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Thesis Information
Title: A Comparison Of Eccentric Strength Among Young, Middle-Aged, And Older Female Adults
Program: Master of Science in Kinesiology
Advisor: Dr. Shawn Simonson, Kinesiology
Committee Members: Dr. Tim Kempf, Kinesiology and Dr. Tyler Johnson, Kinesiology
Abstract
Introduction: As people grow older, they are confronted with the reality of age- related physical changes, which may inhibit their ability to perform activities of daily living (ADLs) and increase their fall risk. While many factors can contribute to these physical changes, muscular power declines faster than strength and is more predictive of fall risk in community-dwelling older adults. This early loss of power may be associated with low physical activity levels, age-related muscle atrophy, or impaired neuromuscular function; however, these findings are inconclusive. One area warranting further investigation involves exploring the contribution of different types of muscle contractions (eccentric, concentric, or isometric) to the decline in power associated with aging, particularly during high-velocity contractions. Purpose: The aim of this study was to compare differences in knee extension peak torque for various types of muscle contractions at three velocities between three female age groups to determine a decline throughout the adult lifespan. Two hypotheses were tested. (1) The older adult (OA) group would produce the lowest force output during high-velocity eccentric knee extensions when compared to the young adult (YA) and middle-aged adult (MA) groups. (2) High-velocity eccentric strength would decline more than high-velocity concentric strength throughout adulthood. Method: Twenty mobile female participants who were not physically active or following an exercise regimen were divided into three age groups: 8 young adults (YA; 18-28 yr), 7 middle-aged adults (MA; 42-52 yr), and 5 older adults (OA; 65-75 yr). Participants completed isometric (ISO), concentric (CON), and eccentric (ECC) knee extensions (dominant leg) using a Biodex System 3 isokinetic dynamometer at three velocities (60 °/s, 180 °/s, and 300 °/s). Descriptive statistics and repeated-measures analysis of variance (ANOVA) with a post-hoc Bonferroni analysis were performed using SPSS software to determine statistical significance (p ≤ 0.05) for each hypothesis. The difference in peak torque was also calculated for each muscle contraction across each age group. Result: Knee extension muscle contraction types are well-preserved from young to middle- aged adults, irrespective of movement speed. However, a decline in muscular strength and power is observed from young to older adults, suggesting an overall deterioration across adulthood. Furthermore, CON strength gradually declines throughout adulthood, while ISO and ECC strength rapidly decline from middle age to elderhood. The magnitude of decline in ECC strength increases with velocity from middle-aged to older adults, in contrast to CON strength. Conclusion: CON declines across adulthood, regardless of movement speed, while ISO and ECC are maintained until middle age before showing a significant decline into elderhood. As ISO strength is not velocity-dependent, it is unlikely to play a role in age-related declining power. Therefore, due to ECC experiencing a rapid decline after middle age, which is further exacerbated at higher velocities, a potential correlation is observed with the rapid decline in power, resulting in the inability to perform ADLs and increasing fall risk.