Researchers used network analysis to investigate the relationship between anatomical and functional connectivity among 36 muscles. Human motor control requires the coordination of muscle activity under the anatomical constraints imposed by the musculoskeletal system. Interactions within the central nervous system are fundamental to motor coordination, but the principles governing functional integration remain poorly understood. 

Anatomical Networks

The physical connections between muscles defined anatomical networks, and functional networks were based on intermuscular coherence assessed during postural tasks. They found a modular structure of functional networks that was strongly shaped by the anatomical constraints of the musculoskeletal system. 

These findings reveal distinct patterns of functional interactions between muscles involved in flexibly organizing muscle activity during postural control. Our network approach to the motor system offers a unique window into the neural circuitry driving the musculoskeletal system.

The human body is a complex system consisting of many subsystems and regulatory pathways. The musculoskeletal system gives the body structure and creates the ability to move. It is made up of more than 200 skeletal bones, connective tissue, and over 300 skeletal muscles.

Muscles are attached to bones through tendinous tissue and can generate movement around a joint when they contract. The central nervous system controls these movements through the spinal motor neurons, which serve as the final common pathway to the muscles. While the anatomical and physiological components of the musculoskeletal system are well characterized, the organizational principles of neural control remain poorly understood.

Musculoskeletal System

Here, they elucidate the interplay between the anatomical structure of the musculoskeletal system and the functional organization of distributed neural circuitry from which motor behaviors emerge.

Anatomical muscle network

Anatomical muscle networks were defined by mapping the physical connections between muscles, based on gross human anatomy. The anatomical network constituted a densely connected, symmetrical network. 

Functional muscle network

Mapping correlated inputs defined functional muscle networks to different muscles. To map functional networks, they measured surface EMG from the same 36 muscles while healthy participants performed different postural tasks. 

Comparison between anatomical and functional networks

The community structures of the anatomical and functional muscle networks were very similar (Rand index, 0.80; adjusted Rand index, 0.36; P < 0.001). The connections between the bilateral forearm and bilateral lower leg muscles in the functional networks, which were absent in the anatomical network, are a marked difference between anatomical and functional networks. 

They used a network approach to study the structure-function relationship of the human musculoskeletal system. Several principles governing the functional relationship between muscles were revealed:

(i) Functional connectivity patterns between muscles are strongly shaped by the anatomical constraints of the musculoskeletal system, with functional connectivity strongest within anatomical modules and decreased as a function of anatomical distance

(ii) Bilateral connectivity between the homologous upper and between the homologous lower extremities is a key characteristic of the functional muscle networks

(iii) The functional relationships are task-dependent, with postural tasks differentially affecting functional connectivity at different frequency ranges.