January Edition: Cardiorespiratory Fitness

Cardiorespiratory fitness (CRF) is one of the strongest predictors of long-term health and survival, yet it is often under-emphasised in discussions about healthy ageing.

This month, The Healthy Ageing Project focuses on why CRF matters for long-term brain and physical health and how to approach it in a way that is realistic, evidence-based, and sustainable.

Why Cardiorespiratory Fitness Matters
for Healthy Ageing

When we talk about healthy ageing, cardiorespiratory fitness (CRF) is often under-emphasised, despite being one of the strongest predictors of long-term health and survival.
CRF reflects how well the heart, lungs, and muscles work together to deliver and use oxygen. Unlike many health markers, it integrates the function of multiple physiological systems. This is one reason CRF appears so consistently as a strong predictor in longevity research.
Importantly, CRF is not fixed. It is highly modifiable across adulthood, making it a meaningful target for improving long-term brain and overall health.
If you’d like to explore this further, you can listen to my conversation with Professor Jeff Coombes, where we discuss the role of cardiorespiratory fitness in health and ageing, how exercise intensity fits within the broader evidence base, and why aerobic fitness remains a key, but often overlooked, component of long-term health.

Research discussed in the interview:

Fitness vs. Fatness on All-Cause Mortality: A Meta-Analysis

Superior Cardiovascular Effect of Aerobic Interval Training Versus Moderate Continuous Training in Heart Failure Patients

Aerobic High-Intensity Intervals Improve V˙O_2max More Than Moderate Training

Cardiorespiratory Fitness and Healthy Ageing Research Overview

Across large observational studies, higher levels of cardiorespiratory fitness (CRF) in adulthood are consistently associated with a lower risk of all-cause mortality. This relationship has been observed across sexes, age groups, and baseline health status, and remains evident after adjustment for traditional cardiovascular risk factors.

CRF reflects the integrated function of the cardiovascular, respiratory, and muscular systems. As such, it captures overall physiological resilience rather than the performance of a single organ system. This integrative nature is one reason CRF has emerged as one of the strongest predictors of longevity in epidemiological research.

Importantly, CRF is highly modifiable across adulthood. Evidence suggests that improvements or maintenance of fitness over time are associated with meaningful reductions in mortality risk, reinforcing the importance of sustained aerobic capacity rather than short-term or episodic training efforts.

Nutrition to Support Cardiorespiratory Fitness

Supporting cardiorespiratory fitness requires adequate fuel.

Chronically low energy availability, particularly low overall energy intake or carbohydrate intake, can impair training quality, recovery, and long-term adherence. For most adults, supporting aerobic activity means eating regularly, meeting energy needs, and avoiding unnecessary dietary restriction.

From a longevity perspective, nutrition is not about optimisation at all costs. It is about supporting behaviours, such as regular movement and aerobic exercise, that can be sustained consistently over many years.

One simple example is overnight oats, which is one of my favourite ways to refuel in the morning. It’s easy to prepare ahead of time, provides a combination of carbohydrate and protein, and works well on days when training or a busy schedule makes consistency more important than perfection.

Calorie & Macronutrient Calculator

This calculator is designed to reduce guesswork and provide a realistic starting point for understanding your energy and macronutrient needs. It focuses on supporting training, cardiorespiratory fitness, and long-term health rather than short-term dieting or rigid rules. The values provided are guides only and are intended to support sustainable, evidence-based decisions over time.

How Cardiorespiratory Fitness Is
Improved in Practice

Cardiorespiratory fitness can be improved through a wide range of exercise approaches, including walking, cycling, swimming, and structured aerobic training.

What matters most is not the specific modality, but the ability to perform activity consistently and progress it gradually over time. Improvements in cardiorespiratory fitness occur when the cardiovascular and respiratory systems are challenged regularly, within an individual’s capacity.

From a longevity perspective, sustainable exercise habits are more important than short-term intensity. Approaches that can be repeated week after week are more likely to support long-term fitness and health.

Regular aerobic activity
Appropriate intensity for the individual
Gradual progression over time
Consistency across months and years

The 4 × 4 Norwegian HIIT Protocol

The 4 × 4 Norwegian high-intensity interval training (HIIT) protocol is a well-studied approach for improving cardiorespiratory fitness. It was originally developed and tested in clinical and population-based research and has since been applied across a range of settings.

The protocol involves repeated periods of higher-intensity aerobic exercise interspersed with active recovery. The intention of the higher-intensity intervals is to sufficiently challenge the cardiovascular system, while recovery periods allow the effort to be repeated safely.

Importantly, the 4 × 4 protocol is not the only way to improve cardiorespiratory fitness. It represents one option that may be appropriate for some individuals, depending on fitness level, experience, and overall health.

Four high-intensity intervals broken up into 2 minutes of building up to a high intensity and 2 minutes of holding the high intensity (=4 minutes)
Followed by three to four minutes of active recovery
Designed to be done two to three times per week
Suitable for individuals with varying fitness levels with proper modifications

Putting this into practice

This month’s focus is on supporting cardiorespiratory fitness through small, repeatable actions.

The goal is not to do everything at once, nor to train at maximal intensity. Instead, the emphasis is on choosing one or two realistic changes that can be maintained consistently over time.

To help you do this, you could add the following suggestions into your schedule:

Add one purposeful aerobic session to your week
Slightly increase the pace or duration of an existing walk
Use the 4 × 4 Norwegian HIIT protocol as an optional session, if appropriate
Monitor effort using perceived exertion or heart rate, rather than chasing numbers

Alternatively, you could use our aerobic exercise schedule for January 2026, that includes a suggested progressive overload.

REMEMBER:

Consistency matters more than intensity. Small changes, repeated over time, are what support long-term fitness and health.