Due to sarcopenia, elderly persons function closely to their maximal physical capacities1,2. Consequently, supplementary weakness, typically occurring during acute illness, can lead rapidly to dependency in activities of daily life (ADL). Grip strength has been widely used in the screening for muscle weakness in the aged, given its simplicity and its correlation with general muscle strength. Sufficiently high maximal strength is determinative for the ability to start functional tasks such as rising from a chair or lifting an object. However, in elderly persons, continuing and completing these tasks necessitates sustained muscle contractions at a nearly maximal intensity. Reduced muscle endurance might therefore explain the occurrence of fatigue, one of the major characteristics of frailty in elderly patients3,4. Surprisingly, resistance to fatigue is not commonly evaluated during geriatric assessment, possibly because elderly patients are often unable to perform the classic endurance tests. Previously, we have described an easy and reliable method to evaluate muscle fatigue resistance in elderly subjects5. For the assessment of fatigue resistance (see figure 1), the subject is first asked to squeeze the large bulb of the Martin Vigorimeter (Elmed, Addison, USA) as hard as possible. The highest of three attempts is noted as the maximal grip strength (in KPa). Then, the subject is instructed to squeeze again the bulb of the vigorimeter as hard as possible and to maintain this maximal pressure. The time (in seconds) during which grip strength drops to 50% of its maximum is recorded as fatigue resistance. By consequence, the outcome on the fatigue resistance test is a measure relative to each individual's maximal strength. Since functional performance depends as well on the strength that can be deployed as on the time during which the strength development can be sustained, we have integrated both parameters into a useful muscle endurance outcome defined as Grip Work6. This can be easily computed using the equation: Grip Work = Maximal Grip Strength * 0.75 * Fatigue Resistance. The calculation of grip work starts from the assumption that the strength drops linearly during the fatigue resistance test. In a recent study7, we have confirmed the validity of that assumption by monitoring continuously the changes in grip strength during the fatigue resistance test in a large and diverse sample of 291 subjects among which 100 young subjects (aged 23±3 years), 100 community-dwelling elderly (aged 74±5 years) and 91 hospitalized geriatric patients (aged 83±5 years). An excellent correlation (Pearson's r=0.98, p References 1. Hortobagyi T, Mizelle C, Beam S, DeVita P. Old adults perform activities of daily living near their maximal capabilities. J Gerontol A Biol Sci Med Sci 2003;58(5):M453-460. 2. Bautmans I, Van Puyvelde K, Mets T. Sarcopenia and functional decline: pathophysiology, prevention and therapy. Acta Clin Belg 2009;64(4):303-316. 3. Fried LP, Tangen CM, Walston J, Newman AB, Hirsch C, Gottdiener J, Seeman T, Tracy R, Kop WJ, Burke G, McBurnie MA. Frailty in Older Adults: Evidence for a Phenotype. J Gerontol A Biol Sci Med Sci 2001;56(3):M146-157. 4. Avlund K, Damsgaard MT, Sakari-Rantala R, Laukkanen P, Schroll M. Tiredness in daily activities among nondisabled old people as determinant of onset of disability. J Clin Epidemiol 2002;55(10):965-973. 5. Bautmans I, Mets T. A fatigue resistance test for elderly persons based on grip strength: reliability and comparison with healthy young subjects. Aging Clin Exp Res 2005;17(3):217-222. 6. Bautmans I, Gorus E, Njemini R, Mets T. Handgrip performance in relation to self-perceived fatigue, physical functioning and circulating IL-6 in elderly persons without inflammation. BMC Geriatr 2007;7:5. 7. Bautmans I, Onyema O, Van Puyvelde K, Pleck S, Mets T. Grip Work Estimation during Sustained Maximal Contraction: Validity and Relationship with Dependency and Inflammation in Elderly Persons. J Nutr Health Aging 2011;15(8):731-736. 8. Bautmans I, Njemini R, Predom H, Lemper JC, Mets T. Muscle endurance in elderly nursing home residents is related to fatigue perception, mobility, and circulating tumor necrosis factor-alpha, interleukin-6, and heat shock protein 70. J Am Geriatr Soc 2008;56(3):389-396. 9. Bautmans I, Njemini R, Lambert M, Demanet C, Mets T. Circulating Acute Phase Mediators and Skeletal Muscle Performance in Hospitalized Geriatric Patients. J Gerontol A Biol Sci Med Sci 2005;60(3):361-367. 10. Mets T, Bautmans I, Njemini R, Lambert M, Demanet C. The influence of celecoxib on muscle fatigue resistance and mobility in elderly patients with inflammation. Am J Geriatr Pharmacother 2004;2(4):230-238. 11. Beyer I, Njemini R, Bautmans I, Demanet C, Bergmann P, Mets T. Inflammation-related muscle weakness and fatigue in geriatric patients. Exp Gerontol 2012;47(1):52-59. 12. Bautmans I, Njemini R, De Backer J, De Waele E, Mets T. Surgery-induced inflammation in relation to age, muscle endurance, and self-perceived fatigue. J Gerontol A Biol Sci Med Sci 2010;65(3):266-273.