August 30, 2026
Exercise triggers a molecule that helps muscles become stronger
Muscles produce a small molecule during exercise that appears to help them build endurance, improve energy use, and adapt to repeated training
ByLuis Arrais
Author
Start running three times a week and, after a month, the same route feels easier. Muscle rebuilds itself to make that happen, and a new study finds it can’t finish the job without one small molecule produced during exercise
Muscles produce that molecule, called L-BAIBA, as they work. Mice that couldn’t produce it trained just as hard but gained far less from the exercise
Nearly all of that evidence comes from mice and from human muscle cells grown in a dish. People in the study gave blood and nothing else
Lee Roberts, Professor of Molecular Physiology and Metabolism at the University of Leeds, led the work
“Our research identifies L-BAIBA as an exercise-induced signal that helps muscles adapt, improve their metabolic capacity and ability to contract, and ultimately enhances physical performance,” Roberts said
Valine breaks down
Muscle moves you, but it also acts like a signaling organ, releasing chemical messages into the blood
One of those signals begins with valine, an amino acid found in protein-rich foods. Eating too little protein has been linked to weaker muscles in older adults
Muscle burns through amino acids, the small units that proteins are built from, and one of them is valine. Take valine apart inside a muscle cell and one of the leftovers is a compound called beta-aminoisobutyric acid, or BAIBA for short
Roberts and his colleagues reported in 2014 that exercise makes muscle produce more BAIBA, and that the extra BAIBA changed how the body burned fat. You can buy it as a supplement now, and it’s one of a long list of compounds chased as an exercise pill
BAIBA also comes in two mirror-image versions, and sorting them out is what this study did first. Only one of them, L-BAIBA, did anything to muscle at all. A single enzyme finishes that version, and it works inside the muscle cell’s mitochondria, the compartments that turn food and oxygen into usable energy
Treated mice ran farther
Young male mice drank BAIBA in their water for six weeks, at 100 milligrams per kilogram of body weight a day. They ended up with about as much of it in their blood as exercise alone can produce
Then the mice met a running wheel. The treated ones turned it more times and ran faster, without going to the wheel any more often than the others did
Their legs had changed underneath. The soleus, a calf muscle built for endurance, weighed more and held more fibers, with extra numbers of the slow, fatigue-resistant kind
Cut out and stimulated in a bath, that muscle pulled harder than a control animal’s
Mitochondria account for part of it. Treated mice had more mitochondria packed into their muscle, and the tissue used oxygen more efficiently
Weeks of endurance training do much the same thing on their own, through the muscle’s usual energy sensor
Trained mice stopped improving
Adding the molecule is one test. The harder one is the reverse: take it away, then train the animal anyway
Roberts’s team injected short strands of DNA into the hind-leg muscles of mice twice a week, which shut down the enzyme that finishes L-BAIBA in that tissue
Ten mice per group then trained on an inclined treadmill for six weeks, four days a week in 45-minute sessions
Trained mice normally finish with more L-BAIBA in their blood. These ones barely did
They quit sooner on a run to exhaustion and topped out at a slower speed, and their calf muscle pulled with less force than a trained animal’s should
The workouts were identical. What the muscle kept from them wasn’t
Sixty volunteers aged 18 to 65 walked a treadmill test at Newcastle University that measured their peak oxygen uptake, the standard yardstick for aerobic fitness
On a later visit, they walked an incline for 45 minutes at 60% of that peak, with blood drawn before they started and the moment they stopped
Resting L-BAIBA tracked fitness. The relationship was weak but statistically significant. The mirror form showed no relationship with fitness, while both forms rose immediately after exercise in men and women
A separate 33 people rode stationary bikes through a 10-week program at Wageningen University
Their L-BAIBA was higher at the end of it, and the mirror form was not. In this group, resting L-BAIBA matched fitness about twice as closely as in the first
None of that shows the molecule made anyone fitter. The human results support the mouse findings, but they do not prove cause and effect
Obese mice recovered lost endurance
Mice fed a high-fat diet for eight weeks grew heavy and cleared sugar from their blood poorly. They also ran less. Half of them then got BAIBA for 14 more weeks while the rest stayed on the diet alone
The treated group recovered its 24-hour running distance. Their soleus regained mass and fiber numbers, and it held its force longer before fatiguing
A mouse on a high-fat diet is not a person with type 2 diabetes, and that gap matters
Anna Morris is the assistant director of Research Strategy and Partnership at Diabetes UK
“Exercise plays an important role in managing type 2 diabetes, but for many people muscle weakness and fatigue can make staying active a real challenge,” said Morris
“While these findings are still at an early stage, they could help shape future approaches that support people with type 2 diabetes to remain active and live healthier, longer lives.”
Human trials have not happened yet
Not one person in the study took L-BAIBA. The human side of the work is blood chemistry: who had how much, and when
Age changed the outcome as well. Young mice grew extra muscle fibers on BAIBA. Mice treated later in adulthood did not; instead, they rebuilt fibers they already had
Older adults are the people who most often lose strength and speed, a loss that simple tests of muscle power can measure. The experiments did not test genuinely old animals
The mice in the first experiment were all male, and every training program here was aerobic. Whether lifting weights sends the same signal is open
“This gives us exciting new insight into how exercise benefits the body and highlights a promising target for future therapies aimed at preserving muscle function in chronic conditions such as diabetes,” Roberts said
The next step is to test L-BAIBA in people. Roberts and his colleagues want to start with patients with type 2 diabetes, then expand to conditions that cause muscle loss, including heart failure and cancer
The full study was published in the journal Nature Communications
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com
—–
