# data[].attributes.body
The ground is frozen, so it very hard.
Is very bump, which needs the backpack to adjust to the changing landscape. Gokyo village is the only village 4750 meters high.
Snow and ice cover everything, making it slick and dangerous. Helecopter pad on Mount Everest. vegetation between ice and snow. Giant bridge
The lake has a beautiful green blue

# data[].attributes.body
Burg Adventures international.
This article tells us about what gear to expect and what is needed to being, on the trail or for
Base camp.
This article is helpful, becouse it tells us what gear we have to plan space for. It also lets us see how much extra storage we can have.

# data[].attributes.attachment_link.readable_text
Important User Information: Remote access to EBSCO's databases is permitted to patrons of subscribing institutions accessing from remote locations for personal, non-commercial use. However, remote access to EBSCO's databases from non-subscribing institutions is not allowed if the purpose of the use is for commercial gain through cost reduction or avoidance for a non-subscribing institution.

# data[].attributes.attachment_link.description
Important User Information: Remote access to EBSCO's databases is permitted to patrons of subscribing institutions accessing from remote locations for personal, non-commercial use. However, remote access to EBSCO's databases from non-subscribing institutions is not allowed if the purpose of the use is for commercial gain through cost reduction or avoidance for a non-subscribing institution.

# data[].attributes.body
Musk deer, and snow lepords

# data[].attributes.attachment_link.readable_text
Trekking season begins this month in the Himalayas, and visitors are sure to experience a common - if jaw-dropping - sight: local porters carrying towering loads on their backs, often supported by a strap over their foreheads.

Their packs are sometimes heavier than their bodies, says Norman Heglund, a muscle physiologist of Belgium's University de Louvain. Think: a 150-plus pound pack on a 125-pound man.

And the porters carry their cargo up and down mountains, day after day, year after year.

Trekkers often wonder how the porters manage such feats of strength and endurance. As a scientist, Heglund had the equipment and experience to find out.

In previous research, he had discovered some invisible tricks of bodily movement that Kikuyu women in Kenya use to carry heavy loads on their heads - altering their gait in subtle ways to conserve energy so they use fewer calories than a Westerner would given the same task. He expected to find similar results among porters, who he says, are "the ones who carry the biggest loads [proportional to body weight] under the worst conditions."

But when he and colleagues measured the movements of Nepalese porters, they reported in a recent study, they didn't find anything particularly special about how they walk.

They simply go. And they keep going.

"They haven't got any trick," Heglund says. "And what they do is pretty amazing."

For the study, he spent half a year in Nepal, where he set up a field site on a busy trade route in the Everest Valley.

The route starts in Jiri, at the end of the road from Kathmandu toward Mt. Everest. From there, professional porters regularly carry food and other goods over about 60 miles of steep terrain that takes more than a week each way and includes more than 26,200 vertical feet of ascents and more than 20,000 feet of descents. Their destination is a bustling marketplace in Namche.

About half a day's walk before Namche, Heglund and his team offered lemonade and cookies to any porter who would agree to get weighed and then filmed while walking over a 10-foot long platform made out of force plates that were placed on a flat stretch of ground. Electronic equipment and computers allowed the researchers to measure how much work went into each stride.

It was a popular offer that revealed just how hardcore the porters are. On average, the men carried nearly 90 percent of their body weight. A quarter of them carried more than 125 percent of their own weight, according to the new study, which appeared in the Journal of Experimental Biology. The heaviest load, Heglund says, totaled 175 percent - or nearly twice as much as the porter's weight. The porters in the study weighed between about 100 and 140 pounds.

The women carried an average of 70 percent of their weight - a good 10 percent more than the heaviest of loads carried by women in the African studies.

Compared to the muscles of European graduate students, the study found, the porters' muscles were slightly more efficient at turning oxygen into work. But there was nothing unusual about their gait or energy use.

That finding emphasizes just how remarkable the human body is, says David Carrier, a comparative biomechanist at the University of Utah in Salt Lake City, who was not involved with the study.

A physically fit American can comfortably carry a backpack loaded with 25 percent of his or her body weight, he says. But even people in good shape start to crack after a day or two in the mountains with twice that much weight on their backs.

Carrier suspects that Nepalese porters adapt over a lifetime of carrying loads, often beginning in childhood. And injuries appeared to be remarkably rare, Heglund found in his informal interviews, perhaps because the porters tend to move slowly. If they were running late for the Saturday morning market, he says, they would walk late into the night to get there in time. But they wouldn't ever go fast.

What all that load carrying does for the long-term health of porters wasn't addressed by the new study. Some recent research has found that compared to other Nepalese groups, porters have worse diets, lower rates of school attendance and higher risk of anemia. A variety of organizations now advocate for porter health, with some progress to report: guidelines now recommend a 66-pound limit for porters who work for the tourism industry, Heglund says. Still lacking are regulations for porters who do commercial work.

The new results are unlikely to provide much in the way of advice for Westerners who want to carry more weight without paying a price, Carrier says. Without a lifetime of practice, we might just be permanently soft.

"What these porters are doing, from our perspective, is sort of unimaginable," he says, even for athletes. "In Western society, we no longer have a real handle on what humans can do physically because we're so far removed from this level of daily work that we physically can't do it anymore."
Emily Sohn is a freelance journalist in Minneapolis who writes regularly about health and science for Nature, the Washington Post,bioGraphic, Hakai and others. More at www.tidepoolsinc.com. On Twitter: @tidepoolsinc

# data[].attributes.attachment_link.title
How Does A Nepalese Porter Carry So Much Weight?

# data[].attributes.attachment_link.description
Trekking season begins this month in the Himalayas, and visitors are sure to experience a common - if jaw-dropping - sight: local porters carrying towering loads on their backs, often supported by a strap over their foreheads. Their packs are sometimes heavier than their bodies, says Norman Heglund, a muscle physiologist of Belgium's University de Louvain.

# data[].attributes.body
Average temperature of mount Everest recorded -19° C. in the summer and -36° C. you can check Mount Everest base camp weather forecast to know the day to day fact. Lowest temperature can reach as low as -40 degrees Celsius

# data[].attributes.attachment_link.readable_text
List of symbols and abbreviations

COM

centre of mass of the whole system (body plus load)

DC

double contact (phase of walking)

energy of the COM relative to the surroundings

internal energy of the lower limbs (+W int,dc)

kinetic energy change of the lower limbs relative to the COM

kinetic energy change of the load relative to the COM

kinetic energy change of the trunk relative to the COM

kinetic energy change of the upper limbs relative to the COM

forward kinetic energy of the COM relative to the surroundings

vertical kinetic energy of the COM relative to the surroundings

gravitational potential energy of the COM relative to the surroundings

step frequency

body mass

total mass (M b+load)

R

recovery of energy due to the pendulum-like transfer of energy of the COM

work done by the back leg during double contact

work done to raise and accelerate the COM relative to the surroundings

work done by the front leg during double contact

work done to accelerate the body segments relative to the COM

work done by one leg against the other during double contact

work done to accelerate the body segments relative to the COM

work done due to the movements of the lower limbs relative to the COM

work done due to the movements of the load relative to the COM

work done due to the movements of the trunk relative to the COM

work done due to the movements of the upper limbs relative to the COM

work done to accelerate forward the COM relative to the surroundings

total positive muscle-tendon work done to maintain locomotion

work done to raise the COM relative to the surroundings

θ

maximal knee flexion during weight acceptance

Positive external work

W ext was calculated as the sum of the increments in the energy-time curve of the COM ( E ext). The methods used to compute the external work are described in detail in Cavagna (1975) and Willems et al. (1995) and will only be summarized here.

The mechanical energy changes of the COM due to its motion in the sagittal plane during a walking stride were determined from the vertical and horizontal components of the ground reaction forces. The mechanical energy changes due to the lateral movements of the COM are small in adults ( Cavagna et al., 1963; Tesio et al., 1998) and were neglected here.

The ground reaction forces were measured by means of a force platform (3 m long and 0.4 m wide) mounted at ground level. The force platform comprised five separate plates, conceptually similar to those described by Heglund (1981). The plates were sensitive to forces in the fore-aft and vertical directions, and had a natural frequency of 250 Hz and a linear response to within 1% of the measured value for forces up to 3000 N. The individual signals from the four bi-axial transducers in each of the plates were digitalized by a 12-bit analog-to-digital converter every 5 ms and processed by means of a personal computer.

A complete stride was selected for analysis only when the subject walked at a relatively constant average height and speed. Specifically, the sum of the increments in both the forward and vertical velocity of the COM could not differ by more than 25% from the sum of the decrements ( Cavagna et al., 1977). According to these criteria, the average difference in the forward velocity of the COM at the beginning and at the end of the selected stride was 0.2±4.0% (mean±s.d., n=1651) of the average walking speed during the stride, and the mean vertical force during the selected stride differed from M b plus any load the subject may be carrying by 0.1±0.8%.

The integration of the vertical and forward components of the force/mass ratio yields the vertical and forward velocity changes of the COM, from which the kinetic energy ( E kv and E kf) can be calculated after evaluation of the integration constants ( Cavagna, 1975; Willems et al., 1995). Integration of the vertical velocity yields the vertical displacement of the COM, from which the gravitational-potential energy ( E p) can be calculated.

The total mechanical energy of the COM at any instant ( E ext) is the sum of E p+ E kv and E kf ( Fig. 1). The sum of the increments in the E ext curve represents the positive W ext done to maintain the movements of the COM relative to the surroundings. Similarly, the positive work done to accelerate the COM forwards ( W kf) is the sum of the increments in the E kf versus time curve, and the positive work done to move the COM against gravity ( W v) is the sum of the increments in the E p+ E kv versus time curve. In order to reduce the effect of noise, the increments in mechanical energy were considered to represent positive work actually done by the muscles and tendons only if the time between two successive maxima was greater than 20 ms.

Walking can be compared to an inverted pendulum in which the potential energy of the COM is transformed into kinetic energy and vice versa ( Cavagna et al., 1976). The energy recovered through the pendulum-like mechanism ( R) is calculated as: (1) where W kf is the positive work due to the velocity changes of the COM in the fore-aft direction, W v is the positive work due to its vertical movements and W ext is the positive external work.

Positive kinetic internal work

The kinetic internal work ( W int,k) is the positive work done to sustain the translational and rotational kinetic energy changes of the body and load segments due to their movements relative to the COM. The method used here is similar to the one used in Willems et al. (1995), which was derived from Cavagna and Kaneko (1977). Consequently, the method is only described briefly here.

W int,k was computed from the movements of the body segments by cinematography. The body was divided into 10 rigid segments: head/neck/trunk, load, two thighs, two 'shank+foot' segments, two upper arms and two 'forearm+hand' segments. Each segment of the right side of the subject is delimited by markers placed at the chin-neck intersection, the great trochanter, the lateral condyle of the femur, the lateral malleolus, the glenohumeral joint, the lateral condyle of the humerus, the dorsal wrist and on the load. The subjects were filmed by a single video camera (PAL, 50 Hz), 6 m lateral and normal to the axis of progression on the force platform. The images were synchronized to the stride selected for the W ext measurements by superimposing the heel strike on the force records to the corresponding frame of the film.

A 'stick man' of the right side of the body was constructed numerically each frame. The left side of the body was reconstructed from the right side data on the assumption that the movements of the segments of left side were equal and 180 deg out of phase with the measurements of the right side. The position of the centre of mass and the moment of inertia of the body segments were calculated using the anthropometric tables of Dempster and Gaughran (1967).

The position of the centre of mass and the moment of inertia of the 'load segment' were calculated by assimilating the load into a cone frustum and assuming that the load in the backpack/basket was homogeneously distributed. The dimensions of the frustum, the load mass and the moment of inertia were calculated for each individual load.

The angular velocity of each segment and the translational velocity of its centre of mass relative to the COM were calculated from the derivative of their position versus time relationship in order to compute the kinetic energy of each segment, i.e. the load , the trunk , the upper limbs and the lower limbs ( Fig. 1).

The kinetic energy versus time curves of the segments within a limb were summed. The positive internal work due to the movements of the limb was then calculated by adding the positive increments in its kinetic energy versus time curve. In order to minimize errors due to noise, the increments in kinetic energy were considered to represent positive work actually done only if the time between two successive maxima was greater than 10-80 ms, depending upon the walking speed. This process was used to compute the internal work of the load , the trunk , the upper limbs and the lower limbs . Then W int,k was computed as the sum of , , and . This procedure allowed energy transfers to occur between the segments of the same limb, but disallowed any energy transfers between the different limbs or the trunk or the load ( Willems et al., 1995; Schepens et al., 2004).

Positive internal work done by one leg against the other

The methods used to compute the internal work done by one leg against the other during the period of double contact ( W int,dc) are the same as in Bastien et al. (2003), and are presented only briefly here.

In walking, during the DC phase when both feet are on the ground, positive work is done by the back leg pushing forwards while negative work is done by the front leg pushing backwards. The positive work done by the ground reaction forces was calculated independently for the back ( W back) and the front ( W front) limb from the time-integral of the power curves taking into account energy transfers, as explained in detail in Bastien et al. (2003). In order to count only the work that is not already measured in W ext, the positive muscular work realized by one leg against the other ( W int,dc) during the DC phase ( Fig. 1) was evaluated by: (2) W int,dc was measured on a single DC phase of the stride and the results obtained were doubled to obtain the W int,dc for the whole stride ( Bastien et al., 2003).

Total positive muscular work

The total work done ( W tot) during walking is the sum of the external and internal work. However, some energy transfers must be taken into account in order to avoid counting the same work twice. W tot is best evaluated when no transfers of energy are allowed between the energy of the COM and the kinetic energy of each segment ( Willems et al., 1995). Schepens et al. (2004) discussed the possible energy transfers between and W int,dc and concluded that both curves should be added instant-by-instant. The sum of the increments of the resulting curve ( Fig. 1) represents the internal work done on a lower limb ().

Consequently W tot was computed as: (3)

Calculation of the muscular efficiency

The muscular efficiency was calculated as the ratio of the mechanical power to the net metabolic power. More precisely, the equations for efficiency were computed from the equations of mass-specific total average power (computed as the total mass-specific work done each stride divided by the stride period, in W kg −1) and the net mass-specific energy consumption rate (in W kg −1) measured on the same subjects ( Bastien et al., 2005a).

Subjects and experimental procedure

Experiments were conducted at Phakding (altitude 2800 m in the Mt Everest valley), in the Solo-Khumbu region of Nepal. Experiments were carried out on 21 Nepalese porters (from the Rai, Sherpa or Tamang ethnic groups) and three European control subjects. All Nepalese subjects carried loads in a wicker basket (doko) supported only by a strap (naamlo) looped over their head ( Bastien et al., 2005a). All control subjects carried loads in typical trekker's backpacks with shoulder and hip support. The experiments involved little discomfort, were performed according to the Declaration of Helsinki, and were approved by the local ethics committees (the Nepal Health Research Council in Kathmandu, and the Commission d'éthique Hospitalo-Facultaire de l'Université catholique de Louvain). Informed written consent was obtained for all subjects.

The kinetic internal work was measured simultaneously with the external work in the 11 Nepalese porters and three European adults at speeds ranging from 0.38 to 2.02 m s −1 with loads ranging from 0 up to 127% M b. A total of 1620 strides were analyzed. An additional 10 porters were also included in the external work measurements while walking slowly or fast, unloaded or carrying their own load (114% M b on average). Table 1 summarizes the subject groups and their physical characteristics.

The control data collected in the present study (three subjects) are in agreement with previously published external work data ( Heglund et al., 1995) on 12 European adults carrying backpack loads ( P=0.528, F=0.398, three-way ANOVA, with W ext in J kg −1 m −1 as the dependent variable, over a speed range of 1.0-1.5 m s −1 and a load range of 0-45% M b). Unfortunately, because the load and speed ranges/classes used in Heglund et al. (1995) are more restrained and different from those used in the present study, the control data from both studies could not be satisfactorily combined.

Statistics

Statistical analyses were performed using SuperAnova (v1.11, Abacus Concepts). The type of statistical tests and results are given in the text as needed.

External mechanical work

The recovery of mechanical energy ( R) and the mass-specific external work per unit distance ( W ext, in J kg −1 m −1) during walking at different speeds under different loading conditions are shown in Fig. 2. R is independent of load for all subjects, and attains a maximum of approximately 65% at a speed of 1.1 m s −1 for the Nepalese porters and 1.4 m s −1 for the control subjects. At high speeds (≥1.4 m s −1), the average R is ∼30% smaller in the Nepalese porters carrying heavy loads (≥100% M b) than in the control subjects. Although there is no evident explanation for the reduction in the average R in the Western subjects, the smaller average R in Nepalese porters is due to a drastic decrease in R for a few Nepalese subjects who clearly show a modification of their walking gait at this extreme load-speed combination. These few porters no longer use a classic walking gait; however, their gait can not be classified as running, as R is >10% and there is no aerial phase ( Cavagna et al., 1991). In contrast, at low speed (0.5 m s −1), the average R is smaller in the control subjects carrying light loads than in Nepalese porters.

The mass-specific external work per unit distance W ext is independent of load at any given speed in both the Nepalese and control subjects ( Fig. 2). This is to be expected because both E p+ E kv and E kf are proportional to the total mass and R does not change with load. The external work in J m −1 must therefore increase in proportion to the added mass, and, when normalized per unit of total mass, W ext must be independent of load at any speed ( Fig. 2). Whatever the load carried, W ext is at a minimum at 0.8 m s −1 for the Nepali porters and at 1.1 m s −1 for control subjects. At lower and higher speeds, W ext increases ( Fig. 2).

Internal mechanical work

The internal work as measured in this study includes the work done to accelerate the body and load segments relative to the COM and the work done by one leg against the other during the DC phase of walking. The mass-specific internal work done per unit distance to move the segments relative to the COM ( W int,k, in J kg −1 m −1) is shown in Fig. 2. The kinetic internal work of the trunk, load and upper limbs segments represents less than 0.05 J kg −1 m −1 at any speed and load because their rotational and translational movements relative to the COM are small. On the contrary, the kinetic internal work due to the lower limbs accounts for almost all the total kinetic internal work. W int,k increases rapidly with walking speed, but at any given speed decreases with increasing load. For example, when walking unloaded in both subject groups, W int,k increases from 0.1 to 0.4 J kg −1 m −1 when speed increases from 0.5 to 1.7 m s −1. However, when walking at 1.4 m s −1, W int,k decreases from 0.3 to 0.2 J kg −1 m −1 when load increases from 0 to 100% M b.

At all speed-load combinations, Nepalese porters and control subjects do not show major differences in kinetic internal work. However, the mean W int,k values for the Nepalese porters tend to be slightly above those of control subjects, particularly at the highest speeds. The latter can be explained by a somewhat higher step frequency at all speeds (particularly the highest speeds) in the Nepalese porters ( Fig. 2). Furthermore, in the control subjects, the step frequency is nearly independent of load at all speeds while, for the Nepalese porters, it tends to increase very smoothly as a function of the load at each walking speed. This results in W int,k for the Nepalese porters being clearly above those of control subjects for heavy loads and high walking speeds.

The work done by one leg against the other during the DC phase ( W int,dc, J kg −1 m −1) is close to zero at low speed during unloaded walking, increasing to its maximum at intermediate speed and decreasing again at higher speeds ( Fig. 2). Furthermore, for speeds <1.4 m s −1, W int,dc increases as a function of load whereas at higher speeds it is relatively independent of load. At low speeds, Nepalese porters present a higher W int,dc as compared with control subjects. Above 1.1 m s −1, it decreases more rapidly with speed for the Nepalese porters, thus ending up with lower W int,dc values than control subjects at high walking speeds ( Fig. 2).

As explained in detail in Schepens et al. (2004), energy transfers can occur between W int,dc and , meaning that the internal work is not simply the sum of W int,k and W int,dc. Nevertheless, W int,dc can represent a large fraction of the total internal work (up to ∼52% in Nepalese porters) at intermediate walking speeds while carrying heavy loads (see comparison between W int and W int,k in Fig. 2). When the calculation of internal work accounts for the positive work done to accelerate the segments relative to the COM ( W int,k) and for the positive work done by the back leg against the front leg during the DC phase ( W int,dc), then our results ( Fig. 2) show that in load carrying: (1) the mass-specific internal work ( W int) is approximately equivalent for the Nepalese porters and the control subjects; and (2) W int increases with increasing walking speed but differently according to the loading condition because (3) W int is independent of load for walking speeds up to 1.1 m s −1 but (4) W int decreases markedly as a function of the load at higher speeds.

Total mechanical work

The mass-specific total work per unit distance W tot (J kg −1 m −1) is the sum of the external and internal work. Both W ext and W int are independent of load at speeds up to 1.1 m s −1; therefore, W tot is also independent of the increasing total mass at these walking speeds ( Fig. 2). On the contrary, at speeds ≥1.1 m s −1, although W ext remains constant, W int decreases with increasing load; therefore, W tot also decreases with the increasing total mass at these walking speeds ( Fig. 2). The differences observed between the external or internal work of Nepalese porters and of control subjects tend to cancel when both W ext and W int are summed; the total mechanical work during load carrying, W tot, is equivalent for all subjects at any load-speed combination.

Muscular efficiency of load carrying

For the Nepalese porters, the muscular efficiency is nearly independent of load, showing a slight increase with speed ( Fig. 3). This efficiency tends to increase slightly with speed also in the control subjects, although it decreases asymptotically with load. Consequently, the Nepalese porters tend to have a lower efficiency than the control subjects when carrying light loads, and a higher efficiency when carrying heavy loads. For example at 0.8 m s −1, the controls are more efficient with loads <35% M b, but the Nepalese porters are more efficient with heavier loads. The Nepalese porters, within the limits of the speeds/loads studied, show a muscular efficiency between 0.15 and 0.3 and the control subjects between 0.15 and 0.4.

Kinetic internal work in load carrying

When carrying a load, the kinetic internal work ( W int,k) could be modified by changes in the step frequency and/or the trajectory of the limb segments. The study on African women ( Maloiy et al., 1986) showed that, for walking between 0.8 to 1.7 m s −1, the step frequency was unaffected by load. The authors assumed, therefore, that the energy requirements for moving the legs and arms relative to the COM would remain the same in unloaded and loaded walking. The factors that influence W int,k during load carrying are discussed below.

Step frequency

Compared with controls at the same load and speed, Nepalese porters show higher step frequencies, most likely because of their small stature and shorter legs ( Table 1). Our data show that the step frequency increases with load at a given walking speed for both control subjects and Nepalese porters (respectively, P<0.001, F=7.89 and P<0.001, F=24.21, two-way ANOVA), even though this increase is small compared with unloaded walking (e.g. at 1.1 m s −1, +6% with a 75% M b load for controls, and +7% with a 150% M b load for Nepalese porters; Fig. 2). These results are in agreement with the studies of Martin and Nelson (1986) and LaFiandra et al. (2003).

In unloaded walking, the pelvis and the shoulders counter-rotate in the horizontal plane, particularly at high walking speed. However, in load carrying, the moment of inertia of the upper body is increased by the load, as suggested by LaFiandra et al. (2003). Probably to avoid excessive torques and unbalance, subjects clearly decrease both pelvic and thoracic rotations when carrying loads ( LaFiandra et al., 2002). Because decreasing pelvic rotation decreases step length, it is not surprising to find a slight increase in step frequency at a given speed with increasing load.

The differences in step frequency observed between Nepalese porters and controls could explain the differences in the kinetic internal work between the two groups. At speeds above 1.1 m s −1, Nepalese porters and controls have equivalent W int,k values when no load is carried, but as load increases the W int,k diverges between the groups because of a more pronounced increase in step frequency due to loading in Nepalese porters ( Fig. 2).

Trunk inclination and movement

When carrying loads, the trunk inclination changes in order to keep the COM over the centre of support on the ground. In our control subjects, the trunk inclination increases up to ∼45 deg for 75% M b loads. To a lesser extent, this was also observed in backpack load carriage by Martin and Nelson (1986) and Kinoshita (1985). Nepalese porters also increase the trunk inclination, reaching a plateau of ∼40 deg for loads greater than 75% M b.

The rotational movement of the trunk in the sagittal plane during the walking stride does not change significantly with load and is equivalent for controls and Nepalese porters (3.50±1.05 and 3.56±1.15 deg for the two groups, respectively). Therefore, the work required to move the trunk () relative to the COM is small in load carrying as well as in unloaded walking. For example, at 1.1 m s −1, with loads of 0-75% M b, represents less than 4% of the kinetic internal work in Nepalese porters as well as in controls.

Lower limb movements

During the initial weight-bearing phase of the walking stride, the knee joint flexes, absorbing the shock during heel strike. In unloaded walking, it has been shown that this flexion increases with walking speed ( Perry et al., 1977; Holt et al., 2003). In load carrying, Kinoshita (1985) reported a decrease in knee angle during the initial weight-bearing phase due to loads as small as 20% M b, although no angle values were reported in the study. On the contrary, Ghori and Luckwill (1985) and Holt et al. (2003) did not report any change in knee flexion during the stance phase while carrying loads up to 50% M b.

Because modifications of the walking gait pattern may result in an increase or decrease in mechanical work performed, the knee flexion as a function of both speed and load was evaluated using the present data. The maximal knee flexion during weight acceptance (θ) was measured as the difference between the knee angle at heel strike and at the moment of maximal flexion at mid-stance. We found that, under any loading condition, θ clearly increases with speed by approximately 15 deg over the 0.5-1.7 m s −1 speed range studied ( P<0.0001, F=86.82 and P<0.0001, F=29.61; two-way ANOVA for the Nepalese porters and controls, respectively). For example, in the unloaded condition, θ is approximately 5 deg at the slowest walking speeds and 20-25 deg at the fastest speeds. Furthermore, for a given walking speed, θ increases significantly with load ( P<0.0001, F=5.61 and P<0.0001, F=6.77; two-way ANOVA for the Nepalese porters and controls, respectively). However, for any load-speed combination, θ is always less than 30 deg, and the extra knee flexion due to load is less than 10 deg. The knee flexion at weight acceptance due to increased loading has, in fact, no clear effect on the lower limb kinetic internal work () and thus on W int,k, because the flexion is modest and occurs when the displacement of the lower limb relative to the COM is slow.

The upper limb and load movements

During unloaded walking, tends to increase with the speed of progression, and accounts for up to ∼18% of W int,k at the highest walking speed. However, when carrying loads above 15% M b, Nepalese porters and control subjects generally have little arm movement relative to the COM because they usually grasp straps attached to the load, and as a consequence, is nearly zero (∼1% of W int,k) at any walking speed.

The internal work done to move the load relative to the COM (, in J kg −1 m −1) is similar in the porters and the control subjects at the same load and speed. For example, represents on average ∼5% of W int,k for controls and ∼6% for Nepalese porters when they carry a load of 75% M b.

Internal work during double contact

The internal work done during the DC phase ( W int,dc) was measured during load carrying for the first time in the present study. Clearly, W int,dc is not negligible particularly at intermediate walking speeds with heavy loads ( Fig. 2). In such conditions and even though all energy transfers are taken into consideration (as explained in the Materials and methods), W int,dc accounts for up to 50% of the total internal work and up to 25% of the total mechanical work done. During load carrying at constant speed, the forward component of the ground reaction forces under each foot increases simply because the total mass increases. As a consequence, if no other influencing factor changes with load, the work done by one foot against the other during the DC phase can be expected to be proportional to the load and thus to be independent of load when normalized per unit mass (J kg −1). Nevertheless, the mass-specific W int,dc per unit distance (J kg −1 m −1) tends to slightly increase with increasing load at speeds <1.4 m s −1, whereas it is independent of load at the highest speeds. The slight increase in W int,dc with load can be explained at least partially by the increase in step frequency (compensating the decrease in step length as explained previously) while the DC phase duration remains unchanged.

As mentioned by Bastien et al. (2003), other factors may also lead to more work being done by one leg against the other, as, for example, the timing of the peak of the forward component of the ground reaction force acting upon the back leg. For instance, that peak is delayed with increasing load, thereby increasing the opportunity to do more W int,dc. Also, the inclined posture accompanying the backpack load carriage may result in more forward-oriented ground reaction force vectors under each foot, as suggested by Kinoshita (1985), and thereby may affect W int,dc. It is worth noting that when W int,dc is taken into account, W int (in J kg −1 m −1) is independent of load for speeds up to 1.1 m s −1; meaning that at low walking speeds, the internal mechanical work done clearly increases in proportion to the load ( Fig. 2). So, the idea that the Nepalese porters might be able to limit this futile work done during the DC phase in order to 'save' some mechanical work during load carrying is not supported.

Total mechanical work

As discussed previously, our results do not show any mechanical work saving strategy during load carrying in Nepalese porters. As for control subjects, they are unable to minimize either external work or internal work at any speed between 0.5 and 1.7 m s −1. Consequently, at a given load and speed, the total mechanical work ( W tot) is equivalent for Nepalese porters and control subjects. As in unloaded walking, W tot (in J kg −1 m −1) in load carrying increases with the speed almost linearly within the 0.8-1.7 m s −1 range, but also tends to increase again at the very lowest speeds. For speeds <1.4 m s −1, W ext and W int are independent of load, thereby W tot is also independent of load, meaning that the total mechanical work done to move 1 kg of body mass or load mass over 1 m is the same whatever the load carried. For speeds ≥1.4 m s −1, W ext is independent of load but W int decreases with speed, thus W tot also decreases with load, meaning that at these speeds more mechanical work is done to move 1 kg of body mass over 1 m than to move 1 kg of load.

Muscular efficiency

At all walking speeds, the muscular efficiency of load carrying is independent of load in the Nepalese porters and decreases with load in the control subjects ( Fig. 3). Consequently, for small loads, control subjects are more efficient, whereas for loads ≥35% M b, Nepalese porters tend to be more efficient. This is due to the fact that (1) the total mechanical work (in J kg −1 m −1) in loaded walking is similar for both groups, and (2) the Nepalese porters have a smaller metabolic cost of carrying 1 kg of load over a distance of 1 m (see fig. 1B in Bastien et al., 2005a).

Our results have been echoed by the on-field load-carrying measurements of Minetti et al. (2006) in the Khumbu valley in Nepal. They highlighted the higher efficiency of the Nepalese porters compared with trained Caucasian mountaineers during both uphill and downhill loaded walking. Our measurements suggest that Nepalese porters are particularly optimized (i.e. the most efficient) when walking slowly with heavy loads; and in fact this speed-load combination is the only one they use. For example, when porters were behind schedule for arriving at the market place, they would consistently walk for longer times, often into the middle of the night, but never at higher speeds.

In conclusion, Nepalese porters accomplish their impressive load carrying without any apparent mechanically determined tricks. Hauling loads roughly equivalent to body mass up 8000 m and down 6300 m in about a week is, by Western standards, an unimaginable feat. The Nepalese porters do the same amount of total mechanical work as control Western subjects when walking at 0.5-1.7 m s −1 while carrying loads ranging from 0 to 120% of body mass. Owing to our experimental design, we can conclude that the Nepalese porters' better economy during load carrying is not related to a reduction in the work to displace the COM, nor in the work to displace the body segments including the trunk and the load, nor in the work done during the DC phase. It seems that the Nepalese porters are optimized for walking slowly with heavy loads. At that speed-load combination, their muscular efficiency is higher than that of the control subjects because they perform approximately the same mechanical work but at a lower net metabolic cost. One of the remaining explanations is that Nepalese porters have developed a skill in minimizing co-contractions to reduce the metabolic cost, without mentioning their high metabolic capacity, thanks to their training, anatomy and adaptation to high altitude. Moreover, the strategy of short intense exercise periods followed by frequent rest periods allows them to work at a high intensity level, spread out over many hours each day.

View Abstract

# data[].attributes.attachment_link.title
The mechanics of head-supported load carriage by Nepalese porters

# data[].attributes.attachment_link.description
In the Everest valley of Nepal, because of the rugged mountain terrain, roads are nothing more than dirt paths and all material must be conveyed on foot. The Nepalese porters routinely carry head-supported loads, which often exceed their body mass, over long distances up and down the steep mountain footpaths.

# data[].attributes.body
They carry 90% of their body wight in there backpacks unlike others

# data[].attributes.body
Anders, M "Backpack Basics." Boys Life

# data[].attributes.body
This articulate is important to us when it tells us that the inter and outer framing and that inner is better for the cold

# data[].attributes.attachment_link.title
Climb Mt. Everest with Berg Adventures: Gear List

# data[].attributes.attachment_link.description
Gearlist for Berg Adventures International expedition to climb Mt. Everest, the world's highest peak. Led by 4 time Everest summitter Wally Berg, founder of Berg Adventures International

# data[].attributes.body
The M.esplorer was design to specifically to solve one of the main problems Mt. Everest Sherpas'  face every day, there lack of Acsees ability, and Duribiliyt. Porters, The sherpas that carry loads,  have to lug around 90 to 120% Of their body weight while climbing, so this is extremely important.This is due to the many built in features of these backpacks. It's tight nite fabrics provides solid, and waterproof protection to last a lifetime. The M.Explorer 3000 has a built in insulated food pack, to provide food that is warm and easy to reach, for your conveyances.This design is for the preference for each daring explorer, allowing what you need where you need it. Along with a solid base to last many excursions. The M.Explorer 3000 has been design so It can Acclimatize each climb and excursion. The M.Exsplorer3000 has been striped of those heavy and stiff zippers, instead replacing it with a series of drawstrings and magnets for a better and tighter fit that is reliable and easy to use. Making you feel sturdy and prepared wherever you go. Whether you're A Messner, Climber without oxygen, or climb normally, the M.explorer 3000 is ideal for you.

# data[].attributes.body
The M.explorer3000 also has movable dividers, so you can keep your gear, your way. This design is for the preference for each daring exsplorer, allowing what you need where you want it. It has a kenetic battery that powers

# data[].attributes.body
pattern

# data[].attributes.body
Fix spelling!