The energy cost of walking or running on sand

Summary Oxygen uptake ( O₂) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3–7 km · h^–1) or running (7–14 km · h^–1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of O₂ to speed and expressed in J · kg^–1 · m^–1 assuming an energy equivalent of 20.9 J · ml O₂ ^–1. At the highest speedsC was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand,C increased linearly with speed from 3.1 J · kg^–1 · m^–1 at 3 km · h^–1 to 5.5 J · kg^–1 · m^–1 at 7 km · h^–1, whereas on a firm surfaceC attained a minimum of 2.3 J · kg^–1 · m^–1 at 4.5 km · h^–1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h^–1,C was about 1.8 times greater on sand than on compact terrain. When running on sandC was approximately independent of the speed, amounting to 5.3 J · kg^–1 · m^–1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand.     

The spring-mass model and the energy cost of treadmill running

During running, the behaviour of the support leg was studied by modelling the runner using an oscillating system composed of a spring (the leg) and of a mass (the body mass). This model was applied to eight middle-distance runners running on a level treadmill at a velocity corresponding to 90% of their maximal aerobic velocity [mean 5.10 (SD 0.33) m?·?s^?1]. Their energy cost of running (C _r ), was determined from the measurement of O₂ consumption. The work, the stiffness and the resonant frequency of both legs were computed from measurements performed with a kinematic arm. The C _r was significantly related to the stiffness (P?r?=??0.80) and the absolute difference between the resonant frequency and the step frequency (P?r?=?0.79) computed for the leg producing the highest positive work. Neither of these significant relationships were obtained when analysing data from the other leg probably because of the work asymmetry observed between legs. It was concluded that the spring-mass model is a good approach further to understand mechanisms underlying the interindividual differences in C _r .     

The energy cost of running increases with the distance covered

Summary The net energy cost of running per unit of body mass and distance (C_r, ml O₂·kg^–1·km^–1) was determined on ten amateur runners before and immediately after running 15, 32 or 42 km on an indoor track at a constant speed. The C_r was determined on a treadmill at the same speed and each run was performed twice. The average value of C_r, as determined before the runs, amounted to 174.9 ml O₂·kg^–1·km^–1 SD 13.7. After 15 km, C_r was not significantly different, whereas it had increased significantly after 32 or 42 km, the increase ranging from 0.20 to 0.31 ml O₂·kg^–1·km^–1 per km of distance (D). However, C_r before the runs decreased, albeit at a progressively smaller rate, with the number of trials (N), indicating an habituation effect (H) to treadmill running. The effects of D alone were determined assuming that C_r increased linearly with D, whereas H decreased exponentially with increasing N, i.e.C _r =C _r0+aD+He^–bN. The C_ro, the true energy cost of running in nonfatigued subjects accustomed to treadmill running, was assumed to be equal to the average value of C_r before the run for N equal to or greater than 7 (171.1 ml O₂·kg^–1·km^–1, SD 12.7;n = 30). A multiple regression of C_r on N and D in the form of the above equation showed firstly that Cr increased with the D covered by 0.123%·km^–1, SEM 0.006 (i.e. about 0.22 ml O₂·kg^–1·km^–1 per km,P<0.001); secondly, that in terms of energy consumption (obtained from oxygen consumption and the respiratory quotient), the increase of C_r with D was smaller, amounting on average to 0.08%·km^–1 (0.0029 J·kg^–1·m^–1,P<0.001) and thirdly that the effects of H amounted to about 16% of C_r0 for the first trial and became negligible after three to four trials.     

Assessment of middle-distance running performance in sub-elite young runners using energy cost of running

The purpose of this study was to assess the validity of v _amax as an indicator of middle-distance running performance in sub-elite young runners, _amax being defined as the quotient maximal oxygen uptake (V˙O _2max) divided by the net energy cost of running (C _r) on a treadmill at a submaximal running velocity (280?m?·?min^?1). The V˙O _2max, ventilatory threshold, _amax, and C _r were assessed in 39 young male sub-elite runners having only small variations in performance level. The relationship between each variable and running performance (at 1500?m, 3000?m, and 5000?m) was evaluated. A trend toward a negative correlation existed between C _r and performance although this was not significant. The V˙O _2max and _amax were significantly related to performance. The _amax accounted for around 50% of the variability in performance whereas other physiological variables selected in this study were responsible, at best, for approximately 39%. The results presented in this study suggested that _amax was a useful indicator of middle-distance running performance in sub-elite young runners with similar performance levels as well as in top elite athletes.     

The energy cost of walking and running with and without a backpack load

Summary The effect of a backpack load (20 kg) on oxygen consumption while walking and running at different speeds was investigated. Fifteen males walked and ran (with and without load) up a 5% sloped treadmill at 6.4, 7.2, 8.0, 9.6, and 11.2 km/h (4, 4.5, 5, 6, and 7 mph). While walking O₂ rose at a rate of 0.6 (l/min)/(km/h) and while running 0.3 (l/min)/(km/h). The mean oxygen consumption at the various speeds was 28.65, 33.78, 40.64, 46.84, 54.48 ml O₂/kg BW/min, respectively, for the whole group without load and 26.52, 32.26, 38.28, 44.26, 48.16, respectively, with load. The breaking point between walking and running was at about 8.2 km/h. Carrying the load increased O₂ at a constant rate, and induced a breaking point between walking and running at a significantly lower speed for the smaller subjects than for the more robust ones. The results indicate that for certain tasks involving endurance and heavy load carriage, people should be selected according to criteria which integrate aerobic capacity and anthropometrical features.     

Increase in energy cost of running at the end of a triathlon

The purpose of the present study was to verify the increase in energy cost of running at the end of a triathlon. A group 11 trained male subjects performed a triathlon (15-km swimming, 40-km cycling, 10-km running). At least 1 week later the subjects ran 10-km as a control at the same pace as the triathlon. Oxygen uptake ( O₂), ventilation ( _E) and heart rate (HR) were measured during both 10-km runs with a portable telemetry system. Blood samples were taken prior to the start of the triathlon and control run, after swimming, cycling, triathlon run and control run. Compared to the control values the results demonstrated that triathlon running elicited a significantly higher (P < 0.005) mean O₂ [51.2 (SEM 0.4) vs 47.8 (SEM 0.4) ml·min^–1·kg^–] _E [86 (SEM 4.2) vs 74 (SEM 5.3) l·min^–1], and HR [162 (SEM 2) vs 156 (SEM 1.9) beats·min^–1)]. The triathlon run induced a greater loss in body mass than the control run [2 (SEM 0.2) vs 0.6 (SEM 0.2) kg], and a greater decrease in plasma volume [14.4% (SEM 1.5) vs 6.7% (SEM 0.9)]. The lactate concentrations observed at the end of both 10-km runs did not differ [2.9 (SEM 0.2) vs 2.5 (SEM 0.2) m·mol·l^–1]. Plasma free fatty acids concentrations were higher (P < 0.01) after the triathlon than after the control run [1.53 (SEM 0.2) to 0.51 (SEM 0.07) mmol·l^–1]. Plasma creatine kinase concentrations rose under both conditions from 58 (SEM 12) to 112 (SEM 14) UI·l^–1 after the triathlon, and from 61 (SEM 7) to 80 (SEM 6) UI·l^–1 after the control run. This outdoor study of running economy at the end of an Olympic distance triathlon demonstrated a decrease in running efficiency.     

Influence of individual energy cost on running capacity in warm, humid environments

Purpose

Challenging environmental conditions including heat and humidity are associated with particular risks to the health of runners and triathletes during prolonged events. The heat production of a runner is the product of its energy cost of running (C _r) by its velocity. Since C _r varies greatly among humans, those individuals with high C _r are more exposed to heat stress in warm and humid conditions. Although risk factor awareness is crucial to the prevention of heat stroke and potential fatalities associated therewith, how C _r affects the highest sustainable velocity (V) at which maximal heat loss matches heat production has not been quantified to date.

Methods

Here, we computed in virtual runners weighting 45–75 kg, the influence of C _r variability from 3.8 to 4.4 J·m^?1·kg^?1 on V. Heat loss by radiation, convection, and conduction was assessed from known equations including body dimensions, running velocity (3.4–6.2 m·s^?1), air temperature (T _a, 10–35 °C) and relative humidity (r _h, 50, 70 and 90 %).

Results

We demonstrated a marked and almost linear influence of C _r on V in hot and humid conditions: +0.1 J·kg^?1·m^?1 in C _r corresponded to ?4 % in V. For instance, in conditions 25 °C r _h 70 %, 65-kg runners with low C _r could sustain a running speed of 5.7 m·s^?1 as compared to only 4.3 m·s^?1 in runners with high C _r, which is huge.

Conclusion

We conclude that prior knowledge of individual C _r in athletes exposed to somewhat warm and humid environments during prolonged running is one obvious recommendation for minimizing heat illness risk.     

Influence of training,sex, age and body mass on the energy cost of running

Summary To highlight the influences of age, sex, body mass (m _b) and running training on the energy cost of running (C _r) young basketball players [38 boys (BB) and 14 girls (BG), aged 14.2 (SD 0.3) and 12.2 (SD 1.9) years, respectively] were selected to be compared to middle-distance runners [27 men (MR) and 14 women (FR) aged 23.7 (SD 3.4) and 23.9 (SD 4.1) years, respectively]. TheC _r was measured during a maximal treadmill test. In each groupC _r and body mass (m _b) and body height were negatively and significantly correlated. A stepwise regression showed that among both the body dimensions measured,m _b was the most important factor in determining the variations ofC _r For the whole group (n=93) the correlation coefficient was 0.72 (P<0.0001). For a givenm _b, there was no significant difference between theC _r of BG, BB and MR: this result would support the hypothesis that the differences inC _r currently attributed to age, running training or sex differences are mainly related tom _b. On the other hand, for a givenm _b, FR showed a significantly lower Cr than the basketball players (P<0.01 for BG and BB) and than MR (P<0.05), thus suggesting that women decrease theirC _r as a response to running training more efficiently than do men.     

The energy cost of walking in children

Size, morphology and motor skills change dramatically during growth and this probably has an effect on the cost of locomotion. In this study, the effects of age and speed on the energy expended while walking were determined during growth. The rate of oxygen consumption and carbon dioxide production were measured in 3- to 12-year-old children and in adults while standing and walking at different speeds from 0.5 m x s(-1) to near their maximum aerobic walking speed. Standing energy expenditure rate decreases with age from 3.42 +/- 0.48 W x kg(-1) (mean +/- SD, n = 6) in the 3- to 4-year-olds to 1.95 +/- 0.22 W x kg(-1) (n = 6) in young adults. At all ages the gross cost of transport has a minimum which decreases from 5.9 J x kg(-1) x m(-1) in 3- to 4-year-olds to 3.6 J x kg(-1) x m(-1) after 10 years of age. The speed at which this minimum occurs increases from 1.2 m x s(-1) to 1.5 m x s(-1) over the same age range. At low and intermediate walking speeds the net cost of transport is similar in children and adults (about 2 J x kg(-1) x m(-1)). In young children walking at their highest speeds the net cost of transport is 70% (3- to 4-year-olds) to 40% (5- to 6-year-olds) greater than in adults.     

Mechanical energy states during running

Summary Changes in total mechanical work and its partitioning into different energy states (kinetic, potential and rotational) during a step cycle of running were investigated on six well trained athletes who ran at the test speeds of 40, 60, 80, and 100% (9.3±0.3 m/s) of maximum. Cinematographic techniques were utilized to calculate the mechanical energy states as described by Norman et al. (1976), using a 13 segment mechanical model of a runner as the basis for the computations. The data showed that both the kinetic and rotational energy increased parabolically but the potential energy decreased linearly with increases in running velocity. The calculated power of the positive work phase increased quadratically with running speed. During the phase when the runner was in contact with the ground, the applied calculations gave similar increases for the positive and negative works, and the power ratio (W _neg/W _pos) stayed the same at all measured speeds. Therefore, it is likely that the method used to calculate the various mechanical energy states did not reflect accurately enough the physiological energy costs at higher running speeds. It may, however, be quite acceptable for estimating the mechanical energy states during walking and slow running, in which case the role of negative work is less and consequently the storage and utilization of elastic energy is small.     

Influence of the oxygen uptake slow component on the aerobic energy cost of high-intensity submaximal treadmill running in humans

During high-intensity running, the oxygen uptake (V˙O₂) kinetics is characterised by a slow component which delays the attainment of the steady-state beyond the 3rd min of exercise. To assess if the aerobic energy cost of running measured at the 3rd min (C ₃) adequately reflects the variability of the true aerobic energy cost measured during the steady-state (C _ss), 13 highly-trained runners completed sessions of square-wave running at intensities above 80% maximal oxygen uptake (V˙O_2max) on a level treadmill. To evaluate the time at which the steady-state V˙O₂ was attained (t _ss), the V˙O₂ responses were described using a general double-exponential equation and t _ss was defined as the time at which V˙O₂ was less than 1% below the asymptotic value given by the model. All the subjects achieved a steady state for intensities equal to or greater than 92% V˙O_2max, and 8 out of 13 achieved it at 99% V˙O_2max. In all cases, t _ss was less than 13 min. For intensities greater than 85% V˙O_2max, C _ss was significantly higher than C ₃ and was positively related to %V˙O_2max (r= 0.44; P < 0.001) while C ₃ remained constant. The C ₃ only explained moderately the variability of C _ss (0.39 < r ² < 0.72, depending on the velocity or the (relative intensity at which the relationship was calculated). Moreover, the excess aerobic energy cost of running the (difference between C _ss and C ₃) was well predicted by age (0.90 < r ² < 0.93). Therefore, when the aerobic profile of runners is evaluated, it is recommended that their running efficiencies at velocities which reflect their race intensities should be determined, with V˙O₂ data being measured at the true steady-state.     

Therapeutic effects of exercise: wheel running reverses stress-induced interference with shuttle box escape

Exercise can reduce symptoms of depression and anxiety in humans, but therapeutic effects of exercise in an animal model of stress-related mood disorders have yet to be demonstrated. In the current study, the authors investigated the ability of wheel running to reverse a long-lasting interference with shuttle box escape produced by uncontrollable stress. Rats who remained sedentary following uncontrollable foot shock demonstrated robust conditioned freezing behavior to the stressor environment and deficits in shuttle box escape learning. Voluntary access to running wheels for 6 weeks, but not 2 weeks, following uncontrollable foot shock reduced the expression of conditioned freezing and reversed the escape deficit. Results demonstrate a long-lasting interference with shuttle box escape that can be reversed by exercise in a duration-dependent fashion.     

The energy cost of cycling in young obese women

In order to evaluate the difference in the energy cost of submaximal cycling between normal weight (NW) and obese (OB) females, nine OB (age 23.2 years±1.6 SE, BMI 40.4±1.2 kg/m²) and nine NW (age 25.6 years±1.8, BMI 21.7±0.6 kg/m²) healthy young women were studied during a graded bicycle ergometer test at 40, 60, 80, 100 and 120 W. At rest and at all workloads, oxygen uptake was higher in OB than in NW women (Student’s t test, P<0.05–0.01), as well as respiratory quotient during all exercise levels (P<0.05–0.01), while similar values of heart rate, pulmonary ventilation and breathing efficiency were found between the two groups. Maximal and anaerobic threshold were higher in OB women, and they also explained the higher oxygen pulse observed during submaximal exercise, but no difference was found when the values were adjusted for fat-free mass. While net mechanical efficiency (ME) was significantly lower in OB (ANOVA, P<0.05), delta ME was similar in both groups, indicating no substantial derangement of muscle intrinsic efficiency in obesity, but suggesting that the increased mass of body segments involved in cycling movements may be chiefly responsible for the higher energy cost of this type of exercise. Comparison of the actual presently measured with that predicted by available cycle ergometry equations at the different workloads indicated inaccuracy of various degrees ranging from 8.4 to −31.9%. It is concluded that the lower mechanical efficiency displayed by obese women in cycling has to be taken into account when prescribing exercise through methods predicting the metabolic load.     

Energy cost of running in similarly trained men and women

Summary The energy demand of running on a treadmill was studied in different groups of trained athletes of both sexes. We have not found any significant differences in the net energy cost (C) during running (expressed in J·kg⁻¹·m⁻¹) between similarly trained groups of men and women. For men and women respectively in adult middle distance runnersC=3.57±0.15 and 3.65±0.20, in adult long-distance runnersC=3.63±0.18 and 3.70±0.21, in adult canoeistsC=3.82±0.34 and 3.80±0.24, in young middle-distance runnersC=3.84±0.18 and 3.78±0.26 and in young long-distance runnersC=3.85±0.12 and 3.80±0.24. This similarity may be explained by the similar training states of both sexes, resulting from the intense training which did not differ in its relative intensity and frequency between the groups of men and women. A negative relationship was found between the energy cost of running and maximal oxygen uptake expressed relative to body weight (for menr=−0.471,p<0.001; for womenr=−0.589,p<0.001). In contrast, no significant relationship was found in either sex between the energy cost of running and . We conclude therefore that differences in sports performance between similarly trained men and women are related to differences in . The evaluation ofC as an additional characteristic during laboratory tests may help us to ascertain, along with other parameters, not only the effectiveness of the training procedure, but also to evaluate the technique performed.