I'm sure that you have seen Fried's phenotype of Frailty;  here's more on pre-frailty:
The Mediterranean Diet Slows Down the Progression of Aging and Helps to Prevent the Onset of Frailty: A Narrative Review. Capurso C, Bellanti F, Lo Buglio A, Vendemiale G. 
Nutrients. 2020; 12(1):35. https://doi.org/10.3390/nu12010035
Here are some criteria from Fried
Pre-frailty factors in community-dwelling 40–75 year olds: opportunities for successful ageing  S. J. Gordon, N. Baker, M. Kidd, A. Maeder & K. A. Grimmer BMC Geriatrics volume 20, Article number: 96 (2020) 
The challenge is to pre-empt the whole darn syndrome.  Functional strength & power are the main priorities even in CR programs;  Thriving in place is key!
Pat.