A brief Foot Tap Test (FTT, 10s of rapid tapping) relies on rapid, repetitive activation of the dorsiflexor muscles and has been shown to be slower in older adults. The source of this slowing is not known, but could include: greater performance variability, slowed central and/or peripheral activation, or slowed muscle contractile properties. PURPOSE: Compare rapid foot tap count (FTC; # in 10s) in young and older adults, and explore the associations between FTC and tapping performance variability (coefficient of variation for intertap interval, CoV-ITI; %), voluntary rate of force development and relaxation during rapid, submaximal contractions (RFD, RFR; Nm·s−1), stimulated rate of force development and relaxation and half-time for force relaxation (T1/2; ms), and ratio of maximal voluntary:stimulated rates of force development. METHODS: 14 young (mean±SD, 24.7±3.2 years, 8F) and 24 older (74.2±4.8 years, 13F) healthy adults tapped their foot as rapidly as possible while seated with knee and hip at ~90° and the ball of the foot on a force plate (AMTI, Watertown MA). A Matlab (Mathworks Inc, Natick MA) program was used to calculate FTC and CoV-ITI. Each leg was tested at least twice and the slower leg was evaluated for voluntary and stimulated contraction speeds. Voluntary RFD and RFR were determined using rapid, submaximal (30-60% of MVC) isometric contractions, with the foot secured to a custom force apparatus. A tetanic contraction (50Hz, 0.5ms) was used to determine stimulated RFD, RFR, and T1/2. Significance set at p<0.05. RESULTS: Compared with young, older adults had a lower tap count (48.5±5.6 and 44.0±6.3, respectively), slower voluntary RFD (0.14±0.04 and 0.10±0.03), and longer T1/2 (79.8±9.3 and 108.2±19.4), with no other differences between groups. CoV-ITI was not associated with FTC in either group. There was a positive association between FTC and voluntary RFD in young (r=0.75) and FTC and RFR in older (r=0.50), with no other significant correlations observed. CONCLUSIONS: Rapid repetitive dorsiflexor movements are slower in older than younger adults, but this difference is not due to a greater variability of performance nor to a slowing of peripheral activation in older adults. Rather, tapping speed was limited by rate of force development in the young adults and by rate of force relaxation in older adults.