Quadriceps strength deficits are known for patients with knee osteoarthritis (OA). Hamstring muscles has been less often investigated and findings are not as clear as for knee extensors. In regard of OA, the neuromuscular function in the sense of Adaptive Force (AF) has never been examined before. The maximal isometric AF (AFisomax) was previously considered to be especially vulnerable to disruptive stimuli and, therefore, was assumed to show deficits in OA patients. The present study investigated AF parameters (AFisomax and maximal AF (AFmax)) as well as the maximal voluntary isometric contraction (MVIC) of hamstring muscles bilaterally of 20 knee OA patients (ART) compared to 19 asymptomatic controls (CON). For each side, MVIC was captured before and after AF measurements. Five AF trials were performed using a pneumatically driven device. Participants should maintain an isometric position despite an increasing load of the device. After reaching AFisomax, the muscle merged into eccentric muscle action whereby the force increased further to AFmax. All torque parameters (normalized to body mass) were significantly lower in ART vs. CON for both sides with almost always very large effect sizes. MVIC deficits (difference between ART and CON) amounted −28% for the more and −30% for the less affected/asymptomatic side. AFmax showed deficits of −36% and −32% and AFisomax of −37% and −24%, respectively. The reduction of AFisomax was not as high as expected, especially related to MVIC or AFmax. The ratio AFmax to MVIC was significantly lower for the more affected side of ART (84 ± 17%) vs. CON (95 ± 7%). The force rise per degree of knee extension was significantly lower for ART vs. CON. The results suggest that in general hamstrings strength deficits are present in OA patients. The hypothesized stronger deficit in maximal holding capacity (AFisomax) in ART vs. CON was not confirmed. It is suggested this might presumably result from the seating measurement position. Knee strain relief might have been present thereby which could have reduced inhibitory nociceptive effects. Importantly, OA patients seem not to be able to generate as much of their possible maximal strength during eccentric action as controls and their force rise per degree of knee extension seems to be diminished. The role of force development especially under muscle lengthening should be considered in further studies to get more specific insights into this aspect of neuromuscular control.