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Journal of Experimental BiologyBioengineeringPeer-reviewed journal article

Older adults do not have a higher metabolic cost than younger adults in outdoor overground walking.

Eline van der KrukiD, Koen JongbloediD, Monica Orlandi, Michael F. MilleriD, Anne K. SilvermaniD

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Abstract

The metabolic cost of walking is widely used to evaluate human performance and effectiveness of clinical interventions. Decades of laboratory research, largely based on treadmill experiments, have established a canonical relationship between walking speed and metabolic cost, and suggested that ageing shifts this relationship upward, implying reduced efficiency in older adults. However, this relationship has not been well tested during overground walking across matched speeds. We compared healthy younger (n=16; 26{+/-}2yr) and older (n=11; 74{+/-}3yr) adults across eight outdoor overground walking trials at different speeds: preferred walking speed (PWS), three fixed speeds (0.8, 1.2, 1.6 m{middle dot}s-{superscript 1}), and four speeds at {+/-}5% and {+/-}10% of PWS. Contrary to our hypothesis, older adults did not show higher gross or net metabolic cost of walking (GCOW and NCOW) than younger adults at any speed; rather, both trended consistently lower in older adults, reaching significance for GCOW at 0.8 m{middle dot}s-{superscript 1} only. Comparisons of resting metabolic rate and respiratory exchange ratio to prior reference groups did not indicate that our older cohort was unusually fit. Independent of age, GCOW was significantly higher at 0.8 m{middle dot}s-{superscript 1} than at the remaining speeds (1.2-1.6 m{middle dot}s-{superscript 1}), confirming that walking at slower speeds increases GCOW. These findings challenge the view that ageing intrinsically increases the energetic cost of walking, suggesting instead that previously reported upward shifts in cost may reflect treadmill-specific constraints or speed effects. Future work is needed to explore direct comparisons of outdoor, overground walking with treadmill walking at fixed speeds in both younger and older adults.

In-depth summary

Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 1 (28 Jul 2026) · CC BY 4.0

Across seven pace-controlled outdoor overground speeds, healthy older adults (n=11) showed no higher gross or net walking cost than younger adults (n=16), trending lower instead.

The ageing-related upward shift in walking metabolic cost rests mostly on treadmill data (only 2 of 19 studies in a recent meta-analysis were overground), and earlier overground comparisons either left speed unmatched or tested only one matched speed. Measuring cost across several speed-matched outdoor conditions separates age effects from speed and treadmill context.

Key results

  1. ShownOlder adults did not incur a higher gross cost of walking (GCOW) at any matched speed. GCOW was lower in older adults overall, but the pairwise difference was significant only at 0.8 m/s.

    GCOW age main effect F(1,195) = 8.29, p = 0.004; no speed × age interaction (p = 0.23); at 0.8 m/s OA 3.13 (SD 0.92) vs YA 3.77 (SD 0.64) J kg⁻¹ m⁻¹, p = 0.04; older-minus-younger difference negative in all seven conditions (−0.28 to −0.64 J kg⁻¹ m⁻¹), e.g., 1.2 m/s 95% CI −0.95 to 0.01, p = 0.053. · 3.5 Gross Cost of Walking (GCOW (J kg⁻¹ m⁻¹)); Discussion

  2. ShownNet cost of walking (NCOW) showed no significant age effect. Older adults' values were still lower in every speed condition, and the confidence intervals were wider than for gross cost because resting variance is added.

    Age main effect F(1,195) = 3.35, p = 0.069; speed × age interaction F(7,195) = 1.02, p = 0.42; age differences −0.05 to −0.32 J kg⁻¹ m⁻¹ across seven conditions (e.g., 0.8 m/s 95% CI −0.89 to 0.26, p = 0.27); pairwise CI widths roughly 0.21–0.51 vs 0.13–0.23 J kg⁻¹ m⁻¹ for GCOW. · 3.6 Net Cost of Walking (NCOW (J kg⁻¹ m⁻¹))

  3. ShownWith pacing-cart control, both age groups walked at matched speeds and cadences. Older adults' preferred speed did not differ from younger adults', although slower speeds were expected after age 65.

    No age main effect on measured speed (F(1,195) = 0.08, p = .775) or cadence (F(1,195) = 1.18, p = 0.28); per-condition cadence differences −3.03 to +1.25 steps/min; older adults' overground PWS 1.41 ± 0.13 m/s, close to a published overground value of 1.37 ± 0.15 m/s. · 3.3 Walking speed and cadence; Discussion

  4. SuggestedIndirect markers did not suggest an unusually fit older cohort. Resting metabolic rate (RMR) trended lower in older adults, and their respiratory exchange ratio (RER) resembled a sedentary rather than an active older reference group.

    RMR 4.32 (younger) vs 3.68 (older) ml kg⁻¹ min⁻¹, p = 0.124, but p<0.01 with one older outlier removed; older RER at 0.8, 1.2, 1.6 m/s was 0.86, 0.85, 0.93 vs 0.82, 0.89, 0.95 (sedentary older) and 0.82, 0.87, 0.88 (active older) in Martin et al. (1992). · 3.2 Resting Metabolic Rate (RMR); 3.4 Respiratory Exchange Ratio (RER); Discussion

  5. ShownPooling both ages, gross cost was raised only at 0.8 m/s and was statistically flat across 1.2 to 1.6 m/s and the preferred-relative speeds. The authors read this as a hyperbolic curve with a near-minimal plateau, not a single U-shaped minimum. Net cost rose with speed.

    GCOW speed effect F(7,195) = 7.35, p < 0.001; 0.8 m/s higher than every other condition (p<0.01); other pairwise CI widths 0.13–0.23 J kg⁻¹ m⁻¹ spanning zero (1.2 vs 1.6 m/s: 95% CI −0.296 to 0.008, p = .062); NCOW at 0.8 m/s, 1.2 m/s and PWS−10% reported lower than the remaining conditions (p < 0.001–0.041), though PWS−5% did not differ from PWS−10% (p = 0.113). · 3.5 Gross Cost of Walking (GCOW (J kg⁻¹ m⁻¹)); 3.6 Net Cost of Walking (NCOW (J kg⁻¹ m⁻¹)); Discussion

Methods, data and reproducibility

Healthy younger and older adults completed eight 6-minute outdoor overground trials (preferred speed, then pacing-cart-controlled fixed and preferred-relative speeds, randomized) with a portable breath-by-breath gas analyzer; gross and net cost from 3-minute steady-state windows were compared via linear mixed-effects models with Bonferroni post hoc tests.

  • Healthy younger adults (aged 23–30 yr, 7 female) completing an outdoor standing resting trial and eight outdoor overground walking trials · human · n = 16
  • Healthy older adults (aged 69–79 yr, 6 female) completing the same outdoor resting and walking protocol · human · n = 11
  • Published treadmill and overground cost-of-walking and RER data (Martin 1992, Malatesta 2003, Berryman 2012, Waters 1988, Larish 1988, Ralston 1958) used as comparators · human
  • Finley and Cody (1970) observational outdoor pedestrian speed and cadence data, replotted as a reference histogram · human · n = 1,106 pedestrians
Methods & tools
COSMED K5 portable breath-by-breath metabolic system (embedded IMU for cadence), Custom pacing cart (Zozen measuring wheel + N317 Retoo bike computer), Slope-based 3-minute steady-state window selection on 0.5 Hz resampled VO2, Linear mixed-effects model (participant random intercept), Bonferroni-corrected post hoc pairwise comparisons, Unpaired t-test
Reproducibility gaps
The text has no code repository or data-sharing statement and does not name the statistical software used.
Limitations (6)
  • Preferred-speed trials lacked pacing-cart control. Participants repeatedly changed speed within these trials, which inflated cost values, so their cost outcomes were discarded and only their mean speed was kept. · stated by the authors
  • Testing ran outdoors from summer to winter (3 °C to 30 °C), participants wore their own clothing, and skin temperature was not measured. A temperature-covariate model showed no age × temperature interaction, but thermal effects on cost cannot be fully excluded. · stated by the authors
  • Older adults' fitness was not measured directly. Representativeness was inferred only by comparing resting metabolic rate and respiratory exchange ratio with the literature, so a more active-than-average cohort cannot be ruled out. · stated by the authors
  • Sample size was not set by a priori power analysis, and the groups were unequal (11 older vs 16 younger). The authors note the study was only partly powered to detect an age effect that may span the full speed range. · stated by the authors
  • The same participants did not walk on a treadmill, so the proposed explanation that treadmill context drove earlier age effects remains tentative. Testing it needs a direct matched-speed overground versus treadmill comparison. · stated by the authors
  • The gross-cost age difference is attributed to the resting component. Resting rate came from a single outdoor standing trial in which removing one older outlier changes the group comparison to significant, so the 0.8 m/s gross-cost finding depends on that measurement. · noted in this summary

Read this if you use metabolic cost of walking as an outcome in ageing or gait research and want speed-matched overground evidence that questions treadmill-derived age effects.

Citations
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