Muscle and Limb Mechanics

Tsianos, George A.; Loeb, Gerald E.

doi:10.1002/cphy.c160009

Cited by 18 publications

(15 citation statements)

References 318 publications

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“…This reaffirms that, despite the relatively brief nature of the express arm response, it is not without a kinetic consequence even on the non-reaching arm. Further, an express arm response on the reaching arm may also influence the kinetic consequences of the ensuing phases of voluntary reach-related activity through repeated activation of the same muscle fiber (31).…”

Section: Comparison To Past Studies and Methodological Considerationsmentioning

confidence: 99%

Express Arm Responses Appear Bilaterally on Upper-limb Muscles in an Arm Choice Reaching Task

Kearsley

Cecala

Kozak

2021

Preprint

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When required, humans can generate very short latency reaches towards a visual target, like catching a phone falling off a desk. During such rapid reaches, express arm responses are the first wave of upper limb muscle recruitment, occurring within ~80-100 ms of target appearance. There is accumulating evidence that express arm responses arise from signaling along the tecto-reticulo-spinal tract, but the involvement of the reticulo-spinal tract has not been well-studied. Since the reticulospinal tract projects bilaterally, we studied whether express arm responses would be expressed bilaterally. Human participants (n = 14; 7 female) performed visually guided reaches in a modified emerging target paradigm where either arm could be used to intercept a target once it emerged below a barrier. We recorded electromyographic activity bilaterally from the pectoralis major muscle. Our analysis focused on target locations where participants reached with the right arm on some trials, and the left arm on others. In support of the involvement of the reticulospinal tract, the express arm response persisted bilaterally regardless of which arm reached to the target. While the latency of the express arm response was the same on the reaching vs non-reaching arm, the response magnitude was slightly larger on the reaching arm, in part due to anticipatory muscle recruitment related to arm choice. Our results support the involvement of the reticulo-spinal tract in mediating the express arm response, and we surmise that the increased magnitude on the arm chosen to move arises from convergence of cortically derived signals with the largely independent express arm response.

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Section: Comparison To Past Studies and Methodological Considerationsmentioning

confidence: 99%

Express Arm Responses Appear Bilaterally on Upper-limb Muscles in an Arm Choice Reaching Task

Kearsley

Cecala

Kozak

2021

Preprint

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“…In summary, the Oropod has limb and body dynamics dominated by velocity and muscle dynamics dominated by length (limb position), whereas real terrestrial organisms have limb dynamics dominated by acceleration and muscle dynamics dominated by length and velocity (Tsianos and Loeb, 2017).…”

Section: Methods and Model Designmentioning

confidence: 99%

A Model for Self-Organization of Sensorimotor Function: The Spinal Monosynaptic Loop

Jones

Kirkland

et al. 2021

Preprint

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Recent spinal cord literature abounds with descriptions of genetic preprogramming and the molecular control of circuit formation. In this paper we explore to what extent circuit formation based on learning rather than preprogramming could explain some prominent aspects of the spinal cord connectivity patterns observed in animals. To test this we developed an artificial organism with a basic musculoskeletal system and proprioceptive sensors, connected to a neural network. We adjusted the initially randomized gains in the neural network according to a Hebbian plasticity rule while exercising the model system with spontaneous muscle activity patterns similar to those observed during early fetal development. The resulting connection matrices support functional self-organization of the mature pattern of Ia to motoneuron connectivity in the spinal circuitry. More coordinated muscle activity patterns such as observed later during neonatal locomotion impaired projection selectivity. These findings imply a generic functionality of a musculoskeletal system to imprint important aspects of its mechanical dynamics onto a neural network, without specific preprogramming other than setting a critical period for the formation and maturation of this general pattern of connectivity. Such functionality would facilitate the successful evolution of new species with altered musculoskeletal anatomy and it may help to explain patterns of connectivity and associated reflexes that appear during abnormal development.

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“…Muscle endurance is the capability to generate and maintain repeated or continuous non-peak forces for long durations (minutes to hours) without fatiguing (Wilkie 1960 ). From a physiological perspective, endurance is largely proportional to the physiological cross-sectional area (PCSA) occupied by slow-twitch, Type I fibers, as well as the density of mitochondria, capillaries, and myoglobin within muscle (Tsianos and Loeb 2017 ). Muscle strength is the maximum tensile force a muscle can generate and is largely proportional and relative to the PCSA occupied by fast-twitch, Type IIa and Iib fibers.…”

Section: Evaluation Of Trade-offs Between Strength Power and Endurancementioning

confidence: 99%

The evolution of human fatigue resistance

2022

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Humans differ from African great apes in numerous respects, but the chief initial difference setting hominins on their unique evolutionary trajectory was habitual bipedalism. The two most widely supported selective forces for this adaptation are increased efficiency of locomotion and improved ability to feed in upright contexts. By 4 million years ago, hominins had evolved the ability to walk long distances but extreme selection for endurance capabilities likely occurred later in the genus Homo to help them forage, power scavenge and persistence hunt in hot, arid conditions. In this review we explore the hypothesis that to be effective long-distance walkers and especially runners, there would also have been a strong selective benefit among Homo to resist fatigue. Our hypothesis is that since fatigue is an important factor that limits the ability to perform endurance-based activities, fatigue resistance was likely an important target for selection during human evolution for improved endurance capabilities. We review the trade-offs between strength, power, and stamina in apes and Homo and discuss three biological systems that we hypothesize humans evolved adaptations for fatigue resistance: neurological, metabolic and thermoregulatory. We conclude that the evolution of endurance at the cost of strength and power likely also involved the evolution of mechanisms to resist fatigue.

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Muscle and Limb Mechanics

Cited by 18 publications

References 318 publications

Express Arm Responses Appear Bilaterally on Upper-limb Muscles in an Arm Choice Reaching Task

Express Arm Responses Appear Bilaterally on Upper-limb Muscles in an Arm Choice Reaching Task

A Model for Self-Organization of Sensorimotor Function: The Spinal Monosynaptic Loop

The evolution of human fatigue resistance

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