Subjective stress, objective heart rate variability-based stress, and recovery on workdays among overweight and psychologically distressed individuals : a cross-sectional study

This is an elec onic ep in o he o iginal a icle. This ep in may di e om he o iginal in pagina ion and ypog aphic de ail. Au ho (s): Ti le: Yea : Ve sion: Please ci e he o iginal e sion: All ma e ial supplied ia JYX is p o ec ed by copy igh and o he in ellec ual p ope y igh s, and duplica ion o sale o all o pa o any o he eposi o y collec ions is no pe mi ed, excep ha ma e ial may be duplica ed by you o you esea ch use o educa ional pu poses in elec onic o p in o m. You mus ob ain pe mission o any o he use. Elec onic o p in copies may no be o e ed, whe he o sale o o he wise o anyone who is no an au ho ised use . Subjec i e s ess, objec i e hea a e a iabili y-based s ess, and eco e y on wo kdays among o e weigh and psychologically dis essed indi iduals : a c oss- sec ional s udy Föh , Tiina; Tol anen, Asko; Myllymäki, Te o; Jä elä-Reijonen, Elina; Ran ala, Sanni; Ko pela, Rii a; Peuhku i, Ka i; Kolehmainen, Ma jukka; Pu onen, Sampsa; Lappalainen, Raimo; Rusko, Heikki; Kujala, U ho Föh , T., Tol anen, A., Myllymäki, T., Jä elä-Reijonen, E., Ran ala, S., Ko pela, R., Peuhku i, K., Kolehmainen, M., Pu onen, S., Lappalainen, R., Rusko, H., & Kujala, U. (2015). Subjec i e s ess, objec i e hea a e a iabili y-based s ess, and eco e y on wo kdays among o e weigh and psychologically dis essed indi iduals : a c oss- sec ional s udy. Jou nal o Occupa ional Medicine and Toxicology, 10(30). h ps://doi.o g/10.1186/s12995-015-0081-6 2015 RESEARCH Open Access Subjec i e s ess, objec i e hea a e a iabili y- based s ess, and eco e y on wo kdays among o e weigh and psychologically dis essed indi iduals: a c oss-sec ional s udy Tiina Föh 1* , Asko Tol anen 2 ,Te oMyllymäki 3 , Elina Jä elä-Reijonen 4 , Sanni Ran ala 5 , Rii a Ko pela 5 ,Ka iPeuhku i 5 , Ma jukka Kolehmainen 4 ,SampsaPu onen 6,7 , Raimo Lappalainen 3 , Heikki Rusko 8 and U ho M. Kujala 1 Abs ac Backg ound: The p esen s udy aimed o in es iga e how subjec i e sel - epo ed s ess is associa ed wi h objec i e hea a e a iabili y (HRV)-based s ess and eco e y on wo kdays. Ano he aim was o in es iga e how physical ac i i y (PA), body composi ion, and age a e associa ed wi h subjec i e s ess, objec i e s ess, and eco e y. Me hods: Wo king-age pa icipan s (n= 221; 185 women, 36 men) in his c oss-sec ional s udy we e o e weigh (body mass index, 25.3–40.1 kg/m 2 ) and psychologically dis essed (≥3/12 poin s on he Gene al Heal h Ques ionnai e). Objec i e s ess and eco e y we e based on HRV eco dings o e 1–3 wo kdays. Subjec i e s ess was assessed by he Pe cei ed S ess Scale. PA le el was de e mined by ques ionnai e, and body a pe cen age was assessed by bioelec ical impedance analysis. Resul s: Subjec i e s ess was di ec ly associa ed wi h objec i e s ess (P= 0.047) and in e sely wi h objec i e eco e y (P= 0.046). These associa ions pe sis ed a e adjus men s o sex, age, PA, and body a pe cen age. Highe PA was associa ed wi h lowe subjec i e s ess (P= 0.037). Olde age was associa ed wi h highe objec i e s ess (P< 0.001). A e u he adjus men o alcohol consump ion and egula medica ion, olde age was associa ed wi h lowe subjec i e s ess (P=0.043). Conclusions: The p esen esul s sugges ha subjec i e sel - epo ed s ess is associa ed wi h objec i e physiological s ess, bu hey a e also appa en ly a ec ed by di e en ac o s. Howe e , some o he ound associa ions among hese o e weigh and psychologically dis essed pa icipan s wi h low in e -indi idual a ia ion in PA a e a he weak and he clinical alue o he p esen indings should be s udied u he among pa icipan s wi h g ea e he e ogenei y o s ess, PA and body composi ion. Howe e , hese indings sugges ha objec i e s ess assessmen p o ides an addi ional aspec o s ess e alua ion. Fu he mo e, he esul s p o ide aluable in o ma ion o de eloping s ess assessmen me hods. Keywo ds: Hea a e a iabili y, Objec i e s ess, Pe cei ed s ess scale, Physiological s ess, Physical ac i i y, Psychological s ess, Reco e y, S ess assessmen , Subjec i e s ess, Wo k- ela ed s ess * Co espondence: [email p o ec ed] 1 Depa men o Heal h Sciences, Uni e si y o Jy äskylä, P.O. Box 35, FIN-40014 Jy äskylä, Finland Full lis o au ho in o ma ion is a ailable a he end o he a icle © 2015 Föh e al. Open Access This a icle is dis ibu ed unde he e ms o he C ea i e Commons A ibu ion 4.0 In e na ional License (h p://c ea i ecommons.o g/licenses/by/4.0/), which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided you gi e app op ia e c edi o he o iginal au ho (s) and he sou ce, p o ide a link o he C ea i e Commons license, and indica e i changes we e made. The C ea i e Commons Public Domain Dedica ion wai e (h p://c ea i ecommons.o g/publicdomain/ze o/1.0/) applies o he da a made a ailable in his a icle, unless o he wise s a ed. Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 DOI 10.1186/s12995-015-0081-6 Backg ound S ess a wo k can be conside ed a majo public heal h isk. In many heo ies and de ini ions, s ess is de e - mined as a psychological o physiological esponse o he o ganism o an ex e nal load [1]. S ess is associa ed wi h psychological dis u bances, as well as physiological changes, such as lowe ed hea a e a iabili y (HRV) [2]. I may e en lead o ca dio ascula diseases i p o- longed [3, 4]. Reco e y om s ess is an impo an issue, as incomple e eco e y is also sugges ed o be a isk ac o o ca dio ascula diseases [5]. Common o he de ini ions o eco e y is ha eco e y occu s when he exposu e o s ess is o e . Reco e y epai s he nega i e e ec s o s ess and i is a p ocess du ing which indi id- ual eco e s o he speci ic baseline le el and is eco - e ed om he possible p e ious loads [1]. Fu he mo e, s ess has de imen al economic consequences due o dec eased job sa is ac ion and inc eased sickness- ela ed absences om wo k [6]. Mos s ess assessmen me hods p ima ily ocus on an indi idual’s subjec i e pe cep ion o s ess. Howe e , HRV has been p oposed o be a good indica o o in es iga ing he physiological e ec s o s ess and eco e y [2, 7]. HRV is he bea - o-bea (R–R in e al) a ia ion in imes be ween he consecu i e hea bea s exp essed in no mal sinus hy hm on an elec oca dio- g am (ECG) eco ding [8, 9]. HRV is e y indi idual and i is modula ed by bo h pa asympa he ic and sympa- he ic ac i i y o he au onomic ne ous sys em (ANS). S ess is associa ed wi h inc eased ac i a ion le el o he body when sympa he ic ac i i y domina es he ANS whe eas eco e y is associa ed wi h educed ac i a ion le el o he body when pa asympa he ic ac i a ion domi- na es he ANS o e sympa he ic ac i i y [10–12]. S udies in es iga ing he associa ion be ween sel - epo ed, psychological s ess and HRV in eal-li e se ings ha e ound con o e sial esul s (e.g. [7, 13–16]). Mos o hese s udies ha e used adi ional ime- o equency- domain measu es o HRV. Howe e , i is also possible o desc ibe he s a e o s ess and eco e y using HRV- de i ed a iables ha include in o ma ion ha is di icul o ob ain om adi ional measu es o HRV [7]. These no el a iables ake in o accoun ac o s such as HRV- de i ed espi a o y a iables and indi idual es ing hea a e (HR) and HRV alues. Due o e y high in e - and in a-indi iduali y o HRV, new app oaches which ake in o accoun indi iduali y in HRV could p o ide add- i ional insigh in o quan i ica ion o s ess and eco e y. Physical ac i i y (PA) can help he indi idual o build esou ces o bu e he nega i e e ec s o s ess and p o- mo e his/he eco e y om s ess [17]. On he o he hand, s ess is sugges ed o be associa ed wi h physical inac i i y (e.g. [7, 18, 19]) and being o e weigh [7, 20]. High s ess le els could a enua e an indi idual’s willingness o abili y o engage in egula exe cise and o be physically ac i e [21], esul ing in ailu e o achie e he bene icial e ec s o PA agains s ess. The p esen s udy aimed o examine he associa ions be ween subjec i e sel - epo ed psychological s ess and objec i e physiological HRV-based measu es o s ess and eco e y on wo kdays. The second aim was o in es- iga e how PA, body composi ion, and age a e associa ed wi h subjec i e s ess, objec i e s ess, and eco e y. Me hods Pa icipan s The p esen c oss-sec ional s udy included indi iduals o di e en occupa ions wi h symp oms o me abolic syn- d ome and psychological dis ess, who me he inclusion c i e ia in an ini ial sc eening and unde wen baseline measu emen s o a con olled and andomized ial called he Elixi s udy [22]. The ini ial pu pose o he Elixi s udy was o in es iga e he e ec o di e en psy- chological in e en ions on psychological and me abolic heal h. Da a collec ion was ca ied ou in h ee Finnish s udy cen e s a he uni e si ies o Helsinki, Jy äskylä, and Kuopio. The inclusion c i e ia we e sel - epo ed body mass index (BMI) o be ween 27–34.9 kg/m 2 , and pe cei ed psychological s ess indica ed by a leas 3/12 poin s on he Gene al Heal h Ques ionnai e [23]. The pa icipan s did no ha e any se e e ch onic illnesses, and any egula ly aken medica ions we e epo ed. De ails o he inclusion and exclusion c i e ia ha e been epo ed p e iously [22]. Fu he inclusion c i e ia speci ically o he p esen seconda y c oss-sec ional baseline analyses we e a ailable da a ega ding objec i e s ess and eco e y (HRV eco d- ing) and subjec i e s ess (Pe cei ed S ess Scale; PSS). Indi iduals who used α-o β-ad ene gic blocking agen s a ec ing he hea we e excluded om he p esen ana- lysis. Howe e , o he egula medica ion was allowed. The inal s udy g oup o he p esen analyses comp ised o 221 indi iduals who also me he addi ional inclusion and exclusion c i e ia. Table 1 p esen s he cha ac e is ics o he pa icipan s. All pa icipan s we e in o med abou he ini ial s udy, and hey signed w i en in o med consen p io o any measu emen s. This s udy was conduc ed acco ding o he Decla a ion o Helsinki, and he s udy p o ocol was app o ed by he e hics commi ee o he Cen al Finland Heal h Ca e Dis ic . Measu emen s Objec i e s ess and eco e y we e de e mined om eco dings o he bea - o-bea R–R in e al in eal-li e se ings o e 1–3 wo kdays. R–R in e al da a we e col- lec ed using a Fi s bea Bodygua d measu emen de ice (Fi s bea Technologies L d, Jy äskylä, Finland). The da a we e hen analyzed using he Fi s bea Analysis Se e Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 2 o 9 so wa e ( e sion 5.3.0.4), which included a powe ul a i ac co ec ion ea u e o i egula ec opic bea s, and signal noise. The o iginal R-R in e al se ies we e esampled a he a e o 5 Hz by using linea in e pola ion o ob ain equidis an ly sampled ime se ies, and second- by-second HRV indices we e calcula ed wi h he sho - ime Fou ie ans o m me hod by using cons an du - a ion Hanning window [24, 25]. The ea e , he so wa e ca ego izes he da a in o di e en physiological s a es such as s ess, eco e y, and physical ac i i y o di e en in en- si ies by aking in o accoun indi idual cha ac e is ics (e.g. he indi idual le els and scales o HR and HRV, and he indi idual ela ionships be ween HRV and au onomic con- ol e.g. [24]). S ess means sympa he ic dominance o he ANS wi hou me abolic equi emen s caused by physical ac i i y whe eas eco e y means pa asympa he ic domin- ance o he ANS. In his ca ego iza ion, second-by-second HRV indices, HRV-de i ed espi a ion a e, oxygen con- sump ion calcula ed by HR, HRV-de i ed espi a ion a e, and on-o kine ics, and pa ame e desc ibing excess-pos exe cise oxygen consump ion a e used wi h neu al ne - wo k da a modeling [25–27] ( o mo e de ails, see he whi e pape s by Fi s bea Technologies L d [28]). The in ensi y o s ess eac ion is calcula ed om he HR, high equency (0.15–0.4 Hz), and low equency (0.04–0.15 Hz) componen s o HRV and espi a o y a i- ables. The in ensi y o s ess is high when HR is ele a ed, HRV is educed, and he equency dis ibu ion o HRV is inconsis en because o changes in espi a o y pe iod. The in ensi y o eco e y is calcula ed om he HR and high equency componen o HRV, and i is high when HR is low and high equency componen o HRV is high and egula . F om he Fi s bea Analysis Se e , he s ess index was used as an indica o o objec i e s ess and he s ess balance alue as an indica o o objec i e eco e y. The s ess index cha ac e izes he magni ude o s ess p ocesses du ing he whole day. This index desc ibes he mean in ensi y o he ecognized s ess eac ions ( heo e ically anging om 0 o ∞, anging in ou ma e ial 88.5 −455.8). The s ess balance alue ( anging om −1 o 1) indica es he p opo ion o ime o s ess and eco - e y eac ions du ing sel - epo ed sleep pe iods du ing he measu emen pe iod. Values om 0.5 o 1 indica e good eco e y, alues om 0 o 0.5 indica e mode a e eco e y, and alues om 0 o −1 indica e weak eco e y [7]. The HRV da a consis ed o success ully eco ded wo kdays, wi h an allowed maximum o 15 % ega ding he g ade o de ec ed and co ec ed a i ac s in R–R in e als. The alues o he HRV-based a iables o s ess and eco e y we e he mean alues o he wo k- days. Da a om wo wo kdays we e included o 191 pa icipan s, om one wo kday o 20 pa icipan s, and om h ee wo kdays o 10 pa icipan s. Fo each moni- o ed day, he pa icipan s epo ed hei wo king hou s, sleeping hou s, and alcohol consump ion in measu e- men dia ies. Alcohol consump ion was epo ed in s anda d uni s o app oxima ely 12 g o e hanol (one uni : 33 cen ili e [cl] bee , 12 cl ed o whi e wine, 8 cl o i ied wine, o 4 cl liquo ). Subjec i e s ess du ing he p eceding mon h was assessed using he 14-i em PSS, which measu es he deg ee o which si ua ions in one’s li e a e s ess ul on a 5-poin scale anging om 0 (ne e ) o 4 ( e y o en) [29]. PSS o al sco es a e gene ally calcula ed by e e sing he sco es o he se en posi i e i ems and hen summa izing he sco es o all 14 i ems. In e nal eliabili y (C onbach’sα) o he PSS was 0.86. To educe he measu emen e o o he PSS sum sco e, we used a ac o ha included all 14 ques ions in he p esen analysis ins ead o he sum sco e. PA was assessed using a ques ionnai e wi h i ems ega ding p esen ac i i y and changes wi hin he las wo mon hs. The ques ionnai e included s uc u ed ques ions co e ing leisu e- ime PA and commu ing ac i i y [30, 31]. A mul iple o he es ing me abolic a e (MET) was assigned o each ac i i y o desc ibe he in ensi y o he o m o PA. The MET indices o each Table 1 Cha ac e is ics o he pa icipan s All (N= 221) Female (N= 185) Male (N= 36) Mean Range Mean Range Mean Range Age (y s) 48 26–60 48 26–60 45 31–60 Weigh (kg) 87.7 64.0–120.1 85.4 64.0–113.9 99.3 83.8–120.1 Heigh (cm) 167.8 149.0–195.6 165.4 149.0–184.8 179.7 167.5–195.6 BMI (kg/[m] 2 ) 31.1 25.3–40.1 31.2 25.3–40.1 30.8 26.3–37.0 Body a % 38.6 12.8–50.8 40.7 28.4–50.8 28.0 12.8–35.1 Physical ac i i y (MET index a ) 3.2 0.0–18.0 3.0 0.0–15.3 4.3 0.1–18.0 Subjec i e s ess (PSS b ) 26.5 7.0–52.0 26.5 7.0–52.0 26.2 17.0–38.0 Objec i e s ess (s ess index) 163.0 88.5–455.8 163.2 88.5–455.8 162.2 89.1–308.3 Objec i e eco e y (s ess balance) 0.35 −1.00–1.00 0.34 −1.00–1.00 0.40 −0.98–1.00 a MET-h/day, based on e ospec i e physical ac i i y ques ionnai e b Pe cei ed S ess Scale Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 3 o 9 o m o PA we e calcula ed by mul iplying he in ensi y (MET), du a ion (h), and equency o he ac i i y, and he MET index was exp essed as he sum sco e o di e - en ac i i ies (MET-h/d). Body composi ion was e alua ed using bioelec ical impedance analysis (InBody720; Jy äskylä, Kuopio/Tani a BC-418 MA; Helsinki) in he mo ning a e 10–12 h o as ing. This de ice p o ides in o ma ion abou he whole body a pe cen age. Body weigh and heigh we e also measu ed du ing he same labo a o y isi . S a is ical analysis S a is ical analyses we e pe o med using Mplus e sion 5.21 [32]. Wi hin his p og am, we used he MLR es ima- o , which comp ises maximum likelihood wi h obus s anda d e o s and wi h scale-co ec ed chi-squa e es alues co ec ing o he e ec o non-no mali y. To analyze he measu emen s uc u e o he PSS sco e, we used con i ma o y ac o analysis (CFA). Based on he esul s o he CFA he la en ac o model was used in he es ima ion o he co ela ions and in s uc u al equa ion modeling analysis o in es iga e he associa ions o objec - i e s ess and eco e y wi h subjec i e s ess, as well as o in es iga e he associa ions o PA, body composi ion, and age wi h objec i e and subjec i e s ess. The signi icance le el o he s udy was se a 0.05. The model i was e alu- a ed using he χ 2 es , compa a i e i index (CFI), Tucke Lewis index (TLI), oo mean squa e e o o app oxima- ion (RMSEA), and s anda dized oo mean squa e esidual (SRMR). Fo a good- i ing model, he χ 2 es is non-signi ican , CFI and TLI a e a leas 0.95, RMSEA is no mo e han 0.06, and SRMR no mo e han 0.08 [33]. Resul s The one- ac o solu ion o he PSS did no su icien ly i he da a (χ 2 (77) = 345.12, P< 0.001; CFI = 0.786; TLI = 0.747; RMSEA = 0.126; SRMR = 0.084); he e o e, he ac o s uc u e was al e ed based on modi ica ion indices. The ac o subjec i e s ess was me ged o con ain wo speci ic ac o s, as co a iance exis ed be ween he esiduals o ques ions 2, 3, 8, 12, 13, and 14 ( ela ed o pe cep ion o uncon ollable li e) and he ques ions 1, 3, 6, and 11 ( ela ed o pe cep ion o o e load) (Fig. 1). This es- ima ed model i he da a well (χ 2 (66) = 109.25, P<0.001; CFI = 0.966; TLI = 0.952; RMSEA = 0.054; SRMR = 0.044). All o he modi ica ion indices we e lowe han 4, indica - ing ha he e we e no addi ional pa ame e s ha would ha e inc eased he i o he model o he analysis. Table 2 p esen s he esul s o he associa ions o sub- jec i e s ess wi h objec i e s ess and eco e y. Subjec - i e s ess co ela ed wi h objec i e s ess ( = 0.139, 95 % CI 0.002 o 0.276, P= 0.047) and wi h objec i e eco e y ( =−0.140, 95 % CI −0.277 o −0.003, P= 0.046) wi hou any adjus men s (Model 1). In Model 2, he associa ions o subjec i e s ess wi h objec i e s ess and eco e y we e adjus ed o sex and age. Subjec i e s ess was associa ed wi h objec i e s ess ( esidual = 0.209, 95 % CI 0.075 o 0.343, P= 0.002) and wi h objec i e eco e y ( esidual =−0.137, 95 % CI −0.275 o 0.000, P= 0.050). Age was posi i ely associa ed wi h objec i e s ess (β= 0.435, 95 % CI 0.327 o 0.543, P<0.001). Sex was no associa ed wi h subjec i e s ess, objec i e s ess, o eco e y. The associa ions o subjec i e s ess wi h objec i e s ess and eco e y we e no in luenced by u he adjus men o alcohol consump ion o o egu- la medica ion. Fig. 1 The s uc u e o he ac o cons uc ed o he ques ions o he Pe cei ed S ess Scale (PSS). Fac o loadings (s anda dized es ima es) o he 14 ques ions, and loadings o he wo speci ic ac o s o esidual a iances Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 4 o 9 Figu e 2 p esen s he associa ion o subjec i e s ess wi h objec i e s ess and eco e y a e adjus men o sex, age, PA, and body a pe cen age. Subjec i e s ess was associa ed wi h objec i e s ess ( esidual = 0.217, 95 % CI 0.084 o 0.351, P= 0.001) and eco e y ( esidual =−0.146, 95 % CI −0.283 o −0.009, P= 0.037). PA was nega i ely associa ed wi h subjec i e s ess (β=−0.149, 95 % CI −0.289 o −0.009, P= 0.037). The nega i e asso- cia ion o subjec i e s ess wi h body a pe cen age was non-signi ican (β=−0.187,95 % CI −0.384 o 0.011, P= 0.064). Objec i e s ess and eco e y we e no associa ed wi h PA o body a pe cen age. Sex was no associa ed wi h subjec i e s ess, objec i e s ess, o eco e y. Age was posi i ely associa ed wi h objec i e s ess (β= 0.439, 95 % CI 0.330 o 0.547, P< 0.001). The e- sul s we e no in luenced by u he adjus men o alcohol consump ion o egula medica ion, excep ha age was nega i ely associa ed wi h subjec i e s ess (β=−0.143, 95 % CI −0.282 o −0.004, P= 0.043). Discussion The p esen indings sugges ha he highe he subjec i e sel - epo ed s ess he highe he objec i e HRV-based s ess and he lowe he objec i e HRV-based eco e y on wo kdays. We also ound ha wi hin ou psychologically dis essed and o e weigh s udy g oup, highe le el o PA was associa ed wi h lowe subjec i e s ess. Ou esul s showed ha highe subjec i e s ess was associa ed wi h highe objec i e s ess when adjus ed o he e ec s o age and sex. This a he weak bu s a is i- cally signi ican associa ion s eng hened a e accoun - ing o PA and body a pe cen age. This inding is in line wi h hose o p e ious s udies. Uusi alo e al. [34] ound ha daily emo ions a wo k and ch onic wo k- ela ed s ess we e associa ed wi h ca diac au onomic unc ion. They used he same HRV-based measu emen me hod as we did, and epo ed ha he associa ions o HRV-based measu es and he adi ional HRV measu es wi h subjec i e s ess we e alike. O he p e ious s udies ha e epo ed simila indings using adi ional ime o equency domain measu es o HRV (e.g. [14, 16]). Collins e al. [14] obse ed ha job s ain and low decision la i ude we e associa ed wi h educed ca diac agal con ol, and ha job s ain was associa ed wi h ele a ed sympa he ic con ol du ing wo king hou s. These esul s o Collins e al. [14] we e ob ained om 24-h ECG eco dings. Addi ionally, o he s udy esul s ob ained om bo h sho - ime [35, 36] and 24-h ECG Table 2 Co ela ions o subjec i e s ess wi h objec i e s ess and eco e y Subjec i e s ess Model 1 Model 2 S.E. 95 % CI P e S.E. 95 % CI P Objec i e s ess (S ess index) 0.139 0.070 0.002 o 0.276 0.047 0.209 0.068 0.075 o 0.343 0.002 Objec i e eco e y (S ess balance) −0.140 0.070 −0.277 o −0.003 0.046 −0.137 0.070 −0.275 o 0.000 0.050 S anda dized model esul s: co ela ion ( ), esidual co ela ion ( e ), s anda d e o (S.E.), 95 % con idence in e al (95 % CI), and P alue Model 1: no adjus men s Model 2: age- and sex adjus ed Fig. 2 Sex-adjus ed associa ions o age, physical ac i i y, and body composi ion wi h subjec i e s ess, wi h objec i e s ess, and wi h eco e y. The p esen ed alues a e s anda dized model esul s (es ima e and s anda d e o ). Residual co ela ion and s anda d e o be ween subjec i e s ess and objec i e s ess and eco e y, and co ela ions be ween age, physical ac i i y, and body composi ion a e also p esen ed Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 5 o 9 eco dings (e.g. [37]) ha e obse ed he associa ion be- ween subjec i e s ess and HRV wi h la ge popula ions. We also ound ha highe subjec i e s ess was associ- a ed wi h lowe objec i e eco e y du ing sleep. This a he weak bu s a is ically signi ican associa ion s eng hened a e aken in o accoun sex, age, PA and body a pe cen - age. This inding suppo s he p e ious s udy, which ound ha daily emo ions a wo k we e associa ed wi h nigh ime adi ional HRV measu es [34]. In con as , Hynynen e al. [13] ound ha low- and high-s essg oupsexhibi edno di e ences in noc u nal adi ional measu es o HRV. Fu he s udies a e needed o in es iga e he associa ion be ween subjec i e s ess and HRV-based eco e y du ing sleep. Reco e y is an impo an ac o in p e en ing he de - imen al e ec s o s ess, as good eco e y du ing sleep has been sugges ed o con e p o ec ion om ca dio ascula disease isk ac o s [2, 38]. An e o - eco e y model shows ha in cases o incomple e eco e y, an employee mus expend ex a e o o pe o m p ope ly a wo k [1]. The p esen esul s showed ha highe le el o PA was weakly bu s a is ically signi ican ly associa ed wi h lowe le els o subjec i e s ess among ou o e weigh pa ici- pan s wi h low in e -indi idual a iabili y in PA. Wi hin ou s udy g oup, PA was no associa ed wi h objec i e s ess o objec i e eco e y. The p esen s udy design does no enable us o d aw any b oade conclusions abou he associa ion be ween PA and subjec i e s ess, and i emains unclea whe he s ess o inac i i y is a cause o a consequence in his ela ionship. Howe e , ou inding o a nega i e associa ion be ween PA and subjec i e s ess suppo s he conclusions o p e ious s udies. Hame [39] sugges s ha egula exe cise may ha e s ess-bu e ing bene i s la gely because exe cise s a e mo e o en in he pos -exe cise window when hey encoun e daily s esso s. In line wi h ou p esen c oss-sec ional inding, Kou onen e al. [18] ound ha inc eased wo k- ela ed s ess was weakly associa ed wi h dec eased PA du ing 6–8yea ollow-up. In con as o ou p esen esul s, we ound in ou p e ious s udy [7] ha a highe le el o PA was associ- a ed wi h lowe objec i e s ess and highe objec i e e- co e y among pa icipan s wi h g ea in e -indi idual a iabili y in hei PA le els. Wi hin ou s udy g oup, body a pe cen age was no associa ed wi h objec i e s ess o eco e y. Acco ding o magni ude-based in e ence wi h con idence in e als [40, 41] ou esul s showed a small nega i e e ec o body a pe cen age on subjec i e s ess. In line wi h his, p e ious indings in la ge s udy g oups sugges ha a highe obesi y le el may con e p o ec ion om bu nou (e.g. [42]). Whe eas, ou p e ious s udy ound ha a mo e a o able body composi ion was associa ed wi h lowe objec i e s ess and highe objec i e eco e y [7] and obesi y is known o cause s ess o he body, as isce al obesi y is a key ac o in me abolic synd ome [43]. He e we also ound ha olde age was associa ed wi h highe objec i e s ess, bu no wi h objec i e eco e y. Addi ionally, he esul s showed an unclea nega i e non-signi ican associa ion be ween age and subjec i e s ess. Ou in e ence is ha any e ec o age on subjec - i e s ess is a mos small. HRV is indi idual, and is known o dec ease wi h age [11]. The objec i e me hod p esen ly used ecognizes s ess and eco e y eac ions and de e mines di e en physiological s a es o he body based on indi idual scaling o HR and HRV da a. The p esen ly used s ess index as an indica o o magni ude o he objec i e s ess eac ions is, howe e , calcula ed om HR, HRV and espi a o y a iables du ing he ecognized s ess s a es on he whole day. The e o e, he aging- ela ed dec ease in HRV likely explains his ind- ing o some ex en and inhibi s us o conclude ha olde employees we e mo e sensi i e o physiological s ess. Whe eas, he p esen ly used s ess balance alue as an indica o o objec i e eco e y was calcula ed om he ecognized s ess and eco e y s a es du ing sleep, and his alue akes in o accoun all indi iduali y in HRV. In he p esen s udy, age did no a ec objec i e eco e y du ing sleep. Howe e , olde pe sons seemed o pe cei e less s ess han hei younge coun e pa s. Fu he esea ch on he associa ion be ween age and objec i e s ess, including he e ec o PA, would be in e es ing and wa an ed. In he p esen s udy, subjec i e s ess was assessed by PSS. This scale has been ound o be a eliable and alid measu e o pe cei ed s ess. To analyze he measu e- men s uc u e o he PSS sco e, we u he used CFA o es whe he he 14 ques ions o he PSS we e consis en wi h he ac o consis ing o hese 14 ques ions. We ound ha he i ac o solu ion included wo speci ic ac o s. Based on he esul s o he CFA and o ge mo e eliable esul s we used his ac o solu ion as a a iable o subjec i e s ess in he p esen analysis. PSS assesses subjec i e s ess du ing he p eceding mon h. So, i is impo an o ake in o accoun ha he p esen esul s p o ide in o ma ion abou he associa ion o pe cei ed s ess o e one mon h wi h he objec i e s ess and eco e y a he end o his mon h. Subjec i e me hods we e used o assess bo h he le el o s ess and he le el o PA. E en hough, i is known ha subjec i e assessmen may include some epo ing bias, i is a commonly used me hod o measu ing s ess. The mos equen ly u ilized ins umen is a ques ionnai e ha has been widely c i icized because i elies on indi idual sel - epo ing. In con as , physiological measu es ep e- sen objec i e da a, which a e conside ed o be mo e eliable as hey a e no a ec ed by an indi idual’scogni- ion, social con ex , o emo ions [44]. The e o e, i is easonable and impo an o de elop objec i e measu es o s ess ha acknowledge he physiological bu den o Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 6 o 9 s ess. The assessmen o PA was based on a ques ion- nai e. Howe e , his ques ionnai e ook in o accoun a long- e m le el o PA and may gi e mo e us ul in o ma- ion abou indi idual’s PA han an objec i e measu emen om a sho pe iod. HRV assessmen is a p omising clinical ool o assessing heal h and iden i ying heal h impai men s [10, 24, 45]. Howe e , due o a limi ed applicabili y o he adi ional measu es o HRV in o changing and uncon ollable eal-li e se ing, i is impo an o de elop me hods ha apply HRV da a and a e able o p o ide aluable in o ma ion on s ess and eco e y in indi iduals’e e yday li e. By u ilizing bo h HRV and addi ional HRV-de i ed in o ma ion i is possible o p oduce knowledge o physiological s a es, such as s ess and eco e y ha is no a ailable om he basic HRV mea- su es which ep esen he a e age le el o he au onomic ac i i y o e a pe iod o he ime. This kind o in o ma ion can also be u ilized in suppo ing li es yle change. P e ious indings also suppo he alidi y and eliabili y o he HRV-based me hod used in he p esen s udy [7, 34]. In addi ion o subjec i e assessmen o s ess, he me hod has been alida ed agains neu oendoc ine esponses o s ess. The indica o s o s ess and eco e y du ing sleep ha e been ound o be associa ed wi h ee sali a y co isol a e awakening [46]. As HRV measu emen is dependen on he du a ion o he R −R in e al eco ding [47], i is a s eng h o he p esen s udy ha HR and HRV da a we e eco ded in eal-li e se ings o e a a he long ime pe iod, usually wo wo kdays. Secondly, he me hod p oduced s ess- and eco e y- ela ed a iables based on he HR, HRV, and espi a o y a iables. These a iables a e mo e in- o ma i e o bo h heal h-ca e p o essionals and pa ien s/ clien s han adi ional measu es o HRV and hey a e sui - able o applica ion in gene al heal h ca e. Al hough, HRV assessmen is a p omising clinical ool o assessing heal h and iden i ying heal h impai men s, se e al poin s mus be conside ed ega ding he HR- and HRV-based measu emen o s ess. HR and HRV a e e y indi idual, and a e dependen on age and sex [10, 11, 24]. HRV dec eases wi h age, and he a ia ion is g ea e among emale popula ion. The e o e, i is impo an o accoun o age and gende , as well as PA, when in es i- ga ing he associa ions o objec i e s ess and eco e y wi h subjec i e s ess. The p esen s udy excluded subjec s who used α-o β-blocke s, as hese d ugs ha e subs an ial e ec s on HR and HRV. Howe e , ou pa icipan s included indi iduals using egula medica ion such as o he ca diac medica ions o psychopha macological, me abolic o analgesic medica ion. This could also po en- ially a ec HR and HRV since many medica ions di ec ly o indi ec ly ac on he ANS [11]. The e o e, we also accoun ed o egula medica ion and alcohol consump- ion in ou p esen analysis. These adjus men s did no a ec he associa ions o objec i e s ess and eco e y wi h subjec i e s ess. Howe e , i is impo an o acknowledge ha he measu emen was accomplished in eal-li e se - ings and i akes pa icipan ’s wo d o con ounding ac o s, such as medica ion and alcohol consump ion. The p esen s udy pa icipan s we e psychologically dis essed and o e weigh composing an ideal s udy g oup o in es iga ing he associa ion o subjec i e s ess wi h objec i e s ess and eco e y. Fu he mo e, hey ep esen a g oup o Finnish wo ke s o di e en occupa ions, mainly ade and o ice wo ke s. Howe e , he e we e limi ed a ia ions in he le els o psychological s ess, a pe cen age and PA wi hin ou pa icipan s. The e o e, hese p esen ly ound associa ions should be s udied u he among mo e he e ogeneous s udy g oup and he p esen esul s can hus be gene alized o o e - weigh indi iduals wi h psychological dis ess. I would ha e been in e es ing o u he s udy he possible gende di e ences; howe e , such analyses we e no easonable wi hin he p esen g oup due o he low numbe o men. Da a collec ion was ca ied ou in h ee s udy cen e s. Howe e , adjus men o s udy cen- e did no a ec he esul s. The e is a ecognized need o u he esea ch abou he eliabili y o HRV measu emen . The esul s o Cip yan & Li schmanno a [48] sugges ha esea che s should be e y cau ious when d awing conclusions based only on sho - e m HRV analysis. Such me hods as p esen ly desc ibed and e alua ed HRV-based me- hod o assessing objec i e s ess and eco e y in eal- li e se ings mainly o e wo wo kdays, a e necessa y o imp o e he eliabili y o HRV analysis and o p o ide in o ma i e and sui able a iables o applica ion in gene al heal h ca e and li es yle counselling. This kind o indi idual counselling would be he op imal way o u ilize HRV-based me hod in s ess assessmen . Real- li e se ing includes se e al uncon ollable con ounding ac o s complica ing he g oup-le el analyzing o he da a. This ac oge he wi h he pa icipan s’low in e - indi idual a ia ion in he main a iables o he p esen s udy esul o he ac ha he ound associa ions a e a he weak. F om he pe spec i e o magni ude-based in e ence wi h con idence in e als [40] he e is a pos- sibili y ha some o ou indings a e somewha i ial. On he whole, he e is a limi ed numbe o s udies ha ha e u ilized long- e m HRV moni o ing and i is di i- cul o compa e he p esen indings wi h he p e ious indings ob ained om sho - e m ECG eco dings and wi h s udies ha ha e used di e en measu es han we did. Ne e heless, based on p e ious e idence, we as- sume ha simila indings o ou p esen indings and o e all conclusion would ha e been eached by using adi ional measu es o HRV. Mo e esea ch wi h la ge s udy popula ions and u he ollow-up s udies a e needed. Föh e al. Jou nal o Occupa ional Medicine and Toxicology (2015) 10:39 Page 7 o 9 Conclusions The p esen esul s sugges ha subjec i e sel - epo ed s ess is associa ed wi h objec i e HRV-based s ess and eco e y. Subjec i e psychological and objec i e physio- logical s ess a e appa en ly a ec ed by di e en ac o s, such as PA. Howe e , some o he ound associa ions among he o e weigh and psychologically dis essed pa icipan s wi h low in e -indi idual a ia ion in PA a e a he weak and he clinical alue o he p esen indings should be s udied u he among pa icipan s wi h g ea e he e ogenei y o s ess, PA and body composi ion. How- e e , hese indings sugges ha he p esen ly desc ibed me hod o objec i e s ess assessmen p o ides an add- i ional and impo an aspec o s ess assessmen . Fu he - mo e, he esul s p o ide aluable in o ma ion o he de elopmen o s ess assessmen me hods. Abb e ia ions ANS: Au onomic ne ous sys em; BMI: Body mass index; CFA: Con i ma o y ac o analyses; CFI: Compa a i e i index; ECG: Elec oca diog am; HR: Hea a e; HRV: Hea a e a iabili y; MET: Mul iple o he es ing me abolic a e; PA: Physical ac i i y; PSS: Pe cei ed s ess scale; RMSEA: Roo mean squa e e o o app oxima ion; SRMR: S anda dized oo mean squa e esidual; TLI: Tucke Lewis index. Compe ing in e es s T. Myllymäki is an employee o and H. Rusko is a s ockowne in Fi s bea Technologies L d. They did no con ibu e o w i ing he conclusions o he s udy. The au ho s decla e ha hey ha e no compe ing in e es s. Au ho s’con ibu ions S udy concep ion and design: TF, AT, RK, MK, RL, UK. Da a acquisi ion: TF, TM, EJ-R, SR, KP, UK. Da a analysis and in e p e a ion: TF, AT, TM, EJ-R, SR, RK, KP, MK, SP, RL, HR, UK. S a is ical analysis: TF, AT. D a ing he manusc ip : TF. C i ical e ision o he manusc ip o impo an in ellec ual con en : TF, AT, TM, EJ-R, SR, RK, KP, MK, SP, RL, HR, UK. Final app o al o he e sion o be published: TF, AT, TM, EJ-R, SR, RK, KP, MK, SP, RL, HR, UK. Ob ained unding: TF, RK, MK, RL, UK. Adminis a i e, echnical, o ma e ial suppo : AT, RK, MK, SP, RL, UK. Acknowledgemen s This s udy was suppo ed by he SalWe Resea ch P og am o Mind and Body (Tekes - he Finnish Funding Agency o Technology and Inno a ion g an 1104/10). T. Föh ’s wo k was suppo ed by a pe sonal g an om he Juho Vainio Founda ion. 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