However, if the chair is at a good height but the keyboard height can't be adjusted to elbow height or lower, then it's necessary to adjust the chair upwards. In this case, a footrest is an option. Conventional wisdom says footrests are always a fine alternative and that chairs and worksurfaces don't need to be lowered if a footrest is available. The truth is that footrests are a distinctly second-class choice because the feet only have one place to be, and leg postures are limited. However, if the chair is already low enough, footrests offer a chance to change leg postures and are recommended.
Conventional wisdom prescribes an upright posture, with the hips at ninety degrees .
When the hips are straightened, the vertebrae of the lower spine are aligned with each other in a way that reduces and evens out pressure on the intervertebral discs. Further, sitting upright is less desirable than reclining. When reclining, the lower back muscles work less and the spine supports less weight, since body weight is held up by the chair's backrest. Conventional wisdom for keyboard height is that it should be at elbow height. This is wrong, or at least too narrow.