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A familiar run through the park, steady breathing, a well-known route: for many people, jogging represents the essence of healthy exercise. Yet valuable as this routine is, regular movement alone does not determine long-term performance capacity and lifetime health. What matters just as much is challenge – and that begins where things start to feel uncomfortable. 

The heart is a muscle – and like every muscle, it adapts to the demands placed upon it. If very intense effort is consistently absent, what declines above all is maximum performance reserve: the ability to deliver enough blood and oxygen during high stress. This reserve determines how robustly the body can respond to strain.

The heart needs ‘controlled panic’

One of the largest cohort studies to date examined more than 122,000 adults, whose cardiorespiratory fitness was measured using treadmill tests and followed over 14 years. The result was clear: The higher the maximum performance capacity of the heart, lungs and circulation, the lower the risk of premature death. 

People with high or very high fitness levels had significantly better survival prospects than those with lower exercise capacity – regardless of age or existing risk factors. In other words, what matters is not only regular activity, but the level of functional performance reserve achieved. Cardiorespiratory fitness improves especially when the heart occasionally works close to its limits. 

When your pulse sounds the alarm – and why that is a good thing

However, training intensity often remains below the threshold required to deliberately improve or maintain maximum performance capacity over time. Only higher intensity effort activates reserves: the heart beats more forcefully, pumps more blood with each beat and becomes more efficient in the long term. At the same time, mitochondria increase their performance capacity and blood vessels remain more elastic. These adaptations are essential for slowing age-related functional decline.

The key to optimal longevity therefore lies not (only) in comfortable steady running, but in the system’s maximum performance capacity. From an evolutionary perspective, this makes perfect sense. The body primarily maintains abilities that it is regularly required to use. If high performance is never called upon, there is little reason for the body to preserve it.

Intensity as the key 

How much strain the heart actually needs remains the subject of ongoing research. What is clear is that both moderate and vigorous activity contribute to health. The World Health Organization recommends at least 150–300 minutes of moderate activity per week or 75–150 minutes of vigorous activity per week.

However, these recommendations mainly define a minimum requirement for basic health – not necessarily the optimal strategy for maintaining maximum function over time. Large cohort studies show that higher cardiorespiratory fitness levels are associated with the lowest mortality risk. In practice, this means the recommended activity volume provides an important foundation. But even a few short periods of higher intensity per week can be enough to maintain functional reserve. 

The red zone hurts

Despite their effectiveness, many people avoid intense effort. The reason lies in the nervous system: high strain activates the same stress responses as a perceived threat. Heart rate and breathing rise abruptly, control briefly feels reduced and the effort becomes uncomfortable. More demanding efforts are therefore often experienced as unpleasant – and these experiences are stored emotionally. If the brain expects overload, avoidance becomes a short-term protective strategy.

But this system is adaptable. The key is gradual exposure: short, manageable intervals with sufficient recovery teach the nervous system that intense effort is safe. Equally important is how the body’s signals are interpreted. A racing pulse can be understood as a sign of capability rather than a warning signal. Anyone who repeatedly manages demanding effort in a controlled way gradually changes the brain’s expectations. Not every run needs to be hard. But occasional, well-dosed intensity sends an important maintenance signal: this system is needed! And that is exactly what helps keep it resilient well into older age.