Simon Marshall

• PhD
• Professor (Associate) at University of California, San Diego

Background Weight loss interventions based solely on text messaging (short message service [SMS]) have been shown to be modestly effective for short periods of time and in some populations, but limited evidence is available for positive longer-term outcomes and for efficacy in Hispanic populations. Also, little is known about the comparative effica...

Background: Few weight loss interventions are evaluated for longer than a year, and even fewer employ social and mobile technologies commonly used among young adults. We assessed the efficacy of a 2 year, theory-based, weight loss intervention that was remotely and adaptively delivered via integrated user experiences with Facebook, mobile apps, te...

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Objectives: This study evaluated school physical and social environment interventions on middle school students' physical activity. Methods: The intervention included opportunities for students' physical activity on-campus before, during, and after school hours involving increased access to sports equipment and trained supervisors. Systematic obser...

Advances in information technology and near ubiquity of the Internet have spawned novel modes of communication and unprecedented insights into human behavior via the digital footprint. Health behavior randomized controlled trials (RCTs), especially technology-based, can leverage these advances to improve the overall clinical trials management proce...

We describe a study that aims to understand physical activity and sedentary behavior in free-living settings. We employed a wearable camera to record 3 to 5 days of imaging data with 40 participants, resulting in over 360,000 images. These images were then fully annotated by experienced staff with a rigorous coding protocol. We designed a deep lear...

The purpose of this study was to compare estimates of sedentary time on weekdays vs. weekend days in older adults and determine if these patterns vary by measurement method. Older adults (N = 230, M = 83.5, SD = 6.5 years) living in retirement communities completed a questionnaire about sedentary behavior and wore an ActiGraph accelerometer for sev...

Wrist accelerometers are being used in population level surveillance of physical activity (PA) but more research is needed to evaluate their validity for correctly classifying types of PA behavior and predicting energy expenditure (EE). In this study we compare accelerometers worn on the wrist and hip, and the added value of heart rate (HR) data, f...

Self-report remains the most common method for collecting epidemiological evidence of the links between travel and health outcomes. This study assesses the validity and reliability of a self-reported travel diary (a modified version of a well-established UK travel diary; The National Travel Survey (NTS)) by comparison with wearable camera data. Acr...

Background: Overweight or obesity is prevalent among college students and many gain weight during this time. Traditional face-to-face weight loss interventions have not worked well in this population. Facebook is an attractive tool for delivering weight loss interventions for college students because of its popularity, potential to deliver strateg...

Background: Active travel is an important area in physical activity research, but objective measurement of active travel is still difficult. Automated methods to measure travel behaviors will improve research in this area. In this paper, we present a supervised machine learning method for transportation mode prediction from global positioning syste...

Introduction: Unhealthy weight loss practices are common among female college students. It is unknown if these practices are also most common among women in the subset of overweight or obese college students or if these practices are related to depression. We examined the relationship between gender, depression, and unhealthy weight loss practices...

The dramatic growth of Web 2.0 technologies and online social networks offers immense potential for the delivery of health behavior change campaigns. However, it is currently unclear how online social networks may best be harnessed to achieve health behavior change. The intent of the study was to systematically review the current level of evidence...

Numerous studies have demonstrated multiple health benefits of being outside and exposure to natural environments. It is essential to accurately measure the amount of time individuals spend outdoors to assess the impact of exposure to outdoor time on health. SenseCam is a wearable camera that automatically captures images. The annotated images prov...

Obesity is a major public health concern in the United States. Eating while doing other activities, including watching television can increase energy intake. However, to our knowledge, no studies have quantified and examined the eating context among adults during everyday life. Existing studies are limited because they rely predominantly on self-re...

The SenseCam data can be used to estimate time spent in specific episodes of sedentary behaviors, as well as some dimensions of sedentary behaviors. However, it is unknown whether SenseCam data can be aggregated to provide an objective estimate of total sedentary time accumulated during a single day. We compared SenseCam-derived day-level estimates...

Machine learning techniques are used to improve accelerometer-based measures of physical activity. Most studies have used laboratory-collected data to develop algorithms to classify behaviors, but studies of free-living activity are needed to improve the ecological validity of these methods. With this aim, we collected a novel free-living dataset t...

To describe the theoretical rationale, intervention design, and clinical trial of a two-year weight control intervention for young adults deployed via social and mobile media. A total of 404 overweight or obese college students from three Southern California universities (Mage=22(+4) years; MBMI=29(+2.8); 70% female) were randomized to participate...

Little is known about the feasibility and acceptability of tailored text message based weight loss programs for English and Spanish-language speakers. This pilot study evaluated the feasibility, acceptability, and estimated impact of a tailored text message based weight loss program for English and Spanish-language speakers. The purpose of this pil...

To explore the relationship between cognitive functioning and time spent at different intensities of physical activity (PA) in free-living older adults. Cross sectional analyses. Continuing care retirement communities. Older adults residing in seven continuing care retirement communities in San Diego County with an average age of 83; 70% were femal...

Background: Girls are less physically active than boys, yet no single study has examined the factors that may explain gender differences in children's physical activity (PA). Methods: This study was a cross-sectional analysis of data from 116 caregivers and their children aged 5-8 years who participated in the MOVE study. Caregivers reported var...

This study evaluated the effect of four active videogames (AVGs) varying in behavioral contingencies (behavior-consequence relations) on adolescent AVG play and overall activity levels over 4 weeks. Each AVG, manufactured by SSD/Xavix(®) (Shiseido Co. of Japan, Tokyo, Japan), was coded and scored for the number of positive and aversive behavioral c...

Context: Between 1974 and 1997, the prevalence of overweight increased 300% among Brazilian children and adolescents. A systematic review was conducted between January 2010 and December 2011 of obesity-related interventions targeting Brazilian children and adolescents. Evidence acquisition: Manuscripts from 1965 to December 2010 were evaluated b...

Background Active transport can contribute to physical activity accumulation and improved health in adults. The built environment is an established associate of active transport behaviours; however, assessment of environmental features encountered during journeys remains challenging. The purpose of this study was to examine the utility of wearable...

Background: Even when objective physical activity (PA) measures are preferred, many intervention studies with Latina women rely on self-reports because they are more feasible and the type and domain of PA is of interest. Purpose: This study examined the sensitivity and specificity of the IPAQ for detecting intervention-related changes in physica...

Research indicates that very short or long durations of sleep and inefficient sleep are associated with higher total cholesterol and risk of type 2 diabetes and hypertension. This study tested the hypothesis that inefficient sleep or short/long sleep durations are associated with an elevated prevalence of type 2 diabetes, dyslipidemia, and hyperten...

Studies have shown relationships between important health outcomes and sedentary behavior, independent of physical activity. There are known errors in tools employed to assess sedentary behavior. Studies of accelerometers have been limited to laboratory environments. To assess a broad range of sedentary behaviors in free-living adults using acceler...

Technologic advances mean automated, wearable cameras are now feasible for investigating health behaviors in a public health context. This paper attempts to identify and discuss the ethical implications of such research, in relation to existing guidelines for ethical research in traditional visual methodologies. Research using automated, wearable c...

Background Accelerometers can identify certain physical activity behaviours, but not the context in which they take place. This study investigates the feasibility of wearable cameras to objectively categorise the behaviour type and context of participants’ accelerometer-identified episodes of activity. Methods Adults were given an Actical hip-moun...

who reportedthatthedeterminantsofsedentarybehaviorandphysicalactivity might be distinct. Over the past 10 years, morethan350articleshavebeenpublishedthathavemeasuredor conceptualized sedentary behavior as a concept dis-tinct from physical activity, and there is now widespreadconceptual and empirical support that the two exert in-dependent and inter...

Physical activity (PA) provides health benefits in older adults. Research suggests that exposure to nature and time spent outdoors may also have effects on health. Older adults are the least active segment of our population, and are likely to spend less time outdoors than other age groups. The relationship between time spent in PA, outdoor time, an...

INDRODUCTION: Sedentary behaviour is independently associated with negative health outcomes but its measurement is a challenge in public health. The study investigates the feasibility of using wearable image capture devices to objectively record, identify and categorize the type and context of an individual’s sedentary behaviours in a free living c...

Fifty years ago the causes of cancer were largely unknown. Since then, it has become clear that a strong relationship exists between obesity and many cancers, particularly postmenopausal breast cancer. A major challenge in understanding the link between obesity and cancer risk has been elucidating the biological basis underlying the association. Al...

Insufficient levels of physical activity are associated with increased morbidity and mortality for many non-communicable diseases, as identified by the Chief Medical Officer reports and WHO. However, many physical-activity-related health associations have been based on self-report measurement, which is limited by recall, comprehension, and social d...

Background: Increasing moderate-to-vigorous-intensity physical activity (MVPA) is an important public health goal. Pedometers are evidence-based devices for increasing daily activity, but studies have not evaluated the comparative efficacy of step cadence goals for increasing MVPA. Purpose: This study aimed to evaluate the efficacy of three pedo...

This study tested the hypothesis that disturbed or very short or long sleep durations are associated with subclinical atherosclerosis, as measured by carotid intima-media thickness (CIMT), in a sample of community-dwelling elderly spousal caregivers.Participants were 126 spousal care givers of a person with Alzheimer's disease who underwent in-home...

Research supports the favorable effects of exercise on physical and psychosocial outcomes in those with arthritis. Few easily disseminated, multi-component, arthritis-specific programs have been evaluated using both physical function and psychosocial measures. Fitness and Exercise for People with Arthritis (FEPA) is a new community-based, 3-month,...

Background: Research examining sedentary behaviour as a potentially independent risk factor for chronic disease morbidity and mortality has expanded rapidly in recent years. Methods: We present a narrative overview of the sedentary behaviour measurement literature. Subjective and objective methods of measuring sedentary behaviour suitable for us...

Background: Research examining sedentary behaviour as a potentially independent risk factor for chronic disease morbidity and mortality has expanded rapidly in recent years. Methods: We present a narrative overview of the sedentary behaviour measurement literature. Subjective and objective methods of measuring sedentary behaviour suitable for use i...

Valid and reliable self-report measures of physical activity (PA) are needed to evaluate the impact of interventions aimed at increasing the levels of PA. However, few valid measures for assessing PA in Latino populations exist. The purpose of this study is to determine whether the GPAQ is a valid measure of PA among Latinas and to examine its sens...

Introduction: Tailoring information is a commonly used health communication technique to individualize behavior change programs. However, few studies have applied individualized tailoring to a text-message intervention. Using tailoring with text-messages may be a powerful behavior change tool as this technology is inexpensive, asynchronous, and is...

Sedentary behavior is associated with adiposity and cardiometabolic risk. To determine the associations between sedentary behavior and measures of adiposity-associated inflammation. Between 2002 and 2005, a total of 1543 Multi-Ethnic Study of Atherosclerosis participants completed detailed health history questionnaires, underwent physical measureme...

The validity of physical activity (PA) self-report measures can be a problem when using these measures with target populations that differ from the population for which the measures were originally developed. Describe an approach to further tailor PA self-report measures to a target community, and report on focus group and cognitive interview findi...

This within-participants, single time-series study tested a train-the-trainer, promotor-based physical activity (PA) intervention to improve fitness and health indicators. Thirty unpaid promotores were trained to promote PA through free exercise classes. Measurements of 337 female community participants at baseline, 6 months, and 12 months assessed...

There is growing interest in the role of sedentary behavior as a risk factor for poor health, independent of physical activity (PA). To guide the spectrum of descriptive, analytic, and intervention studies on sedentary behavior, the authors advocate a behavioral epidemiology framework. This 5-phase framework is useful because it outlines a series o...

Individuals with medical conditions report more depressive symptoms than those without such conditions. This study assessed whether physical activity (PA) plays a mediational role in the association between medical conditions and depressive symptoms among Latino adults. Adjusting for socioeconomic factors, those who reported having been diagnosed w...

Evidence suggests that Latina women appear to be less physically active than women of other racial/ethnic groups. This study evaluated how different domains of physical activity (PA) contributed to overall levels of PA among low-income Latinas, the validity of Latinas' self-reported PA, and potential moderators of self-report bias in PA. A communit...

Opportunities for young people to be sedentary have increased during leisure time, study time, and transportation time. This review paper focuses on sedentary behaviors among young people aged 2-18 years and includes evidence of the relationship between sedentary behavior and health risk indicators, an overview of public health recommendations, the...

Screen time, especially television viewing, is associated with risk of overweight and obesity in children. Although several interventions have been developed to reduce children's screen time, no systematic review of these interventions exists to date. This is a systematic review and meta-analysis of interventions targeting a reduction in children's...

One day a group of 15 adventuresome older adults, ages 67 to 87, gathered in a gymnasium at San Diego State University, which had been transformed into a video-gaming arcade, to engage in exercise using new interactive technology. Alongside the video screens, computers and game consoles, participants could be seen laughing, clapping hands, watching...

BACKGROUND: Boys are more physically active than girls, yet no single study has examined a comprehensive array of factors that sufficiently explain these differences. The purpose of this study was to examine multilevel factors that may explain gender differences in children's moderate-to-vigorous physical activity (MVPA). METHODS: A multilevel fram...

Identifying adults' physical activity patterns across multiple life domains could inform the design of interventions and policies. Cluster analysis was conducted with adults in two U.S. regions (Baltimore/Washington, DC, n = 702; Seattle, WA [King County], n = 987) to identify different physical activity patterns based on adults' reported physical...

The purpose of this research was to investigate the relationship between distance to school and levels of physical activity and sedentary behavior in UK adolescents. Participants were 1385 adolescents (boys n = 531; mean age 14.7 years). Boys living within two miles of school and girls living within 5 miles of school were more likely to report high...

Television (TV) viewing is a highly prevalent sedentary behavior in young people and has played a significant role in the assessment of sedentary behaviors. An important question to be addressed is to what extent TV viewing is a suitable indicator, or marker, of overall levels of sedentary behavior in children and adolescents. This has not yet been...

Identification of non-modifiable correlates of physical activity and sedentary behaviour in youth contributes to the development of effective targeted intervention strategies. The purpose of this research was to examine the relationships between family circumstances (e.g. socio-economic status, single vs. dual parent household, presence/absence of...

Table S4. Relationship between individual family circumstance variables and minutes per day using a computer adjusted for age and season. Results table describing the relationship between family circumstance variables and minutes per day of computer use.

Table S6. Relationship between individual family circumstance variables and minutes per day in sports and exercise adjusted for age and season. Results table describing the relationship between family circumstance variables and minutes per day in sports and exercise.

Table S5. Relationship between individual family circumstance variables and minutes per day in social sedentary behaviours adjusted for age and season. Results table describing the relationship between family circumstance variables and minutes per day in social sedentary behaviours.

Table S7. Relationship between individual family circumstance variables and minutes per day in active travel adjusted for age and season. Results table describing the relationship between family circumstance variables and minutes per day in active travel.

Table S3. Relationship between individual family circumstance variables and minutes per day TV viewing adjusted for age and season. Results table describing the relationship between family circumstance variables and minutes per day of TV viewing.

It is a public health recommendation to accumulate at least 150 minutes per week of moderate intensity physical activity. Although pedometers are widely used as a physical activity-monitoring tool, they are unable to measure activity intensity. Translating current physical activity recommendations into a pedometer-based guideline could increase the...

There is great interest in young people's overweight and obesity. Few data, however, describe when sedentary and physically active behaviors are likely to occur during the day or how these behaviors are related to location. The purpose of this study was to describe sedentary and active leisure-time behaviors of adolescents across the day and settin...

The association of overall obesity and abdominal adiposity in predicting risk of all-cause mortality in white and black adults was compared. This prospective study included a national sample of 3219 non-Hispanic white and 2,561 non-Hispanic black adults 30 to 64 years of age enrolled in the third National Health and Nutrition Examination Survey dur...

Results of studies comparing overall obesity and abdominal adiposity or body fat distribution with risk of mortality have varied considerably. We compared the relative importance and joint association of overall obesity and body fat distribution in predicting risk of mortality. Participants included 5,799 men and 6,429 women aged 30-102 years enrol...

Exergames are video games that use exertion-based interfaces to promote physical activity, fitness, and gross motor skill development. The purpose of this paper is to describe the development of an organizing framework based on principles of learning theory to classify and rank exergames according to embedded behavior change principles. Behavioral...

To use ecological momentary assessment to describe how adolescent boys in the United Kingdom spend their leisure time. Design. Cross-sectional, stratified, random sample from secondary schools in 15 regions within the United Kingdom. The data are from a larger study of adolescent lifestyles (Project STIL). A total of 561 boys with a mean age of 14....

To report time and prevalence of leisure time sedentary and active behaviors in adolescents. Cross-sectional, stratified, random sample from schools in 14 districts in Scotland, 2002-03, using ecological momentary assessment (n=385 boys, 606 girls; mean age 14.1 years; range 12.6-16.7 years). This is a method of capturing current behavioral episode...

The present study examined physical activity and sedentary behavior patterns of adolescents between 15.30h and 18.30h. The sample for this study is 1,484 (boys: n = 561; girls: n = 923). Boys and girls reported 21 and 19 min of physical activity and 24 and 26 min of homework respectively during this period. Technology-based sedentary behavior (TV v...

Previous studies of leptin with cardiovascular disease (CVD) risk factors have been limited by clinical samples or lack of representation of the general population. This cross-sectional study, designed to examine whether leptin or insulin may mediate the endogenous relation of obesity with metabolic, inflammatory, and thrombogenic cardiovascular ri...

There has been tremendous interest in assessing and promoting physical activity among children, due in large part to the highly publicized increase in the prevalence of pediatric obesity. The purpose of this chapter is to describe the issues associated with measuring physical activity and sedentary behavior in youth. Definitions and key concepts re...

As interest in the public health challenge of youth inactivity increases, the ambitious Youth Physical Activity and Sedentary Behavior sets a standard for addressing a problem with worldwide implications. Drawing on the contributions of a diverse group of international experts, this reference challenges professionals, researchers, and students to i...

The purpose of this study was to use ecological momentary assessment to investigate the patterning of physical activity and sedentary behaviours in UK adolescents and to examine if different lifestyle groups differ on key explanatory variables. A total of 1,371 (38% boys, mean age 14.7 years) adolescents completed diaries every 15 min for 3 weekday...

To use ecological momentary assessment to describe how adolescent girls in the United Kingdom spend their leisure time. Cross-sectional, stratified, random sample from secondary schools in 15 regions within the United Kingdom. The data are from a larger study of adolescent lifestyles (Project STIL). A total of 923 girls with a mean age of 14.7 year...

The aims of this study were to determine 1) prevalence of leisure-time physical inactivity in a nationally representative sample of non-Hispanic white, non-Hispanic black, and Hispanic men and women; 2) prevalence of leisure-time inactivity by racial/ethnic group across social class indicators; and 3) the relationship between leisure-time inactivit...

To assess cross-sectional and longitudinal relations between television (TV) viewing and girls' body mass index (BMI), weight status, and percentage of body fat. Participants included 169 girls who were measured at ages 7, 9, and 11 years. Height and weight were measured and used to calculate girls' BMI and to classify their weight status. Girls' p...

The purpose of this systematic review was to (i) estimate the prevalence and dose of television (TV) viewing, video game playing and computer use, and (ii) assess age-related and (iii) secular trends in TV viewing among youth (< or = 18 yr). Ninety studies published in English language journals between 1949 and 2004 were included, presenting data f...

An emerging threat to public health is seen in the dramatic rise in obesity status of Canadians, especially among young people. In addressing the possible factors responsible for these dramatic increases, this paper outlines the importance of understanding sedentariness as an important health behaviour, distinct from physical activity, and identify...

Changes in body composition and body image during puberty will impact on sedentary behavioural choices. The study aimed to investigate the effects of changes in pubertal status, body composition and body image on changes in time spent being sedentary. Eighty-three school students aged 10-15 years were studied at 6-month intervals. BMI and percentag...

To review the empirical evidence of associations between television (TV) viewing, video/computer game use and (a) body fatness, and (b) physical activity. Meta-analysis. Published English-language studies were located from computerized literature searches, bibliographies of primary studies and narrative reviews, and manual searches of personal arch...

School physical education (PE) is highly recommended as a means of promoting physical activity, and randomized studies of health-related PE interventions in middle schools have not been reported. We developed, implemented, and assessed an intervention to increase physical activity during middle-school PE classes. Twenty-four middle schools (approxi...

There is growing concern over the effects of sedentary lifestyles on the health of young people. Recent rapid increases in juvenile obesity have received a great deal of attention in the scientific and popular press and have been attributed partly to television viewing, computer games and other sedentary behaviours. These are thought to compete wit...

The purpose of this study was to review the published empirical correlates of television/video viewing among youth (2 to 18 years). A descriptive semi-quantitative review was conducted based on 68 primary studies. Variables consistently associated with TV/video viewing were ethnicity (non-white +), parent income (-), parent education (-), body weig...

Assessing time spent in sedentary behaviours in relation to pubertal status, anthropometric differences, and body image will improve insight into the prevalence and determinants of such behaviours during adolescence. The study aimed to investigate the effects of age, puberty, gender, body composition, and sleep on sedentary behaviour. Participants...