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Krahl A, Lipphaus A, Sander PM, Witzel U. Determination of muscle strength and function in plesiosaur limbs: finite element structural analyses of Cryptoclidus eurymerus humerus and femur. PeerJ 2022; 10:e13342. [PMID: 35677394 PMCID: PMC9169670 DOI: 10.7717/peerj.13342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 04/05/2022] [Indexed: 01/13/2023] Open
Abstract
Background The Plesiosauria (Sauropterygia) are secondary marine diapsids. They are the only tetrapods to have evolved hydrofoil fore- and hindflippers. Once this specialization of locomotion had evolved, it remained essentially unchanged for 135 Ma. It is still controversial whether plesiosaurs flew underwater, rowed, or used a mixture of the two modes of locomotion. The long bones of Tetrapoda are functionally loaded by torsion, bending, compression, and tension during locomotion. Superposition of load cases shows that the bones are loaded mainly by compressive stresses. Therefore, it is possible to use finite element structure analysis (FESA) as a test environment for loading hypotheses. These include muscle reconstructions and muscle lines of action (LOA) when the goal is to obtain a homogeneous compressive stress distribution and to minimize bending in the model. Myological reconstruction revealed a muscle-powered flipper twisting mechanism. The flippers of plesiosaurs were twisted along the flipper length axis by extensors and flexors that originated from the humerus and femur as well as further distal locations. Methods To investigate locomotion in plesiosaurs, the humerus and femur of a mounted skeleton of Cryptoclidus eurymerus (Middle Jurassic Oxford Clay Formation from Britain) were analyzed using FE methods based on the concept of optimization of loading by compression. After limb muscle reconstructions including the flipper twisting muscles, LOA were derived for all humerus and femur muscles of Cryptoclidus by stretching cords along casts of the fore- and hindflippers of the mounted skeleton. LOA and muscle attachments were added to meshed volumetric models of the humerus and femur derived from micro-CT scans. Muscle forces were approximated by stochastic iteration and the compressive stress distribution for the two load cases, "downstroke" and "upstroke", for each bone were calculated by aiming at a homogeneous compressive stress distribution. Results Humeral and femoral depressors and retractors, which drive underwater flight rather than rowing, were found to exert higher muscle forces than the elevators and protractors. Furthermore, extensors and flexors exert high muscle forces compared to Cheloniidae. This confirms a convergently evolved myological mechanism of flipper twisting in plesiosaurs and complements hydrodynamic studies that showed flipper twisting is critical for efficient plesiosaur underwater flight.
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Affiliation(s)
- Anna Krahl
- Institute of Geoscience, Section Paleontology, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn, Germany,Biomechanics Research Group, Chair of Product Development, Faculty of Mechanical Engineering, Ruhr-Universität Bochum, Bochum, Germany,Paleontological Collection Fachbereich Geowissenschaften, Eberhard-Karls-Universität Tübingen, Tübingen, Germany
| | - Andreas Lipphaus
- Biomechanics Research Group, Chair of Product Development, Faculty of Mechanical Engineering, Ruhr-Universität Bochum, Bochum, Germany
| | - P. Martin Sander
- Institute of Geoscience, Section Paleontology, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn, Germany
| | - Ulrich Witzel
- Biomechanics Research Group, Chair of Product Development, Faculty of Mechanical Engineering, Ruhr-Universität Bochum, Bochum, Germany
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Donatelli CM, Lutek K, Gupta K, Standen EM. Body and Tail Coordination in the Bluespot Salamander ( Ambystoma laterale) During Limb Regeneration. Front Robot AI 2021; 8:629713. [PMID: 34124171 PMCID: PMC8193843 DOI: 10.3389/frobt.2021.629713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Accepted: 05/14/2021] [Indexed: 01/04/2023] Open
Abstract
Animals are incredibly good at adapting to changes in their environment, a trait envied by most roboticists. Many animals use different gaits to seamlessly transition between land and water and move through non-uniform terrains. In addition to adjusting to changes in their environment, animals can adjust their locomotion to deal with missing or regenerating limbs. Salamanders are an amphibious group of animals that can regenerate limbs, tails, and even parts of the spinal cord in some species. After the loss of a limb, the salamander successfully adjusts to constantly changing morphology as it regenerates the missing part. This quality is of particular interest to roboticists looking to design devices that can adapt to missing or malfunctioning components. While walking, an intact salamander uses its limbs, body, and tail to propel itself along the ground. Its body and tail are coordinated in a distinctive wave-like pattern. Understanding how their bending kinematics change as they regrow lost limbs would provide important information to roboticists designing amphibious machines meant to navigate through unpredictable and diverse terrain. We amputated both hindlimbs of blue-spotted salamanders (Ambystoma laterale) and measured their body and tail kinematics as the limbs regenerated. We quantified the change in the body wave over time and compared them to an amphibious fish species, Polypterus senegalus. We found that salamanders in the early stages of regeneration shift their kinematics, mostly around their pectoral girdle, where there is a local increase in undulation frequency. Amputated salamanders also show a reduced range of preferred walking speeds and an increase in the number of bending waves along the body. This work could assist roboticists working on terrestrial locomotion and water to land transitions.
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Affiliation(s)
| | - Keegan Lutek
- Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Keshav Gupta
- Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Emily M Standen
- Department of Biology, University of Ottawa, Ottawa, ON, Canada
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Rivera G, Neely CMD. Patterns of fluctuating asymmetry in the limbs of freshwater turtles: Are more functionally important limbs more symmetrical? Evolution 2020; 74:660-670. [PMID: 31989579 DOI: 10.1111/evo.13933] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 01/09/2020] [Accepted: 01/17/2020] [Indexed: 01/05/2023]
Abstract
Understanding how selective forces influence patterns of symmetry remains an active area of research in evolutionary biology. One hypothesis, which has received relatively little attention, suggests that the functional importance of morphological characters may influence patterns of symmetry. Specifically, it posits that for structures that display bilateral symmetry, those with greater functional importance should display lower levels of asymmetry. The aim of this study was to examine the patterns of fluctuating asymmetry (FA) present in the limb bones of freshwater turtles in the family Emydidae. Aquatic emydid turtles of the subfamily Deirochelyinae employ a hindlimb-dominant swimming style, suggesting that hindlimbs should display lower levels of FA. Consistent with the morpho-functional hypothesis of symmetry, we found a strong, clade-wise pattern of humeral-biased FA in aquatic Deirochelyinae. In contrast, some emydids of the subfamily Emydinae possess more terrestrial tendencies. As terrestrial locomotion places more equal importance on fore- and hindlimbs, we predicted that such behaviors may minimize differences in FA. No clade-wise pattern was detected in the subfamily Emydinae. We also detected a phylogenetic signal in FA within the femur and discovered that FA has evolved at vastly different rates between the fore- and hindlimbs.
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Affiliation(s)
- Gabriel Rivera
- Department of Biology, Creighton University, Omaha, NE, 68178
| | - Cally M Deppen Neely
- Biology Department, Swarthmore College, Swarthmore, PA, 19081.,Present address: , 11604 Piney Lodge Road, Gaithersburg, MD, 20878
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Mayerl CJ, Hicks KE, Blob RW. Differences in kinematic plasticity between freshwater turtle species underlie differences in swimming performance in response to varying flow conditions. Biol J Linn Soc Lond 2019. [DOI: 10.1093/biolinnean/blz051] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
The distribution and performance of aquatic vertebrates can be linked strongly to their ability to perform in variable conditions of flowing water. Performance in these variable conditions can be affected by both morphology and behaviour, and animals that experience more variable environments often show greater behavioural plasticity that improves performance in those environments. One common metric of performance is swimming stability, which can constitute a majority of the daily energy budget of swimming animals. We compared the body oscillations arising from recoil forces of the limbs of two species of freshwater turtles as they swam in different flow conditions: the lentic specialist Emydura subglobosa and the habitat generalist Chrysemys picta. We found that E. subglobosa experienced more limited oscillations in still water than C. picta, but that C. picta had a greater kinematic response to increased flow speed that might contribute to their improved performance in flowing water. These results provide insight into how secondarily aquatic tetrapods respond to the functional demands of variation in flow, helping to build understanding of the relationship between energetics, kinematics and performance of such lineages in different environments.
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Affiliation(s)
- Christopher J Mayerl
- Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, OH, USA
| | - Kirsten E Hicks
- Department of Biological Sciences, Clemson University, Clemson, SC, USA
| | - Richard W Blob
- Department of Biological Sciences, Clemson University, Clemson, SC, USA
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5
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Dickson BV, Pierce SE. Functional performance of turtle humerus shape across an ecological adaptive landscape. Evolution 2019; 73:1265-1277. [PMID: 31008517 DOI: 10.1111/evo.13747] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 03/11/2019] [Accepted: 04/08/2019] [Indexed: 01/24/2023]
Abstract
The concept of the adaptive landscape has been invaluable to evolutionary biologists for visualizing the dynamics of selection and adaptation, and is increasingly being used to study morpho-functional data. Here, we construct adaptive landscapes to explore functional trade-offs associated with variation in humerus morphology among turtles adapted to three different locomotor environments: marine, semiaquatic, and terrestrial. Humerus shape from 40 species of cryptodire turtles was quantified using a pseudolandmark approach. Hypothetical shapes were extracted in a grid across morphospace and four functional traits (strength, stride length, mechanical advantage, and hydrodynamics) measured on those shapes. Quantitative trait modeling was used to construct adaptive landscapes that optimize the functional traits for each of the three locomotor ecologies. Our data show that turtles living in different environments have statistically different humeral shapes. The optimum adaptive landscape for each ecology is defined by a different combination of performance trade-offs, with turtle species clustering around their respective adaptive peak. Further, species adhere to pareto fronts between marine-semiaquatic and semiaquatic-terrestrial optima, but not between marine-terrestrial. Our study demonstrates the utility of adaptive landscapes in informing the link between form, function, and ecological adaptation, and establishes a framework for reconstructing turtle ecological evolution using isolated humeri from the fossil record.
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Affiliation(s)
- Blake V Dickson
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Stephanie E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
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Mayerl CJ, Youngblood JP, Rivera G, Vance JT, Blob RW. Variation in Morphology and Kinematics Underlies Variation in Swimming Stability and Turning Performance in Freshwater Turtles. Integr Org Biol 2018. [DOI: 10.1093/iob/oby001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Among swimming animals, stable body designs often sacrifice performance in turning, and high turning performance may entail costs in stability. However, some rigid-bodied animals appear capable of both high stability and turning performance during swimming by propelling themselves with independently controlled structures that generate mutually opposing forces. Because such species have traditionally been studied in isolation, little is known about how variation within rigid-bodied designs might influence swimming performance. Turtles are a lineage of rigid-bodied animals, in which most species use contralateral limbs and mutually opposing forces to swim. We tested the stability and turning performance of two species of turtles, the pleurodire Emydura subglobosa and the cryptodire Chrysemys picta. Emydura subglobosa exhibited both greater stability and turning performance than C. picta, potentially through the use of subequally-sized (and larger) propulsive structures, faster limb movements, and decreased limb excursions. These data show how, within a given body design, combinations of different traits can serve as mechanisms to improve aspects of performance with competing functional demands.
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Affiliation(s)
- C J Mayerl
- Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA
| | - J P Youngblood
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - G Rivera
- Department of Biology, Creighton University, Omaha, NE 68178, USA
| | - J T Vance
- Department of Biology, College of Charleston, Charleston, SC 29424, USA
| | - R W Blob
- Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA
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Mayerl CJ, Sansone AM, Stevens LM, Hall GJ, Porter MM, Rivera G, Blob RW. The impact of keels and tails on turtle swimming performance and their potential as models for biomimetic design. BIOINSPIRATION & BIOMIMETICS 2018; 14:016002. [PMID: 30403189 DOI: 10.1088/1748-3190/aae906] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Stability and turning performance are two key metrics of locomotor performance in animals, and performance in both of these metrics can be improved through a variety of morphological structures. Aquatic vehicles are often designed with keels and rudders to improve their stability and turning performance, but how keels and rudders function in rigid-bodied animals is less understood. Aquatic turtles are a lineage of rigid-bodied animals that have the potential to function similarly to engineered vehicles, and also might make use of keels and rudders to improve their stability and turning performance. To test these possibilities, we trained turtles to follow a mechanically controlled prey stimulus under three sets of conditions: with no structural modifications, with different sized and shaped keels, and with restricted tail use. We predicted that keels in turtles would function similarly to those in aquatic vehicles to reduce oscillations, and that turtles would use the tail like a rudder to reduce oscillations and improve turning performance. We found that the keel designs we tested did not reduce oscillations in turtles, but that the tail was used similarly to a rudder, with benefits to both the magnitude of oscillations they experienced and turning performance. These data show how variation in the accessory structures of rigid-bodied animals can impact swimming performance, and suggest that such variation among turtles could serve as a biomimetic model in designing aquatic vehicles that are stable as well as maneuverable and agile.
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Affiliation(s)
- Christopher J Mayerl
- Department of Biological Sciences, Clemson University, Clemson, SC 29634, United States of America. Author to whom any correspondence should be addressed
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Stevens LM, Blob RW, Mayerl CJ. Ontogeny, morphology and performance: changes in swimming stability and turning performance in the freshwater pleurodire turtle, Emydura subglobosa. Biol J Linn Soc Lond 2018. [DOI: 10.1093/biolinnean/bly140] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Lucy M Stevens
- Department of Biological Sciences, Clemson University, Clemson, SC, USA
| | - Richard W Blob
- Department of Biological Sciences, Clemson University, Clemson, SC, USA
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Mayerl CJ, Blob RW. A novel, bounding gait in swimming turtles: implications for aquatic locomotor diversity. ACTA ACUST UNITED AC 2017; 220:3611-3615. [PMID: 28807934 DOI: 10.1242/jeb.164103] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 08/08/2017] [Indexed: 11/20/2022]
Abstract
Turtles are an iconic lineage in studies of animal locomotion, typifying the use of slow, alternating footfalls during walking. Alternating movements of contralateral limbs are also typical during swimming gaits for most freshwater turtles. Here, we report a novel gait in turtles, in which the pleurodire Emydura subglobosa swims using a bounding gait that coordinates bilateral protraction of both forelimbs with bilateral retraction of both hindlimbs. Use of this bounding gait is correlated with increased limb excursion and decreased stride frequency, but not increased velocity when compared with standard swimming strokes. Bounding by E. subglobosa provides a second example of a non-mammalian lineage that can use bounding gaits, and may give insight into the evolution of aquatic flapping. Parallels in limb muscle fascicle properties between bounding turtles and crocodylids suggest a possible musculoskeletal mechanism underlying the use of bounding gaits in particular lineages.
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Affiliation(s)
| | - Richard W Blob
- Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA
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10
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Blob RW, Mayerl CJ, Rivera ARV, Rivera G, Young VKH. "On the Fence" versus "All in": Insights from Turtles for the Evolution of Aquatic Locomotor Specializations and Habitat Transitions in Tetrapod Vertebrates. Integr Comp Biol 2016; 56:1310-1322. [PMID: 27940619 DOI: 10.1093/icb/icw121] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Though ultimately descended from terrestrial amniotes, turtles have deep roots as an aquatic lineage and are quite diverse in the extent of their aquatic specializations. Many taxa can be viewed as "on the fence" between aquatic and terrestrial realms, whereas others have independently hyperspecialized and moved "all in" to aquatic habitats. Such differences in specialization are reflected strongly in the locomotor system. We have conducted several studies to evaluate the performance consequences of such variation in design, as well as the mechanisms through which specialization for aquatic locomotion is facilitated in turtles. One path to aquatic hyperspecialization has involved the evolutionary transformation of the forelimbs from rowing, tubular limbs with distal paddles into flapping, flattened flippers, as in sea turtles. Prior to the advent of any hydrodynamic advantages, the evolution of such flippers may have been enabled by a reduction in twisting loads on proximal limb bones that accompanied swimming in rowing ancestors, facilitating a shift from tubular to flattened limbs. Moreover, the control of flapping movements appears related primarily to shifts in the activity of a single forelimb muscle, the deltoid. Despite some performance advantages, flapping may entail a locomotor cost in terms of decreased locomotor stability. However, other morphological specializations among rowing species may enhance swimming stability. For example, among highly aquatic pleurodiran turtles, fusion of the pelvis to the shell appears to dramatically reduce motions of the pelvis compared to freshwater cryptodiran species. This could contribute to advantageous increases in aquatic stability among predominantly aquatic pleurodires. Thus, even within the potential constraints of a body plan in which the body is encased by a shell, turtles exhibit diverse locomotor capacities that have enabled diversification into a wide range of aquatic habitats.
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Affiliation(s)
- Richard W Blob
- *Department of Biological Sciences, Clemson University, Clemson, SC, 29634, USA
| | | | | | - Gabriel Rivera
- Department of Biology, Creighton University, Omaha, NE, 68178, USA
| | - Vanessa K H Young
- *Department of Biological Sciences, Clemson University, Clemson, SC, 29634, USA
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Mayerl CJ, Brainerd EL, Blob RW. Pelvic girdle mobility of cryptodire and pleurodire turtles during walking and swimming. ACTA ACUST UNITED AC 2016; 219:2650-8. [PMID: 27340204 DOI: 10.1242/jeb.141622] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 06/15/2016] [Indexed: 11/20/2022]
Abstract
Movements of the pelvic girdle facilitate terrestrial locomotor performance in a wide range of vertebrates by increasing hind limb excursion and stride length. The extent to which pelvic movements contribute to limb excursion in turtles is unclear because the bony shell surrounding the body presents a major obstacle to their visualization. In the Cryptodira, which are one of the two major lineages of turtles, pelvic anatomy indicates the potential for rotation inside the shell. However, in the Pleurodira, the other major suborder, the pelvis shows a derived fusion to the shell, preventing pelvic motion. In addition, most turtles use their hind limbs for propulsion during swimming as well as walking, and the different locomotor demands between water and land could lead to differences in the contributions of pelvic rotation to limb excursion in each habitat. To test these possibilities, we used X-ray reconstruction of moving morphology (XROMM) to compare pelvic mobility and femoral motion during walking and swimming between representative species of cryptodire (Pseudemys concinna) and pleurodire (Emydura subglobosa) turtles. We found that the pelvis yawed substantially in cryptodires during walking and, to a lesser extent, during swimming. These movements contributed to greater femoral protraction during both walking and swimming in cryptodires when compared with pleurodires. Although factors related to the origin of pelvic-shell fusion in pleurodires are debated, its implications for their locomotor function may contribute to the restriction of this group to primarily aquatic habits.
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Affiliation(s)
| | - Elizabeth L Brainerd
- Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
| | - Richard W Blob
- Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA
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de Brouwer AJ, de Poel HJ, Hofmijster MJ. Don't rock the boat: how antiphase crew coordination affects rowing. PLoS One 2013; 8:e54996. [PMID: 23383024 PMCID: PMC3559869 DOI: 10.1371/journal.pone.0054996] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Accepted: 12/20/2012] [Indexed: 12/14/2022] Open
Abstract
It is generally accepted that crew rowing requires perfect synchronization between the movements of the rowers. However, a long-standing and somewhat counterintuitive idea is that out-of-phase crew rowing might have benefits over in-phase (i.e., synchronous) rowing. In synchronous rowing, 5 to 6% of the power produced by the rower(s) is lost to velocity fluctuations of the shell within each rowing cycle. Theoretically, a possible way for crews to increase average boat velocity is to reduce these fluctuations by rowing in antiphase coordination, a strategy in which rowers perfectly alternate their movements. On the other hand, the framework of coordination dynamics explicates that antiphase coordination is less stable than in-phase coordination, which may impede performance gains. Therefore, we compared antiphase to in-phase crew rowing performance in an ergometer experiment. Nine pairs of rowers performed a two-minute maximum effort in-phase and antiphase trial at 36 strokes min−1 on two coupled free-floating ergometers that allowed for power losses to velocity fluctuations. Rower and ergometer kinetics and kinematics were measured during the trials. All nine pairs easily acquired antiphase rowing during the warm-up, while one pair’s coordination briefly switched to in-phase during the maximum effort trial. Although antiphase interpersonal coordination was indeed less accurate and more variable, power production was not negatively affected. Importantly, in antiphase rowing the decreased power loss to velocity fluctuations resulted in more useful power being transferred to the ergometer flywheels. These results imply that antiphase rowing may indeed improve performance, even without any experience with antiphase technique. Furthermore, it demonstrates that although perfectly synchronous coordination may be the most stable, it is not necessarily equated with the most efficient or optimal performance.
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Affiliation(s)
- Anouk J de Brouwer
- MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands.
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Rivera ARV, Rivera G, Blob RW. Forelimb kinematics during swimming in the pig-nosed turtle, Carettochelys insculpta, compared with other turtle taxa: rowing versus flapping, convergence versus intermediacy. ACTA ACUST UNITED AC 2012; 216:668-80. [PMID: 23125335 DOI: 10.1242/jeb.079715] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Animals that swim using appendages do so by way of rowing and/or flapping motions. Often considered discrete categories, rowing and flapping are more appropriately regarded as points along a continuum. The pig-nosed turtle, Carettochelys insculpta, is unusual in that it is the only freshwater turtle to have limbs modified into flippers and swim via synchronous forelimb motions that resemble dorsoventral flapping, traits that evolved independently from their presence in sea turtles. We used high-speed videography to quantify forelimb kinematics in C. insculpta and a closely related, highly aquatic rower (Apalone ferox). Comparisons of our new data with those previously collected for a generalized freshwater rower (Trachemys scripta) and a flapping sea turtle (Caretta caretta) allow us to: (1) more precisely quantify and characterize the range of limb motions used by flappers versus rowers, and (2) assess whether the synchronous forelimb motions of C. insculpta can be classified as flapping (i.e. whether they exhibit forelimb kinematics and angles of attack more similar to closely related rowing species or more distantly related flapping sea turtles). We found that the forelimb kinematics of previously recognized rowers (T. scripta and A. ferox) were most similar to each other, but that those of C. insculpta were more similar to rowers than to flapping C. caretta. Nevertheless, of the three freshwater species, C. insculpta was most similar to flapping C. caretta. 'Flapping' in C. insculpta is achieved through humeral kinematics very different from those in C. caretta, with C. insculpta exhibiting significantly more anteroposterior humeral motion and protraction, and significantly less dorsoventral humeral motion and depression. Based on several intermediate kinematic parameters and angle of attack data, C. insculpta may in fact represent a synchronous rower or hybrid rower-flapper, suggesting that traditional views of C. insculpta as a flapper should be revised.
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Affiliation(s)
- Angela R V Rivera
- Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
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