Theunissen et al. (2021) examined whether the energy cost and biomechanics of self-paced and matched-speed fixed-paced locomotion are different. Resting metabolic rate (RMR) and Energy Expenditure during activity were determined with indirect calorimetry using Maastricht Instruments’ Omnical.


In a variety of research and clinical settings, treadmill locomotion is frequently preferred to overground locomotion. Treadmills provide greater control over environmental conditions, allow for the assessment of multiple consecutive strides, and take up less space. Treadmill locomotion is typically carried out at a user-imposed (fixed) speed, whereas overground locomotion is carried out at a self-paced pace. The constant speed of treadmill locomotion may compensate for the natural variability in locomotion speed that occurs during overground locomotion. Additionally, it can help reduce the variability of neuromuscular and stride dynamics. As a result, self-paced treadmill applications have gained interest in both patient and healthy populations, ranging from studies quantifying muscle fatigue during walking in individuals with Multiple Sclerosis to VO2max testing in healthy athletes.

Despite the growing popularity of self-paced treadmill locomotion, few studies have examined the effects of self-paced versus matched speed fixed-paced locomotion, with the majority of studies revealing no clinically significant difference. Two studies compared spatiotemporal parameters, kinematics and kinetics, one study compared muscle activity, and two studies compared dynamic stability during walking in the two conditions. Indeed, Sloot et al. discovered that differences in spatiotemporal, kinetic, and kinematic parameters between self-paced and matched speed fixed-paced walking did not exceed the clinically relevant threshold. Additionally, variability in spatiotemporal, kinetic, and kinematic parameters is reported to be slightly greater during self-paced walking than during fixed-paced walking.

While it is well established that gait variability is a strong predictor of energetic cost of walking (Cw), no study has compared the energetics and gait variability of self-paced versus fixed-paced treadmill locomotion. Seethapathi and Srinivasan recently demonstrated that oscillated walking at a fixed speed increased the Cw when compared to constant walking at a fixed speed. Increased mechanical braking and propulsion forces required to redirect the center of mass at oscillating speeds most likely explained the increased Cw. The magnitude of the oscillating walking speed, on the other hand, may not accurately reflect the natural variability observed during self-paced treadmill walking.

Goal of the study

The primary objective of this study was to determine whether the Cw differed between self-paced and matched-speed fixed-pace treadmill walking in healthy adults. A secondary objective was to examine differences in spatiotemporal and sagittal-plane kinematic outcomes for the lower limb. Finally, because variability in spatiotemporal and kinematic patterns is reported to be greater during self-paced treadmill walking than in fixed-paced walking, it is expected that the Cw will exhibit greater variability as well. A secondary objective is to compare the variability of the energetic cost and spatiotemporal parameters of walking in self-paced and matched-speed fixed-pace treadmill walking.


All participants completed a single test session and were instructed to abstain from strenuous activity for 24 hours prior to the session, as well as eating and drinking (except for water) for up to 3 hours prior to the session to maintain a metabolic resting state. When entering the laboratory, a stadiometer was used to determine height (SECA, model 213, Hamburg, Germany). After that, participants were instructed to lie comfortably supine for 35 minutes while their resting metabolic rate (RMR) was measured using a ventilated hood connected to an indirect calorimeter (Omnical, Maastricht Instruments). During the measurement, a soothing nature documentary was screened and participants were instructed not to fall asleep. Following resting metabolism measurements, 26 retroreflective skin markers were attached using a modified lower-limb and trunk marker set (Human Body Model v2), and body mass was determined using force platforms during subject calibration van den Bogert et al.

The computer-assisted rehabilitation environment (CAREN, Motek) system was used to assess kinematic outcomes during walking. It combines an instrumented split-belt treadmill (ForceLink, Culemborg, The Netherlands) with a 12-camera three-dimensional motion capture system (VICON NEXUS v2.7, Oxford Metrics Group, Oxford, UK) (Supplementary File 1). Participants wore a face mask while walking, and respiratory gasses were measured using the indirect calorimeter.


The primary objective of this study was to compare the energy costs associated with self-paced and fixed-speed treadmill walking. Self-paced treadmill walking was expected to result in a lower Cw due to the increased natural variability associated with daily locomotion. Our findings indicate that there are no significant differences in energy cost between self-paced and fixed-paced treadmill walking at any walking speed. Additionally, there were few significant differences between self-paced and fixed-paced conditions in terms of mean spatiotemporal outcomes and sagittal-plane lower-limb kinematics. When significant differences between conditions were observed, their magnitude was below the threshold for clinical relevance. Similarly, there was no difference in the variability of Cw and the majority of biomechanical outcomes between conditions.

The study’s findings are consistent with previous research indicating that the spatiotemporal and kinematic differences between self-paced and matched speed fixed-paced walking do not exceed the clinically relevant threshold. Although no significant differences in mean outcomes were observed, self-paced walking was associated with greater (within-trial) variability in walking speed (i.e., higher fluctuations during a walking trial).

The overall variability of energy costs, on the other hand, was not significantly different, with a mean difference of 0.85%. Likewise, the variability of spatiotemporal outcomes was either not significantly different between conditions or was of trivial magnitude. The similar variability in most outcomes observed during self-paced treadmill walking contrasts with previous research findings that self-paced walking is more variable than fixed-paced walking.

Overall, because there are no significant differences in the mean energetics and biomechanics of self-paced and fixed-paced treadmill walking, these findings suggest that self-paced walking can be used interchangeably with fixed-paced walking in healthy young adults. Self-paced walking, on the other hand, may better represent natural movement variability for the majority, but not all, outcomes and thus be more suitable for studying variability under controlled conditions.

Fig. 1 shows a raincloud plot depicting the net cost of walking at various speeds in both conditions. Individual data points are represented by dots. The box and whiskers indicate the median and interquartile range, respectively.

How can we help you with your research?

Maastricht Instruments has created research equipment for indirect calorimetry measurements. Along with our indirect calorimetry products, you may contact us for product & software support, measurement methods and protocols, validation techniques, data processing and interpretation, and other technological requirements for your study.

“The Omnical metabolic cart seems to be the most valid system among metabolic carts for assessing both, RMR and RER.” – Juan M. Alcántara Alcántara, 2020

If you’re interested to learn more about our indirect calorimetry metabolic cart, whole-body room calorimeter systems, or accelerometry add-ons, kindly contact us.


Kyra Theunissen, Bas Van Hooren, Guy Plasqui, Kenneth Meijer, Self-paced and fixed speed treadmill walking yield similar energetics and biomechanics across different speeds, Gait & Posture, Volume 92, 2022, Pages 2-7, ISSN 0966-6362,