Slow and steady is not as easy as it sounds: interlimb coordination at slow speed is associated with elevated attentional demand especially in older adults.

The present study investigated age-related changes in the attentional demands associated with interlimb coordination involving upper and lower limbs performed at three different movement frequencies. Younger and older adults performed rhythmical, 180° out-of-phase flexion-extension movements of the knee and elbow with either ipsilateral (right arm, right leg) or contralateral (right arm, left leg) limbs at 20, 60, and 100 % of each individual's maximum movement frequency. A concurrent vocal reaction time task (dual task) was used to assess attentional load. There were two major findings: (1) The attentional cost associated with undertaking the required coordination patterns was greatest at the slowest movement frequency, and this additional attentional load was most pronounced for older adults; (2) the manipulation of movement frequency had a distinct effect on the coordination performance: moving at the fastest frequency degraded the accuracy and stability of coordination, while moving at the slowest movement frequency led to increased temporal variability, particularly in older adults. Coordination performance at slowest movement frequency required the greatest cognitive demand in older adults relative to other movement frequencies, suggesting that going 'slow and steady' is not necessarily less attentionally demanding for older adults.