Gross Cost Of Transport Research Articles

Understanding the influence of context on real-world walking energetics.

Speeds that minimize energetic cost during steady-state walking have been observed during lab-based investigations of walking biomechanics and energetics. However, in real-world scenarios, humans walk in a variety of contexts that can elicit different walking strategies, and may not always prioritize minimizing energetic cost. To investigate whether individuals tend to select energetically optimal speeds in real-world situations and how contextual factors influence gait, we conducted a study combining data from lab and real-world experiments. Walking kinematics and context were measured during daily life over a week (N=17) using wearable sensors and a mobile phone. To determine context, we utilized self-reported activity logs, GPS data and follow-up exit interviews. Additionally, we estimated energetic cost using respirometry over a range of gait speeds in the lab. Gross and net cost of transport were calculated for each participant, and were used to identify energetically optimal walking speed ranges for each participant. The proportion of real-world steady-state stride speeds within these ranges (gross and net) were identified for all data and for each context. We found that energetically optimal speeds predicted by gross cost of transport were more predictive of walking speeds used during daily life than speeds that would minimize net cost of transport. On average, 82.2% of all steady-state stride speeds were energetically optimal for gross cost of transport for all contexts and participants, while only 45.6% were energetically optimal for net cost of transport. These results suggest that while energetic cost is a factor considered by humans when selecting gait speed in daily life, it is not the sole determining factor. Context contributes to the observed variability in movement parameters both within and between individuals.

At their own pace: Optimal walking speed in children and adolescents

AbstractObjectivesAn important factor for human walking behavior is the speed at which an individual—adult or non‐adult—is able to move at a minimum energetic cost. Our aim was to assess the extent to which juveniles walking with adults force the group to set a pace that is energetically too costly for adults by comparing the optimal walking speed of juveniles and adults.Materials and methodsAn experimental study was carried out indoors in a sample of 74 children and adolescents of both sexes, between 7 and 14 years of age. Volunteers walked on a treadmill at six different speeds, and the gross cost of transport (CoT), minimum gross energy cost (minCoT), and optimal locomotion speed (OLS) were determined for each individual. These values were compared with the optimal values for adults, as reported in the literature.ResultsOur results show that OLS is similar in boys and girls, and that there are no sex differences in minCoT. Older individuals, as a consequence of their larger size, spend more energy at their optimal speed than younger children.DiscussionJuveniles are not a real burden for the rest of the group in foraging societies, neither in energetic terms nor in locomotor efficiency, being able to achieve optimal walking speeds similar to adults. The so‐called energetic dilemma for sex‐mixed walking groups does not affect juveniles when moving together with adults or in sex‐mixed parties.

Preferred walking speed on rough terrain: is it all about energetics?

Humans have evolved the ability to walk very efficiently. Further, humans prefer to walk at speeds that approximately minimize their metabolic energy expenditure per unit distance (i.e. gross cost of transport, COT). This has been found in a variety of population groups and other species. However, these studies were mostly performed on smooth, level ground or on treadmills. We hypothesized that the objective function for walking is more complex than only minimizing the COT. To test this idea, we compared the preferred speeds and the relationships between COT and speed for people walking on both a smooth, level floor and a rough, natural terrain trail. Rough terrain presumably introduces other factors, such as stability, to the objective function. Ten healthy men walked on both a straight, flat, smooth floor and an outdoor trail strewn with rocks and boulders. In both locations, subjects performed five to seven trials at different speeds relative to their preferred speed. The COT-speed relationships were similarly U-shaped for both surfaces, but the COT values on rough terrain were approximately 115% greater. On the smooth surface, the preferred speed (1.24±0.17 m s-1) was not found to be statistically different (P=0.09) than the speed that minimized COT (1.34±0.03 m s-1). On rough terrain, the preferred speed (1.07±0.05 m s-1) was significantly slower than the COT minimum speed (1.13±0.07 m s-1; P=0.02). Because near the optimum speed the COT function is very shallow, these changes in speed result in a small change in COT (0.5%). It appears that the objective function for speed preference when walking on rough terrain includes COT and additional factors such as stability.

P 097—Metabolic cost of transport in over-ground and treadmill walking of healthy elderly and effects of a treadmill familiarization protocol

BackgroundPrevious research has shown that the mechanics of walking on a treadmill is similar to walking overground. However it might be true that the energetics of walking is not similar between overground and treadmill, especially for older adults.We hypothesized that a lack of or inadequate familiarization on a treadmill would increase the Metabolic Cost of Transport (MCoT) in older adults due to increased levels of anxiety and the novelty of the locomotor task. Methods10 healthy elderly (5 males and 5 females, mean age of 75.3 SD(6.3) years) were recruited and they walked first at their overground Preferred Walking Speed (PWS) for 8 min to reach a steady state of oxygen consumption in the morning. After that the same speed was imposed on a dual-belt treadmill and they walked for 15 min to properly familiarize themselves with the treadmill. This was called the familiarization session (Session 1). In the afternoon they repeated both the overground and treadmill walking again in the same order and with the same protocol. This session was called the post-familiarization session (Session 2). ResultsThe group average of the overground PWS was 1.28 SD(0.11) m/s (4.61 SD(0.40) km/hr). During the familiarization session, the group average of the Gross Cost of Transport (GCoT) was 3.47 SD(0.35) J/kg/m while walking overground and 4 SD(0.65) J/kg/m while walking on a treadmill. The Net Cost of Transport (NCoT) was 2.64 SD(0.37) J/kg/m while walking overground and 3.14 SD(0.64) J/kg/m while walking on a treadmill. During the post-familiarization session, the group average of the GCoT was 3.84 SD(0.35) J/kg/m while walking overground and 3.94 SD(0.67) J/kg/m while walking on a treadmill. The NCoT was 2.76 SD(0.39) J/kg/m while walking overground and 2.90 SD(0.68) J/kg/m while walking on a treadmill.Both the GCoT and NCoT were statistically significantly higher on a treadmill than overground during the familiarization session. This elevation was not present during the post-familiarization session. There were also no statistically significant differences in the Resting Metabolic Rate (RMR) between before walking overground and before walking on a treadmill in either the familiarization or the post-familiarization session. Discussion and ConclusionThis shows that the energetics of walking can be different for even healthy elderly on a treadmill if they are not or inadequately familiarized to it. This underlines the importance of adequate familiarization to treadmill walking for elderly in trying to understand the MCoT in this population.

Influence of lower limb configuration on walking cost in Late Pleistocene humans

It has been proposed that Neandertals had about 30% higher gross cost of transport than anatomically modern humans (AMH) and that such difference implies higher daily energy demands and reduced foraging ranges in Neandertals. Thus, reduced walking economy could be among the factors contributing to the Neandertals' loss in competition with their anatomically modern successors. Previously, Neandertal walking cost had been estimated from just two parameters and based upon a pooled-sex sample. In the present study, we estimate sex-specific walking cost of Neandertals using a model accounting for body mass, lower limb length, lower limb proportions, and other features of lower limb configuration. Our results suggest that Neandertals needed more energy to walk a given distance than did AMH but the difference was less than half of that previously estimated in males and even far less pronounced in females. In contrast, comparison of the estimated walking cost adjusted to body mass indicates that Neandertals spent less energy per kilogram of body mass than AMH thanks to their lower limb configuration, males having 1–5% lower and females 1–3% lower mass-specific net cost of transport than AMH of the same sex. The primary cause of high cost of transport in Neandertal males is thus their great body mass, possibly a consequence of adaptation to cold, which was not fully offset by their cost-moderating lower limb configuration. The estimated differences in absolute energy spent for locomotion between Neandertal and AMH males would account for about 1% of previously estimated daily energy expenditure of Neandertal or AMH males.

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature-controlled, Brett-type swimming-tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L(F) ), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U(crit)) was 102·5 ± 13·7 cm s⁻¹ or 4·6 ± 0·9 L(F) s⁻¹. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U(max,c)) was 99·4 ± 14·4 cm s⁻¹ or 4·5 ± 0·9 L(F) s⁻¹. Oxygen consumption rate (M in mg O₂ min⁻¹) increased with swimming speed and with fish mass, but mass-specific M (mg O₂ kg⁻¹ h⁻¹) as a function of relative speed (L(F) s⁻¹) did not vary significantly with fish size. Mean standard metabolic rate (R(S) ) was 170 ± 38 mg O₂ kg⁻¹ h⁻¹, and the mean ratio of M at U(max,c) to R(S) , an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U(opt) ), at which the gross cost of transport was a minimum of 2·14 J kg⁻¹ m⁻¹, was 3·8 L(F) s⁻¹. In a subset of the fish studied (19·7-22·7 cm L(F) , 106-164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L(F) . The mean propulsive wavelength was 86·7 ± 5·6 %L(F) or 73·7 ± 5·2 %L(T) . Mean ±s.d. yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L(F) ; 23·4, 25·3 and 26·4 cm L(T) ), were 4·6 ± 0·1 and 17·1 ± 2·2 %L(T) , respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.

Cardiac and Metabolic Physiology of Early Larval Zebrafish (Danio rerio) Reflects Parental Swimming Stamina

Swimming stamina in adult fish is heritable, it is unknown if inherited traits that support enhanced swimming stamina in offspring appear only in juveniles and/or adults, or if these traits actually appear earlier in the morphologically quite different larvae. To answer this question, mature adult zebrafish (Danio rerio) were subjected to a swimming performance test that allowed separation into low swimming stamina or high swimming stamina groups. Adults were then bred within their own performance groups. Larval offspring from each of the two groups, designated high (LHSD) and low stamina-derived larvae (LLSD), were then reared at 27°C in aerated water (21% O2). Routine (fH,r) and active (fH,a) heart rate, and routine and active mass-specific oxygen consumption were recorded from 5 days post fertilization (dpf) through 21 dpf, and gross cost of transport and factorial aerobic metabolic scope were derived from measurements. Heart rate generally ranged between 150 and 225 bpm in both LHSD and LLSD populations. However, significant (P < 0.05) differences existed between the LLSD and LHSD populations at 5 and 14 dpf in fH,r and at days 10 and 15 dpf in fH,a. was 0.04–0.32 μmol mg−1 h−1, while was 0.2–1.2 μmol mg−1 h−1. Significant (P < 0.05) differences between the LLSD and LHSD populations in occurred at 7, 10, and 21 dpf and in at 7 dpf. Gross cost of transport was ∼6–10 μmol O2·μg−1 m−1 at 5 dpf, peaking at 14–19 μmol O2 μg−1 m−1 at 7–10 dpf, before falling again to 5–6 μmol O2 μg−1 m−1 at 21 dpf, with gross cost of transport significantly higher in the LLSD population at 7 dpf. Collectively, these data indicate that inherited physiological differences known to contribute to enhanced stamina in adult parents also appear in their larval offspring well before attainment of juvenile or adult features.

Disrupted flow sensing impairs hydrodynamic performance and increases the metabolic cost of swimming in the yellowtail kingfish,Seriola lalandi

The yellowtail kingfish, Seriola lalandi, shows a distribution of anaerobic and aerobic (red and pink) muscle fibres along the trunk that is characteristic of active pelagic fishes. The athletic capacity of S. lalandi is also shown by its relative high standard metabolic rate and optimal (i.e. least cost) swimming speed. To test the hypothesis that lateral line afferent information contributes to efficient locomotion in an active pelagic species, the swimming performance of S. lalandi was evaluated after unilateral disruption of trunk superficial neuromasts (SNs). Unilaterally disrupting the SNs of the lateral line impaired both swimming performance and energetic efficiency. The critical swimming speed (U(crit); mean ± s.d., N=12) for unilaterally SN-disrupted fish was 2.11±0.96 fork lengths (FL) s(-1), which was significantly slower than the 3.66±0.19 FL s(-1) U(crit) of sham SN-disrupted fish. The oxygen consumption rate (mg O(2) kg(-1) min(-1)) of the unilaterally SN-disrupted fish in a speed range of 1.0-2.2 FL s(-1) was significantly greater than that of the sham SN-disrupted fish. The least gross cost of transport (GCOT; N=6) for SN-disrupted fish was 0.18±0.06 J N(-1) m(-1), which was significantly greater than the 0.11±0.03 J N(-1) m(-1) GCOT for sham SN-disrupted fish. The factorial metabolic scope (N=6) of the unilaterally SN-disrupted fish (2.87±0.78) was significantly less than that of sham controls (4.14±0.37). These data show that an intact lateral line is important to the swimming performance and efficiency of carangiform swimmers, but the functional mechanism of this effect remains to be determined.

Evidence for energy savings from aerial running in the Svalbard rock ptarmigan (Lagopus muta hyperborea)

Svalbard rock ptarmigans were walked and run upon a treadmill and their energy expenditure measured using respirometry. The ptarmigan used three different gaits: a walking gait at slow speeds (less than or equal to 0.75 m s(-1)), grounded running at intermediate speeds (0.75 m s(-1) < U < 1.67 m s(-1)) and aerial running at high speeds (greater than or equal to 1.67 m s(-1)). Changes of gait were associated with reductions in the gross cost of transport (COT; J kg(-1) m(-1)), providing the first evidence for energy savings with gait change in a small crouched-postured vertebrate. In addition, for the first time (excluding humans) a decrease in absolute metabolic energy expenditure (rate of O(2) consumption) in aerial running when compared with grounded running was identified. The COT versus U curve varies between species and the COT was cheaper during aerial running than grounded running, posing the question of why grounded running should be used at all. Existing explanations (e.g. stability during running over rocky terrain) amount to just so stories with no current evidence to support them. It may be that grounded running is just an artefact of treadmill studies. Research investigating the speeds used by animals in the field is sorely needed.

Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway ( Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l − 1 ), mulloway oxygen consumption rate (M· o 2) increased exponentially with swimming speed to a maximum velocity ( U crit) of 1.7 ± < 0.1 body lengths s − 1 (BL s − 1 ) ( n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg − 1 h − 1 ) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT min, 0.14 ± 0.01 mg kg − 1 m − 1 ) and optimum swimming velocity ( U opt, 1.3 ± 0.2 BL s − 1 ) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s − 1 . The critical dissolved oxygen level was 1.80 mg l − 1 for mulloway swimming at 0.9 BL s − 1 . This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l − 1 ), M· o 2 increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg − 1 h − 1 for 75%, 50% and 25% saturation respectively). However, U crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s − 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT min (0.09 ± 0.01 mg kg − 1 m − 1 ) and U opt (0.8 ± 0.1 BL s − 1 ) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.

Respirometry and swimming dynamics of the giant australian cuttlefish, sepia apama (mollusca, cephalopoda)

Swimming dynamics of the giant Australian cuttlefish, Sepia apama, were investigated using swimtunnel respirometry. Relationships between jet pressure, fin frequency, swimming speed and oxygen consumption were defined. Laboratory calibration of swimming parameters is necessary to allow estimates of swimming costs in the field. Jet pressure was the best predictor of oxygen consumption with an averaged equation of MO2 = 722 (jet pressure) + 107 r 2 = 0.51. Individually, fin frequency and jet pressure correlated highly to swimming speed, but due to the complicated usage of finning and jetting, the correlation between swimming speed and oxygen consumption was weaker. Cuttlefish were not optimal swimtunnel subjects and could not swim at high speeds for extended periods. At 15°C and a swimming speed of 0.06 m s−1, the gross cost of transport was calculated to be 10.1 kg−1 m −1, with a net cost of 4.1 kg−1 m−1.

The Forces Acting on Swimming Squid

ABSTRACT Analysis of ciné films and intramantle pressure records for squid Loligo opalescens Berry swimming in a tunnel respirometer provided estimates of all the forces acting in the horizontal and vertical planes for swimming speeds from 0·1 to 0·5 ms−1. Different speeds used different gaits; fin thrust was only important below 0·2 ms−1, ‘anaerobic’ circular muscles were recruited only at supracritical speeds, and hyperinflation caused by contraction of the radial muscle was not seen in steady swimming. The extent, rate and frequency of contraction of the obliquely striated circular muscles varied little with speed, and jet thrust was matched to speed primarily by active pressure control through adjustments in the size of the funnel orifice. Hydrodynamic lift production to compensate for negative buoyancy during enforced horizontal swimming in the tunnel required 30–90% of the total force over the speed range studied and appears less efficient than direct use of jet thrust. This suggests a new rationale for ‘climb-and-glide’ swimming which reduces previous estimates of the gross cost of transport for squid under natural conditions by at least 35%, with no loss of speed. The cost of accelerating water into the mantle of a squid moving at high speed appears to have been underestimated in previous studies. A simulation of a series of escape jets predicts a maximum speed of 8 body lengths s−1 (14ms−1), reached after only two jets, because of the high deceleration during refilling.

Energetics of Trail Running, Load Carriage, and Emigration in the Column-Raiding Army Ant Eciton hamatum

For workers at 28°C, standard $\dot{V}O_{2} = 0.166 M^{.84}$ where $\dot{V}O_{2}$ is ml h⁻¹ and M is mass in g. At the same temperature, pupal $\dot{V}O_{2} = 0.156 M_{.83}$. Gross cost of transport (GCOT) and net cost of transport (NCOT) decreased with body mass and running speed, log GCOT = 0.87-(1.05 log s)-(0.55 log M) and log NCOT = 0.51-(0.92 log S)-(0.66 log M) where GCOT and NCOT are ml O₂ g⁻¹ km⁻¹, S is cm s⁻¹, and M is mass in g: The energetics of load carriage was measured in workers carrying pupae. The mean $\dot{V}O_{2}$ Of laden ants (mean mass .0108 g) was 5.72 ml O₂ g⁻¹ h⁻¹. The mean respiratory exchange ratio of inactive ants in a bivouac was 0.72, that of unladen workers while running was 0.68, and that of pupae was 0.64. A model is developed and presented as a computer program (BASIC) to predict the energy spent for maintaining a raiding column, for colony emigration, and for a colony while in bivouac. The energetic performance of Eciton hamatum is compared with that of a leaf-cutting a...