How to identify patients with low muscle mass linked to physical capacity and physical activity in heart failure
Authors: Tinggaard A B , Skou M K , Jessen N , Wiggers H 
Published: October 2022

Abstract

Introduction
Skeletal muscle wasting is frequent in heart failure (HF) patients, and low muscle mass (MM) is associated with increased morbidity and mortality. Current recommendations suggest the usage of dual-energy X-ray absorptiometry (DXA)-derived appendicular lean mass (ALM) adjusted for height squared to identify low MM. However, it has recently been suggested that ALM adjusted for body mass index (BMI) has a higher predictive value. The relationships between low MM, muscle strength, exercise capacity and daily physical activity (PA) are poorly understood in heart failure with reduced ejection fraction (HFrEF).

Purpose
This study examined the relationships between low MM defined by two different indices and muscle strength, physical capacity tests and accelerometer measurements.

Methods
A total of 104 HFrEF patients underwent DXA, maximal isometric knee-extensor strength test, cardiopulmonary exercise testing, 6-minute walking test and accelerometry. Two adjusted indices for low MM were assessed: ALM/m2 and ALM/BMI. We performed Pearson correlations to examine the relationships between low MM and muscle strength, exercise capacity and daily PA. Furthermore, we identified patients with low MM based on the two indices. For ALM/m2 we used guideline-recommended cut-offs and for ALM/BMI we used the mean value since no cut-offs has been validated.

Results
The ALM/m2-index showed no significant correlation to peak oxygen uptake (VO2peak), 6-minute walking distance (6MWD), average PA or daily time spent in moderate-to-vigorous physical activity (MVPA). A moderate correlation was found to maximal muscle strength was found (r=0.61, p&lt;0.001).
The ALM/BMI-index was moderately correlated to maximal muscle strength (r=0.65, p&lt;0.001), VO2peak (r=0.40, p&lt;0.001), 6MWD (r=0.41, p&lt;0.001), average daily PA (r=0.27, p=0.012) and daily time spent in MVPA (r=0.29, p=0.007).
Patients with low MM identified by ALM/m2 did not differ from patients with preserved MM with regards to VO2peak, 6MWD or accelerometer measurements. A difference in maximal muscle strength was found (95.7±35.6 Nm vs 116±44.8, p=0.02).
Patients with low MM identified by ALM/BMI had lower maximal muscle strength (94.8±36.1 Nm vs 121.9±44.4 Nm, p=0.001), lower VO2peak (13.2±3.5 mL/kg/min vs 16.4±3.7 mL/kg/min, p&lt;0.001), shorter 6MWD (370.5±99.4 m vs 467.3±93.9 m, p&lt;0.001), average daily PA (15.1±4.4 ENMO* vs 17.3±5.3 ENMO*, p=0.04) and daily time spent in MVPA (14.2±16.7 min vs 24.7±21.6 min, p=0.01) compared to patients with preserved MM.

Conclusion
In HFrEF patients low MM identified by ALM/BMI seems to correlate better to well-established markers for physical capacity (VO2peak and 6MWD), muscle strength and daily PA compared to ALM/m2. No cut-offs have been established for ALM/BMI and there is a need for longitudinal studies to determine the association with mortality in HFrEF patients.
*ENMO = Euclidean Norm Minus One, an acceleration metric.

Funding Acknowledgement
Type of funding sources: Foundation. Main funding source(s): The Karen Elise Jensens Foundation