Robert J. Brychta

Sedentary Activity Associated With Metabolic Syndrome Independent of Physical Activity

OBJECTIVE This study examined the association between objectively measured sedentary activity and metabolic syndrome among older adults. RESEARCH DESIGN AND METHODS Data were from 1,367 men and women, aged ≥60 years who participated in the 2003–2006 National Health and Nutrition Examination Survey (NHANES). Sedentary time during waking hours was measured by an accelerometer (<100 counts per minute). A sedentary bout was defined as a period of time >5 min. A sedentary break was defined as an interruption in sedentary time (≥100 counts per minute). Metabolic syndrome was defined according to the Adult Treatment Panel (ATP) III criteria. RESULTS On average, people spent 9.5 h (65% of wear time) as sedentary. Compared with people without metabolic syndrome, people with metabolic syndrome spent a greater percentage of time as sedentary (67.3 vs. 62.2%), had longer average sedentary bouts (17.7 vs. 16.7 min), had lower intensity during sedentary time (14.8 vs. 15.8 average counts per minute), and had fewer sedentary breaks (82.3 vs. 86.7), adjusted for age and sex (all P < 0.01). A higher percentage of time sedentary and fewer sedentary breaks were associated with a significantly greater likelihood of metabolic syndrome after adjustment for age, sex, ethnicity, education, alcohol consumption, smoking, BMI, diabetes, heart disease, and physical activity. The association between intensity during sedentary time and metabolic syndrome was borderline significant. CONCLUSIONS The proportion of sedentary time was strongly related to metabolic risk, independent of physical activity. Current results suggest older people may benefit from reducing total sedentary time and avoiding prolonged periods of sedentary time by increasing the number of breaks during sedentary time.

Evolution of accelerometer methods for physical activity research

The technology and application of current accelerometer-based devices in physical activity (PA) research allow the capture and storage or transmission of large volumes of raw acceleration signal data. These rich data not only provide opportunities to improve PA characterisation, but also bring logistical and analytic challenges. We discuss how researchers and developers from multiple disciplines are responding to the analytic challenges and how advances in data storage, transmission and big data computing will minimise logistical challenges. These new approaches also bring the need for several paradigm shifts for PA researchers, including a shift from count-based approaches and regression calibrations for PA energy expenditure (PAEE) estimation to activity characterisation and EE estimation based on features extracted from raw acceleration signals. Furthermore, a collaborative approach towards analytic methods is proposed to facilitate PA research, which requires a shift away from multiple independent calibration studies. Finally, we make the case for a distinction between PA represented by accelerometer-based devices and PA assessed by self-report.

Association of Sedentary Time with Mortality Independent of Moderate to Vigorous Physical Activity

Background Sedentary behavior has emerged as a novel health risk factor independent of moderate to vigorous physical activity (MVPA). Previous studies have shown self-reported sedentary time to be associated with mortality; however, no studies have investigated the effect of objectively measured sedentary time on mortality independent of MVPA. The objective our study was to examine the association between objectively measured sedentary time and all-cause mortality. Methods 7-day accelerometry data of 1906 participants aged 50 and over from the U.S. nationally representative National Health and Nutrition Examination Survey (NHANES) 2003–2004 were analyzed. All-cause mortality was assessed from the date of examination through December 31, 2006. Results Over an average follow-up of 2.8 years, there were 145 deaths reported. In a model adjusted for sociodemographic factors, lifestyle factors, multiple morbidities, mobility limitation, and MVPA, participants in third quartile (hazard ratio (HR):4.05; 95%CI:1.55–10.60) and fourth quartile (HR:5.94; 95%CI: 2.49–14.15) of having higher percent sedentary time had a significantly increased risk of death compared to those in the lowest quartile. Conclusions Our study suggests that sedentary behavior is a risk factor for mortality independent of MVPA. Further investigation, including studies with longer follow-up, is needed to address the health consequences of sedentary behavior.

Temperature-Acclimated Brown Adipose Tissue Modulates Insulin Sensitivity in Humans

In rodents, brown adipose tissue (BAT) regulates cold- and diet-induced thermogenesis (CIT; DIT). Whether BAT recruitment is reversible and how it impacts on energy metabolism have not been investigated in humans. We examined the effects of temperature acclimation on BAT, energy balance, and substrate metabolism in a prospective crossover study of 4-month duration, consisting of four consecutive blocks of 1-month overnight temperature acclimation (24°C [month 1] → 19°C [month 2] → 24°C [month 3] → 27°C [month 4]) of five healthy men in a temperature-controlled research facility. Sequential monthly acclimation modulated BAT reversibly, boosting and suppressing its abundance and activity in mild cold and warm conditions (P < 0.05), respectively, independent of seasonal fluctuations (P < 0.01). BAT acclimation did not alter CIT but was accompanied by DIT (P < 0.05) and postprandial insulin sensitivity enhancement (P < 0.05), evident only after cold acclimation. Circulating and adipose tissue, but not skeletal muscle, expression levels of leptin and adiponectin displayed reciprocal changes concordant with cold-acclimated insulin sensitization. These results suggest regulatory links between BAT thermal plasticity and glucose metabolism in humans, opening avenues to harnessing BAT for metabolic benefits.

Persistent metabolic adaptation 6 years after "The Biggest Loser" competition.

To measure long‐term changes in resting metabolic rate (RMR) and body composition in participants of “The Biggest Loser” competition.

Analysis of raw microneurographic recordings based on wavelet de-noising technique and classification algorithm: wavelet analysis in microneurography

We propose a new technique for analyzing the raw neurogram which enables the study of the discharge behavior of individual and group neurons. It utilizes an ideal bandpass filter, a modified wavelet de-noising procedure, an action potential detector, and a waveform classifier. We validated our approach with both simulated data generated from muscle sympathetic neurograms sampled at high rates in five healthy subjects and data recorded from seven healthy subjects during lower body negative pressure suction. The modified wavelet method was superior to the classical discriminator method and the regular wavelet de-noising procedure when applied to simulated neuronal signals. The detected spike rate and spike amplitude rate of the action potentials correlated strongly with number of bursts detected in the integrated neurogram (r = 0.79 and 0.89, respectively, p < 0.001). Eight major action potential waveform classes were found to describe more than 81% of all detected action potentials in all subjects. One class had characteristics similar in shape and in average discharge frequency (27.4/spl plusmn/5.1 spikes/min during resting supine position) to those of reported single vasoconstrictor units. The newly proposed technique allows a precise estimate of sympathetic nerve activity and characterization of individual action potentials in multiunit records.

Brown Fat Activation Mediates Cold-Induced Thermogenesis in Adult Humans in Response to a Mild Decrease in Ambient Temperature

CONTEXT The contribution of brown adipose tissue (BAT) to the energy balance in humans exposed to sustainable cold has not been completely established, partially because of measurement limitations of both BAT activity and energy expenditure (EE). OBJECTIVE The objective of the study was to characterize the role of BAT activation in cold-induced thermogenesis (CIT). DESIGN This study was a single-blind, randomized crossover intervention. SETTING The study was conducted at the National Institutes of Health Clinical Center. STUDY PARTICIPANTS Thirty-one healthy volunteers participated in the study. INTERVENTIONS The intervention included mild cold exposure. MAIN OUTCOMES CIT and BAT activation were the main outcomes in this study. METHODS Overnight EE measurement by whole-room indirect calorimeter at 24 °C or 19 °C was followed by 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography (PET) scan. After 36 hours, volunteers crossed over to the alternate study temperature under identical conditions. BAT activity was measured in a 3-dimensional region of interest in the upper torso by comparing the uptake at the two temperatures. RESULTS Twenty-four volunteers (14 males, 10 females) had a complete data set. When compared with 24 °C, exposure at 19 °C resulted in increased EE (5.3 ± 5.9%, P < .001), indicating CIT response and mean BAT activity (10.5 ± 11.1%, P < .001). Multiple regression analysis indicated that a difference in BAT activity (P < .001), age (P = .01), and gender (P = .037) were independent contributors to individual variability of CIT. CONCLUSIONS A small reduction in ambient temperature, within the range of climate-controlled buildings, is sufficient to increase human BAT activity, which correlates with individual CIT response. This study uncovers for the first time a spectrum of BAT activation among healthy adults during mild cold exposure not previously recognized by conventional PET and PET-computed tomography methods. The enhancement of cold-induced BAT stimulation may represent a novel environmental strategy in obesity treatment.

Redefining the roles of sensors in objective physical activity monitoring

BACKGROUND Because physical activity researchers are increasingly using objective portable devices, this review describes the current state of the technology to assess physical activity, with a focus on specific sensors and sensor properties currently used in monitors and their strengths and weaknesses. Additional sensors and sensor properties desirable for activity measurement and best practices for users and developers also are discussed. BEST PRACTICES We grouped current sensors into three broad categories for objectively measuring physical activity: associated body movement, physiology, and context. Desirable sensor properties for measuring physical activity and the importance of these properties in relationship to specific applications are addressed, and the specific roles of transducers and data acquisition systems within the monitoring devices are defined. Technical advancements in sensors, microcomputer processors, memory storage, batteries, wireless communication, and digital filters have made monitors more usable for subjects (smaller, more stable, and longer running time) and for researchers (less costly, higher time resolution and memory storage, shorter download time, and user-defined data features). FUTURE DIRECTIONS Users and developers of physical activity monitors should learn about the basic properties of their sensors, such as range, accuracy, and precision, while considering the data acquisition/filtering steps that may be critical to data quality and may influence the desirable measurement outcome(s).

Objective measurements of daily physical activity patterns and sedentary behaviour in older adults: Age, Gene/Environment Susceptibility-Reykjavik Study

BACKGROUND objectively measured population physical activity (PA) data from older persons is lacking. The aim of this study was to describe free-living PA patterns and sedentary behaviours in Icelandic older men and women using accelerometer. METHODS from April 2009 to June 2010, 579 AGESII-study participants aged 73-98 years wore an accelerometer (Actigraph GT3X) at the right hip for one complete week in the free-living settings. RESULTS in all subjects, sedentary time was the largest component of the total wear time, 75%, followed by low-light PA, 21%. Moderate-vigorous PA (MVPA) was <1%. Men had slightly higher average total PA (counts × day(-1)) than women. The women spent more time in low-light PA but less time in sedentary PA and MVPA compared with men (P < 0.001). In persons <75 years of age, 60% of men and 34% of women had at least one bout ≥10 min of MVPA, which decreased with age, with only 25% of men and 9% of women 85 years and older reaching this. CONCLUSION sedentary time is high in this Icelandic cohort, which has high life-expectancy and is living north of 60° northern latitude.

Employment and physical activity in the U.S.

BACKGROUND Physical inactivity is a risk factor for obesity, cardiovascular disease, hypertension, and other chronic diseases that are increasingly prevalent in the U.S. and worldwide. Time at work represents a major portion of the day for employed people. PURPOSE To determine how employment status (full-time, part-time, or not employed) and job type (active or sedentary) are related to daily physical activity levels in American adults. METHODS Cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) were collected in 2003-2004 and analyzed in 2010. Physical activity was measured using Actigraph uniaxial accelerometers, and participants aged 20-60 years with ≥4 days of monitoring were included (N=1826). Accelerometer variables included mean counts/minute during wear time and proportion of wear time spent in various intensity levels. RESULTS In men, full-time workers were more active than healthy nonworkers (p=0.004), and in weekday-only analyses, even workers with sedentary jobs were more active (p=0.03) and spent less time sedentary (p<0.001) than nonworkers. In contrast with men, women with full-time sedentary jobs spent more time sedentary (p=0.008) and had less light and lifestyle intensity activity than healthy nonworkers on weekdays. Within full-time workers, those with active jobs had greater weekday activity than those with sedentary jobs (22% greater in men, 30% greater in women). CONCLUSIONS In men, full-time employment, even in sedentary occupations, is positively associated with physical activity compared to not working, and in both genders job type has a major bearing on daily activity levels.