Energy expenditure of transfemoral amputees during floor and treadmill walking with different speeds

Abstract

Background:

Walking energy expenditure, calculated as the percent utilization of the maximal aerobic capacity, is little investigated in transfemoral amputees.

Objectives:

Compare the energy expenditure of healthy participants (control participants) and transfemoral amputees walking with their respective preferred walking speeds on the treadmill (T_PWS) and floor (F_PWS).

Study design:

Randomized cross-over study.

Methods:

Oxygen uptake (VO₂) was measured when walking with the F_PWS and T_PWS. VO_2max was measured by an incremental treadmill test.

Results:

Mean ± standard deviation VO_2max of the transfemoral amputees and control participants were 30.6 ± 8.7 and 49.0 ± 14.4 mL kg⁻¹ min⁻¹, respectively (p < 0.05). T_PWS for the transfemoral amputees and control participants was 0.89 ± 0.2 and 1.33 ± 0.3 m s⁻¹, respectively (p < 0.01). F_PWS for the transfemoral amputees and control participants was 1.22 ± 0.2 and 1.52 ± 0.1 m s⁻¹, respectively (p < 0.01). Walking on floor with the F_PWS, the energy expenditure of the transfemoral amputees and control participants was 54% and 31% of VO_2max, respectively (p < 0.01). Walking on the treadmill with the T_PWS, the energy expenditure of the transfemoral amputees and control participants was 42% and 29% of the VO_2max, respectively (p < 0.05).

Conclusion:

Energy expenditure is higher for the transfemoral amputees than the control participants, regardless of walking surface. There are minimal differences in energy expenditure between treadmill and floor walking for the control participants but large differences for the transfemoral amputees.

Clinical relevance

During walking, the transfemoral amputees expend a larger percentage of their maximal aerobic capacity than healthy participants. With a low VO_2max, ordinary activities, such as walking, become physically more challenging for the transfemoral amputees than the control participants, and this may, in turn, have a negative effect on the walking range of the transfemoral amputees.

Keywords

Gait rehabilitation

Background

Measurements of oxygen uptake and calculations of the energy cost of walking (C_w) are widely used as a tool for evaluating the energy expenditure (EE) of prosthetic ambulation.^1–5 Investigating healthy participants (control participants (CONs)). Parvataneni et al.⁶ found that at comparable walking speeds, oxygen uptake was higher during treadmill walking compared to floor walking. In contrast, Pearce et al.⁷ found that the oxygen uptake of CON during floor walking was higher than during treadmill walking. Other studies,^5,8 however, have found no differences in oxygen uptake when comparing treadmill and floor walking. Thus, the literature is not always in agreement regarding the EE of treadmill and floor walking.^5–7,9 Treadmill walking is often used during rehabilitation of prosthetic walkers,⁴ but the question is if this type of walking provides a realistic environment for evaluating prosthetic walking on other surfaces. Thus, it is important to measure the EE of prosthetic ambulation on different surfaces to clarify the usability of treadmills in a therapeutic setting. To our knowledge, only one previous study has actually compared the EE of prosthetic users during both treadmill and floor walking.⁵ The unilateral transfemoral amputees (TFAs) in the study of Traballesi et al.⁵ were amputated because of vascular diseases and had, in average, used their prosthesis for only 2 months. Thus, their preferred walking speeds (PWFs) on the treadmill and floor were very slow. It is also demonstrated that vascular amputees walk at a substantially higher relative aerobic load (percent of VO_2max) than people amputated because of trauma,¹⁰ and consequently, the findings of Traballesi et al.⁵ may not be representative for prosthetic users amputated for other reasons than vascular diseases and with long experience as prosthetic walkers. In addition, there is little information about the prosthetic users’ subjective rating of physical effort when walking on different surfaces, and how the perception of exertion corresponds to the physiological measurements of EE. Consequently, the main objective of this study was to investigate the EE of experienced prosthetic walkers and CONs walking with their treadmill and floor PWFs on both the treadmill and the floor. In addition, we investigated the association between EE and subjective ratings of perceived exertion (RPEs) in these walking situations.

Methods

Participants

Eight (four females and four males) nonsmoking unilateral TFAs and eight (four females and four males) nonsmoking CONs were recruited for this study. The respective mean ± standard deviation (SD) age (years), height (cm), weight (kg), and self-reported physical fitness (SPF; 1–5 scale) of the TFA and CON groups were 37.0 ± 10.9 and 39.0 ± 12.3 years, 175.5 ± 4.6 and 170.0 ± 7.4 cm, 73.6 ± 10.4 and 72.7 ± 14.2 kg, and 2.6 ± 0.5 and 2.6 ± 0.5. The weight of the TFAs is including their prosthesis. There were no significant differences in physical characteristics between the TFA and the CON groups. Details relating to the type of prosthesis used by the TFAs, because of amputation and so on, are given in Table 1.

Table 1.

Aspects of the prostheses and prosthetic use (n = number).

Characteristics	n
Left side amputation	5
Right side amputation	3
Microprocessor knee	5
Advanced hydraulic knee	3
ICS or MAS	7
Quadrilateral socket	1
Carbon foot	7
Prosthetic foot with hydraulic ankle joint	1

ICS: ischial containment socket; MAS: Marlo anatomical socket.

Inclusion criteria of TFAs were age between 20 and 60 years and to have a unilateral transfemoral amputation for at least 2 years for reasons other than vascular diseases. In average, the TFAs had used their prosthesis for a period of 15.8 years (range: 3–39 years). Inclusion criteria of the CON group were to have no orthopedic problems and to have similar weight, height, age, and SPF as the TFAs. The SPF was evaluated by a 5-point Likert scale (1 = very good, 3 = average, and 5 = very poor). Exclusion criterion for both the groups was the use of medication that could affect heart rate (HR) or EE. All participants were accustomed to treadmill walking. Written informed consent was obtained from all participants, and this study was approved by the Regional Committee for Medical Research Ethics in Regional Committee for Medical Research Ethics in Norway.

Study design and walking experiments

In this study, TFAs and CONs walked with their treadmill preferred walking speed (T_PWS) and floor preferred walking speed (F_PWS) on both the treadmill and the floor. In addition to the walking tests, a VO_2max test was also conducted. Details on the sequence of the different tests are shown in Table 2. On each testing occasion, the participants were instructed to report to the laboratory in the morning, 2 h after eating a standardized low-fat breakfast (bread, jam, sliced ham, juice, low-fat milk, and no coffee or tea) and to avoid exercise and alcohol 24 h prior to testing.

Table 2.

Study design.

Time (min)	Test day 1	Test day 2
20	Determination of preferred walking speeds (PWSs) on the treadmill and floor	–
10	Resting on a chair	Resting on a chair
7	Walking on the treadmill with the T_PWS	Walking on floor with the F_PWS
2	Resting on a chair	Resting on a chair
7	Walking on the treadmill with the F_PWS	Walking on the floor with the T_PWS
30	Resting on a chair	–
20	VO_2max testing on the treadmill	–

T_PWS: preferred walking speed on the treadmill; F_PWS: preferred walking speed on the floor; Time (min): duration of an activity; TFAs: transfemoral amputees; CONs: control participants; SD: standard deviation.

The sequence of treadmill and floor testing and the sequence of walking speeds within each test day were randomized. For the TFAs and CONs, the mean time (±SD) between tests was 10 ± 7 and 8 ± 3 days, respectively. The participants were blinded for the actual walking speeds and no verbal feedback of walking speeds was given to the participants during testing.

The floor walking tests were performed with the participants walking along a 40-m indoor track, while the treadmill walking tests were performed on a calibrated Woodway ELG70 treadmill (Woodway, Weil am Rhein, Germany). On the floor, the walking speed was monitored by an optical gait analysis system (OptoGait; Microgate, Bolzano-Bozen, Italy) to keep the actual walking speed as close as possible to the determined T_PWS and F_PWS. Verbal instructions such as “walk a little slower/walk a little faster,” were given when the participants needed to adjust their walking speed during floor trials. On the treadmill, walking speeds were set by the control display on the treadmill, and all participants walked on the treadmill without any aids and with minimal and only occasional support from the handrails.

VO_2max testing

The maximal oxygen uptake (VO_2max) test of the TFA group was performed according to a walking protocol with constant speed but progressively increasing inclinations of the treadmill.⁹ During VO_2max testing, the TFAs were allowed to have one hand resting lightly on the handrail to assist in keeping balance. The VO_2max of the CON group was tested with a treadmill running protocol with constant inclination but progressively increasing treadmill speed.⁹ The VO₂ measurements were considered maximal when the oxygen uptake did not increase >2 mL kg⁻¹ min⁻¹ (plateau in VO₂) despite increasing workload and with respiratory exchange ratio (RER) values > 1.05.⁸

Physiological measurements

During both treadmill and floor testing, the participants used a portable breath-by-breath oxygen analyzer (Cortex MetaMax 3B; Cortex Biophysik, Leipzig, Germany). Oxygen uptake (VO₂), lung ventilation (VE), RER, and HR were continuously monitored by telemetry in real time to verify steady-state conditions. Each walking interval lasted 7 min to enable the participants to reach steady-state conditions,⁵ and data reported on physiological measurements are average values over the last 2 min of each walking interval. The oxygen analyzer was calibrated for barometric pressure, gas, and volume, according to the manufacturer’s instructions.

Statistics

Normal distribution of the data was investigated by the Kolmogorov–Smirnov test. Within-group comparisons were analyzed with Student’s t-tests, while between-group comparisons were analyzed by independent t-tests. The association between the F_PWS determined prior to floor and treadmill experiments and the actual floor walking speeds measured by the OptoGait system was investigated by Pearson’s correlation test. The significance level was set at p < 0.05. The data were analyzed by the SPSS version 20. Results are presented as means ± SDs.

Results

VO_2max

The mean ± SD maximal oxygen uptake of the CON group was 3.58 ± 1.2 L min⁻¹ (49.0 ± 14.4 mL kg⁻¹ min⁻¹) and significantly higher (p < 0.05) than for the TFA group (2.27 ± 0.79 L min⁻¹, 30.6 ± 8.7 mL kg⁻¹ min⁻¹).

Percent VO_2max during walking

For both the TFA and the CON groups, the percent utilization of the maximal aerobic capacity (% VO_2max) when walking with the F_PWS on the floor was comparable to when walking on the treadmill with the F_PWS (Figure 1). Similarly, the % VO_2max when the TFA and CON groups were walking with their T_PWS on the floor was similar to when walking on the treadmill with this walking speed. Walking on the floor with their F_PWS, the TFAs utilized a higher percentage of their VO_2max compared to when walking on the floor with the T_PWS (p < 0.01), while for the CONs, there was a trend for higher percentage utilization of the VO_2max (p = 0.08) for the same comparison. Walking on the treadmill with the F_PWS, both the TFA and the CON groups had a higher % VO_2max compared to treadmill walking with the T_PWS (TFAs; p < 0.01, CONs; p < 0.05). When walking with the F_PWS, the % VO_2max of the TFA group was increased compared to the CON group, both when walking on the floor (p < 0.01) and when walking on the treadmill (p < 0.01). Correspondingly, when walking with the T_PWS, the TFAs also had an increased percentage utilization of the VO_2max compared to the CONs, both on the treadmill (p < 0.05) and on the floor surface (p < 0.01). In general, the TFAs used about 53% of their VO_2max when walking with the F_PWS and about 42% of their VO_2max when walking with the T_PWS. For the CONs, the corresponding values were about 31% and 27% of VO_2max, thus a less pronounced difference than for the TFAs. When walking at similar walking speeds, different walking surfaces had no effect on the % VO_2max for either group.

Figure 1.

Values are mean ± SD. For the CONs, there was a trend for higher percentage utilization of the VO_2max during floor walking with the F_PWS compared to floor walking with the T_PWS (p = 0.08).

Walking speeds

In average, for the TFAs, T_PWS was about 73% of their F_PWS, while for the CONs, their T_PWS was about 88% of their F_PWS (Table 3). There was a close correlation between the OptoGait measurements of the F_PWS during floor walking and the F_PWS determined prior to the floor and treadmill walking experiments (both groups collectively; r = 0.994, p < 0.0001). In addition, there was a close correlation between the OptoGait measurements of the T_PWS when using this speed on the floor and the T_PWS set by the treadmill control panel during treadmill walking (r = 0.998, p < 0.001).

Table 3.

Walking speed, oxygen uptake, walking economy, and ratings of perceived exertion during floor and treadmill walking.

Speed	Surface	Walking speed (m s⁻¹)		VO₂ (mL kg⁻¹ min⁻¹)		Cw (mL kg⁻¹ m⁻¹)		RPE, scale 0–10
		CONs	TFAs	CONs	TFAs	CONs	TFAs	CONs	TFAs
F_PWS	Floor	1.52 ± 0.1	1.22 ± 0.2	14.6 ± 1.9	15.8 ± 3.5	0.15 ± 0.01	0.21 ± 0.04	0.4 ± 0.5	2.2 ± 1.3
			^††				^†††		^††
	Treadmill	1.52 ± 0.1	1.22 ± 0.2	15.5 ± 2.6	15.6 ± 2.8	0.17 ± 0.02	0.21 ± 0.02	1.1 ± 0.3	3.0 ± 1.4
			^††				^†††		^††
T_PWS	Floor	1.33 ± 0.2	0.90 ± 0.2	13.2 ± 4.0	12.4 ± 1.5	0.16 ± 0.02	0.23 ± 0.04	0.4 ± 0.5	1.5 ± 1.2
		^*	^***,††	^*	^**		^†††		^*,†
	Treadmill	1.33 ± 0.3	0.89 ± 0.2	13.4 ± 4.4	12.4 ± 2.1	0.17 ± 0.02	0.23 ± 0.03	0.5 ± 0.8	1.8 ± 1.3
		^§	^{§§§,††}	^§			^§,†††		^§,†

T_PWS: preferred walking speed on the treadmill; F_PWS: preferred walking speed on the floor; Time (min): TFAs: transfemoral amputees (n = 8); CONs: control participants (n = 8); SD: standard deviation; VO₂: oxygen uptake; C_w: walking economy; RPE: rating of perceived exertion.

Values are means ± SD. RPEs were scored immediately at the termination of each walking interval. The reported values of F_PWS and T_PWS (m s⁻¹) when walking on the floor are the actual measured values by the OptoGait system, while the F_PWS and T_PWS values reported during treadmill walking are the values set by the control panel on the treadmill.

p < 0.05, **p < 0.01, ***p < 0.001 (F_PWS on the floor vs T_PWS on the floor); ^§p < 0.05, ^§§§p < 0.001 (F_PWS on the treadmill vs T_PWS on the treadmill); ^†p < 0.05, ^††p < 0.01, ^†††p < 0.001 (TFAs vs CONs).

Oxygen uptake during walking

For the TFA and CON groups, oxygen uptake was similar when walking at the same absolute speeds on the treadmill and floor; hence, the types of walking surface do not influence EE when walking speeds are comparable (Table 3). The oxygen uptake (mL kg⁻¹ min⁻¹) of both the TFA and the CON groups was, however, higher when walking on the floor with the F_PWS compared to floor walking with the T_PWS (TFAs; p < 0.01, CONs; p < 0.05). Similarly, when walking on the treadmill, for the TFA and CON groups, oxygen uptake was also higher when walking with the F_PWS compared to oxygen uptake during treadmill walking with the T_PWS (TFAs; p < 0.01, CONs; p < 0.05).

Walking economy

The C_w (mLO₂ kg⁻¹ m⁻¹) of the TFA and CON groups when walking on the floor with their F_PWS was similar to the C_w during floor walking with the respective T_PWS (Table 3). For the TFAs, when walking on the treadmill with their T_PWS, the C_w was higher than when walking on the treadmill with their F_PWS (p < 0.05). Compared to the CONs, the C_w of the TFAs was higher when walking with their F_PWS on the floor and treadmill (both comparisons; p < 0.001). Correspondingly, the TFAs also had a higher C_w than the CONs when walking with their T_PWS on the treadmill and floor (both comparisons; p < 0.001). In general, for the TFAs, walking economy was 120%–150% of the CONs’ walking economy.

RPEs

When walking with the F_PWS on the floor, the TFAs had a higher RPE compared to floor walking with the T_PWS (p < 0.05) (Table 3). Similarly, during treadmill walking, the TFAs had a higher RPE score when walking with the F_PWS compared to when walking with the T_PWS (p < 0.05). For the CONs, the RPE scores were similar both during T_PWS and F_PWS walking, and in general, the RPE scores of the CON group were little affected by either walking speed or type of surface. When walking with their F_PWS, the TFA group had a higher RPE score than the CON group both on the floor (p < 0.01) and on the treadmill (p < 0.01). Similarly, when walking with their T_PWS, the TFA group also had higher RPE scores than the CON group on the floor (p < 0.05) and treadmill (p < 0.05).

Discussion

Recently, we have documented similar oxygen uptakes of TFA and CON groups when walking on the treadmill with the T_PWS.⁹ The present results extend these findings, and when walking with the same relative speed (T_PWS and F_PWS), the TFA and CON groups had similar oxygen uptakes both during floor and treadmill walking. The VO₂ of the TFA and CON groups when walking with their T_PWS was about 12–13 mL kg⁻¹ min⁻¹ and about 15–16 mL kg⁻¹ min⁻¹ when walking with their F_PWS. The type of walking surface (floor and treadmill) did not influence VO₂ measurements. In normal walking, the rate of oxygen uptake is dependent on the walking speed,² and the curve of the energy–speed relation is approximately linear below a walking speed of 1.67 m s⁻¹.¹ Thus, the higher VO₂ of both the groups during F_PWS walking in this study is the result of the faster walking speeds.

Relating to this, results from our laboratory (data not shown) demonstrate that when TFAs walk with the same T_PWS and F_PWS as the CONs (i.e. 1.33 and 1.52 m s⁻¹), the mean ± SD oxygen uptake of the TFAs during floor walking increased to 17.8 ± 3.6 and 21.7 ± 6.4 mL kg⁻¹ min⁻¹, respectively. Hence, at the same absolute walking speeds as the CONs, the oxygen uptake of the TFAs is considerably higher than that of the CONs. In line with this, many studies have shown that prosthetic walkers select a slower PWF than CONs,^9,10 even though it is possible for prosthetic walkers to walk at quite fast speeds.¹¹ Why prosthetic walkers have a slower PWS than able-bodied individuals is less clear, but it is suggested that individuals adopt a “natural” speed of walking that corresponds to a minimal value of the EE,¹² and we are currently investigating this in a follow-up study.

While the rate of oxygen uptake per minute is a common index of the EE of a physical activity, the walking economy (C_w) is widely used for evaluating the walking efficiency during prosthetic ambulation.^2,3,5,13,14 Some studies have, however, demonstrated similar oxygen uptake values of lower limb amputees when walking on different surfaces but with comparable (relative) walking speeds.^5,9 Since the C_w is calculated as the relative oxygen uptake divided by the walking speed, a slow treadmill PWS will ultimately cause a higher oxygen cost value (C_w) on the treadmill compared to floor walking with a faster walking speed.¹⁰ To put this in perspective, if the TFAs walked faster than their predetermined PWS, the C_w would probably decline despite an increase in the relative oxygen uptake, and one could then argue that the effort exerted was lower during the faster walking speed. This can be clearly demonstrated by inspecting Table 3. For example, the C_w of the TFAs is 0.23 mL kg⁻¹ m⁻¹ when walking on the treadmill with the T_PWS. Walking on the same surface, but with a faster speed (i.e. the F_PWS), the oxygen uptake increases, but there is a significant decrease in the C_w from 0.23 to 0.21 mL kg⁻¹ m⁻¹, that is, a better walking economy. Normally, one would conclude that improvements in the walking efficiency would result in less fatigue and less physical exertion. By inspecting the RPEs following treadmill and floor walking, it is evident that this is not the case. The faster walking speeds are associated with the higher RPE ratings but with the lower C_w values. For the TFAs, walking was rated significantly harder when walking on the treadmill with the F_PWS (RPE = 3.0, C_w = 0.21) compared to treadmill walking with the T_PWS (RPE = 1.8, C_w = 0.23).

In summary, it may not be correct to judge the physical burden of prosthetic ambulation based on the C_w alone. In our opinion, the C_w is probably best suited for comparing the energy cost of walking before and after an exercise rehabilitation intervention.

Consequently, it is necessary to use other indicators than the C_w for judging the physical effort of prosthetic ambulation, especially if one is to make meaningful comparisons to able-bodied people. One way of doing this is by measuring the maximal aerobic capacity (VO_2max) of the individuals in question, and based on this, one can then calculate the EE during, for example, walking in percent of the individuals’ maximal aerobic capacity (% VO_2max). The VO_2max is widely accepted as the single best measure of cardiovascular fitness;¹⁵ hence, using % VO_2max as an indicator of the physical burden of ambulation is, physiologically speaking, a more meaningful measure of physical effort than C_w.

Recent studies show that lower limb amputees adapt to a more sedentary lifestyle following the amputation,¹⁶ and consequently, their aerobic capacity becomes gradually reduced and lower than comparable able-bodied individuals.⁹ The consequences of physical deconditioning are that activities, such as walking, become physically more challenging as the TFAs have to use a larger percentage of their maximal aerobic capacity than CONs to perform normal activities of daily life. This is clearly demonstrated by data from this study. When walking with their T_PWS, the TFAs used about 42% of their VO_2max (both surfaces), compared to about 54%, when walking with their F_PWS (Figure 1). In comparison, the CONs used only about 27% and 32% of their VO_2max when walking at the same relative speeds. Thus, walking with the F_PWS is substantially harder for the TFAs compared to the CONs, even though the CONs walk at a faster absolute speed than the TFAs. Relating to this, Wezenberg et al.¹⁰ recently measured the VO_2max of both CONs and traumatic and vascular lower limb amputees and calculated the participants’ % VO_2max during treadmill walking. Wezenberg et al.¹⁰ observed that traumatic lower limb amputees used about 50% of their VO_2max during treadmill walking, but since this study did not differentiate between transtibial amputees and TFAs, we speculate that this figure would be even higher for the TFAs alone.

The literature is otherwise somewhat limited on this topic, and earlier studies have merely calculated the participants VO_2max based on prediction equations.^13,17,18 Only a few studies have used a graded exercise test to assess the relative aerobic load of prosthetic walking in relation to TFAs’ VO_2max.^9,19 Collectively, the existing literature indicates that healthy above knee amputees use close to 50% of their VO_2max (mean 46%) during normal walking,^9,13,17–19 while CONs use about 30% of their VO_2max at comparable walking speeds.^9,17,18 In summary, it is safe to say that TFAs tax a larger proportion of their maximal aerobic capacity during ordinary walking than able-bodied individuals, and this may, in turn, have a negative effect on the development of fatigue during sustained walking periods.

Relating to this, it is argued that lower limb amputees need to tolerate an exercise intensity greater than 50% of their VO_2max for successful prosthetic ambulation.²⁰ Since the TFAs in this study used about 54% of their VO_2max when walking with their F_PWS (1.22 m s⁻¹), this speed may be close to what can be maintained for longer periods of time. Walking with about the same F_PWS as the CONs (1.52 m s⁻¹), the oxygen uptake of the TFAs increased to about 22 mL kg⁻¹ min⁻¹ as previously described (unpublished data). This is equivalent to 73% of their VO_2max, which probably is well above the lactate threshold of most sedentary TFAs.^17,21,22 Consequently, traumatic TFAs have the capacity to walk just as fast as CONs, but a walking speed above the lactate threshold of the TFAs would probably not be a sustainable walking speed.

Limitations of this study

One limitation of this study may be that data are collected from a homogenous and relatively small group of healthy TFAs with no vascular or other diseases; thus, the present results may not be representative for other groups of lower limb amputees, which are less fit than our sample. As shown by Wezenberg et al.,¹⁰ vascular TFAs may have substantially lower VO_2max values than the TFA group in this study, and TFAs amputated for vascular reasons use an even greater percentage of their VO_2max during ordinary walking than traumatic lower limb amputees. It remains also to investigate whether TFAs with less sophisticated knee components are able to change their walking speeds as comfortably as the participants in this study.

Conclusion

This study has demonstrated that the rate of oxygen uptake, C_w, and % VO_2max is similar for both the TFA and the CON groups when walking with the same speed on different surfaces. Thus, walking surface per se does not influence EE of the CON and TFA groups when walking with similar relative speeds. Because of faster walking speeds, overground walking is more physically challenging than walking on the treadmill, and this must be considered when choosing the model for rehabilitation for lower limb amputees. In addition, the consequences of low VO_2max are that activities, such as walking, become physically more challenging as the TFAs have to use a larger percentage of their maximal aerobic capacity than CONs to perform normal activities of daily life. Classifying the EE of TFAs by calculating the percent utilization of their VO_2max during walking is a suitable method for judging the physical effort of prosthetic walking.

Footnotes

Acknowledgements

The authors thank the Sophies Minde Foundation in Norway for financial support of this study.

Author contribution

IMS and TG designed the study and the experiments, carried out the experiments, analyzed the data, and wrote this article. PM, NK, TV., GS., and FTW. designed the study, carried out the experiments, analyzed the data, and revised this article.

Declaration of conflicting interests

The authors declare that there is no conflicts of interest.

Funding

This study was partially funded by Sophies Minde Foundation in Norway (grant number 23/09).

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Energy expenditure of transfemoral amputees during floor and treadmill walking with different speeds

Abstract

Background:

Objectives:

Study design:

Methods:

Results:

Conclusion:

Clinical relevance

Keywords

Background

Methods

Participants

Study design and walking experiments

VO2max testing

Physiological measurements

Statistics

Results

VO2max

Percent VO2max during walking

Walking speeds

Oxygen uptake during walking

Walking economy

RPEs

Discussion

Limitations of this study

Conclusion

Footnotes

Acknowledgements

Author contribution

Declaration of conflicting interests

Funding

References

VO_2max testing

VO_2max

Percent VO_2max during walking