Is this lumbar stenosis?cycling my left leg can pedal normal when the spine is flexed but upon extending spine left leg has no power and is "dragging"

See below: It llok like spinal stenosis indeed. See your doctor for the imaging studies of your lower back.

It is a possibility: If this is bothering you get it checked by your physician who can decide if an imaging study is indicated such as a MRI or ct of the lower back. Typically, with sitting or a bent over/flexed position, the spinal canal is more open and with standing erect or upright the canal has a narrower caliber as does the nerve exiting holes known as neuroforamen.

Spinal stenosis: I completely agree; due to the erect position in the lumbar spine, some of the ligaments can fold-into the nerve tunnels and even the central spinal canal; narrowing the space available for the nerves that live there, and thus making the symptoms in your legs worse. This is called neurogenic claudication.