Which stimulus is most likely to increase pain in a patient with lumbar spinal stenosis?

In patients with lumbar spinal stenosis, lumbar spine extension is the stimulus most likely to increase pain. This condition involves a narrowing of the spinal canal, which can lead to compression of the spinal nerves. When the lumbar spine is extended, it exacerbates the narrowing of the spinal canal and can further irritate the neural structures, leading to increased pain.

In contrast, other activities such as forward bending often alleviate compression in the spinal canal by reducing the lordotic curve, and sitting for prolonged periods, while it may not be ideal for everyone, doesn't actively compress the nerves in the same way. Walking can also help with pain management as it encourages movement and blood circulation, which may relieve some symptoms of spinal stenosis. Thus, lumbar spine extension clearly stands out as the activity that most directly contributes to an increase in pain for these patients.