اثرات ارگونومیک حمل بار بر هزینه انرژی راه رفتن شیب
|کد مقاله||سال انتشار||تعداد صفحات مقاله انگلیسی||ترجمه فارسی|
|6639||2008||6 صفحه PDF||سفارش دهید|
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Applied Ergonomics, Volume 39, Issue 2, March 2008, Pages 144–149
We examined the effects of load on the energy cost of walking (Cw), being defined as the ratio of the 2-min steady-state oxygen consumption to the speed, and economical speed (ES) during level and gradient walking. Ten men walked on a treadmill at various speeds with and without a load on their back at 0% and ±5% gradients. Significantly lower Cw values were observed only when the load was carried on the back during level walking at slower speeds. The ES was significantly decreased by less than 5% when the load was carried on the back. Significant gradient differences were also observed in the ES in the load and no load conditions. These results would be applicable to a wider range of occupational and leisure tasks
Recent studies revealed that the energy expenditure during walking with load does not always increase linearly as a function of the carrying weight (Abe et al., 2004; Stuempfle et al., 2004). Charteris et al., 1989a and Charteris et al., 1989b and Maloiy et al. (1986) have proposed a ‘free-ride’ hypothesis that the energy expenditure during walking with load carried on the head does not necessarily increase in African women if the load is less than 20% of their body mass. Recently, a similar phenomenon to the free-ride was also found in Nepalese porters ( Bastien et al., 2005a and Bastien et al., 2005b). In relation to such an energy-saving phenomenon during walking with load, it was worth noting that the load was always carried on the upper part of the body, such as on the head (Bastien et al., 2005a; Charteris et al., 1989a and Charteris et al., 1989b; Maloiy et al., 1986) and on the back (Abe et al., 2004; Stuempfle et al., 2004). Another point in common in previous studies was the fact that such a phenomenon was observed at slower walking speeds only. Thus, Abe et al. (2004) pointed out that a similar phenomenon to the free-ride could be found only when the load was carried on the back at slower walking speeds, and further suggested that an interaction between the rotative torque functioning around the center of body mass and an excessive burden on the lower leg muscles comprehensively affected the energetics of walking (Fig. 1). If a similar phenomenon to the free-ride can be found not only during level walking but also during gradient walking, then the practical benefit will be applicable to a wider range of occupational and leisure tasks. Indeed, as recently discussed by Bastien et al. (2005b), the argument with regard to the energetics of gradient walking with load is still open. We hereby hypothesized that a phenomenon similar to the free-ride could be found not only during level walking but also during gradient walking, because the possible explanation for a similar phenomenon to the free-ride proposed by Abe et al. (2004) appeared to be independent of the gradient of the terrain. The first purpose of this study was to examine whether a similar phenomenon to the free-ride would be found not only during level walking but also during gradient walking. It has been reported that there exists a specific walking speed that can minimize the metabolic energy cost of walking per unit distance (Cw: ml/kg/m) in each person (Saibene and Minetti, 2003). The walking speed corresponding to the minimum energy cost per unit distance has been called the economical speed (ES) or optimal speed (Falola et al., 2000). With reference to the ergonomic implications, considerations of ES seems to be significant for an establishment of workers’ safety and for a reduction of workers’ physical stress, however, as far as we know, no information has been available with respect to the alteration of the ES between level and gradient walking with load. It was interesting to note that the ES was significantly decreased if the load was carried on the back on a flat terrain (Falola et al., 2000), but was not decreased in another study (Bastien et al., 2005b). In a previous study the energy cost of walking reached minimum at a −10% gradient (Margaria, 1938). Minetti et al. (2003) indicated that the ES decreased as a function of positive gradient, but the load was not carried in those previous studies. Here, it was also hypothesized that the ES obtained from each gradient would be slower in the load condition than in the no load condition. However, it was assumed that the percentage decrease in the ES during level and gradient walking with load would not be great so much when compared to the ‘15%’ load of the subjects’ body mass, if a similar phenomenon to the free-ride appeared not only during level walking but also during gradient walking with load. Therefore, the second purpose of this study was to examine the effects of load carriage on the ES during level and gradient walking.
نتیجه گیری انگلیسی
A similar phenomenon to the free-ride could be observed only when the load was carried on the back during level walking at slower speeds. The ES was significantly decreased by less than 5% when the load was carried on the back. Those results would be induced by different mechanisms, but the information about the alteration of the ES during gradient walking with load will be useful for the outdoor work management.