Changes in normalized mutual information in response to strength training: An ancillary analysis of a quasi-randomized controlled trial.

The aim of the present investigation was twofold. (1) to assess test-retest reliability of normalized mutual information (NMI) values extracted from the surface electromyography (sEMG) signal of muscles pairs of the upper body during dynamic bench press at a high load, and (2) to assess changes in NMI values from before to after a five-week quasi-randomized controlled bench press training intervention. For test-retest reliability, 20 strength trained males (age 25 ± 2 years, height 1.81 ± 0.07 m) performed two three-repetition maximum (3RM) tests in bench press, while sEMG was recorded from six upper body muscles. Tests were separated by 8.2 ± 2.9 days. For the training intervention, 17 male participants (age 26 ± 5 years, height 1.80 ± 0.07 m) trained bench press specific strength training for 5 weeks (TRA), while 13 male participants (age 23 ± 3 years, height 1.80 ± 0.08 m) constituted a control group (CON). 3RM bench press test and sEMG recordings were carried out before and after the intervention period. The NMI values ranged from poor to almost perfect reliability, with the majority displaying substantial reliability. TRA displayed a significant decrease in NMI values during the concentric phase for two agonist-agonist muscle pairs, while one agonist-agonist and two agonist-antagonist muscle pairs increased the NMI values during the eccentric phase. The observed changes did not exceed the minimal detectable threshold, and we therefore cannot surely ascertain that the changes observed in NMI values reflect genuine neural adaptations.

Rowing exercise increases cardiorespiratory fitness and brachial artery diameter but not traditional cardiometabolic risk factors in spinal cord-injured humans.

PURPOSE: This study assessed the effects of upper-body rowing exercise on cardiorespiratory fitness, traditional cardiometabolic risk factors, and vascular health in individuals with spinal cord injury (SCI). METHODS: Seventeen male and female adults with chronic (> 1 yr) motor-complete and incomplete SCI (level of injury: C4-L3) were randomized to control (CON, n = 9) or exercise (UBROW, n = 8). Participants in UBROW performed 12-week, 3 weekly sessions of 30-min upper-body ergometer rowing exercise, complying with current exercise guidelines for SCI. Cardiorespiratory fitness ([Formula: see text]O2peak), traditional risk factors (lipid profile, glycemic control) as well as inflammatory and vascular endothelium-derived biomarkers (derived from fasting blood samples) were measured before and after 6 (6W) and 12 weeks (12W). Brachial artery resting diameter and flow-mediated dilation (FMD) were determined by ultrasound as exploratory outcomes. RESULTS: UBROW increased [Formula: see text]O2peak from baseline (15.1 ± 5.1 mL/kg/min; mean ± SD) to 6W (16.5 ± 5.3; P < 0.01) and 12W (17.5 ± 6.1; P < 0.01). UBROW increased resting brachial artery diameter from baseline (4.80 ± 0.72 mm) to 12W (5.08 ± 0.91; P < 0.01), with no changes at 6W (4.96 ± 0.91), and no changes in CON. There were no significant time-by-group interactions in traditional cardiometabolic blood biomarkers, or in unadjusted or baseline diameter corrected FMD. Explorative analyses revealed inverse correlations between changes (∆12W-baseline) in endothelin-1 and changes in resting diameter (r = - 0.56) and FMD% (r = - 0.60), both P < 0.05. CONCLUSION: These results demonstrate that 12 weeks of upper-body rowing complying with current exercise guidelines for SCI improves cardiorespiratory fitness and increases resting brachial artery diameter. In contrast, the exercise intervention had no or only modest effects on traditional cardiometabolic risk factors. The study was registered at Clinicaltrials.gov (N-20190053, May 15, 2020).

Physical Activity Barriers in Danish Manual Wheelchair Users: A Cross-sectional Study.

OBJECTIVE: To identify physical activity barrier prevalence and severity among manual wheelchair users (MWCUs) and test whether barrier impact is associated with self-reported physical activity level (PAL). DESIGN: Cross-sectional survey. The Barriers to Physical Activity Questionnaire for People with Mobility Impairments (BPAQ-MI) was translated from English to Danish and administered online. The BPAQ-MI includes barriers within 4 domains and 8 subdomains and queries if an item hindered physical activity participation in the last 3 months (yes/no). If "yes," participants graded barrier severity from very small (1) to very big (5). Barrier impact scores were summed within and across domains. SETTING: General community. PARTICIPANTS: Danish MWCUs (N=181; 52.5% female, mean age, 48±14y.). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: PAL was rated from not active (1) to extremely active (10). Individual barrier prevalence (frequency, %) and severity (median [interquartile range]) was computed. Unadjusted (Spearman rank correlations, domains, subdomains) and adjusted (multivariate linear regression, subdomains) associations between PAL and barrier impact were computed. RESULTS: The 5 most prevalent barriers were reported by ≥49.6% of participants (2 intrapersonal and 3 community). The 5 most severe barriers all had a median of 5 (1 organizational and 4 community). Unadjusted analysis showed that PAL was inversely associated with total intrapersonal (r=-0.487, P<.01) and overall (r=-0.241, P<.01) impact and the intrapersonal "health" (r=-0.477, P<.01) and "beliefs/attitudes"(r=-0.307, P<.01) subdomains. Adjustment for shared variance revealed only the "health" subdomain impact score was independently associated with PAL (P<.001). CONCLUSIONS: Intrapersonal barriers were highly prevalent. Health-related barriers were inversely related to PAL. When organizational and community barriers were present, they were rated as particularly severe. These results provide novel information that can guide the design of future interventions aiming to increase MWCUs PALs.

Physical-work ability and chronic musculoskeletal complaints are related to leisure-time physical activity: Cross-sectional study among manual workers aged 50-70 years.

AIMS: To investigate the associations between both high- and low-intensity leisure-time physical activity on physical-work ability and chronic musculoskeletal complaints among manual workers aged 50-70 years. METHODS: In this cross-sectional study, 1763 manual workers (mean age 57.1, SD ± 4.7 years) replied to questions about leisure-time physical activity, physical-work ability, chronic musculoskeletal complaints as well as health and lifestyle factors. Ordinal and binomial logistic regression models were constructed to assess the influence of the duration of both low- and high-intensity physical activity on physical-work ability and chronic musculoskeletal complaints, respectively. Models were adjusted for gender, age, smoking, alcohol intake, body mass index, physical-work demand, work experience, chronic disease and, regarding physical-work ability, also for chronic musculoskeletal complaints. RESULTS: A statistically significant association between greater physical-work ability and high-intensity physical activity was found for workers engaged in 3-4 h/wk and ⩾ 5 h/wk (OR 1.59, 95% CI 1.15-2.19 and OR 1.56, 95% CI 1.10-2.22, respectively). For both high- and low-intensity physical activity, a duration of 3-4 h/wk was associated with lower odds of reporting chronic musculoskeletal complaints in the knees (OR 0.65, 95% CI 0.42-1.00 and OR 0.61, 95% CI 0.38-0.99, respectively). CONCLUSIONS: Engaging in ⩾ 3 h/wk of high-intensity leisure-time physical activity was associated with greater physical-work ability among manual workers aged 50-70 years. Both high- and low-intensity physical activity related to lower odds of having chronic musculoskeletal complaints in the knees.

Later stages of diabetic neuropathy affect the complexity of the neuromuscular system at the knee during low-level isometric contractions.

INTRODUCTION: This study evaluates the complexity of force and surface electromyography (sEMG) during knee extension and flexion at low-level isometric contractions in individuals with different degrees of diabetic peripheral neuropathy (DPN). METHODS: Ten control and 38 diabetic participants performed isometric contractions at 10%, 20%, and 30% of maximal voluntary contraction. Knee force and multichannel sEMG from vastus lateralis (VL) and biceps femoris were acquired. The SD of force and sample entropy (SaEn) of both force and sEMG were computed. RESULTS: Participants with moderate DPN demonstrated high force-SD and low force-SaEn. Severely affected participants showed low SaEn in VL at all force levels. DISCUSSION: DPN affects the complexity of the neuromuscular system at the knee for the extension task during low-level isometric contractions, with participants in the later stages of the disease (moderate and severe) demonstrating most of the changes. Muscle Nerve 57: 112-121, 2018.

Effects of a Participatory Ergonomics Intervention With Wearable Technical Measurements of Physical Workload in the Construction Industry: Cluster Randomized Controlled Trial.

BACKGROUND: Construction work frequently involves heavy physical work, and a reduction of the physical workload should have high priority. Technological development has made it possible to obtain field measurements with surface electromyography (sEMG), kinematics measured with inertial measurement units (IMUs), and video recordings. However, no studies have used these methods simultaneously to detect situations with excessive physical workload (events) during a working day. Thus, knowledge about these specific events may combat work-related risk factors. Participatory ergonomics (PE) has shown promising results, but whether it can be used as a tool to reduce the physical workload during construction work remains unknown. OBJECTIVE: This cluster randomized controlled trial investigated whether a PE intervention with technical measurements consisting of IMUs, sEMG, heart rate monitoring, and video recordings of physical workload could reduce the number of events with excessive physical workload during a working day. Furthermore, other outcomes were obtained from questionnaires. METHODS: A total of 80 male full-time construction workers (aged 19 to 67 years) were randomized at the cluster level (gang) to a PE intervention consisting of 3 workshops (7 gangs and 32 workers) or to a control group (8 gangs and 48 workers). The physical workload was recorded by technical measurements, that is, IMUs, sEMG, heart rate monitoring, and video recordings during a full working day at baseline and 3 and 6 months' follow-up. On the basis of the technical measurements, a custom-made computer program detected the situations (events) where the construction workers were exposed to excessive physical workload and used in the intervention. Differences in the number of events from baseline to follow-up between intervention and control were evaluated using linear mixed models (intention-to-treat), with individual nested in cluster as a random factor. Furthermore, questionnaires were filled out on test days. RESULTS: The results of the primary outcome showed no change in the number of events with excessive physical workload. However, compared with the control group, the other outcomes showed decreased general fatigue after a typical working day (P=.001) and increased influence on own work (P=.04). CONCLUSIONS: This PE intervention with technical measurements did not reduce the number of events with excessive physical workload during construction work. However, the intervention led to decreased general fatigue and increased influence on own work. TRIAL REGISTRATION: ClinicalTrials.gov NCT02498197; https://clinicaltrials.gov/ct2/show/NCT02498197 (Archived by WebCite at http://www.webcitation.org/74SZ3DIWS).

External and Internal Focus of Attention Increases Muscular Activation During Bench Press in Resistance-Trained Participants.

Kristiansen, M, Samani, A, Vuillerme, N, Madeleine, P, and Hansen, EA. External and internal focus of attention increases muscular activation during bench press in resistance-trained participants. J Strength Cond Res 32(9): 2442-2451, 2018-Research on the effects of instructed attentional focus during execution of strength training exercises is limited and has thus far only been performed on single-joint exercises. The aim of this study was to compare the effects of instructed internal (INT) and external (EXT) focus of attention with a baseline measurement of no instructed focus of attention (BASE) on the surface electromyographic (EMG) amplitude during a free-weight bench press exercise in resistance-trained participants. Twenty-one resistance-trained male participants performed bench press at 60% of their 3-repetition maximum, with BASE, EXT, and INT. The order of EXT and INT was randomized and counterbalanced. Electromyographic data were recorded from 13 muscles of the upper and lower body. Subsequently, mean and peak EMG amplitudes were computed. EXT and INT resulted in significantly increased mean EMG amplitude of 6 upper-body muscles as compared with BASE (p ≤ 0.05). In addition, EXT and INT also resulted in increased peak EMG amplitude of 3 upper-body muscles as compared with BASE (p ≤ 0.05). These results show that muscular activation is increased during bench press, when applying an instructed focus of attention compared with a baseline measurement with no focus instructions (BASE).

Accuracy of identification of low or high risk lifting during standardised lifting situations.

The aim was to classify lifting activities into low and high risk categories (according to The Danish Working Environment Authority guidelines) based on surface electromyography (sEMG) and trunk inclination (tri-axial accelerometer) measurements. Lifting tasks with different weights, horizontal distance and technique were performed. The lifting tasks were characterised by a feature vector composed of either the 90th, 95th or 99th percentile of sEMG activity level and trunk inclinations during the task. Linear Discriminant Analysis and a subject-specific threshold scheme were applied and lifting tasks were classified with an accuracy of 65.1-65.5%. When lifts were classified based on the subject-specific threshold scheme from low and upper back accelerometers, the accuracy reached 52.1-58.1% and 72.7-78.1%, respectively. In conclusion, the use of subject-specific thresholds from sEMG from upper trapezius and erector spinae as well as inclination of the upper trunk enabled us to identify low and high risk lifts with an acceptable accuracy. Practitioner Summary: This study contributes to the development of a method enabling the automatic detection of high risk lifting tasks, i.e. exposure to high biomechanical loads, based on individual sEMG and kinematics from an entire working day. These methods may be more cost-effective and may complement observations commonly used by practitioners.

Variability in spatio-temporal pattern of trapezius activity and coordination of hand-arm muscles during a sustained repetitive dynamic task.

The spatio-temporal distribution of muscle activity has been suggested to be a determinant of fatigue development. Pursuing this hypothesis, we investigated the pattern of muscular activity in the shoulder and arm during a repetitive dynamic task performed until participants' rating of perceived exertion reached 8 on Borg's CR-10 scale. We collected high-density surface electromyogram (HD-EMG) over the upper trapezius, as well as bipolar EMG from biceps brachii, triceps brachii, deltoideus anterior, serratus anterior, upper and lower trapezius from 21 healthy women. Root-mean-square (RMS) and mean power frequency (MNF) were calculated for all EMG signals. The barycenter of RMS values over the HD-EMG grid was also determined, as well as normalized mutual information (NMI) for each pair of muscles. Cycle-to-cycle variability of these metrics was also assessed. With time, EMG RMS increased for most of the muscles, and MNF decreased. Trapezius activity became higher on the lateral side than on the medial side of the HD-EMG grid and the barycenter moved in a lateral direction. NMI between muscle pairs increased with time while its variability decreased. The variability of the metrics during the initial 10 % of task performance was not associated with the time to task termination. Our results suggest that the considerable variability in force and posture contained in the dynamic task per se masks any possible effects of differences between subjects in initial motor variability on the rate of fatigue development.

Inter-day reliability of surface electromyography recordings of the lumbar part of erector spinae longissimus and trapezius descendens during box lifting.

BACKGROUND: Low back pain and neck-shoulder pain are the most reported types of work-related musculoskeletal disorders, and performing heavy lifting at work and working with trunk rotation increase the risk of developing work-related musculoskeletal disorders. Surface electromyography (sEMG) provides information about the electrical activity of muscles. Thus it has the potential to retrieve indirect information about the physical exposure of specific muscles of workers during their actual work. This study aimed to investigate the inter-day reliability of absolute and normalized amplitude of sEMG measurements obtained during repeated standardized reference lifts. METHODS: The inter-day reliability of sEMG of the erector spinae longissimus and trapezius descendens muscles was tested during standardized box lifts. The lifts were performed with loads of 3, 15 and 30 kg from floor to table and from table to table in three conditions, i.e., forearm length (short reaching distance), ¾ arm length (long reaching distance) and forearm length with trunk rotation. Absolute and normalized root mean square (absRMS and normRMS) values were extracted. In line with the guidelines for reporting reliability and agreement studies, we reported relative and absolute reliability estimated by intra class correlation (ICC3,K), standard error of measurement (SEM) and minimal detectable change in percent (MDC). RESULTS: The ICC3,K was higher for absRMS compared with normRMS while SEM and maximal voluntary contraction (MVC) were similar. A total of 50 out of 56, i.e., 89%, and 41 out of 56, i.e., 73%, of the lifting situations were in the range from moderate to almost perfect for absRMS and normRMS, respectively. The SEM and MDC shoved more variation in the lifting situations performed from floor to table and in the trapezius descendens muscle than in the erector spinae longissimus muscle. CONCLUSION: This reliability study showed that maximum absRMS and normRMS were found to have a fair to substantial relative inter-day reliability for most lifts but were more reliable when lifting from table to table than from floor to table for both trapezius descendens and erector spinae muscles. The relative inter-day reliability was higher for absolute compared with normalized sEMG amplitudes while the absolute reliability was similar.

Integration of active pauses and pattern of muscular activity during computer work.

Submaximal isometric muscle contractions have been reported to increase variability of muscle activation during computer work; however, other types of active contractions may be more beneficial. Our objective was to determine which type of active pause vs. rest is more efficient in changing muscle activity pattern during a computer task. Asymptomatic regular computer users performed a standardised 20-min computer task four times, integrating a different type of pause: sub-maximal isometric contraction, dynamic contraction, postural exercise and rest. Surface electromyographic (SEMG) activity was recorded bilaterally from five neck/shoulder muscles. Root-mean-square decreased with isometric pauses in the cervical paraspinals, upper trapezius and middle trapezius, whereas it increased with rest. Variability in the pattern of muscular activity was not affected by any type of pause. Overall, no detrimental effects on the level of SEMG during active pauses were found suggesting that they could be implemented without a cost on activation level or variability. Practitioner Summary: We aimed to determine which type of active pause vs. rest is best in changing muscle activity pattern during a computer task. Asymptomatic computer users performed a standardised computer task integrating different types of pauses. Muscle activation decreased with isometric pauses in neck/shoulder muscles, suggesting their implementation during computer work.

Interface Pressure Behavior During Painful Cuff Algometry.

OBJECTIVE: Cuff algometry is used for the psychophysical assessment of deep-tissue pain sensitivity. The cuff pressure homogeneity may affect the pain sensitivity assessment and potentially be improved by alternative cuff designs optimizing the pressure distribution. The aim of this study was to investigate the relationship between pain sensitivity, inflation pressure, and distribution of interface pressure between the skin and cuff during stimulation with a conventional air tourniquet and a novel tourniquet including a water tube interfacing the air cuff with the skin. METHODS: Air and water cuff stimulations were applied separately on the right lower leg of 12 subjects until the tolerance pain threshold. The inflation pressure was controlled and recorded by a computer-control program, while the interface pressure distribution was measured by a flexible pressure sensor mat located between the cuff and skin. RESULTS: The mean interface pressure across the entire stimulation surface was not significantly different from inflating pressure during air-cuff algometry. For the water cuff there was a significant reduction in the mean interface pressure compared with the inflating pressure at both the detection and tolerance pain levels (P < 0.002). The interface pressure distribution of the water cuff around the limb was significantly more homogeneous compared with the air cuff (P < 0.03). This homogeneity showed a significant correlation with pain sensitivity (P < 0.008). CONCLUSION: Cuff systems with a liquid medium optimize the homogeneity of the interface pressure distribution. However, the deviation of the interface pressure from the inflating pressure is crucial as it counteracts the effects of pressure homogeneity on pain sensitivity in water-cuff algometry.

Effects of concurrent physical and cognitive demands on muscle activity and heart rate variability in a repetitive upper-extremity precision task.

PURPOSE: Most previous studies of concurrent physical and cognitive demands have addressed tasks of limited relevance to occupational work, and with dissociated physical and cognitive task components. This study investigated effects on muscle activity and heart rate variability of executing a repetitive occupational task with an added cognitive demand integral to correct task performance. METHODS: Thirty-five healthy females performed 7.5 min of standardized repetitive pipetting work in a baseline condition and a concurrent cognitive condition involving a complex instruction for correct performance. Average levels and variabilities of electromyographic activities in the upper trapezius and extensor carpi radialis (ECR) muscles were compared between these two conditions. Heart rate and heart rate variability were also assessed to measure autonomic nervous system activation. Subjects also rated perceived fatigue in the neck-shoulder region, as well as exertion. RESULTS: Concurrent cognitive demands increased trapezius muscle activity from 8.2% of maximum voluntary exertion (MVE) in baseline to 9.0% MVE (p = 0.0005), but did not significantly affect ECR muscle activity, heart rate, heart rate variability, perceived fatigue or exertion. CONCLUSION: Trapezius muscle activity increased by about 10%, without any accompanying cardiovascular response to indicate increased sympathetic activation. We suggest this slight increase in trapezius muscle activity to be due to changed muscle activation patterns within or among shoulder muscles. The results suggest that it may be possible to introduce modest cognitive demands necessary for correct performance in repetitive precision work without any major physiological effects, at least in the short term.

Effects of 5 Weeks of Bench Press Training on Muscle Synergies: A Randomized Controlled Study.

Kristiansen, M, Samani, A, Madeleine, P, and Hansen, EA. Effects of 5 weeks of bench press training on muscle synergies: A randomized controlled study. J Strength Cond Res 30(7): 1948-1959, 2016-The ability to perform forceful muscle contractions has important implications in sports performance and in activities of daily living. However, there is a lack of knowledge on adaptations in intermuscular coordination after strength training. The purpose of this study was therefore to assess muscle synergies before and after 5 weeks of bench press training. Thirty untrained male subjects were randomly allocated to a training group (TRA) or a control group (CON). After the pretest, TRA completed 5 weeks of bench press training, before completing a posttest, whereas subjects in CON continued their normal life. During test sessions, surface electromyography (EMG) was recorded from 13 different muscles. Muscle synergies were extracted from EMG data using nonnegative matrix factorization. To evaluate differences between pretest and posttest, we performed a cross-correlation analysis and a cross-validation analysis, in which the synergy components extracted in the pretest session were recomputed, using the fixed synergy components from the posttest session. Two muscle synergies accounted for 90% of the total variance and reflected the concentric and eccentric phase, respectively. TRA significantly increased 3 repetition maximum in bench press with 19.0% (25th; 75th percentile, 10.3%; 21.7%) (p < 0.001), whereas no change occurred in CON. No significant differences were observed in synergy components between groups. However, decreases in correlation values for intragroup comparisons in TRA may suggest that the synergy components changed, whereas this was not the case in CON. Strength and conditioning professionals may consider monitoring changes in muscle synergies in training and rehabilitation programs as a way to benchmark changes in intermuscular coordination.

Functional connectivity between core and shoulder muscles increases during isometric endurance contractions in judo competitors.

PURPOSE: The aim of this study was to assess the surface electromyogram (SEMG) changes within and between muscles of the torso and shoulder region during static endurance contraction in elite judokas. We hypothesized an increased functional connectivity of muscles from the shoulder and torso regions during sustained isometric contraction. METHODS: Twelve healthy, right-handed judo competitors participated in the study. The SEMG signals from the dominant trapezius (upper, middle and lower part), deltoideus anterior, serratus anterior, and pectoralis major muscles were recorded during isometric endurance contraction consisting of bilateral arm abduction at 90°. The normalized mutual information (NMI) was computed between muscle pairs as an index indicating functional connectivity. RESULTS: The NMIs increased significantly during endurance test for 10 of the 15 muscle pairs (P < 0.001). CONCLUSION: We concluded that the increases in NMIs highlighted functional changes in the interplay between core and shoulder muscles during an endurance contraction in elite judokas.

Ipsilateral resistance exercise prevents exercise-induced central sensitization in the contralateral limb: a randomized controlled trial.

PURPOSE: This study aimed to investigate the hypothesis that a repeated bout of eccentric exercise (ECC2) would result in smaller increase in the sensitivity of spinal nociceptive system, and smaller decrease in the local muscle blood oxygenation response in both the ipsilateral and the contralateral tibialis anterior muscle (TA) when compared with the initial bout (ECC1). It was hypothesized that the magnitude of the repeated bout effect (RBE) would be greater for the ipsilateral side than the contralateral side. METHODS: Twenty-six healthy young men performed two bouts of high-intensity eccentric exercise of TA separated by 2 weeks. Half of the participants used the same leg for both bouts (IPSI) and the other half used the contralateral leg for ECC2 (CONTRA). Nociceptive withdrawal reflex threshold (NWRT) and local muscle blood oxygenation were assessed for the exercised TA muscle before, immediately after, and one day after exercise. RESULTS: Significant decreases in NWRT and muscle oxygenation were observed after ECC1 (p < 0.05), but NWRT did not change after ECC2 in both groups. Smaller decreases in muscle oxygenation were observed after ECC2 than ECC1 in both groups with a similar magnitude of the difference between bouts, but an increase in muscle oxygen re-perfusion before ECC2 was only observed in the IPSI group. CONCLUSION: These results suggest that contralateral RBE was associated with spinal facilitation of the neuronal pathways situated at a homologous innervation level, and it is unlikely that oxygen re-perfusion improvement plays a major role in the contralateral RBE.

Participatory intervention with objectively measured physical risk factors for musculoskeletal disorders in the construction industry: study protocol for a cluster randomized controlled trial.

BACKGROUND: There is high prevalence of back pain and neck-shoulder pain among blue collar workers in Denmark. Excessive physical exposures such as heavy lifting or working with bended or twisted back are risk factors for back pain among workers in the construction industry. Technical evaluation of awkward postures and kinematics of upper/ lower extremities (accelerometry) during work combined with the level of muscular activity (EMG) and video recordings can improve quantification of physical exposure and thereby can facilitate designing preventive strategies. Participatory ergonomics potentially increase the success of interventions aimed at reducing excessive physical exposures. The objectives of this study are to; 1) determine which work-tasks in selected job-groups involve excessive physical load of the back and shoulders during a normal working day (measured with accelerometers, EMG and video recordings). And 2) investigate whether a participatory intervention can reduce the excessive physical workloads, drawing on measurements from phase 1. METHODS/DESIGN: A two-armed parallel-group, single-blind, cluster randomized controlled trial with allocation concealment will be conducted in the Danish construction industry. Approximately 20 construction gangs (≈ 80 subjects) will be recruited and randomized at the cluster level (gang). We will record in situ physical workload using technical measurements (EMG, accelerometers and video recordings) during a working day before and after the intervention. Based on these measurements a physical load matrix for each worker will be developed. The participatory intervention consist of three workshops: 1) One at baseline, involving presentation of video clips of the work-tasks with excessive physical load customized for each gang, followed by a participatory development of solutions on how to reduce excessive workloads, leading to development of an action plan on how to implement these solutions at the workplace. 2) A second workshop where the implemented solutions will be further developed and qualitatively evaluated during group discussions. 3) A final workshop at follow-up to enhance long-time organizational sustainability of the implemented solutions. DISCUSSION: The results will provide knowledge about the level of physical exposure of the back and shoulders during specific work tasks in the construction industry, and will provide information on options to implement participatory interventions aiming at reducing excessive physical workload. TRIAL REGISTRATION: ClinicalTrials.gov (NCT02498197), registered 29 June 2015.

Adaptation of local muscle blood flow and surface electromyography to repeated bouts of eccentric exercise.

The aim of this randomized controlled crossover study was to investigate the effect of a bout of unaccustomed eccentric exercise (ECC) followed by a consecutive bout of the same intensity on local muscle blood flow, amplitude, and frequency of the electromyographic (EMG) signal from the exercised tibialis anterior muscle. Sixteen healthy male participants (age, 25.7 (0.6) years; body mass index 24.8 (1) kg·m(-2) participated in this study. Two identical bouts of high-intensity ECC were performed on the tibialis anterior muscle 7 days apart. Control sessions involving no exercise were performed 4 weeks either before or after the exercise sessions. Changes in local total blood flow [ΔtHb], EMG root mean square, and median power frequency were recorded during isometric maximum voluntary contraction of ankle dorsiflexion. Measurements were performed before, immediately after, and the day after both ECCs (ECC1 and ECC2). The participants rested quietly in a chair in the control session. Eccentric exercise 1 led to a significant decrease in [ΔtHb] on the day after (p ≤ 0.05), whereas ECC2 did not. Median power frequency decreased significantly in ECC2 compared with ECC1 (p < 0.01). Root mean square was unchanged in all the instants. The present study showed that adaptation is depicted in the local muscle blood flow and the frequency contents of the EMG after an unaccustomed ECC inducing muscle soreness. These alterations provide a potential mechanism for a rapid adaptation, which decreases susceptibility of the muscle to develop further soreness in the subsequent ECC bout.