Relationship between sleep and muscle strength among Chinese university students: a cross-sectional study

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1 J Musuloskelet Neuronl Intert 2017; 17(4): Journl of Musuloskeletl nd Neuronl Intertions Originl Artile Reltionship etween sleep nd musle strength mong Chinese university students: ross-setionl study Y. Chen 1, Y. Cui 2,3, S. Chen 1, Z. Wu 1 1 Deprtment of physil edution, Dlin Institute of Siene nd Tehnology, Dlin, People s Repuli of Chin; 2 Deprtment of physil edution, Huiyin Institute of Tehnology, Huin, People s Repuli of Chin; 3 Division of iomedil engineering for helth nd welfre, Tohoku University Grdute Shool of Biomedil Engineering, Sendi, Jpn Astrt Ojetives: Poor sleep qulity nd short sleep durtion re ssoited with n inresed risk for musle mss redution. Thus, they my lso influene musle strength. This study imed to investigte the ssoition etween sleep qulity nd durtion, nd musle strength in university students. Methods: This ross-setionl study omprised 10,125 university students ged yers. Hndgrip strength ws mesured using hndheld digitl dynmometer. Sleep qulity nd durtion were mesured using self-reported questionnire. Results: After djusting for onfounding ftors, positive ssoition etween sleep qulity nd musle strength ws oserved in oth mle nd femle students. Moreover, men with shorter sleep durtion (<6 hours) hd poorer musle strength thn tht of men who slept for 7-8 hours nd over 8 hours in the finl djusted model. There ws no signifint differene in the ssoition of sleep durtion nd musle strength etween men who slept 7-8 hours nd those who slept for more thn 8 hours. No signifint ssoition ws oserved etween sleep durtion nd musle strength in femle students. Conlusions: Good sleep qulity is ssoited with greter musle strength, while short sleep durtion my e risk ftor for deresed musle strength in university students. Keywords: Sleep Qulity, Sleep Durtion, Musle Strength, Cross-Setionl Study, College Students Introdution Musle wekness hs onsistently een reported s n independent risk ftor for flls 1, hip frtures 2, nd dverse physiologil hnges, suh s gluose intolerne 3 nd loss of one minerl density 4. Further, hndgrip strength s representtion of musle strength is lso strong inditor of helth sttus, sed on the inidene of disility, moridity, nd mortlity in dult popultions 5-7. Individuls who mintin greter hndgrip strength re t lower risk for disility nd joint impirment. In ddition, these individuls tend to live The uthors hve no onflit of interest. Corresponding uthor: Yufei Cui, PhD, Deprtment of Physil Edution, Huiyin Institute of Tehnology, 1 Meiheng Rod, Huin , People s Repuli of Chin E-mil: yufei_ig@hotmil.om Edited y: F. Ruh Aepted 28 June 2017 longer thn those with low hndgrip strength. A previous study hs lso demonstrted tht even in middle-ged individuls, the risk of mortlity in those with lower grip strength ws more thn twie the risk in those with higher grip strength 8. Menwhile, sleep is homeostti proess nd periodi iologil stte tht is ruil to physil nd mentl helth 9. Previous studies showed tht oth short (<7 hours) nd prolonged (>8 hours) sleep durtion re relted to inresed mortlity 10, nd inresed risk of hypertension 11, dietes 12, nd oesity 13. In ddition, insuffiient or non-restortive sleep my led to inility to onentrte, ognitive deteriortion nd deresed qulity of life Moreover, reent study suggested tht ojetive short sleep durtion is ssoited with elevted inflmmtion in dolesents 17, nd sleep disruptions re ssoited with impired seretion of trophi ftors suh s insulin-like growth ftor-1 (IGF-1) 18. As inflmmtion is n importnt risk ftor for deresed musle strength, nd IGF-1 is lso n importnt modultor of musle mss nd funtion 19, we speulted tht sleep sttus might e ftor tht ffets musle strength. Although severl studies demonstrted the reltionship etween sleep 327

2 Tle 1. Chrteristis of mle nd femle prtiipnts ording to sleep qulity. Sleep qulity Poor Norml Good Trend p Mle prtiipnts n BMI (kg/m 2 ) 23.1 ( ) 23.2 ( ) 23.3 ( ) Grde (%) First yer Seond yer Third yer Fourth yer Minority re (%) Physil tivity Living sttus (dormitory; %) Smoking sttus (%) Smoker Drinking sttus (%) Drinking everydy Drink osionlly Non-drinker Depressive symptom (%) Regulr onsumption of Femle prtiipnts n BMI (kg/m 2 ) 21.2 ( ) 21.2 ( ) 21.2 ( ) Grde (%) First yer Seond yer Third yer Fourth yer Minority re (%) Physil tivity Living sttus (dormitory; %) Smoking sttus (%) Smoker Drinking sttus (%) Drinking everydy Drink osionlly Non-drinker Depressive symptom (%) Regulr onsumption of BMI: ody mss index; PA: physil tivity. Otined using ANOVA for ontinuous vriles nd x 2 test for proportionl vriles. Men; 95% CI in prentheses (ll suh vlues). nd musle mss, no study hs yet shown the reltionship etween sleep durtion nd sleep qulity, nd musle strength in young dults. Thus, we designed ross-setionl study to investigte the reltionship etween sleep durtion nd qulity, nd musle strength in Chinese ollege students. Methods Study popultion The study ws sed on n nnul physil exmintion, whih ws rried out for monitoring physil helth of 328

3 Tle 2. Chrteristis of mle nd femle prtiipnts ording to sleep durtion. Sleep durtion (h/d) <7 7-8 >8 Τrend p Mle prtiipnts n BMI (kg/m 2 ) 23.1 ( ) 23.2 ( ) 23.3 ( ) Grde (%) First yer Seond yer Third yer Fourth yer Minority re (%) Physil tivity Living sttus (dormitory; %) Smoking sttus (%) Smoker Drinking sttus (%) Drinking everydy Drink osionlly Non-drinker Depressive symptom (%) Regulr onsumption of Femle prtiipnts n BMI (kg/m 2 ) 21.3 ( ) 21.2 ( ) 21.1 ( ) Grde (%) First yer Seond yer Third yer Fourth yer Minority re (%) Physil tivity Living sttus (dormitory; %) Smoking sttus (%) Smoker Drinking sttus (%) Drinking everydy Drink osionlly Non-drinker Depressive symptom (%) Regulr onsumption of BMI: ody mss index; PA: physil tivity. Otined using ANOVA for ontinuous vriles nd x 2 test for proportionl vriles. Men; 95% CI in prentheses (ll suh vlues). university students t Dlin Institute of Siene nd Tehnology. All students were invited to prtiipte in physil exmintion. Those who hd physil disility, rdiovsulr diseses, respirtory diseses, or who hd speil reson tht ould not prtiipte were exluded efore physil exmintion. Prtiiption rte ws 91.8%. We invited ll students who hd undergone the physil exmintion in 2015 to prtiipte in this study (n = 10,711). 329

4 Among these, 10,570 students greed to prtiipte nd provided informed onsent for their dt to e nlyzed. This study ws pproved y the Humn Investigtion Review Committee of Dlin Institute of Siene nd Tehnology. We exluded sujets whose questionnire dt or physil funtion dt were unville (n=445). Therefore, the finl study popultion omprised 10,125 sujets (6,251 men nd 3,874 women). Mesurement of sleep We ssessed sleep qulity nd durtion y using selfreported questionnire inluding sleep-relted questions. Students were sked to rte diffiulties with inititing nd mintining sleep on five-point sle: 1, <1 dy per month; 2, 1-3 dys per month; 3, 4-7 dys per month; 4, 8-15 dys per month; nd 5, 16 dys per month. A sore of 1 or 2 indited good sleep qulity, 3 indited norml sleep qulity, nd 4 or 5 indited poor sleep qulity. Sleep durtion ws ssessed y self-reported sleep hours t night in the pst month, nd ws then divided into 3 tegories: <7 hours, 7-8 hours, nd >8 hours. The use of hypnotis ws ssessed through the question hve you used hypnoti drugs in the pst month? the possile nswers were yes nd no. Mesurement of musle strength Musle strength ws determined on the sis of hndgrip strength nd ws mesured using dynmometer (TKK 5401, Tkei Kiki Kogyo Co., Tokyo, Jpn). The grip strength ws mesured twie for eh hnd. Students were sked to squeeze the hndle s hrd s possile in stnding position with the rm stright down. The mximum fore pplied ws used in the nlysis. Mesurement of other vriles Body mss index (BMI) ws lulted s weight/height 2 (kg/m 2 ). Dily physil tivity (PA) ws determined using the Interntionl Physil Ativity Questionnire (IPAQ), nd totl dily PA ws lulted s follows: METs h/week 20. PA ws divided into two tegories: nd 23 MET hours/ week 21. Depressive symptoms were ssessed using the Self-rting Depression Sle (SDS). An SDS sore 45 ws defined s the depressed group 22. Informtion on student ge, sex, grde, living sttus, smoking nd drinking sttus ws otined y onduting questionnire survey. Sttistil nlysis All sttistil nlyses were performed using SPSS/PC sttistil softwre version 17.0 for windows (SPSS, In., Chigo, IL, USA). Grip strength ws used s dependent vrile, nd sleep qulity nd sleep durtion were used s independent vriles. Differenes etween the sleep tegories were exmined using nlysis of vrine for ontinuous vriles nd logisti regression nlysis for proportionl vriles. ANCOVA ws performed to exmine the reltionship etween sleep sttus nd grip strength in Model 1 nd Model 2. Bonferroni-orreted p vlues were used to ompre sleep qulity nd sleep durtion etween the groups. A p vlue <0.05 ws onsidered sttistilly signifint in ll nlyses. Results These ross-setionl dt were otined from 10,125 sujets (6,251 men [61.7%] nd 3,874 women [38.3%]). Tle 1 summrizes the hrteristis of the students ording to self-reported sleep qulity. The proportion of mle students who reported high physil tivity signifintly higher ross the sleep qulity tegories (p for trend= 0.033). The proportion of femle students in third yer of university or those who osionlly drnk lohol ws higher ross the sleep qulity tegories (p for trend= 0.026, nd 0.003, respetively). On the ontrry, the proportion of femle students in the fourth yer of university ws lower ross the sleep qulity tegories (p for trend= 0.016). The hrteristis of the students ording to dily sleep durtion re presented in Tle 2. The proportion of mle students who drnk lohol every dy ws signifintly lower ross the sleep durtion tegories (p for trend= 0.012). The proportion of femle students who reported high physil tivity or hd depressive symptoms ws higher ross the sleep durtion tegories (p for trend= 0.005, nd 0.026, respetively). Tle 3 shows the djusted ssoition etween sleep qulity nd grip strength. In Model 1 of mle students, the grip strengths were 40.1 (95% CI; ) newton, 41.3 (95% CI; ) newton, nd 42.1 (95% CI ) newton in poor, norml, nd good sleep qulity tegories, respetively (p for trend <0.001). The grip strength of femle students in Model 1 were 25.3 (95% CI; ) newton, 25.6 (95% CI; ) newton, nd 25.7 (95% CI; ) newton for poor, norml, nd good sleep qulity tegories, respetively (p for trend= 0.030). Moreover, in Model 2, n ssoition similr to tht oserved in Model 1 ws oserved etween sleep qulity nd grip strength in oth mle (p for trend <0.001) nd femle students (p for trend= 0.001). Tle 4 shows the djusted ssoition etween sleep durtion nd grip strength. In Model 1 of mle students, the grip strengths were 40.2 (95% CI; ) newton, 41.8 (95% CI; ) newton, nd 41.4 (95% CI ) newton for tegories of sleep durtion <7 hours, 7-8 hours, nd >8 hours, respetively (p for trend <0.001). Grip strength ws lower in the students in the <7 hour sleep durtion tegory thn tht in students in the 7-8 hour nd >8 hour sleep durtion tegories (Bonferroni-orreted p<0.05). In ddition, this ssoition did not hnge when we djusted more onfounding ftors in Model 2 (p for trend <0.001). No signifint ssoition ws found etween sleep durtion nd grip strength in femle students. 330

5 Tle 3. Adjusted reltionship etween sleep qulity nd grip strength (newton). Sleep qulity Poor Norml Good trend p Men n Model ( ) 41.3 ( )* 42.1 ( )*, <0.001 Model 2 d 40.1 ( ) 41.2 ( )* 42.4 ( )*, <0.001 Women n Model ( ) 25.6 ( ) 25.7 ( ) Model 2 d 25.2 ( ) 25.5 ( ) 25.9 ( )* Vriles re expressed s estimted geometris mens (95% CI). Otined using ANCOVA. Adjusted for ody mss index nd re. d Further djusted for grde, physil tivity, living sttus, smoking nd drinking hits, rekfst, depressive symptoms nd Hypnoti drug. * Signifintly different to poor sleep qulity, p<0.05 (Bonferroni-orreted). Signifintly different to norml sleep qulity, p<0.05 (Bonferroni-orreted). Tle 4. Adjusted reltionship etween sleep durtion nd grip strength (newton). Sleep durtion (h/d) < >8 trend p Men n Model ( ) 41.8 ( )* 41.4 ( )* <0.001 Model 2 d 40.1 ( ) 41.7 ( )* 41.9 ( )* <0.001 Women n Model ( ) 25.6 ( ) 25.5 ( ) Model 2 d 25.4 ( ) 25.6 ( ) 25.7 ( ) Vriles re expressed s estimted geometris mens (95% CI). Otined using ANCOVA. Adjusted for ody mss index nd re. d Further djusted for grde, physil tivity, living sttus, smoking nd drinking hits, rekfst, depressive symptoms nd Hypnoti drug. * Signifintly different to <7 hour sleep durtion, p<0.05 (Bonferroni-orreted). Disussion In the present study, we found tht sleep qulity ws positively ssoited with musle strength, nd short sleep durtion ws ssoited with redued musle strength. Even fter djusting for numer of potentilly onfounding vriles, these ssoitions did not hnge. To our knowledge, this is the first study to investigte the ssoition etween sleep durtion nd sleep qulity, nd musle strength in young dults. A ross-setionl study inluding 1,196 elderly prtiipnts found tht poor sleep qulity is ssoited with not only redued musle mss, ut lso deresed grip strength in older women 23. The results of the study prtilly greed with those of the present study. However, in our study, we found positive ssoition etween sleep qulity nd grip strength in oth mle nd femle ollege students. A previous study demonstrted tht inresed IGF-1 is ssoited with improved sleep qulity 24. IGF-1 is n noli hormones tht plys n importnt roles in protein synthesis nd, thus, in mintenne of musle mss 25. Reent findings from n epidemiologil study showed tht low plsm IGF-1 levels re ssoited with poor knee extensor musle strength nd slow wlking speed 26. Moreover, IGF-1 is rpidly redued under onditions of sleep deprivtion 27. Sleep deprivtion is ssoited with two outomes: inreses in the seretion of toli hormones, suh s ortisol 28,29, nd hnges in the pttern of rhythmi seretion of noli hormones, 331

6 suh s testosterone 30. These previous studies indited tht mintining good sleep qulity nd optiml sleep durtion ould inrese musle mss nd prevent its loss. On the ontrry, it hs een proven tht high musle mss reltes to high musle strength 31. Thus, we speulted tht good sleep qulity nd optiml sleep durtion re indiretly ssoited with higher musle strength. However, signifint ssoition etween sleep durtion nd grip strength ws only found in mle, ut not in femle. A possile explntion ould e onsidered. Biologil onditions unique to women, inluding menstrul yles nd femle hormones, were suggested to e relted to sleep pttern nd sleep durtion 32,33. Wheres, severl previous reports indited tht grip strength deresed during oth the folliulr nd lutel phses 34. In ddition, delyed musle reovery in femle ws found during menstrul phse 35. It is onsiderle tht menstrul yles nd femle hormones might e n importnt meditor, whih might influene the ssoition etween sleep durtion nd musle strength in femle. Our study hs some limittions. First, self-reported sleep qulity nd sleep durtion ws used in our nlysis rther thn tul mesurement of sleep qulity nd durtion. Thus, rell is inevitly existed. Seond, the ross-setionl design preludes defining usl reltionships. Prospetive or interventionl studies re required to lrify the uslity. Third, lthough we djusted for numer of potentil onfounding vriles, we ould not exlude the possiility tht other ovrites my hve influened the ssoition etween sleep sttus nd musle strength. The present people-sed survey dt indited tht sleep qulity ws positively ssoited with musle strength, nd short sleep durtion ws ssoited with n inresed risk for redution of musle strength in ollege students. Considering tht long sleep durtion ws not reommended, mintining sleep durtion of 7-8 hours my e preferle for musle strength. Redued sleep qulity nd sleep durtion might e potentil risk ftors for musle strength. 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