Inter-limb transfer of ballistic motor skill following non-dominant limb training in young and older adults

We recently reported considerably less inter-limb transfer in older, compared to young, adults following dominant (right) hand motor training (Hinder et al. in J Appl Physiol 110:166-175, 2011). This occurred despite the fact that both age groups exhibited similar performance improvements in the trained limb. However, asymmetries can exist with respect to the degree of transfer observed in some tasks, depending upon which limb undertakes the training. Accordingly, here we investigated inter-limb transfer following left hand ballistic motor training in young (n = 15; mean age 21.2 years) and older (n = 15; mean age 70.3 years) right handers. Following motor training that required participants to maximally abduct the left index finger, both groups exhibited significant performance improvements in the trained left hand. Moreover, the extent of inter-limb transfer was substantial and indistinguishable between the two age groups. Transcranial magnetic stimulation revealed that both age groups exhibited bilateral increases in cortical excitability following unilateral training, indicating that unilateral training affects both the trained and untrained hemisphere. However, only for young adults was the extent of the performance gain in the trained hand able to predict the degree of transfer. These findings suggest that different mechanisms may mediate inter-limb transfer of ballistic motor tasks for older and young adults. Because such tasks evoke similar neural responses to those observed following strength training (Selvanayagam et al. in J Appl Physiol 111:367-375, 2011; Carroll et al. in Acta Physiol 202:119-140, 2011), our findings have important implications for rehabilitation paradigms following stroke or limb immobilisation due to injury.