Reproducibility and relationship of single-joint strength vs multi-joint strength and power in aging individuals.

INTRODUCTION: Reliable and sensitive muscle strength/power assessments are essential when evaluating age-related and/or training-induced changes in maximal strength and power. AIM: To investigate the reproducibility and inter-relationship of single-joint isokinetic/isometric leg muscle strength vs multi-joint mechanical muscle function during counter-movement jump (CMJ) in moderately trained aging individuals (age 72.3+/-6.6).
RESULTS: The within-subject coefficient of variation (CV(w-s)) for the single-joint test showed good reproducibility (<10%) for quadriceps and hamstring strength (except for hamstring isometric). Plantar flexion demonstrated good to moderate reproducibility (CV(w-s) range: 10.4-17.2%). Excellent to good CV(w-s) (<10%) was observed for all concentric CMJ parameters, except for plantar flexor mean work (CV(w-s)=13%). Eccentric CMJ parameters demonstrated good to moderate reproducibility (CV(w-s) range: 8.1-18.2%). Isokinetic and isometric quadriceps, hamstring and plantar flexor single-joint strength measurements were found to correlate with several CMJ parameters.
CONCLUSION: Single-joint and multi-joint strength and power assessment tests of the lower limbs appear to be reproducible in aging individuals. Furthermore, associations between single-joint strength and multi-joint CMJ power and force variables exist. To evaluate functional capacity in elderly people further investigations must be carried out to identify specific power/strength parameters that are most tightly linked to functional performance.