Performing a set of isometric muscular contractions to varied amplitudes with instructions to generate force most rapidly reveals a strong linear relationship between peak forces (PF) achieved and corresponding peak rates of force development (RFD). The slope of this relationship, termed the RFD scaling factor (RFD-SF), quantifies the extent to which RFD scales with contraction amplitude. Such scaling allows relative invariance in the time required to reach PF regardless of contraction size. Considering the increasing use of this relationship to study quickness and consequences of slowness in older adults and movement disorders, our purpose was to further develop the protocol to measure RFD-SF. Fifteen adults (19-28 years) performed 125 rapid isometric contractions to a variety of force levels in elbow extensors, index finger abductors, and knee extensors, on 2 days. Data were used to determine (1) how the number of pulses affects computation of the RFD-SF, (2) day-to-day reliability of the RFD-SF, and (3) the nature of RFD-SF differences between diverse muscle groups. While sensitive to the number of pulses used in its computation (P<.05), RFD-SF was reliable when computed with >50 pulses (ICC>.7) and more so with 100-125 pulses (ICC=.8-.92). Despite differences in size and function across muscles, RFD-SF was generally similar (i.e., only 8.5% greater in elbow extensors than in index finger abductors and knee extensors; P=.049). Results support this protocol as a reliable means to assess how RFD scales with PF in rapid isometric contractions as well as a simple, non-invasive probe into neuromuscular health.

Physical quickness is less in older adults with implications for fall prevention, movement initiation, and activities of daily living. The purpose was to compare control of rapid contractions in young and older adults within two diverse muscle groups: powerful elbow extensors (EE) and dexterous index finger abductors (IFA). Most-rapid force pulses to a variety of levels were recorded and peak force and rate of force development (RFD) were analyzed with linear regression. The resulting slope represents the dependent variable of interest, the RFD-scaling factor (RFD-SF). RFD-SF of EE and IFA strongly correlated both overall (r = .87, p < .01) and separately in young (r = .60, p < .05) and older (r = .77, p < .01) adults. RFD-SF values were different between muscle groups (F1,28 = 19.1, p < .001) and also less in elderly (F1,28 = 32.6, p< .001). We conclude that RFD-SF provides a sensitive assessment of muscle quickness that can be used to evaluate neuromuscular function in aging humans.

PURPOSE The aim was to determine the feasibility of a six-week speed-based exercise program that could be used to initiate new exercise behaviors and improve rapid movement in older adults approaching frailty. METHODS The intervention group included 14 older adults (3 males, 11 females, mean (SD) age: 70 (7.6) years, height: 1.6 (.11) m, mass: 76.8 (12.0) kg, BMI: 27.7(4.7)). The control group included 12 older adults (6 males, 6 females, mean (SD) age: 69.2 (6.9) years, height: 1.7 (.09) m, mass: 78.2 (10.9) kg, BMI: 25.3 (2.7)). Subjects included active older adults, including regular exercisers, but none were engaged in sports or exercises with an emphasis on speed (e.g. cycling spin classes or tennis). Stationary recumbent cycling was selected to minimize fall risk and low pedaling resistance reduced musculoskeletal and cardiovascular load. Two weekly 30-minute exercise sessions consisted of interval training in which subjects pedaled at preferred cadence and performed ten 20-s fast cadence intervals separated by 40-s of active recovery at preferred cadence. RESULTS Significant Group by Time interactions (p<.05) supported a 2-s improvement in the timed up and go test and a 34% improvement in rapid isometric knee extension contractions in the exercise group but not in controls. Central neural adaptations are suggested because this lower extremity exercise program also elicited significant improvements in the untrained upper extremities of the exercise group (elbow extension RFD-SF and 9-Hole Peg Test, p<.05). CONCLUSION These results demonstrate that a relatively low dose of speed-based exercise can improve neuromuscular function and tests of mobility in older adults. Such a program serves as a sensible precursor to subsequent, more vigorous training or as an adjunct to a program where a velocity emphasis is lacking.