The proposed research addresses the central question of how muscles function under dynamic conditions of locomotor activity. It does so in the context of how muscle function is modulated in relation to muscle architecture and fiber composition to accommodate changes in locomotor requirement. These questions will be addressed by making in vivo recordings of force (tendon buckle transducers), length change (sonomicrometry) and neural activation (electromyography) of key limb muscles in two animal models: quadrupedal goats and bipedal guinea fowl. Measurements will be obtained from animals trained to move over a range of speeds on a treadmill at different gaits and grades (level vs incline vs decline) to address the following hypotheses: (i) regional activation and fractional length change within muscles that have focal skeletal attachments is uniform both along a fascicle axis and between differing fascicle regions, but may vary in muscles with broader attachments and more complex architectures; as a result, (ii) the timing and strain of activated fascicles are homogeneous within a muscle performing a given motor task; and (iii) proximal muscles with long fibers account for the majority of mechanical work modulation; whereas distal short-fibered muscles with long tendons contract isometrically for more economical force production and tendon elastic savings. Differences in mechanical work rate with locomotor grade will be related to observed changes in the in vivo force-length behavior of key limb muscles. Recordings made while animals accelerate from rest will provide a second context to evaluate work modulation in relation to muscle architecture. Ground reaction force-platform and high-speed video recordings will also be carried out to integrate the in vivo force, length and EMG measurements of individual muscles into whole-limb mechanics. These studies have important consequences for understanding patterns of motor recruitment in relation to locomotor strategy and how regional differences in motor unit organization (and fiber type) may influence the neural control of movement. Prior work in this area has been limited by studies of motor function under more quasi-steady ranges of movement and/or indirect assessment of muscle length change and force development. Although an overarching goal is to understand factors that influence normal and age-related changes in human motor function, animal studies allow direct experimental approaches for assessing the dynamics of motor function that are likely to apply to humans. Consequently, the proposed studies will have value for developing more effective physical, occupational and rehabilitative therapies, as well as for sports and exercise training, and prosthetics design.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR047679-03
Application #
6895507
Study Section
Special Emphasis Panel (ZRG1-GRM (01))
Program Officer
Nuckolls, Glen H
Project Start
2003-06-01
Project End
2008-05-31
Budget Start
2005-06-01
Budget End
2006-05-31
Support Year
3
Fiscal Year
2005
Total Cost
$261,170
Indirect Cost
Name
Harvard University
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
082359691
City
Cambridge
State
MA
Country
United States
Zip Code
02138
Arnold, Allison S; Lee, David V; Biewener, Andrew A (2013) Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade. J Exp Biol 216:2201-12
Higham, Timothy E; Biewener, Andrew A (2011) Functional and architectural complexity within and between muscles: regional variation and intermuscular force transmission. Philos Trans R Soc Lond B Biol Sci 366:1477-87
Daley, Monica A; Biewener, Andrew A (2011) Leg muscles that mediate stability: mechanics and control of two distal extensor muscles during obstacle negotiation in the guinea fowl. Philos Trans R Soc Lond B Biol Sci 366:1580-91
Carroll, Andrew M; Biewener, Andrew A (2009) Mono- versus biarticular muscle function in relation to speed and gait changes: in vivo analysis of the goat triceps brachii. J Exp Biol 212:3349-60
McGuigan, M Polly; Yoo, Edwin; Lee, David V et al. (2009) Dynamics of goat distal hind limb muscle-tendon function in response to locomotor grade. J Exp Biol 212:2092-104
Higham, Timothy E; Biewener, Andrew A (2009) Fatigue alters in vivo function within and between limb muscles during locomotion. Proc Biol Sci 276:1193-7
Daley, Monica A; Voloshina, Alexandra; Biewener, Andrew A (2009) The role of intrinsic muscle mechanics in the neuromuscular control of stable running in the guinea fowl. J Physiol 587:2693-707
Carroll, Andrew M; Lee, David V; Biewener, Andrew A (2008) Differential muscle function between muscle synergists: long and lateral heads of the triceps in jumping and landing goats (Capra hircus). J Appl Physiol 105:1262-73
Higham, Timothy E; Biewener, Andrew A (2008) Integration within and between muscles during terrestrial locomotion: effects of incline and speed. J Exp Biol 211:2303-16
Lee, David V; McGuigan, M Polly; Yoo, Edwin H et al. (2008) Compliance, actuation, and work characteristics of the goat foreleg and hindleg during level, uphill, and downhill running. J Appl Physiol 104:130-41

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