Hi Chrissy,
My short answer would be "no." These machines are not strictly contraindicated, but their safety is entirely dependent on the specific underlying cause of the low-back pain (LBP) and sciatica.
LBP is sometimes categorized into "Directional Preferences." Whether a seated elliptical or upright bike helps or hurts depends on whether the patient is Flexion Intolerant or Extension Intolerant.
Flexion vs. Extension
Flexion Intolerant (Common in Disc Herniations)
If the sciatica is caused by a bulging or herniated disc, sitting (flexion) usually makes it worse. Upright Bike: Often risky. The forward-leaning posture increases "intradiscal pressure," which can push the disc material further against the nerve. If the patient is riding an upright bike, they should keep their lumbar spine as straight as possible or even slightly extended. Seated Elliptical: Generally safer than the bike because the back is supported, but the "pedaling" motion can sometimes create a "slump" position that irritates the nerve.
Extension Intolerant (Common in Spinal Stenosis)
If the sciatica is caused by narrowing of the spinal canal (stenosis), the patient usually feels better when sitting or leaning forward. Upright Bike: Often recommended. Leaning forward opens the spinal canal and relieves nerve pressure. Seated Elliptical: Usually very well tolerated.
I hope this helps a little.