The Metabolic Cost of Overground and Treadmill Walking in Healthy Young and Older Adults
Authors:   , Das Gupta Sauvik 
Published: March 2023

The Metabolic Cost of Walking (MCoW) is typically expressed either in terms of Gross Cost of Walking (GCoW) or Net Cost of Walking (NCoW). MCoW is defined as the metabolic energy expended per meter travelled and is an important variable in daily life. From the literature we can see that increased MCoW for elderly compared to young might lead to elderly becoming fatigued and sedentary. Increased fatigue and sedentarism limits their functional possibilities, thereby affecting the overall quality of life. The motivation for this doctoral project was that we wanted to know the reasons why elderly have a higher MCoW compared to young, especially during overground walking. We were interested in overground walking since it is the ecologically relevant mode of walking. However, before trying to know why elderly have a higher MCoW than young we wanted to see whether this finding of elevated MCoW for elderly was valid in the first place and if so, specifically for overground walking. To answer our research questions, we conducted three studies in this thesis. We started with a systematic review and meta-analysis and reported on this study in Chapter 1 of this thesis. Then we followed it up with two experimental studies and then reported on them in Chapters 2 and 3 of this thesis.

To summarise, from the studies conducted in this thesis, we were able to show that the commonly reported elevation in MCoW for Older Adults (OA) over Young Adults (YA) is not due to age per se but is probably due to the differential reaction to treadmills by healthy YA and OA. In Chapters 2 and 3 we have shown that OA react differently to overground and treadmill walking (elevated MCoW on treadmills compared to overground) at their overground Preferred Walking Speed (PWS), which we directly imposed on the treadmills. YA do not react differently to overground and treadmill walking at the same speed as they have similar MCoW. Due to this differential reaction to overground and treadmill walking by YA and OA walking energetics are different between the two groups.

In conclusion, through this thesis we have shown how to have age as the only differentiating factor between YA and OA while trying to learn about the differences in MCoW between the cohorts. There were no differences in anthropometrics, physical activity and fitness levels and overground PWS between our YA and OA. Our main finding is that we have shown there are no differences in overground MCoW between them. As overground walking is the ecologically relevant mode of walking, overground MCoW should be considered important. Due to the differential reaction of YA and OA to treadmills, treadmills are not suitable for comparison of MCoW between the two populations.

The results of similar overground MCoW of YA and OA could have some clinical implications. For example, these results could be interpreted in the way that if people adopt a healthy and active lifestyle from an early age, when they grow old, they can have similar levels of PWS and MCoW like a young person. Comparable levels of PWS would generally mean that mobility and daily life gait will not be affected and similar levels of MCoW will mean that elderly will expend the same amount of energy after walking the same distance as a young person. Overall this will imply that elderly will be able to lead a normal healthy lifestyle, not become fatigued and sedentary, and we can achieve the goals of healthy aging in our society.