Original research
Comparing self-reported physical activity and sedentary time to objective fitness measures in a military cohort

https://doi.org/10.1016/j.jsams.2018.05.023Get rights and content

Abstract

Objectives

Regular vigorous physical activity (PA) and high levels of physical fitness (PF) confer health benefits. Conversely, sedentary time is a risk factor for chronic illness, independent of PA. We evaluated associations between self-reported PA, sedentary time, and objective PF measures in military Service members.

Design

Cross-sectional study including 10,105 Air Force Millennium Cohort participants with a valid physical fitness assessment (PFA).

Methods

Linear regression assessed associations between self-report PA, screen time, and usual activity and abdominal circumference (AC) and VO2 max; logistic regression was used for PFA failure. We stratified by age and sex.

Results

Men who self-reported high versus low levels of PA had greater AC (19–29 years: β = 0.23 in., 95% CI 0.07, 0.39; 30–39 years: β = 0.45 in., 95% CI 0.17, 0.72). High versus low self-reported PA was also associated with greater VO2Max (β =: 0.81–1.41 mL/kg/min). Self-reported strength training for ≥2 days/week was associated with greater VO2Max in 19–29 year old men (β = 0.84 mL/kg/min, 95% CI 0.09, 0.60) and 30–39 year old women (β = 0.74 mL/kg/min, 95% CI 0.02, 1.46). For younger men and women,<2 h of screen time/day was associated with greater VO2Max (Males 19–29 years: β = 0.23 mL/kg/min, 95% CI 0.44, 1.26; Females 19–29 years: β = 0.83 mL/kg/min, 95% CI 0.25, 1.42). PA was not associated with PFA failure, while screen time was (Males OR: 0.32–0.65, 95% CI 0.17–0.92, p < 0.001–0.016).

Conclusions

Self-reported PA and screen time were associated with some objective PF measures, including VO2Max and AC. However, screen time alone was associated with PFA failure.

Introduction

Regular vigorous physical activity (PA) contributes long-term health benefits, such as reduced risk of hypertension, coronary artery disease, and Type 2 diabetes.1, 2, 3 Similarly, high levels of physical fitness have been linked to better overall health and reduced risk of sudden cardiac death.4, 5 A growing body of evidence indicates that sedentary time is a risk factor for chronic illness, independent of PA.6, 7 Department of Defense (DoD) regulations require that “Service members (SM) shall maintain physical readiness through appropriate nutrition, health, and fitness habits.8” While some Service members may be at duty stations that afford opportunities for unit or individual physical training during working hours, the DoD does not regulate, require, or systematically assess SMs’ physical activity. However, physical fitness components (such as cardiorespiratory endurance, body composition) are assessed on an annual or semi-annual basis in the military using standardized physical fitness assessments (PFAs). Recent studies found 57%–75% of military populations met the Healthy People 2010 guidelines for moderate or vigorous PA, but 60% of active duty SMs were nonetheless overweight or obese.9, 10

The degree to which U.S. SMs’ usual physical activity habits correspond to objectively measured physical fitness from required PFAs has not been empirically evaluated.11 Our study was undertaken to address this gap using self-reported physical activity measures from active duty Airmen enrolled in the Millennium Cohort Study and their corresponding objective PFA measures. We hypothesized that those with greater self-reported physical activity would have lower abdominal circumference (AC), greater cardiorespiratory fitness, and higher odds of passing the Air Force Physical Fitness Assessment. Understanding relationships between self-reported PA and physical fitness assessments could lead to the development of evidence-based strategies to support and encourage physical activity for SMs, ultimately resulting in higher levels of physical combat readiness and lower risk of injuries and chronic illness.

Section snippets

Methods

We conducted a cross-sectional study using Air Force participants enrolled in the Millennium Cohort Study (MCS) to investigate any association between self-reported physical activity and sedentary behaviors, and objective physical fitness measures from Air Force PFAs. The MCS was created in response to an Institute of Medicine (IOM) report, Measuring Health, which recommended systematic collection of longitudinal, population-based data on the health of Service members to study health effects of

Results

Self-reported high PA levels were most frequently reported by younger men and women (19–29 years old, 49.2% and 48.4%, respectively), while self-reported strength training ≥2 times per week was most often reported by younger men (74.6%, Table 1). Younger men also more frequently reported high usual daily activity (37.8%). Notably, only 19% of younger men reported very high screen time (8+ hours per day watching TV/videos or at a computer), while approximately 29–38% of all other age and sex

Discussion

An overwhelming majority (81.5%) of Air Force men and women of all ages in this study reported they met or exceeded physical activity recommendations (as outlined in the 2008 Physical Activity Guidelines).14 Associations between these measures and objective physical fitness outcomes varied by age and sex. Counterintuitively, men with medium to high self-reported PA and younger women with greater self-reported strength training had greater AC than those with less activity. However, men reporting

Conclusions

Our study showed that Airmen who meet guidelines for PA based on 2008 Physical Activity Guidelines for Americans3 have slightly greater abdominal circumference but greater fitness level based on VO2Max. Findings from this study indicate self-reported PA levels may serve as an indicator of some objective measures of physical fitness for Airmen, including VO2Max, but did not predict the odds of failing the PFA. Furthermore, our study indicates that at least in men, independent of PA, screen time

Practical implications

  • •

    Physical activity and strength training do not appear to decrease abdominal circumference in a large cohort of active duty Air Force members. Holistic approaches to health which incorporate other important factors such as nutrition and sleep should be promoted.

  • •

    In Airmen, only low screen time, and not physical activity, affected the odds of failing the physical fitness test. Strategies to improve PFA pass rates should include programs to reduce sedentary time.

  • •

    To improve combat readiness and

Acknowledgements

Celan Alo, MD, MPH (for organizing and supplying USAF Fitness data from the Air Force’s Fitness Management System) and Amanda Pietrucha (analyst at Naval Health Research Center). This work was supported through the Military Operational Medicine Research Program, US Army Medical Research and Materiel Command (Fort Detrick, Maryland), Work Unit No. 60002. The Office of Research and Development Cooperative Studies Program, Department of Veterans Affairs. VA Puget Sound Health Care System,

Disclaimer

The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of the Army, Department of the Air Force, Department of Veterans Affairs, Department of Defense, or the U.S. Government. Approved for public release; distribution unlimited. Human subjects participated in this study after giving their free and informed consent. This research was conducted in compliance with all applicable federal

References (23)

  • E.G. Wilmot et al.

    Sedentary time in adults and the association with diabetes, cardiovascular disease and death: systematic review and meta-analysis

    Diabetologia

    (2012)

    • Cited by (10)

    • The Millennium Cohort Study: The first 20 years of research dedicated to understanding the long-term health of US Service Members and Veterans

      2022, Annals of Epidemiology
      Citation Excerpt :

      Another study found that a greater number of life stressors and prior infectious gastroenteritis were associated with subsequent inflammatory bowel disease (e.g., Crohn's disease and ulcerative colitis) [85,86]. In addition to respiratory and autoimmune health, several investigations have examined the potential associations between military service and cardiometabolic conditions and its precursors, including obesity [33,36,66,87–91], hypertension [33,36,92,93], heart disease [36,94], and type 2 diabetes [33,36,95,96]. While service members tend to be healthier than their civilian counterparts overall, service members and veterans similarly gain weight over time [36].

    • Assessment of muscle-strengthening exercise in public health surveillance for adults: A systematic review

      2021, Preventive Medicine
      Citation Excerpt :

      Rates of participation (‘yes’ or ‘no’) in muscle-strengthening exercise (>0 times/week) were reported within over half of the studies (55.8%) with rates varying from as low as 1.1% (Aggio et al., 2018) to 76.9% (Cheng et al., 2007). Prevalence rates, assessed against the muscle-strengthening exercise guideline (≥2 times/week), were reported in 78 (50.0%) of the articles and varied from 3.2% (Blackwell and Clarke, 2016) to 69.9% (de la Motte et al., 2019). Twenty articles (12.8%) reported rates of participation (‘yes’ or ‘no’) and prevalence (≥2 times/week) (Strain et al., 2016; Bennie et al., 2016a; Bennie et al., 2018a; Humphries et al., 2018; Merom et al., 2012b; Harada et al., 2008; Hong et al., 2013; Stamatakis et al., 2018; Strain, 2018; Bakker et al., 2017; Byrne et al., 2016; Wald et al., 2014; Churilla et al., 2012a; Dankel et al., 2016b; Evenson et al., 2016; Galuska et al., 2002; Kurka et al., 2015; Chevan, 2008; Schoenborn et al., 2013; Grnøtved et al., 2014).

    • Classification of young healthy individuals with different exercise levels based on multiple musculoskeletal ultrasound images

      2020, Biomedical Signal Processing and Control
      Citation Excerpt :

      The differences in a person’s musculoskeletal structure has been attributed to many aspects including age [1], gender [2], muscle health status [3–5], and even exercise level/frequency [6]. Among the above factors, exercise level is the only one that can be actively adjusted; it is both an important factor related to athletic ability [7] and also a common means to improve an individual’s health status [8,9]. A further study of this differences may be useful for the development of new methods to conduct assessments of muscle state/quality, which may subsequently lead to novel and objective methods to guide effective exercises in terms of muscle status.

    • Regional differences in BMI, obesity, and exercise frequency in a large veteran service organization: A secondary analysis of new veteran member surveys from Team Red, White &amp; Blue

      2018, Preventive Medicine Reports
      Citation Excerpt :

      Further, regarding this point, it is possible that what constitutes FE could vary from person to person. Some research has shown that differences in self-report and objective measures of physical activity and medical conditions differ among military veterans (de la Motte et al., 2018; Smith et al., 2008). The items assessing anxious/depressed mood were broad (Thomas et al., 2015).

    • Is Self-Efficacy for Exercise Predictive of Leisure-Time Physical Activity among Police Officers? A Pilot Study

      2022, Sustainability (Switzerland)

    • Baseline Physical Activity Behaviors and Relationships with Fitness in the Army Training at High Intensity Study

      2022, Journal of Functional Morphology and Kinesiology
    View all citing articles on Scopus
    View full text
    Published by Elsevier Ltd on behalf of Sports Medicine Australia.