Abstract
Currently available data on the energetics of isolated muscle preparations are based on bouts of less than 10 muscle contractions, whereas metabolic energy consumption is mostly relevant during steady state tasks such as locomotion. In this study we quantified the energetics of small fiber bundles of mouse soleus muscle during prolonged (2 min) series of contractions. Bundles (N = 9) were subjected to sinusoidal length changes, while measuring force and oxygen consumption. Stimulation (five pulses at 100 Hz) occurred either during shortening or during lengthening. Movement frequency (2–3 Hz) and amplitude (0.25–0.50 mm; corresponding to ± 4–8% muscle fiber strain) were close to that reported for mouse soleus muscle during locomotion. The experiments were performed at 32°C. The contributions of cross-bridge cycling and muscle activation to total metabolic energy expenditure were separated using blebbistatin. The mechanical work per contraction cycle decreased sharply during the first 10 cycles, emphasizing the importance of prolonged series of contractions. The mean ± SD fraction of metabolic energy required for activation was 0.37 ± 0.07 and 0.56 ± 0.17 for concentric and eccentric contractions, respectively (both 0.25 mm, 2 Hz). The mechanical efficiency during concentric contractions increased with contraction velocity from 0.12 ± 0.03 (0.25 mm 2 Hz) to 0.15 ± 0.03 (0.25 mm, 3 Hz) and 0.16 ± 0.02 (0.50 mm, 2 Hz) and was -0.22 ± 0.08 during eccentric contractions (0.25 mm, 2 Hz). The percentage of type I fibers correlated positively with mechanical efficiency during concentric contractions, but did not correlate with the fraction of metabolic energy required for activation.
Highlights
Metabolic energy consumption is an important variable in whole body movement tasks
During periodic movements that occur in walking, metabolic energy expenditure is difficult to predict as the net external mechanical work done on the body is typically much smaller than the positive mechanical work delivered by the muscle fibers; the difference equalling the negative mechanical work done by the muscle fibers
In order to realize this potential, musculoskeletal models must be developed that accurately predict both mechanical and metabolic behavior. The latter requires detailed knowledge of the separate contribution to metabolic energy consumption of all relevant processes which occur during muscular contraction
Summary
Metabolic energy consumption is an important variable in whole body movement tasks. For tasks in which predominantly positive or negative muscle fiber mechanical work is performed, the relationship between mechanical behavior and metabolic energy expenditure is well established (Abbott et al, 1952; Woledge et al, 1985; Chavarren and Calbet, 1999; Linari et al, 2003).Muscle Efficiency and Activation Costduring periodic movements that occur in walking, metabolic energy expenditure is difficult to predict as the net external mechanical work done on the body is typically much smaller than the positive mechanical work delivered by the muscle fibers; the difference equalling the negative mechanical work done by the muscle fibers. The rate of change of the total mechanical energy of the body, within one movement cycle, is not one-to-one related to the sum of muscle fiber mechanical power, due to elastic energy storage and return in tendons and co-contraction of antagonist muscles. This further complicates estimation of the total positive muscle fiber mechanical work and metabolic energy expenditure during periodic movements. In order to realize this potential, musculoskeletal models must be developed that accurately predict both mechanical and metabolic behavior The latter requires detailed knowledge of the separate contribution to metabolic energy consumption of all relevant processes which occur during muscular contraction
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
