Iyengar is the other most commonly practiced form of physical yoga. Iyengar is the perfectionist's yoga, as it gives emphasis to precision and alignment in all postures, and students are taught to spend a greater amount of time in each posture in order to fully experience it. There are several Iyengar studios in the city, one of which is the Iyengar Institute of San Francisco. A very low-impact Iyengar class that might be well suited for people sustaining physical injuries or suffering from insomnia due to high levels of stress is Restorative Yoga. Restoratives are meditative poses in which the body is supported with props and held for extended periods of time. Neurological research shows that in terms of brainwave activity and cell regeneration, 20 minutes in a well-supported restorative pose is equal to 2 hours worth of good sleep.