Bed Height for Older Sleepers: The Seat-Height Rule That Minimises Sit-to-Stand Effort, and the Fall Energy Cost of Exceeding It

Bed height is usually set by furniture fashion — deep mattresses on high frames — but for an older sleeper the height of the bed's top surface decides both how hard it is to stand up in the morning and how far there is to fall at night. This paper models sit-to-stand effort as a stated power of the ratio between the sleeper's popliteal height and the effective, compressed bed height. For a popliteal height of 42 cm, standing from a 45 cm bed top requires an effort index of 103.7, against 100.0 at the recommended height and 57.1 from a fashionable 65 cm top — the effort curve is steep below knee height and flat above it. Raising the top to 75 cm raises the energy of a roll-out fall for a 70 kg sleeper from 316 J at the recommended height to 515 J. The rule that emerges — bed top at popliteal height plus the mattress's seated compression — is measurable with a tape in under a minute. This study is simulated, not measured.