I agree that carnitine might be considered in some cases.

I have a severe b6 deficiency which is known to cause muscle weakness problems. I also know that people with food allergies can benefit from b6 so far as their allergic reactions are concerned.

I did have low potassium levels as a result of my other deficiencies. Low potassium is not that common but can be consistent with mucsle weakness too. Of course the low potassium would also require sufficient b6.

I don't think you are grabbing at straws. I think sometimes you do have to look at every little thing to figure out what is the underlying cause of the overall health problems sometimes.

I never realized how I was prone to fatigue until I developed a severe case of fatigue. I can look back now and realize I had a number of problems that can be explained by my nutritional deficiencies.

Your child could have less muscle strength (especially upper body) because of some health problem or because of nutritional deficiencies. I think this could also impact on your child's posture, and possibly other things, like ability to play sports or coordination. Of course, not all of these may be related to just one thing, one specific nutritional deficiency, it might be more than one thing causing these different problems.

I have problems with my grip strength that I never experienced before I started supplementing. When you start to treat your deficiencies that is when you can see more of the signs of what the deficiencies can cause because your body is always burning through the nutrients which can cause the symptoms to appear with greater frequency.