Facilitating ambulatory heart rate variability analysis using accelerometry-based classifications of body position and self-reported sleep.

Objective.This study aimed to examine differences in heart rate variability (HRV) across accelerometer-derived position, self-reported sleep, and different summary measures (sleep, 24 h HRV) in free-living settings using open-source methodology.Approach.HRV is a biomarker of autonomic activity. As it is strongly affected by factors such as physical behaviour, stress, and sleep, ambulatory HRV analysis is challenging. Beat-to-beat heart rate (HR) and accelerometry data were collected using single-lead electrocardiography and trunk- and thigh-worn accelerometers among 160 adults participating in the SCREENS trial. HR files were processed and analysed in the RHRV R package. Start time and duration spent in physical behaviours were extracted, and time and frequency analysis for each episode was performed. Differences in HRV estimates across activities were compared using linear mixed models adjusted for age and sex with subject ID as random effect. Next, repeated-measures Bland-Altman analysis was used to compare 24 h RMSSD estimates to HRV during self-reported sleep. Sensitivity analyses evaluated the accuracy of the methodology, and the approach of employing accelerometer-determined episodes to examine activity-independent HRV was described.Main results.HRV was estimated for 31 289 episodes in 160 individuals (53.1% female) at a mean age of 41.4 years. Significant differences in HR and most markers of HRV were found across positions [Mean differences RMSSD: Sitting (Reference) - Standing (-2.63 ms) or Lying (4.53 ms)]. Moreover, ambulatory HRV differed significantly across sleep status, and poor agreement between 24 h estimates compared to sleep HRV was detected. Sensitivity analyses confirmed that removing the first and last 30 s of accelerometry-determined HR episodes was an accurate strategy to account for orthostatic effects.Significance.Ambulatory HRV differed significantly across accelerometry-assigned positions and sleep. The proposed approach for free-living HRV analysis may be an effective strategy to remove confounding by physical activity when the aim is to monitor general autonomic stress.

Single parent status and children's objectively measured level of physical activity.

BACKGROUND: Single-parent family status has been investigated as a possible psychosocial determinant of children's level of physical activity (PA)-although with mixed and inconclusive results. Prevailing evidence of the importance of two-parent family status as a resource for children's PA is based on a mix of subjective and objective measurements of PA. Objectives: To investigate if the level of PA among children living with a single parent was lower compared to children living with two parents by means of a meta-analysis of published and unpublished studies. We restricted our analysis to studies with objective measurements of PA. METHODS: Data sources: The databases, Social Science Citation Index, PsycINFO, PubMed, and EBSCO were searched (1987-2013). Study eligibility criteria: Observational studies comparing objectively measured PA between single-parent children and children from two-parent families. Study appraisal and synthesis methods: We used guidelines from the Cochrane Handbook of Systematic Reviews of Interventions and a modified version of the Newcastle-Ottawa Scale overall to assess the quality of the included studies. We refrained from calculation of summary scores. RESULTS: Twelve studies met the following inclusion criteria of which six were unpublished: (a) child age (6-18 years) and (b) objectively measured level of PA. Meta-analysis revealed pooled estimates of -0.01 for boys (95 % CI -0.04-0.03, p = 0.77, I2 = 6.5 %, p = 0.38) and 0.01 for girls (95 % CI -0.03-0.04, p = 0.62, I2 = 21.0 %, p = 0.24), respectively. Estimates show no differences in objectively measured physical activity between children living in single-parent families compared to children living with two parents. Analyses investigating seven potential moderators did not yield any statistical significant effect size estimates. No evidence of heterogeneity between studies was observed. Limitations: Retrieved articles were assessed by several of the authors. Blinding of the authors was not feasible, as most of the authors have been involved in the studies. CONCLUSIONS: No evidence was found suggesting that children of single-parent families are in special need of extraordinary measures to facilitate their level of PA.