Whether your goals are performance-based or aesthetic, building muscle is likely to feature somewhere in your training plan. But how much muscle you carry – and how much you can ultimately gain – is influenced by a host of factors, including genetics, age, training history, nutrition and your resistance training programme.

If you’ve been keeping track of your muscle mass percentage, you might also be wondering how your numbers compare. While there isn’t a single ‘ideal’ muscle mass percentage for men, research can give us an indication of how skeletal muscle mass varies across different age groups.

The following figures come from a study published in the Journal of Applied Physiology, which examined skeletal muscle mass in 468 adults aged 18 to 88 years, including 268 men.

Rather than relying on scales or other indirect measures of body composition, the researchers measured skeletal muscle using whole-body MRI scans. Muscle mass was then expressed as a percentage of total body weight.

Across all 268 men, skeletal muscle accounted for an average of 38.4% of body mass, although this varied between individuals and age groups.

It’s worth noting that the study was published in 2000 and compared people of different ages at a single point in time rather than following the same individuals as they aged. The participants were also healthy, self-selected adults, and relatively few were over 70, so these figures should be treated as rough reference values rather than targets for what your muscle mass percentage should be.

Unless you’re taking part in a research study, it’s unlikely your muscle mass will be measured using a whole-body MRI. Instead, most people who track their muscle mass percentage will encounter bioelectrical impedance analysis (BIA), the technology used in many smart scales and body composition machines found in gyms.

However, BIA has limitations and provides an estimate rather than a direct measurement. MRI is considered one of the most accurate methods of measuring skeletal muscle mass, while DEXA scans can also provide a detailed assessment of body composition, although they measure lean mass rather than skeletal muscle directly.

To increase your muscle mass, focus on the following fundamentals:

1/ Resistance Training

It may sound obvious, but if you want to build muscle, resistance training needs to be a consistent part of your programme. Whether you’re lifting weights, using machines or performing bodyweight exercises, your muscles need enough resistance to stimulate adaptation and growth.

2/ Progressive Overload

A large part of that adaptation comes from applying the principle of progressive overload. As your muscles adapt, you’ll need to continue providing a sufficient stimulus. That could mean gradually increasing the weight, reps or sets you perform over time.

Progressive overload doesn’t necessarily mean adding more weight every workout. Improving your technique, increasing your range of motion or progressing to a more challenging exercise can also increase the demands placed on your muscles.

3/ Adequate Nutrition

You’ll also need to eat enough to support your training and recovery. While you don’t necessarily need to be in a calorie surplus to gain muscle – particularly if you’re new to resistance training, returning after a break or have higher levels of body fat – a modest surplus can help maximise muscle growth.

More isn’t necessarily better. Eating substantially more calories doesn’t guarantee faster muscle growth and is more likely to increase fat gain alongside muscle.

Protein intake matters too. Around 1.6g of protein per kilogram of body weight per day is a useful, evidence-based target for supporting muscle growth in most people who resistance train, although individual requirements will vary.

4/ Get Enough Rest

Finally, don’t overlook recovery. Training provides the stimulus for your muscles to adapt, but adequate rest is what allows that process to take place.

Giving muscle groups enough time to recover between challenging sessions, eating well and getting sufficient sleep will help you get the most from the work you’re putting in at the gym.

If there’s one thing Kori Sampson knows, it’s how to optimise your body composition for performance. To tap into his knowledge as an elite athlete and coach, we asked him to create a 4-week plan to help you move faster, recover quicker and keep pushing when the fatigue sets in – all while improving your muscle-to-fat ratio.

Ready to build muscle, burn fat and come out the other side looking, feeling and performing better? Click here to get 14 days of free access to the plan via the Men’s Health app.