Behavioral markers of motor reserve: stability, lateralization, and consistency

Motor reserve has been phenomenologically defined as the capacity to maintain motor performance despite aging-related or disease-related changes, but its objective kinematic basis remains insufficiently characterized. We operationalized motor reserve using measures from a sensor-equipped glove and tested whether they capture inter-individual differences beyond chronological aging.

We enrolled 100 healthy adults (50 older and 50 younger) with a deliberately bimodal age distribution contrasting a young baseline with an older sample of interest. The glove recorded finger-level contact events during four tapping tasks (self-paced, maximum-velocity, synchronization to a 2-Hz metronome, and continuation after metronome withdrawal), each performed under right-hand, left-hand, and bilateral conditions. Motor reserve was assessed with the Motor Reserve Index questionnaire. Candidate kinematic indices were constructed to capture endogenous timing stability, externally paced velocity, bimanual coordination, touch-duration lateralization, and cross-context consistency (ClinicalTrials.gov database n° NCT07634055).

The central finding concerns which kinematic dimensions survive adjustment for chronological age. Aging affected a broad set of glove-derived parameters, most strongly under external pacing. After formal assessment of age confounding, three of the five candidate axes-endogenous timing stability, touch-duration lateralization, and cross-context consistency-retained an association with the Motor Reserve Index questionnaire (MRIq) independent of age, whereas externally paced velocity tracked age rather than reserve. A residual index (rMR) combining the three retained axes was associated with MRIq within the older group and predicted it out-of-sample (leave-one-out r = +0.50; r = +0.42 under nested cross-validation). Supporting analyses showed that the association was absent in the younger group, that the group-by-index interaction was significant, and that rMR was related to MRIq but not to cognitive reserve (CRIq) or to general neuropsychological performance.

These findings provide initial evidence for a candidate kinematic index of motor reserve in healthy aging. Motor reserve was not reducible to global motor speed or chronological age but expressed as a multidimensional profile of timing stability, lateralized motor organization, and consistency across task contexts.