Factors Associated with the Risk of Falls of Nursing Home Residents Aged 80 or Older

For Peer Review Factors associated wit h the risk of falls of nursing home residents aged 80 or older. Journal: Rehabilitation Nursing Journal Manuscript ID: RNJ-15-01-000467.R1 Manuscript Type: Feature Keywords: Falls, Older adults, Mobility RNJ Proof For Peer Review Falls in nursing home residents 1 TITLE Factors associated with the risk of falls of nursing home residents aged 80 or older Page 1 of 33 RNJ Proof For Peer Review Falls in nursing home residents 2 ABSTRACT Background: Falls are the leading cause of mortality and morbidity in older and represents one of the major and most costly public health problems worldwide. Purpose: Evaluate the influences of lower limb muscle performance, static balance, functional independence and quality of life on fall risk as assessed with the Timed Up and Go test. Design: Crosssectional. Methods: Fifty-two residents aged 80 or older were assessed and distributed in one of the two study groups according to the time to complete the Timed Up and Go Test. A Kistler force platform and linear transducer was used to determinate lower limb muscle performance. Postural Stability was measured by recording the center of pressure. The EuroQol-5 dimension was used to assess Health-Related Quality of Life and the Barthel Index was used to examine functional status. Student t-test was performed to evaluate the differences between groups. Correlations between variables were analyzed using Spearman or Pearson coefficient. ROC analysis was used to determine the cut-off points related to a decrease in the risk of a fall. Findings: Participants of no-fall risk group showed better lower limb performance, quality of life, and functional status. Cut-off points were determined for each outcome. Conclusions: Risk of falls in nursing home residents over the age of 80 is associated with lower limb muscle performance, functional status and quality of Life. Clinical Relevance: Cut-off points can be used by clinicians when working toward fall prevention and could help in determining the optimal lower limb muscle performance level for preventing falls Keywords: Nursing homes, Lower extremity, Aging, Accidental falls, Quality of life. Page 2 of 33RNJ Proof For Peer Review Falls in nursing home residents 3 Key Practice Points: • Fifty-two nursing home residents aged 80 or older were grouped according to the time taken to complete the Timed up and Go Test. • Participants in the ‘no risk of falls’ group reported better (higher score) functional status and quality of life when compared with those in the ‘with risk of falls’ group • The risk of falling was associated with lower limb muscle performance as assessed by 30-s CSTS-peak power, 30-s CSTS-peak force and 30-s CSTS-velocity in nursing home residents over 80 years of age. • Cut-off points could help in determining the optimal lower limb muscle performance level for preventing falls in older adults aged 80 years or more who are living in nursing home Page 3 of 33 RNJ Proof For Peer Review Falls in nursing home residents 4 Falls are one of the major and most costly public health problems worldwide.(Hartholt et al., 2011) About 30% of community-dwelling older adults fall at least once a year and this percentage increases to 43% for those living in nursing homes (Rubenstein & Josephson, 2002) and 50% for those over the age of 80 (Inouye, Brown, & Tinetti, 2009). Thus, falls are the leading cause of mortality (Petridou et al., 2007) and morbidity (Health Quality, 2008) among older adults. Independence in activities performed on a daily basis is compromised in people susceptible to falls (Chu, Chiu, & Chi, 2006). Due to reduced function in those who fall, health-related quality of life (HRQoL) is often reduced in this population (Iglesias, Manca, & Torgerson, 2009). Due to the prevalence of falls, it is important to identify fall risk-related factors to effectively design interventions that address this issue. Despite the fact that fall risk is multifactorial, reduced strength is the most common cause of falls among nursing home residents (Joyner, 2005; Robbins et al., 1989; Rubenstein & Josephson, 2002). Moreover, older people living in nursing homes experience reduced mobility and poor balance when compared with their peers living in the community (Nitz & Josephson, 2011). In addition, it has been suggested that lower limb power may have more influence than muscle strength on static balance (Orr, 2010). Therefore, these factors seem to be directly related to fall risk and the resulting functional dependency that lead to a poor quality of life (Caserotti, 2010). Despite this, few studies have been conducted to determine the association between the risk of a fall and lower limb muscle performance, movement speed, functional status and HRQoL in nursing home residents over 80 years of age (Orr, 2010). Therefore, the aim was to study the influences of these parameters on fall risk as assessed with the Timed Up and Go (TUG) test in nursing home residents over 80 years of age. Page 4 of 33RNJ Proof For Peer Review Falls in nursing home residents 5 Methods Participants and Study Design A cross-sectional study was conducted. Participants were recruited from 2 local nursing homes (both in Seville, Spain). Fifty-two volunteers gave their written informed consent after receiving detailed information about the aims and study procedures. The inclusion criteria required that participants had to be more than 79 years old and be living in a nursing home. Participants were excluded if they had cognitive or functional disorders, comorbidities, acute thrombosis or its high risk, not well balanced with medical treatment or severe vertigo that prevented them from following instructions during the tests. The study was approved by the Ethics Committee of the University of Seville (Seville, Spain) and was conducted following the ethical guidelines of the Declaration of Helsinki. Procedures and Outcome Measures All outcome measures were performed by one researcher with previously experience in this procedures. Participants were asked to report their age and gender. The number of years in the nursing home, health conditions and medications were also recorded. Participants’ weight, height, and waist and hip circumference were measured, and body-mass index (BMI; kg/m 2 ) and waist-to-hip ratio were calculated. Body-fat percentage (BF %) was also estimated using a handheld impedance analyser (Omron BF-306, Omron Healthcare Europe BV, Hoofddorp, The Netherlands) according to the manufacturer´s instructions (Deurenberg et al., 2001). Page 5 of 33 RNJ Proof For Peer Review Falls in nursing home residents 6 The TUG test is one of the most common tests used in older populations to examine balance, gait speed and functional ability related to the performance of basic daily life activities (Herman, Giladi, & Hausdorff, 2011; Podsiadlo & Richardson, 1991). This test has demonstrated good inter-rater reliability, with an intra-class correlation of 0.80 (Yeung, Wessel, Stratford, & MacDermid, 2008). It has been suggested that a score of 13.5 seconds or more in the TUG test increases the risk of falls in older adults living in the community (Allison, Painter, Emory, Whitehurst, & Raby, 2013; Gunter, White, Hayes, & Snow, 2000; Shumway-Cook, Brauer, & Woollacott, 2000). Fall risk was assessed using the TUG test (Podsiadlo & Richardson, 1991). The participants had to stand up from a standard chair, walk 3 meters to and around a cone, and return to the chair in a comfortable and safe walking speed (Podsiadlo & Richardson, 1991). The best time of 2 trials (1-minute rest period between trials) were recorded. Those participants scoring 13.5 seconds or more were considered to be at risk of falls (Allison et al., 2013; Gunter et al., 2000; Shumway-Cook et al., 2000)and this value was used to determine placement into the 2 study groups. The EuroQol-5 dimension (EQ-5D) was used to assess Health-Related Quality of Life (HRQoL) of the participants in the study. EQ-5D has a good test retest reliability (van Agt, Essink-Bot, Krabbe, & Bonsel, 1994). This test includes five dimensions (mobility, personal care, usual activities, pain/discomfort and anxiety/depression), each of which has three levels (no problems, some problems, or extreme problems/unable to). The juxtaposition of the levels for these five dimensions correlates to a five-digit number, which reflect 243 possible health status values. These health status values can be converted to a health functional index or a ‘utility’ (EQ-5D UTILITY) , using time-trade off values (EuroQol utility: 1=full functional quality Page 6 of 33RNJ Proof For Peer Review Falls in nursing home residents 7 of life, 0=death). The EQ-5D-3L also includes a vertical 20-cm Visual Analogue Scale (EQ5D VAS ) which is used by participants to rate their own health between 0 (worst imaginable health state) and 100 (best imaginable health state), thereby providing an overall numerical estimate of their HRQoL (EuroQol, 1990). The Barthel Index (BI) was used to assess functional status. BI has fair to good interratter reliability in elderly population (Richards et al., 2000) and excellent inter-ratter reliability (r=0.849) in rehabilitation patients (Rollnik, 2011).This test is comprised of 10 items (bathing, grooming, feeding, dressing, bowels, bladder, toilet uses, stairs, transfer and mobility) that measure a person's activities of daily living. Total scores are calculated by summing the individual item scores. Scores are weighted and range from 0 (dependence) to 100 (independence) (Mahoney & Barthel, 1965). Lower limb muscle performance was assessed using the 30-seconds Chair Sit to Stand (30-s CSTS) test (J. Rikli, 2001). This test has an excellent test-retest reliability (r=0.89) and an excellent inter-ratter reliability (r = 0.95) (Jones, Rikli, & Beam, 1999). The participants were instructed to perform the task starting and finishing in the seated position. The number of times within 30 seconds that the participant could raise to a full stand from a seated position “as fast as possible”, with the back straight and feet flat on the floor without using the arms, was counted. Peak velocity of each repetition as well as the average velocity of an approximate center of mass point was recorded using a linear transducer (Model TF-100, TForce System Ergotech, Murcia, Spain) and peak force was recorded by a Kistler force platform, type 9281A (Kistler Instruments AG, Winterthur, Switzerland). Peak force was then Page 7 of 33 RNJ Proof For Peer Review Falls in nursing home residents 8 normalized by weight. From these data, the maximum power was calculated (peak force normalized by weight of participants multiplied by peak velocity). Postural Stability was measured using a Kistler force platform, type 9281A (Kistler Instruments AG, Winterthur, Switzerland) by recording the anterior-posterior (AP) and medial-lateral (ML) center of pressure (COP) excursions in a quiet standing posture. These parameters (AP and ML COP excursions), sampled at 1000 Hz, were calculated for 3 tasks, including a dual-task cognitive challenge: (1) standing on the force platform with the eyes open, (2) standing on the force platform with the eyes open and performing a cognitive task and (3) standing on the force platform with the eyes closed. For each condition, 3 trials were performed. Each trial lasted 30 seconds and was followed by a rest period of 1 minute. Participants were asked to keep their feet at the width of their hips and in a natural, comfortable position during tests. For data analysis, only the final 20 seconds of each trial were used (Prieto, Myklebust, Hoffmann, Lovett, & Myklebust, 1996). The cognitive task was counting backwards by 3’s as fast and as accurately as possible, beginning with a randomly selected number from a range of 100–200. The importance of this test is that the successful performance of dual-task situations affords increased levels of attentional demand for the regulation of balance (Woollacott & Shumway-Cook, 2002) and higher levels of postural sway and greater stride-to-stride variability have been shown during dual-tasking compared to single-tasking in older adults (Granacher, Bridenbaugh, Muehlbauer, Wehrle, & Kressig, 2011). Statistical Analysis Page 8 of 33RNJ Proof For Peer Review Falls in nursing home residents 15 Participants who exhibited a high risk of falling in the current study also demonstrated lower functional status as assessed by means of the Barthel Index. These results are consistent with the findings of other studies conducted with community-dwelling adults aged 79 or older (Ferrer et al., 2012; Grundstrom, Guse, & Layde, 2012). This relationship has also been confirmed in healthy community-dwelling older adults (Chu et al., 2006; Okamura et al., 2009) as well as older women who were attending a geriatric outpatient clinic (Aoyama, Suzuki, Onishi, & Kuzuya, 2011). This fact could reflect the importance of maintaining good functional status in order to perform daily life activities (Brach & VanSwearingen, 2002). Therefore, the dimensions that correlated with an increased risk of falling were mobility, selfcare, and daily life activities (Painter et al., 2012), hence supporting the relationship between risk of falling and HRQoL as assessed by the EQ-5D found in this study (Davis et al., 2012; Ozcan, Donat, Gelecek, Ozdirenc, & Karadibak, 2005). As a practical novelty, several cut-off points have been determined in this study. These points could help in determining the optimal lower limb muscle performance level for preventing falls in older adults aged 80 years or more who are living in nursing homes. For example, a goal to prevent falls could be to achieve a peak force of 11.09 N/Kg. or 6.5 times in 30-s CSTS. Similar conclusions could be made for all of the physical components being evaluated (peak and average velocity and peak power). These cutoff points calculated using ROC curves can be used by clinicians when working toward fall prevention as a way of establish a starting point for designing an effective intervention that should include exercises aimed to improve strength and power at lower limb. Whole-body vibration including dynamic exercises seems to be an efficacy alterternative. Ultimately, the aim is to improve Page 15 of 33 RNJ Proof For Peer Review Falls in nursing home residents 16 performance of ADL and lastly quality of life of nursing home residents. (Álvarez-Barbosa et al., 2014). Study Limitations Some limitations need to be recognized in this study. An important shortcoming of this study is the fact that accuracy of 13.5 s as TUG cut-score to discriminate fallers from not fallers is controversial (Schoene et al., 2013). Shcone et al, concluded in a meta-analysis that TUG might not be useful for discriminating fallers from non-fallers in healthy, highfunctioning population of older adults but would be of more use in less-healthy, lowerfunctioning group. Moreover, the selected TUG cut-score has been validated among community dwelling older people and using standard method (i.e. natural comfortable pace). Here, a modification of the test (i.e. doing the task as fast as possible) was applied (T. J. Rikli, 2001). Besides, authors didn’t have access to fall history. Thus, participants might be incorrectly classified into fallers or not fallers. However, the aim of this study was not to differentiate between those that fell from those that didn’t. We were looking here at those at risk of falling (i.e. future falls) and factors associated to this risk of falling. With this purpose, the TUG test was used. Some authors have claimed the usefulness of the TUG test to discriminate between those older adults living in nursing homes that are at risk of falling and those that not (Schoene et al., 2013). Another study use 13.5 as cut-score to discriminate frail elderly people at risk of falling from those that are not at risk of falling according to the TUG test score (Podsiadlo & Richardson, 1991). In any case, it seems that TUG test is related to some of the fall risk factors (i.e. lower limb function) (Podsiadlo & Richardson, 1991) so working with this test may still provide advantages. A further shortcoming was related to the research design used. Because a cross-sectional design was used, a causative interpretation is Page 16 of 33RNJ Proof For Peer Review Falls in nursing home residents 17 not possible. Another shortcoming is the incidental character of our sample which introduces some level of selection bias. Moreover, a risk of self-selection bias needs to be recognized as data were not obtained on those that decided not to take part in the study due to the voluntary nature of the study. Along with these limitations, the small sample size does not allow for definitive conclusions (therefore statistical power achieved for static balance variables and were below accepted threshold) but the results provide an indication of what further research may show. Future, larger prospective studies are required to confirm the relationships demonstrated in the current study. CONCLUSIONS The results of the current study show that the risk of falls in older adults aged 80 years or more who are living in nursing homes is associated with lower limb muscle performance (peak power and velocity), functional status and HRQoL. 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J Orthop Sports Phys Ther, 38(7), 410-417. doi: 10.519/jospt.2008.2657 Page 20 of 33RNJ Proof For Peer Review Falls in nursing home residents 21 Page 21 of 33 RNJ Proof For Peer Review Manuscript - Rehabilitation Nursing: RNJ-15-01-000467 titled, "Factors associated with the risk of falls of nursing home residents aged 80 or older," Dear editor and reviewers, This letter accompanies the resubmission of a research article titled “Factors associated with the risk of falls of nursing home residents aged 80 or older + to the Rehabilitation Nursing.. We are thankful for the excellent feedback that we received and have taken appropriate action to resolve the outstanding issues with this article. In the remainder of the letter, we will outline (in red) how we have incorporated the feedback from the referees into a new draft. Reviewer: 1 This is a nicely written manuscript. One concern I have is the "cut-off points" you refer to in the discussion section. The only "cut off point" I see noted is the TUG cut off point. Can you clarify that either in the results or the discussion. Also, many of the measurement tools used in the study may not be tools used to assess patients in the nursing home setting. What are the implications for this and how can the results be used in the nursing home setting? Finally, please include psychometric properties for all of the measurement tools. Thank you. Thanks for commenting on these issues. The TUG cut off point is a pre-existing, previously validated cut-off points used to discriminate between people at risk of falls and people without risk of falling. The rest of the cut-off points result from the ROC curves analyses performed on the rest of the study variables (and using risk of falling as state variable). This has been clarified in both the results and discussion sections. We agree on that some of the assessment performed in this study might not be feasible for most of the nursing home residents (this is also noticed in limitations). However, the results from this study might be useful to design exercise programs aimed to reduce the risk of falling in the nursing home population. This is now in the manuscript. The psychometric properties of instruments have been added to the manuscript Reviewer: 2 This is a well-written, well-designed study that adds to the literature of rehabilitation nursing. Make sure your citations are all in correct APA format. Thanks for your comments on our work. References have been checked. Reviewer: 3 Major concern: the cut-off level for each test is not clearly explained in the discussion section. The authors need to revise this section and elaborate more on the cut-off level for each test. Page 22 of 33RNJ Proof For Peer Review Thanks for your comments in this issue. We have provided with more information on cut-off points and their implications. Minor concern 1. Page 2, abstract: Consider adding a background/introduction statement A background has been added to the abstract according to your suggestions 2. Page 2, abstract: The clinical relevance subsection in the abstract needs to be revised – see comment below on the conclusion section below The clinical relevance subsection in abstract has been revised according to your suggestion 3. Page 2, abstract: Methods: there is not mentioning of TUG test TUG test is mentioned now in the abstract 4. Page 4, paragraph 1, lines 4, 8 and 9: Please check how to cite the reference in the text throughout the entire manuscript. For example: “age of 80. (Inouye, Brown, & Tinetti, 2009)” change it to “age of 80 (Inouye, Brown, & Tinetti, 2009).” References have been checked. 5. Page 4, paragraph 2, line 3: Joyner, 2005, is this a reference for the statement that “risk if multifactorial” or is it for “reduced strength”? The current placement of the reference is inappropriate Thanks for commenting on this issue. Reference “Joyner, 2005” has been relocated to the end of the sentence as is the appropriate place for that reference. 6. Page 5, paragraph 2: Any inclusion criteria other than the age and living in nursing homes? exclusion criteria other than ability to follow instruction? Any comorbidity, physical abilities For example: the TUG was used in this study and the TUG requires that the participant is able to walk without any assistance. Is that in the inclusion and exclusion criteria? We have now provided with more details on the inclusion and exclusion criteria. Thanks for commenting on this. 7. Page 6, paragraph 1, line 10: Was the instruction for the TUG to perform the skill “as fast as possible” for the TUG we use the comfortable walking speed. This is important issue when using the 13.5 seconds as cut off level. The authors should provide more details explaining how they used the 13.5 seconds as cut off level to discriminate between faller and non faller, were TUG in other studies used the 13.5 tested at comfortable speed or fast speed? TUG test was administered following guidelines (Podsiadlo and Richardson, 1991): “in a comfortable and safe walking speed”. Studies references in the text referring to the chosen TUG cut-off point performed the TUG test with following same instructions. This is now modified in the manuscript Page 23 of 33 RNJ Proof For Peer Review 8. Page 5: Procedures and Outcome Measures: who performed the assessment? Was one person? How much experience in those tests? Assessment was performed always by one researcher with previous experience on the assessment of the same outcomes. This has been added to the manuscript. 9. Page 6, paragraph 1, lines 11-12: Please revise The sentence in line 11-12 has been reorganised to clarify the idea. 10. Page 6, paragraph 1, lines 8 and 13: The reference was listed in 8 as “Shumway, Brauer and Woollacott while in line 13 it was listed Shumway, when I checked the reference list, the list has only Shumway, Brauer and Woollacott. Please revise. Also check the same reference on page 12, paragraph 3, line 6 Thanks for commenting on this issue. According to APA style, when a study has more than one author, the first time that appears in the text, all authors must be mentioned, after that, when you cited this study again you should cited only with the first author. For that reason in line 8 the reference was cited as “Shumway, Brauer and Woollacott” and after that the same study is cited “Shumway et al,” 11. Page 7, paragraph 1, lines 4-5: Please revise, please check the referencing style of the journal on how to cite this reference This citation has been revised and modified according to the APA style 12. Graphs: I suggest that the authors add graphs that show the difference between fallers and non fallers Thanks for commenting on this issue. The authors prefer to keep the results of the study in table format so that the magnitudes and differences between groups can be better appreciated. 13. Page 17, paragraph 1, lines 3-5: This statement needs to be revised, there is no discussion in the manuscript on how the cut-off level can be used to guide the intervention for preventing falls. A paragraph has been added to explain how the info on the cut-off points could be useful to guide interventions for preventing falls in nursing home residents. Reviewer 4 Areas of Strength: Aside from the reference citations that are not in APA format which make the article hard to read; the topic is of interest and pertinent to rehabilitation nurses. Thanks for your comment. References have been checked and now are in APA format. Page 24 of 33RNJ Proof For Peer Review Table 5. Correlation coefficients between risk of falls (Timed Up and Go test score ≥13.5) and lower limb performance, quality of life or functional independence in the participants in the study (n=52) Variables Timed Up and Go Test (s) Lower limb performance 30 - s C STS (number of times) - 0.524** (a) 30 - s C STS Vmax (cm/s) - 0.715** (a) 30-s CSTS Vmed (cm/s) -0.707** (a) 30-s CSTS Peak force (N/kg) -0.233** (a) 30 - s C STS Power (W) - 0. 712 ** (a) Quality of Life (EQ-5D dimensions) Mobility (1-2)A negative 0.595** (b) Self-care (1-2) 0.631** (b) Daily Activities (1 - 2) 0.777** (b) Pain/Discomfort (1 - 2) 0.127 (b) Anxiety/Depression (1-2) 0.354* (b) EQ-5D UTILITY (0-1) -0.713** (a) EQ - 5D VAS (0 - 100) - 0.456** (a) Functional Independence (Barthel index) Barthel (0-100) -0.659** (a) Dependent (1-2) 0.512** (b) Static balance Eyes Open ML/AP 0.040 (a) Eyes Open coginitive interference ML/AP - 0.174 (a) Eyes Closed ML/AP -0.083 ( a) Pearson (a) or Spearman (b) correlation coefficients. 30-s CSTS Vmax: Peak velocity as determined by the 30 seconds sit to stand test; 30-s CSTS Vmed: Average velocity as determined by the 30 seconds sit to stand test; 30-s CSTS Peak force: Peak force as determined by the 30 seconds sit to stand test and normalized by weight of participants; 30-s CSTS Peak Power: Peak power as determined by the 30 seconds sit to stand test; Dependent: 1 No dependence (score of 70 or less on the Barthel Index) and 2 Dependent (score of less than 100 on the Barthel Index); ML/AP: Anterior-posterior/Medial lateral center of pressure excursion; ratio For quality of life dimensions (i.e., mobility, self-care, daily activities, pain/discomfort and anxiety/depression) 1 means no problems and 2 means problems. ** Correlation is significant at 0.01 level * Correlation is significant at 0.05 level Page 31 of 33 RNJ Proof For Peer Review Table 6. Association between the risk of falling (Timed Up and Go score ≥13.5) and Quality of life dimensions (EQ-5D) or functional Independence (Barthel Index = 100) in the study participants (n=52) Variables OR (95%CI) P value Quality of Life (EQ-5D) dimensions Mobility 16.87 (4.01 to 69.38) <0.001 Self Care 13.15 (2.60 to 66.62) <0.001 Daily activities 36.37 (4.28 to 308.72) <0.001 Pain/Discom fort 0.63 (0.192 to 2.08) 0.451 Anxiety/Depresion 2.68 (0.726 to 9.92) 0.132 Functional Independence (Barthel Index) 9.00 (2.31 to 35.06) <0.001 EQ-5D: European Quality of Life questionnaire; x 2 : chi square value; OR: Odds ratio Page 32 of 33RNJ Proof For Peer Review Table 7. Cut-off scores, sensitivity, specificity, and area under the receiver-operating curve for the variables that statistically differ between those with and without risk of falls among participants of the study (n=52) Variables Cut-off Sensitivity (%) Specificity (%) AUC (cm 2 ) p SE AUC 95% Interval Confidence 30-s CSTS (number of times) 6.50 71 60 0.744 0.003 0.069 0.609 to 0.878 30-s CSTS Vmax (cm/s) 0.45 81 74 0.873 <0.001 0.049 0.777 to 0.969 30-s CSTS Vmed (cm/s) 0.38 81 80 0.889 <0.001 0.046 0.798 to 0.979 30-s CSTS Peak Power (W) 5.07 81 70 0.863 <0.001 0.050 0.765 to 0.962 30-s CSTS Peak force (N/Kg) 11.09 67 77 0.679 0.031 0.086 0.511 to 0.847 AUC: area under the receiver-operating curve (maximum=1.0); SE: standard error; 30-s CSTS Vmax: Peak velocity as determined by the 30 seconds sit to stand test; 30-s CSTS Vmed: Average velocity as determined by the 30 seconds sit to stand test; 30-s CSTS Peak force: Peak force as determined by the 30 seconds sit to stand test and normalized by weight of participants; 30-s CSTS Peak Power: Peak power as determined by the 30 seconds sit to stand test; p: statistical significance set at 0.05. 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