Background info

The humanoids in my Kepler Bb story have stronger muscles at every stage. This makes it much easier for babies to go through physical milestones and thus the shortening of time before reaching any given physical milestone. Communication also is sped up. However the eating milestones are slowed down.

Milestones

Newborn: none

3 months: sitting without support, saying single words

6 months: standing, saying phrases and short sentences

9 months: walking, questioning, fruits and veggies

12 months: running and jumping, normal communication

etc.

Why stronger?

Stronger muscles are easier to develop than bigger muscles, especially if it is genetic like in these humanoids.

Muscle injuries and their effects

1st degree arm muscle injury:

very sore for most movements(most movements somehow involve the arms, even laying down)

1st degree chest muscle injury:

No heavy lifting

1st degree abdominal muscle injury:

Not much for normal movements, Exercise hurts

1st degree back muscle injury:

A lot of pain on all fours, Breach birth vaginally is much worse.

1st degree leg muscle injury:

Similar to arm muscle injury

2nd degree arm muscle injury:

Can't move much

2nd degree chest muscle injury:

Strength drastically decreased

2nd degree abdominal muscle injury:

abdominal pressure from movement of abdominal organs

2nd degree back muscle injury:

bad balance

2nd degree leg muscle injury:

Similar to arm muscle injury

3rd degree muscle injury:

Complete immobility of that part, surgery is absolutely needed.

Injury of multiple muscles:

Loss of strength

Muscle injury -> Muscle growth?

The way I designed these humanoids, muscle injury leads to muscle growth more than just muscle soreness. The only exception is 3rd degree muscle injury. This conserves muscle mass.

Now the way I see it, this requires a special organ or part of an organ specialized for protein storage.

How else could they grow muscles or conserve muscle mass from injury without causing protein deficiency everywhere else including their 2 hearts and circulatory systems?