Muscle size explains low passive skeletal muscle force in heart failure patients.
BACKGROUND
Alterations in skeletal muscle function and architecture have been linked to the compromised exercise capacity characterizing chronic heart failure (CHF). However, how passive skeletal muscle force is affected in CHF is not clear. Understanding passive force characteristics in CHF can help further elucidate the extent to which altered contractile properties and/or architecture might affect muscle and locomotor function. Therefore, the aim of this study was to investigate passive force in a single muscle for which non-invasive measures of muscle size and estimates of fiber force are possible, the soleus (SOL), both in CHF patients and age- and physical activity-matched control participants.


METHODS
Passive SOL muscle force and size were obtained by means of a novel approach combining experimental data (dynamometry, electromyography, ultrasound imaging) with a musculoskeletal model.


RESULTS
We found reduced passive SOL forces (∼30%) (at the same relative levels of muscle stretch) in CHF vs. healthy individuals. This difference was eliminated when force was normalized by physiological cross sectional area, indicating that reduced force output may be most strongly associated with muscle size. Nevertheless, passive force was significantly higher in CHF at a given absolute muscle length (non length-normalized) and likely explained by the shorter muscle slack lengths and optimal muscle lengths measured in CHF compared to the control participants. This later factor may lead to altered performance of the SOL in functional tasks such gait.


CONCLUSIONS
These findings suggest introducing exercise rehabilitation targeting muscle hypertrophy and, specifically for the calf muscles, exercise that promotes muscle lengthening.
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, United States; The School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, Australia.
Fausto Antonio
FA
Panizzolo
Advanced Heart Failure and Cardiac Transplant Service, Royal Perth Hospital, Perth, WA, Australia; School of Physiotherapy and Exercise Science, Curtin University, Perth, WA, Australia.
Andrew J
AJ
Maiorana
The School of Sport Science, Exercise and Health, The University of Western Australia , Crawley , WA , Australia.
Louise H
LH
Naylor
Envision Medical Imaging , Perth , WA , Australia.
Lawrence G
LG
Dembo
Centre for Musculoskeletal Research, Griffith Health Institute, Griffith University , Gold Coast , QLD , Australia.
David G
DG
Lloyd
The School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, Australia; Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom.
Daniel J
DJ
Green
The School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, WA, Australia; Biomechanics Laboratory, Department of Kinesiology, The Pennsylvania State University, University Park, PA, United States.
Jonas
J
Rubenson
Heart failure; Passive force; Skeletal muscle; Soleus; Ultrasound
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