Researchers discovered that chronic kidney disease—a condition where kidneys don’t work properly—weakens the tough cords that connect muscles to bones, called tendons. Using rats with kidney disease, scientists found that their tendons tore more easily than healthy rats’ tendons. This is important because people with kidney disease sometimes experience sudden tendon ruptures that can be very painful and limit their ability to move. This study is the first to prove that kidney disease directly damages tendons, which could help doctors develop new treatments to prevent these injuries in patients with kidney problems.

The Quick Take

  • What they studied: Whether chronic kidney disease weakens tendons and makes them more likely to tear or break
  • Who participated: 32 young adult rats (16 male and 16 female) divided into two groups: one with normal kidney function and one with kidney disease induced by a special diet
  • Key finding: Rats with kidney disease had tendons that tore at 24% lower stress levels than healthy rats, meaning their tendons were significantly weaker and more fragile
  • What it means for you: If you have chronic kidney disease, you may have a higher risk of tendon injuries. This research suggests the need for protective strategies, though more human studies are needed before specific recommendations can be made. Talk to your doctor about monitoring tendon health if you have kidney disease.

The Research Details

Scientists used two groups of young rats to compare how kidney disease affects tendon strength. One group ate normal food and maintained healthy kidneys, while the other group ate food containing a substance called adenine that damages kidneys, similar to how chronic kidney disease develops in humans. After 9 weeks, the researchers removed the tendons from both groups and tested them in a machine that pulled on the tendons until they broke, measuring exactly how much force was needed to cause failure.

The researchers tested two different tendons: the Achilles tendon (the large tendon in the back of the ankle) and the tibialis anterior tendon (in the front of the shin). They measured several important properties including how much weight the tendon could hold before breaking, how strong it was relative to its size, and the actual thickness of the tendon.

This approach allowed scientists to directly compare tendon quality between healthy and diseased kidneys in a controlled setting, establishing the first clear link between kidney disease and tendon weakness.

This research design is important because it proves that kidney disease directly causes tendon problems, rather than just being a coincidence. By using a controlled animal model, researchers could isolate the effect of kidney disease from other factors that might affect tendon health. This type of evidence is necessary before doctors can develop treatments to prevent tendon injuries in kidney disease patients.

This study was published in The Journal of Physiology, a respected scientific journal. The researchers used equal numbers of male and female rats to check if sex differences existed. They used standard statistical methods to analyze their data. However, the study used only 16 rats per group, which is a relatively small sample size. Additionally, because this was conducted in rats rather than humans, the results may not directly apply to people with kidney disease—more human research is needed to confirm these findings.

What the Results Show

The main discovery was that tendons from rats with kidney disease were significantly weaker than tendons from healthy rats. Specifically, the tibialis anterior tendon in diseased rats tore at 24% lower stress levels, meaning it required much less force to break. This indicates that kidney disease fundamentally changes the structure or composition of tendons, making them more fragile.

The researchers also found that kidney disease affected other body tissues. Muscle strength in the plantar flexor muscles (calf muscles) decreased by 13% in rats with kidney disease. Even more dramatically, bone strength in the femur (thighbone) decreased by 41% in male rats with kidney disease, though this effect was less pronounced in females.

These findings suggest that kidney disease doesn’t just weaken one type of tissue—it appears to have widespread effects on the entire musculoskeletal system, including muscles, bones, and tendons. This comprehensive weakening could explain why people with kidney disease sometimes experience multiple injuries or have difficulty with physical activities.

The study revealed interesting sex differences in how kidney disease affects the body. While both males and females showed tendon weakness, the bone weakness was much more severe in males (41% decrease) compared to females. This suggests that males with kidney disease may be at higher risk for bone fractures. The researchers also confirmed that the adenine diet successfully created kidney disease by measuring creatinine levels (a marker of kidney function), which were nearly three times higher in diseased rats compared to healthy rats.

Before this study, doctors had noticed that people with chronic kidney disease sometimes experienced sudden tendon ruptures, but there was no scientific explanation for why this happened. This research is the first to directly prove that kidney disease causes tendon weakness in a controlled experiment. Previous research had shown that kidney disease causes muscle wasting and bone loss, but tendon damage had never been scientifically demonstrated. This study fills an important gap by showing that kidney disease affects the entire musculoskeletal system, not just muscles and bones.

The study used only rats, not humans, so we cannot be certain these findings apply directly to people with kidney disease. The sample size was relatively small (16 rats per group), which limits the strength of the conclusions. The study only lasted 9 weeks, so we don’t know if tendon damage gets worse over longer periods or if it can be reversed. The researchers only tested two tendons from the lower leg, so we don’t know if kidney disease affects tendons throughout the entire body. Finally, this was a cross-sectional study (a snapshot in time) rather than following the same animals over time, which limits what we can conclude about how kidney disease progressively damages tendons.

The Bottom Line

Based on this research, people with chronic kidney disease should be aware that they may have increased risk of tendon injuries. While this study doesn’t provide specific prevention strategies yet, reasonable precautions might include avoiding sudden, intense physical activities and being cautious with activities that put stress on tendons. Anyone with kidney disease who experiences sudden pain in their tendons or difficulty moving should contact their doctor immediately. More research is needed before specific exercise or treatment recommendations can be made with confidence.

This research is most relevant to people with chronic kidney disease and their doctors. It may also interest people at risk for kidney disease (such as those with diabetes or high blood pressure) who want to understand potential complications. Healthcare providers treating kidney disease patients should be aware of this tendon weakness risk when counseling patients about physical activity. This research is less immediately relevant to people with healthy kidneys, though it contributes to our overall understanding of how kidney disease affects the body.

This study doesn’t address how quickly tendon damage develops or how long it takes to become noticeable. In the rat study, significant weakening occurred within 9 weeks, but human kidney disease typically develops over months or years. People with kidney disease should monitor for signs of tendon problems (pain, swelling, difficulty moving) rather than expecting sudden changes. If tendon damage has already occurred, recovery would depend on the severity and would require medical treatment.

Want to Apply This Research?

  • Users with chronic kidney disease should track any tendon-related symptoms weekly, including ankle pain, calf pain, shin pain, or difficulty with activities like walking or climbing stairs. Rate pain on a scale of 0-10 and note what activities triggered it. This helps identify patterns and provides important information to share with healthcare providers.
  • If you have kidney disease, consider modifying high-impact activities (like running or jumping) and replacing them with lower-stress exercises (like walking or swimming). Gradually increase activity intensity rather than sudden intense workouts. Warm up thoroughly before exercise and cool down afterward. Avoid sudden changes in your exercise routine.
  • Set weekly reminders to check in on tendon health and note any new pain or changes in mobility. If pain develops or worsens, contact your healthcare provider promptly. Track which activities cause discomfort so you can adjust your routine. Share this tracking data with your doctor during regular kidney disease check-ups to help them monitor your overall musculoskeletal health.

This research was conducted in rats and has not yet been tested in humans. While it provides important scientific evidence that kidney disease may weaken tendons, individual results may vary. If you have chronic kidney disease and experience sudden pain, swelling, or difficulty moving in your joints or muscles, contact your healthcare provider immediately. Do not use this information to self-diagnose or self-treat tendon problems. Always consult with your doctor or nephrologist before making changes to your exercise routine or treatment plan based on this research. This information is for educational purposes only and should not replace professional medical advice.