Objectives: Previously, we developed and validated an easy test to measure muscle fatigability during sustained maximal handgrip contraction in older persons using a Martin Vigorimeter device. This study aimed at validating the equation to estimate grip work (GW) during sustained maximal handgrip contraction, by monitoring continuously the grip strength (GS) decay using a Jamar Dynamometer-like (JD) device. Design: Cross sectional, explorative study. Setting: Data collection took place at The National Research Centre for the Working Environment in Copenhagen, Denmark. Participants: 962 subjects, belonging to a subgroup of the Copenhagen Aging and Midlife Biobank, were enrolled. Methods: GS was recorded continuously during sustained maximal contraction until it dropped to 50% of its maximum and fatigue resistance (FR, time to fatigue) was noted. GW, area under the force-time curve, was compared to its estimate which was calculated as GWestimated=GSmax*0.75*FR. Results: Excellent correlation was found between GWestimated and GWmeasured (R²=0.98 p<0.001). The equation slightly overestimated GW by 6.04 kg*s (95% CI[-0.08, 12.15]) with a coefficient of variation method error of 6%. Conclusion: GW estimation is a valid parameter reflecting muscle work output during a sustained maximal grip effort in healthy middle-aged community-dwelling persons when using a JD. GW estimation is a promising outcome parameter in comprehensive geriatric assessment and its validation for commonly used instruments in geriatric practice will increase its clinical implementation.