Sleep deprivation and obesity in adults: a brief narrative review

Background/aims

Obesity and sleep deprivation are two epidemics that pervade developed nations. Their rates have been steadily rising worldwide, especially in the USA. This short communication will explore the link between the two conditions and outline the proposed mechanisms behind their relationship.

Methods

Studies on the topic of sleep and obesity were reviewed, and findings were used to develop a theoretical model for the biological link between short sleep duration and obesity.

Results

Individuals who regularly slept less than 7  hours per night were more likely to have higher average body mass indexes and develop obesity than those who slept more. Studies showed that experimental sleep restriction was associated with increased levels of ghrelin, salt retention and inflammatory markers as well as decreased levels of leptin and insulin sensitivity.

Conclusions

There may be a link between obesity and sleep deprivation. We recommend further investigations are to elucidate the potential mechanisms.

Effect of altering breathing frequency on maximum voluntary ventilation in healthy adults

Background

Compared to other pulmonary function tests, there is a lack of standardization regarding how a maximum voluntary ventilation (MVV) maneuver is performed. Specifically, little is known about the variation in breathing frequency (f_R) and its potential impact on the accuracy of test results. This study examines the effect of several preselected values for f_R and one self-selected f_R (f_Rself) on MVV.

Methods

Ten participants performed MVV maneuvers at various f_R values, ranging from 50 to 130 breaths·min^− 1 in 10 breaths·min^− 1 intervals and at one f_Rself. Three identical trials with 2-min rest periods were conducted at each f_R, and the sequence in which f_R was tested was randomized. Ventilation and related parameters were measured directly by gas exchange analysis via a metabolic measurement system.

Results

A third-order polynomial regression analysis showed that MVV = − 0.0001(f_R)³ + 0.0258(f_R)²–1.38(f_R) + 96.9 at preselected f_R and increased up to approximately 100 breaths·min^− 1 (r² = 0.982, P < 0.001). Paired t-tests indicated that average MVV values obtained at all preselected f_R values, but not f_Rself, were significantly lower than the average maximum value across all participants. A linear regression analysis revealed that tidal volume (V_T) = − 2.63(MVV) + 300.4 at preselected f_R (r² = 0.846, P < 0.001); however, this inverse relationship between V_T and MVV did not remain true for the self-selected f_R. The V_T obtained at this f_R (90.9 ± 19.1% of maximum) was significantly greater than the V_T associated with the most similar MVV value (at a preselected f_R of 100 breaths·min^− 1, 62.0 ± 10.4% of maximum; 95% confidence interval of difference: (17.5, 40.4%), P < 0.001).

Conclusions

This study demonstrates the shortcomings of the current lack of standardization in MVV testing and establishes data-driven recommendations for optimal f_R. The true MVV was obtained with a self-selected f_R (mean ± SD: 69.9 ± 22.3 breaths·min^− 1) or within a preselected f_R range of 110–120 breaths·min^− 1. Until a comprehensive reference equation is established, it is advised that MVV be measured directly using these guidelines. If an individual is unable to perform or performs the maneuver poorly at a self-selected f_R, ventilating within a mandated f_R range of 110–120 breaths·min^− 1 may also be acceptable.

A Systematic Method to Detect the Metabolic Threshold from Gas Exchange during Incremental Exercise

Incremental exercise consists of three domains of exercise intensity demarcated by two thresholds. The first of these thresholds, derived from gas exchange measurements, is defined as the metabolic threshold (V̇O₂θ) above which lactate accumulates. Correctly and reliably identified, V̇O₂θ is a non-invasive, sub-maximal marker of aerobic function with practical value. This investigation compared variability in selection of V̇O₂θ among interpreters with different levels of experience as well as from auto-detection algorithms employed by a commercially available metabolic cart (MC). Ten healthy young men performed three replicates of incremental cycle exercise during which gas exchange measurements were collected breath-by-breath. Two experienced interpreters (E) and four novice interpreters (N) determined V̇O₂θ from plots of specific response variables. Interpreters noted methods used and confidence in their selections. V̇O₂θ was automatically determined by the MC. Interclass correlations indicated that E agreed with each other (mean difference, 21 mL·min^-1) and with the MC (23 mL·min^-1), but not with N (-664 to 364 mL·min^-1); N did not agree among themselves. Despite good overall agreement between E and MC, differences >500 mL·min^-1 were seen in 50% of individual cases. N expressed unduly higher confidence and used different V̇O₂θ selection strategies compared with E. Experience and use of a systematic approach is essential for correctly identifying V̇O₂θ. Current guidelines for exercise testing and interpretation do not include recommendations for such an approach. Data from this study suggests that this may be a serious shortcoming. Until an alternative schema for V̇O₂θ detection is developed prospectively, strategies based on the present study will give practitioners a systematic and consistent approach to threshold detection.

Wrist-worn triaxial accelerometry predicts the energy expenditure of non-vigorous daily physical activities

OBJECTIVES

Triaxial accelerometry is commonly used to estimate oxygen uptake (VO₂) and energy expenditure in health and fitness studies. We tested the correlation of a triaxial accelerometer in terms of a summation of vector magnitudes with gravity subtracted (SVMgs) and measured VO₂ for different daily physical activities.

DESIGN

Original research, cross-sectional.

METHODS

Twenty volunteers wore a triaxial accelerometer on both wrists while performing 12 assigned daily physical activities for 6min for each activity. The VO₂ was determined by indirect calorimetry using a portable metabolic measurement system. The last 3min of each activity was assumed to represent steady-state. The VO₂ measured during these periods was averaged and converted into metabolic equivalents (METs).

RESULTS

The range of VO₂ for all activities was 0.18-3.2L/min (0.8-12.2 METs). Significant differences in SVMgs existed between accelerometer placements on the dominant (120.9±8.7gmin) versus non-dominant hand (99.9±6.8gmin; P=0.016) for the lowest levels of physical activity defined as <1.5 METs. Piecewise linear regression model using 6 METs as the transition point showed similar significant correlations for the non-dominant wrist (r²=0.85; P<0.001) and the dominant wrist (r²=0.86; P<0.001). Using the non-dominant wrist below 6 METs, the slope of the relationship between SVMgs and METs was 105.3±4.3 (95% CI 96.9 to 113.7) indicating an increase in SVMgs of approximately 100 units for every MET increase in oxygen uptake.

CONCLUSIONS

Wrist-worn triaxial accelerometry reliably predicted energy expenditure during common physical activities <6 METs. More consistent correlations were found when the accelerometer was worn on the non-dominant wrist rather than the dominant wrist.

Inter- and intra-rater agreement of static posture analysis using a mobile application

[Purpose] To determine the intra- and inter-rater agreement of a mobile application, PostureScreen Mobile^® (PSM), that assesses static standing posture. [Subjects and Methods] Three examiners with different levels of experience of assessing posture, one licensed physical therapist and two untrained undergraduate students, performed repeated postural assessments of 10 subjects, fully clothed or minimally clothed, using PSM on two nonconsecutive days. Anterior and right lateral images were captured and seventeen landmarks were identified on them. Intraclass correlation coefficients (ICCs) were calculated for each of 13 postural measures to evaluate inter-rater agreement on the first visit (fully or minimally clothed), as well as intra-rater agreement between the first and second visits (minimally clothed). [Results] Eleven postural measures were ultimately analyzed for inter- and intra-rater agreement. Inter-rater agreement was almost perfect (ICC≥0.81) for four measures and substantial (0.60<ICC≤0.80) for three measures during the fully clothed exam. During the minimally clothed exam, inter-rater agreement was almost perfect for four measures and substantial for four measures. Intra-rater agreement between two minimally clothed exams was almost perfect for two measures and substantial for five measures. [Conclusion] PSM is a widely available, inexpensive postural screening tool that requires little formal training. To maximize inter- and intra-rater agreement, postural screening using this mobile application should be conducted with subjects wearing minimal clothing. Assessing static standing posture via PSM gives repeatable measures for anatomical landmarks that were found to have substantial or almost perfect agreement. Our data also suggest that this technology may also be useful for diagnosing forward head posture.

Exercise responses in patients with chronically high creatine kinase levels

INTRODUCTION

Elevated serum creatine kinase (CK) is often taken to reflect muscle disease, but many individuals have elevated CK without a specific diagnosis. How elevated CK reflects muscle metabolism during exercise is not known.

METHODS

Participants (46 men, 48 women) underwent incremental exercise testing to assess aerobic performance, cardiovascular response, and ventilatory response. Serum lactate, ammonia, and CK were measured at rest, 4 minutes into exercise, and 2 minutes into recovery.

RESULTS

High-CK and control subjects demonstrated similar aerobic capacities and cardiovascular responses to incremental exercise. Those with CK ≥ 300 U/L exhibited significantly higher lactate and ammonia levels after maximal exercise, together with increased ventilatory responses, whereas those with CK ≥200 U/L but ≤ 300 U/L did not.

CONCLUSIONS

We recommend measurement of lactate and ammonia profiles during a maximal incremental exercise protocol to help identify patients who warrant muscle biopsy to rule out myopathy. Muscle Nerve 56: 264-270, 2017.

Metabolic responses to a loaded movement training workout

BACKGROUND

Few studies have investigated the metabolic demands of functional exercise. We determined the oxygen cost, heart rate (HR) response, and energy expenditure (EE) both during and immediately following a loaded movement training (LMT) workout.

METHODS

Ten participants (5 male, age 23.5±3.7 years, VO2peak 53.3±6.4 mL/kg/min) completed baseline resting metabolic rate testing, a maximal oxygen uptake (VO2) test, and a familiarization trial. After 48 hours' rest, participants completed a 19-minute LMT protocol using functional exercise equipment, consisting of 10 x 60-second work intervals followed by 60 seconds of rest. VO2, HR, respiratory exchange ratio (RER), and EE were measured during the entire LMT protocol and for 45 minutes post-exercise.

RESULTS

Participants had a mean VO2 of 65.3±4.1% VO2peak, HR of 91.8±4.0% HRmax, RER of 1.06±0.06, EE of 13.0±3.0 kcal/min (0.176±0.021 kcal/kg/min), and rating of perceived exertion of 17.3±1.6. The mean overall caloric expenditure was 247 kcal. Post-exercise metabolic recovery data showed a mean overall excess post-exercise oxygen consumption (EPOC) of 7.89±3.78 L. EE remained elevated through 15 minutes, VO2 through 30 minutes, and HR through 45 minutes (P<0.05). RER remained depressed throughout the 45-minute collection (P<0.05).

CONCLUSIONS

LMT meets the American College of Sports Medicine's recommendations for improving cardiovascular fitness and achieving the daily caloric expenditure from exercise. It may be used to improve cardiovascular fitness and body composition in healthy adults.

Validation of Biofeedback Wearables for Photoplethysmographic Heart Rate Tracking

The purpose of this study was to examine the validity of HR measurements by two commercial-use activity trackers in comparison to ECG. Twenty-four healthy participants underwent the same 77-minute protocol during a single visit. Each participant completed an initial rest period of 15 minutes followed by 5 minute periods of each of the following activities: 60W and 120W cycling, walking, jogging, running, resisted arm raises, resisted lunges, and isometric plank. In between each exercise task was a 5-minute rest period. Each subject wore a Basis Peak (BPk) on one wrist and a Fitbit Charge HR (FB) on the opposite wrist. Criterion measurement of HR was administered by 12-lead ECG. Time synced data from each device and ECG were concurrently and electronically acquired throughout the entire 77-minute protocol. When examining data in aggregate, there was a strong correlation between BPk and ECG for HR (r = 0.92, p < 0.001) with a mean bias of -2.5 bpm (95% LoA 19.3, -24.4). The FB demonstrated a moderately strong correlation with ECG for HR (r = 0.83, p < 0.001) with an average mean bias of -8.8 bpm (95% LoA 24.2, -41.8). During physical efforts eliciting ECG HR > 116 bpm, the BPk demonstrated an r = 0.77 and mean bias = -4.9 bpm (95% LoA 21.3, -31.0) while the FB demonstrated an r = 0.58 and mean bias = -12.7 bpm (95% LoA 28.6, -54.0). The BPk satisfied validity criteria for HR monitors, however showed a marginal decline in accuracy with increasing physical effort (ECG HR > 116 bpm). The FB failed to satisfy validity criteria and demonstrated a substantial decrease in accuracy during higher exercise intensities.

Effect of Exercise Training on Striatal Dopamine D2/D3 Receptors in Methamphetamine Users during Behavioral Treatment

Methamphetamine use disorder is associated with striatal dopaminergic deficits that have been linked to poor treatment outcomes, identifying these deficits as an important therapeutic target. Exercise attenuates methamphetamine-induced neurochemical damage in the rat brain, and a preliminary observation suggests that exercise increases striatal D2/D3 receptor availability (measured as nondisplaceable binding potential (BPND)) in patients with Parkinson's disease. The goal of this study was to evaluate whether adding an exercise training program to an inpatient behavioral intervention for methamphetamine use disorder reverses deficits in striatal D2/D3 receptors. Participants were adult men and women who met DSM-IV criteria for methamphetamine dependence and were enrolled in a residential facility, where they maintained abstinence from illicit drugs of abuse and received behavioral therapy for their addiction. They were randomized to a group that received 1 h supervised exercise training (n=10) or one that received equal-time health education training (n=9), 3 days/week for 8 weeks. They came to an academic research center for positron emission tomography (PET) using [(18)F]fallypride to determine the effects of the 8-week interventions on striatal D2/D3 receptor BPND. At baseline, striatal D2/D3 BPND did not differ between groups. However, after 8 weeks, participants in the exercise group displayed a significant increase in striatal D2/D3 BPND, whereas those in the education group did not. There were no changes in D2/D3 BPND in extrastriatal regions in either group. These findings suggest that structured exercise training can ameliorate striatal D2/D3 receptor deficits in methamphetamine users, and warrants further evaluation as an adjunctive treatment for stimulant dependence.

Predictors of depression outcomes among abstinent methamphetamine-dependent individuals exposed to an exercise intervention

BACKGROUND AND OBJECTIVES

This paper expands on a study investigating depression outcomes in response to an 8-week exercise intervention among methamphetamine (MA) dependent individuals in early recovery.

METHODS

A total of 135 MA-dependent individuals enrolled in residential treatment were randomly assigned to either a structured exercise intervention or a structured health education control group. Both groups were similar in format: 60-minute sessions, offered three times a week over an 8-week study period.

RESULTS

Results showed that at the 8-week trial endpoint, participants randomized to the exercise intervention showed significantly greater reduction in depression symptom scores than participants randomized to the health education group, and that participants who attended the greatest number of exercise sessions derived the greatest benefit. This paper further analyzes study data to uncover individual predictors of depression response to exercise and finds that among participants randomized to exercise treatment, individuals with the most severe medical, psychiatric, and addiction disease burden at baseline showed the most significant improvement in depressive symptoms by study endpoint.

CONCLUSIONS

Our findings suggest that exercise in moderate dose is effective at treating depressive symptoms in individuals in early recovery from addiction, and furthermore, that treatment with exercise appears to be particularly beneficial to individuals who suffer from severe medical, psychiatric, and addictive disorders.

Reverse fiber type disproportion: A distinct metabolic myopathy

INTRODUCTION

In this investigation we characterized the physiological and metabolic responses to incremental exercise in 13 subjects with a predominance of type II fibers on muscle biopsy.

METHODS

Subjects underwent incremental exercise testing with measures of maximum oxygen uptake ( V˙O2 max), maximum heart rate (fc max), chronotropic index (fc / V˙O2 slope), maximum ventilation ( V˙emax), blood lactate, ammonia, and creatine kinase (CK) levels. Muscle fiber type was determined by myosin ATPase histochemistry.

RESULTS

Muscle biopsies showed more type II fibers (75%) in subjects compared with normal individuals (P < 0.01). Subjects exhibited normal V˙O2 max and end-exercise lactate, whereas ammonia and CK levels at maximum exercise were significantly higher.

CONCLUSIONS

Subjects with type II muscle fiber predominance exhibited exaggerated increases in ammonia and elevated CK levels during exercise. Predominance of type II fibers on muscle biopsy is the opposite finding of congenital fiber type disproportion; we suggest these patients be referred to as having "reverse fiber type disproportion." Muscle Nerve 54: 86-93, 2016.

Effect of supervised, periodized exercise training vs. self-directed training on lean body mass and other fitness variables in health club members

Conventional wisdom suggests that exercise training with a personal trainer (PTr) is more beneficial for improving health-related fitness than training alone. However, there are no published data that confirm whether fitness club members who exercise with a PTr in the fitness club setting obtain superior results compared with self-directed training. We hypothesized that club members randomized to receive an evidence-based training program would accrue greater improvements in lean body mass (LBM) and other fitness measures than members randomized to self-training. Men, aged 30-44 years, who were members of a single Southern California fitness club were randomized to exercise with a PTr administering a nonlinear periodized training program (TRAINED, N = 17) or to self-directed training (SELF, N = 17); both groups trained 3 days per week for 12 weeks. Lean body mass was determined by dual-energy x-ray absorptiometry. Secondary outcomes included muscle strength 1 repetition maximum (1RM), leg power (vertical jump), and aerobic capacity (V[Combining Dot Above]O2max). TRAINED individuals increased LBM by 1.3 (0.4) kg, mean (SEM) vs. no change in SELF, p = 0.029. Similarly, significantly greater improvements were seen for TRAINED vs. SELF in chest press strength (42 vs. 19%; p = 0.003), peak leg power (6 vs. 0.6%; p < 0.0001), and V[Combining Dot Above]O2max (7 vs. -0.3%; p = 0.01). Leg press strength improved 38 and 25% in TRAINED and SELF, respectively (p = 0.14). We have demonstrated for the first time in a fitness club setting that members whose training is directed by well-qualified PTrs administering evidence-based training regimens achieve significantly greater improvements in LBM and other dimensions of fitness than members who direct their own training.

Validation of the firefighter WFI treadmill protocol for predicting VO2 max

BACKGROUND

The Wellness-Fitness Initiative submaximal treadmill exercise test (WFI-TM) is recommended by the US National Fire Protection Agency to assess aerobic capacity (VO2 max) in firefighters. However, predicting VO2 max from submaximal tests can result in errors leading to erroneous conclusions about fitness.

AIMS

To investigate the level of agreement between VO2 max predicted from the WFI-TM against its direct measurement using exhaled gas analysis.

METHODS

The WFI-TM was performed to volitional fatigue. Differences between estimated VO2 max (derived from the WFI-TM equation) and direct measurement (exhaled gas analysis) were compared by paired t-test and agreement was determined using Pearson Product-Moment correlation and Bland-Altman analysis. Statistical significance was set at P < 0.05.

RESULTS

Fifty-nine men performed the WFI-TM. Mean (standard deviation) values for estimated and measured VO2 max were 44.6 (3.4) and 43.6 (7.9) ml/kg/min, respectively (P < 0.01). The mean bias by which WFI-TM overestimated VO2 max was 0.9ml/kg/min with a 95% prediction interval of ±13.1. Prediction errors for 22% of subjects were within ±5%; 36% had errors greater than or equal to ±15% and 7% had greater than ±30% errors. The correlation between predicted and measured VO2 max was r = 0.55 (standard error of the estimate = 2.8ml/kg/min).

CONCLUSIONS

WFI-TM predicts VO2 max with 11% error. There is a tendency to overestimate aerobic capacity in less fit individuals and to underestimate it in more fit individuals leading to a clustering of values around 42ml/kg/min, a criterion used by some fire departments to assess fitness for duty.

Firefighter health and fitness assessment: a call to action

Sudden cardiac deaths experienced by firefighters in the line of duty account for the largest proportion of deaths annually. Several fire service standards for fitness and wellness have been recommended but currently only 30% of U.S. fire departments are implementing programs for this purpose. The Department of Homeland Security Science and Technology Directorate has initiated the Physiological Health Assessment System for Emergency Responders (PHASER) program aiming to reduce these line-of-duty deaths through an integration of medical science and sensor technologies. Confirming previous reports, PHASER comprehensive risk assessment has identified lack of physical fitness with propensity for overexertion as a major modifiable risk factor. We sought to determine if current levels of fitness and cardiovascular disease (CVD) risk factors in a contemporary cohort of firefighters were better than those reported over the past 30 years. Fifty-one firefighters from a Southern California department were characterized for physical fitness and CVD risk factors using standard measures. Overall, physical fitness and risk factors were not different from previous reports of firefighter fitness and most subjects did not achieve recommended fitness standards. Considering the lack of widespread implementation of wellness/fitness programs in the U.S. fire service together with our findings that low physical fitness and the presence of CVD risk factors persist, we issue a call to action among health and fitness professionals to assist the fire service in implementing programs for firefighters that improve fitness and reduce CVD risk factors. Fitness professionals should be empowered to work with fire departments lending their expertise to guide programs that achieve these objectives, which may then lead to reduced incidence of sudden cardiac death or stroke.

Deployment of remote advanced electrocardiography for improved cardiovascular risk assessment in career firefighters

INTRODUCTION

Firefighters perform strenuous muscular work while wearing heavy, encapsulating personal protective equipment in high temperature environments, under chaotic and emotionally stressful conditions. These factors can precipitate sudden cardiac events in firefighters with underlying cardiovascular disease. The purpose of this pilot study was to deploy and explore the feasibility of the resting "advanced" 12-lead electrocardiogram (A-ECG) as a remote firefighter risk assessment tool for improved assessment of cardiac risk.

MATERIALS AND METHODS

Conventional 12-lead resting electrocardiograms (ECGs) were collected for 5 min by using high-fidelity PC-based ECG hardware and software while subjects (n=21) rested comfortably. Raw data from the ECG system were securely transported via a secure network to a server where they were archived and processed. Authorized personnel performed both conventional ECG and A-ECG analyses from each digital recording, generating A-ECG "scores" in a blinded fashion. A separate cohort of firefighters (n=6) was trained to administer the A-ECG and rated the system's usability and frequency of technical problems.

RESULTS

Of the 21 uniformed personnel who completed testing, only 1 had a positive A-ECG score for coronary artery disease, which was subsequently confirmed by a cardiologist. All other subjects were classified as healthy by A-ECG. Firefighters trained to administer the A-ECG responded favorably in rating the usability of the system.

CONCLUSIONS

We have demonstrated that a new technology, A-ECG, can be deployed for remote firefighter risk assessment being performed by firefighters themselves and interpreted centrally. This simple, time- and cost-effective approach can help identify individuals potentially at increased risk for line-of-duty death due to underlying cardiovascular disease.

Evaluation of a wearable physiological status monitor during simulated fire fighting activities

A physiological status monitor (PSM) has been embedded in a fire-resistant shirt. The purpose of this research study was to examine the ability of the PSM-shirt to accurately detect heart rate (HR) and respiratory rate (RR) when worn under structural fire fighting personal protective equipment (PPE) during the performance of various activities relevant to fire fighting. Eleven healthy, college-aged men completed three activities (walking, searching/crawling, and ascending/descending stairs) that are routinely performed during fire fighting operations while wearing the PSM-shirt under structural fire fighting PPE. Heart rate and RR recorded by the PSM-shirt were compared to criterion values measured concurrently with an ECG and portable metabolic measurement system, respectively. For all activities combined (overall) and for each activity, small differences were found between the PSM-shirt and ECG (mean difference [95% CI]: overall: -0.4 beats/min [-0.8, -0.1]; treadmill: -0.4 beats/min [-0.7, -0.1]; search: -1.7 beats/min [-3.1, -.04]; stairs: 0.4 beats/min [0.04, 0.7]). Standard error of the estimate was 3.5 beats/min for all tasks combined and 1.9, 5.9, and 1.9 beats/min for the treadmill walk, search, and stair ascent/descent, respectively. Correlations between the PSM-shirt and criterion heart rates were high (r = 0.95 to r = 0.99). The mean difference between RR recorded by the PSM-shirt and criterion overall was 1.1 breaths/min (95% CI: -1.9 to -0.4). The standard error of the estimate for RR ranged from 4.2 breaths/min (treadmill) to 8.2 breaths/min (search), with an overall value of 6.2 breaths/min. These findings suggest that the PSM-shirt provides valid measures of HR and useful approximations of RR when worn during fire fighting duties.