Muscle Fatigability

Muscle fatigability refers to how quickly your muscles tire out and lose strength during continuous activity. It’s essentially your muscle endurance capacity – how long they can keep working before feeling exhausted. ie, While grip strength reflects peak force, fatigability measures how long that force can be sustained. https://pmc.ncbi.nlm.nih.gov/articles/PMC5668469/

Think of it this way: if grip strength tells you how strong your muscle is at a single moment, muscle fatigability tells you how long that strength can last. This aspect of fitness is crucial for staying active and independent in daily life. With good muscle endurance, you can do tasks like climbing stairs or carrying groceries longer without needing to stop and rest.

Muscle fatigability isn’t just about your muscles – it also reflects broader health factors like energy metabolism and even your body’s stress and immune responses. https://pmc.ncbi.nlm.nih.gov/articles/PMC5668469/

Scientists consider muscle endurance to be a key part of your overall “vitality capacity,” which is the combination of systems that keep you resilient as you age.

Researchers suggest that muscle endurance declines are associated with slower walking speeds, reduced daily function, and higher chronic inflammation in older adults. Improving muscle endurance is therefore vital for overall health and vitality. https://www.mdpi.com/2308-3417/10/2/52

Muscle fatigability is measured using a simple yet effective test called the Fatigue Resistance test. During this sustained grip strength test, with your dominant hand, you squeeze the Eforto bulb as hard as possible and continue squeezing until your muscles become exhausted. The test automatically ends when your grip strength falls below 50% of your initial maximum.

Throughout the test, the device continuously records your grip pressure, showing how your force decreases as your muscles tire.

The test results in two key measures:

Fatigue Resistance (FR): This indicates how long (in seconds) you can maintain your grip above (50%) half your maximum strength.

Grip Work (GW), which represents the total amount of "work" your hand muscles performed during the test. Think of it as the overall effort (labor) your muscles put forth, measured by the area under the force-time curve captured during your test.
https://www.sciencedirect.com/science/article/pii/S1279770723006152?via%3Dihub
https://pubmed.ncbi.nlm.nih.gov/30697635/#:~:text=until%20it%20dropped%20to%2050,FR

To provide a fair and personalized interpretation, we adjust your Grip Work based on your body weight, resulting in a relative score called GW_rel (Grip Work relative to body weight). This adjustment ensures that results are fair regardless of your size, as naturally larger individuals can typically exert more total force.

The Eforto app automatically performs these calculations, displaying your GWrel score clearly after the test. This measure has been validated scientifically as a reliable indicator of muscle endurance and is linked to important health outcomes.

Note: The validated Eforto test includes built-in safeguards to ensure you squeeze at maximum effort, preventing inaccurate results from submaximal squeezing.

To properly understand muscle endurance we need to personalise the test outcomes according to strength, gender and body weigth.

This integrated measure GW_rel (grip work relative to body weight) follows a similar age related trend as for grip strength.

Health experts have defined certain cut-off values to classify GW_rel for adults into categories regardless age. These categories are based on health risk and help you interpret your number and understand if it’s ideal or if it indicates a potential problem. They are usually given separately for men and women.

The Eforto app will display Fatigue Resistance in seconds but we use the more informative GW_rel for the classification into three “traffic light” zones for easy interpretation:

Men:

Women:

Here’s how to interpret the color-coded categories for GW_rel:

Normal (Green): Your muscle endurance is normal for a healthy adult. This means you can sustain muscle effort for a long time. A high GWrel indicates excellent muscular stamina and is often seen in fit individuals. You likely generate good strength and fatigue less quickly during physical tasks and exercise.

At Risk (Yellow): Your muscle endurance is below average. Your muscles tire faster than normal, which might cause fatigue during longer activities. Low GWrel is common in older adults or those who are less active, and it may be an early warning sign to improve your strength and endurance.

Very Low (Red): Your endurance capacity is significantly low. This means you are weak and fatigue very quickly. Very low GWrel levels are often seen in frailty or certain health conditions, and they can greatly affect daily function (for example, making it hard to open jars or carry groceries). If you’re in this red zone, it’s important to take action (through training or medical guidance) to investigate and improve your muscle endurance.

A low muscle endurance score isn’t just a fitness issue – it can be a red flag for your health. Research shows that people with low grip endurance (especially if accompanied by feelings of fatigue) tend to have higher risks of various negative outcomes:

Frailty and Functional Decline: Low GW_rel is strongly linked to physical frailty in older adults. Even in people over 80 who felt okay, those with lower grip work were far more likely to be in a pre-frail or frail state compared to robust peers. In one study, older adults with both low muscle endurance and high fatigue were much more likely to be frail than those with good endurance.

Frailty means reduced reserve and resilience, making it harder to recover from illnesses or injuries. It’s also associated with loss of independence.

Chronic Inflammation: Low muscle endurance often goes hand-in-hand with inflammation in the body. For example, one clinical study found that elders with better grip endurance had significantly lower levels of the inflammatory marker IL-6 in their blood. Conversely, those in the low endurance group tended to have elevated IL-6 and other inflammatory markers. Chronic, low-grade inflammation can contribute to muscle loss, fatigue, and health problems over time. Thus, a poor GW_rel might indicate underlying inflammatory or metabolic issues.

Higher Risk of Hospitalization and Fatigue: Because low endurance is a core aspect of frailty, it’s linked to higher rates of hospitalization and other bad outcomes. Frail individuals (often characterized by weak and fatigable muscles) have about a 1.8× higher risk of hospitalization and greater risk of falls and disabilities compared to non-frail individuals. Even at mid-life, people reporting high fatigue and low muscle endurance show more biological signs of stress (like inflammation) and may be on a trajectory toward frailty if nothing is done. Practically, if your muscles tire quickly, you’ll likely feel more exhausted doing daily tasks, which can spiral into a more sedentary lifestyle and further declines in strength – a vicious cycle.

In short, a Low or Very Low GW_rel isn’t something to ignore. It’s a signal that your body’s “vitality tank” is low, which can predict greater risks of illness or loss of function.

The good news is that you can often improve your muscle endurance with the right steps (see below). But if your score is very low or dropping over time, it’s wise to take action sooner rather than later.

The empowering part about muscle endurance is that it can be improved at any age. Here are ways to boost your GWrel and overall muscle stamina:

Progressive Exercise Training: Incorporate regular strength and endurance exercises for your muscles. Resistance training (like hand-grip exercises, weight lifting, or resistance band workouts) is especially effective at increasing muscle strength and fatigue resistance. Aim to challenge your muscles a few times a week, gradually increasing difficulty. Research shows that older adults who did resistance exercise improved their muscle endurance and strength – and gains were even greater when protein supplementation was added. Even daily activities like squeezing a stress ball or using a grip strengthener can help build endurance in your hands and forearms. Consistency is key: muscles adapt over weeks and months, so stick with a routine.

Optimal Nutrition: Muscles need fuel and nutrients to perform and recover. Make sure you eat enough protein (from foods like lean meats, fish, eggs, dairy, legumes, etc.) since protein provides the building blocks for muscle repair. Older adults, in particular, often benefit from higher protein intake to counter muscle loss. Studies indicate that adequate dietary protein helps preserve muscle mass and function with aging. Vitamin D and magnesium are also important – low levels have been associated with weaker muscle performance and fatigue, so consider foods or supplements to ensure you meet daily requirements. Additionally, a diet rich in fruits and vegetables (like a Mediterranean-style diet) has been linked to better muscle function and lower frailty risk. In short, eating a balanced diet with plenty of protein and micronutrients will give your muscles the resources to build endurance.

Rest and Recovery: Improving endurance isn’t just about exercise and diet – recovery matters too. Muscles actually get stronger during the rest periods between workouts. Make sure you’re getting enough sleep (which is when your body repairs muscle fibers) and allowing recovery days after intense exercise. If you push yourself hard every single day without rest, you risk overtraining and actually increasing fatigability. Balance activity with recovery, listen to your body’s signals, and avoid extreme fatigue. Proper recovery (including techniques like stretching, massage, or light activities on rest days) will help your muscles adapt and reduce soreness or injury, enabling you to train consistently over time.

Address Health Issues: Sometimes low muscle endurance can be influenced by underlying medical conditions – for example, anemia, chronic infections/inflammation, thyroid issues, or other problems can sap your energy. Managing chronic conditions with your doctor’s help, correcting nutrient deficiencies (iron, B12, etc.), and reducing sources of chronic inflammation (e.g. through weight management or medications if needed) can all improve your muscular endurance indirectly. Essentially, a healthier body = more endurance.

By focusing on these areas – exercise, nutrition, and recovery – you can gradually raise your GW_rel. Many studies on older adults show it’s never too late to improve: people in their 70s and 80s have significantly increased their grip endurance after targeted training programs. And if you’re younger, building up your endurance now will give you a higher reserve as you age.

While improving fitness is great, it’s important to know when low muscle endurance might signal something that needs medical attention. You should consider talking to your healthcare provider if:

Your GW_rel is in the Very Low (red) zone for your age, or it’s persistently Low despite training. Extremely low grip endurance could indicate an underlying issue. For instance, research has noted that older adults with the lowest endurance often have ongoing inflammatory or health problems contributing to their frailty. A doctor can check for any medical causes of your low endurance – such as nutritional deficiencies, hormonal imbalances, or chronic diseases – and help address them.

You experience excessive fatigue, weakness, or declining function in daily life. If everyday tasks are leaving you unusually exhausted or your grip strength/endurance is getting worse over time, it’s wise to get a professional evaluation. High self-perceived fatigue combined with low muscle endurance is a red flag for future frailty. Your doctor might perform tests for conditions like anemia or chronic fatigue syndrome, evaluate your muscle health more thoroughly, or refer you to a specialist (for example, a physical therapist or geriatrician) for further assessment.

You have other symptoms along with low endurance. Pay attention to signs like unintended weight loss, frequent falls, severe joint pain, or swelling – these alongside poor muscle performance warrant a check-up. Low grip endurance is used in geriatric assessments because it correlates with overall health status. It’s better to identify and treat a potential issue early (whether it’s sarcopenia, inflammatory arthritis, or something else) than to ignore it.

Remember, fitness metrics are not destiny – they’re clues about your health. A low GWrel doesn’t mean something is definitely wrong, but it gives you and your doctor useful information. They may advise interventions like supervised exercise programs, physical therapy, or nutritional counseling that are tailored to your situation. In some cases, improving muscle endurance can dramatically improve quality of life and outcomes (for example, increasing strength can help prevent falls and frailty-related hospitalizations). So don’t hesitate to seek medical advice if your muscle endurance is very low or if you’re concerned. Takeaway: Muscle fatigability is a vital sign for your functional health. By understanding your GWrel level and working to improve it, you’re investing in a more energetic, independent future. Use the Eforto app’s insights to track your progress, and involve healthcare professionals when needed. Small improvements – a few extra seconds of grip hold, a few more kPa of strength – can add up to big gains in your vitality and resilience over time. Stay active, nourish your muscles, and keep an eye on that GWrel – your future self will thank you!