Effects of exercise referral schemes enhanced with behavioural self-management strategies on functional capacity and self-reported disability in community-dwelling older adults. Secondary results from the SITLESS multi-country, three-armed randomized controlled trial.

BACKGROUND: Exercise referral schemes (ERS) are an effective strategy for increasing physical activity (PA) in older adults. Behavioural self-management strategies (SMS) may augment the maintenance of PA and associated benefits in this population, resulting in preservation of the functional capacity and prevention of disability over the long-term. AIM: The primary aim was to investigate the long-term (22-months) effects of ERS enhanced with SMS on functional capacity assessed by the Short Physical Performance Battery (SPPB) compared to ERS (primary comparison) and a control condition (CTRL).Secondarily, between-group effects after 4 and 16 months on the SPPB and self-reported disability outcomes were investigated. METHODS: 1360 physically inactive community-dwelling older adults ≥65 years from four European countries were randomized into (i) 16 weeks ERS enhanced with SMS (ERS-SMS), (ii) ERS alone and (iii) CTRL. In addition to SPPB, self-reported function and disability were assessed by the short-form late life function and disability index and with a six-item activity of daily living questionnaire. RESULTS: No long-term effects were found for the SPPB-score in ERS-SMS vs ERS (0.21 point, 95% CI [-0.04, 0.46]). Significant group × time effects were observed for the SPPB-score after 4 months in favour of ERS-SMS over CTRL (0.51 point, 95% CI [0.29, 0.73]) and ERS (0.46 point, 95% CI [0.24, 0.68]). CONCLUSION: The study did demonstrate differences, in favour of ERS + SMS, but on SPPB these were small, and not sustained over time. The additional effect of SMS was inconsistent and uncertain.

Cost-effectiveness of a programme to address sedentary behaviour in older adults: results from the SITLESS RCT.

BACKGROUND: This study details the within-trial economic evaluation and long-term economic model of SITLESS, a multi-country, three-armed randomized controlled trial comparing a combined intervention of exercise referral schemes (ERS) enhanced by self-management strategies (SMS) against ERS alone and usual care (UC). METHODS: A cost-utility analysis, conducted from the base-case perspective of the National Health Service and personal and social services, estimated the incremental cost per incremental quality-adjusted life year (QALY) and years in full capability (YFC). A secondary analysis combined the costs with a broad set of outcomes within a cost-consequence framework, from a societal perspective. A Markov-type decision-analytic model was developed to project short-term changes in physical activity to long-term outcomes and costs, over a 5- and 15-year time horizon. RESULTS: The results of the within-trial analysis show that SMS+ERS is highly likely to be cost-effective compared to ERS alone (ICER €4270/QALY), but not compared to UC. Participants allocated to the SMS+ERS group also showed an improvement in YFC compared to ERS alone and UC. The long-term analysis revealed that SMS+ERS is likely to be a cost-effective option compared to ERS and UC over a 5-year, but not with a 15-year horizon, being then dominated by ERS alone. CONCLUSION: This research provides new evidence that SMS is a cost-effective add-on to ERS strategies. This economic evaluation informs the case for further, cost-effective, refinement of lifestyle change programmes targeted to older adults, with the aim of ultimately reducing the impact of non-communicable diseases in this population.

Associations of sedentary behavior bouts with community-dwelling older adults' physical function.

The study aim was to explore associations between sedentary behavior (SB) bouts and physical function in 1360 community-dwelling older adults (≥65 years old). SB was measured using an ActiGraph wGT3X + accelerometer for seven consecutive days at the dominant hip and processed accordingly. Various SB bout lengths were assessed including: 1- to 9-minutes; 10- to 29-minutes; 30- to 59-minutes; and ≥60-minutes, as well as maximum time spent in a SB bout. Total SB time was adjusted for within the SB bout variables used (percentage SB time in the SB bout length and number of SB bouts per total SB hour). Physical function was assessed using the 2-minute walk test (2MWT), 5-times sit-to-stand (chair stand) test, and unipedal stance test (UST). Hierarchical linear regression models were utilized. Covariates such as moderate-vigorous physical activity (MVPA), demographic and health characteristics were controlled for. Lower percentage time spent in ≥60-minute SB bouts was significantly (P < .05) associated with longer 2MWT distance while lower numbers of ≥60-minute SB bouts were associated with longer 2MWT distance, shorter chair stand time and longer UST time. There were mixed associations with physical function for 10- to 29-minute SB bouts. In a large cohort of European older adults, prolonged SB bouts lasting ≥60-minutes appear to be associated with reduced physical function after controlling for MVPA and numerous other important covariates. Besides reducing SB levels, these findings suggest there is a need to regularly interrupt prolonged SB to improve physical function in older adults.

Associations between objectively measured physical activity, sedentary behaviour and time in bed among 75+ community-dwelling Danish older adults.

BACKGROUND: Older adults are recommended to sleep 7-8 h/day. Time in bed (TIB) differs from sleep duration and includes also the time of lying in bed without sleeping. Long TIB (≥9 h) are associated with self-reported sedentary behavior, but the association between objectively measured physical activity, sedentary behavior and TIB is unknown. METHODS: This study was based on cross-sectional analysis of the Healthy Ageing Network of Competence (HANC Study). Physical activity and sedentary behaviour were measured by a tri-axial accelerometer (ActiGraph) placed on the dominant wrist for 7 days. Sedentary behavior was classified as < 2303 counts per minute (cpm) in vector magnitude and physical activity intensities were categorized, as 2303-4999 and ≥ 5000 cpm in vector magnitude. TIB was recorded in self-reported diaries. Participants were categorized as UTIB (usually having TIB 7-9 h/night: ≥80% of measurement days), STIB (sometimes having TIB 7-9 h/night: 20-79% of measurement days), and RTIB (rarely having TIB 7-9 h/night: < 20% of measurement days). Multinominal regression models were used to calculate the relative risk ratios (RRR) of being RTIB and STIB by daily levels of physical activity and SB, with UTIB as the reference group. The models were adjusted for age, sex, average daily nap length and physical function. RESULTS: Three hundred and fourty-one older adults (median age 81 (IQR 5), 62% women) were included with median TIB of 8 h 21 min (1 h 10 min)/day, physical activity level of 2054 (864) CPM with 64 (15) % of waking hours in sedentary behavior. Those with average CPM within the highest tertile had a lower RRR (0.33 (0.15-0.71), p = 0.005) for being RTIB compared to those within the lowest tertile of average CPM. Accumulating physical activity in intensities 2303-4999 and ≥ 5000 cpm/day did not affect the RRR of being RTIB. RRR of being RTIB among highly sedentary participants (≥10 h/day of sedentary behavior) more than tripled compared to those who were less sedentary (3.21 (1.50-6.88), p = 0.003). CONCLUSIONS: For older adults, being physically active and less sedentary was associated with being in bed for 7-9 h/night for most nights (≥80%). Future longitudinal studies are warranted to explore the causal relationship sbetween physical activity and sleep duration.

Impact of musculoskeletal pain on balance and concerns of falling in mobility-limited, community-dwelling Danes over 75 years of age: a cross-sectional study.

BACKGROUND: In older adults, musculoskeletal pain is associated with increased concerns of falling, reduced balance and increased occurrence of falls. In younger adults, the intensity of neck pain and low back pain is associated with increased postural sway. It is not known if pain further impairs balance and concerns of falling in mobility-limited older adults, and if so, whether this is associated with different intensities of pain. OBJECTIVE: This study examined whether mobility-limited older adults with mild or intense neck pain and/or low back pain have significantly increased postural sway as measured by centre of pressure (COP) changes and concerns of falling compared to those without pain. METHODS: 48 older adults with a gait speed of < 0.9 m/s from Odense, Denmark were recruited through the public health service. Self-reported neck pain, low back pain, and concerns of falling were recorded on questionnaires. Sway range, velocity and area were recorded on a force plate in a comfortable standing stance. Pain intensity was rated on an 11 point numerical rating scale (0-10). Participants were sub-grouped into mild (0-4) and intense (> 5) neck pain or low back pain. RESULTS: Intense neck pain was associated with increased anterior-posterior sway range and area of sway. Intense low back pain was associated with increased concerns of falling. CONCLUSION: Intense neck pain in mobility-limited older adults is associated with significant changes in postural balance, and intense low back pain is associated with significantly higher concerns of falling.

Neck pain, concerns of falling and physical performance in community-dwelling Danish citizens over 75 years of age: A cross-sectional study.

AIMS: The aim of this study was to determine the associations between neck pain, concerns of falling and physical performance in older people. METHODS: Cross-sectional study of 423 community-dwelling Danes aged 75 years and older. Measures consisted of self-reported neck pain, physical performance (Short Physical Performance Battery), self-reported psychological concerns related to falling (Falls Efficacy Scale International), depression (Major Depression Inventory), cognitive function (Mini Mental State Examination), self-reported low-back pain and self-reported history of falls. Associations between neck pain and fear of falling were determined using multivariable logistic regression modelling. RESULTS: Bothersome neck pain that limits daily activities is significantly associated with concerns of falling (unadjusted odds ratio (OR) 3.29, 95% confidence interval (CI) 1.54-7.03) and impaired physical performance (unadjusted OR 2.26, 95% CI 1.09-4.69). However, these relationships became nonsignificant after adjusting for potential confounders. Bothersome neck pain and concerns of falling is attenuated by depression, and the relationship between bothersome neck pain and decreased physical performance is attenuated by concerns of falling, depression and previous history of falls. CONCLUSIONS: Bothersome neck pain in older people is associated with increased concerns of falling and decreased physical performance that are two known risk factors for falls in older people. However, these relationships are complicated by other variables, particularly depression.

Need to Revise Classification of Physical Activity Intensity in Older Adults? The Use of Estimated METs, Measured METs, and V̇O2 Reserve.

BACKGROUND: Multiples of resting metabolic rate (RMR) are often used to classify physical activity intensity, a concept known as the metabolic equivalent of task (MET). However, the METs metrics may misclassify physical activity intensity in older adults because of age-related changes in RMR and maximal aerobic capacity (V˙O2max). This study aimed to (i) compare classifications of activity intensity by estimated (METsestimated) and measured (METsmeasured) METs and (ii) compare physical activity classified by absolute (METsmeasured) versus relative intensity (%V˙O2Reserve) in older adults. METHODS: Ninety-eight adults aged 75-90 years participated in the study. RMR and V˙O2 during sitting, standing, daily activities, and 6-minute walking test were measured. V˙O2Reserve was defined as the difference between V˙O2max and RMR. Moderate and vigorous intensity was classified as 3 and 6 METs and 40% and 60% of V˙O2Reserve, respectively. Paired t tests and a confusion matrix were used to investigate aims 1 and 2, respectively. RESULTS: METsmeasured was 24% lower than the standard 1 MET of 3.5 mL O2·min-1·kg-1. METsestimated underestimated the intensity during daily and walking activities when compared to METsmeasured. Nevertheless, when comparing METsmeasured to percentages of V˙O2Reserve, a mismatch was shown for moderate intensity in 47%-67% of the participants during daily activities and 21% of the participants during self-selected gait speed. CONCLUSIONS: Applying METsestimated for older adults leads to potential underestimation of physical activity intensity, suggesting that current classification metrics should be revised for older adults. V˙O2Reserve is a candidate metric for establishing precise physical activity intensity cut points for older adults. Clinical Trials Registration Number: NCT04821713.

Boosting enjoyment and social inclusion to increase physical activity and reduce sedentary behaviour among older adults: protocol for a feasibility study to test the JOIN4JOY approach in five European countries.

INTRODUCTION: Programmes for older people aimed at increasing physical activity (PA) and reducing sedentary behaviour (SB) traditionally focus on achieving functional and health improvements. Focusing on enjoyment and social inclusion could strengthen adherence and help reach older people with social disadvantages. The aim of this study is to assess the feasibility and acceptability of the Join4Joy approach in PA programmes and its assessment tools. METHODS AND ANALYSIS: A multicentric, pragmatic, pre-post feasibility study using mixed methods will be conducted. The intervention will consist of a PA programme boosting enjoyment and social inclusion, grounded on a co-creation process. Trainers will offer twelve, 1-hour weekly sessions of structured, supervised, group-based PA. Participants will be encouraged to increase activity in daily living. 144 older people will be recruited from the community and nursing homes in Spain, Denmark, Italy, Germany, and France. Additionally, participants and trainers will be invited to join virtual communities of practice to share their experiences across settings and countries. Qualitative procedures will be used to explore the acceptability of the design via interviews and focus groups with participants and trainers. Quantitative methods will be used to assess uptake, adherence, retention, reach, satisfaction, enjoyment (PACES questionnaire), physical function (e.g., Short Physical Performance Battery), quality of life (EQ-5D-5L scale), perceived improvement (Patient Global Impression of Improvement scale-I), activities of daily living (Barthel index) and SB and PA patterns (IPAQ and accelerometry). The degree and type of participation in virtual communities of practice will also be assessed. SPSS software will be used for the analysis of quantitative variables. Qualitative data will be analysed using reflective thematic analysis following Braun and Clarke (2006). ETHICS AND DISSEMINATION: A favourable report by the Research Ethics Committee of UVic-UCC (282/2023) was obtained on 26 June 26th, 2023. Participation and withdrawal will be voluntary. Participants' (or their legal guardians', when necessary) written permission will be required. Results of the study will be disseminated through publication of scientific articles, presentations at sport and health-related professional conferences and congresses, as well as through social media and via the Join4Joy website. STUDY REGISTRATION: ClinicalTrials.gov, NCT06100835.

Older Adults' Experiences of a Physical Activity and Sedentary Behaviour Intervention: A Nested Qualitative Study in the SITLESS Multi-Country Randomised Clinical Trial.

BACKGROUND: The SITLESS programme comprises exercise referral schemes and self-management strategies and has been evaluated in a trial in Denmark, Spain, Germany and Northern Ireland. The aim of this qualitative study was to understand the implementation and contextual aspects of the intervention in relation to the mechanisms of impact and to explore the perceived effects. METHODS: Qualitative methodologies were nested in the SITLESS trial including 71 individual interviews and 12 focus groups targeting intervention and control group participants from postintervention to 18-month follow-up in all intervention sites based on a semi-structured topic guide. RESULTS: Overarching themes were identified under the framework categories of context, implementation, mechanisms of impact and perceived effects. The findings highlight the perceived barriers and facilitators to older adults' engagement in exercise referral schemes. Social interaction and enjoyment through the group-based programmes are key components to promote adherence and encourage the maintenance of targeted behaviours through peer support and connectedness. Exit strategies and signposting to relevant classes and facilities enabled the maintenance of positive lifestyle behaviours. CONCLUSIONS: When designing and implementing interventions, key components enhancing social interaction, enjoyment and continuity should be in place in order to successfully promote sustained behaviour change.

Accelerometer-Measured Sedentary and Physical Activity Time and Their Correlates in European Older Adults: The SITLESS Study.

BACKGROUND: Sedentary behavior (SB) and physical activity (PA) are important determinants of health in older adults. This study aimed to describe the composition of accelerometer-measured SB and PA in older adults, to explore self-reported context-specific SB, and to assess sociodemographic and functional correlates of engaging in higher levels of SB in participants of a multicenter study including four European countries. METHOD: One thousand three hundred and sixty community-dwelling older adults from the SITLESS study (61.8% women; 75.3 ±â€…6.3 years) completed a self-reported SB questionnaire and wore an ActiGraph accelerometer for 7 days. Accelerometer-determined compositional descriptive statistics were calculated. A fixed-effects regression analysis was conducted to assess the sociodemographic (country, age, sex, civil status, education, and medications) and functional (body mass index and gait speed) correlates. RESULTS: Older adults spent 78.8% of waking time in SB, 18.6% in light-intensity PA, and 2.6% in moderate-to-vigorous PA. Accelerometry showed that women engaged in more light-intensity PA and walking and men engaged in higher amounts of moderate-to-vigorous PA. Watching television and reading accounted for 47.2% of waking time. Older age, being a man, single, taking more medications, being obese and overweight, and having a slower gait speed were statistically significant correlates of more sedentary time. CONCLUSIONS: The high amount of SB of our participants justifies the need to develop and evaluate interventions to reduce sitting time. A clinically relevant change in gait speed can decrease almost 0.45 percentage points of sedentary time. The distribution of context-specific sedentary activities by country and sex showed minor differences, albeit worth noting.

Exercise referral schemes enhanced by self-management strategies to reduce sedentary behaviour and increase physical activity among community-dwelling older adults from four European countries: protocol for the process evaluation of the SITLESS randomised controlled trial.

INTRODUCTION: SITLESS is a randomised controlled trial determining whether exercise referral schemes can be enhanced by self-management strategies to reduce sedentary behaviour and increase physical activity in the long term, in community-dwelling older citizens. The intervention is complex and requires a process evaluation to understand how implementation, causal mechanisms and context shape outcomes. The specific aims are to assess fidelity and reach of the implementation, understand the contextual aspects of each intervention site, evaluate the mechanisms of impact, and explore perceived effects. METHODS AND ANALYSIS: Following the Medical Research Council guidance on complex interventions, a combination of qualitative and quantitative procedures is applied, including observational checklists and attendance registries, standardised scales (ie, Marcus's Self-Efficacy Questionnaire, Physical Activity Self-Regulation Scale and the Lubben Social Network Scale) at baseline, postintervention and follow-up assessments, semistructured questionnaires gathering contextual characteristics, and participant observations of the sessions. Semistructured interviews and focus groups with the participants and trainers are conducted at postintervention and during the follow-up to explore their experiences. Outcomes from the standardised scales are analysed as moderators within the impact evaluation. Descriptive results on context and perceived effects complement results on impact. The qualitative and quantitative findings will help to refine the logic model to finally support the interpretation of the results on the effectiveness of the intervention. ETHICS AND DISSEMINATION: The study design was approved by the respective Ethical Committee of Ramon Llull University, Southern Denmark, Northern Ireland and Ulm University. Participation is voluntary, and all participants are asked to sign informed consent before starting the study. A dissemination plan operationalises how to achieve a social impact by reaching academic and non-academic stakeholders. A data management plan describes the specific data sets and regulates its deposition and curation. All publications will be open access. TRIAL REGISTRATION NUMBER: NCT02629666; Pre-results.

Cost-effectiveness of exercise referral schemes enhanced by self-management strategies to battle sedentary behaviour in older adults: protocol for an economic evaluation alongside the SITLESS three-armed pragmatic randomised controlled trial.

INTRODUCTION: Promoting physical activity (PA) and reducing sedentary behaviour (SB) may exert beneficial effects on the older adult population, improving behavioural, functional, health and psychosocial outcomes in addition to reducing health, social care and personal costs. This paper describes the planned economic evaluation of SITLESS, a multicountry three-armed pragmatic randomised controlled trial (RCT) which aims to assess the short-term and long-term effectiveness and cost-effectiveness of a complex intervention on SB and PA in community-dwelling older adults, based on exercise referral schemes enhanced by a group intervention providing self-management strategies to encourage lifestyle change. METHODS AND ANALYSIS: A within-trial economic evaluation and long-term model from both a National Health Service/personal social services perspective and a broader societal perspective will be undertaken alongside the SITLESS multinational RCT. Healthcare costs (hospitalisations, accident and emergency visits, appointment with health professionals) and social care costs (eg, community care) will be included in the economic evaluation. For the cost-utility analysis, quality-adjusted life-years will be measured using the EQ-5D-5L and capability well-being measured using the ICEpop CAPability measure for Older people (ICECAP-O) questionnaire. Other effectiveness outcomes (health related, behavioural, functional) will be incorporated into a cost-effectiveness analysis and cost-consequence analysis.The multinational nature of this RCT implies a hierarchical structure of the data and unobserved heterogeneity between clusters that needs to be adequately modelled with appropriate statistical and econometric techniques. In addition, a long-term population health economic model will be developed and will synthesise and extrapolate within-trial data with additional data extracted from the literature linking PA and SB outcomes with longer term health states.Methods guidance for population health economic evaluation will be adopted including the use of a long-time horizon, 1.5% discount rate for costs and benefits, cost consequence analysis framework and a multisector perspective. ETHICS AND DISSEMINATION: The study design was approved by the ethics and research committee of each intervention site: the Ethics and Research Committee of Ramon Llull University (reference number: 1314001P) (Fundació Blanquerna, Spain), the Regional Committees on Health Research Ethics for Southern Denmark (reference number: S-20150186) (University of Southern Denmark, Denmark), Office for Research Ethics Committees in Northern Ireland (ORECNI reference number: 16/NI/0185) (Queen's University of Belfast) and the Ethical Review Board of Ulm University (reference number: 354/15) (Ulm, Germany). Participation is voluntary and all participants will be asked to sign informed consent before the start of the study.This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 634 270. This article reflects only the authors' view and the Commission is not responsible for any use that may be made of the information it contains.The findings of the study will be disseminated to different target groups (academia, policymakers, end users) through different means following the national ethical guidelines and the dissemination regulation of the Horizon 2020 funding agency.Use of the EuroQol was registered with the EuroQol Group in 2016.Use of the ICECAP-O was registered with the University of Birmingham in March 2017. TRIAL REGISTRATION NUMBER: NCT02629666; Pre-results.

The SITLESS project: exercise referral schemes enhanced by self-management strategies to battle sedentary behaviour in older adults: study protocol for a randomised controlled trial.

BACKGROUND: Older adults are the fastest growing segment of the world's population. Recent evidence indicates that excessive sitting time is harmful to health, independent of meeting the recommended moderate to vigorous physical activity (PA) guidelines. The SITLESS project aims to determine whether exercise referral schemes (ERS) can be enhanced by self-management strategies (SMSs) to reduce sedentary behaviour (SB), increase PA and improve health, quality of life and function in the long term, as well as psychosocial outcomes in community-dwelling older European citizens from four countries, within a three-armed pragmatic randomised controlled trial, compared with ERS alone and also with general recommendations about PA. METHODS: A total of 1338 older adults will be included in this study, recruited from four European countries through different existing primary prevention pathways. Participants will be randomly allocated into an ERS of 16 weeks (32 sessions, 45-60 min per session), ERS enhanced by seven sessions of SMSs and four telephone prompts, or a control group. Outcomes will be assessed at baseline, month 4 (end of ERS intervention), month 16 (12 months post intervention) and month 22 (18 months post intervention). Primary outcomes will include measures of SB (time spent sedentary) and PA (counts per minute). Secondary outcomes will include muscle and physical function, health economics' related outcomes, anthropometry, quality of life, social networks, anxiety and depressive symptoms, disability, fear of falling, executive function and fatigue. A process evaluation will be conducted throughout the trial. The full analysis set will follow an intention-to-treat principle and will include all randomised participants for whom a baseline assessment is conducted. The study hypothesis will be tested with mixed linear models with repeated measures, to assess changes in the main outcomes (SB and PA) over time (baseline to month 22) and between study arms. DISCUSSION: The findings of this study may help inform the design and implementation of more effective interventions to reduce SB and increase PA levels, and hence improve long-term health outcomes in the older adult population. SITLESS aims to support policy-makers in deciding how or whether ERS should be further implemented or restructured in order to increase its adherence, impact and cost-effectiveness. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02629666 . Registered 19 November 2015.

Voluntary muscle activation improves with power training and is associated with changes in gait speed in mobility-limited older adults - A randomized controlled trial.

Incomplete voluntary muscle activation may contribute to impaired muscle mechanical function and physical function in older adults. Exercise interventions have been shown to increase voluntary muscle activation, although the evidence is sparse for mobility-limited older adults, particularly in association with physical function. This study examined the effects of 12weeks of power training on outcomes of voluntary muscle activation and gait speed in mobility-limited older adults from the Healthy Ageing Network of Competence (HANC) study. We included 37 older men and women with a usual gait speed of <0.9m/s in the per-protocol analysis: n=16 in the training group (TG: 12weeks of progressive high-load power training, 2 sessions per week; age: 82.3±1.3years, 56% women) and n=21 in the control group (CG: no interventions; age: 81.6±1.1years, 67% women). Knee extensor muscle thickness (ultrasonography), strength (isokinetic dynamometry), voluntary activation (interpolated twitch technique), and gait speed (2-min maximal walking test) were assessed at baseline and post-intervention. At baseline, TG and CG were comparable for all measures. Post-intervention, significant between-group changes (TG vs. CG; p<0.05) were observed for voluntary muscle activation (+6.2%), muscle strength (+13.4Nm), and gait speed (+0.12m/s), whereas the between-group change in muscle thickness was non-significant (+0.08cm). Improvements in voluntary muscle activation were associated with improvements in gait speed in TG (r=0.67, p<0.05). Importantly, voluntary muscle activation is improved in mobility-limited older adults following 12-weeks of progressive power training, and is associated with improved maximal gait speed. Incomplete voluntary muscle activation should be considered one of the key mechanisms influencing muscle mechanical function and gait speed in older adults.