Lifestyle Desk-
For years, conversations about health and aging have revolved around numbers. Weight is checked regularly. BMI is calculated using an online tool. Some people also look up their daily calorie needs through a BMI calculator or a BMR calculator. These measurements are familiar and easy to track, which is why they often become the default markers of health.
But do these numbers really explain how well a person will age? And more importantly, do they tell us how long someone is likely to live?
According to doctors and researchers studying aging, the answer is increasingly no. A growing body of evidence suggests that physical strength, especially in the legs, plays a much bigger role in longevity than body weight or BMI alone.
Why BMI and weight tell only part of the story
BMI was never designed to predict longevity at an individual level. It is a simple ratio of height and weight. It does not distinguish between fat and muscle. It does not reflect balance, mobility, or strength.
Two people can have the same BMI and very different health outcomes. One may have strong muscles and good mobility. The other may struggle with basic movement despite appearing “normal” on a BMI chart. This limitation is often overlooked when people rely too heavily on a BMI calculator as a standalone measure of health.
Research involving older adults has shown this clearly. People with lower leg strength face higher risks of illness, disability, and early death, even when their BMI falls within a healthy range. In other words, being lean or having an acceptable BMI does not guarantee resilience in later life.
Leg strength and everyday independence
Leg strength supports almost every movement we take for granted. Standing up from a chair. Walking across a room. Climbing stairs. Catching yourself when you lose balance. These actions rely heavily on muscles in the thighs, hips, and lower legs.
As people age, these movements become increasingly important. Those who maintain strong lower-body muscles tend to stay independent for longer. They recover faster after illness. They are less likely to suffer serious falls.
Studies tracking elderly populations have found that individuals with stronger legs experience fewer hospital visits and are less likely to require long-term care. Weak legs, on the other hand, often mark the beginning of reduced mobility and dependence.
Muscle loss starts earlier than most expect
Muscle loss is often associated with old age, but it usually begins much earlier. After the age of 30, adults who are inactive can lose three to five per cent of muscle mass each decade. The legs are among the first areas affected.
This gradual decline, known as sarcopenia, does not always show up on the scale. Body weight may remain unchanged, especially if muscle loss is offset by fat gain. BMI may also stay stable.
Yet strength, balance, and walking speed quietly deteriorate. Over time, this increases the risk of falls, fractures, and long periods of immobility, all of which shorten healthy lifespan.
Simple strength tests that predict outcomes
One of the most telling indicators of leg strength does not involve machines or lab tests. It involves a chair.
The chair stand test asks a person to sit down and stand up repeatedly for 30 seconds without using their hands. The number of repetitions offers a surprisingly accurate snapshot of lower-body strength.
Research across several countries has shown that people who perform poorly on this test face higher risks of death from heart disease and other causes. These findings hold true regardless of BMI, age, or body weight.
This challenges the idea that health can be summarised by size alone. What the body can do often matters more than what it weighs.
Building stronger legs at any age
The encouraging part of this research is that muscle strength can improve at almost any age. Even people in their sixties, seventies, and beyond can regain strength with appropriate activity.
Simple exercises such as chair squats, step-ups, wall-supported squats, and resistance band movements help build strength in the legs. Regular walking also plays a role in maintaining muscle and balance.
Experts generally recommend two to three strength-focused sessions per week, along with daily movement. Adequate protein intake and rest are also important for muscle repair.
The aim is not athletic performance. It is the ability to move safely, recover from illness, and remain independent.
Rethinking routine health tracking
Most routine health checks still focus on weight, BMI, blood pressure, and lab values. While these are useful, they overlook functional ability.
Many researchers now argue that basic strength and mobility tests should be included in health assessments, especially from middle age onward. How easily you stand up from a chair or climb stairs may reveal more about your future health than repeated visits to a BMI calculator or BMR calculator.
These observations are simple, practical, and meaningful.
Conclusion
Longevity is not decided by weight alone. A BMI calculator and/or a BMR calculator offer useful reference points, but they do not capture how well the body functions over time. Strong legs support movement, independence, brain health, and recovery from illness. Shifting focus from numbers on a scale to physical strength may be one of the most practical steps people can take to improve both lifespan and quality of life.