A new study suggests that the body’s internal clock not only controls sleep but also affects how quickly muscles recover from injury. Researchers at Northwestern Medicine found that muscle injuries heal faster when they occur during the body’s natural waking hours, at least in mice.
The study, published in Science Advances, could have important implications for shift workers, aging, and conditions like obesity and diabetes.
Why Time of Injury Matters
The body runs on an internal clock called the circadian rhythm, which regulates processes like sleep, metabolism, and hormone production. Every cell in the body follows this rhythm, including muscle stem cells, which play a key role in repairing damaged muscle.
Previous research had already shown that mice regenerate muscle faster when injured during their waking hours. This new study aimed to understand why that happens. Scientists used a technique called single-cell sequencing to study injured and uninjured muscle cells at different times of the day.
They found that the inflammatory response, which is crucial for healing, was much stronger when injuries occurred during wakeful hours.
One key finding was that muscle stem cells send stronger signals to immune cells right after injury when it happens during the active period. These immune cells, called neutrophils, are the body’s first responders for healing muscle damage. The stronger the signal, the better the muscle regeneration.
The Role of NAD+ in Healing
Another discovery was that the muscle stem cell clock controls the production of NAD+, a molecule that helps generate energy and is involved in metabolism. The researchers found that increasing NAD+ levels in muscle stem cells boosted inflammation in a way that actually helped speed up healing.
To test this, scientists used genetically modified mice that produced more NAD+ in their muscle stem cells. These mice showed faster muscle repair, confirming that NAD+ plays a crucial role in the healing process.
How This Research Could Help People
The findings could be especially useful for understanding how aging and obesity affect healing. As people age or develop metabolic conditions like diabetes, their circadian rhythms become disrupted. These disruptions are linked to slower muscle recovery and reduced immune function.
This study raises new questions: Do these circadian disruptions directly slow down healing? Could targeting NAD+ levels improve muscle regeneration in older adults or people with obesity?
The research also provides insight into how shift work, jetlag, or changes like daylight saving time might impact muscle recovery. If injury recovery depends on the body’s internal clock, disruptions to this clock could delay healing and recovery from workouts, surgeries, or injuries.
What’s Next?
Moving forward, the scientists want to learn more about how NAD+ interacts with the immune system and whether this could be used to improve treatments for muscle injuries. Research in circadian biology has mostly focused on individual cells, but new technology now allows scientists to study how different cell types interact under stress and during healing.
“This is a really exciting new frontier,” says lead researcher Professor Clara Peek. “Understanding how circadian rhythms impact muscle regeneration could help us find new ways to improve healing, especially in aging and metabolic diseases.”
In the future, doctors might be able to use this knowledge to optimize surgery times, recovery plans, and even exercise routines based on a person’s internal clock, making healing faster and more effective.
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The research findings can be found in Science Advances.
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