Gait selection in the ostrich: mechanical and metabolic characteristics of walking and running with and without an aerial phase

It has been argued that minimization of metabolic-energy costs is a primary determinant of gait selection in terrestrial animals. This view is based predominantly on data from humans and horses, which have been shown to choose the most economical gait (walking, running, galloping) for any given speed. It is not certain whether a minimization of metabolic costs is associated with the selection of other prevalent forms of terrestrial gaits, such as grounded running (a widespread gait in birds). Using biomechanical and metabolic measurements of four ostriches moving on a treadmill over a range of speeds from 0.8 to 6.7 m s(-1), we reveal here that the selection of walking or grounded running at intermediate speeds also favours a reduction in the metabolic cost of locomotion. This gait transition is characterized by a shift in locomotor kinetics from an inverted-pendulum gait to a bouncing gait that lacks an aerial phase. By contrast, when the ostrich adopts an aerial-running gait at faster speeds, there are no abrupt transitions in mechanical parameters or in the metabolic cost of locomotion. These data suggest a continuum between grounded and aerial running, indicating that they belong to the same locomotor paradigm.     

Running energetics of the North American river otter: do short legs necessarily reduce efficiency on land?

Semi-aquatic mammals move between two very different media (air and water), and are subject to a greater range of physical forces (gravity, buoyancy, drag) than obligate swimmers or runners. This versatility is associated with morphological compromises that often lead to elevated locomotor energetic costs when compared to fully aquatic or terrestrial species. To understand the basis of these differences in energy expenditure, this study examined the interrelationships between limb morphology, cost of transport and biomechanics of running in a semi-aquatic mammal, the North American river otter. Oxygen consumption, preferred locomotor speeds, and stride characteristics were measured for river otters (body mass=11.1 kg, appendicular/axial length=29%) trained to run on a treadmill. To assess the effects of limb length on performance parameters, kinematic measurements were also made for a terrestrial specialist of comparable stature, the Welsh corgi dog (body mass=12.0 kg, appendicular/axial length=37%). The results were compared to predicted values for long legged terrestrial specialists. As found for other semi-aquatic mammals, the net cost of transport of running river otters (6.63 J kg(-1)min(-1) at 1.43 ms(-1)) was greater than predicted for primarily terrestrial mammals. The otters also showed a marked reduction in gait transition speed and in the range of preferred running speeds in comparison to short dogs and semi-aquatic mammals. As evident from the corgi dogs, short legs did not necessarily compromise running performance. Rather, the ability to incorporate a period of suspension during high speed running was an important compensatory mechanism for short limbs in the dogs. Such an aerial period was not observed in river otters with the result that energetic costs during running were higher and gait transition speeds slower for this versatile mammal compared to locomotor specialists.     

The energy expenditure of snowshoeing in packed vs. unpacked snow at low-level walking speeds

Snowshoeing is currently ranked as one of the top 20 participatory sports in the United States, and the number of participants almost tripled, from 440,000 to 1.2 million in 1998. Despite this large increase in participation, no scientific evidence exists to quantify any physiologic response to the activity. Therefore, the purpose of this investigation was to assess the energy expenditure of snowshoeing at selected low-level speeds and evaluate its acceptability as a form of aerobic conditioning exercise. Ten habitually active subjects (7 men, 3 women, mean age = 24 +/- 3.9 years, mass = 76.6 +/- 14.5 kg, height = 173.7 +/- 9.6 cm) were recruited. Steady state heart rate data were determined from 2 treadmill tests at 4 and 6 mph. Steady state heart rates at 4 mph and 6 mph from treadmill speeds were then reproduced outdoors under 2 snow conditions, packed, and unpacked snow, while caloric expenditure and speed were determined. Expired gases were collected in Douglas bags for both snowshoe and treadmill trials and then analyzed and corrected indoors for the fractional concentrations of carbon dioxide and oxygen. Data analyses indicate that caloric expenditure during snowshoeing may be considerably higher than previously reported. Snowshoeing on packed snow at 2.95 mph elicited a similar heart rate and energy expenditure response as walking on a treadmill at 4 mph or snowshoeing in unpacked snow at 2.04 mph (Vo(2) = 18.18 +/- 0.8 ml x kg(-1) x min(-1)). Snowshoeing on packed snow at 3.97 mph elicited the same heart rate and energy expenditure response as walking on a treadmill at 6 mph or snowshoeing on unpacked snow at 2.87 mph (Vo(2) = 36.72 +/- 0.8 ml x kg(-1) x min(-1)). Furthermore, increasing walking speed on snow by just 1 mph at slow speeds (2 and 3 mph) resulted in approximately twice the energy expenditure. Our data indicate that current estimates of energy expenditure while snowshoeing underestimate by greater than 50%. Apparently the energy expenditure during snowshoeing is much higher than previously considered and varies considerably because of snow terrain. Furthermore, energy expenditure levels similar to walking can be achieved on snowshoes at much slower speeds. This study represents an original investigation into energy expenditure during snowshoeing.     

Effects of size, sex, and voluntary running speeds on costs of locomotion in lines of laboratory mice selectively bred for high wheel-running activity

Selective breeding for over 35 generations has led to four replicate (S) lines of laboratory house mice (Mus domesticus) that run voluntarily on wheels about 170% more than four random-bred control (C) lines. We tested whether S lines have evolved higher running performance by increasing running economy (i.e., decreasing energy spent per unit of distance) as a correlated response to selection, using a recently developed method that allows for nearly continuous measurements of oxygen consumption (VO2) and running speed in freely behaving animals. We estimated slope (incremental cost of transport [COT]) and intercept for regressions of power (the dependent variable, VO2/min) on speed for 49 males and 47 females, as well as their maximum VO2 and speeds during wheel running, under conditions mimicking those that these lines face during the selection protocol. For comparison, we also measured COT and maximum aerobic capacity (VO2max) during forced exercise on a motorized treadmill. As in previous studies, the increased wheel running of S lines was mainly attributable to increased average speed, with males also showing a tendency for increased time spent running. On a whole-animal basis, combined analysis of males and females indicated that COT during voluntary wheel running was significantly lower in the S lines (one-tailed P=0.015). However, mice from S lines are significantly smaller and attain higher maximum speeds on the wheels; with either body mass or maximum speed (or both) entered as a covariate, the statistical significance of the difference in COT is lost (one-tailed P> or =0.2). Thus, both body size and behavior are key components of the reduction in COT. Several statistically significant sex differences were observed, including lower COT and higher resting metabolic rate in females. In addition, maximum voluntary running speeds were negatively correlated with COT in females but not in males. Moreover, males (but not females) from the S lines exhibited significantly higher treadmill VO2max as compared to those from C lines. The sex-specific responses to selection may in part be consequences of sex differences in body mass and running style. Our results highlight how differences in size and running speed can account for lower COT in S lines and suggest that lower COT may have coadapted in response to selection for higher running distances in these lines.     

Gait Transitions in Human Infants: Coping with Extremes of Treadmill Speed

Spinal pattern generators in quadrupedal animals can coordinate different forms of locomotion, like trotting or galloping, by altering coordination between the limbs (interlimb coordination). In the human system, infants have been used to study the subcortical control of gait, since the cerebral cortex and corticospinal tract are immature early in life. Like other animals, human infants can modify interlimb coordination to jump or step. Do human infants possess functional neuronal circuitry necessary to modify coordination within a limb (intralimb coordination) in order to generate distinct forms of alternating bipedal gait, such as walking and running? We monitored twenty-eight infants (7–12 months) stepping on a treadmill at speeds ranging between 0.06–2.36 m/s, and seventeen adults (22–47 years) walking or running at speeds spanning the walk-to-run transition. Six of the adults were tested with body weight support to mimic the conditions of infant stepping. We found that infants could accommodate a wide range of speeds by altering stride length and frequency, similar to adults. Moreover, as the treadmill speed increased, we observed periods of flight during which neither foot was in ground contact in infants and in adults. However, while adults modified other aspects of intralimb coordination and the mechanics of progression to transition to a running gait, infants did not make comparable changes. The lack of evidence for distinct walking and running patterns in infants suggests that the expression of different functional, alternating gait patterns in humans may require neuromuscular maturation and a period of learning post-independent walking.     

Workload comparison between hiking and indoor physical activity

ABSTRACT: Fattorini, L, Pittiglio, G, Federico, B, Pallicca, A, Bernardi, M, and Rodio, A. Workload comparison between hiking and indoor physical activity. J Strength Cond Res 26(10): 2883-2889, 2012-Walking is a physical activity able to maintain and improve aerobic fitness. This activity can easily be performed in all seasons both outdoors and indoors, but when it is performed in its natural environment, the use of specific equipment is required. In particular, it has been demonstrated that the use of trekking boots (TBs) induces a larger workload than those used indoors. Because an adequate fitness level is needed to practice hiking in safety, it is useful to know the energy demand of such an activity. This research aims at defining the metabolic engagement of hiking on natural paths with specific equipment at several speeds and comparing this with indoor ones (on a treadmill). This can thence be used to define the load that better reflects the one required to walk on natural paths. The walking energy cost (joules per kilogram per meter) at several speeds (0.28, 0.56, 0.84, 1.11, and 1.39 m·s)-on level natural terrain while wearing suitable footwear (TBs) and on a treadmill at various raising slopes (0, 1, 2, 3, 4%) while wearing running shoes-was measured in 14 healthy young men (age 23.9 ± 2.9 years, stature 1.75 ± 0.04 m, and body mass 72.9 ± 6.3 kg). A physiological evaluation of all the subjects was performed before energy cost measurements. The results showed that outdoors, the oxygen uptake was consistently less than the ventilatory threshold at all speeds tested and that a 3% slope on the treadmill best reflects the outdoor walking energy expenditure. These findings will prove useful to plan proper training for hiking activity or mixed (outdoors and indoors) training program.     

Energy cost of walking and gait instability in healthy 65- and 80-yr-olds.

This study tested whether the lower economy of walking in healthy elderly subjects is due to greater gait instability. We compared the energy cost of walking and gait instability (assessed by stride to stride changes in the stride time) in octogenarians (G80, n = 10), 65-yr-olds (G65, n = 10), and young controls (G25, n = 10) walking on a treadmill at six different speeds. The energy cost of walking was higher for G80 than for G25 across the different walking speeds (P < 0.05). Stride time variability at preferred walking speed was significantly greater in G80 (2.31 +/- 0.68%) and G65 (1.93 +/- 0.39%) compared with G25 (1.40 +/- 0.30%; P < 0.05). There was no significant correlation between gait instability and energy cost of walking at preferred walking speed. These findings demonstrated greater energy expenditure in healthy elderly subjects while walking and increased gait instability. However, no relationship was noted between these two variables. The increase in energy cost is probably multifactorial, and our results suggest that gait instability is probably not the main contributing factor in this population. We thus concluded that other mechanisms, such as the energy expenditure associated with walking movements and related to mechanical work, or neuromuscular factors, are more likely involved in the higher cost of walking in elderly people.     

Stability-normalised walking speed: A new approach for human gait perturbation research

In gait stability research, neither self-selected walking speeds, nor the same prescribed walking speed for all participants, guarantee equivalent gait stability among participants. Furthermore, these options may differentially affect the response to different gait perturbations, which is problematic when comparing groups with different capacities. We present a method for decreasing inter-individual differences in gait stability by adjusting walking speed to equivalent margins of stability (MoS). Eighteen healthy adults walked on a split-belt treadmill for two-minute bouts at 0.4 m/s up to 1.8 m/s in 0.2 m/s intervals. The stability-normalised walking speed (MoS = 0.05 m) was calculated using the mean MoS at touchdown of the final 10 steps of each speed. Participants then walked for three minutes at this speed and were subsequently exposed to a treadmill belt acceleration perturbation. A further 12 healthy adults were exposed to the same perturbation while walking at 1.3 m/s: the average of the previous group. Large ranges in MoS were observed during the prescribed speeds (6–10 cm across speeds) and walking speed significantly (P < 0.001) affected MoS. The stability-normalised walking speeds resulted in MoS equal or very close to the desired 0.05 m and reduced between-participant variability in MoS. The second group of participants walking at 1.3 m/s had greater inter-individual variation in MoS during both unperturbed and perturbed walking compared to 12 sex, height and leg length-matched participants from the stability-normalised walking speed group. The current method decreases inter-individual differences in gait stability which may benefit gait perturbation and stability research, in particular studies on populations with different locomotor capacities. [Preprint: https://doi.org/10.1101/314757]     

Influence of higher-grade walking on metabolic demands in young untrained Japanese women

The primary purpose of this study was to document the physiological responses of level walking and running (LW/R) at various speeds, and grade walking (GW) at various grades on a treadmill. Twenty-four young untrained Japanese women performed 2 tests on the specially designed treadmill for a higher grade exercise. The first test was the LW/R with increase of speeds, 33.3, 66.7, 91.7, and 116.7 m.min(-1). The first 3 progressions were for walking and the last progression was for running. The second test was the GW with increase of grades 0, 10, 20, and 30% with the velocity of 33.3 m.min(-1) in all progressions. The different combinations of speeds and grade for the progressions used in this study were selected based on the results of preliminary pilot studies, so that the percent heart rate maximim (%HRmax) was reached at the minimum intensities recommended to allow improving cardiorespiratory fitness by the American College of Sports Medicine (ACSM). Significant (p 相似文献   

Gait‐specific metabolic costs and preferred speeds in ring‐tailed lemurs (Lemur catta), with implications for the scaling of locomotor costs

Metabolic costs of resting and locomotion have been used to gain novel insights into the behavioral ecology and evolution of a wide range of primates; however, most previous studies have not considered gait‐specific effects. Here, metabolic costs of ring‐tailed lemurs (Lemur catta) walking, cantering and galloping are used to test for gait‐specific effects and a potential correspondence between costs and preferred speeds. Metabolic costs, including the net cost of locomotion (COL) and net cost of transport (COT), change as a curvilinear function of walking speed and (at least provisionally) as a linear function of cantering and galloping speeds. The baseline quantity used to calculate net costs had a significant effect on the magnitude of speed‐specific estimates of COL and COT, especially for walking. This is because non‐locomotor metabolism constitutes a substantial fraction (41–61%, on average) of gross metabolic rate at slow speeds. The slope‐based estimate of the COT was 5.26 J kg^?1 m^?1 for all gaits and speeds, while the gait‐specific estimates differed between walking (0.5 m s^?1: 6.69 J kg^?1 m^?1) and cantering/galloping (2.0 m s^?1: 5.61 J kg^?1 m^?1). During laboratory‐based overground locomotion, ring‐tailed lemurs preferred to walk at ～0.5 m s^?1 and canter/gallop at ～2.0 m s^?1, with the preferred walking speed corresponding well to the COT minima. Compared with birds and other mammals, ring‐tailed lemurs are relatively economical in walking, cantering, and galloping. These results support the view that energetic optima are an important movement criterion for locomotion in ring‐tailed lemurs, and other terrestrial animals. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Cost of transport and optimal swimming speed in farmed and wild European silver eels (Anguilla anguilla)

A swimming speed of 0.4 meters per second (m s(-1)) is the minimal speed for European female silver eels to reach the spawning sites in the Sargasso Sea in time. As silver eels cease feeding when they start their oceanic migration, the cost of transport (COT) should be minimised and the swimming speed optimised to attain the highest energetic efficiency. In this study, we have investigated the optimal swimming speed (U(opt)) of silver eels since U(opt) may be higher than the minimal swimming speed and is more likely to resemble the actual cruise speed. A variety of swimming tests were performed to compare endurance swimming between farmed eels and wild eels, both in freshwater and in seawater. The swimming tests were run with 101 silver female eels (60-96 cm, 400-1500 g) in 22 Blazka-type swim tunnels in a climatised room at 18 degrees C with running freshwater or seawater. Tests were run at 0.5-1.0 m s(-1) with increments of 0.1 m s(-1), and either 2 h or 12 h intervals. Remarkably, both tests revealed no changes in oxygen consumption (M O2) and COT over time. U(opt) values ranged between 0.61 and 0.68 m s(-1) (0.74-1.02 BL s(-1)) for the different groups and were thus 53-70% higher than the minimal speed. At U(opt), the COT was 37-50 mg O2 kg(-1) km(-1). These relatively very low values confirm our earlier observations. COT values in seawater were about 20% higher than in freshwater. Assuming that migrating female silver eels cruise at their U(opt), they will be able to cover the distance to the Sargasso Sea in 3-4 months, leaving ample time for final maturation and finding mates.     

Improvement in running economy after 6 weeks of plyometric training

This study determined whether a 6-week regimen of plyometric training would improve running economy (i.e., the oxygen cost of submaximal running). Eighteen regular but not highly trained distance runners (age = 29 +/- 7 [mean +/- SD] years) were randomly assigned to experimental and control groups. All subjects continued regular running training for 6 weeks; experimental subjects also did plyometric training. Dependent variables measured before and after the 6-week period were economy of running on a level treadmill at 3 velocities (women: 2.23, 2.68, and 3.13 m.s(-1); men: 2.68, 3.13, and 3.58 m.s(-1)),VO(2)max, and indirect indicators of ability of muscles of lower limbs to store and return elastic energy. The last were measurements during jumping tests on an inclined (20 degrees ) sled: maximal jump height with and without countermovement and efficiencies of series of 40 submaximal countermovement and static jumps. The plyometric training improved economy (p < 0.05). Averaged values (m.ml(-1).kg(-1)) for the 3 running speeds were: (a). experimental subjects-5.14 +/- 0.39 pretraining, 5.26 +/- 0.39 posttraining; and (b). control subjects-5.10 +/- 0.36 pretraining, 5.06 +/- 0.36 posttraining. The VO(2)max did not change with training. Plyometric training did not result in changes in jump height or efficiency variables that would have indicated improved ability to store and return elastic energy. We conclude that 6 weeks of plyometric training improves running economy in regular but not highly trained distance runners; the mechanism must still be determined.     

Relationship between the efficiency of muscular work during jumping and the energetics of running

The running economy of seventeen athletes was studied during running at a low speed (3.3 m X s-1) on a motor-driven treadmill. The net energetic cost during running expressed in kJ X kg-1 X km-1 was on average 4.06. As expected, a positive relationship was found between the energetic cost and the percentage of fast twitch fibres (r = 0.60, n = 17, p less than 0.01). In addition, the mechanical efficiency during two different series of jumps performed with and without prestretch was measured in thirteen subjects. The effect of prestretch on muscle economy was represented by the ratio between the efficiency of muscular work performed during prestretch jumps and the corresponding value calculated in no prestretch conditions. This ratio demonstrated a statistically significant relationship with energy expenditure during running (r = -0.66, n = 13, P less than 0.01), suggesting that the elastic behaviour of leg extensor muscles is similar in running and jumping if the speeds of muscular contraction during eccentric and concentric work are of similar magnitudes.     

Faster top running speeds are achieved with greater ground forces not more rapid leg movements.

We twice tested the hypothesis that top running speeds are determined by the amount of force applied to the ground rather than how rapidly limbs are repositioned in the air. First, we compared the mechanics of 33 subjects of different sprinting abilities running at their top speeds on a level treadmill. Second, we compared the mechanics of declined (-6 degrees ) and inclined (+9 degrees ) top-speed treadmill running in five subjects. For both tests, we used a treadmill-mounted force plate to measure the time between stance periods of the same foot (swing time, t(sw)) and the force applied to the running surface at top speed. To obtain the force relevant for speed, the force applied normal to the ground was divided by the weight of the body (W(b)) and averaged over the period of foot-ground contact (F(avge)/W(b)). The top speeds of the 33 subjects who completed the level treadmill protocol spanned a 1.8-fold range from 6.2 to 11.1 m/s. Among these subjects, the regression of F(avge)/W(b) on top speed indicated that this force was 1.26 times greater for a runner with a top speed of 11.1 vs. 6.2 m/s. In contrast, the time taken to swing the limb into position for the next step (t(sw)) did not vary (P = 0.18). Declined and inclined top speeds differed by 1.4-fold (9.96+/-0.3 vs. 7.10+/-0.3 m/s, respectively), with the faster declined top speeds being achieved with mass-specific support forces that were 1.3 times greater (2.30+/- 0.06 vs. 1.76+/-0.04 F(avge)/ W(b)) and minimum t(sw) that were similar (+8%). We conclude that human runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground.     

Physiological cost of running while wearing spring-boots

The purpose of the study was to investigate the physiological cost of running in spring-boots compared with running in running shoes at different speeds. During testing, subjects (n = 7) completed running trials while wearing spring-boots and running shoes. Three speed conditions (2.23, 2.68, and 3.13 m.s(-1)) were completed per shoe condition (i.e., spring-boots and running shoes). Rate of oxygen consumption (Vo(2)), heart rate (HR), rating of perceived exertion (RPE), and stride frequency were recorded for each condition. Order of shoe conditions was balanced, with speeds tested continuously from slow to fast. There was no difference in Vo(2), HR, or RPE between shoe conditions across speeds (p > 0.05). Stride frequency was lower during running in spring-boots vs. running shoes at each speed (speed of spring-boots vs. running shoes for 2.23 m x s(-1): 69.9 +/- 2.9 strides x min(-1) vs. 75.6 +/- 3.5 strides x min(-1); for 2.68 m x s(-1): 71.3 +/- 5.2 strides x min(-1) vs. 79.4 +/- 5.0 strides x min(-1); for 3.13 m x s(-1): 73.6 +/- 7.3 strides x min(-1) vs. 83.1 +/- 8.2 strides x min(-1); p < 0.05). Despite the added mass to the lower extremity and change in stride frequency during running in spring-boots, the physiological cost of running was similar to that of running in running shoes. Exercising while running in spring-boots may provide less impact force with no change in running economy.     

Energetics of kayaking at submaximal and maximal speeds

The energy cost of kayaking per unit distance (C(k), kJ x m(-1)) was assessed in eight middle- to high-class athletes (three males and five females; 45-76 kg body mass; 1.50-1.88 m height; 15-32 years of age) at submaximal and maximal speeds. At submaximal speeds, C(k) was measured by dividing the steady-state oxygen consumption (VO(2), l x s(-1)) by the speed (v, m x s(-1)), assuming an energy equivalent of 20.9 kJ x l O(-1)(2). At maximal speeds, C(k) was calculated from the ratio of the total metabolic energy expenditure (E, kJ) to the distance (d, m). E was assumed to be the sum of three terms, as originally proposed by Wilkie (1980): E = AnS + alphaVO(2max) x t-alphaVO(2max) x tau(1-e(-t x tau(-1))), were alpha is the energy equivalent of O(2) (20.9 kJ x l O(2)(-1)), tau is the time constant with which VO(2max) is attained at the onset of exercise at the muscular level, AnS is the amount of energy derived from anaerobic energy utilization, t is the performance time, and VO(2max) is the net maximal VO(2). Individual VO(2max) was obtained from the VO(2) measured during the last minute of the 1000-m or 2000-m maximal run. The average metabolic power output (E, kW) amounted to 141% and 102% of the individual maximal aerobic power (VO(2max)) from the shortest (250 m) to the longest (2000 m) distance, respectively. The average (SD) power provided by oxidative processes increased with the distance covered [from 0.64 (0.14) kW at 250 m to 1.02 (0.31) kW at 2000 m], whereas that provided by anaerobic sources showed the opposite trend. The net C(k) was a continuous power function of the speed over the entire range of velocities from 2.88 to 4.45 m x s(-1): C(k) = 0.02 x v(2.26) (r = 0.937, n = 32).     

Metabolic equivalents during scooter exercise

The purpose of this study was to determine the metabolic equivalents (METs) for scooter exercise (riding a scooter, scootering) and to examine the energy expenditure and the heart rate response, so that the results can be used in health promotion activities. Eighteen young adults (10 males and 8 females) participated in scootering on a treadmill at three different speeds for six minutes each. Before, during, and after the exercise, pulmonary ventilation, oxygen uptake (VO(2)), carbon dioxide product, respiratory exchange ratio (R), and heart rate (HR) were measured. These measurements kept steady states from the 3rd to 6th minute of each different speed session. The MET values acquired during scootering at 80 m.min(-1), 110 m.min(-1), and 140 m.min(-1) were 3.9, 4.3, and 5.0, respectively. Calculated using VO(2) (ml.kg(-1).min(-1))x[4.0+R], the energy consumption for scootering at each speed was 67.0+/-10.6, 73.3+/-10.2, and 84.8+/-7.9 cal.kg(-1).min(-1), respectively. The regression equation between scootering speed (X, m.min(-1)) and VO(2) (Y, ml.kg(-1).min(-1)) is Y=0.062X+8.655, and the regression equation between HR (X, beats.min(-1)) and VO(2)reserve (Y, %) is Y=0.458X-11.264. These equations can be applied to both females and males. Thus, scootering at 80 to 140 m.min(-1) might not be sufficient to improve the cardiorespiratory fitness of young male adults similar to the participants, but it may contribute many healthy benefits to most female adults and even male adults, and improve their health and fitness at the faster speeds.     

Contractile behavior of the forelimb digital flexors during steady-state locomotion in horses (Equus caballus): an initial test of muscle architectural hypotheses about in vivo function

The forelimb digital flexors of the horse display remarkable diversity in muscle architecture despite each muscle-tendon unit having a similar mechanical advantage across the fetlock joint. We focus on two distinct muscles of the digital flexor system: short compartment deep digital flexor (DDF(sc)) and the superficial digital flexor (SDF). The objectives were to investigate force-length behavior and work performance of these two muscles in vivo during locomotion, and to determine how muscle architecture contributes to in vivo function in this system. We directly recorded muscle force (via tendon strain gauges) and muscle fascicle length (via sonomicrometry crystals) as horses walked (1.7 m s(-1)), trotted (4.1 m s(-1)) and cantered (7.0 m s(-1)) on a motorized treadmill. Over the range of gaits and speeds, DDF(sc) fascicles shortened while producing relatively low force, generating modest positive net work. In contrast, SDF fascicles initially shortened, then lengthened while producing high force, resulting in substantial negative net work. These findings suggest the long fibered, unipennate DDF(sc) supplements mechanical work during running, whereas the short fibered, multipennate SDF is specialized for economical high force and enhanced elastic energy storage. Apparent in vivo functions match well with the distinct architectural features of each muscle.     

Comparison of lower extremity kinematic curves during overground and treadmill running

Researchers conduct gait analyses utilizing both overground and treadmill modes of running. Previous studies comparing these modes analyzed discrete variables. Recently, techniques involving quantitative pattern analysis have assessed kinematic curve similarity in gait. Therefore, the purpose of this study was to compare hip, knee and rearfoot 3-D kinematics between overground and treadmill running using quantitative kinematic curve analysis. Twenty runners ran at 3.35 m/s ± 5% during treadmill and overground conditions while right lower extremity kinematics were recorded. Kinematics of the hip, knee and rearfoot at footstrike and peak were compared using intraclass correlation coefficients. Kinematic curves during stance phase were compared using the trend symmetry method within each subject. The overall average trend symmetry was high, 0.94 (1.0 is perfect symmetry) between running modes. The transverse plane and knee frontal plane exhibited lower similarity (0.86-0.90). Other than a 4.5 degree reduction in rearfoot dorsiflexion at footstrike during treadmill running, all differences were ≤1.5 degrees. 17/18 discrete variables exhibited modest correlations (>0.6) and 8/18 exhibited strong correlations (>0.8). In conclusion, overground and treadmill running kinematic curves were generally similar when averaged across subjects. Although some subjects exhibited differences in transverse plane curves, overall, treadmill running was representative of overground running for most subjects.     

The influence of body weight support on ankle mechanics during treadmill walking

The use of body weight support (BWS) systems during locomotor retraining has become routine in clinical settings. BWS alters load receptor feedback, however, and may alter the biomechanical role of the ankle plantarflexors, influencing gait. The purpose of this study was to characterize the biomechanical adaptations that occur as a result of a change in limb load (controlled indirectly through BWS) and gait speed during treadmill locomotion. Fifteen unimpaired participants underwent gait analysis with surface electromyography while walking on an instrumented dual-belt treadmill at seven different speeds (ranging from 0.4 to 1.6 m/s) and three BWS conditions (ranging from 0% to 40% BWS). While walking, spatiotemporal measures, anterior/posterior ground reaction forces, and ankle kinetics and muscle activity were measured and compared between conditions. At slower gait speeds, propulsive forces and ankle kinetics were unaffected by changing BWS; however, at gait speeds ≥approximately 0.8 m/s, an increase in BWS yielded reduced propulsive forces and diminished ankle plantarflexor moments and powers. Muscle activity remained unaltered by changing BWS across all gait speeds. The use of BWS could provide the advantage of faster walking speeds with the same push-off forces as required of a slower speed. While the use of BWS at slower speeds does not appear to detrimentally affect gait, it may be important to reduce BWS as participants progress with training, to encourage maximal push-off forces. The reduction in plantarflexor kinetics at higher speeds suggests that the use of BWS in higher functioning individuals may impair the ability to relearn walking.