Purpose: To improve our understanding about the underlying factors of aging-related speaking rate decline, the authors sought to determine if lip and jaw speeds are physiologically constrained in older adults.

Method: Thirty-six females-10 young adults (ages 22-27 years), 9 middle-aged adults (ages 45-55 years), 10 young-old adults (65-74 years), and 7 very old adults (ages 87-95 years)completed metronome-paced syllable repetitions while moving the lower lip or jaw to a fixed target with each repetition. Metronome paces incrementally increased from 1.4 Hz to 6.7 Hz. Lip and jaw movements were tracked using a 3-dimensional motion capture system.

Results: Older adults' maximum percent increase in lip and jaw peak speed was comparable to or tended to be even greater than that of middle-aged and young adults. By contrast, lip and jaw stiffness, indexed by peak speed-displacement ratios, tended to decrease with age during fast and very fast repetition rates and were associated with mildly prolonged movement durations.

Conclusions: The findings suggest that lip and jaw speeds are not constrained in older adults. The trend of reduced stiffness during fast rates, however, suggests that fine-force regulation becomes difficult for older adults. Thus, older adults may implement reduced habitual speaking rates as a behavioral strategy to compensate for diminished articulatory control.