The 24-hour day is spent engaging in activities that include light-physical activity (LPA), moderate-vigorous physical activity (MVPA), sedentary time (i.e., sitting/lying/reclining posture with energy expenditure <1.5 METs, while awake), and sleep. These behaviors are mutually exclusive and time spent in one behavior affects the time spent in another. The time among these 24-hour behaviors is also associated with cardiometabolic health outcomes, including adiposity. Assessing specific behavioral contexts and their relationship within the 24-hour day is underdeveloped, this includes recreational sedentary screen time (rSST). rSST is sedentary time with televisions, computers, smartphones, tablets, inactive video games, and its relationship with other 24-hour behaviors is underdeveloped. This dissertation works evaluates the relationship between rSST and 24-hour behaviors, and adiposity in adults. The first study reviewed the existing observational and experimental evidence for rSST and its relationship with 24-hour behaviors by conducting a scoping review. From the 75 experimental and observational studies included, the evidence supported an overall positive association between rSST and non-screen sedentary behavior, an overall negative association between rSST with physical activity, and overall positive and negative associations between rSST with various sleep variables. The second study assessed the daily associations between rSST and 24-hour behaviors and how associations are influenced by age, sex, chronotype, and week- or weekend days. The findings include significant negative associations at between- and within-person levels for rSST with non-screen sedentary time, standing, LPA, MVPA, and sleep that were differentially influenced by age, chronotype, and week- or weekend day. The third study examined reallocating time between rSST and 24-hour behaviors and the associations with adiposity (i.e., body mass index, body fat percentage, and waist circumference). The results showed significant associations of replacing non-screen sedentary time with MVPA for both body fat percentage and waist circumference; and no significant associations between rSST and 24-hour behaviors for body mass index. Overall, this dissertation work provides important insights into the relationships between rSST and 24-hour behaviors and their relation to adiposity. These findings can be used to inform future intervention development targeting multiple behavior changes and improving health outcomes.

Parkinson's Disease (PD) is a progressive neurodegenerative disorder that affects movement and balance control. Falls are a common and often debilitating consequence of PD, and reactive balance control is critical in preventing falls. This dissertation aimed to determine the adaptability and neural control of reactive balance responses in people with PD. Aim 1 investigated whether people with PD at risk for falls can improve their reactive balance responses through a 2-week, 6-session training protocol. The study found that reactive step training resulted in immediate and retained improvements in stepping, as measured by the anterior-posterior margin of stability (MOS), step length, and step latency during backward stepping. The second aim explored the neural mechanisms behind eliciting and learning reactive balance responses in PD. The study investigated the white matter (WM) correlates of reactive stepping and responsiveness to step training in PD. White matter was not significantly correlated with any baseline stepping outcomes. However, greater retention of step length was associated with increased fractional anisotropy (FA) within the left anterior corona radiata, left posterior thalamic radiation, and right and left superior longitudinal fasciculi. Lower radial diffusivity (RD) within the left posterior and anterior corona radiata were associated with retention of step latency improvements. These findings highlight the importance of WM microstructural integrity in motor learning and retention processes in PD. The third aim examined the role of the somatosensory system in reactive balance control in people with PD. The tactile and proprioceptive systems were perturbed using vibrotactile stimulation during backward feet-in-place balance responses. The results showed that tactile and proprioceptive stimulation had minimal impact on reactive balance responses. Small effects were observed for delayed tibialis anterior (TA) onsets with proprioceptive stimulation at a medium intensity. Overall, this dissertation provides insights into improving reactive balance responses and the underlying neural mechanisms in PD, which can potentially inform the development of targeted interventions to reduce falls in people with PD.

The health benefits of sufficient moderate-to-vigorous physical activity (MVPA) and sleep arewell-supported, with established links to decreased cancer risk, cardiometabolic health, all-cause mortality, and psychiatric symptomatology—including stress-related phenomena—for those who engage in 150 min MVPA/week and get at least 7 hours sleep/night. The latter outcome has rapidly become a major public health concern as our nation grapples with the impact of prolonged COVID-19 pandemic stress, which has triggered an onslaught of depression, anxiety, and PTSD throughout the population. Thus, while strategies to decrease stress are desperately needed, many Americans fall short of the very MVPA and sleep recommendations that have been shown to increase their capacity to cope. The purpose of the present study was to explore time-varying associations of MVPA and sleep with momentary perceived stress in adults forced to work from home due to the COVID-19 pandemic. Thirty remote-working adults (86.7% women; mean age 37.5 years, SD = 10.4 years) wore GENEActiv accelerometers on the wrist to capture MVPA and sleep data, and answered four Ecological Momentary Assessments (EMAs) per day regarding perceived stress, for fourteen days straight. Between- and within-person variations in MVPA, sleep quality rating (SQR), total sleep time (TST), and sleep efficiency (SE) were analyzed via multilevel models to determine whether certain changes in these parameters might lead to decreased perceived momentary stress. Between-person models revealed a significant negative effect of SQR on perceived stress levels the next day, beta= -.651, SE= .303, P= .04. Mean MVPA, TST, and SE were not significant inter-individual predictors of momentary stress. However, within persons, higher than normal MVPA (beta= -.005, SE= .002, P= .015), SQR (beta= -.277, SE= .071, P <.001), TST (beta= -.001, SE= .000, P = .004), and SE (beta= -.524, SE= .242, P = .031) were all associated with significant decreases in momentary stress, with individuals experiencing incremental benefits with each additional minute of MVPA and TST. In conclusion, daily fluctuations in MVPA and sleep habits correlate more strongly with momentary stress than do typical levels of these behaviors; this presents an attainable strategy for individuals to enhance their capacity to cope.

Excessive gestational weight gain (EGWG) affects 50% of US pregnant women and may be an important contributor to obesity in both the mother and child. Novel strategies to prevent EGWG are needed to reduce the risk of adverse health outcomes for the mother and child. This dissertation presents three manuscripts that 1) propose a novel model to explain how prenatal yoga may prevent EGWG through behavioral, psychological/emotional, and physical factors, 2) test the feasibility and preliminary efficacy of a prenatal yoga intervention to prevent EGWG compared to a pregnancy education comparison group, and 3) qualitatively investigate pregnant women’s experiences participating in a prenatal yoga intervention to prevent EGWG. In manuscript two, 49 women were recruited and randomized to a 12-week prenatal yoga intervention (n=23) or a time-matched pregnancy education comparison group (n=26). A satisfaction survey was administered at post-intervention to assess feasibility outcomes (e.g., acceptability, demand). Mindfulness, emotion regulation, self-awareness, sleep quality, depression, anxiety, and perceived stress were assessed at baseline and post-intervention (12-weeks) and GWG was assessed weekly. Linear mixed models were used to analyze pre-post changes in primary (i.e., GWG during pregnancy) and secondary (i.e., mindfulness, emotion regulation, self-awareness, sleep quality, depression, anxiety, and stress) outcomes. In manuscript three, interviews were conducted with pregnant women who participated in the prenatal yoga intervention (n=13). Interview responses were summarized using an inductive approach to thematic analysis. Findings in manuscript two suggest that prenatal yoga was a feasible method to prevent EGWG with high enjoyment and satisfaction reported among participants. The average number of prenatal yoga sessions attended was 8.84 (SD = 3.85). There was no significant group differences on the rate of GWG or total GWG throughout the intervention and a significant group x time interaction effect for stress (p=.03). In manuscript three, twelve themes were identified among the data and were organized into the following categories (three themes each): 1) experiences of prenatal yoga, 2) prenatal yoga and weight, 3) barriers to prenatal yoga, and 4) facilitators of prenatal yoga. This initial evidence suggests that prenatal yoga has potential as a strategy to prevent EGWG in pregnant women.

Most studies that explored the health benefits of interrupting sitting time focused on using different modalities (i.e., comparing walking vs standing breaks)33,36,59. However, experimental studies that directly compare patterns of interrupting sitting time through standing only are needed to advance the field. This study aimed to (i) determine if there is a difference in glucose response between continuous sitting (CS) and two intermittent standing regimes (high frequency, low duration breaks (HFLD) and low frequency, high duration breaks (LFHD)) and (ii) to determine if there is a difference in glucose response between the two strategies (HFLD vs. LFHD).

Ten sedentary employees (mean±SD age 46.8±10.6 years; 70% female) with impaired fasting glucose (mean glucose= 109.0±9.8 mg/dL) participated. Eligible participants were invited to three 7.5 hour laboratory visits where they were randomized to perform each study conditions: (i) CS, (ii) HFLD and (iii) LFHD. Standardized meals (breakfast and lunch) were given with each meal providing 33% of the participant’s total daily caloric needs following a typical American diet (50-60% carbohydrates, 25-30% fat, and 10-20% protein). Participants wore an activPAL device to measure compliance with the sit-stand condition and a continuous glucose monitor to measure post-prandial glucose response. Post-prandial mean glucose, incremental area under the curve and mean amplitude glycemic excursion between conditions were evaluated using linear mixed models.

Participants demonstrated high compliance with the study condition. The results indicated that the mean glucose of the HFLD condition were significantly lower (p< .01) than the CS condition with mean difference of -7.70 (-11.98, -3.42) mg/dL·3.5h and -5.76 (-9.50, -2.03) mg/dL·7h for lunch and total time, respectively. Furthermore, the mean post-prandial glucose during lunch and total time were significantly lower in the HFLD condition compared to the LFHD condition with mean difference of -9.94 (-14.13, -5.74) mg/dL·3.5h and -6.23 (-9.93, -2.52) mg/dL·7h, respectively. No differences were found between the CS and LFHD conditions.

This study provides evidence favoring the use of frequent interruptions in sitting time to improve glycemic control of prediabetic individuals. In contrast, less frequent, although longer bouts of standing resulted in similar post-prandial glucose profile to that of the continuous sitting condition despite total standing time being equal to the LFHD condition.

Many individual-level behavioral interventions improve health and well-being. However, most interventions exhibit considerable heterogeneity in response. Put differently, what might be effective on average might not be effective for specific individuals. From an individual’s perspective, many healthy behaviors exist that seem to have a positive impact. However, few existing tools support people in identifying interventions that work for them, personally.

One approach to support such personalization is via self-experimentation using single-case designs. ‘Hack Your Health’ is a tool that guides individuals through an 18-day self-experiment to test if an intervention they choose (e.g., meditation, gratitude journaling) improves their own psychological well-being (e.g., stress, happiness), whether it fits in their routine, and whether they enjoy it.

The purpose of this work was to conduct a formative evaluation of Hack Your Health to examine user burden, adherence, and to evaluate its usefulness in supporting decision-making about a health intervention. A mixed-methods approach was used, and two versions of the tool were tested via two waves of participants (Wave 1, N=20; Wave 2, N=8). Participants completed their self-experiments and provided feedback via follow-up surveys (n=26) and interviews (n=20).

Findings indicated that the tool had high usability and low burden overall. Average survey completion rate was 91%, and compliance to protocol was 72%. Overall, participants found the experience useful to test if their chosen intervention helped them. However, there were discrepancies between participants’ intuition about intervention effect and results from analyses. Participants often relied on intuition/lived experience over results for decision-making. This suggested that the usefulness of Hack Your Health in its current form might be through the structure, accountability, and means for self-reflection it provided rather than the specific experimental design/results. Additionally, situations where performing interventions within a rigorous/restrictive experimental set-up may not be appropriate (e.g., when goal is to assess intervention enjoyment) were uncovered. Plausible design implications include: longer experimental and phase durations, accounting for non-compliance, missingness, and proximal/acute effects, and exploring strategies to complement quantitative data with participants’ lived experiences with interventions to effectively support decision-making. Future work should explore ways to balance scientific rigor with participants’ needs for such decision-making.

Through three investigations, this dissertation examined properties of the family and early care and education center (ECEC) environments related to preschool-aged children’s cardiovascular fitness (CVF) and gross locomotor skills (GLS). Investigation one used a systematic review and meta-analysis to synthesize the effectiveness of school-based interventions at improving CVF, in preschool-aged children. For investigations two and three product- and process-based measures of GLS were collected from children in ECECs (n=16), using the progressive aerobic cardiovascular endurance run (PACER; n=144) and the CHAMPS motor skill protocol (CMSP; n=91), respectively. Investigation two and three examined family factors and ECEC factors for associations with measures of GLS, respectively.

Investigation one revealed a moderate-to-large effect size for school-based interventions (n=10) increasing CVF (g=0.75; 95%CI [0.40-1.11]). Multi-level interventions (g=.79 [0.34-1.25]) were more effective than interventions focused on the individual (g=0.67 [0.12-1.22]). In investigations two and three children (78.3% Hispanic; mean ± SD age 53.2±4.5 months) completed a mean ± SD 3.7±2.3 PACER laps and 19.0±5.5 CSMP criteria. Individual and family factors associated with PACER laps included child sex (B=-0.96, p=0.03) and age (B=0.17, p<0.01), parents’ promotion of inactivity (B=0.66, p=0.08) and screen time (B=0.65, p=0.05), and parents’ concern for child’s safety during physical activity (B=-0.36, p=0.09). Child age (B=0.47, p<0.01) and parent employment (B=2.29, p=0.07) were associated with CMSP criteria. At the ECEC level, policy environment quality (B=-0.17; p=0.01) was significantly associated with number of PACER laps completed. Outdoor play environment quality (B=0.18; p=0.03), outdoor play equipment total (B=0.32; p<0.01) and screen time environment quality (B=0.60; p=0.02) were significantly associated with CMSP criteria. Researchers, ECEC teachers and policy makers should promote positive environmental changes to preschool-aged children’s family and ECEC environments, as these environments have the potential to improve CVF and GLS more than programs focused on the child alone.

The purpose of this dissertation was 1) to develop noninvasive strategies to assess skeletal muscle size, architecture, and composition in young and old adults (study #1) and 2) evaluate the impact of chemotherapeutic treatment on skeletal muscle satellite cells and capillaries (study #2). For study #1 ultrasound images were obtained from the quadriceps muscles of young (8 m, 8 f) and older (7 m, 5 f) participants on two occasions, separated by 5-15 days. Images were collected while the participants were both standing and supine, and were analyzed for muscle thickness, pennation angle, and echogenicity. In addition, test-retest reliability and ICCs were evaluated for each posture and when imaging sites remained marked or were re-measured from visit #1 to visit #2. Generally, in both younger and older adults muscle thickness was greater and echogenicity was lower in the anterior quadriceps when images were collected standing versus supine. Maintaining the imaging site between visits did not influence test re-test reliability for either age group. Older adults exhibited smaller muscle thickness, lower pennation angle and increased echogenicity. Further, variability for the use of ultrasound to determine muscle thickness and pennation angle was greater in older versus younger adults. Findings from study #1 highlight several methodological considerations for US-based assessment of skeletal muscle characteristics that should be considered for improving reproducibility and generalizability of US to assess skeletal muscle characteristics and function across the aging spectrum. This is particularly relevant given the emerging use of ultrasound to assess skeletal muscle characteristics in healthy and clinical populations. In the second study, ovariectomized female Sprague-Dawley rats were randomized to receive three bi-weekly intraperitoneal injections of the chemotherapeutic drug, Doxorubicin (DOX) (4mg/kg; cumulative dose 12mg/kg) or vehicle (VEH; saline). Animals were euthanized 5d following the last injection, and the soleus (SOL) and extensor digitorum longus (EDL) muscles were dissected and prepared for immunohistochemical and RT-qPCR analyses. Relative to VEH, cross-sectional area (CSA) of the SOL and EDL muscle fibers were 26% and 33% smaller, respectively, in DOX animals (P<0.05). In the SOL satellite cell and capillary densities were 39% and 35% lower, respectively, in DOX animals (P<0.05), whereas in the EDL satellite cell and capillary densities were unaffected by DOX administration (P>0.05). In the SOL MYF5 mRNA expression was increased in DOX animals (P<0.05), while in the EDL MGF mRNA expression was reduced in DOX animals (P<0.05). Chronic DOX administration is associated with reduced fiber size in multiple skeletal muscles, however DOX appears to impact the satellite cell and capillary densities in a muscle-specific manner. These findings from study #2 highlight that therapeutic targets to protect skeletal muscle from DOX may vary across muscles. Collectively, these findings 1) improve the ability to examine muscle size and function in younger and older adults, and 2) identify promising therapeutic targets to protect skeletal muscle from the harmful effects of chemotherapy treatment.

The purpose of this study was to examine the feasibility and preliminary efficacy of a theory-driven and a atheoretical reminder point-of-choice (PoC) prompt interventions on reducing workplace sedentary behavior in office workers with self-reported low usage (<4 hours per day) of their sit-stand workstations in the standing position. The design of this study was a cross-over trial including randomization into either the theory-driven or atheoertical reminder condition, after completion of a no prompt control condition. Participants (N=19) included full-time, primarily female, Caucasian, middle-aged office workers. The primary aim of this study was to assess the feasibility of these two PoC prompt conditions on reducing sedentary behaviors through the use of a Therapy Evaluation Questionnaire. The secondary aim of this study was to assess the preliminary efficacy of the two PoC prompt conditions on reducing sedentary behaviors relative to no-prompt control using the activPAL micro device. For the primary aim, descriptive means adjusted for ordering effect were computed. For the secondary aim, mixed-effects regression models were used to cluster for observations within-persons and were adjusted for age, gender, race, job-type, and ordering effects. During the no-prompt control, participants spent 267.90 ± 68.01 sitting and 170.20 ± 69.34 min/8hr workday standing. The reminder PoC prompt condition significantly increased sanding time (b[se] = 24.52 [11.09], p=0.034) while the theory-driven PoC condition significantly decreased time spent in long sitting bouts b[se] = -34.86 [16.20], p=0.036), both relative to no prompt control. No statistically significant reductions in sitting time were seen in either PoC prompt condition. Furthermore, no statistically significant differences between the two PoC prompt conditions were observed. This study provides feasibility insight in addition to objective measures of sedentary behaviors regarding the use of PoC prompt interventions in the workplace.

Having accurate measurements of sedentary behaviors is important to understand relationships between sedentary behaviors and health outcomes and to evaluate changes in interventions and health promotion programs designed to reduce sedentary behaviors. This dissertation included three projects that examined measurement properties of wearable monitors used to measure sedentary behaviors. Project one examined the validity of three monitors: the ActiGraph GT3X+, activPAL™, and SenseWear 2. None of the monitors were equivalent with the criterion measure of oxygen uptake to estimate the energy cost of sedentary and light-intensity activities. The ActivPAL™ had the best accuracy as compared with the other monitors. In project two, the accuracy of ActiGraph GT3X+and GENEActiv cut-points used to assess sedentary behavior were compared with direct observation during free-living conditions. New vector magnitude cut-points also were developed to classify time spent in sedentary- and stationary behaviors during free-living conditions. The cut-points tested had modest overall accuracy to classify sedentary time as compared to direct observation. New ActiGraph 1-minute vector cut-points increased overall accuracy for classifying sedentary time. Project 3 examined the accuracy of the sedentary sphere by testing various arm elevation- and movement-count configurations using GENEActiv and ActiGraph GT3X+ data obtained during free-living conditions. None of the configurations were equivalent to the criterion measure of direct observation. The best configuration of the GENEActiv was: worn on the dominant wrist at 15 degrees below the horizontal plane with a cut-point <489 for each 15-second interval. The best configuration for the ActiGraph was: worn on the non-dominant wrist at 5° below the horizontal plane with a cut-point of <489 counts for each 15-second interval. Collectively, these findings indicate that the wearable monitors and methods examined in this study are limited in their ability to assess sedentary behaviors and light intensity physical activity. Additional research is needed to further understand the scope and limitations of wearable monitors and methods used to assess sedentary behaviors and light intensity physical activity.