Meaning of the phrasal verb "clamp down" in cotext

Question

Here it goes:

When you clamp down to hold your breath and tighten your trunk muscles, you create a pressure gradient between the inside and the outside.

Answer 1

it means:

When you try to hold your breath[...]

In other words, "when you attempt or make an effort to hold your breath[...]".

The Oxford Learners' Dictionary

to take strict action in order to prevent something, especially crime.

Based on this, I would assume that it roughly means the same thing.