Figure 1.

Hypothesized evolution of degradation of physiologic integrity underlying the progression of frailty. Physiologic integrity of the system is defined by the maintenance of equilibrium in the face of stressors. The level of integrity is theorized to be a function of physiological reserves represented by both the depth of each convex curve and the degree of its curvature, with greater depth and curvature representing greater reserve. Both episodic (e.g. stroke, fall) and chronic insults (e.g. chronic inflammation) are hypothesized to degrade return to equilibrium and decrease integrity of the system to respond to a subsequent stressor. Progression of frailty consists of a series of downward transitions between states of equilibrium of decreasing integrity; and at some critical tipping point, the system becomes overwhelmed and can no longer harness the resources needed to maintain integrity, leading to frailty.