Estimates of energy expenditure using the RT3 accelerometer in patients with systemic lupus erythematosus

doi:10.4236/health.2010.26089

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Vol.2, No.6, 603-608 (2010) Health

doi:10.4236/health.2010.26089

Estimates of energy expenditure using the RT3

accelerometer in patients with systemic lupus

erythematosus

Tim K. Tso1*, Wen-Nan Huang2, Chen-Kang Chang3

1Department of Food Science, National Chiayi University, Chia-Yi, Taiwan, China;

*Corresponding Author: timtso@mail.ncyu.edu.tw

2Department of Allergy, Immunology and Rheumatology, Taichung Veterans General Hospital, Taichung, Taiwan, China

3Sport Science Research Center, Taiwan Sport University, Taichung, Taiwan, China

Received 16 November 2009; revised 15 January 2010; accepted 1 February 2010.

ABSTRACT

This study aimed to characterize energy expen-

diture patterns using the tri-axial accelerometer

and to identify the association of energy exp-

enditure with clinical parameters in patients with

systemic lupus erythematosus (SLE). Estimates

of energy expenditures represented by total ac-

tivity calorie (TA), physical activity calorie (PA),

total activity calorie per body weight (TABW),

and physical activity calorie per body weight

(PABW) of 49 female SLE patients were ass-

essed using the RT3 tri-axial accelerometer

(StayHealthy, Monrovia, CA) in a seven-day per-

iod. SLE patients in the highest body mass ind-

ex (BMI) tertile showed significantly lower valu-

es of TABW compared to those in the lowest

tertile, while SLE patients in the lowest TABW

tertile showed significantly higher body weight,

waist circumference, BMI, SLE disease activity

index (SLEDAI), dosage of prednisone, and

blood pressure. There was a high prevalence of

metabolic syndrome and SLE patients with

metabolic syndrome showed significantly lower

TABW. In addition, both TABW and PABW sig-

nificantly but negatively correlated with SLEDAI.

In conclusion, the RT3 accelerometer is suitable

for evaluating total and physical activity-related

energy expenditure in patients with SLE. TABW

measured by the tri-axial accelerometer is inv-

ersely related with body weight status and dise-

ase activity in SLE patients. This suggests that

estimates of energy expenditure by the tri-axial

accelerometer may be applied in the manage-

ment of SLE.

Keywords: Accelerometer; Body mass index;

Energy Expenditure; Systemic Lupus Erythematosus

1. INTRODUCTION

Systemic lupus erythematosus (SLE) is a chronic auto-

immune disease characterized not only by the activation

of T and polyclonal B cells but also by a wide variety of

immunologic abnormalities [1]. Previous studies demo-

nstrate that SLE patients present with limitations in ex-

ercise capacity and reduced quality of life due to various

clinical complaints [2]. The exercise intolerance of SLE

patients is associated with a reduced aerobic capacity of

peripheral muscles [3], such that SLE patients are less

aerobically fit, with reduced exercise capacity, reduced

muscle strength, more fatigue, and greater disability

compared to sedentary controls [4].

The incidence of SLE is higher in females than in

males. There is strong evidence on the relationship bet-

ween physical activity and the primary prevention of

chronic health problems in women [5]. Estimates of en-

ergy expenditure provided a better indicator of physical

activity. However, methods to assess energy expenditure

have strengths and limitations [6].

The RT3 accelerometer, an integrated tri-axial accel-

erometer giving output measures in medio-lateral, ante-

rior-posterior, and vertical dimensions, is a valid tool for

assessing physical activity [7-9]. Although its reliability,

validation, and application in measuring physical active-

ity in different population have been reported [10-15],

the relationship between disease activity and energy ex-

penditure measured by the RT3 accelerometer in SLE

patients has not been previously established.

This study aimed to characterize energy expenditure

patterns using the RT3 accelerometer and identify any

relationship between energy expenditure and clinical

parameters in SLE patients.

T. K. Tso et al. / HEALTH 2 (2010) 603-608

604

2. MATERIALS AND METHODS

Forty-nine (49) Chinese female SLE patients aged 20-50

years who fulfilled the American College of Rheuma-

tology criteria [16] and had no contraindications to

physical activity were randomly selected from the outpa-

tient clinics of Taichung Veterans General Hospital

(Taichung, Taiwan). The hospital’s ethical committee

approved the study and all SLE patients provided written

informed consent.

Energy expenditure was assessed using the RT3 Tri-

axial Activity Measurement and Recording System (Stay-

Healthy, Monrovia, CA, USA). The RT3 was a relatively

small device (the size of a pager) and used an integrated

tri-axial accelerometer. These were worn by the SLE

patients in nylon pouches secured to a belt at the waist-

line above each hip during the seven-day period. The

patients’ profiles, including age, height, and weight,

were entered into the RT3 accelerometer and the accel-

eration was measured periodically. Information obtained

was then converted into energy expenditure estimates

that included total activity calorie (TA), physical activity

calorie (PA), total activity calorie per body weight

(TABW), and physical activity calorie per body weight

(PABW).

Anti-dsDNA was measured by enzyme-linked immu-

nosorbent assay using a Quanta LiteTM dsDNA Kit

(INOVA Diagnostics Inc., San Diego, CA, USA). Quan-

titative determinations of serum C3 and C4 were con-

ducted using N Antisera to Human Complement Factor

reagents with the Behring Nephelometers (Dade Behring,

Inc., Newark, DE, USA). Disease activity was deter-

mined using the SLE Disease Activity Index (SLEDAI)

[17], while enzymatic methods were used to determine

circulating concentrations of total cholesterol (Beckman

TC Reagent) and triglyceride (TG) (Beckman TG Re-

agent). Magnesium-dextran sulfate precipitation reagent

was used to separate high-density lipoprotein-cholesterol

(HDL-C), which was then assessed enzymatically.

Low-density lipoprotein-cholesterol (LDL-C) was det-

ermined by the Friedewald equation [18].

Metabolic syndrome was based on the National Cho-

lesterol Education Program (NCEP/ATP III) definition

[19]. SLE patients were defined as having metabolic

syndrome in the presence of three or more of the fol-

lowing criteria: waist circumference > 88 cm; systolic

blood pressure > 130 mm Hg or diastolic blood pressure

> 85 mmHg; HDL-C < 50 mg/dL; TG > 150 mg/dL; and

fasting blood glucose > 110 mg/dL.

Statistical analyses were performed using the Statisti-

cal Package of Social Sciences (SPSS) 10.0 for Win-

dows (SPSS Inc., Chicago, IL, USA). Tested variables

for comparison of means were expressed as mean ±

standard deviation and 95% confidence interval. The

distribution of tested variables was examined graphically

for normality. Kruskal-Wallis test and Mann-Whitney U

test were used to examine the mean differences of en-

ergy expenditure between the SLE patients stratified by

BMI and metabolic syndrome. Analysis of variance

(ANOVA) was also used to examine the mean differen-

ces of test parameters among SLE patients stratified by

tertiles of TABW as measured by the RT3 accelerometer.

In addition, Pearson’s or Spearman correlation analysis

was used accordingly to examine the relationships be-

tween estimates of energy expenditure and test variables.

A p value < 0.05 was considered significant for all sta-

tistical analyses in this study.

3. RESULTS

All of the patients were non-smokers, performed regular

daily activities, and did not attend any supervised exer-

cise training program during the experiment period. Av-

erage estimates of energy expenditures measured by the

RT3 accelerometer were 1730 ± 218 Kcal/day TA, 284 ±

108 Kcal/day PA, 26 ± 3 Kcal/kg/day TABW, and 4 ± 1

Kcal/kg/day PABW. Thirty-six patients (74%) had a

normal BMI (< 25 kg/m2), nine (18%) were overweight

(25-29.9 kg/m2), and four (8%) were obese (> 30 kg/m2).

Compared to patients with normal BMI, overweight or

obese patients had higher SLEDAI (mean: 3.38 ± 2.50, n

= 13 vs. 1.28 ± 1.80, n = 36, p = 0.013) and lower

TABW (mean: 23.42 ± 1.92 Kcal/kg/day, n = 13 vs.

27.25 ± 2.60 Kcal/kg/day, n = 36, p < 0.001). The me-

dian SLEDAI value in all patients was 2 and only 31%

of patients had SLEDAI scores higher than 3, indicating

that most of the patients had stable or moderately active

disease status [20]. However, SLEDAI significantly cor-

related with body weight (r = 0.434, p = 0.002) and BMI

(r = 0.379, p = 0.007). Both TABW (r = –0.303, p =

0.034) and PABW (r = –0.301, p = 0.035) negatively

correlated with SLEDAI.

Estimates of energy expenditure measured by the RT3

accelerometer in SLE patients stratified by BMI were

shown in Table 1. SLE patients in the highest BMI ter-

tile showed significantly higher TA and PA, and signify-

cantly lower TABW compared to those in the lowest

tertile. In addition, there was a significant negative cor-

relation between BMI and TABW (r = –0.668, p <

0.001).

Estimates of energy expenditure in SLE patients with

and without metabolic syndrome were shown in Table 2.

According to the NCEP/ATP III definition, 21 patients

(43%) met the criteria for metabolic syndrome. They had

significantly higher TA and PA, and significantly lower

TABW.

T. K. Tso et al. / HEALTH 2 (2010) 603-608

605

Table 1. Estimates of energy expenditure by RT3 accelerometer in SLE patients stratified by body mass index (n = 49)a.

Body mass index (kg/m2) tertiles

< 20.5 kg/m2 20.5 - 23.6 kg/m2 > 23.6 kg/m2

Overall P valueb

TA (Kcal/day) 1611 ± 118 (1549 – 1674) 1696 ± 263 (1561 – 1831) 1886 ± 147 (1808 – 1964) < 0.001*

TABW (Kcal/kg/day) 28.11 ± 2.10 (26.99 – 29.22) 26.50 ± 2.97 (24.97 – 28.02) 24.09 ± 2.35 (22.84 – 25.34) < 0.001*

PA (Kcal/day) 244 ± 79 (202 – 287) 263 ± 98 (213 – 313) 347 ± 119 (284 – 411) 0.027*

PABW (Kcal/kg/day) 4.22 ± 1.19 (3.58 – 4.85) 4.10 ± 1.30 (3.43 – 4.77) 4.56 ± 1.54 (3.74 – 5.38) 0.694

Abbreviations: TA, Total activity calorie; TABW, Total activity calorie per body weight; PA, Physical activity calorie; PABW, Physical activity calorie

per body weight

aValues are expressed as mean ± standard deviation and 95% confidence interval.

bStatistical significance (*p < 0.05) as determined by the Kruskal-Wallis test.

Table 2. Estimates of energy expenditure by RT3 accelerometer in SLE patients with and without metabolic syndromea.

SLE patients without

metabolic syndrome (n = 28)

SLE patients with

metabolic syndrome (n = 21) P valueb

TA (Kcal/day) 1668 ± 149 (1602 – 1734) 1894 ± 267 (1772 – 2016) 0.001*

TABW (Kcal/kg/day) 31.56 ± 2.70 (30.36 – 32.76) 29.78 ± 4.25 (27.85 – 31.72) 0.009*

PA (Kcal/day) 264 ± 101 (220 – 309) 390 ± 226 (287 – 493) 0.039*

PABW (Kcal/kg/day) 4.97 ± 1.79 (4.18 – 5.77) 6.06 ± 3.53 (4.45 – 7.67) 0.409

Abbreviations: TA, Total activity calorie; TABW, Total activity calorie per body weight; PA, Physical activity calorie; PABW, Physical activity calorie

per body weight

aValues are expressed as mean ± standard deviation and 95% confidence interval.

bStatistical significance (*p<0.05) was determined by Mann-Whitney U test.

The mean differences of anthropometric measure-

ments, disease activity-related variables, and lipid profile

between patients stratified into tertiles based on TABW

were shown in Table 3. SLE patients in the lowest

TABW tertile showed higher body weight, waist circ-

umference, BMI, SLEDAI, dosage of prednisone, and

blood pressure. Patients in the higher TABW tertile

tended to have reduced concentrations of total cholest-

erol, TG and LDL-C but the differences were not statis-

tically significant.

4. DISCUSSION

This study evaluated estimates of energy expenditure by

using the RT3 accelerometer in 49 female SLE patients.

The major finding was that estimates of energy expen-

diture represented as daily TABW and PABW were

negatively associated with disease activity.

There is a number of assessments available for evalu-

ating physical activity, such as self-administered ques-

tionnaires of physical activity, pedometers, accelerome-

ters, and supervised cardio-vascular training programs

[11,21,22]. However, each method has its own strengths

and limitations. The RT3 accelerometer is used to assess

physical activity in children [10,11], adolescents [11],

overweight adults [12], pregnant women [13], individu-

als with multiple sclerosis [14], and older adults with

coronary heart disease [15]. Klassen et al. report that the

RT3 accelerometer can detect a significant difference

between moderately active and active individuals with

multiple sclerosis [14]. Chu et al. have demonstrated that

RT3 movement counts increases in a linear manner with

scaled oxygen uptake from stationary to vigorous inten-

sity movement in children [10]. In the present study, the

RT3 accelerometer is used to assess estimates of energy

expenditure in SLE patients and is proven to be user-

friendly and an acceptable measure of free-living physic-

cal activity in such population. The RT3 accelerometer

appears to distinguish estimates of energy expenditure in

SLE patients with varying clinical characteristics.

Recent studies demonstrate the beneficial effects of

exercise in SLE patients in terms of improving fatigue,

physical function, aerobic fitness, and quality of life

[22-25]. Aerobic exercises performed on a treadmill do

not aggravate disease activity at any time during an ex-

ercise period and may provide some benefits on fatigue

T. K. Tso et al. / HEALTH 2 (2010) 603-608

606

Table 3. Characteristics of SLE patients in the respective tertiles of total activity calorie per body weight (n = 49)a.

Total activity calorie per body weight (Kcal/kg/day) tertiles

< 24.91 (Kcal/kg/day) 24.91-27.17 (Kcal/kg/day) > 27.17 (Kcal/kg/day)

Overall P valueb

Weight (kg) 66.87 ± 9.95 (61.56 – 72.17) 55.74 ± 6.10 (52.49 – 58.99) 50.15 ± 6.12 (47.00 – 53.29) <0.001*

BMI (kg/m2) 26.96 ± 4.69 (24.45 – 29.46) 22.03 ± 1.93 (20.99 – 23.06) 20.62 ± 2.30 (19.43 – 21.80) <0.001*

Waist circumference (cm) 88.39 ± 12.65 (81.09 – 95.69) 78.70 ± 8.77 (73.85 – 83.55) 74.89 ± 5.49 (71.72 – 78.06) 0.002*

Anti-dsDNA (IU/ml) 129.14 ± 181.57 (32.38 – 225.89)115.49 ± 133.08 (44.57 – 186.40)151.50 ± 195.41 (51.03 – 251.97) 0.833

C 3 (mg/dl) 84.58 ± 22.73 (72.46 – 96.69) 93.93 ± 20.71 (82.89 – 104.96)89.34 ± 16.77 (80.72 – 97.97) 0.429

C 4 (mg/dl) 16.09 ± 9.19 (11.19 – 20.99) 16.20 ± 9.61 (11.08 – 21.32) 18.11 ± 9.08 (13.44 – 22.78) 0.781

SLEDAI 3.38 ± 2.28 (2.16 – 4.59) 1.00 ± 1.79 (0.05 – 1.95) 1.18 ± 1.74 (0.28 – 2.07) 0.002*

Prednisone (mg/day) 12.03 ± 5.18 (9.27 – 14.79) 6.88 ± 4.13 (4.67 – 9.08) 7.79 ± 6.67 (4.37 – 11.22) 0.023*

TC (mmol/l) 5.32 ± 1.18 (4.70 – 5.95) 5.21 ± 1.01 (4.67 – 5.75) 4.65 ± 0.86 (4.21 – 5.09) 0.139

TG (mmol/l) 1.48 ± 0.77 (1.07 – 1.89) 0.99 ± 0.34 (0.81 – 1.17) 1.20 ± 0.50 (0.94 – 1.46) 0.061

LDL-C (mmol/l) 2.94 ± 1.03 (2.39 – 3.49) 2.82 ± 0.72 (2.44 – 3.20) 2.49 ± 0.60 (2.19 – 2.80) 0.264

HDL-C (mmol/l) 1.71 ± 0.49 (1.45 – 1.97) 1.93 ± 0.62 (1.61 – 2.26) 1.61 ± 0.47 (1.37 – 1.85) 0.207

TC/HDL-C 3.36 ± 0.88 (2.86 – 3.87) 2.83 ± 0.50 (2.55 – 3.10) 3.15 ± 0.76 (2.71 – 3.59) 0.144

SBP (mmHg) 153 ± 29.22 (136.13 – 169.87)126.13 ± 28.37 (110.42 – 141.84)121.29 ± 14.92 (112.67 – 129.90) 0.004*

DBP (mmHg) 91.14 ± 19.35 (79.97 – 102.32)78.67 ± 16.70 (69.42 – 87.92) 74.43 ± 12.99 (66.93 – 81.93) 0.029*

Abbreviations: BMI, body mass index; C3, complement factor 3; C4, complement factor 4; SLEDAI, systemic lupus erythematosus disease activity

index; TC, total cholesterol; TG, triglyceride; LDL-C, low-density lipoprotein-cholesterol; HDL-C, high-density lipoprotein-cholesterol; SBP, systolic

blood pressure; DBP, diastolic blood pressure

aValues are expressed as mean ± standard deviation and 95% confidence interval.

bStatistical significance (*p < 0.05) as determined by ANOVA test.

and physical function in SLE patients with low disease

activity [25]. In a 12-week supervised cardio-vascular

training program, SLE patients have shown improved

exercise tolerance, aerobic capacity, oxygen pulse, fat-

igue, quality of life, depression, and functional capacity

[22]. In a pilot study on the effect of exercise in SLE

patients, both aerobic and range of motion/muscle

strengthening types of exercises are safe and do not

worsen SLE disease activity [23]. In the present study,

SLE patients with lowest TABW tertile show higher

SLEDAI and dosage of prednisone. It also identifies

both TABW and PABW to be inversely correlated with

SLEDAI, suggesting that improved daily energy expen-

diture may be beneficial to disease management in SLE.

Obesity is independently associated with impaired

functional capacity and health-related quality of life in

patients with SLE [26] and disease activity is predictive

of deleterious increases in BMI [27]. Although only 26%

of patients in this study are overweight or obese with

BMI > 25 kg/m2, they have higher SLEDAI and lower

TABW. SLE patients in the lowest TABW tertile show

the highest body weight, waist circumference, BMI,

SLEDAI, dosage of prednisone, and blood pressure, as

well as a positive correlation between BMI and SLEDAI

(r = 0.379, p = 0.007). Taken together, the findings here

suggest that less energy expenditure corresponding to

increased BMI may aggravate, at least partly, the disease

activity in female SLE patients. However, due to lack of

self-reported information about the time record and

types of activity when the RT3 accelerometer was on

and off, physical activity intensity and metabolic equiv-

alent energy expenditure cannot be completely evaluated.

Recent studies demonstrate a higher prevalence of in-

sulin resistance and metabolic syndrome in SLE patients

[28,29]. The high prevalence of metabolic syndrome is

confirmed in the present study wherein 21 of 49 (43%)

SLE patients have metabolic syndrome using the NCEP/

ATP III definition. Physical activity energy expenditure

can predict progression towards metabolic syndrome in

middle-aged healthy Caucasians [30]. SLE patients with

metabolic syndrome in the present study show signify-

cantly lower TABW. In addition, patients with higher

T. K. Tso et al. / HEALTH 2 (2010) 603-608

607

TABW tend to have reduced concentrations of total cho-

lesterol, TG, and LDL-cholesterol. However, the lipid

profiles of most patients in this study are within normal

range and not considered dyslipidemic [19], which can

limit possible effect of physical activity-related energy

expenditure on circulating lipid levels.

In conclusion, as increasing physical activity can be a

component of lifestyle interventions designed to improve

quality of life and functional capacity in SLE patients,

this study demonstrates the relationship among estimates

of energy expenditure measured by RT3 accelerometer,

disease activity, and components of metabolic syndrome.

Incorporating physical activity-related energy expendi-

ture into the clinical management of SLE may be bene-

ficial.

5. ACKNOWLEDGEMENTS

This study was supported by a research grant from the National Sci-

ence Council of Taiwan (NSC 96-2413-H-415-006-MY2). The authors

wish to thank the Biostatistics Task Force of Taichung Veterans Gen-

eral Hospital for their assistance in the statistical analysis. The authors

also thank Ms Ging-Yi Lin for her technical assistance.

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