Gait Stance phase Swing phase Running speed = stride length stride rate (frequency)

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Text of Gait Stance phase Swing phase Running speed = stride length stride rate (frequency)

  • GaitStance phaseSwing phase

    Running speed = stride length stride rate (frequency)

  • Lowering CG during the last 2 strides before takeoffPlaces joint at more optimal angles to produce torqueStretches muscles to be used during takeoffIncreases passive tensionIncreases active tensionIncreased # of actin-myosin cross-bridgesMuscle spindles stretch reflexIncreases muscle calcium levelsImpulse:Ft = mv

  • Measure of Metabolic EfficiencyO2 cost of locomotionRequirements:Steady state measureEnergy utilization almost 100% aerobicValid, reliable system of measure

  • Applications for measuring gait efficiency (oxygen cost of locomotion)1. Improve athletic performance?2. Improve quality of lifeA. agingLower work and aerobic capacityLess efficient gaitwalking/running at a given speed requires a higher % of work capacityB. stroke (rehab)C. orthopedic problemsJoint injury/surgeryArthritisBone fractures3. Minimizing injury risk at the workplaceLifting, walking with a heavy load

  • Categorization of the factors that affect running economyExternal energyAgeSegmental mass distributionBiomechanical variablesInternal energyHeart rateVentilationTemperatureOthersVO2maxTraining statusFatigueMood stateBailey and Pate, 1991

  • Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate)

    1. Muscle fiber typeSlow twitch fibers are more efficient than fast twitch fibers2. Internal work of muscles and jointsA.V. Hills concept of the oxygen cost of shortening (each stride consumes a quantifiable and predictable amount of energy)He stated that 3 contractile properties held true for all vertebrate striated muscle:1) maximal force per cross-sectional area2) maximal work per gram of muscle during a contraction3) maximal efficiency of chemical energy mechanical workInfluence of running gait: metabolic energy consumed per stride per mass of muscle: 5 J/stride/kg

  • Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate)

    3. Complex pendulum swing of limbsf = 1/(2)(ag/l)Where: ag = acceleration due to gravity l = distance from axis of rotation to center of mass (gravity)Logically, the most efficient running speed will match the dynamic pendulum frequency of the limbsKeep in mind that this is a dynamic frequency which changes as joint angles change in a multi-segmented limb

  • Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate)

    4. Strain energy returnArch of the footAchiles tendonRaped stretch of muscles

    Up to 50% of mechanical energy needed for running can be stored in these structures (Bennet, M.S. Biomechanics in Sport, 1988)For a 50kg man running at 4.5 m/s, each arch stores approximately 17J of energy at midstancean additional 35J can be stored in the Achilles tendon

  • Spring oscillation frequencyf = 1/(2)(k/m)

    Where

    f = frequencyk = spring constant (stiffness)m = unit mass

  • Remember: connective tissue and skeletal muscle are viscoelastic

    They store and return energy well when stretched (or otherwise deformed) rapidly

    They dissipate energy when stretched slowly

  • Economic runners have:1. Lower impact forces/kg mass2. Shank (tibia) angle of ankle closer to vertical at heel strikeLittle valgus or varusLess pronation or supination of ankle during stance phase3. Smaller plantar flexion angle during at end puss-off phase4. Lower velocity of knee during foot plant

  • Kayano, 1986

  • Kayano, 1986Mean patters of the arch of the footMeasured in different areas

  • Ker et al., 1987

    70 kg man17 J/step : Arch42 J/step: Achilles tendon + gastroc

    Estimated total work needed / step: 100J

  • Saibene, 1990Rate of energy expenditure and rate ofmechanical work -

    walking at 1 km/hr

  • Kubo et al, 1999

  • Ideal (fantasy) linear oxygen cost of running data

  • We can TRY to make oxygen costof locomotion curves linearDose of Reality

  • Alinearity of O2 cost (C.R.Taylor et al.)

  • O2 costandstride length

  • Preferred gait in locomotion (walk, trot, canter, running, gallop) is usually one at which the oxygen cost is lowest when expressed against running speed:(ml O2/kg/min) / (m/sec)

  • Body weight and O2 cost of locomotion Taylors lab - Harvard measured 100s ofanimals O2 cost oflocomotion

    Suni, dik dik, AfricanGoat, sheep, waterbuck,Eland, Zebu cattle

  • Exceptions:Kangaroos, ducks, geese, lionsVO2 --> ml O2/kg 0.70/min

    resting metabolic rate stride cost

    5 J/stride/kg - A.V. Hill

    Emet/mb = 10.7 Mb-0.316 + 6.03 Mb-0.303

  • VO2 --> ml O2/kg 0.70/min

    resting metabolic rate stride cost

    oxygen cost of running for child higher than adult

    mechanics less efficient up to age 7

    Size a factor up to age 16-18

  • Applications: running velocity = SL SR

  • Gait StrategiesExpert sprinters high stride rateExpert speed skaters high stride rateExpert marathon runners long stride lengthExpert cross-country skies long stride lengths

  • A) pendulumf 1/L

    B) T (torque) = F * d = I *

    where I = m*r2 (rod, cylinder)