My Keplerians are humanoids but they have a special organ and special hormones for protein storage. Not only that but they don't get muscle atrophy from injury. Take the abdominal muscles for example. If a Keplerian who wants to build muscle does too many bodyweight exercises, they will get a first degree muscle injury: Sort of like this, injured and swollen but still intact(tears are microscopic). When they get this injury, a hormone is released to break the stored protein down into amino acids and bring it to the injured muscle. Why stored protein? Well my Keplerians naturally eat a high protein diet so eating even more protein is not needed. There will be some muscle growth after this injury heals.
This means that the muscle, macroscopically is torn but not completely torn. There won't be a hole, just a tear or possibly multiple tears This still leads to muscle growth.
Now, if the weight is not what they are used to carrying as a load but instead heavier, the injury is going to be even worse. The muscle will rupture. It might not rupture completely but there certainly will be a hole where the abdominal muscles are supposed to be.
That is a third degree muscle tear and as you can see from the image, it leads to hernias. Complete rest though can prevent these hernias from occuring. It might lead to a rash or a backache but that is certainly better than a hernia. So much protein is used to heal a third degree muscle tear that none goes to muscle growth. However, with their naturally high protein diet, muscle breakdown is prevented. So muscle mass is conserved.
But is this plausible? Is it plausible that muscle injury leads to muscle growth even when it is second degree? Is it plausible that muscle mass is conserved in a third degree muscle injury simply due to a naturally high protein intake? What would prevent this from being plausible?