There are two kinds of heat we can experience in a Yoga asana practice: a peripheral heat and a core heat. A similar (and easier to achieve) experience can be found in food. Spices like black pepper create a peripheral heat that can be felt in the bodies extremities (hot face, runny nose, sweat, etc). Then there are spices such as ginger which create a heat that is felt in the abdominal area (also considered good for digestion).
One of the motivations for the alchemy of breathing in asana experiment is to experience these two qualities of heat in practice. If you review the breathing patterns in the experiment you will find that the variations are based on the holds – the pauses between inhaling and exhaling (the inhale and exhale remained consistent througout the experiment).
The hold after the inhale (Antah Kumbhaka) is a stimulating practice that generates peripheral heat. When challenged, and the breath runs out, most people gravitate automatically towards holding their breath after the inhale (partly because it can be forced!). A common symptom of the peripheral heat is of-course sweating.
The hold after the exhale (Bahya Kumbaka) is a centering practice (attention is placed on the abdomen). This generates a core heat, felt mostly in the abdominal. It is a concentrated heat that purifies. Though it also has stimulating qualities – it is more about containment. This hold cannot be forced (try!) – instead it offers a practice of surrender. Advanced Yoga energetic practices place an emphasis on the exhale and the hold after the exhale, and centered around the abdominal area.
These qualities comes into play when designing a practice. Asana sequences can be used to both stimulate energy and bring it to the center – using a combination of postures and breathing formulas. Pranayama regulates energy flow and meditation directs it. The overall practice would vary for individual practitioners and life circumstances, and a relevant mode of practice.