Muscle growth can be broken down into three simple factors:
1) Progressive weight training.
2) An energy surplus.
3) Adequate protein.
If one of these three factors is not met, it can be said that rates of muscle growth will become blunted.
However, athletes have the pursuit of gaining the maximum amount of muscle mass whilst minimising gains in fat mass.
Ultimately, gaining body mass will be a by-product of building muscle.
Unfortunately, we can’t entirely be sure how much muscle and how much fat is gained per kg of body mass (unless we accurately assess body composition in a lab). Therefore, we typically have to estimate changes in body composition.
Smith et al (2021) examined the inter-individual differences in muscle growth of trained individuals over the course of six weeks.
During this time, the participants completed three sessions/week (upper/lower/full body split) and were instructed to gain weight at the rate of 0.45kg (1lbs) per week. Therefore, the six-week intervention goal was to gain 2.7kg (6lbs).
To support rates of weight gain, they were provided a 650kcal ‘weight gainer’ and were told to maintain their normal diet.
If body mass wasn’t increasing on a weekly basis at the desired rate, they were told to either increase food or supplemental calories until they did.
On average, their starting calorie intake was 46.8kg/kg and increased to 52.3kcal/kg. Protein intake ranged considerably from 1.6-4.8g/kg per day.
As expected, the combination of high protein, high calories and progressive training resulted in body mass and muscle mass gain. When looking at averages, the participants gained all their weight entirely via muscle.
But not so fast: When you look at the individual data points, some individuals gained a lot of muscle, some stayed the same, and one person actually lost. This means that some individuals lost fat, some stayed the same and some gained.
Interestingly, when you give individuals the same weight training programme and asked to eat an appropriate amount of food to gain 0.55% body mass per week, you’ll get a different outcome.
This could partially be due to the differences in protein intake, albeit the lowest reported was 1.6g/kg (more than adequate). Knowing that previous studies looking at very high protein intakes (4.4g/kg) greatly improved body composition whilst being overfed, this could be a variable we need to consider also.
More interestingly, similar, substantial improvements in muscular performances were seen despite different outcomes in muscle mass.
Lastly, the participant characteristics (e.g., training status, age, sex, level of effort) are also a factor we need to consider.
Long story short, when setting rates of body mass gain with athletes, we can’t use a cookie cutter approach. We need to individualise, monitor and adjust accordingly.

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