Publications

OBJECTIVES: Factors that are responsible for age-related neurologic deterioration of noncognitive and cognitive processes may have a shared cause. We sought to examine the temporal, directional associations of handgrip strength and cognitive function in a national sample of aging Americans. DESIGN: Longitudinal panel. SETTING: Enhanced interviews that included physical, biological, and psychosocial measures were completed in person. Core interviews were often conducted over the telephone. PARTICIPANTS: The analytic sample included 14,775 Americans aged at least 50 years who participated in at least 2 waves of the 2006-2016 waves of the Health and Retirement Study. MEASURES: Handgrip strength was measured with a hand-held dynamometer. Participants were considered cognitively intact, mildly impaired, or severely impaired according to the Telephone Interview of Cognitive Status questionnaire. Separate lagged general estimating equations analyzed the directional associations of handgrip strength and cognitive function. RESULTS: The overall time to follow-up was 2.1 +/- 0.4 years. Every 5 kg higher handgrip strength was associated with 0.97 [95% confidence interval (CI) 0.93, 0.99] lower odds for both future cognitive impairment and worse cognitive impairment. Those who were not weak had 0.54 (CI 0.43, 0.69) lower odds for future cognitive impairment and 0.57 (CI 0.46, 0.72) lower odds for future worse cognitive impairment. Conversely, any (beta = -1.09; CI -1.54, -0.64), mild (beta = -0.85; CI -1.34, -0.36), and severe cognitive impairment (beta = -2.34; CI -3.25, -1.42) predicted decreased handgrip strength. Further, the presence of any, mild, and severe cognitive impairment was associated with 1.82 (CI 1.48, 2.24), 1.65 (CI 1.31, 2.08), and 2.53 (CI 1.74, 3.67) greater odds for future weakness, respectively. CONCLUSIONS/IMPLICATIONS: Strength capacity and cognitive function may parallel each other, whereby losses of functioning in 1 factor may forecast losses of functioning in the other. Handgrip strength could be used for assessing cognitive status in aging Americans and strength capacity should be monitored in those with cognitive impairment.

BACKGROUND: Discovering how certain health factors contribute to functional declines may help to promote successful aging. AIMS: To determine the independent and joint associations of handgrip strength (HGS) and cognitive function with instrumental activities of daily living (IADL) and activities of daily living (ADL) disability decline in aging Americans. METHODS: Data from 18,391 adults aged 50 years and over who participated in at least one wave of the 2006-2014 waves of the Health and Retirement Study were analyzed. A hand-held dynamometer assessed HGS and cognitive functioning was examined with a modified version of the Telephone Interview of Cognitive Status. IADL and ADL abilities were self-reported. Participants were stratified into four distinct groups based on their HGS and cognitive function status. Separate covariate-adjusted multilevel models were conducted for the analyses. RESULTS: Participants who were weak, had a cognitive impairment, and had both weakness and a cognitive impairment had 1.70 (95% confidence interval (CI) 1.57-1.84), 1.97 (CI 1.74-2.23), and 3.13 (CI 2.73-3.59) greater odds for IADL disability decline, respectively, and 2.26 (CI 2.03-2.51), 1.26 (CI 1.05-1.51), and 4.48 (CI 3.72-5.39) greater odds for ADL disability decline, respectively. DISCUSSION: HGS and cognitive functioning were independently and jointly associated with IADL and ADL disability declines. Individuals with both weakness and cognitive impairment demonstrated substantially higher odds for functional decline than those with either risk factor alone. CONCLUSIONS: Including measures of both HGS and cognitive functioning in routine geriatric assessments may help to identify those at greatest risk for declining functional capacity.

BACKGROUND: Gender and ethnicity are factors which influence strength, and hand dominance could be a critical component of handgrip strength (HGS) testing. Providing such HGS percentiles across the lifespan may help to identify weakness-related health concerns. We sought to generate growth charts and curves for HGS by gender and ethnicity in a nationally-representative sample of Americans aged 6-80 years. METHODS: Data from 13,617 participants in the 2011-2012 and 2013-2014 waves of the National Health and Nutrition Examination Survey were analyzed. HGS was measured with a handgrip dynamometer. Age, gender, ethnicity, and hand dominance were self-reported. Body Mass Index (BMI) was calculated from height and body mass. Measures of absolute HGS and HGS normalized to BMI were separately included in parametric quantile regression analyses for determining the 10th-90th percentiles across ages by gender and ethnicity. Similar models were also conducted by hand dominance. RESULTS: Differences in absolute HGS and HGS normalized to BMI quantiles across ages existed for each ethnicity regardless of gender. In men, absolute HGS generally increased until about 25 years of age, began to decline around age 30 years, and regressed into older adulthood. In women, absolute HGS appeared to rise starting at age 6 years, peaked between 20 and 30 years of age, but was maintained into mid-life before declining in older adulthood. Similar results were found for HGS normalized to BMI. CONCLUSIONS: Our findings provide percentile charts for HGS capacity that could be utilized for comparing individual measures of HGS to those from a United States population-representative sample.

BACKGROUND/OBJECTIVES: Examining handgrip strength (HGS) asymmetry and weakness together may extend the predictive capacity of HGS for capturing possible health problems such as cognitive impairment. The purpose of this study was to determine the associations of HGS asymmetry and weakness on lower cognitive functioning in a national sample of aging Americans. DESIGN: Longitudinal panel. SETTING: Participant residences. PARTICIPANTS: The analytic sample included 17,163 Americans aged 65.0 years (standard deviation = 10.1 years) who participated in the 2006 to 2016 waves of the Health and Retirement Study (HRS). MEASUREMENTS: A handgrip dynamometer was used to measure HGS; weakness was defined as HGS below 26 kg (men) or below 16 kg (women). Persons with HGS above 10% stronger on either hand were considered as having any HGS asymmetry. Those with HGS that was more than 10% stronger on their dominant or nondominant hand were considered as having dominant or nondominant HGS asymmetry, respectively. The Telephone Interview of Cognitive Status determined lower cognitive functioning (/=65 years). Covariate-adjusted linear mixed-effects models analyzed the associations of each HGS asymmetry and weakness group on lower cognitive functioning. RESULTS: Relative to those with symmetric HGS and no weakness, each HGS asymmetry and weakness group had greater odds for lower cognitive functioning: 1.15 (95% confidence interval [CI] = 1.03-1.27) for any HGS asymmetry alone, 1.64 (95% CI = 1.21-2.23) for weakness alone, and 1.95 (95% CI = 1.51-2.53) for any HGS asymmetry and weakness. Each HGS asymmetry dominance and weakness group also had greater odds for lower cognitive functioning: 1.12 (95% CI = 1.01-1.25) for asymmetric dominant HGS alone, 1.27 (95% CI = 1.05-1.53) for asymmetric nondominant HGS alone, 1.64 (95% CI = 1.21-2.23) for weakness alone, 1.89 (95% CI = 1.39-2.57) for weakness and asymmetric dominant HGS, and 2.10 (95% CI = 1.37-3.20) for weakness and asymmetric nondominant HGS. CONCLUSION: The presence of both HGS asymmetry and weakness may predict accelerated declines in cognitive functioning.

OBJECTIVES: To develop an evidence-based definition of sarcopenia that can facilitate identification of older adults at risk for clinically relevant outcomes (eg, self-reported mobility limitation, falls, fractures, and mortality), the Sarcopenia Definition and Outcomes Consortium (SDOC) crafted a set of position statements informed by a literature review and SDOC's analyses of eight epidemiologic studies, six randomized clinical trials, four cohort studies of special populations, and two nationally representative population-based studies. METHODS: Thirteen position statements related to the putative components of a sarcopenia definition, informed by the SDOC analyses and literature synthesis, were reviewed by an independent international expert panel (panel) iteratively and voted on by the panel during the Sarcopenia Position Statement Conference. Four position statements related to grip strength, three to lean mass derived from dual-energy x-ray absorptiometry (DXA), and four to gait speed; two were summary statements. RESULTS: The SDOC analyses identified grip strength, either absolute or scaled to measures of body size, as an important discriminator of slowness. Both low grip strength and low usual gait speed independently predicted falls, self-reported mobility limitation, hip fractures, and mortality in community-dwelling older adults. Lean mass measured by DXA was not associated with incident adverse health-related outcomes in community-dwelling older adults with or without adjustment for body size. CONCLUSION: The panel agreed that both weakness defined by low grip strength and slowness defined by low usual gait speed should be included in the definition of sarcopenia. These position statements offer a rational basis for an evidence-based definition of sarcopenia. The analyses that informed these position statements are summarized in this article and discussed in accompanying articles in this issue of the journal. J Am Geriatr Soc 68:1410-1418, 2020.

This article provides an overview of the pathways the nervous system uses to create movement, and apply this knowledge to explain current therapeutic interventions for functional rehabilitation. The first section focuses on motor control hierarchy, where we describe how the motor system is organized in a conceptual hierarchical system to communicate across the central and peripheral nervous systems. The second section focuses on preparation and initiation of voluntary movement, where we explain the function of distinct regions of the brain, and how those regions consolidate and integrate their processing to engage in motor planning, formation and initiation of movement commands, and organization of sequential motor actions. The third section focuses on descending motor pathways, where we provide an anatomical description of how motor neurons navigate the various descending pathways from the cerebrum, or brainstem, to innervate their bodily targets. The fourth section focuses on feedforward and feedback mechanisms, where we discuss how sensory feedback and feedforward mechanisms impact movement regulation. The fifth section focuses on neural development of motor control, where we explain the basic developmental properties of motor control, from embryological development through adult maturation. The last section focuses on therapeutic approaches to motor rehabilitation, where we describe current therapeutic strategies clinicians use to enhance sensory, motor, and cognitive abilities for rehabilitation.

The authors describe the effects of an ethanol extract of maca root on glucose uptake and metabolism in cultured 3T3-L1 adipocytes. The extract stimulates glucose uptake and shares many features of an insulin mimetic: increased phosphorylation of insulin receptor (IR), increased phosphorylation of Akt downstream of IR, and inhibition of glucose uptake by LY294002, an inhibitor of PI3K, which mediates Akt phosphorylation. However, the extract also inhibits mitochondrial oxygen consumption. The effect on glucose uptake is biphasic, and inhibition of mitochondrial respiration is associated with decreased glucose uptake at high concentrations. When the authors examined the effects of a well-characterized mitochondrial poison, oligomycin, for comparison, completely parallel effects on the insulin signaling pathway and the same biphasic effect on glucose uptake were observed. It is concluded that stimulation of the insulin pathway by the extract is an indirect effect of mitochondrial inhibition rather than direct stimulation of the pathway itself. These results have practical implications for assessing the potential benefit of natural products in glucose homeostasis and caution against concentrated extracts from maca for use in humans.

Background: Age-related declines in physical function lead to decreased independence and higher healthcare costs. Individuals who meet the endurance and resistance exercise recommendations can improve their physical function and overall fitness, even into their ninth decade. However, most older adults do not exercise regularly, and the majority of those who do only perform one type of exercise, and in doing so are not getting the benefits of endurance or resistance exercise. Herein we present the study protocol for a randomized clinical trial that will investigate the potential for high-intensity interval training (HIIT) to improve maximal oxygen consumption, muscular power, and muscle volume (primary outcomes), as well as body composition, 6-min walk distance, and muscular strength and endurance (secondary outcomes). Methods and Analysis: This is a single-site, single-blinded, randomized clinical trial. A minimum of 24 and maximum of 30 subjects aged 60-75 that are generally healthy but insufficiently active will be randomized. After completion of baseline assessments, participants will be randomized in a 1:1:1 ratio to participate in one of three 12-week exercise programs: stationary bicycle HIIT, stationary bicycle moderate-intensity continuous training (MICT), or resistance training. Repeat assessments will be taken immediately post intervention. Discussion: This study will examine the potential for stationary bicycle HIIT to result in both cardiorespiratory and muscular adaptations in older adults. The results will provide important insights into the effectiveness of interval training, and potentially support a shift from volume-driven to intensity-driven exercise strategies for older adults. Clinical Trial Registration: This trial is registered with ClinicalTrials.gov (registration number: NCT03978572, date of registration June 7, 2019).