The relationship between isokinetic and isometric knee muscle strength and maximal step-up height after stroke: A pilot study

Abstract

BACKGROUND: A novel way to evaluate muscle strength and functioning in the lower limbs is to measure how high a person could step up on a platform, the so called Maximal Step-up Test (MST). Studies of healthy persons and overweight women have shown that the maximal step-up height (MSH) is associated with both muscle strength and physical function, but no study has assessed persons after stroke. OBJECTIVE: To evaluate the relationship between isokinetic and isometric knee muscle strength and maximal step-up height after stroke. METHODS: A convenience sample of 21 ambulatory persons with stroke (13 men and eight women; mean age 63 +/- 12 years; mean time since stroke onset 26 +/- 36 months). Isokinetic concentric knee extension and knee flexion strength at 60 degrees/s and isometric knee extension strength at 90. were measured for both lower limbs with a Biodex dynamometer. Maximal step-up height was measured using a 40 cm x 60 cm platform, which could be raised from 3 cm to 45 cm with 3 cm intervals. The relationship between knee muscle strength (normalized to body weight) and the maximal step-up height was analysed with the Pearson's correlation coefficient (r). RESULTS: There were significant but only moderate relationships between the paretic isokinetic knee extension, and flexion, strength and maximal step-up height, r = 0.49; p < 0.05, and r = 0.57; p < 0.01, respectively. CONCLUSION: These moderate relationships indicate that muscle weakness is only partially associated with maximal step-up height after stroke. The MST may therefore have limited value in the assessment of muscle strength after stroke. (Less)