Gait

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

2. Lowering CG during the last 2 strides before takeoff • Places joint at more optimal angles to produce torque • Stretches muscles to be used during takeoff • Increases passive tension • Increases active tension • Increased # of actin-myosin cross-bridges • Muscle spindles  stretch reflex • Increases muscle calcium levels • Impulse: F•t = m•v

3. Measure of Metabolic Efficiency • O2 cost of locomotion • Requirements: • Steady state measure • Energy utilization almost 100% aerobic • Valid, reliable system of measure

4. Applications for measuring gait efficiency (oxygen cost of locomotion) • 1. Improve athletic performance? • 2. Improve quality of life • A. aging • Lower work and aerobic capacity • Less efficient gait • walking/running at a given speed requires a higher % of work capacity • B. stroke (rehab) • C. orthopedic problems • Joint injury/surgery • Arthritis • Bone fractures • 3. Minimizing injury risk at the workplace • Lifting, walking with a heavy load

5. Categorization of the factors that affect running economy • External energy • Age • Segmental mass distribution • Biomechanical variables • Internal energy • Heart rate • Ventilation • Temperature • Others • VO2max • Training status • Fatigue • Mood state Bailey and Pate, 1991

6. Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate) • 1. Muscle fiber type • Slow twitch fibers are more efficient than fast twitch fibers • 2. Internal work of muscles and joints • A.V. Hill’s 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 area • 2) maximal work per gram of muscle during a contraction • 3) maximal efficiency of chemical energy  mechanical work • Influence of running gait: metabolic energy consumed per stride per mass of muscle: 5 J/stride/kg

7. Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate) 3. Complex pendulum swing of limbs f = 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 limbs • Keep in mind that this is a dynamic frequency which changes as joint angles change in a multi-segmented limb

8. Physical constructs contributing to efficiency of locomotion(not mentioned b Bailey and Pate) 4. Strain energy return • Arch of the foot • Achiles’ tendon • Rapid 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 midstance…an additional 35J can be stored in the Achilles tendon

9. Spring oscillation frequency f = 1/(2)(k/m) Where f = frequency k = spring constant (stiffness) m = unit mass

10. 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

11. Economic runners have: • 1. Lower impact forces/kg mass • 2. Shank (tibia) angle of ankle closer to vertical at heel strike • Little valgus or varus • Less pronation or supination of ankle during stance phase • 3. Smaller plantar flexion angle during at end puss-off phase • 4. Lower velocity of knee during foot plant

12. Kayano, 1986

13. Mean patters of the arch of the foot Measured in different areas Kayano, 1986

14. Ker et al., 1987 70 kg man 17 J/step : Arch 42 J/step: Achilles’ tendon + gastroc Estimated total work needed / step: 100J

15. Rate of energy expenditure and rate of mechanical work - walking at 1 km/hr Saibene, 1990

16. Kubo et al, 1999

17. Ideal (fantasy) linear oxygen cost of running data

18. We can TRY to make oxygen cost of locomotion curves linear Dose of Reality

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

20. O2 cost and stride length

21. Preferredgait 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)

22. Body weight and O2 cost of locomotion Taylor’s lab - Harvard measured 100s of animals O2 cost of locomotion Suni, dik dik, African Goat, sheep, waterbuck, Eland, Zebu cattle

23. VO2 --> 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 Exceptions: Kangaroos, ducks, geese, lions

24. 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…

25. Applications: running velocity = SL • SR

26. Gait Strategies • Expert sprinters – high stride rate • Expert speed skaters – high stride rate • Expert marathon runners – long stride length • Expert cross-country skies – long stride lengths

31. A) pendulum f  1/L • B) T (torque) = F * d = I *  where I = m*r2 (rod, cylinder)