mechanics

Scaling of musculoskeletal performance. Maximum force output by single muscles scales as body mass^0.67, similar to how the surface area of an object scales with its mass. One consequence of this is that as (geometrically similar) animal body size increases occur, animal mass may outpace the maximum force production capacity of body mass-supporting muscles. Yet, maximum locomotor performance of whole animals scales as body mass^1.0 across a large range of body size, as demonstrated here. Noteworthy, this study showed that a highly variable set of animal musculoskeletal designs have a remarkably consistent common upper limit to mass-specific force output during maximum performance. Why this is the case is not very evident, nor do we know much about how animals achieve this.

We have previously examined this question in flying dragonflies (here), but they are not the only organisms that transmit force output by single muscles via musculoskeletal linkages (tendons and other skeletal components). Internal musculoskeletal dynamics and force distribution mechanisms inside animals are often unknown or at best understudied. We continue to investigate such mechanisms and dynamics in different types of animal motors, for one to establish to what extent the dragonfly “solution” to unequal scaling of single muscle force output and body weight support requirements is unique or more general among animals.

Body weight sensation. A long term goal of the lab is to determine if/how animals know at a physiological level how much they weigh, and, if so, how they make homeostatic adjustments in response to changes in body weight. Skeletal muscle is a likely source tissue for this type of plasticity as well as for the location of required sensors, as weight-bearing muscles receive mechanical feedback regarding body weight and consume ATP in order to generate forces sufficient to (at least) counteract gravity.

We know that skeletal muscle can respond to increased and decreased load by hypertrophy and atrophy, but the molecular and biochemical mechanisms that muscles use to sense and adjust to changes in body weight are poorly understood. We focus our work in this area on the regulation of expression of sarcomere genes encoding proteins that function at the interface between thin and thick filaments. Specifically, we work on mechanisms controlling expression of the troponin complex, and within that, of troponin T. These thin filament regulatory proteins play a large role in regulating muscle force output and energy consumption by controlling the calcium sensitivity of actomyosin cross-bridge activation. The troponin T gene is alternatively spliced and gives rise to several splice variants that differ in way they encode troponin T proteins.

We have made some progress examining mechanisms involved in body weight sensation in rodents (see here), fruit flies (see here) and are currently extending this project using cockroaches as the study system.