Assessment of habitual physical activity and energy expenditure in dialysis patients and relationships to nutritional parameters

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1 Clin i cal Nephrology, Vol. 75 No. 3/2011 ( ) Assessment of habitual physical activity and energy expenditure in dialysis patients and relationships to nutritional parameters Original 2011 Dustri-Verlag Dr. K. Feistle ISSN DOI /CNP75218 A. Cupisti 1, A. Capitanini 2, G. Betti 3, C. D Alessandro 1 and G. Barsotti 1 1 Division of Nephrology, Department of Internal Medicine, University of Pisa, Pisa, 2 Nephrology and Dialysis, Pescia Hospital, Pescia, and 3 Nephrology and Dialysis, Massa-Carrara Hospital, Massa-Carrara, Italy Physical activity in dialysis patients Key words phys i cal ac tiv ity energy ex pen di ture dialysis nu tri tion pa - ram e ters exercise CKD Re ceived May 10, 2010; ac cepted in re vised from July 6, 2010 Cor re spon dence to A. Cupisti, MD, PhD Di vi sion of Nephrology, De part ment of In ter nal Med i cine, Uni ver sity of Pisa, Via Roma 67, Pisa, It aly acupisti@med.unipi.it Ab stract. Back ground and aim: As sess - ment of phys i cal ac tiv ity level and of en ergy expenditure is important in the clinical and nu tri tional care of di al y sis pa tients, but it is not so easy to ac com plish. The SenseWear Armband (SWA) is a novel multisensory de - vice that is worn on the up per arm and col lects a va ri ety of phys i o logic data re lated to phys i - cal ac tiv ity. Thus, du ra tion and in ten sity of physical activity is recorded and expressed as METs (Met a bolic Equiv a lent Task), and en - ergy ex pen di ture is es ti mated. The aim of our study was to as sess interdialytic spon ta ne ous physical activity in stable chronic hemo - dialysis (HD) pa tients and the re la tion to nu - tritional status and dietary nutrient intake. Pa - tients and meth ods: In 50 sta ble pa tients on main te nance hemodialysis treat ment and 33 nor mal sub jects (con trol group), level of spon ta ne ous phys i cal ac tiv ity and es ti mated daily energy expenditure was assessed by SWA and re lated to bio chem is try and anthro - pometry data, bioelectric im ped ance vec tor anal y sis, and en ergy and nu tri ent in take in for - ma tion com ing from a 3-day food re call. Re - sults: In re spect to con trols, HD pa tients showed lower mean daily METs value (1.3 ± 0.3 vs. 1.5 ± 0.2, p < 0.01), a lower time spent on activities > 3 METs (89 ± 85 vs. 143 ± 104 min/day, p < 0.05), lower num ber of steps per day (5,584 ± 3,734 vs. 11,735 ± 5,130, p < 0.001), re sult ing in a lower es ti mated en - ergy ex pen di ture (2,190 ± 629 vs. 2,462 ± 443 Kcal/day, p < 0.05). 31 out of the 50 HD pa - tients (62%) had a mean daily value < 1.4 METs and hence were de fined as sed en tary. They dif fered from the ac tive pa tients for higher age (63 ± 12 vs. 54 ± 12 y, p < 0.01), lower en ergy in take (26.1 ± 6.4 vs ± 11.3 Kcal/day, p < 0.05) and lower phase an - gle (5.5 ± 1.0 vs. 6.3 ± 0.9, p < 0.05). SWAbased es ti ma tion of daily en ergy ex pen di ture was neg a tively re lated to age (r = 0.31, p < 0.05), whereas pos i tive re la tions were ob - served with BMI (r = 0.51, p < 0.001), phase an gle (r = 0.40, p < 0.01), se rum phos phate (r = 0.49, p < 0.001) and al bu min (r = 0.41, p < 0.01). The mean daily METs val ues were strongly re lated to nor mal ized en ergy in take (r = 0.47, p < 0.001) and also to pro tein in take (r = 0.33, p < 0.05) and to phase an gle (r = 0.38, p < 0.01). Mul ti ple re gres sion anal y sis showed that en ergy in take and di etary pro tein in take were in de pend ently re lated to the in - tensity of physical activity. Con clu sion: Our findings indicate that poor physical activity is highly prevalent in stable dialysis patients even when free from phys i cal or neu ro log i cal dis abil i ties or se vere comorbid con di tions. The level and in ten sity of phys i cal ac tiv ity is pos i tively re lated to body composition and to di etary nu tri ent in take. This con firms the strong interrelationship between exercise and nutrition, which in turn are as so ci ated with sur - vival, re ha bil i ta tion and qual ity of life in di al - ysis patients. Introduction Pre vi ous stud ies have re ported that the limits of physical capability are largely re - duced in hemodialysis (HD) pa tients when com pared with healthy sub jects [1, 2, 3]. Di - alysis patients may suffer from cardiovascu - lar dis ease, di a be tes, mal nu tri tion, and de - pres sion, which limit their ex er cise ca pac ity. Nevertheless, evidence exists that mainte - nance of regular physical exercise may favor re ha bil i ta tion of pa tients and cor rec tion of several cardiovascular, metabolic and nutri - tional abnormalities. Data from the literature suggest that inactivity is associated with in - creased mor tal ity risk [4, 5, 6], whereas phys - i cal ex er cise is re lated to qual ity of life and nu tri tion [7, 8, 9, 10]. Namely, reg u lar phys i - cal activity may ameliorate appetite and

2 Phys i cal ac tiv ity in di al y sis pa tients 219 main tain mus cle mass. In turn, adequate energy and protein intake are mandatory for physical performance and good nutritional status. Sev eral ep i de mi o log i cal stud ies showed that pro tein and en ergy in take in di al y sis pa - tients is largely lower than rec om mended [11, 12]. The min i mum en ergy re quire ment should be no less than the to tal en ergy ex pen - di ture that is due to rest ing en ergy ex pen di - ture (60 75%) plus en ergy con sumed dur ing phys i cal ac tiv ity (25 40%). There fore, eval - uation of physical activity is important to as - sess nutritional requirements. This indicates that it would be valu able to de ter mine rest en - ergy ex pen di ture as well as the type, quan tity and intensity of physical activity in order to plan per son al ized di etary and re ha bil i ta tion pro grams and to test the ef fi cacy of spe cific interventions in HD patients. Physical activ - ity re cords and ques tion naires pro vide a sin - gle, con ve nient, low-cost es ti ma tion of phys i - cal ac tiv ity and/or en ergy ex pen di ture, but they are quite sub jec tive and not very re li able meth ods [13, 14, 15]. More re li able quan ti fi - ca tion of spon ta ne ous phys i cal ac tiv ity can be obtained by tri-axial accelerometers, that is, elec tronic de vices worn on the waist to de tect move ments in three planes of mo tion, namely mediolateral, anteroposterior, and vertical. Electric transducers and microprocessors detect accelerations and convert them into digital signals [2, 16]. The SenseWear Armband is a multi - sensory de vice in clud ing a two-axis ac cel er - om e ter, heat flux sen sor, skin tem per a ture sen sor, near-body am bi ent tem per a ture sen - sor, and gal vanic skin re sponse sen sor. It is worn on the up per arm and col lects a va ri ety of phys i o logic data re lated to phys i cal ac tiv - ity. Duration and intensity of physical activity are re corded and daily en ergy ex pen di ture is es ti mated by soft ware based on a pro pri etary al go rithm [17]. This mul ti ple sen sor ar ray was de signed to over come the lim i ta tions of other ob jec tive or sub jec tive en ergy ex pen di - ture as sess ment tools [18], and it has been val - i dated and used in a number of physiological and pathological conditions [19, 20, 21, 22]. The aim of our study was to as sess inter - dialytic spon ta ne ous phys i cal ac tiv ity by SWA in sta ble chronic hemodialysis (HD) pa - tients and the re la tion to nu tri tional sta tus and dietary nutrient intake. Patients and methods Patients 50 sta ble pa tients (32 male, 18 fe male; aged 59 ± 13 y) on main te nance HD treat ment (time on di al y sis 89 ± 78 months), who had no ma jor skel e tal, mus cu lar or neu ro log i cal dis - abil i ties, or had not re ported se vere im pair - ment with walk ing, were qual i fied for enroll - ment in the study. Pa tients with se vere car diac fail ure (Stage IV NYHA), or re spi ra tory in suf fi ciency, can - cer, de men tia, psy chi at ric or neu ro logic dis - eases, and inflammatory systemic diseases were excluded. Hospitalization within the last three months, ther a pies with ste roids and/or immunosuppressive drugs were also con sid - ered as exclusion criteria. The underlying renal diseases were chronic glomerulonephritis in 13 cases, di a betic ne - phrop athy in 6 cases, vas cu lar nephro pathy in 10 cases, polycystic kid ney dis ease in 8 cases, chronic in ter sti tial nephropathy in 5 and un - known in 8 cases. All the pa tients were on a thrice-weekly HD treat ment, for min utes; 23 pa tients were on on- line hemo - dia fil tration, 19 pa tients on stan dard bi car - bon ate di al y sis and 8 pa tients on acetate- free bio filtra tion. In all the cases syn thetic and highly biocompatible mem branes were used (low-flux and high flux poly sulphone, AN69, polyammide). Vascular access was native arteriovenous fis tula in 41 cases, arteriovenous graft in 6 cases and per ma nent cen tral vein cath e ter in 3 cases. 33 nor mal sub jects, com pa ra ble for age, sex and body mass in dex, served as con trols. All pa tients gave their in formed con sent to the study that was ap proved by the Eth ics Committee of the Pisa University Hospital. Physical activity and energy expenditure assessment The level of phys i cal ac tiv ity and es ti - mated daily to tal en ergy ex pen di ture (TEE) un der free-liv ing con di tions were as sessed by SenseWear Armband (SWA, BodyMedia, Pitts burgh, PA, USA). This de vice is worn on the up per arm (the nondominant one or that is free from arteriovenous fis tula or graft) over the tri ceps mus cle, in the mid dle tract be -

3 Cupisti, Capitanini, Betti et al. 220 tween acromion and olecranon pro cesses. Sub jects were in structed to main tain their usual daily life hab its while wear ing the mon - i tor and to re move it only for showers or water activities. The SWA de vice col lects a va ri ety of phys i o logic data through mul ti ple sen sors (a two-axis accelerometer, heat flux sensor, skin tem per a ture sen sor, near-body am bi ent tem - per a ture sen sor, and gal vanic skin re sponse sen sor) that are up loaded and an a lyzed us ing soft ware (InnerView Re search Software, Version 6.1). This mul ti chan nel ap proach, which in te - grates information from a biaxial accelerometer and heat-re lated sen sors, has shown to pro vide ad di tional in for ma tion that can not be ob tained solely from move ment sen sors and it has high sen si tiv ity in de tect ing even small changes in en ergy ex pen di ture as so ci ated with com plex ac tiv i ties. The SWA re ports ac - tual wear time, avoid ing the con sid er able chal lenge in de ter min ing whether a mon i tor was worn or not. These fea tures pro vide sev - eral advantages over traditional uniaxial accelerometers for assessing physical activity. The va lid ity of to tal en ergy ex pen di ture (TEE) es ti mates from the SWA has been sup - ported in stud ies us ing both in di rect cal o rim e - try and dou bly la beled wa ter [22]. The SWA has been val i dated both un der lab o ra tory con - di tions and un der free liv ing con di tions, and it has po ten tial advantages in accuracy when compared with traditional accelerometrybased monitors [17, 18, 19, 20, 21]. One of the eas i est ways for quan ti fy ing the intensity of a physical activity is the Metabolic Equiv a lent Task (MET) method. Kilocalories and metabolic equivalent are converted using the fol low ing equa tion: MET = Kcal/h/Kg b.w. One MET is the en ergy ex pended at rest. Thus, two METs in di cate twice the en ergy ex pended at rest, three METs tri ple the rest ing en ergy ex - pen di ture, and so on. For example, such activities as reading, lis ten ing to mu sic, and knit ting cor re spond ap prox i mately to METs. Walk ing slowly cor re sponds to METs; walk ing at 3 km/h or cy cling at 8 km/h cor re spond to 2 3 METs; play ing vol ley ball, cy cling at 10 km/h, and house hold clean ing cor re spond to 3 4 METs; walk ing at 6 km/h, cy cling at 16 km/h, skat ing at 15 km/h, or dig ging cor re - spond approximately to 5 6 METs. Mea sure ments were car ried out dur ing a mid- week interdialytic pe riod of 48 h and included num ber of steps and min utes spent in phys i cal ac tiv ity with an in ten sity > 3 MET/min, be tween 6 and 9 MET/min, or > 9 MET/min. Mean daily METs val ues may be con sid - ered as a mea sure of the mean daily ac tiv ity level; for ex am ple, a daily av er age value < 1.4 METs de fines a sed en tary pa tient, whereas average values > 1.6 METs are associated with an ac tive life style. To tal en ergy ex pen di ture (re ported as 24 h av er age value) was eval u ated by a pro pri etary algorithm using information of movement, skin temperature, heat flow, near-body temperature and gal vanic skin re sponse, to gether with data about age, height, weight and gen der. To tal en ergy ex pen di ture was also eval u - ated us ing a pre dic tion equa tion, con sist ing of an es ti ma tion of rest ing en ergy ex pen di ture mul ti plied by an ac tiv ity fac tor. Namely, rest - ing en ergy ex pen di ture was cal cu lated us ing the Harris-Benedict formula and the activity fac tor var ied from 1.2 for min i mal phys i cal ac tiv ity, up to 1.5 for mod er ate but sig nif i cant phys i cal ac tiv ity and up to 1.8 for high physical activity [23]. Nutritional assessment Nu tri tional pa ram e ters in cluded bio - chemistry, bioelectric impedance vector anal - y sis (BIVA), height, and body weight be fore and af ter di al y sis. Body mass in dex (BMI) was calculated as follows: post-dialysis body weight (kg)/height 2 (m 2 ). Predialysis bio - chemical determinations included serum albumin, C reactive protein, phosphorus, calcium, and hematocrit. Se rum al bu min was mea - sured by the nephelometric method. De - creased al bu min lev els can be sug ges tive of protein malnutrition and/or inflammation [24] and rep re sent an un fa vor able prog nos tic sign. Se rum urea level was de ter mined be fore and after dialysis treatment to calculate a sin - gle pool Kt/V. BIVA was per formed at the end of the hemodialysis ses sion with a bioelectrical im - pedance analyzer (BIA/STA, Akern, Flor - ence, It aly) with a dis tal, tetrapolar tech nique, de liv er ing an ex ci ta tion cur rent at 50 khz [25]. BIVA pa ram e ters were mea sured in du -

4 Phys i cal ac tiv ity in di al y sis pa tients 221 plicate. BIVA gives two bioelectric pa ram e - ters: body re sis tance (R) and reactance (Xc), and the im ped ance vec tor (Z) is a com bi na - tion of R and Xc across tis sues. The arc tan - gent of Xc/R is called phase an gle (PA), which is a de rived mea sure ob tained from the re la tion be tween the di rect mea sures of re sis - tance and reactance re flect ing hydration sta - tus and soft tis sue cel lu lar mass. Re duced phase an gle re flects in creased ex tra- to intracellular wa ter ra tio as well as a de crease in body cell mass; it is a pre dic tor of sur vival in a num ber of dis eases and also in the di al y sis pop u la tion, where phase an gle val ues lower than 4.0 are as so ci ated with in creased mor - tal ity risk [26]. A BIVA-de rived parameter with prog nos tic value is also the body cell mass in dex (BCMI): val ues < 8.0 kg/m 2 are associated with unfavorable prognosis. Dietary nutrient intake assessment All the sub jects were seen in di vid u ally by reg is tered di eti cians to col lect a 3-day food re cord for en ergy and nu tri ent in take as sess - ment. The 3-day re calls were col lected by in - ter views dur ing which the sub jects were pro - vided with a color photo at las of com mon foods and their serv ings in or der to help them in es ti mat ing the real amounts of con sumed food. The 3-day di etary re call in cluded a di al - y sis day, a week end day and a nondialysis day as sug gested by re cent guide lines [23, 27]. Dietary composition was assessed with a computerized diet software (MetaDieta, Meteda, AP, It aly). To tal en ergy and nu tri ent in takes and their dis tri bu tion among meals were ex am ined. The daily in take for each stud ied nu tri ent was calculated as the average of the 3-day food records. Daily energy requirement was estimated by cal cu la tion of daily en ergy ex pen di ture, by Harris-Benedict equation multiplied by an ac - tivity factor, according to EBPG guide line on Nutrition [23]. Statistical analysis A statistical package, StatView 5 re lease for per sonal com puter, was used for processing data. Descriptive statistics are given as mean ± stan dard de vi a tion. Sta tis ti - cal anal y sis was per formed by Stu dent s t-test for un paired data. Lin ear cor re la tion anal y sis was per formed by Pearson s test. Stepwise multiple correlation analysis was used to study all the significant relationships with phys i cal ac tiv ity and en ergy ex pen di ture. Differences were considered to be statistically sig - nif i cant when p < Results Pa tients and con trols did not dif fer as far as body weight (71 ± 17 vs. 69 ± 13 kg), BMI (24.8 ± 4.6 vs ± 3.3 kg/m 2 ), and phase an gle (5.79 ± 1.04 vs ± 0.85 ) were con - cerned. In com par i son with con trols, HD pa tients showed lower daily av er age METs value (1.3 ± 0.3 vs. 1.5 ± 0.2, p < 0.01), a lower time spent on ac tiv i ties > 3 METs (89 ± 85 vs. 143 ± 104 min/d, p < 0.05), lower num ber of steps per day (5,584 ± 3,734 vs. 11,735 ± 5,130, p < 0.001), re sult ing in a lower es ti mated to tal en ergy ex pen di ture (2,190 ± 629 vs. 2,462 ± 443 kcal/d, p < 0.05). In HD pa tients, a trend to a lower energy expenditure, calculated by SWA, was ob served in di al y sis days com - pared to nondialysis days (2,145 ± 558 vs. 2,388 ± 708 kcal/d, p = 0.07, respectively). Dietary protein intake was significantly lower in the HD pa tients than in con trol sub - jects (68.0 ± 18.2 vs ± 29.7 g/d, 1.01 ± 0.35 vs ± 0.32 g/kg/d, p < 0.05), whereas to tal en ergy in take were more sim i lar (2,214 ± 618 vs. 2,462 ± 443 kcal/d, 28.5 ± 9.0 vs ± 5.8 kcal/kg/d, re spec tively). BIVA anal y sis showed sim i lar phase an gle val ues in pa tients and con trols (5.8 ± 1.0 vs. 5.7 ± 0.8 ), but BCMI was lower in HD pa - tients (8.5 ± 2.0 vs. 9.5 ± 2.0 kg/m 2, p < 0.05). Twelve of the 50 stud ied HD pa tients showed daily mean val ues of en ergy ex pen di - ture be tween 1.4 and 1.6 METs, and 7 pa tients over 1.6 METs; of con se quence, 31 out of the 50 stud ied pa tients (62%) had a mean daily value < 1.4 METs, and thus they were de fined as sed en tary. The prev a lence of a sed en tary con di tion was sig nif i cantly lower in the con - trol group (18%, p < 0.01). Table 1 shows some clin i cal data of the sed en tary and non-sed en tary di al y sis pa tients. Data about physical activity parameters derived by SWA elab o ra tion anal y sis in the two groups are re - ported in Table 2.

5 Cupisti, Capitanini, Betti et al. 222 Ta ble 1. Clin i cal and bio chem i cal data of the study sub jects, di vided by sed en - tary (< 1.4 METs) and ac tive ( 1.4 METs). Ac tive n = 19 Sed en tary n = 31 Age, y 53.6 ± ± 12.5 < Di al y sis age, months 123 ± ± 48 < 0.02 Kt/V 1.4 ± ± 0.2 ns BMI, kg/m ± ± 4.9 ns Phase an gle, 6.3 ± ± 1.0 < 0.01 S. Al bu min, g/dl 3.9 ± ± 0.4 ns npna, g/kg/d 1.16 ± ± 0.24 ns He mo glo bin, g/dl 12.0 ± ± 1.3 ns Hematocrit, % 37.3 ± ± 4.1 ns CRP, mg/dl 0.5 ± ± 0.4 ns ipth, pg/ml 319 ± ± 209 ns Ca P, mg 2 /dl ± ,5 ± 12,5 HCO 3, mmol/l 19.6 ± ± 1.8 = 0.03 EPO dose, IU/w 7210 ± ± 7984 ns EPO res I 10.5 ± ± 8.8 ns Ta ble 2. Data from Sense-Wear Arm-band (SWA), and com par i son of To tal En ergy Ex pen di ture (TEE) with data from pre dic tion equa tion and di etary re - calls. Data from SWA Ac tive n = 19 Sed en tary n = 31 Eval u at ing the du ra tion and in ten sity of phys i cal ac tiv ity, we ob served that 11 pa tients had a phys i cal ex pen di ture greater than 3 METs for min utes, 8 pa tients for min utes and 15 pa tients for over 120 min utes, while 16 pa tients spent fewer than 30 min utes on 3 METs activities. Finally, only p p-value METs, 24 h mean 1.7 ± ± 0.1 < Time on 3 6 METs, min/d 165 ± ± 26 < Time on > 6 METs, min/d 10 ± 10 0 ± 0 < Steps, n./d 8681 ± ± 1890 < Activity energy expenditure, kcal /d 799 ± ± 132 < SWA TEE, kcal/kg/d 35.0 ± ± Data from pre dic tion equa tion Equa tion TEE, kcal/kg/d 32.4 ± ± 5.2 ns Data from di etary re calls Di etary en ergy in take, kcal/kg/d 32.4 ± ± 6.4 < 0.05 Di etary pro tein in take, g/kg/d 1.04 ± ± 0.25 ns 5 pa tients were able to per form a phys i cal ac - tiv ity over 6 METs beyond 5 minutes. Us ing the SWA-de rived cal cu la tions, daily TEE neg a tively cor re lated with age (r = 0.33, p < 0.05), whereas pos i tive cor re la - tions were ob served with BMI (r = 0.51, p < 0.001), phase an gle (r = 0.404, p < 0.01) phos - phate (r = 0.49, p < 0.001), se rum PTH (r = 0.32, p < 0.05) and al bu min (r = 0.38, p < 0.01). In ad di tion, sig nif i cant cor re la tions were also found be tween daily to tal en ergy ex pen di ture and en ergy in take (r = 0.37, p < 0.01) and in par tic u lar with com plex car bo hy drates di - etary in take (r = 0.48, p < 0.001). Sim i larly, the mean daily METs val ues were di rectly re lated to nor mal ized pro tein (r = 0.36, p < 0.01) and en ergy in take (r = 0.42, p < 0.01) (Figure 1). In our se ries, the min utes spent on a phys i - cal ac tiv ity over 3 METs correlated positively with di al y sis vin tage (r = 0.41, p < 0.01), phase an gle (r = 0.36, p < 0.01) and BCMI (r = 0.41, p < 0,01), and also to nor mal ized en - ergy (r = 0.51, p < 0.001) (Fig ure 2) and pro - tein (r = 0.37, p < 0.01) di etary in take. No re la tion ship was ob served be tween parameters of physical activity and CRP, Kt/V, he mo glo bin or hematocrit. Mul ti ple re gres sion anal y sis showed that en ergy in take and di etary pro tein in take were in de pend ently re lated to TEE eval u ated by SWA and to the time of mild to mod er ate phys i cal ac tiv ity. As a whole, the es ti mated daily en ergy ex pen di ture was sim i lar when us ing SWA or the pre dic tion equa tion (31.4 ± 7.2 vs ± 4.7 kcal/kg/b.w., re spec tively). However, differences exist where sedentary or active dialysis patients are concerned. Table 2 shows that when us ing SWA, as ex - pected, sed en tary pa tients had a lower en ergy ex pen di ture than non-sed en tary pa tients; how ever, no dif fer ence re sulted when us ing the pre dic tion equa tion. The con clu sion is that daily en ergy ex pen di ture es ti mated by the pre dic tion equa tion is higher than that re - corded by SWA in sed en tary patients, while a trend to underestimate occurs in active patients (Table 2). The anal y sis of 3-day di etary re calls showed that sed en tary ate less than ac tive pa tients (Ta ble 2), and as a whole, re ported en ergy in take is lower than es ti mated en ergy ex pen di ture by SWA and also by the pre dic -

6 Phys i cal ac tiv ity in di al y sis pa tients 223 Fig ure 1. Re la tion ship be tween mean daily METs val ues (as a mea sure of the mean daily ac tiv ity level) and the di etary en ergy in take in the hemo - dialysis stud ied pa tients. Fig ure 2. Re la tion ship be tween min utes spent at phys i cal ac tiv ity > 3 METs (as a mea sure of in ten sity of phys i cal per for mance) and the di etary en ergy in - take in the hemodialysis stud ied pa tients. tion equa tion, both in pa tients and in con trols (Ta ble 2). Discussion The re sults of the study in di cate that the level of ex er cise is quite low in di al y sis pa - tients and that it is re lated to age, body com - po si tion and di etary nu tri ent in take. They confirm that levels of physical activity were as so ci ated with phase an gle [2], as an in di ca - tor of body com po si tion and nu tri tional in - take [32] among pa tients with ESRD and that these pa tients were less ac tive than sed en tary con trols. These sim i lar con clu sions were ob - tained us ing dif fer ent meth ods for both phys i - cal ac tiv ity mea sure ment (namely SWA or tri-axis accelerometers) and dietary nutrient in take as sess ment (3-day food re call or food fre quency ques tion naires). In ad di tion, we also ob served an as so ci a tion be tween phase an gle and min utes spent in ac tiv i ties greater than 3 METs, that is, with the intensity of the physical exercise The level of habitual physical activity mea sured with a sim ple method, SWA, in sta - ble HD pa tients is di rectly cor re lated with phase an gle and BCMI, which are mark ers of nu tri tional sta tus and pre dic tors of sur vival in di al y sis pa tients. Namely, the lower the phys - i cal ac tiv ity, the lower the phase an gle, en ergy intake and protein intake. Im ple men ta tion of reg u lar phys i cal ac tiv - ity is im por tant to ame lio rate qual ity of life, re ha bil i ta tion and even sur vival [28, 29], but ex er cise ca pac ity in chronic HD pa tients is gen er ally re duced be cause of the high prev a - lence of physical disabilities, social and psy - cho log i cal prob lems, and rel e vant comorbid con di tions. Phys i cal ex er cise is not for ev ery - one, but it re quires in di vid ual pre scrip tion. Dialysis staff commitment is important for the safety and suc cess of phys i cal ac tiv ity programs, whereas dedicated exercise profes sion als may be needed depending on the type of the exercise training [30]. Assessment of ha bit ual ac tiv ity is not easy. Baecke self-administered habitual physical activ ity ques tion naire or the Five- City Pro ject 7-day recall physical activity questionnaire can be used, but they give only in di rect mea sure - ments and are highly de pend ent on a pa tient s men tal skill and col lab o ra tion. Pe dom e ters are very use ful de vices, but they count steps in a sim i lar way dur ing walk ing or run ning and, there fore, they do not give any in for ma - tion about the tim ing and in ten sity of phys i cal ac tiv ity. In ad di tion, pe dom e ters may not re - cord phys i cal ac tiv ity in types of ex er cise dif - fer ent from walk ing or run ning, and so es ti - ma tion of en ergy ex pen di ture is far from accurate. Mean while, sev eral stud ies have shown that SWA can give an ac cu rate as sess ment of daily physical activity in general population [13]. This method is sim ple, noninvasive and low-cost. The ma jor ad van tage of us ing SWA

7 Cupisti, Capitanini, Betti et al. 224 in am bu la tory set tings is that it can re cord spon ta ne ous phys i cal ac tiv ity for long pe ri - ods of time and so eval u ate daily en ergy ex - pen di ture, the tim ing, du ra tion and in ten sity of phys i cal ex er cise, and time spent dur ing rest ing and sleep ing. Our ex pe ri ence con - firms that the SWA was user-friendly in terms of easy attachment/detachment, minimal dis - com fort, and little or no interference in daily life activities. Al though the use of SWA has been val i - dated in healthy in di vid u als or ath letes, there are not enough data to es tab lish the ref er ence values for SWA-determined physical activity in dif fer ent groups of chron i cally ill pa tients. Phase an gle was the only nu tri tional pa ram e - ter that showed di rect re la tion ship with phys i - cal ac tiv ity pa ram e ters, such as the daily mean METs val ues, the min utes spent in ac - tivities > 3 METs, or the daily TEE. It means that lower phase an gle val ues, which are as so - ci ated with higher mor tal ity rate in di al y sis patients, are associated with a sedentary con - di tion, and poor phys i cal per for mance ca pac - ity. More over, low phys i cal ac tiv ity is also as - so ci ated with low en ergy and pro tein in take and con trib utes to de creased mus cle tone and mass; in other words, poor phys i cal ac tiv ity is strongly as so ci ated with mal nu tri tion and to changes pre dic tive of poor prog no sis. On the other hand, good phys i cal ac tiv ity in creases lean body mass, in creases food in take and con trib utes to the main te nance of good nu tri - tional sta tus. It may ame lio rate a pa tient s prog - nosis, quality of life, and rehabilitation. It must be un der lined that our se ries in - cluded stable HD patients, without pathologies preventing them from performing physical activity. Hemoglobin levels reached target levels in most of the pa tients, so no re la tion ship was expected with physical activity parameters. Similarly, no relationship was observed with dialysis dose and with inflammation markers as al ready re ported in the lit er a ture [31, 32]. Spon ta ne ous phys i cal ac tiv ity tended to be lower on di al y sis days. This was al ready ob - served by Majchrzak et al. us ing a tri-ax ial ac - celerometer: physical activity was lower on di al y sis days when com pared with non - dialysis days, and this de crease was at trib uted to the lack of move ments dur ing the 4-hour HD pro ce dure [16]. In for ma tion from the 3-day re call in di - cated that daily en ergy in take was lower than to tal en ergy ex pen di ture es ti mated by SWA in both in pa tients and con trols (Ta ble 2). This prob a bly re flects the ten dency to un der es ti - ma tion of the food di etary re call method. Ob - vi ously there could be a po ten tial un der es ti - ma tion of en ergy and nu tri ents in take through di etary in ter views, which could rep re sent a limitation of this kind of investigation. Even if the food re cord anal y sis rep re sents the most valid and sim ple tool for nu tri ent and cal o rie es ti ma tion, the oc cur rence of a con scious or un con scious underreporting is largely known and re cently con firmed in healthy adults [33] as well as in renal failure patients [34, 35]. Furthermore, dietary intake may differ among a di al y sis day, a week end day and a nondialysis day. This is the rea son we used the av er age val ues of these 3 days, ac cord ing to Kid ney Dis ease Out comes Qual ity Ini tia - tive (K/DOQI) Rec om men da tion for Nu tri - tional Man age ment [23, 27]. This method pro vides a closer in sight into di etary hab its, and it is pre ferred by pa tients who do not al - ways com ply with ac cu rate recordings for a longer period. 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