What CraigB said. I have an ice pack on my knee as I type this. Lots of the spin instructors are not riders and will put you thru all manner of hoops during a class that has no relation to riding. Its a bit embrassing but if I start hurting during a mash a thon I settle into a fast cadence climb and sweat just as much. Might experiment with raising seat so your knee isnt quite so bent.