B.K.S. Iyengar, who will be 90 years old this year, has systematized over 200 classical yoga Asanas and 14 different types of Pranayamas from the simple to the incredibly difficult. These have been structured so as to allow a beginner to progress safely from basic postures to the most advanced as they gain flexibility, strength and sensitivity in mind, body and spirit. Correct body alignment allows the body to develop harmoniously in an anatomically correct way so that the student suffers no injury or pain when practicing correctly. Mr. Iyengar has also developed the use of props to help the body into the correct positions required. Props are objects like wooden blocks, chairs, blankets and belts that help one adjust or support the body in the different postures so that the student can work in a range of motion that is safe and effective. The other two key aspects of asana practice in the Iyengar system are correct sequencing in which there is a powerful cumulative effect achieved by practicing asanas in particular sequences. The concept of timings means postures are held for considerable lengths of time to let the effects of the poses penetrate deeper within. He also explored the way poses could help people recover from illness or injury. Mr. Iyengar's unrelenting emphasis on correct anatomical alignment and methods of working has refined the therapeutic aspects of Yoga. Thus the practice of Iyengar yoga will often result in eliminating aches and pains, improve posture etc. Iyengar Yoga can also be used to treat many ailments, including extremely serious medical conditions, under the supervision of a suitably experienced teacher.