Heel Risk ExplorerThe mechanics
Sourced numbers drive these controls.
The curve is the theoretical dividing line between combinations of pressure and time under load that left muscle intact and combinations that damaged it, as measured in rat muscle: a brief load is tolerated at high pressure, but after about two hours even a modest pressure crosses the line. Below the curve tissue survived; the shaded region above it is where damage occurred. The blue mark is your scenario, the effective pressure at the heel held for the time you have set.
What is happening
In this model, this load held this long is enough for the direct squashing of tissue against the heel bone to be doing real harm to the tissue.
In this model, the single change that moves the picture most is taking the heel out of contact altogether.
The surface applies about 88 mmHg (11.7 kPa) at the skin over the calcaneus. Inside, the thin tissue between bone and surface concentrates that load; the only human measurements of such concentration were made at the buttock while sitting, where stress in muscle was roughly double the surface figure, and no heel equivalent exists. This page therefore shows the concentration as an illustration only. (Linder-Ganz 2007, human buttock, n=6; Gefen 2010)
At 2.0 hours of loading, the damage threshold measured in rat muscle sits near 67 mmHg: above about 240 mmHg cells die in under an hour, and beyond 2 hours the threshold falls to about 67 mmHg. Deep damage typically develops between the first hour and 4 to 6 hours of sustained loading. (Linder-Ganz 2006, rat; Gefen 2008)
The tissue does not behave like a spring. From the moment the load goes on it creeps: in sheep adipose tissue tested ex vivo, tissue was roughly three times stiffer at the instant of loading than after settling, and most of the settling happened within about 2 minutes. The heel keeps sinking into whatever it rests on, so by the timescales on this page the deformation has already reached its full depth. (Gefen and Haberman 2007, sheep, ex vivo)
Shear is present at the interface. In human hand tissue, adding shear roughly halved the pressure needed to shut off blood flow, so the ischaemic process runs at lower pressures than pressure alone would need. (Bennett 1979, human, n=4; Gerhardt 2008, human, n=22)
Where the UK guidance points next
The same for every scenario: what exists, not advice generated for a person.
Pressure ulcer prevention. NICE guidance CG179 asks clinicians to discuss, with adults at high risk of a heel pressure ulcer, “a strategy to offload heel pressure”. The 2025 International Guideline goes further for heels at risk: as good practice, the heel fully free of the support surface.
Diabetes and the foot. If a real foot with an active diabetic foot problem is in front of you, the pathway already exists: NICE guidance NG19 says refer within 1 working day to the multidisciplinary foot care service or foot protection service, and immediately to acute services if the problem threatens the limb or the person.
Reading the mechanics in full. The article this tool accompanies: Pressure and Shear: What the Words Mean, and on what the guideline’s floating heel standard means in practice: Floating Heels.
The person
Same load, different tissue. Sourced directions, not weights: these move the band at most one step.
The two damage processes
Both run whenever loaded tissue sits above its threshold.
