Sun Lun Method
The late Sun Lun Sayadaw developed an unusual meditation method based on an initial phase of fast, hard breathing, followed by mindfulness on bodily sensations. He was considered an Arahant in his native land, Burma.
PTBF incorporates this method of hard breathing in the first part of the meditation but it is optional to use. People who have heart problems, breathing difficulties or are pregnant are discouraged from using this method.
Here is a 3-min instruction by Venerable U Wara, successor of the Sun Lun tradition, on how to do the hard breathing:
Source: raunetty Youtube Page (https://www.youtube.com/@raunetty)
Here is a 15-min video showing a laywoman giving pointers on how to practise this method correctly:
Source: Kateryna Kuzmenko Youtube Page (https://www.youtube.com/@katerynakuzmenko6935)