Differences in the daily activity of patients with diabetic foot ulcers compared to controls in their free‐living environments

ABSTRACT

The aims of our study were to investigate multiple daily activity outcomes in patients with diabetic foot ulcers (DFU) compared to diabetic peripheral neuropathy (DPN) and diabetes (DM) controls in their free‐living environments. We examined daily activity outcomes of 30 patients with DFU, 23 DPN and 20 DM. All patients wore a validated multi‐sensor device for > 5 days (>22 hours per day) to measure their daily activity outcomes: steps, energy expenditure (kJ), average metabolic equivalent tasks (METs), physical activity (>3·0 METs) duration and energy expenditure, lying duration, sleep duration and sleep quality. We found that DFU patients recorded fewer median (interquartile ranges, IQR) daily steps [2154 (1621–4324)] than DPN [3660 (2742–7705)] and DM [5102 (4011–7408)] controls (P < 0·05). In contrast, DFU patients recorded more mean ± SD daily energy expenditure (kJ) (13 006 ± 3559) than DPN (11 085 ± 1876) and DM (11 491 ± 1559) controls (P < 0·05). We found no other differences in daily activity outcomes (P > 0·1). We conclude that DFU patients typically take fewer steps but expend more energy during their normal daily activity than DPN and DM controls. We hypothesise that the increased energy expenditure for DFU patients may be due to wound healing or an inefficient gait strategy. Further investigations into this energy imbalance in DFU patients may improve healing in future.

Introduction

Diabetic foot ulcers (DFU) are a leading cause of hospitalisation and amputation 1, 2. The most common pathway to developing a DFU had been hypothesised to be high plantar pressure in combination with high daily activity in people with diabetic peripheral neuropathy (DPN) 3, 4. Studies have now confirmed that high plantar pressure is a risk factor for developing DFU in people with DPN 5, 6; however, in contrast, other studies have identified that it is actually low daily activity that is a risk factor for developing DFU in people with DPN 3, 4, 7, 8. Subsequently, these low daily activity findings have many hypothesising that interventions that gradually increase daily activity in people with DPN – in combination with appropriate offloading of high plantar pressures – may also improve their rehabilitation, physical fitness, plantar tissue health and prevention of DFU 3, 4, 8, 9.

Those studies reporting low daily activity in the free‐living environments of patients with DPN have mainly measured daily steps as their daily activity outcome of interest 3, 4, 7, 8. However, laboratory‐based studies that have measured other daily activity outcomes in laboratory‐controlled environments have reported contrasting findings 8, 10, 11, 12, 13, 14. Some of the laboratory‐based studies report patients with DPN have a low ability to perform short tasks representative of typical daily activity 10, 11, 12, whereas others report that patients with DPN have high standing durations 13 and high energy expenditure when performing other short tasks representative of typical daily activity 8, 14. With these contrasting findings, it appears important that we gain a more comprehensive understanding of a range of daily activity outcomes in the free‐living environments of patients with DPN and DFU before we make any future recommendations to gradually increase daily activity in these patients.

To our knowledge, no study has simultaneously investigated multiple daily activity outcomes in patients with DPN and DFU in their free‐living environments. Thus, the primary aim of this study was to investigate multiple daily activity outcomes in patients with DFU compared to DPN and diabetes controls in their free‐living environments. The secondary aim was to investigate the same daily activity outcomes in subgroups of patients with DFU. We hypothesised that patients with DFU would display lower daily activity levels across a range of outcomes compared to controls.

Methods

Study design

This was a cross‐sectional study conducted in three outpatient diabetes clinics in Brisbane, Australia. The Human Research Ethics Committee at The Prince Charles Hospital, Brisbane, Australia provided ethical approval for the study (Ethics No. HREC/12/QPCH/234). Written informed consent was voluntarily obtained from all individual participants in this study.

Setting and participants

Eligible participants were adult (>18 years) patients with type 2 diabetes mellitus attending one of the three diabetes clinics. Participants were allocated into three groups: patients with (i) active plantar neuropathic DFU (DFU group), (ii) DPN and no DFU history (DPN group) and (iii) no DPN or DFU history (DM group). Type 2 diabetes mellitus was defined as a documented medical diagnosis of type 2 diabetes mellitus in the patient's medical record 15. A DFU was defined as an existing active full‐thickness wound on the plantar surface of the foot 15, 16. DPN was defined as a lack of protective sensation to a 10‐gram monofilament on at least two of three plantar forefoot locations on one foot 15, 16.

Subgroups of the DFU group were also analysed: (i) patients with a history of minor amputation compared to those without any amputations and (ii) patients wearing a non‐removable knee‐high offloading device compared to those wearing other offloading devices. Minor amputations were defined as an amputation distal to the ankle 15, 16. A non‐removable knee‐high offloading device was defined as a total contact cast or instant total contact cast 5, 15. Other offloading devices were defined as either removable ankle‐high devices, therapeutic footwear or felted foam in appropriate off‐the‐shelf footwear 5, 15

Exclusion criteria for all groups included patients with conditions considered to potentially adversely impact normal daily activity, including patients with: (i) peripheral artery disease (PAD), defined as a toe systolic pressure of <70 mmHg 2, 15; (ii) major amputation, an amputation proximal to the ankle 15, 16; (iii) mobility impairment, an inability to walk without a mobility aide 2; and any documented medical diagnosis in the patient's medical record of (iv) painful DPN (i.e. we only included those with painless DPN in those groups with DPN), (vi) sleep apnoea or (vii) cognitive impairment 2, 15. All the above clinical tests and medical record reviews to determine the eligibility of the participants were performed for the purposes of this study by the senior podiatry coinvestigator at the three diabetes clinics.

Sample size

Sample size calculations were based on reported means and standard deviations (±SD) for daily steps: 8000 ± 3500 in patients with DPN 3, 8, 13 and 5500 ± 3000 in patients with DFU history 3, 8. In order to detect a difference in daily steps, both groups were calculated to need 25 participants when using a one‐sided test with a power of 80% and an alpha level of 0·05. We decided to also conservatively include 25 participants in the DM group as reported daily steps in patients with diabetes were 10 500 ± 4000 3, 17. Thus, 75 participants were required.

Participant characteristics

All participant characteristics were assessed and collected for the purposes of this study by the senior podiatry coinvestigator at the three diabetes clinics. Participant characteristics were collected using the Queensland High Risk Foot Form (QHRFF) 15. The QHRFF is valid and reliable for the capture of multiple self‐reported and clinically diagnosed characteristics administered by clinicians with a range of foot disease experience 15. All QHRFF characteristic definitions and criteria have been reported in detail elsewhere 2, 15. In brief, for this study, the QHRFF captured demographic (age, gender, indigenous status); diabetes (type, duration, HbA1c); comorbidity history (hypertension, dyslipidaemia, cardiovascular disease, chronic kidney disease, current smoker); foot risk factors (previous amputation history, previous DFU history, DPN, PAD, foot deformity); DFU: ulcer surface area (mm²), defined as multiplying the longest edge by the widest edge of the ulcer surface in mm; DFU: deep ulcer, defined as scoring a 2 (‘wound penetrating to tendon or capsule’) or 3 (‘wound penetrating to bone or joint’) according to the University of Texas Diabetic Wound Classification System 18; DFU: infected ulcer, according to the International Working Group on the Diabetic Foot classification system, defined as at least two clinical signs or symptoms of infection in or around the DFU 16; and foot treatment (offloading device) characteristics 15. Offloading devices were categorised into either ‘non‐removable knee‐high’ offloading devices or ‘other’ offloading devices 5. Foot deformity was defined as having at least three of the following characteristics: small muscle wastage, bony prominence, prominent metatarsal heads, hammer/claw toes, limited joint mobility or Charcot deformity on one foot 2, 15. Additionally, body mass index (BMI) was collected and calculated as the participant's body mass (kg) divided by the square of the participants height (m).

Daily activity outcomes

Daily activity outcomes were captured using the SenseWear Armband (‘armband’) (Model MF‐SW; BodyMedia Inc., Pittsburgh, PA, 19) and Epworth Sleepiness Scale 20. According to the manufacturers' specifications, the armband is a light‐weight (45 g), multi‐sensor device that incorporates multiple sensors to measure multiple parameters, including a tri‐axial accelerometer sensor to measure motion, body position and steps (calibrated range ±1·0 g); heat flux sensor to measure the rate at which heat dissipates from the body (0 to 300·0 W/m²); galvanic skin response sensor to measure skin impedance, which reflects the sweat response of the body (56 kOhms to 20 MOhms); and skin temperature sensor to measure the surface temperature of the body (20–40°C) 19. The armband converts these measured parameters in conjunction with the participant's demographic characteristics (age, gender, height and weight) using proprietary algorithms to determine the estimated daily activity outcomes of daily steps (mean error <9%), energy expenditure and metabolic equivalent tasks (METs) (mean error <5%) and lying and sleep duration (mean error <10%) 19. A MET is a measure of the average energy cost of an activity, with one MET defined as an adult sitting quietly, or approximately 1 kcal/kg/hour 19.

The armband has also been independently validated to measure these daily activity outcomes in the free‐living environments of different patient cohorts, such as healthy, older, diabetes, rheumatoid arthritis and chronic obstructive pulmonary disease patients 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. Estimated daily steps 21, 22, 23, energy expenditure and METs 23, 24, 25, 26, 27, 28 and lying and sleep durations 29, 30 have been validated in comparison to the gold standard criterion measures of manual step counts 21, 22, 23, indirect calorimetry or doubly labelled water techniques 23, 24, 25, 26, 27, 28 and polysomnography, respectively 29, 30. Furthermore, the armband is now regularly used as the research gold standard criterion measure to test consumer‐wearable activity monitors (such as Fitbits) 31, 32, has been used to measure daily activity outcomes in numerous studies investigating cohorts of people with diabetes 33, 34, 35 and by studies conducted by members of our team 36, 37. For this study, the armband captured the following estimated daily activity outcomes of interest: steps, energy expenditure (kJ), average METs, physical activity (>3 METs) duration (minutes) and energy expenditure (kJ), lying duration (minutes) and sleep duration (minutes) 19. Physical activity was defined as a moderate‐intensity activity exceeding three METs 19, 25, 26.

The Epworth Sleepiness Scale is a validated self‐administered questionnaire for screening daytime sleepiness and was used in this study to capture the daily activity outcome of sleep quality 20. The tool uses eight questions with an ordinal scale (0: ‘never doze’ to 3: ‘high chance of dozing’) to determine the severity of daytime sleepiness 20. The total combined score (0–24) allows the categorisation of a participant's daytime sleepiness, which is an indicator of their quality of sleep at night; a score of <10 is defined as normal, 10–16 indicates abnormal sleepiness and >16 dangerous sleepiness 20.

Procedure

All consenting eligible participants first had their demographic, diabetes, comorbidity, foot risk factors, foot ulcer and foot treatment characteristics captured using the QHRFF 15. Second, participants completed the Epworth Sleepiness Scale 20. Finally, an armband was attached to participants' upper arm over the triceps muscle at the mid‐point of the humerus 19. Participants were asked to wear the armband continuously for 1 week and only remove it for showers and other water‐based activities 19. Participants were given no new advice on daily activity except that the device recorded their daily activity. The armband automatically records the time periods it is being worn by participants and captures daily activity data 19. To be included, each participant was required to have worn the armband for at least 22 hours per day for at least 5 days (with at least one of those days a weekend day) 19, 25, 26, 38.

Statistical analysis

All data were analysed using SPSS 22.0 for Windows (SPSS Inc., Chicago, IL) or GraphPad Software. We used histograms and Kolmogorov‐Smirnov tests to test for normality of distributions for continuous variables. For those continuous variables with normal distributions, we reported means and standard deviations (±SD) and tested differences between groups using analysis of variance (ANOVA) with Fisher's least significant difference post‐hoc tests for three groups and Student's t‐tests for two groups. For those continuous variables without normal distributions, we reported medians and interquartile ranges (IQR) and tested differences between groups using Kruskal‐Wallis tests for three groups and Mann–Whitney U‐test for two groups. For categorical variables, we reported proportions and tested differences between groups using Pearson's chi‐squared tests for three groups, chi‐squared with continuity correction for two groups or Fisher's exact test if two cells had expected counts <5. A significance of P < 0·05 was used throughout.

Results

Overall, 77 eligible participants were recruited for this study: 30 DFU, 24 DPN and 23 DM. Of those, four (5·2%) participants had their armband mechanically fail to record any data for their week of wear and had to be excluded: three DM and one DPN. Table 1 reports the remaining 73 included participants' characteristics. Those with DPN were of older age (68 ± 9 years) than those with DFU (57 ± 11 years) and DM (60 ± 10 years) (P < 0·01). Those with DFU recorded more foot deformities (73·3%) than those with DPN (17·4%) and DM (0%) (P < 0·01). Otherwise, there were no differences between groups for all other participant characteristics (all, P > 0·05). Those with a DFU had a median (IQR) ulcer surface area of 50 (8–264) mm²; 10% were infected, and 6·7% were deep ulcers.

Table 1.

Participant characteristics and daily activity outcomes for each group (number (%) or mean ± SD unless otherwise stated ^*)

	Total	DM	DPN	DFU	P value
Participant characteristics
Numbers	73	20	23	30
Age	61 ± 11	60 ± 10	68 ± 9**	57 ± 11	0·001*
Men	50 (68·5%)	11 (55·0%)	15 (62·5%)	24 (80·0%)	0·162
Indigenous	1 (1·4%)	0	0	1 (3·3%)	0·484
BMI	33 ± 6	32 ± 6	32 ± 5	33 ± 7	0·814
Diabetes duration (years)	13 ± 9	11 ± 6	15 ± 9	13 ± 10	0·352
HbA1c (%)*	7·7 (6·7–9·9)	8·3 (6·7–9·5)	7·6 (7·2–7·9)	7·5 (6·7–10·1)	0·860
Hypertension	39 (53·4%)	9 (45·0%)	14 (60·9%)	16 (53·3%)	0·582
Dyslipidaemia	30 (41·1%)	8 (40·0%)	12 (52·2%)	10 (33·3%)	0·382
CVD	14 (19·2%)	3 (15·0%)	5 (21·7%)	6 (20·0%)	0·846
CKD	7 (9·6%)	1 (5·0%)	1 (4·3%)	5 (16·7%)	0·229
Smoker	12 (16·4%)	4 (20·0%)	1 (4·3%)	7 (23·3%)	0·160
Previous amputation	13 (17·8%)	0	0	13 (43·3%)	NA
Previous DFU	28 (38·4%)	0	0	28 (93·3%)	NA
PAD	0	0	0	0	NA
DPN	53 (72·6%)	0	23 (100%)	30 (100%)	NA
Foot deformity	26 (35·6%)	0	4 (17·4%)	22 (73·3%)**	<0·001*
DFU: ulcer surface area (mm2)* , †	50 (8–264)	0	0	50 (8–264)	NA
DFU: deep ulcer‡	2 (2·7%)	0	0	2 (6·7%)	NA
DFU: infected ulcer§	3 (4·1%)	0	0	3 (10%)	NA
Daily activity outcomes
Steps*	3810 (2033–6302)	5102 (4011–7408)	3660 (2742–7705)	2154 (1621–4324)**	0·002*
Energy expenditure (kJ)	11 986 ± 2753	11 491 ± 1559	11 089 ± 1876	13 006 ± 3559**	0·025*
Average METs	1·2 ± 0·2	1·2 ± 0·2	1·2 ± 0·2	1·2 ± 0·2	0·648
Physical activity (>3·0 METs) energy expenditure (kJ)*	943 (525–1854)	1096 (600–1666)	859 (402–1486)	976 (520–1940)	0·626
Physical activity (>3·0 METs) energy expenditure duration (minutes)*	40 (21–70)	47 (26–73)	37 (18–60)	40 (20–69)	0·623
Lying down duration (minutes)	518 ± 109	512 ± 98	540 ± 129	507 ± 101	0·529
Sleep duration (minutes)	409 ± 97	404 ± 113	430 ± 104	395 ± 80	0·431
Epworth Sleepiness Score	7·7 ± 4·3	6·7 ± 2·5	7·2 ± 4·4	8·8 ± 5·0	0·188

^*Median (IQR).

^†Ulcer surface area, defined as multiplying the longest edge by the widest edge of the ulcer surface in mm.

^‡Deep ulcer, defined as an ulcer scoring a 2 or 3 on the University of Texas Diabetic Wound Classification System.

^§Infected ulcer, defined as an ulcer with at least two clinical signs or symptoms of infection in or around the DFU.

BMI, body mass index; CKD, chronic kidney disease; CVD, cardiovascular disease; DFU, diabetic foot ulcer, defined as an existing active full thickness wound on the plantar surface of the foot; DM, diabetes mellitus; DPN, diabetic peripheral neuropathy, defined as a lack of protective sensation to a 10‐g monofilament; HbA1c, glycated haemoglobin; kJ, kilojoules; METs, metabolic equivalent of tasks; NA, not applicable to test as part of inclusion or exclusion criteria for groups; PAD, peripheral arterial disease, defined as a toe systolic pressure of <70 mmHg.

^*Represents a difference between the three groups (P < 0·05); ^** represents the group that is different to the other groups (P < 0·05).

Table 1 also reports the daily activity outcomes of the 73 included participants. Those with DFU recorded fewer median (IQR) daily steps [2154 (1621–4324)] than those with DPN [3660 (2742–7705)] and DM [5102 (4011–7408)] (both, P < 0·05). Additionally, those with DFU recorded more mean ± SD daily energy expenditure (kJ) (13 006 ± 3559) than those with DPN (11 085 ± 1876) and DM (11 491 ± 1559) (both, P < 0·05). There were no other differences between groups for all other daily activity outcomes (all, P > 0·05).

Table 2 reports the findings for DFU subgroups; 13 (43%) had a minor amputation, 17 (57%) had not had an amputation, 8 (27%) wore non‐removable knee‐high offloading devices, and 22 (73%) wore other offloading devices. Those with a minor amputation had a longer duration of diabetes, higher average METs, longer physical activity duration and lower Epworth Sleepiness Scale score than those without a minor amputation (all, P > 0·05). There were no differences between characteristics or daily activity outcomes for those wearing a non‐removable knee‐high offloading device compared to those wearing other offloading devices (all, P > 0·05).

Table 2.

Participant characteristics and daily activity outcomes for each DFU subgroup [number (%) or mean ± SD unless otherwise stated^*]

	No amputation	Minor amputation	P value	Other offloading device	Non‐removable offloading device	P value
Participant characteristics
Numbers	17	13		22	8
Age	55 ± 13	58 ± 10	0·500	56 ± 12	59 ± 9	0·504
Men	12 (70·6%)	12 (92·3%)	0·196	17 (77·3%)	7 (87·5%)	0·918
Indigenous	1 (5·9%)	0	1·000	1 (4·5%)	0	1·000
BMI	35 ± 7	31 ± 6	0·085	32 ± 7	36 ± 6	0·243
Diabetes duration (years)	9 ± 5	18 ± 12	0·023*	12 ± 11	13 ± 7	0·982
HbA1c (%)*	9·9 (7·2–10·2)	6·8 (6·3–7·9)	0·078	8·4 (7·0–9·9)	7·5 (6·5–10·2)	0·788
Hypertension	10 (58·8%)	6 (46·2%)	0·749	11 (50%)	5 (62·5%)	0·847
Dyslipidaemia	5 (29·4%)	5 (38·5%)	0·896	5 (22·7%)	5 (62·5%)	0·108
CVD	4 (23·5%)	2 (15·4%)	0·672	3 (13·6%)	3 (37·5%)	0·300
CKD	3 (17·6%)	2 (15·4%)	1·000	3 (13·6%)	2 (25·0%)	0·589
Smoker	3 (23·1%)	4 (23·5%)	1·000	6 (27·3%)	1 (12·5%)	0·638
Previous amputation	0	13 (100%)	NA	8 (36·4%)	5 (62·5%)	0·242
Previous DFU	15 (88·2%)	13 (100%)	0·492	20 (90·9%)	8 (100%)	1·000
PAD	0	0	NA	0	0	NA
DPN	17 (100%)	13 (100%)	NA	22 (100%)	8 (100%)	NA
Foot deformity	10 (58·8%)	12 (92·3%)	0·092	16 (72·7%)	6 (75·0%)	1·000
DFU: ulcer surface area (mm2)* , †	50 (8–150)	71 (8–310)	0·675	49 (8–246)	111 (8–637)	0·496
DFU: deep ulcer‡	2 (11·8%)	0	0·492	2 (9·1%)	0	1·000
DFU: infected ulcer§	2 (11·8%)	1 (7·7%)	1·000	2 (9·1%)	1 (12·5%)	1·000
Daily activity outcomes
Steps*	1864 (1081–4324)	2762 (1864–4057)	0·305	2033 (1621–4563)	2901 (1732–4121)	0·743
Energy expenditure (kJ)	13 042 ± 4142	12 960 ± 2780	0·952	13 217 ± 3934	12 427 ± 2349	0·599
Average METs	1·1 ± 0·2	1·3 ± 0·3	0·036*	1·2 ± 0·3	1·1 ± 0·2	0·222
Physical activity (>3·0 METs) energy expenditure (kJ)*	746 (341–1395)	1876 (634–3328)	0·149	976 (520–2048)	1000 (303–1692)	0·302
Physical activity (>3·0 METs) energy expenditure duration (minutes)*	29 (16–42)	69 (47–152)	0·008*	37 (20–69)	51 (21–66)	0·935
Lying down duration (minutes)	496 ± 102	521 ± 101	0·520	506 ± 106	510 ± 93	0·923
Sleep duration (minutes)	376 ± 80	420 ± 76	0·142	395 ± 85	394 ± 69	0·977
Epworth Sleepiness Score	10·5 ± 4·6	6·6 ± 4·8	0·034*	8·6 ± 5·3	9·3 ± 4·2	0·772

BMI, body mass index; CKD, chronic kidney disease; CVD, cardiovascular disease; DFU, diabetic foot ulcer, as an existing active full thickness wound on the plantar surface of the foot; DM, diabetes mellitus; DPN, diabetic peripheral neuropathy, defined as a lack of protective sensation to a 10‐g monofilament; HbA1c, glycated haemoglobin; kJ, kilojoules; METs, metabolic equivalent of tasks; NA, not applicable to test as part of inclusion or exclusion criteria for groups; PAD, peripheral arterial disease, defined as a toe systolic pressure of <70 mmHg.

^*Median (IQR).

^†Ulcer surface area, defined as multiplying the longest edge by the widest edge of the ulcer surface in mm.

^‡Deep ulcer, defined as an ulcer scoring a 2 or 3 on the University of Texas Diabetic Wound Classification System.

^§Infected ulcer, defined as an ulcer with at least two clinical signs or symptoms of infection in or around the DFU.

^*Represents a difference between the two groups (P < 0·05).

Discussion

Patients with DFU took fewer steps but expended more energy during their daily activity than those with DPN or DM. Otherwise, people with DFU showed no differences from controls in other daily activity outcomes, including physical activity, lying duration and sleep. Interestingly, there were no differences in daily steps or energy expenditure for subgroups of patients with DFU. These findings suggest patients with DFU expend more energy to perform the same daily activities than controls do in their normal everyday environments.

The interpretation of our daily steps findings, in conjunction with those from previous similar studies, helps confirm the notion that DPN patients' developing DFU have lower daily walking activity and further suggests that daily walking activity progressively decreases as the severity of DPN increases and DFU develop 3, 4, 7, 8, 11. To our knowledge, only one previous study has specifically investigated a DFU group compared to DPN controls, and they also found that patients with DFU walked less than those with DPN 8. Interestingly, similar to our findings, this previous study also found no statistical differences in daily steps in DFU patients with a minor amputation history compared to those without an amputation history 8. This suggests that minor amputations do not negatively impact the daily walking activity of patients with DFU 8. Additionally, although we only had a small subsample of DFU patients wearing a non‐removable knee‐high offloading device, our findings indicate that unlike their significant effect on reducing high plantar pressures, these gold standard devices may not limit daily steps when compared to other offloading devices as much as previously thought 5, 9. Overall, these findings indicate that patients with DFU are significantly less active in terms of daily walking activity than patients with DPN and DM.

To our knowledge, only one previous study has also investigated energy expenditure in patients with DFU 8. The previous study used the total heart beat index, which is a short laboratory‐controlled energy expenditure measure conducted over a 2‐minute walk 8, whereas we measured energy expenditure over 5 days in patients' free‐living environments. Regardless, both studies reported similar energy expenditure findings which suggested that patients with DFU use significantly more daily energy expenditure than DPN controls 8. Additionally, another recent study used a gas analyser to measure energy expenditure during short laboratory‐controlled treadmill walking in DPN patients and also found that patients with more severe DPN expended more energy than those with mild DPN 14. Overall, these findings indicate that patients with DFU expend more energy during their daily activities than patients with DPN and DM.

All other daily activity outcomes investigated in our study showed that DFU patients were no different to DPN or DM controls. First, our average daily MET findings indicate that patients with diabetes are quite sedentary in their day‐to‐day free‐living environments, regardless of the DPN severity. Second, our daily moderate‐intensity physical activity findings showed no differences and also suggest that patients with diabetes are sedentary, regardless of DPN severity. However, higher BMI have been associated with lower daily physical activity levels in patients with diabetes, and our findings may just be a product of the successful matching of our groups for high BMI 11. Third, we found no differences in daily lying duration between our groups and, reassuringly, our DPN patient findings (540 minutes per day) aligned very closely with the only other known study that reported DPN patients' daily lying duration (550 minutes per day) 13. Last, our study found no differences for daily sleep duration or quality. This was in contrast to a previous study that found lower daily sleep duration and quality in DPN patients 12. Yet, unlike this previous study 12, we excluded patients with painful DPN (i.e. we only included painless DPN in those groups with DPN) or sleep apnoea, which are known to negatively impact on sleep 39, 40, and their exclusion may explain why we did not find any daily sleep differences 12.

Overall, the interpretation of our free‐living daily activity outcome findings, together with those of previous laboratory‐based studies, suggests that patients with DFU expend more daily energy than controls to perform the same daily activities. A number of hypotheses may explain this imbalance between daily steps and daily energy expenditure in DFU patients. First, the offloading devices worn by DFU patients may be heavier than the typical off‐the‐shelf footwear worn by DPN and DM patients, and thus, DFU patients expend more energy during daily walking activity to carry their heavier offloading devices. However, we were unable to find any differences in the daily walking activity or daily energy expenditure outcomes of our subgroups of DFU patients who wore heavier non‐removable, knee‐high, offloading devices compared to those DFU patients who wore other offloading devices considered to be of similar weight to typical off‐the‐shelf footwear. Second, DFU patients may perform additional non‐walking daily activities that expend additional energy than controls; for instance, a previous study reported that people with DPN have comparatively high standing durations, which may increase daily energy expenditure 13. However, again, we were unable to find any differences between our groups in other daily activity outcomes in our study. Third, a DFU may be an indicator of significantly deteriorating general health as daily energy expenditure has been found to increase just to maintain normal daily activity as the severity of many health conditions worsens 41, 42. However, we reported very similar demographic and comorbidity characteristics in our groups, indicating they had similar general health status. Fourth, as reported in other wound types 42, 43, it may be that the patients' active wound (DFU) requires significantly increased energy to heal, which accounts for the increased daily energy expenditure in DFU patients. Last, and possibly most plausibly, DFU patients may have a highly energy‐inefficient gait caused by the DFU or the severe DPN underlying the DFU. Previous studies suggest that patients with severe DPN adopt a highly rigid energy‐inefficient gait strategy to compensate for a lack of balance, inelastic lower leg tendons from non‐enzymatic glycation and foot deformities that result from DPN 14, 44. This gait strategy may arguably be the most likely hypothesis of all to explain the increased daily energy expenditure of DFU patients to perform less daily walking activity in their free‐living environments 14, 44.

Regardless, our daily activity findings in patients' free‐living environments are consistent with the findings from laboratory‐based studies and indicate that DFU patients, on average, walk less than controls but use more energy in doing so. These findings warrant a number of future recommendations. First, laboratory‐based studies are now needed to confirm if DFU patients do adopt a different gait strategy and in turn use more energy to perform the same walking tasks as controls in controlled environments. Second, future studies should measure additional daily activity outcomes in DFU patients that were not captured in our study and that may impact daily activity, such as plantar pressures, standing durations, bouts of activity and upper body activities. Third, longitudinal studies are recommended to investigate if daily steps and energy expenditure remain different over time in DFU patients and if these differences also occur in patients with healing versus non‐healing DFU. Last, as recommended by others, future studies are still required to investigate the gradual increase of daily activity in DPN and DFU patients and the impact on their physical fitness, plantar tissue health and DFU prevention and healing 3, 4, 8, 9, but only when appropriate offloading of plantar pressures and monitoring of a range of daily activity outcomes are also incorporated.

Strengths and limitations

This study has several strengths. First, our study was adequately powered based on the findings of previous daily activity studies. Second, we excluded patients with other conditions that would potentially adversely impact normal daily activity, such as those with PAD, painful DPN, major amputation, mobility aide to ambulate and sleep apnoea. Third, groups were well‐matched, except for age and foot deformities; however, age was matched for the DFU and DM group, and the prevalence of foot deformities are known to increase as DPN severity increases as per our groups 5, 6. Fourth, all participant characteristics were captured using valid and reliable tools 2, 15 and according to international reporting standards for diabetic foot studies 45. Fifth, we used a multi‐sensor device to measure the multiple daily activity outcomes we reported, and this device has been tested to be valid and reliable to measure these multiple different daily activity outcomes in the free‐living conditions of cohorts of patients with different conditions 21, 22, 23, 24, 25, 26, 27, 28, 29, 30; this device has also been successfully used for the same purposes in multiple other diabetes studies 33, 34, 35. Last, we used a validated sleep quality tool to help corroborate the sleep duration findings 20.

However, this study also has several limitations. First, like most other studies in this field, our study was cross‐sectional, and any differences identified cannot be confirmed as causal. Second, we were unable to match the age of the DPN to the DFU group; however, we were able to match the age of the DM to the DFU group, which also showed differences in daily activity outcomes. Third, although the multi‐sensor armband device has been validated to measure the different daily activity outcomes used in our study in very similar patient cohorts (with similar foot complications) to those with DPN or DFU investigated in our study (such as diabetes, older age, pulmonary disease and rheumatoid arthritis cohorts) 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, it has not been specifically validated in patients with DPN or DFU, and further validity studies to test these daily activity outcomes in patients with DFU and DPN are required. Fourth, apart from offloading devices, we did not measure other concurrent treatments that may have impacted daily activity. Last, we did not capture any clinical outcomes or standardise the DFU group to any particular phase of DFU healing. A very recent study suggested that patients with DFU report different daily walking activity in different phases of DFU healing 46, and our study was unable to indicate if daily activity findings were indicative of better or worse clinical outcomes.

In conclusion, this is the first study to simultaneously measure a range of daily activity outcomes in patients with DPN and DFU in their free‐living environments. Findings suggest that people with DFU are as sedentary as patients with DPN and DM; however, patients with DFU take fewer daily steps and expend more energy during daily activities than patients with DPN and DM. It is recommended that future studies investigate the relationship between daily steps and daily energy expenditure to confirm if these findings remain over time and if this impacts the clinical outcomes of DFU prevention and healing.