Muscle force, work and cost: a novel technique to revisit the Fenn effect

Area of Science:

• Muscle Physiology
• Bioenergetics
• Biomechanics

Background:

• Muscle force generation relies on cross-bridge cycling fueled by ATP.
• Fenn's effect (1920s) noted altered energetic cost with muscle shortening/lengthening, but magnitude remains unclear.
• Quantifying the 'Fenn effect' and 'negative Fenn effect' is crucial for understanding muscle energetics.

Purpose of the Study:

• To quantitatively resolve the magnitude of the Fenn effect and its negative counterpart.
• To measure ATP cost during muscle contractions involving work.
• To investigate the relationship between force-time integral and energy cost.

Main Methods:

• Developed a novel technique combining magnetic resonance spectroscopy with an in vivo force clamp.
• Directly quantified the Fenn effect (E=I+W) and negative Fenn effect (E=I-W) in the first dorsal interosseous (FDI) muscle.
• Measured ATP cost across varying forces and durations, maintaining a constant force-time integral (FTI).

Main Results:

• A proportional, linear increase in energy cost was observed as the FTI increased with load.
• Muscle shortening significantly increased the energetic cost of force production.
• Muscle lengthening slightly reduced the energetic cost of force production, supporting the Fenn effect.

Conclusions:

• The study quantitatively supports the Fenn effect in the first dorsal interosseous muscle.
• Findings suggest an elastic element within the FDI muscle may help maintain cross-bridge force.
• Further research is needed to explore these effects across different muscle types, velocities, and lengths.