Internal Work and Oxygen Consumption of Impaired and Normal Walking

1. Internal Work and Oxygen Consumption of Impaired and Normal Walking Sylvain Grenier, M.A. D.G.E. Robertson, Ph.D. Biomechanics Laboratory School of Human Kinetics University of Ottawa

2. Purpose • To compare the absolute work method with absolute power method in calculating work for impaired and normal gait, using physiological oxygen consumption measures as verification.

3. Methodology Subject Trials • subjects: 4 male, 4 female; • Five normal gait trials per subject selected • one trial each with splinted knee selected • one trial each with splinted ankle selected • the conditions were applied in random order

4. Methodology Video • three-dimensional video (30 Hz) • markers: both sides all joints • Ariel digitization (60 Hz) • Biomech Motion Analysis System

5. Methodology Treadmill and Force • VO2 standing baseline value (Pierrynowski,1980; Stainsby,1980) • 3 min walking VO2 steady state • speed chosen, then metronome set • force data collected for a full gait cycle • 2 AMTI force platforms • data from the first FS was carried over assuming symmetry (Cappozzo et al. 1976)

6. = E - E T T o f Work equations work Absolute method Absolute power method External w ork: N N J ' W = ( D E ) W = M w D t å å å ext ext i i S j j i i = 1 i = 1 j = 1 Internal w ork: é ù N N J é ù ' W = D E - W W ' = M w D t - W ê ú å å å ê ú int T ext int i i ext i j j ê ú ë û i = 1 i = 1 j = 1 ë û

7. Absolute Power (AP) integration of joint moment x angular velocity (power) assumes: one muscle per joint no elastic storage pos. and neg. work equal mechanically Absolute Work (AW) change of instanteous energy location of summation limits energy exchanges I.e., if types of energy are separated then summed; between and within exchanges are permitted, but between any two segments Work equations

8. power output power input ( + ) EXTERNAL INTERNAL work OXYGEN COST BIOMECHANICAL COST = PHYSIOLOGICAL COST Mechanical Efficiency work output ME = = x 100 x 100 work input = ME x 100 ME x 100 Biomechanical cost: internal work mass * velocity

9. Results: Mechanical Efficiency

10. Mechanical Efficiency • efficiency varies based on these assumptions: • baseline VO2 • value given to negative work • if internal work is included • calculation of antisymmetrical movements • elastic energy storage • assumption re: biarticular muscles

11. Mechanical Efficiency • calculated using AP method • likely overestimates because: • includes elastic storage twice • model assumes no intercompensation, • biarticular muscles are not allowed • negative power at one joint cannot be used to power the neighbouring joint • Assume negative work = positive work • all increased Internal work/ O2 cost

12. Mechanical Efficiency • calculated using AW method • likely under estimates • calculates net work vs. produced work • assumptions of energy transfer limitations contradict Law of Conservation of energy • I.e., potential to kinetic • asymmetrical motion does not require energy • all decreased internal work/ O2 cost

13. Differences between conditions

14. Differences between conditionswithin subjects

15. Direction of Difference Wilcoxon signed ranks test *

16. Normal Walking • Normal walking data is similar to previous data from other published research

17. Mean of subjects: Normal ankle CTO CFS A2 A1 • A1: eccentric plantar flexor during early to midstance • A2: concentric plantar flexor at push-off

18. Normal Knee CTO CFS K2 K1 K4 K3 • K1: eccentric flexor moment; absorbing impact • K2: concentric extensor; midstance to toe-off • K3: eccentric flexor; shortly before toe-off until max knee flexion • K4: eccentric extensor; late swing

19. Normal Hip CTO CFS H3 H1 H1 H2 • H1: concentric extension; moving CM forward • H2: eccentric flexor; lowering the CM • H3: concentric flexor; to swing the leg forward

20. Discussion • Direction of difference: • perhaps humans are optimized for adaptability rather than efficiency • LK trials tended to be lower • induced changes in 3D or rotation not visible to planar analysis (Kerrigan, et al. (1997) • values similar to other researchers • Winter 1.09 J/kg.m (1979) • our data: • AW = 1.90 J/kg.m • AP = 3.05 J/kg.m

21. Discussion • Efficiency • obviously > 100% not possible • subtracting effect of elastic storage, biarticular muscles • internal work increases, efficiency decreases to about 65-70% • compared to most efficient engines today: about 60%

22. Conclusion • AP IBC seems to indicate that locked knee internal work is less than in the normal case. • Both AP & AW seem to indicate that locked ankle gait is more efficient than normal • Binomial test shows that AP method can distinguish between normal and impaired conditions. • VO2 seems most consistent but not significant

23. Recommendations • four or five cameras; increase accuracy • do a three dimensional analysis; determine if energy lost is in the frontal plane • use three force plates; increase the accuracy • have one extreme condition with both ankle and knee of one leg restricted

24. Acknowledgments • Thanks to Heidi Sveistrup, Ph.D., for all her assistance and for the use of her lab. • Thanks to Peter Stothart, Ph.D., for his guidance during my supervisor’s absence.