You can take some simple steps to spare your back and knees. Some light stretching before sitting can make the experience more comfortable and prevent stiffness.

Buddhist practitioner and yoga teacher Cyndi Lee writes,

The notion of union is at the heart of both hatha yoga and meditation practice. Yoga, from the Sanskrit yuj, to yoke or bind, refers to the union of apparent opposites: masculine and feminine energies, small mind and big Mind, inner vision and outer awareness, steadiness and ease. We think of yoga as a balancing of mind and body. But where is the balance when your meditating body is so uncomfortable that instead of watching your thoughts arising and passing, your mind is totally focused on your aching back or knees?

For Cyndi Lee’s five-minute stretch designed for meditators, click here.