The Metabolic Cost of Walking in healthy young and older adults - A Systematic Review and Meta Analysis

Abstract

The Metabolic Cost of Walking (MCoW) is an important variable of daily life that has been studied extensively. Several studies suggest that MCoW is higher in Older Adults (OA) than in Young Adults (YA). However, it is difficult to compare values across studies due to differences in the way MCoW was expressed, the units in which it was reported and the walking speed at which it was measured. To provide an overview of MCoW in OA and YA and to investigate the quantitative effect of age on MCoW, we have conducted a literature review and performed two meta-analyses. We extracted data on MCoW in healthy YA (18-41 years old) and healthy OA (≥59 years old) and calculated, if not already reported, the Gross (GCoW) and Net MCoW (NCoW) in J/kg/m. If studies reported MCoW measured at multiple speeds, we selected those values for YA and OA at which MCoW was minimal. All studies directly comparing YA and OA were selected for meta-analyses. From all studies reviewed, the average GCoW in YA was 3.4 ± 0.4 J/kg/m and 3.8 ± 0.4 J/kg/m in OA (~12% more in OA), and the average NCoW in YA was 2.4 ± 0.4 J/kg/m and 2.8 ± 0.5 J/kg/m in OA (~17% more in OA). Our meta-analyses indicated a statistically significant elevation of both GCoW and NCoW (p < 0.001) for OA. In terms of GCoW, OA expended about 0.3 J/kg/m more metabolic energy than YA and about 0.4 J/kg/m more metabolic energy than YA in terms of NCoW. Our study showed a statistically significant elevation in MCoW of OA over YA. However, from the literature it is unclear if this elevation is directly caused by age or due to an interaction between age and methodology. We recommend further research comparing MCoW in healthy OA and YA during "natural" over-ground walking and treadmill walking, after sufficient familiarization time.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1

Flow-diagram of the search and selection strategy followed using PRISMA method.

Figure 2

Metabolic Cost of Walking across the mean age in each study. (A) Gross Cost of Walking across age. (B) Net Cost of Walking across age. Black solid circles represent YA and the red solid circles OA. Each of the circles is a mean GCoW value or a mean NCoW value from a selected study. The dashed straight lines (black and red) show the mean metabolic cost of a particular age-group for both GCoW and NCoW–.

Figure 3

Overview of the results of the meta-analysis using a random effects model on the differences in Gross Metabolic Cost of Walking between YA and OA. A positive Mean Difference (MD) means that OA have higher GCoW than YA. The position of the red squares corresponds to the MD value per study and the horizontal black line to the 95% CI. The size of the square is proportional to the relative weight of that study w(%) to compute the overall MD (blue diamond and vertical black dashed line). The width of the diamond represents the 95% CI of the overall MD and the blue arrow represents the 95% PI of the overall MD. If a 95% CI spans zero (indicated by the red vertical dashed line), that study has found no significant elevation in GCoW. This meta-analysis shows a significant overall increase in GCoW of OA over YA (p < 0.001). Note that the p-value mentioned in the forest plot is the p-value for the Cochran’s Q heterogeneity test.

Figure 4

Overview of the results of the meta-analysis using a random effects model on the differences in Net Metabolic Cost of Walking between YA and OA. Symbols and conventions are the same as in Fig. 3. This meta-analysis shows a significant overall increase in NCoW of OA over YA (p < 0.001). Note again that the p-value mentioned in the forest plot is the p-value for Cochran’s Q heterogeneity test.

Figure 5

Leave-one-out plot of the meta-analysis on GCoW. The blue diamond now represents the pooled MD with its 95% CI, and the red diamonds represent the pooled MD along with its 95% CI when leaving out the study indicated. The arrows represent the 95% PI for the overall pooled MD. This figure shows that leaving out any of the studies does not cause the 95% CI to span zero for any of the red diamonds. Thus, the statistical significance of the elevation of GCoW in OA is not affected by leaving out any one of the studies.

Figure 6

Leave-one-out plot of the meta-analysis on NCoW. Symbols and conventions are the same as in Fig. 5. As with GCoW, the statistical significance of the elevation of NCoW in OA is not affected by leaving out any one of the studies.