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You’re doing cardio… but is it working against your results?

Male runner sprints on a track in the golden sunlight

March 18, 2026
Cardio, FatLoss, Hypertrophy, Recovery, Strength

My nephew flew out here for spring break and had asked me a handful of questions yesterday that I realize a lot of you may have. So, I thought I’d share!

Cardio is one of the most misunderstood tools in fitness. Some people treat it like the key to fat loss, while others avoid it entirely out of fear it will cost them muscle. It’s usually talked about in extremes, but the reality sits somewhere in between.

A large 2021 review of 43 studies, including over 1,000 participants, comparing strength training alone to strength combined with cardio found that higher volumes of endurance work can interfere with muscle and strength gains when not properly balanced.

Understanding how cardio actually works makes it easier to use it without working against your results.

1 → Does cardio “burn” fat?

Simple answer: Cardio uses fat as fuel, but daily intake and activity determine fat loss.

Long answer: Cardio does use fat as fuel. It also uses carbohydrates. The ratio between the two varies based on intensity. Energy systems shift throughout any exercise session based on how hard and how long you are working. Lower intensity exercise uses a higher percentage of fat while higher intensity exercise uses more carbohydrates.

Using energy during your workout does not equal losing body fat or gaining muscle. Those are determined by how much food you eat compared to how much your body uses over the course of the day and how you train. If you consistently eat more than your body needs, it will be stored. If you consistently use more than you eat, your body will slowly begin to use what it has stored. If intake stays too low for too long (undereating in an effort to lose weight), your body can adapt by using less energy, which can slow progress.

2 → Can cardio “eat” into muscle?

Short answer: The activity of cardio alone won’t lead to muscle wasting, commonly called muscle breakdown.

Long answer: Muscle loss occurs when your overall lifestyle and activity does not support maintaining muscle.

That usually comes down to:

Eating too little
Not eating enough protein
Lack of resistance training
Too much overall fatigue over time
Competing adaptations (your body adapting to endurance instead of strength)
Poor recovery

When those things are addressed, adding cardio will not cause muscle loss.

3 → What about short versus long cardio?

Short answer: Your body’s response is affected by both the length of time and the intensity of the cardio.

Long answer: Short cardio sessions are typically performed at a moderate to higher intensity. They’re efficient, but they still add stress on top of your other training. Because they’re shorter, they don’t drain your body the same way longer sessions do. They use quick energy, but they don’t keep your body working long enough to create the same level of fatigue.

That matters when your goal is to build or maintain muscle. Your body needs enough energy and recovery to keep prioritizing strength training. When cardio starts to get longer or more frequent, it adds more overall demand. Over time, that can make it harder for your body to keep up with both.

Shorter sessions are easier to fit in without adding as much fatigue, which is why they’re less likely to interfere with your strength training or muscle.

This is why I generally recommend short duration, bodyweight HIIT sessions. They take little time and planning. You can throw one together in 5 minutes and they don’t leave you so drained that it starts adding to your stress to fit your strength training into your day.

Long cardio sessions are typically going to be at a lower intensity. They help increase total daily energy expenditure and can help with heart health. When performed at low intensity, they can even be used to aid recovery. Walking is a perfect example of this. On days I just need to move but not stress my body, I will throw on a backpack weighted to about 10% of my body weight and go for a walk. It helps keep my heart rate up while releasing stress and lets me get some extra steps in.

4 → So which is better?

Short answer: Like everything else, they both have their place.

Long answer: For fat loss, both types can be useful. As long as you pay attention to how much you eat versus how much your body uses over time, your body will respond appropriately. If your body uses more than you eat, you will lose body fat. That is called energy balance.

For muscle gains/training, shorter sessions or lower intensity cardio are easier to add without impacting strength training performance or recovery. When you add longer cardio sessions, or multiple sessions per day, you start putting a greater demand on your body, making it harder for your body to support hypertrophy (muscle gains). Your body will first burn through its main fuel source, carbohydrates. When those run low and you haven’t eaten enough to replenish them, your body will begin to break down glycogen stored in your muscles. (Glycogen is the stored form of carbohydrates in your body. It’s kept in your muscles and liver and used as a quick energy source, especially during higher-intensity activity.) It will also start looking elsewhere to help fuel your activity.

Cardio for the sake of cardio is not beneficial for building muscle.

For health, a mix of both is great!

The take home message…

Using cardio appropriately helps support fat loss, muscle retention, and performance so your training continues to move in the right direction. If you’ve been unsure how to balance cardio with your training, you’re not the only one.

Stop burning random energy. Start auditing your recovery infrastructure.

Cardio is a powerful tool, but when it’s unmanaged, it becomes a severe drain on your most valuable resource: time. If you are piling long cardio sessions on top of a high-stress schedule, insufficient protein, and poor sleep architecture, you aren’t burning fat – you are just forcing your body to burn through its valuable energy stores just to stay afloat.

An upgraded body doesn’t run on random guesswork. It requires precision.

Take The Performance Audit to stop reacting to symptoms, map your biological friction points, and see exactly where your training and lifestyle systems are supporting your goals – or quietly blunting your progress.

[CLICK HERE TO ACCESS THE PERFORMANCE AUDIT]

Primary Reference

Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis
This is an updated systematic review and meta-analysis of 43 studies comparing concurrent aerobic + strength training versus strength training alone in healthy adults. The outcomes of interest were maximal strength, explosive strength, and muscle hypertrophy. It also looked at potential moderators such as aerobic training type, training modality, exercise order, training frequency, age, and training status. https://link.springer.com/article/10.1007/s40279-021-01587-7

Other References

Does Cardio Burn Fat?
Hall KD et al. (2017)
Energy balance and its components: implications for body weight regulation
This narrative review explains how body weight is regulated through the balance between energy intake (what you eat) and energy expenditure (what your body uses). It breaks down how metabolism adapts over time and why fat loss is not determined by a single workout, but by consistent patterns across days and weeks.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3302369/

Short vs Long Cardio
Gibala MJ et al. (2012)
Physiological adaptations to low-volume, high-intensity interval training
This paper examines how short, high-intensity cardio sessions can produce meaningful improvements in fitness and metabolic function with less total time. It shows that shorter sessions can be effective while placing less overall training volume on the body.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3381816/

Which Is Better
Del Pozo Cruz B et al. (2023)
Daily steps and all-cause mortality: a meta-analysis
This meta-analysis of over 200,000 participants found that even lower step counts are associated with reduced mortality risk, with benefits increasing as daily steps rise. It supports the idea that both lower-intensity and higher-volume activity contribute to overall health.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9289978/

This article was originally published inside The Executive Health Brief – a private weekly brief containing curated insights on sustaining high-level performance for leaders, visionaries, big dreamers, and change-makers. Join the brief to get ahead of the risk before it becomes a crisis.

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About Sharon Aldeguer
Sharon is the Total Body Strategist. She works with high-performers to build custom systems for their movement, nutrition, and mental focus. Her goal is simple: give you a highly reliable body that looks and feels powerful, handles heavy cognitive days, and projects the exact kind of confident, magnetic presence your role demands. To work with her, apply for an Executive Performance Audit today!

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