Why Cardio Alone Doesn’t Work

“I’ve been running for almost a year, and my weight has barely moved.” I hear some version of this sentence more often than almost anything else in this job. It usually comes with a mix of frustration and confusion — the person has been consistent, they’ve put in the kilometres, and the results just haven’t followed.

The honest answer is that cardio alone was probably never going to get them all the way there, and understanding why can save a lot of wasted effort.

Your body adapts, and that’s the problem

The human body is remarkably good at becoming efficient at whatever you repeatedly ask it to do. The first few weeks of a new running routine burn a noticeable amount of energy partly because your body hasn’t optimised for it yet. Over time, your cardiovascular system, your running economy, and your muscle recruitment all improve — which is great for your fitness, but it also means the same 5km loop burns fewer calories than it did when you started. The exercise that once created a deficit slowly stops creating one.

Appetite has a way of catching up

There’s also a less-discussed side effect of regular cardio: it tends to increase hunger, and without noticing, a lot of people end up eating back some or all of what they burned. This isn’t a willpower failure — it’s a fairly normal physiological response. But it does mean that “I exercised, so I can eat a bit more” can quietly erase the very deficit the exercise was meant to create.

Muscle is the piece that’s usually missing

The third factor is the one I bring up most with clients: without any strength training, there’s no real stimulus for the body to build or even maintain muscle mass. Muscle tissue is metabolically active — it’s part of what determines your resting metabolic rate, the energy your body burns just existing. Pure cardio, especially at a moderate steady pace, does very little to build or protect that muscle. Over months and years, this can mean your baseline calorie burn is actually working against you rather than for you.

What tends to work better

None of this means cardio is a waste of time — it has real benefits for heart health, endurance, and mental wellbeing. But if fat loss is the goal, the evidence and my own experience with clients both point the same direction: a foundation of strength training, combined with a moderate amount of cardio and attention to overall eating habits, produces far more consistent results than cardio by itself.

If you’ve hit a plateau like this, it’s rarely a sign you need to run further or faster. More often, it’s a sign your programme is missing a piece — and that piece is usually strength work.