Nemaflex: A Microfluidic Tool for Measuring Muscle Strength in C. Elegans Across Lifespan

Maintenance of physical fitness is essential for an individual’s health and well-being. In fact, a decrease in physical fitness indicates an increased risk of hospitalization and a higher mortality risk, especially in elderly populations. While there are many aspects of physical fitness, a decline in muscle strength correlates with poor physical performance. Loss of muscle strength alone is a prognostic indicator for a variety of disorders including dynapenia, cancer, and neuromuscular diseases. Although it is straightforward to record muscle strength in people, it is not feasible to conduct whole life studies looking at the impact of genetics on muscle health. Promisingly, prospective life-long studies can be accomplished in the roundworm C. elegans. The nematode body wall muscles have similarities to the human muscle and strikingly also deteriorate with age much like in humans which makes C. elegans a premier genetic model for muscle strength investigations.

Building on recent advances in microfluidic tools for mechanobiology, in this study we report a soft deformable micropillar based device, NemaFlex, for quantifying muscle strength in C. elegans. Animals crawl through the pillars pushing them, allowing extraction of local forces from pillar displacements. It is expected that the forces fluctuate depending on animal’s behavior, velocity, body shape and position with respect to pillar, making quantitation of animal strength thus far elusive. Driven by the need to anchor NemaFlex for high throughput muscle strength assays, we develop a robust experimental protocol and analysis workflow for quantifying maximum strength in C. elegans and its genetic mutants. We also configure NemaFlex for recording strength virtually from ‘womb to tomb’ providing insights into how muscle strength changes during development and declines with age.

We find that forced contractions, such as induced by an acetylcholine agonist, show the same maximum strength as the untreated animals suggesting NemaFlex quantitates true strength. We tested mutants with neuronal defects (unc-17) and impaired sarcomeres (unc-52 and unc-112) and observe changes that verify the neuromuscular origin of strength. We also address how animal size affects muscle strength, allowing accurate comparisons among worms at different developmental stages or among mutants with size variations. We profile strength across the lifespan for individual worms, and our results show that strength increases 7-fold from the young adult followed by a sharp late-age decline—providing the first direct evidence of muscle strength loss due to aging, similar to dynapenia in humans. In summary, NemaFlex is a powerful tool to conduct prospective life-long investigations of muscle strength in C. elegans.