Isotonic Force Steadiness of the Leg Extensors is Dependent on Intensity and Contraction Type in Pre-Clinically Disabled Older Adults

Abstract

0835 Various studies have indicated that apparently healthy older adults have reduced steadiness during eccentric contractions and at low intensities in the finger and elbow flexor muscles, with no difference in the knee extensors. Because of their difficulty performing tasks of everyday living, pre-clinically disabled older adults may show altered steadiness patterns compared to previous research in older adults. Purpose: The purpose of this study was to determine the effect of contraction type and intensity on isotonic and isometric steadiness in pre-clinically disabled older adults. Methods: Thirty older subjects (aged 74.7 ± 7.64 years) with difficulty performing either a chair rise or stair ascent/descent tasks were enrolled into the study. Following assessment of maximal voluntary contraction (MVC), subjects performed two concentric, eccentric and isometric contractions at three different intensities. During isotonic tasks subjects lifted and lowered a load at 0.23 rad/sec with 5%, 30% and 65% of MVC. During isometric tasks, subjects were asked to hold 10, 25 & 30% of MVC. Fluctuations around the average force level during isotonic tasks and coefficient of variation for force during isometric tasks were used for statistical analysis. Data was analyzed using a two-way (Factors: contraction type*intensity for isotonic contractions) and one-way (Factor: intensity for isometric contractions) repeated measures analysis of variance. Results: For isotonic contractions, there was no intensity*contraction type interaction (p = 0.88). However, subjects were significantly less steady during high intensity compared to low intensity contractions (5% = 0.08 ± 0.04, 30% = 0.15 ± 0.09, 65% = 0.22 ± 0.14; p 0.00). Additionally, the main effect for intensity showed that older adults were less steady during concentric (0.17 ± 0.12) compared to eccentric (0.13 ± 0.10) contractions. Subjects showed similar force fluctuations between each intensity during isometric contractions (10% = 1.5 ± 1.3, 25% = 1.3 ± 1.1, 50% = 1.2 ± 0.58; p = 0.23). Conclusion: These results suggest that pre-clinically disabled older adults show reduced steadiness at higher intensities and during concentric contractions.