Bandas (pronounced bah-n-daas) are locks in Yoga whereby you ‘lock’ the energy in a particular area thereby stimulating that region. For example, the Jalandara Banda or the Throat lock is where you press the chin into the base of the neck while holding your breath. At the same time you think and feel the throat region. This stimulates the thyroid. Jalandara banda can be combined with other asanaa such as Shoulder Stand where it is ideal to press the chin into the base of the throat. The focus of the energies or the circulation in that region is what stimulates the area. The Throat chakra or the energy center in the throat call the Vishuddhi Chakra gets stimulated. People who lack communicating abilities or aspire for more are advised to practice Jalandara Banda. As you are holding the breath, there will be strain in your heart IF you over do it. The key is to retain the breath as long as you are comfortable without having to gasp for air at the end. Best learnt from an experienced yoga teacher as always. One can combine the Throat lock along with the Uddiyana Banda also, but that isn’t necessary.