Isometric, Eccentric, and Concentric Strength in Trained and Untrained Older Adults: A Pilot Study

Abstract

Background: Despite an overall decrease in muscular strength, older adults maintain eccentric (ECC) strength in greater proportions compared to isometric (ISO) and concentric (CON) strength. While resistance training is promoted for older adults, the impact of resistance training on ISO, ECC, and CON strength is relatively unknown. Objective: The purpose of this study was to compare peak ISO, ECC and CON knee extensor moments between trained and untrained older individuals. Methods: A quasi-experimental design with a two-group comparison, ex post facto, was conducted. Twenty older adults (8 females, 69.6 ± 6.1 years, 80.5 ± 16.4 kg, 1.7 ± 0.1 m) were allocated to two groups, one undergoing resistance training (n =10) and one not (n = 10). An isokinetic dynamometer measured ISO, ECC, and CON knee extensor moments. Peak knee extensor moments (Nm) and ECC: ISO ratio were analyzed using a Kruskal-Wallis test (α = 0.05). Spearman Rank-Order Correlations were run on paired combinations of peak ISO, ECC, and CON moments for both groups. Results: The trained group had significantly greater peak ISO moment (183.8 vs 137.1 Nm, p = 0.013, d = 1.3) but significantly lower ECC: ISO ratio (p = 0.028, d = 1.1). The trained group exhibited stronger correlations for ECC-ISO (rs = 0.79 vs. 0.65), ECC-CON (rs = 0.93 vs. 0.59), and CON-ISO (rs = 0.93 vs. 0.78) compared to the untrained group. Conclusions: The findings demonstrate older adults maintain eccentric and concentric strength, regardless of training status. However, trained participants had a more balanced ECC: ISO ratio, due to their increased peak ISO strength possibly due to their resistance training.