Read time: 3.5 minutes

It’s arguably the most accessible form of exercise.

Walking has a number of benefits - both physical and psychological.

But is it enough to keep muscle loss at bay across the lifespan?

A new study has the answers.

Let’s dive in.

First, what do we know about whether aerobic exercise can increase muscle mass?

To be clear, resistance training is our most effective tool for building muscle and strength.

But that doesn’t mean other exercise types aren’t effective at all for these outcomes.

There’s certainly some evidence aerobic training can build muscle:

• Some studies have even found aerobic training (cycling in particular) can increase the size of the quadriceps (thigh) muscles similarly to resistance training
• But, others have found superior muscle growth with resistance training

To set the record straight, I co-authored a 2019 meta-analysis of 21 studies comparing muscle growth with resistance training or aerobic training.

In that analysis, we found resistance training does promote greater muscle growth of the knee extensor (quadriceps) muscles.

But again: the question is not what is “best” - but whether aerobic training can be enough to build muscle.

And particularly when we're talking about the most common form of aerobic training in the context of age-related muscle loss.

Enter this latest study.

Here's what they did:

The study combined the results of 4 trials in a total of 238 individuals aged 53 on average with overweight or obesity.

As an aside, the age of the participants in this study is important - because muscle loss begins as early as our 30’s and accelerates from our 60’s and beyond.

So by middle age, we‘re right at the cusp of rapid muscle loss.

Anyway, back to the study…

Each of the 4 studies involved:

• 12 to 24 weeks of walking (sometimes combined with jogging)
• Performed 4-5 times per week
• And at a moderate intensity (defined as 50-75% of VO2max)

The effects of walking on muscle mass, adipose (fat) tissue, and cardiorespiratory fitness was assessed and compared to a control group who remained inactive.

What made this study even more impactful was the use of a gold standard measure of muscle size (MRI scans) and in multiple body regions (both the upper and lower body).

Together this gives us:

• More confidence in the accuracy of the changes in muscle mass
• And, paints a more complete picture of muscle changes in areas involved in the exercise or not

So, did aerobic exercise influence muscle mass?

Before we get to muscle, it’s important to mention walking or jogging had positive effects on:

• Body weight
• Waist circumference
• Cardiorespiratory fitness
• And on total, subcutaneous, and visceral adipose (fat)

Benefits we generally expect from an aerobic exercise program.

The question of course is: what happened to muscle mass?

Here’s how 3-6 months of walking or jogging 4-5 times per week impacted muscle:

• Whole-body muscle mass was reduced (by -0.31 kg)
• Upper-body muscle mass was reduced (by -0.27 kg)
• Lower-body muscle mass was maintained

So together this suggests walking/jogging does not increase, but may preserve, muscle mass. And, only in muscle groups involved in the exercise.

Did diet impact the muscle changes?

A valid question.

Luckily the study did control for the influence of diet.

Given diet can impact changes in body weight, all participants were asked to consume a caloric intake sufficient to maintain their body weight.

That way, any changes in body weight would be more likely due to the exercise itself.

Aside from energy intake, another key factor that influences changes in muscle mass is protein intake.

Participants in the study were asked to consume a “healthy, balanced” diet containing about 50% carbohydrate, 20% protein, and 30% fat.

But a key question was whether participants were actually consuming "sufficient" protein - as defined by the Recommended Dietary Allowance (RDA) of 0.8 g/kg/day.

To verify this, total caloric and macronutrient intake was assessed in a group of participants from 1 of the 4 trials and found:

• No differences between the exercise and control group
• Participants were meeting the RDA for protein (0.8 g/kg/day)

So, this together suggests:

• The observed weight loss was likely due to increased energy expenditure from exercise, and not because of changes in dietary intake
• The failure of aerobic exercise to increase muscle mass was likely not due to insufficient protein intake or nutrition

Take-home messages

Clearly aerobic exercise like walking or jogging has many benefits.

This latest study suggests moderate-intensity walking may be "enough" to maintain muscle to a certain extent. At least in the lower body, and in middle-age (before larger declines in muscle mass occur).

The fact remains that resistance training is our best tool for not only maintaining - but improving - muscle mass, regardless of our age.

So if you’re currently walking or jogging regularly - then great.

But adding in some resistance training (even basic movements like sit to stands) is more likely to fend off muscle loss - for as long as possible.

Thanks for reading!

Until next week,

Jackson

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IMPORTANT:

The information contained herein is of general nature only and does not constitute personal advice. You should not act on any information without considering your personal needs, circumstances, and objectives. Any exercise program may result in injury. We recommend you obtain advice specific to your circumstances from an appropriate health professional before starting any exercise program.