VRWorkout VS pymuscle

I doubt I'll convince the parent, but for the curious about why this comment is utterly wrong and uninformed let's look at how muscles work.

In a given set of muscles you have dozens to thousands of motor units. Each is activated by a motor neuron. When recruited the muscle fibers in a motor unit begin producing (or trying to produce) force. The interesting thing is that they arn't all recruited at the same time, when you use 'a muscle' your actually invoking a complex process of recruitment of sub units within that muscle. Moreover these units are not created equally. Some can produce force for a long period of time and are usually weaker, some can produce force very rapidly but tire quickly. This is why when you try to produce a small static force for a long period of time (e.g. hold your arms out straight) your muscles will eventually start shaking and eventually give out. As one set of motor units begin to fatigue the signal to the whole muscle increases, recruiting fast action motor units which are worse at slow holding, and eventually they and all the units are fatigued and you can't produce continued force.

If you'd like to play around with a simulation of the above process you can, it's older code but it may still check out:

https://github.com/iandanforth/pymuscle

And to specifically address the issue of 'building muscle', as I've noted there are lots of sub components with different roles. Each of those can grow over time for different reasons and fatigue is one of the main signals for growth. Not the only one, but the notion that the only way to build muscle is to 'tear up' your muscles with huge lifts is both outdated and wrong.