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Heavily loaded walking on steep paths in hypoxia: the power and economy of Nepalese porters
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Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
1983; Farley et al., 1993) and morphological variations with size were taken from allometric equations (Alexander et al., 1981; Biewener, 1989; Medler, 2002). Was used an empirical equation relating metabolic power with muscular force and speed (Minetti and Alexander, 1997). Our model predicts qualitatively the pattern of mass specific metabolic rate variations with speed and body mass (Taylor et al., 1982) and the linear inverse relationship between metabolic rate and the time of foot contact (Kram and Taylor, 1990). It provides an explanation of the energy saving on macropodids (Dawson and Taylor, 1973). The model could provide theoretical understanding on energetic cost changes with gravity, loads or inclines, topics already studied experimentally by other authors. References Alexander R.McN., Jayes A.S., Maloiy G.M.O., Wathuta E.M. (1981). J. Zool. (London) 194: 539-552. Alexander R.McN., Jayes A.S. (1983). J. Zool. (London) 201: 135-152. Biewener A.A. (1989). Science 245: 45-48. Dawson T.J., Taylor C.R. (1973). Nature 246: 313-314. Farley C.T., Glasheen J., McMahon T.A. (1993). J. Exp. Biol. 185: 71-86. Hoyt D.E, Wickler S.J., Cogger E.A. (2000). J. Exp. Biol. 203: 221-227. Kram R., Taylor C.R. (1990). Nature 346: 265-267. Medler S. (2002). Am J Physiol Regulatory Integrative Comp Physiol. 283(2): R368378. Minetti A.E., Alexander R.M. (1997). J. Theor. Biol. 186: 467-476. Taylor C.R., Heglund N.C., Maloiy G.M.O. (1982). J. Exp. Biol. 97: 1-21. 4993 We, 14:45-15:00 (P33) A muscle-driving model of human walking and estimate of metabolic expenditure on muscles W. Wang 1, R. Crompton 2, A. Minetti 3, M. Gunther2, W. Sellers4, R. Abboud 1, R.McN. Alexander5. 1Institute of Motion Analysis and Research, University
of Dundee, Dundee, UK, 2Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool, UK, 3Institute of Human Physiology I, University of Milan, Milano, Italy, 4Department of Anatomy, University of Manchester, Manchester, UK, 5Department of Biology, University of Leeds, Leeds, UK Muscles are the primary sources to produce any performances, and consuming metabolic energy. To investigate the relationship between muscle work and metabolic energy, we built a model of whole human, consisting of the head, trunk, arms, legs, feet, etc. The lower limbs were driven by two groups of muscles. The foot was reconstructed using finite element surfaces to contact ground and thereby, generate ground reaction force (GRF). The muscles, using the Hill muscle model, include the contractile and serial/parallel elastic elements. A mixed algorithm, including direction-varying and random-hunt concepts, was used to search for muscle activities which make the model walking. The 'success' of the model was evaluated by the comparison of between simulated RGFs and experimental ones, between simulated muscle activities and EMGs, and between simulated and experimental kinematic data. The results show that the musculoskeletal model can simulate human walking reasonably accurately. The muscular parameters, e.g. velocity and work, can be obtained. Consequently, the metabolic expenditure for the muscle activity can be estimated (following Alexander 2002). E.g., on a simulation of human walking at 0.75 m/s, simulated mean of sum metabolic energy is about 2 W/kg, while experimentally physiological metabolic amount is around 3.725W/kg (Taylor et al. 1982). Many factors influence on the estimated metabolic values, e.g. efficiency between muscle work and heat, negative muscle work, heat dissemination, etc. The issues are discussed. This study shows a hybrid-model, consisting finite element foot, muscle driving leg and whole body, which can be used in simulation of musculoskeletal system performances. References Alexander R.McN. (2002). Comparat. Biochem. Physiol. A 133: 1001-1011. Taylor et al. (1982). J. Exp. Biol 97: 1-21. 7192 We, 15:00-15:15 (P33) Skeletal muscle energetics: insight from heat production and metabolic energy turnover measurements J. Gonz~lez-Alonso. Centre for Sports Medicine and Human Performance.
Brunel University, Uxbridge, UK A general assumption in muscle energetics is that total energy turnover and mechanical efficiency are constant during exercise, implying that the metabolic pathways involved in ATP production have the same efficiency. In vitro studies, however, indicate that heat liberation during ATP utilisation varies from 35 kJ (mol ATP) -1 when ATP resynthesis comes from pure PCr splitting to 72kJ(mol ATP) -1 when oxidative phosphorylation provides the energy for ATP resynthesis, with glycolysis having an intermediate value. To assess total muscle energy turnover during exercise in humans and test the validity of the above assumption, we measured heat production, power output,
Oral Presentations oxygen uptake, lactate production, and ATP and PCr hydrolysis in young subjects during 180s of intense one-legged knee-extensor exercise. Total heat production was estimated by measuring heat stored in the contracting muscles as well as that dissipated from the muscle. We found that the rate of heat production increased throughout exercise, being 2-fold higher at 180s compared to the initial 5 s, with a t 1/2 of 38 s. With heat production increasing during exercise while power output was constant, the estimated mechanical efficiency declined from an initial value of 53±6% to 36±5% at the end of exercise. Concomitant estimates of aerobic and anaerobic energy metabolism suggested a very close match between the metabolic energy yield and the total energy turnover. The efficiency of conversion of chemical energy to mechanical power output is therefore high in the transition from rest to exercise, and then gradually declines corresponding to the change in the predominant pathway of ATP production shifting from PCr splitting at the onset of exercise to oxidative phosphorylation after -60 s of exercise. 6485 We, 15:15-15:30 (P33) Heavily loaded walking on steep paths in hypoxia: the power and economy of Nepalese porters A.E. Minetti 1,3, L.P. Ardig62, E Formenti 3. 1Institute of Human Physiology I,
Faculty of Medicine, University of Mliano, Italy, 2Motion Science Faculty, University of Verona, Italy, 3Institute of Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Cheshire, Alsager, UK Carrying loads in the Himalaya is one of the toughest occupations on earth. Porters face extreme ranges in loads, steepness, altitude and climate for 6-8 hours a day, many months a year, since they are boys. It has been previously shown that, when carrying loads on flat terrain, porters' metabolic economy is higher than in Caucasians [1], while the reasons for that are still unknown. We measure heavy loaded porters both during 90 km trekking in Nepal and at two different altitudes (3490 and 5050 m a.s.l.) where they were compared to Caucasian mountaineers during (22%) gradient walking. The remarkably high porters' performance (+60% in speed, +39% mechanical power) is only partly explained by the lower cost of loaded walking (-20%), being also the result of a better cardio-vascular adaptation to altitude, which generates a higher mass specific metabolic power (+30%). A better pendulum-like mechanics cannot be claimed as the determinant of these results because the steepness was such to prevent any interchange between potential and kinetic energy of the body centre of mass [2]. Nepalese porters show higher efficiency, regardless of uphill (and faster) or downhill (at the same speed) loaded walking. By measuring the oscillations of the load-head-trunk segment and analysing the different components of the mechanical work during load carrying, we suggest that the better economy of porters is likely the result of a more consistent and smooth balance of the loaded body above the hip, an achieved motor skill devoted to energy minimization. References [1] Bastien G.J., Schepens B., Willems P.A., Heglund N.C. Science 2005; 308: 1755. [2] Minetti A.E., Ardig5 L.P., Saibene E J. Physiol. 1993; 472: 725-735.
2.5. Muscle Mechanics 5846 Th, 08:15-08:30 (P37) On the elastic and viscoelastic properties of passive muscle tissue in compression M. Van Loocke, C.K. Simms, C.G. Lyons. Trinity Centre for Bioengineering,
Trinity College Dublin, Ireland Very little attention has been placed to date on the compressive behaviour of muscle tissue. These properties are however on prime interest to fully characterise human body models used in impact biomechanics and in the study of decubitus. This research aims to study the behaviour of skeletal muscle under compressive loading. Quasi-static and dynamic unconfined compression experiments have been conducted on porcine muscle samples oriented at various angles from the muscle fibre direction. During dynamic tests sinusoidal excitation was applied to the samples at frequencies ranging up to 200 Hz. Results from the quasi-static tests show that the weakest direction in the tissue is at 450 from the fibre direction. This is related to the particular connection between adjacent fibre fascicles which allows shearing between these during compression. This behaviour was reproduced using a simple finite element model where muscle tissue is represented as a matrix in which fibres are embedded. A variant of a model by Li et al. has been fitted to the quasi-static data. This model gives a good fit to experimental data and also yields good prediction of muscle behaviour (Van Loocke et al.).
Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
1983; Farley et al., 1993) and morphological variations with size were taken from allometric equations (Alexander et al., 1981; Biewener, 1989; Medler, 2002). Was used an empirical equation relating metabolic power with muscular force and speed (Minetti and Alexander, 1997). Our model predicts qualitatively the pattern of mass specific metabolic rate variations with speed and body mass (Taylor et al., 1982) and the linear inverse relationship between metabolic rate and the time of foot contact (Kram and Taylor, 1990). It provides an explanation of the energy saving on macropodids (Dawson and Taylor, 1973). The model could provide theoretical understanding on energetic cost changes with gravity, loads or inclines, topics already studied experimentally by other authors. References Alexander R.McN., Jayes A.S., Maloiy G.M.O., Wathuta E.M. (1981). J. Zool. (London) 194: 539-552. Alexander R.McN., Jayes A.S. (1983). J. Zool. (London) 201: 135-152. Biewener A.A. (1989). Science 245: 45-48. Dawson T.J., Taylor C.R. (1973). Nature 246: 313-314. Farley C.T., Glasheen J., McMahon T.A. (1993). J. Exp. Biol. 185: 71-86. Hoyt D.E, Wickler S.J., Cogger E.A. (2000). J. Exp. Biol. 203: 221-227. Kram R., Taylor C.R. (1990). Nature 346: 265-267. Medler S. (2002). Am J Physiol Regulatory Integrative Comp Physiol. 283(2): R368378. Minetti A.E., Alexander R.M. (1997). J. Theor. Biol. 186: 467-476. Taylor C.R., Heglund N.C., Maloiy G.M.O. (1982). J. Exp. Biol. 97: 1-21. 4993 We, 14:45-15:00 (P33) A muscle-driving model of human walking and estimate of metabolic expenditure on muscles W. Wang 1, R. Crompton 2, A. Minetti 3, M. Gunther2, W. Sellers4, R. Abboud 1, R.McN. Alexander5. 1Institute of Motion Analysis and Research, University
of Dundee, Dundee, UK, 2Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool, UK, 3Institute of Human Physiology I, University of Milan, Milano, Italy, 4Department of Anatomy, University of Manchester, Manchester, UK, 5Department of Biology, University of Leeds, Leeds, UK Muscles are the primary sources to produce any performances, and consuming metabolic energy. To investigate the relationship between muscle work and metabolic energy, we built a model of whole human, consisting of the head, trunk, arms, legs, feet, etc. The lower limbs were driven by two groups of muscles. The foot was reconstructed using finite element surfaces to contact ground and thereby, generate ground reaction force (GRF). The muscles, using the Hill muscle model, include the contractile and serial/parallel elastic elements. A mixed algorithm, including direction-varying and random-hunt concepts, was used to search for muscle activities which make the model walking. The 'success' of the model was evaluated by the comparison of between simulated RGFs and experimental ones, between simulated muscle activities and EMGs, and between simulated and experimental kinematic data. The results show that the musculoskeletal model can simulate human walking reasonably accurately. The muscular parameters, e.g. velocity and work, can be obtained. Consequently, the metabolic expenditure for the muscle activity can be estimated (following Alexander 2002). E.g., on a simulation of human walking at 0.75 m/s, simulated mean of sum metabolic energy is about 2 W/kg, while experimentally physiological metabolic amount is around 3.725W/kg (Taylor et al. 1982). Many factors influence on the estimated metabolic values, e.g. efficiency between muscle work and heat, negative muscle work, heat dissemination, etc. The issues are discussed. This study shows a hybrid-model, consisting finite element foot, muscle driving leg and whole body, which can be used in simulation of musculoskeletal system performances. References Alexander R.McN. (2002). Comparat. Biochem. Physiol. A 133: 1001-1011. Taylor et al. (1982). J. Exp. Biol 97: 1-21. 7192 We, 15:00-15:15 (P33) Skeletal muscle energetics: insight from heat production and metabolic energy turnover measurements J. Gonz~lez-Alonso. Centre for Sports Medicine and Human Performance.
Brunel University, Uxbridge, UK A general assumption in muscle energetics is that total energy turnover and mechanical efficiency are constant during exercise, implying that the metabolic pathways involved in ATP production have the same efficiency. In vitro studies, however, indicate that heat liberation during ATP utilisation varies from 35 kJ (mol ATP) -1 when ATP resynthesis comes from pure PCr splitting to 72kJ(mol ATP) -1 when oxidative phosphorylation provides the energy for ATP resynthesis, with glycolysis having an intermediate value. To assess total muscle energy turnover during exercise in humans and test the validity of the above assumption, we measured heat production, power output,
Oral Presentations oxygen uptake, lactate production, and ATP and PCr hydrolysis in young subjects during 180s of intense one-legged knee-extensor exercise. Total heat production was estimated by measuring heat stored in the contracting muscles as well as that dissipated from the muscle. We found that the rate of heat production increased throughout exercise, being 2-fold higher at 180s compared to the initial 5 s, with a t 1/2 of 38 s. With heat production increasing during exercise while power output was constant, the estimated mechanical efficiency declined from an initial value of 53±6% to 36±5% at the end of exercise. Concomitant estimates of aerobic and anaerobic energy metabolism suggested a very close match between the metabolic energy yield and the total energy turnover. The efficiency of conversion of chemical energy to mechanical power output is therefore high in the transition from rest to exercise, and then gradually declines corresponding to the change in the predominant pathway of ATP production shifting from PCr splitting at the onset of exercise to oxidative phosphorylation after -60 s of exercise. 6485 We, 15:15-15:30 (P33) Heavily loaded walking on steep paths in hypoxia: the power and economy of Nepalese porters A.E. Minetti 1,3, L.P. Ardig62, E Formenti 3. 1Institute of Human Physiology I,
Faculty of Medicine, University of Mliano, Italy, 2Motion Science Faculty, University of Verona, Italy, 3Institute of Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Cheshire, Alsager, UK Carrying loads in the Himalaya is one of the toughest occupations on earth. Porters face extreme ranges in loads, steepness, altitude and climate for 6-8 hours a day, many months a year, since they are boys. It has been previously shown that, when carrying loads on flat terrain, porters' metabolic economy is higher than in Caucasians [1], while the reasons for that are still unknown. We measure heavy loaded porters both during 90 km trekking in Nepal and at two different altitudes (3490 and 5050 m a.s.l.) where they were compared to Caucasian mountaineers during (22%) gradient walking. The remarkably high porters' performance (+60% in speed, +39% mechanical power) is only partly explained by the lower cost of loaded walking (-20%), being also the result of a better cardio-vascular adaptation to altitude, which generates a higher mass specific metabolic power (+30%). A better pendulum-like mechanics cannot be claimed as the determinant of these results because the steepness was such to prevent any interchange between potential and kinetic energy of the body centre of mass [2]. Nepalese porters show higher efficiency, regardless of uphill (and faster) or downhill (at the same speed) loaded walking. By measuring the oscillations of the load-head-trunk segment and analysing the different components of the mechanical work during load carrying, we suggest that the better economy of porters is likely the result of a more consistent and smooth balance of the loaded body above the hip, an achieved motor skill devoted to energy minimization. References [1] Bastien G.J., Schepens B., Willems P.A., Heglund N.C. Science 2005; 308: 1755. [2] Minetti A.E., Ardig5 L.P., Saibene E J. Physiol. 1993; 472: 725-735.
2.5. Muscle Mechanics 5846 Th, 08:15-08:30 (P37) On the elastic and viscoelastic properties of passive muscle tissue in compression M. Van Loocke, C.K. Simms, C.G. Lyons. Trinity Centre for Bioengineering,
Trinity College Dublin, Ireland Very little attention has been placed to date on the compressive behaviour of muscle tissue. These properties are however on prime interest to fully characterise human body models used in impact biomechanics and in the study of decubitus. This research aims to study the behaviour of skeletal muscle under compressive loading. Quasi-static and dynamic unconfined compression experiments have been conducted on porcine muscle samples oriented at various angles from the muscle fibre direction. During dynamic tests sinusoidal excitation was applied to the samples at frequencies ranging up to 200 Hz. Results from the quasi-static tests show that the weakest direction in the tissue is at 450 from the fibre direction. This is related to the particular connection between adjacent fibre fascicles which allows shearing between these during compression. This behaviour was reproduced using a simple finite element model where muscle tissue is represented as a matrix in which fibres are embedded. A variant of a model by Li et al. has been fitted to the quasi-static data. This model gives a good fit to experimental data and also yields good prediction of muscle behaviour (Van Loocke et al.).