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First published online May 18, 2006
Journal of Experimental Biology 209, 2050-2063 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02226

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The energetic costs of trunk and distal-limb loading during walking and running in guinea fowl Numida meleagris : I. Organismal metabolism and biomechanics

Richard L. Marsh^*, David J. Ellerby, Havalee T. Henry and Jonas Rubenson

Department of Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA

View larger version (18K): [in a new window]   Fig. 1. Approximate position and method of attachment of distal limb and trunk loads. Birds were either limb- or trunk-loaded. Both loading conditions are shown here for illustrative purposes. The limb load was placed near the distal end of the tarsometatarsal segment.

View larger version (11K): [in a new window]   Fig. 2. Metabolic rate (W; see Materials and methods) as a function of treadmill speed in guinea fowl with no load (closed circles), trunk load (open circles) or distal limb load (open triangles). The data were collected at 0.5 m s-1 intervals under all conditions, but the loaded data are offset slightly on the speed axis for clarity. Values are means ± 1 s.e.m. (N=6).

View larger version (16K): [in a new window]   Fig. 3. Fractional increases in net metabolic rate at different speeds in trunk-loaded guinea fowl. Net metabolic rates were calculated by subtracting the resting metabolic rate of the bird sitting quietly in a darkened box on the treadmill from the rates measured at the different speeds. Fractional increases were then calculated by subtracting the unloaded net metabolic rate from the loaded net metabolic rate and dividing by the unloaded net metabolic rate. The broken line indicates the fractional increase in total mass (body mass plus load) produced by loading the trunk. Values are means ± 1 s.e.m. (N=6).

View larger version (19K): [in a new window]   Fig. 4. Mean stance (closed symbols) and swing (open symbols) durations during unloaded (circles), trunk-loaded (squares) and distal limb-loaded (triangles) locomotion. Values are means ± 1 s.e.m. (N=6). Closely spaced points are offset slightly on the speed axis for clarity.

View larger version (17K): [in a new window]   Fig. 5. Horizontal and vertical coordinates of the proximal end of the tarsometatarsal segment (A) and segment angle (B) in a representative bird unloaded (closed symbols) and limb-loaded (open symbols), running at 1.5 m s-1. Horizontal coordinates from the video were corrected for tread speed and thus the total distance moved in A indicates the stride length. Data were collected at 0.004 s intervals from foot-down to the next foot-down.

View larger version (16K): [in a new window]   Fig. 6. The components of the energy in a single unloaded tarsometatarsal segment as a function of time during one stride in a representative bird running at 1.5 m s-1. Horizontal (EK,x; solid black line), vertical (EK,y; broken red line) and rotational (Erot; dotted blue line) kinetic energies are indicated. The green broken and dotted line indicates the gravitational potential energy (Eg) referenced to zero at the lowest point in the stride. The vertical line indicates the stance swing transition. (Please note that the dip in EK,x shown during in swing phase is representative in that a decrease in this mechanical energy term occurred during mid-swing in 4 of the 5 birds measured. However, the magnitude of the mid-swing decrease in EK,x in the example shown was the largest found.)

View larger version (17K): [in a new window]   Fig. 7. Total mechanical energy of a single tarsometatarsal segment as a function of time during one stride in a representative bird running at 1.5 m s-1. Broken line, unloaded segmental energy; solid line, loaded segmental energy. The vertical line indicates the stance-swing transition.

View larger version (13K): [in a new window]   Fig. 8. (A) Mean sum of the positive increments in mechanical energy (Epos) of both tarsometatarsal segments as a function of treadmill speed, in the unloaded (closed symbols) and loaded (open symbols) segments. Circles, total Epos over the whole stride; triangles, Epos for swing phase only. (B) Mean mechanical power of the unloaded (closed circles) and loaded (open circles) tarsometatarsal segments, calculated by dividing total Epos for the stride by the stride duration. Values are means ± 1 s.e.m. (N=6).

View larger version (16K): [in a new window]   Fig. 9. Mean increments in metabolic (circles) and mechanical (diamonds) power, calculated as loaded power minus unloaded power. Values are means ± 1 s.e.m. (N=6). Numbers between the metabolic and mechanical power indicate the mean delta efficiency (± 1 s.e.m.) calculated by dividing the mechanical power increment by the metabolic power increment.

View larger version (20K): [in a new window]   Fig. 10. Mean metabolic response to trunk loading or to head-supported loads in walking mammals and guinea fowl. The ratio of net loaded to net unloaded metabolic rate is plotted as a function of the ratio of loaded (body mass plus load) to unloaded body mass (body mass only). The solid lines with a slope of 1.0 are included for reference. (A) All the data. (B) Measurements in which the mass ratio was less than 1.5 times the unloaded body mass. Solid circles, five human studies with the load applied in back packs (Soule et al., 1978; Pierrynowski et al., 1981; Duggan and Haisman, 1992; Lloyd and Cooke, 2000; Quesada et al., 2000). Open circles, human data for loads carried in a waist pack (Griffin et al., 2003). Open inverted triangles, two studies of human males carrying loads on their heads: American men (Soule and Goldman, 1969); Indian men (Datta et al., 1975). Open squares enclosing x, African women carrying head loads (Jones, 1989). Open circles enclosing +, Napalese porters carrying loads resting on their backs with a tump line around the head (Bastien et al., 2005) (G. J. Bastien and N. C. Heglund, personal communication). Open circles enclosing x, two studies of children carrying back packs (Hong et al., 2000; Merati et al., 2001). Plus signs, large quadrupeds (horse, Brahman cattle and water buffalo) (Lawrence and Stibbards, 1990). The asterisk indicates the ratio for guinea fowl walking at 0.5 m s-1. Net metabolic rates were calculated as the active metabolic rate minus the resting rate. For human studies in which resting metabolic rate was not given, we used an approximate value of 1.5 W kg-1, which was based on the available data for standing humans in references cited here.

View larger version (22K): [in a new window]   Fig. 11. Mean metabolic response to trunk loading in running mammals and guinea fowl. The solid line with a slope of 1.0 is included for reference. Net metabolic ratios were calculated as in Fig. 10. Solid circles, fit humans (Davies, 1980; Taylor et al., 1982; Epstein et al., 1987; Thorstensson, 1986; Bilzon et al., 2001). Open circles, very well trained adult humans, most of whom competed in distance or middle distance events (Cureton et al., 1978; Cooke et al., 1991; Bourdin et al., 1995). Open triangles, children (Thorstensson, 1986; Cooke et al., 1991; Davies, 1980). Plus signs, quadrupeds ranging in size from rats to horses (Taylor et al., 1980; Wickler et al., 2001) (S. J. Wickler, personal communication). Asterisks, values for guinea fowl running at 1.0 and 1.5 m s-1. For the human studies not providing resting metabolic rates, the resting values were calculated as for the data in Fig. 10. Resting rates for the quadrupeds (Taylor et al., 1980) were calculated as 1.2 times the basal value obtained by entering the body mass (Mb) in the allometric equation, BMR b=3.89Mb0.76 (Peters, 1983).

View larger version (16K): [in a new window]   Fig. 12. Increase in metabolic rate due to distal limb loading in walking and running mammals and guinea fowl. The data were calculated by subtracting the loaded metabolic rate from the unloaded metabolic rate and dividing by the mass of the added load. Closed circles, walking and running humans (Soule and Goldman, 1969; Jones et al., 1984; Martin, 1985; Miller and Stamford, 1987; Claremont and Hall, 1988; Bhambhani et al., 1989). Open squares, trotting dogs (Steudel, 1990a). Open triangles, trotting horses (Wickler et al., 2004). Horse data were calculated from original data provided by S. J. Wickler (personal communication).