Muscle Snatch: elementary analysis

Question

I'll take this video of Oleksiy Torokhtiy as reference.

I have some simple questions about this movement.

1. As far as I'm concerned, the legs do not flex after the pull is complete like in a Snatch, but thei remain straight. I see also that the legs do not seem to boost the lift, as Oleksiy Torokhtiy keeps his feet entirely on the floor. So my first question is: providing that the legs do not boost the lift, should the upper body boost it with an explosive movement, or should the upper body perform it in a slow and controlled way (with the purpose of maximizing the upper body strength)? Simply put, does the Muscle Snatch belong to the black part or to the white part in the following Yin and Yang scheme from Starting Strength?

2. After the "deadlift" phase, which are the involved muscles? I'd say front and lat delts (I imagine there is a component of both frontal and lateral raises), the upper traps (shrugs), the lower traps and serratus anterior (scapula upwards rotation). Do the pull muscles (biceps, lats, rear delts etc) do some work on the way up? Which muscles perform the elbow rotation around the bar?

3. Let's consider the following screenshot: isn't such a critical position for the wrists (flexed) and elbows (floating and flaring)? If I were to keep my elbows in such a position with a weight, I'll suffer a lot. I understand that this is an instant of the muscle snatch, but is it safe?

Answer 1

I see also that the legs do not seem to boost the lift, as Oleksiy Torokhtiy keeps his feet entirely on the floor.

If by "boost", you mean that the legs are used explosively to pull the bar as high as possible, then this can still be done with the feet flat on the ground, and this is the aim of the first part of this movement. In a complete snatch, the feet need to move into the squat (or split) position, so they must come off the floor, but this is not required for a muscle snatch, as it has no squat component. Torokhtiy seems to prefer keeping his feet flat in this and the snatch high pull, both of which seem to be more commonly done with a triple extension, in which the heels are raised while the toes stay on the ground.

Simply put, does the Muscle Snatch belong to the black part or to the white part in the following Yin and Yang scheme from Starting Strength?

That's a very strict categorisation, which appears to just be intended to demonstrate the different purposes of the deadlift and power clean, without any intent of categorising any other exercises. While any snatch variation will be much closer in function to a power clean than a deadlift, the purpose of a muscle snatch is to train the lifter for getting under the bar as quickly as possible in the snatch. It's purely an assistance exercise for the snatch, and doesn't really have much benefit outside of that.

After the "deadlift" phase, which are the involved muscles?

Most likely it is the anterior and lateral deltoids, and the external rotators (infraspinatus and teres minor) that are making a small contribution to help continue the upwards movement of the bar.

Let's consider the following screenshot: isn't such a critical position for the wrists (flexed) and elbows (floating and flaring)? If I were to keep my elbows in such a position with a weight, I'll suffer a lot. I understand that this is an instant of the muscle snatch, but is it safe?

It's fine, and this same movement is commonly used to train the external shoulder rotators. When you say "you'll suffer a lot", do you just mean you wouldn't be able to lift or hold the weight? If so, that could happen with any exercise, and just indicates that the weight is too heavy.