Biomechanics Papers

  1. Duty factor is defined as the time limbs are supporting the body as a fraction of one stride cycle
    Which paper says it is approx. equal for any mammal for a given Froude number?
    Alexander 1983
  2. Alexander 1983 explains the concept of dynamic similarity. What is it?
    If two creatures are DS, they are mechanically the same. Any measurement of time, length or mass on one creature can be applied to the other by using a scale factor.
  3. Define Froude Number

    h is usually leg length. Froude number is used to compare over speeds of locomotion as it is dimensionless
  4. What is the main hypothesis of Alexander 1983?
    What is the result?
    Can locomotion in animals be generalised using dynamic similarity and Froude numbers?

    Yes - works best with cursorial mammals (typically >5kg) but works for bipeds/birds too
  5. What is the same for all cursorial mammals at the same Froude number? (Alexander 1983)
    • Relative power output ( chart?chf=bg,s,00000000&cht=tx&chl=%5Cfrac%7BP%7D%7Bmgu%7D&chs=70x66 )
    • Duty factor
  6. Using arguments in Alexander 1983 - why is a large animal limited in max run speed?
    • Weight proportional to volume of body assuming animals are similar densities.
    • Stress = Weight/Area = chart?chf=bg,s,00000000&cht=tx&chl=%5Cfrac%7B%5BL%5D%5E3%7D%7B%5BL%5D%5E2%7D&chs=54x96 =[L]
    • Stress scales with size
    • At any given Froude number, larger animals will experience higher stresses
    • If stress limitations are the same across animals, then large animals cannot attain higher Froude numbers and are limited in speed
  7. Alexander 1983 shows that stride length differs between cursorial and non-cursorial animals. What trends show that are to do with stride length?
    Stride Length/Hip Height ratio is similar for individual groups of animals
  8. Which paper shows that dynamic similarity applies across multiple breeds of horse?
    Bullimore 2006
  9. In Bullimore 2006, which property was consistent between the horses?
    Relative stride length/duty factor at a given Froude number

    RSL = stride length/leg length
  10. What is the main hypothesis of Hoyt 1982? What is the result of it?
    Do animals change gait to minimise energetic cost of transport?

    Yes, each gait has an optimum speed that minimises cost of transport
  11. Hoyt 1982 used what methods to conduct their experiment?
    3 horses were ran on treadmills and they changed gaits on command. They used Omeasurements to gauge metabolic cost
  12. Horses were shown to use the same amount of metabolic energy regardless of which gait they used as long as they moved at their optimum speeds within those gaits. Metabolic energy cost increased outside the optimum.
    Which paper presented this?
    Hoyt 1982
  13. Alexander 1979 is the earliest sizing paper. What was its main findings?
    • Bone lengths and diameters generally scale with geometrical similarity or chart?chf=bg,s,00000000&cht=tx&chl=%5BM%5D%5E%7B%5Cfrac%7B1%7D%7B3%7D%7D&chs=76x64
    • Bovidae scale with elastic similarity however
  14. Bones have similar loading capabilities (accounting for dimensions) between animals.
    Which paper supports this?
    Biewener 1982
  15. Which papers could be used to support the phrase "Bone lengths scale according to dynamic similarity"?
    • Alexander 1979
    • Biewener 1982
  16. In Biewener 1982 it is unknown whether small animals are over-specified in bone strength or large animals have weak bones but have other adaptations to reduce stress loading.
    Why might small animals be over-specified?
    • They do a larger amount of 'manoeuvres'. Actions that have large accelerations or unpredictable moves that may incite very large stresses on their skeleton
    • They accelerate harder when moving
  17. In Biewener 1982 it is unknown whether small animals are over-specified in bone strength or large animals have weak bones but have other adaptations to reduce stress loading.
    What adaptations/relationships could large animals feature?
    • Bone orientation/curvature changes compared to the vector of peak ground force. (legs become more upright - r/R tie in)
    • There exists an inverse relationship between duty factor and PGF (large animals share load between legs more of the time)
    • There exists an inverse relationship between size and PGF
  18. The concept of effective mechanical advantage (r/R) in animal limbs is introduced in this paper. Which is it?
    What happens to animal's legs as they increase in size?
    • Biewener 1989
    • They become straighter and the animal stands more upright. (Rabbit vs Elephant)
  19. What lengths does the effective mechanical advantage equation refer to? (r/R)
    • r = muscle contact point to ankle joint
    • R = ankle joint to ground contact point (the point that reaction force acts through)
  20. What was the main hypothesis of Garland 1983? What was the result?
    How does maximum running speed vary with body mass?

    • MRS scales dynamically in mammals so that MRS ~ chart?chf=bg,s,00000000&cht=tx&chl=%5BM%5D%5E%7B%5Cfrac%7B1%7D%7B6%7D%7D&chs=76x64
    • Slight polynomial regression however - optimal mass for MRS is 119kg
  21. "Elastic properties of muscle tendons do not vary with size and the ability to store elastic energy is the same in small and large animals"
    Which paper supports this?
    Pollock 1994
  22. "Terrestrial animals account for larger stresses in larger body sizes by changing shape or dimensions rather than material properties"
    Which paper supports this?
    Pollock 1994
  23. What is the main hypothesis of Doke 2005? What is the result?
    • Is fast leg swinging metabolically costly? How much energy is used for fast leg swing during locomotion?
    • Paper claims it is 30% of walking cost at 1.3m/s
  24. What methods/models were used in Doke 2005?
    • Participants put in aparatus that held their body up and were told to swing legs to the beat of a metronome. Frequency was adjusted to their preferred walking frequency. Oconsumption was measured.
    • Pendulum model used so that metabolic rate should be proportional to frequency4
  25. In Doke 2005, it was said that metabolic cost depended on two components and it was difficult to distinguish their individual contributions. What were these?
    • Force/Time
    • Work
  26. Metabolic cost was seen to increase in certain conditions of leg swing in Doke 2005. Which conditions?
    Short durations of force production increased metabolic cost. So swinging leg quickly increases cost of transport (link with muscle studies of red vs white muscle?)
  27. What was the main hypothesis of Jesse 2005? What was the result?
    What fraction of energetic cost of running is used for initiating then propagating leg swing?

    Found to be about 20%
  28. Jesse 2005 found that ~20% of the cost of transport for running is used for leg swing. They also proposed that their found value could be inaccurate. Why?
    • Researchers felt they did not fully eliminate the need for muscle recruitment during leg swing but did not apply higher forces for risk of injuring participants. (so could be >20%)
    • They felt their method added propulsive forces to the feet so overall metabolic rate was reduced anyway. (so could be <20%)
  29. What method was used to find leg swing cost in Jesse 2005?
    Runners were placed on treadmills (3m/s) and their feet were attached to cables. External swing assist (ESA) forces were applied to feet as a percentage of body weight (max 4%). Difference in Oconsumption measured between normal/ESA running.
  30. What is the main hypothesis of Jinger 2005? What is the result?
    • What fraction of energetic cost of walking is used for leg swing?
    • 10%
  31. How did Jinger 2005 improve on the method used in Jesse 2005?
    • Jesse used only external swing assist (ESA) forces on the feet which adds forward propulsion. Jinger applied a force to the waist of each participant and measured difference in Oconsumption between waist force applied only and waist force/ESA applied. 
    • Jesse felt not all muscle activation removed. Therefore, Jinger used a slower speed (3m/s -> 1.25ms)
  32. Why is the method used to estimate leg swing cost in March 2004 valid?
    The muscles recruited during running/walking in guinea fowl along with their aerobic limit is well documented. Therefore, blood flow rate through specific muscles could be measured to indicate metabolic cost during different phases of stride. This cannot be done in humans as muscle recruitment scheme is more complicated.
  33. March 2004 used 15μm microspheres to measure blood flow rate. How?
    • Microspheres injected into left ventricle
    • Distribution of spheres proportional to flow rate
    • Count the number of spheres in a particular tissue and normalise against the total number of spheres flowing out of heart (which is checked periodically).
  34. What percentage of total cost of transport, independent of speed, was reported in March 2004?
  35. Why are guinea fowl often used in biomechanics experiments? (reasons taken from March 2004)
    • Muscles involved in locomotion confined to hind limbs - no division of labour between front/back legs
    • Extensive EMG activity is documented so can partition their strides into swing/stance phases easily
    • Aerobic limit is well defined
    • Good treadmill runners. Repeatable Ovs speed curves
  36. What is the main hypothesis of Rubenson 2009? What is the result?
    Is mechanical work a good predictor of cost of limb swing?

    No. Muscle efficiency increased with speed so it is a non-linear relationship. Muscles also never worked at their accepted max efficiency - so that value can't be used either
  37. "Limb swing has greater efficiency at increased speed of locomotion" 
    What paper supports this quote?
    Rubenson 2009
  38. What is the main finding of Wilson 2003?
    Horses are shown to store elastic energy in their muscles during a gallop in a 'catapult' system. This allows to generate much more force in a short time than normal muscle action
  39. Wilson 2003 shows that 243J are released by a horse's biceps in 0.11s - equating to 4400W. 
    How heavy is the bicep in question? How heavy would a normal muscle have to be to achieve the same power output using normal contractions?
    • Horse bicep is 0.4kg
    • Using the rule that a muscle works at about 90W/kg, 50kg of muscle is required to achieve 4400W normally.
  40. What is the main hypothesis of Biewener 1999? The result?
    How does muscle use vary depending on environmental conditions?

    Found that muscles can alter their functions depending on the operating conditions. Not necessarily linked to specific environments but more to difficulty of task for relative speeds.
  41. What does a force-length diagram look like for isometric contraction/activation of muscles?
    Image Upload 1
  42. What does a force-length diagram look like for concentric contraction/activation of muscles?
    • Image Upload 2
    • Note: Clockwise is eccentric
  43. What is notable about a duck's locomotion in water (paddling) vs on land (walking)? (Biewener 1999)
    • They are fundamentally similar! No evidence of any isometric muscle function - so no efficient movement.
    • Therefore - noted that a duck's terrestrial ability is limited by the requirements of paddling. (aka non-optimised for either but at least capable of both)
  44. "Muscle contractions move from isometric action when walking on level surfaces to concentric action when walking on inclines"
    Which paper supports this?
    Biewener 1999
  45. What differences are found in eel muscle use between water and land? (Biewener 1999)
    • Muscles activate for lonnger periods on land
    • Muscles activate at a greater intensity on land
    • This is probably to counteract increased load bearing due to higher reaction forces
  46. "There are two different types of muscle fibres - red and white - that have different properties and uses"
    Which paper best supports this quote?
    Rome 1988
  47. What are red muscles used for? Why? (Rome 1988)
    They have a low max shortening velocity but act very efficiently and have low fatigue wear. They are used for slow, repetitive movements. E.g. Carp use them primarily at speeds of 0.2-0.4m/s
  48. What are white muscles used for? Why? (Rome 1988)
    They have a high max shortening velocity but act inefficiently and suffer from fatigue. Used infrequently and only at times when maximal movements are necessary. E.g. Carp need these muscles for their startle response so they can escape quickly. Necessary for survival.
  49. "Muscles fulfil different mechanical roles during locomotion based on their morphology"
    Which paper best supports this?
    Daley 2003
  50. What is the main hypothesis of Gabaldon 2004? What was the result?
    Does output of individual muscles change in parallel with the demand for work on the body?

    Yes - muscles adapt to the mechanical work required. They could lengthen to absorb force when going downhill. They could shorten to produce work for going uphill.
  51. According to Kumala 2016, what is human locomotion limited by?
    Humans are constrained by their ankle muscles at all locomotion speeds. They worked at their capacity in the study whereas other joints were not at capacity.
  52. The research conducted in Kumala 2016 is relevant to which fields?
    • Sports performance
    • Rehabilitation for patients (e.g. cerebral palsy)
    • Sports therapy
  53. What is the main hypothesis for McGowan 2005? What was the result?
    Which joints (for wallabies) are used to modulate mechanical power when changing speed?

    Ankle joints have the greatest influence (89% of variation)
  54. Wallaby ankle muscle force exceeded their theoretical maximum in McGowan 2005. What does this indicate?
    Work is produced somewhere else and transferred down the limb to the ankle. Work produced in the hip muscles is enacted at the end of the leg instead of being produced at the ankle directly.
  55. "Elastic energy storage tendons do not limit the ability to speed up or slow down"
    Which paper makes this finding?
    McGowan 2005
  56. Bullimore 2003 argues that animals that are geometrically similar cannot be dynamically similar. This is because some factor is invariant with size. What is that factor?
    Tendon elastic modulus. Animals must distort in shape to account for the fact that tendons have shared properties between animals.
  57. Bullimore 2003 suggests that if animals of all sizes are dynamically similar - some animals must be distorted geometrically. How are they distorted?
    • The limb moment arm between the peak ground force (PGF) and muscle tendon unit (MTU) in a limb changes length with animal size.
    • E.g. larger animals have a lower ratio of MTU strain to PGF. Smaller animals have a higher ratio. (r/R in other papers)
  58. Unberger 2010 used a computer simulation to model human walking and drew metabolic cost conclusions from that. How was metabolic cost calculated?
    The model could make instantaneous predictions of required work and rate of heat production for individual muscles. The mech. and thermal energy rates were combined to find metabolic power. Integrating by stride cycle time and summing all muscles found metabolic energy cost.
  59. Unberger 2010 estimated a metabolic cost of what percent for leg swing at a walker's preferred speed? How did it change outside of preferred speed?
    • preferred: 29%
    • -20% preferred: 35%
    • +20% preferred: 24%
  60. Blanco 2003 made a mechanical model that predicts the maximal run speed of mammals. It is a limited model that can only be applied to a range of animals. What range?
    Body mass >20kg
  61. What was the main aim of Blanco 2003? The result?
    To use mechanical principles to generate a model that can predict max run speed and test its validity on living animals. 

    Pretty alright model - chart?chf=bg,s,00000000&cht=tx&chl=v_%7Bmax%7D%20%3D%20stride%20freq(%5Cfrac%7BhorizontalCOMmovement%7D%7Bduty%20factor%7D)&chs=676x74
  62. What is the main hypothesis of Denny 2003? Result?
    Are there absolute limits to the speeds at which animals can run?

    Tentatively yes. The model he uses shows a plateau but he has extrapolated a lot of data. Sudden advances in technology/understanding could invalidate the model
  63. Denny 2003 uses what kind of approach in the paper?
    Population modelling. He assumes that by having larger and larger populations - by chance there ought to be better runners. He uses historical data to predict how run speed changes with population and extrapolates
  64. Denny 2003 found a plateau in speeds for horse and dog racing. Selective breeding may have enforced the absolute limit in speeds. Why?
    • Thoroughbred horses are descended from the same 12-29 males and this is the only breed used. Lack of genetic diversity may mean a faster horse could be found outside this gene pool. 
    • Dogs are less inbred but their morphology is very malleable (chihuahua to great dane). There could be a shape of dog that is yet to be bred for that could be faster than greyhounds
  65. What is the aim of Fuentes 2016?
    To make a theoretical basis to support the statistical model presented in Garland 1983 for an animal's max run speed vs their body mass.
  66. Fuentes 2016 puts forwards reasoning as to why large animals are restricted in their maximum speed. What are the reasons?
    • The mechanical model shows that stress is proportional to stride length.
    • Large animals have larger stride length so experience more stress in their bones/tendons. 
    • As larger animals approach stress limitations, stride length limitations are reached too.
    • After some threshold of body mass, stress cannot be permitted to increase so stride length doesn't increase.
    • V ~ stride frequency (which has a documented allometry of chart?chf=bg,s,00000000&cht=tx&chl=M%5E%7B-0.15%7D&chs=100x34.
    • Large animals get slower as they increase body mass.
  67. Fuentes 2016 puts forwards reasoning as to why small animals are restricted in their maximum speed. What are the reasons?
    • They are not restricted by maximum stress limitations as they do not approach the max stride length. 
    • Allometry between body mass and top speed is positive for small animals.
    • Suggested that limitation is power output averaged over the stride time
  68. What was the hypothesis of Self 2012? The result?
    Horses operate at constant power and trade off metabolic work of forward locomotion for potential energy. Aka, they go slower up hill and faster downhill

    Horses run fastest at level and get slower on both inclines and declines. They are limited by being quadrapeds
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Biomechanics Papers
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