Light-intensity physical activity derived from count or activity types is differently associated with adiposity markers.

AIM: The aim of this study was to compare the association between count- and activity type-based definitions of light-intensity physical activity (LIPA) and adiposity markers. METHODS: A total of 516 Danish workers participated in 1-4 days of hip- and thigh-based accelerometer measurements. Three definitions of average daily time spent in LIPA were derived: LIPA (1) time spent between 100 and 2029 CPM, LIPA (2) time spent moving and slow walking, and LIPA (3) time spent moving, walking slow, and standing. Adiposity markers were body mass index (BMI), body fat percentage, and waist circumference. The cross-sectional association between the three LIPA definitions and adiposity markers was analyzed and interpreted using compositional regression models followed by reallocation of time between LIPA, moderate-to-vigorous physical activity (MVPA), and sedentary behavior (SB), respectively. RESULTS: The geometric means of daily time (min/day) spent in LIPA 1, LIPA 2, and LIPA 3 were 326, 102, and 274, respectively. We found the direction and strength of the association between the relative importance of daily time spent in LIPA and the adiposity markers to depend on the LIPA definition. For example, reallocating 30 minutes from MVPA to LIPA 1, LIPA 2 and LIPA 3 were associated with a 2.97 (95% CI: 0.68; 5.27), -0.71 (95% CI: -1.43; 0.02), and -0.45 (95% CI: -1.01; 0.11) difference in BMI, respectively. CONCLUSION: Our findings highlight the need for caution when comparing results from studies using different definitions of LIPA.

Detection of kneeling and squatting during work using wireless triaxial accelerometers.

Occupational kneeling and squatting are well-documented risk factors for knee disorders. A method using 3 wireless accelerometers to detect and discriminate kneeling and squatting during work were developed based on data from a semi-standardised laboratory protocol. The method was tested for validity under free-living working conditions. The developed method showed high sensitivity (88-99%) and specificity (98-99%) for detection of kneeling and squatting during the semi-standardised laboratory conditions. During free-living working conditions, kneeling showed very high sensitivity (94%) and specificity (99%), while squatting results were non-conclusive due to limited duration of squatting during the free-living working conditions. This method shows great promise for long-term technical measurement of kneeling and squatting during normal working conditions using wireless accelerometers. The method opens up possibilities for using technical measurements to provide valid exposure assessments and intervention evaluations of kneeling and squatting, as well as increased feasibility for technical measurements in large cohort studies. Practitioner summary: Quantification of kneeling and squatting during work is important for prevention, but limited by either imprecise or costly methods. This study developed and validated an inexpensive wireless accelerometer-based measurement method that can be used by practitioners and researchers for long-term measurements of kneeling and squatting during free-living working conditions.

Comparison of physical behavior estimates from three different thigh-worn accelerometers brands: a proof-of-concept for the Prospective Physical Activity, Sitting, and Sleep consortium (ProPASS).

BACKGROUND: Pooling data from thigh-worn accelerometers across multiple studies has great potential to advance evidence on the health benefits of physical activity. This requires harmonization of information on body postures, physical activity types, volumes and time patterns across different brands of devices. The aim of this study is to compare the physical behavior estimates provided by three different brands of thigh-worn accelerometers. METHODS: Twenty participants volunteered for a 7-day free-living measurement. Three accelerometers - ActiGraph GT3X+, Axivity AX3 and ActivPAL Micro4 - were randomly placed in a vertical line on the midsection of the right thigh. Raw data from each accelerometer was processed and classified into 8 physical activities and postures using the Acti4 software. Absolute differences between estimates and the respective coefficient of variation (CV) were calculated. RESULTS: We observed very minor differences between physical behavior estimates from three different accelerometer brands. When averaged over 24 h (1,440 min), the absolute difference (CV) between accelerometers were: 1.2 mins (0.001) for lying/sitting, 3.4 mins (0.02) for standing, 3.5 mins (0.06) for moving, 1.9 mins (0.03) for walking, 0.1 mins (0.19) for running, 1.2 mins (0.19) for stair climbing, 1.9 mins (0.07) for cycling. Moreover, there was an average absolute difference of 282 steps (0.03) per 24 h. CONCLUSIONS: Physical behaviors were classified with negligible difference between the accelerometer brands. These results support harmonization of data from different thigh-worn accelerometers across multiple cohorts when analyzed in an identical manner.

Different autonomic responses to occupational and leisure time physical activities among blue-collar workers.

PURPOSE: The differential effect of occupational and leisure time physical activity on cardiovascular health is termed the physical activity health paradox. Cardiac autonomic modulation could bring insights about the underlying mechanism behind this differential effect. The aim was to compare heart rate variability (HRV) during different activities (sitting, standing and moving) at work and leisure among blue-collar workers. METHODS: One hundred thirty-eight workers from the NOMAD cohort were included. Data from physical activity and HRV were obtained for 3-4 days using tri-axial accelerometers (Actigraph GT3X+) and a heart rate monitor (Actiheart). HRV indices were determined during sitting, standing and moving both at work and leisure. Linear mixed-models with two fixed factors (activities and domains) were applied to investigate differences in HRV indices adjusting for individual and occupational factors. RESULTS: The results showed significant effects of domain (p < 0.01), physical activity type (p < 0.01) and interaction between domain and activity type (p < 0.01) on HRV indices. Mean heart rate (IBI) and parasympathetic measures of HRV (RMSSD and HF) were lower for sitting (p < 0.01) and higher for moving (p < 0.01) during work compared with leisure, while no difference between domains was found for standing (p > 0.05). Sympathovagal balance (LF/HF) was higher during work for sitting and moving (p < 0.01), but showed no difference for standing (p = 0.62). CONCLUSIONS: Differences in cardiac autonomic modulation between work and leisure were found, indicating sympathetic predominance during work and parasympathetic predominance during leisure for sitting. Autonomic responses can be part of the mechanism that explains the differential effect of occupational and leisure time physical activity on health.

Neck and shoulder muscle strength in patients with tension-type headache: A case-control study.

INTRODUCTION: Tension-type headache (TTH) is highly prevalent in the general population, and it is characterized by increased muscle tenderness with increasing headache frequency and intensity. AIM: The aim of this case-control study was to compare muscle strength in neck and shoulder muscles in TTH patients and healthy controls by examining maximal voluntary isometric contraction (MVC) during shoulder abduction, neck flexion and extension as well as the extension/flexion strength ratio of the neck. METHODS: Sixty TTH patients and 30 sex- and age-matched healthy controls were included. Patients were included if they had TTH ≥8 days per month. The MVC neck extensor and flexor muscles were tested with the participant seated upright. MVC shoulder abduction was tested with the individual lying supine. RESULTS: Compared to controls TTH patients had significantly weaker muscle strength in neck extension (p = 0.02), resulting in a significantly lower extension/flexion moment ratio (p = 0.03). TTH patients also showed a tendency toward significantly lower muscle strength in shoulder abduction (p = 0.05). Among the 60 TTH patients, 25 had frequent episodic TTH (FETTH), and 35 had chronic TTH (CTTH). CONCLUSION: Patients with TTH exhibited decreased muscle strength in the neck extensor muscles, inducing a reduced cervical extension/flexion ratio compared to healthy people.

Is aerobic workload positively related to ambulatory blood pressure? A cross-sectional field study among cleaners.

PURPOSE: Cardiovascular disease is prevalent among workers with high levels of occupational physical activity. The increased risk may be due to a high relative aerobic workload, possibly leading to increased blood pressure. However, studies investigating the relation between relative aerobic workload and ambulatory blood pressure (ABP) are lacking. The aim was to explore the relationship between objectively measured relative aerobic workload and ABP. METHODS: A total of 116 cleaners aged 18-65 years were included after informed consent was obtained. A portable device (Spacelabs 90217) was mounted for 24-h measurements of ABP, and an Actiheart was mounted for 24-h heart rate measurements to calculate relative aerobic workload as percentage of relative heart rate reserve. A repeated-measure multi-adjusted mixed model was applied for analysis. RESULTS: A fully adjusted mixed model of measurements throughout the day showed significant positive relations (p < 0.001): a 1% increase in mean relative aerobic workload was associated with an increase of 0.42 ± 0.05 mmHg (95% CI 0.32-0.52 mmHg) in systolic ABP and 0.30 ± 0.04 mmHg (95% CI 0.22-0.38 mmHg) in diastolic ABP. Correlations between relative aerobic workload and ABP were significant. CONCLUSIONS: Because workers may have an elevated relative aerobic workload for several hours each working day, this relationship may elucidate a mechanism behind the increased risk for cardiovascular disease among workers exposed to high levels of occupational physical activity.

Validity of the Acti4 method for detection of physical activity types in free-living settings: comparison with video analysis.

This study examined the ability of the Acti4 software for identifying physical activity types from accelerometers during free-living with different levels of movement complexity compared with video observations. Nineteen aircraft cabin cleaners with ActiGraph GT3X+ accelerometer at the thigh and hip performed one semi-standardised and two non-standardised sessions (outside and inside aircraft) with different levels of movement complexity during working hours. The sensitivity for identifying different activity types was 75.4-99.4% for the semi-standardised session, 54.6-98.5% outside the aircraft and 49.9-90.2% inside the aircraft. The specificity was above 90% for all activities, except 'moving' inside the aircraft. These findings indicate that Acti4 provides good estimates of time spent in different activity types during semi-standardised conditions, and for sitting, standing and walking during non-standardised conditions with normal level of movement complexity. The Acti4 software may be a useful tool for researchers and practitioners in the field of ergonomics, occupational and public health. Practitioner Summary: Being inexpensive, small, water-resistant and without wires, the ActiGraph GT3X+ by applying the Acti4 software may be a useful tool for long-term field measurements of physical activity types for researchers and practitioners in the field of ergonomics, occupational and public health.

Reduced neck-shoulder muscle strength and aerobic power together with increased pericranial tenderness are associated with tension-type headache in girls: A case-control study.

BACKGROUND: Tension-type headaches (TTH) are common among children worldwide and mean a potential risk of disability and medication overuse headache. The associated mechanisms, however, remain unsolved. Our study investigated muscle strength in the neck-shoulder region, aerobic power and pericranial tenderness in girls with TTH compared with healthy controls. METHODS: A blinded case-control study comprising 41 girls with TTH and 41 age-matched healthy controls. Standardised testing of isometric maximal voluntary contraction (MVC) and force steadiness of neck flexion and extension, as well as MVC and rate-of-force development of dominant shoulder, was conducted. VO2 max was recorded by a submaximal ergometer test and pericranial tenderness by standardised manual palpation. Logistic regression analyses were applied. RESULTS: Girls with TTH demonstrated significantly higher pericranial tenderness than controls, in correlation with headache frequency (r = 0.66, p < 0.001). Results indicated that the odds ratio of girls having headache are 7.6 (95% CI 1.4-40.9) for weak to strong shoulder muscles; weak to average neck-shoulder strength OR 3.1 (95% CI 1.2-8.1); neck flexion strength OR 1.3 (95% CI 1.0-1.6) and 5.2 (95% CI: 1.4-19.6) for each unit of decrease in VO2 max. CONCLUSIONS: Reduced neck-shoulder strength and aerobic power together with increased pericranial tenderness are associated with TTH in girls. Future interventions should be directed towards health promoting patient educational programmes on enhanced physical exercising. Much more exact and detailed research in young girls and boys are needed.

Heart rate variability analysis using robust period detection.

OBJECTIVE: Heart rate variability (HRV) analysis, which is an important tool for activity assessment of the cardiac autonomic nervous system, very often includes the estimation of power spectra for series of interbeat intervals (IBI). Ectopic beats and artifacts have a destructive effect on the standard methods (Fourier transform, FFT) for frequency analysis. This study investigates an alternative method for calculation of the periodogram using a robust period detection (RPD). METHOD: Error free IBI series of 5 minutes for 221 subjects during one day were artificially distorted by randomly changing IBI values by ±15-40%. The low to high frequency rate (LF/HF) were calculated from periodograms estimated by the FFT, RPD and Lomb (LSP) methods for both error free and distorted series and for series with removed beats. Log transformed LF/HF values for series with distorted/removed beats were compared to undistorted values by linear regression. RESULTS: For series with 10% of distorted IBI values the regression analysis between distorted and undistorted series showed a goodness of fit, coefficient and intercept of 0.98, 0.94 and 0.02, respectively. In comparison, the values of these parameters were (0.34, 0.46, -1.61) and (0.28, 0.42,-1.32) for the FFT and LSP methods, respectively. Similarly, the comparison between series with removed and undistorted beats yielded goodness of fit, coefficient and intercept of (0.98, 0.96, -0.01), (0.93, 0.78, -0.02) and (0.98, 0.95, 0.19) for RPD, FFT and LSP, respectively. CONCLUSION: The RPD method demonstrated superior performance compared to the FFT and LSP method by estimation of power spectral characteristics for HRV analysis.

Validity of the Acti4 software using ActiGraph GT3X+accelerometer for recording of arm and upper body inclination in simulated work tasks.

The validity of inclinometer measurements by ActiGraph GT3X+ (AG) accelerometer, when analysed with the Acti4 customised software, was examined by comparison of inclinometer measurements with a reference system (TrakStar) in a protocol with standardised arm movements and simulated working tasks. The sensors were placed at the upper arm (distal to the deltoid insertion) and at the spine (level of T1-T2) on eight participants. Root mean square errors (RMSEs) values of inclination between the two systems were low for the slow- and medium-speed standardised arm movements and in simulated working tasks. Fast arm movements caused the inclination estimated by the AG to deviate from the reference measurements (RMSE values up to ∼10°). Furthermore, it was found that AG positioned at the upper arm provided inclination data without bias compared to the reference system. These findings indicate that the AG provides valid estimates of arm and upper body inclination in working participants. PRACTITIONER SUMMARY: Being inexpensive, small, water-resistant and without wires, ActiGraph GT3X+ seems to be a valid mean for direct long-term field measurements of arm and trunk inclinations when analysed by the Acti4 customised software.

Physical activities at work and risk of musculoskeletal pain and its consequences: protocol for a study with objective field measures among blue-collar workers.

BACKGROUND: Among blue-collar workers, high physical work demands are generally considered to be the main cause of musculoskeletal pain and work disability. However, current available research on this topic has been criticised for using self-reported data, cross-sectional design, insufficient adjustment for potential confounders, and inadequate follow-up on the recurrent and fluctuating pattern of musculoskeletal pain. Recent technological advances have provided possibilities for objective diurnal field measurements of physical activities and frequent follow-up on musculoskeletal pain.The main aim of this paper is to describe the background, design, methods, limitations and perspectives of the Danish Physical Activity cohort with Objective measurements (DPhacto) investigating the association between objectively measured physical activities capturing work and leisure time and frequent measurements of musculoskeletal pain among blue-collar workers. METHODS/DESIGN: Approximately 2000 blue-collar workers are invited for the study and asked to respond to a baseline questionnaire, participate in physical tests (i.e. muscle strength, aerobic fitness, back muscle endurance and flexibility), to wear accelerometers and a heart rate monitor for four consecutive days, and finally respond to monthly text messages regarding musculoskeletal pain and quarterly questionnaires regarding the consequences of musculoskeletal pain on work activities, social activities and work ability for a one-year follow-up period. DISCUSSION: This study will provide novel information on the association between physical activities at work and musculoskeletal pain. The study will provide valid and precise documentation about the relation between physical work activities and musculoskeletal pain and its consequences among blue-collar workers.

Kettlebell swing targets semitendinosus and supine leg curl targets biceps femoris: an EMG study with rehabilitation implications.

BACKGROUND: The medial hamstring muscle has the potential to prevent excessive dynamic valgus and external rotation of the knee joint during sports. Thus, specific training targeting the medial hamstring muscle seems important to avoid knee injuries. OBJECTIVE: The aim was to investigate the medial and lateral hamstring muscle activation balance during 14 selected therapeutic exercises. STUDY DESIGN: The study design involved single-occasion repeated measures in a randomised manner. Sixteen female elite handball and soccer players with a mean (SD) age of 23 (3) years and no previous history of knee injury participated in the present study. Electromyographic (EMG) activity of the lateral (biceps femoris - BF) and medial (semitendinosus - ST) hamstring muscle was measured during selected strengthening and balance/coordination exercises, and normalised to EMG during isometric maximal voluntary contraction (MVC). A two-way analysis of variance was performed using the mixed procedure to determine whether differences existed in normalised EMG between exercises and muscles. RESULTS: Kettlebell swing and Romanian deadlift targeted specifically ST over BF (Δ17-22%, p<0.05) at very high levels of normalised EMG (73-115% of MVC). In contrast, the supine leg curl and hip extension specifically targeted the BF over the ST (Δ 20-23%, p<0.05) at very high levels of normalised EMG (75-87% of MVC). CONCLUSION: Specific therapeutic exercises targeting the hamstrings can be divided into ST dominant or BF dominant hamstring exercises. Due to distinct functions of the medial and lateral hamstring muscles, this is an important knowledge in respect to prophylactic training and physical therapist practice.

Effects of kettlebell training on postural coordination and jump performance: a randomized controlled trial.

The aim of this study was to investigate the effectiveness of a worksite intervention using kettlebell training to improve postural reactions to perturbation and jump performance. This single-blind randomized controlled trial involved 40 adults (n = 40) from occupations with a high prevalence of musculoskeletal pain and discomfort (mean age 44 years, body mass index 23 kg·m, 85% women). A blinded examiner took measures at baseline and follow-up. Participants were randomly assigned to a training group-doing kettlebell swings 3 times a week for 8 weeks-or to a control group. The outcome measures were postural reactions to sudden perturbation and maximal countermovement jump height. Compared with the control group, the training group had a significant decreased stopping time after perturbation (-109 ms, 95% confidence interval [-196 to -21]). Jump height increased significantly in the training group (1.5 cm, 95% confidence interval [0.5 to 2.5]), but this was nonsignificantly different from control. Kettlebell training improves postural reactions to sudden perturbation. Future studies should investigate whether kettlebell training can reduce the risk of low back injury in occupations with manual material handling or patient handling where sudden perturbations often occur.

A 24-h assessment of physical activity and cardio-respiratory fitness among female hospital cleaners: a pilot study.

The aim of this study was to evaluate the feasibility of methods for objective 24-h sampling of physical activity among cleaners. Twenty cleaners participated in three 24-h measurements. Amount of steps, heart rate (HR), cardio-respiratory fitness, body mass index (BMI) and blood pressure were measured. The methods were feasible for the objective 24-h sampling of physical activity and cardio-respiratory fitness among cleaners. Measurements showed that the cleaners walked 20,198 ± 4,627 steps per day. During working hours, the average cardio-respiratory load was 25 ± 6% of heart rate reserve (HRR). The cleaners had a low estimated cardio-respiratory fitness (34 mlO2/kg/min), a high BMI (50%, >25 kg/m(2)) and blood pressure (50%, >120/>80 mmHg). The high amount of steps, the relatively high cardiovascular load at work and low cardio-respiratory fitness illustrate the need for further investigation of the relationship between physical activity at work and in leisure, and cardiovascular health in this population. PRACTITIONER SUMMARY: This study evaluated the feasibility of methods for objective 24-h sampling of physical activity among cleaners; the methods used were found to be feasible. The cleaners had a high cardiovascular load at work and low cardio-respiratory fitness, suggesting that there is a need for further investigations.

Cardiorespiratory fitness, cardiovascular workload and risk factors among cleaners; a cluster randomized worksite intervention.

BACKGROUND: Prevalence of cardiovascular risk factors is unevenly distributed among occupational groups. The working environment, as well as lifestyle and socioeconomic status contribute to the disparity and variation in prevalence of these risk factors. High physical work demands have been shown to increase the risk for cardiovascular disease and mortality, contrary to leisure time physical activity. High physical work demands in combination with a low cardiorespiratory fitness infer a high relative workload and an excessive risk for cardiovascular mortality. Therefore, the aim of this study is to examine whether a worksite aerobic exercise intervention will reduce the relative workload and cardiovascular risk factors by an increased cardiorespiratory fitness. METHODS/DESIGN: A cluster-randomized controlled trial is performed to evaluate the effect of the worksite aerobic exercise intervention on cardiorespiratory fitness and cardiovascular risk factors among cleaners. Cleaners are eligible if they are employed ≥ 20 hours/week, at one of the enrolled companies. In the randomization, strata are formed according to the manager the participant reports to. The clusters will be balanced on the following criteria: Geographical work location, gender, age and seniority. Cleaners are randomized to either I) a reference group, receiving lectures concerning healthy living, or II) an intervention group, performing worksite aerobic exercise "60 min per week". Data collection will be conducted at baseline, four months and 12 months after baseline, at the worksite during working hours. The data collection will consist of a questionnaire-based interview, physiological testing of health and capacity-related measures, and objective diurnal measures of heart rate, physical activity and blood pressure. Primary outcome is cardiorespiratory fitness. DISCUSSION: Information is lacking about whether an improved cardiorespiratory fitness will affect the cardiovascular health, and additionally decrease the objectively measured relative workload, in a population with high physical work demands. Previous intervention studies have lacked robust objective measurements of the relative workload and physical work demands. This study will monitor the relative workload and general physical activity before, during after the intervention, and contribute to the understanding of the previously observed opposing effects on cardiovascular health and mortality from occupational and leisure time physical activity. TRIAL REGISTRATION: The study is registered as ISRCTN86682076.

Comparison of two systems for long-term heart rate variability monitoring in free-living conditions--a pilot study.

OBJECTIVE: A number of small portable systems that can measure HRV are available to address questions related to autonomic regulation in free-living subjects. However, ambulatory HRV measurements obtained through use of these systems have not previously been validated against standard clinical measurements such as Holter recordings. The objective of this study was to validate HRV obtained using a commonly used system, Actiheart, during occupational and leisure-time activities. METHOD: Full-day ambulatory electrocardiography (ECG) signals were recorded from 8 females simultaneously using Actiheart and Holter recorders, and signals were processed to RR-interval time series. Segments of 5-minute duration were sampled every 30 minutes, and spectral components of the heart rate variability were calculated. Actiheart and Holter values were compared using Deming regression analysis and Bland-Altman plots. RESULTS: In total, 489 segments were available with an HRV value from both Actiheart and Holter recordings after filtering out segments with >10% interpolated beats. No systematic differences between Actiheart and Holter HRV were found. The random deviations between Actiheart and Holter were comparable to the repeatability standard deviation between consecutive Holter measurements. DISCUSSION: The results show that Actiheart is suited as a stand-alone ambulatory method for heart rate variability monitoring during occupational and leisure-time activities.

Neck pain and postural balance among workers with high postural demands - a cross-sectional study.

BACKGROUND: Neck pain is related to impaired postural balance among patients and is highly prevalent among workers with high postural demands, for example, cleaners. We therefore hypothesised, that cleaners with neck pain suffer from postural dysfunction. This cross-sectional study tested if cleaners with neck pain have an impaired postural balance compared with cleaners without neck pain. METHODS: Postural balance of 194 cleaners with (n = 85) and without (N = 109) neck pain was studied using three different tests. Success or failure to maintain the standing position for 30 s in unilateral stance was recorded. Participants were asked to stand on a force platform for 30 s in the Romberg position with eyes open and closed. The centre of pressure of the sway was calculated, and separated into a slow (rambling) and fast (trembling) component. Subsequently, the 95% confidence ellipse area (CEA) was calculated. Furthermore a perturbation test was performed. RESULTS: More cleaners with neck pain (81%) failed the unilateral stance compared with cleaners without neck pain (61%) (p < 0.01). However, the risk of failure in unilateral stance was statistically elevated in cleaners with concurrent neck/low back pain compared to cleaners without neck/low back pain (p < 0.01), whereas pain at only neck or only low back did not increase the risk. Impaired postural balance, measured as CEA (p < 0.01), rambling (p < 0.05) and trembling (p < 0.05) was observed among cleaners with neck pain in comparison with cleaners without neck pain in the Romberg position with eyes closed, but not with eyes open. CONCLUSIONS: Postural balance is impaired among cleaners with neck pain and the current study suggests a particular role of the slow component of postural sway. Furthermore, the unilateral stance test is a simple test to illustrate functional impairment among cleaners with concurrent neck and low back pain. TRIAL REGISTRATION: ISRCTN96241850.

Muscle oxygenation and glycolysis in females with trapezius myalgia during stress and repetitive work using microdialysis and NIRS.

The aim of this investigation was to study female workers active in the labour market for differences between those with trapezius myalgia (MYA) and without (CON) during repetitive pegboard (PEG) and stress (STR) tasks regarding (1) relative muscle load, (2) trapezius muscle blood flow, (3) metabolite accumulation, (4) oxygenation, and (5) pain development. Among 812 female employees (age 30-60 years) at 7 companies with high prevalence of neck/shoulder complaints, clinical examination identified 43 MYA and 19 CON. At rest, during PEG, and STR the trapezius muscle was measured using (1) EMG and MMG, (2) microdialysis, and (3) NIRS. Further, subjective pain ratings were scored (VAS). EMGrms in %MVE (Maximal Voluntary EMG-activity), was significantly higher among MYA than CON during PEG (11.74 +/- 9.09 vs. 7.42 +/- 5.56%MVE) and STR (5.47 +/- 5.00 vs. 3.28 +/- 1.94%MVE). MANOVA showed a group and time effect regarding data from the microdialysis: for MYA versus CON group differences demonstrated lower muscle blood flow and higher lactate and pyruvate concentrations. Potassium and glucose only showed time effects. NIRS showed similar initial decreases in oxygenation with PEG in both groups, but only in CON a significant increase back to baseline during PEG. VAS score at rest was highest among MYA and increased during PEG, but not for CON. The results showed significant differences between CON and MYA regarding muscle metabolism at rest and with PEG and STR. Higher relative muscle load during PEG and STR, insufficient muscle blood flow and oxygenation may account for the higher lactate, pyruvate and pain responses among MYA versus CON.

Reproducibility and seasonal variation of ambulatory short-term heart rate variability in healthy subjects during a self-selected rest period and during sleep.

Although ambulatory measurements of heart rate variability (HRV) are widely used, the reproducibility and seasonal variation of ambulatory sampled short-term HRV measurements in healthy participants has not been investigated before. In the present study we collected ambulatory ECGs from 19 healthy participants monthly for 12 months, and for a sub-group of 12 participants weekly for one month. Frequency-domain HRV-metrics were calculated for 5 min ECG segments during (i) a 15-min self-selected rest period (awake period), and (ii) a 30-min sleep period starting 45 min after estimated sleep onset. Total, within- and between-subject coefficient of variation (CV) and seasonal variation were estimated for ln (TP), ln (LFP), ln (HFP), ln (LF/HF), LFnu, HFnu, the mean heart period and the ECG derived respiratory frequency.The within- and between-subject CV varied considerably between different variables, from < 10% for ln (TP) and ln (LFP) to >100% for ln (LF/HF). Within- and between-subject CV of ln (HFP), LFnu and HFnu were 10-40%. A weak, but significant, seasonal variation was found for ln (TP) (p = 0.05), ln (LFP) (p<0.05) and the respiratory frequency (p<0.01), but the seasonal variation did not affect the within-subject CV. Furthermore, sample size calculations demonstrated that the reproducibility was sufficient for ambulatory HRV measurements to be used to study autonomic cardiac regulation in healthy populations.

Stress reactions to cognitively demanding tasks and open-plan office noise.

OBJECTIVES: To investigate the effects of cognitively demanding work tasks and office noise on heart rate variability (HRV), cardiovascular responses and electromyography (EMG) activity in the trapezius muscles. METHODS: Ten female volunteers were exposed to simulated open-plan office noise for 35 min (Leq 65 dBA), while engaged in cognitively demanding tasks. Task performance, self-rated stress and energy, affective state, perceived exertion in the shoulders and in the head, EMG in the left and right trapezius muscle, blood pressure, heart period length, HRV, and salivary cortisol were measured. RESULTS: Cognitively demanding work tasks were associated with changes in HRV, systolic blood pressure and EMG that reflects increased sympathetic activity in the autonomic nervous system. No effect of noise was observed, except for a higher rating of perceived exertion in the head and, contrary to expectations, a 4% lower diastolic blood pressure in the noise conditions. CONCLUSIONS: Psychophysiological measures reflected the mental load imposed by cognitive work tasks. Short-term exposure to office noise resulted in increased ratings of perceived exertion in the head, but not in physiological stress reactions.