healthier, more consistently activated muscle might also support healthy aging more broadly is an “emerging scientific hypothesis.”¹ In other words, it has not been tested.

How it fits the field

Researchers have studied the aging nerve-muscle junction for years. A 2020 review co-written by Nishimune described age-related declines in the function and structure of human junctions. It also discussed possible ways to slow those changes.³ That review explained that sodium channels sit in small folds of the muscle surface at the junction, where they help generate the muscle’s electrical signal.³

A separate review published in January 2026 in Molecular Diagnosis & Therapy said sarcopenia has traditionally been seen as a problem of shrinking muscle fibers. It noted that newer evidence points to damage at the junction as an early and important event.⁴ That review listed several changes seen at aging junctions, including the loss of motor nerve cells and the breaking up of the receptor clusters that receive nerve signals.⁴ It also discussed drug strategies aimed at different parts of the junction. It suggested pairing such drugs with exercise and nutrition, and using blood markers to spot problems early.⁴ The new study focuses on the muscle’s side of the hand-off. The company calls it a “previously underappreciated postsynaptic mechanism,” meaning a problem on the receiving end of the signal.¹

The drug already in trials

NMD Pharma’s lead drug, ignaseclant, partly blocks ClC-1. It is being tested in rare nerve and muscle diseases, not in age-related weakness.¹²

• Charcot-Marie-Tooth disease, the most common inherited nerve-and-muscle disorder.² In February 2026, the company reported early, headline results from a Phase 2a trial (an early test of whether a drug helps patients). It said patients showed improvements in muscle strength, movement and their own reports of how they felt.¹ Arnold presented these results at the 2026 Muscular Dystrophy Association Clinical & Scientific Conference.² The sources do not say how many patients took part, and the results are described by the company and the university rather than in a published paper.
• SMA: the company has completed an early study in adults, with results expected in the second half of 2026.¹
• gMG: a larger Phase 2b trial in patients with certain antibodies is expected to report in the first quarter of 2027. It follows an earlier Phase 2a study that the company called positive.¹

For age-related weakness, the company says it is working on newer ClC-1 drugs. It will start with moderate-to-severe sarcopenia.¹ Arnold said he is optimistic that ignaseclant itself could eventually help older adults with sarcopenia.² No trial in older adults is described in the sources.

What to watch next

• Whether other labs, working without the company, find the same signal failure in weak older adults.
• Results from NMD Pharma’s SMA study, expected in the second half of 2026, and its gMG trial, expected in early 2027.¹
• Any announcement of a first trial of a ClC-1 drug in older adults with age-related weakness, and how the company chooses to measure benefit in that group.