Test-retest reliability data of functional performance, strength, peak torque and body composition assessments in two different age groups of Kosovan adults

This article reports test-retest reliability data of laboratory- and field-based performance tests as well as body composition analyses of younger and older Kosovan adults. In total, 57 healthy young (18–35 years) and 61 older (>60 years) participants took part in two identical test sessions, with a median [25(th) – 75(th) percentile] of 14 [13–21] days in between. Functional performance tests included 30-s chair stand test (CST), 30-s arm curl test (ACT), six-minutes walking test (6MWT), sit and reach test, timed up and go test (TUG), as well as the assessment of gait speed (GS) at normal and fast pace. Isometric handgrip strength (HGS) was used to estimate strength of the dominant hand. Isokinetic peak torque (PT) and average power (AvgP) for knee extension and flexion were determined at velocities of 60°/s and 120°/s. Body composition assessments included body fat percentage, skeletal muscle mass (SMM) and index (SMI) as well as appendicular skeletal muscle mass (ASMM) and index. Secondary endpoints included self-perceived health status and potential co-morbidities. All performance test outcomes as well as body fat percentage, SMM, ASMM, and self-perceived health were significantly better in young as compared to older participants (p < 0.001). Improvements from test to retest were observed for CST (p < 0.001), PT(flexion) (60°/s: p = 0.001, 120°/s: p = 0.041), AvgP(flexion) (60°/s: p < 0.001, 120°/s: p < 0.001), AvgP(extension) (120°/s: p = 0.050), but also for SMM (p = 0.021) and SMI (p = 0.021). Only for CST and HGS a time x age group interaction was detected (p < 0.05). Acceptable reliability (ICC > 0.7) was observed for all parameters in both age groups, except for some of the measures from the isokinetic dynamometry, where ICCs were generally lower in older participants, but fell below 0.7 for AvgP(flexion) at 60°/s (ICC = 0.6) and at 120°/s (ICC = 0.67) as well as for PT(flexion) at 120°/s (ICC = 0.69). These data's importance lay upon their potential use in epidemiological studies observing muscle strength, peak torque, power, physical performance and body composition over various age groups, either in the same or similar populations, or for comparison to other populations.