Objective: The aim of this study was to investigate age-related changes of multi-finger synergy during aconstant force production task with and without an additional mechanical constraint.Method: Fourteen elderly subjects (age: 78.50 ± 4.63 yrs, height: 157.29 ± 8.97 cm, weight: 65.13 ± 6.93 kg)and 14 young subjects (age: 21.13 ± 1.35 yrs, height: 171.57 ± 8.43 cm, weight: 70.29 ± 16.77 kg) participatedin this study. The subjects were asked to place their index and middle fingers on two force transducersfixed on a small non-moving teeterboard and produce 10 N by pressing the sensors while watching forcefeedback on a computer screen under the no additional constraint condition (NAC). The subjects alsoperformed the same task with an additional mechanical constraint (AC) where the subjects were asked tobalance a teeterboard that could be rotated by finger forces. An uncontrolled manifold approach was usedto calculate within-trial and between-trial multi-finger synergy indices, variance in uncontrolled subspace(VUCM), and variance in subspace orthogonal to UCM subspace (VORT). Two-way repeated measured ANOVAwas performed with the within-factor of task condition (with and without an additional constraint) andthe between factor of groups (elderly and young).Results: The elderly group showed significantly increased within-trial VORT in AC compared with NAC (p< .05) while the young group showed no significant difference between AC and NAC. There was nosignificant group difference for within-trial VUCM. Between-trial VORT remained unchanged between groupsand conditions. However, between-trial VUCM for the elderly group significantly decreased in AC as comparedto NAC, along with no significant difference for the young group. For multi-finger synergy, there was nosignificant group difference of within-trial synergy. However, between-trial synergy for the elderly groupsignificantly decreased in AC as compared to NAC (p < .05).Conclusion: Our results indicate that aging decreased consistency (i.e., ability to perform the task on amoment-to-moment basis) with an additional mechanical constraint. In addition, aging was associatedwith decreased multi-finger synergy on a trial-to-trial basis.