Relationships among measures of physical fitness in adult patients with heart failure

Objectives: To describe the relationships among 3 measures of physical fitness (exercise capacity, muscle function and functional capacity) in patients with heart failure, and to determine whether these measures are influenced by impairment of movement.Methods: Secondary analysis of baseline data from the Italian subsample (n= 96) of patients with heart failure enrolled in a randomized controlled trial, the HF-Wii study. Exercise capacity was measured with the 6-min walk test, muscle function was measured with the unilateral isotonic heel-lift, bilateral isometric shoulder abduction and unilateral isotonic shoulder flexion, and functional capacity was measured with the Duke Activity Status Index. Principal component analysis was used to detect covariance of the data.Results: Exercise capacity correlated with all of the tests related to muscle function (r=0.691-0.423, p< 0.001) and functional capacity (r = 0.531). Moreover, functional capacity correlated with muscle function (r=0.482-0.393). Principal component analysis revealed the bidimensional structure of these 3 measures, thus accounting for 58% of the total variance in the variables measured.Conclusion: Despite the correlations among exercise capacity, muscle function and functional capacity, these measures loaded on 2 different factors. The use of a wider range of tests will help clinicians to perform a more tailored assessment of physical fitness, especially in those patients with heart failure who have impairment of movement.