Are You Gaining Muscle or Fat? • Common Purpose

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Are You Gaining Muscle or Fat?


Words by Common Purpose Team

Published 7th October 2021

When gaining weight, it can be difficult to tell whether you’re gaining muscle or fat, especially without a professional’s help, or advanced measuring equipment (DEXA, Bod Pod, bioimpedance etc.). Yet, there are some tell-tale signs that you can monitor yourself. We will talk through some of these general signs, and highlight some of the ways we can get a good indication of body composition changes.

Steadily gaining weight while not exercising or monitoring nutrition probably indicates some fat gain


If you are not exercising regularly (especially resistance training) and/or monitoring your nutritional intake, it is more likely that the steady weight gain over time will come from fat, as opposed to muscle.

Gaining muscle requires proper training and a nutrition strategy 


Gaining muscle is hard. You need to be focusing your nutrition to be in a slight caloric surplus, focusing on a specific balance of proteins, fats and carbohydrates, whilst also performing a progressive resistance training program with enough intensity and frequency (we suggest at least three times a week).


If you are not adhering to this style of nutrition and training program, it is unlikely an increase in weight will be from muscle.


There are many other factors involved weight fluctuations that can create “noise” 


It’s important to note that weight fluctuations are normal and are influenced by other factors that aren’t muscle or fat. For example, your hydration status, water retention (affected by carbohydrate, salt and creatine), changes in your training program, stress hormones and even the amount of food in your digestive system can all cause weight gain or loss (sometimes as much as 5kg per day!).


Having said this, the influence of these factors are generally volatile (changes day to day)  and can be viewed as “noise”. So tracking averages and trends over time is the best way to get a more accurate indication of body composition in terms of muscle and fat, because fat and muscle gains/losses are slow and steady.

How can you be sure whether you have gained muscle or fat? 


If you have recognised that you are consistently increasing in weight over several months and you want to be sure whether it is fat or muscle, here’s how to tell.

Body fat scales (bioelectrical impedance)


Body fat scales use a technology called bioelectrical impedance analysis. The scales send a small electrical current through your body, measuring resistance on its journey. The higher amount of resistance the current meets, the more fat in the body as fat is a poorer conductor of electricity than muscle. 


These scales do have an error rate, so should not be taken as 100% truth, they should only be taken as an estimate of body fat composition. By using the same set of scales every time, and collecting multiple data points, you can mitigate this error rate and get a good indication of body composition.


Body composition testing


Most professionals, and some gyms, should be able to give you a body composition test to determine your body fat and muscle split. Using a measuring tape and fat callipers, they can work out your body fat % and muscle gain. This can also give indications of how these changes are distributed throughout your body. Try to have this done monthly if you are trying to measure your progress accurately, and we would suggest the same professional carrying it out each time.


DIY measurement


If you are looking for a do-it-yourself option then you will need access to a set of weighing scales and a body fat calliper


First of all, step on the scales and note down your weight. 


Second, measure your body fat using the instructions on the fat calliper. 


Third, multiply your weight by your body-fat percentage. Example: 185 lbs. X 17.5% (or .175) = 32.4 lbs. of fat


Finally, subtract the amount of fat (in pounds) from the bodyweight you measured first. This final sum will leave you with your lean weight which you can monitor once a month.


Looking for a professional opinion? 

We believe in the journey, and our fitness programs go beyond the gym. By focusing on our four pillars balanced nutrition, progressive and engaging exercise, recovery and restoration alongside mindset we help bring our clients to a new level of confidence, ability and fitness. If you are looking to take your training to the next level, call us at our London Mayfair gym space.