Occupational health hazards resulting from elevated work rate situations.

Some occupational health hazards resulting from an elevated rate of work due to recent mechanization and automatization are discussed on the basis of results of health examinations. A rapid increase of a cervicobrachial disorder among young cash register and packing machine operators has been observed. Switching to the use of electronic cash registers has been shown to have only limited efficacy due to increased operation speed, and high-speed complex finger and hand movements of packer operators have also proven to be as hazardous as key-board operations. The high incidence of low-back pain, in particular gradually developing pain, among workers in electric power supply work has been suggested to be the result of quick and intensified work to meet increasing supply demand. Likewise, the workload of electric locomotive and bullet train drivers has increased in accordance with increased train speeds, and has been shown to have had significant effects on their health particularly in regards to neural strain, intra-cab environment such as air pressure change, vibration, and noise, and rotation on irregular shifts. New steps seem required therefore to meet the new health problems arising from a combination of modern technological changes and elevated working speeds.     

Shoulder muscle load and muscle fatigue among industrial sewing-machine operators

Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMG_max), while the average mean load was 15% EMG_max, and the average peak load was 23% EMG_max. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during. the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.     

Threshold of Musculoskeletal Pain Intensity for Increased Risk of Long-Term Sickness Absence among Female Healthcare Workers in Eldercare

Purpose

Musculoskeletal disorders increase the risk for absenteeism and work disability. However, the threshold when musculoskeletal pain intensity significantly increases the risk of sickness absence among different occupations is unknown. This study estimates the risk for long-term sickness absence (LTSA) from different pain intensities in the low back, neck/shoulder and knees among female healthcare workers in eldercare.

Methods

Prospective cohort study among 8,732 Danish female healthcare workers responding to a questionnaire in 2004–2005, and subsequently followed for one year in a national register of social transfer payments (DREAM). Using Cox regression hazard ratio (HR) analysis we modeled risk estimates of pain intensities on a scale from 0–9 (reference 0, where 0 is no pain and 9 is worst imaginable pain) in the low back, neck/shoulders and knees during the last three months for onset of LTSA (receiving sickness absence compensation for at least eight consecutive weeks) during one-year follow-up.

Results

During follow-up, the 12-month prevalence of LTSA was 6.3%. With adjustment for age, BMI, smoking and leisure physical activity, the thresholds of pain intensities significantly increasing risk of LTSA for the low back (HR 1.44 [95%CI 1.07–1.93]), neck/shoulders (HR 1.47 [95%CI 1.10–1.96]) and knees (HR 1.43 [95%CI 1.06–1.93]) were 5, 4 and 3 (scale 0–9), respectively, referencing pain intensity of 0.

Conclusion

The threshold of pain intensity significantly increasing the risk for LTSA among female healthcare workers varies across body regions, with knee pain having the lowest threshold. This knowledge may be used in the prevention of LTSA among health care workers.     

Musculoskeletal discomfort and feeling of fatigue among female professional workers: the need for ergonomics consideration.

Subjective feeling of general fatigue and physiological strain were studied in one hundred female professional employees of industrial worker and full-time nurses. Using an interview questionnaire the feeling of fatigue were studied. The subjects were asked to indicate on the body diagram all the areas of musculoskeletal pain from which they perceived discomfort. Furthermore physical strength test consisting of grip test, back and leg strength test were carried out before and after work on all subjects. The results indicated that the two groups of employees showed different symptoms of "pain" and/or "fatigue," with regard to the different parts of body. It was also noted that the physical strength after work was lower for both groups as compared to before work and even lower for the industrial workers than the nurses. The feeling of fatigue between the two investigated groups was not significantly different, but for the musculoskeletal pain was highly significantly different. The worker group used also more pain-killing drugs for releasing the muscle pain. It was evident that ergonomics intervention for female professional workers was of great importance and urgency, particularly for making the workplace more human. Improvement of the working conditions, better organization of work, and ergonomics interventions are suggested as necessary measures for reduction of pain and feeling of discomfort.     

Early warning signs of an acute myocardial infarction and their influence on symptoms during the acute phase,with comparisons by gender

Background: Identifying early warning signs of an acute myocardial infarction (AMI) may aid in the early diagnosis of coronary artery disease.Objectives: This study was conducted to assess early warning signs (prodromal symptoms) of AMI, with comparisons made by gender. Another aim was to determine whether these early warning signs had any influence on the patients' acute symptoms of AMI.Methods: This was a multicenter, cross-sectional study of Norwegian patients (aged ≤75 years) hospitalized with their first AMI. A self-administered questionnaire was used to gather information on prodromal symptoms, defined as pain in the chest, pain in the shoulder or back, radiating pain or numbness in the arms, dyspnea, and fatigue. Symptoms were reported for the year before AMI and during the acute stage. Logistic regression analyses were used to examine the association between prodromal symptoms and acute symptoms and the effect of medical history (hypertension, diabetes, and hypercholesterolemia).Results: The self-administered questionnaire had a 72% response rate; the study included 149 women and 384 men diagnosed with first-time AMI. Symptoms occurring during the year before AMI included pain in the chest in 45% (240/533), shoulder or back pain in 51% (270/533), arm pain in 38% (205/533), dyspnea in 33% (176/533), and fatigue in 62% (330/533). There were no statistically significant gender differences. The risk of experiencing chest symptoms in the acute phase was >5 times higher in women who had experienced prodromal symptoms in the chest (adjusted odds ratio [OR] = 5.11; 95% CI, 1.38-18.88) and nearly 3 times higher in men (OR = 2.80; 95% CI, 1.17–6.70). The risk of experiencing shoulder or back pain was almost 5 times higher in men with prodromal shoulder or back pain (OR = 4.96; 95% CI, 3.01–8.19), but no statistically significant association was found in women. The risk of experiencing radiating arm pain or numbness in the acute phase was more than doubled in women with prodromal arm pain (OR = 2.68; 95% CI, 1.19–6.20) and more than tripled in men with prodromal arm pain (OR = 3.11; 95% CI, 1.90–5.07). The risk of experiencing dyspnea in the acute phase was more than doubled in women with prodromal dyspnea (OR = 2.67; 95% CI, 1.25–5.71) and >5 times higher in men with prodromal dyspnea (OR = 5.73; 95% CI, 3.42–9.62). Finally, the risk of fatigue was almost tripled in women (OR = 2.97; 95% CI, 1.28–6.85) and more than doubled in men (OR = 2.51; 95% CI, 1.54–4.11). Hypertensive women, but not men, were less likely to experience chest symptoms in the acute phase (OR = 0.29; 95% CI, 0.10–0.82).Conclusions: Almost half of the study patients (45%) experienced prodromal chest symptoms the year before their first AMI. These prodromal symptoms predicted the symptoms that occurred during the acute stage of AMI, with some differences between the sexes.     

A hip abduction exercise prior to prolonged standing increased movement while reducing cocontraction and low back pain perception in those initially reporting low back pain

Persons who develop low back pain from prolonged standing exhibit increased muscle cocontraction, decreased movement and increased spine extension. However, it is unclear how these factors relate to pain development. The purpose of this study was to use hip abductor fatigue to manipulate muscle activity patterns and determine its effects on standing behaviours and pain development. Forty participants stood for two hours twice, once following a hip abductor fatigue exercise (fatigue), and once without exercise beforehand (control). Trunk and gluteal muscle activity were measured to determine cocontraction. Lumbo-pelvic angles and force plates were used to assess posture and movement strategies. Visual analog scales differentiated pain (PDs) and non-pain developers (NPDs). PDs reported less low back pain during the fatigue session, with females having earlier reductions of similar scale than males. The fatigue session reduced gluteal and trunk cocontraction and increased centre of pressure movement; male and female PDs had opposing spine posture compensations. Muscle fatigue prior to standing reduced cocontraction, increased movement during standing and reduced the low back pain developed by PDs; the timing of pain reductions depended on spine postures adopted during standing.     

The effect of tactile and verbal guidance during scapulothoracic exercises: An EMG and kinematic investigation

BackgroundClinician-led training through tactile and verbal guidance to improve muscle activity and joint motion are a common but understudied focus of therapeutic interventions for shoulder pain. The purpose of this study was to determine if clinician guidance changes scapulothoracic muscle activity and kinematics compared to unguided shoulder exercises.MethodsEleven participants with shoulder pain were studied. Electromyographic (EMG) sensors were placed on the serratus anterior and upper and lower trapezii. Scapulothoracic and sternoclavicular kinematics were collected using electromagnetic sensors. Five common resisted shoulder exercises were performed with the following guidance: unguided, combined (verbal and tactile cues), and verbal guidance only. One-way repeated measures ANOVAs determined the effect of guidance versus unguided conditions for each exercise.ResultsNine of ten combinations of exercise and guidance techniques demonstrated a significant effect of guidance for either muscle activity or joint kinematics. The guidance condition with the most frequent significant improvements across all variables was the combined condition. The exercises with the most frequent significant improvements across all variables were the external rotation exercises. Variables improved most frequently were: upper:lower trapezius EMG ratio (up to 11%), sternoclavicular elevation (up to 6°) and scapulothoracic internal rotation positioning (up to 8°), and sternoclavicular retraction displacement (up to 5°).ConclusionShoulder muscle activity and kinematics during exercises can be modified by tactile and verbal guidance. Most improvements in muscle activity occurred with verbal guidance during external rotation exercises. Most improvements in joint positioning and movement occurred with combined guidance during external rotation exercises.     

Upper extremity kinematic and kinetic adaptations during a fatiguing repetitive task

Repetitive low-force contractions are common in the workplace and yet can lead to muscle fatigue and work-related musculoskeletal disorders. The current study aimed to investigate potential motion adaptations during a simulated repetitive light assembly work task designed to fatigue the shoulder region, focusing on changes over time and age-related group differences. Ten younger and ten older participants performed four 20-min task sessions separated by short breaks. Mean and variability of joint angles and scapular elevation, joint net moments for the shoulder, elbow, and wrist were calculated from upper extremity kinematics recorded by a motion tracking system. Results showed that joint angle and joint torque decreased across sessions and across multiple joints and segments. Increased kinematic variability over time was observed in the shoulder joint; however, decreased kinematic variability over time was seen in the more distal part of the upper limb. The changes of motion adaptations were sensitive to the task-break schedule. The results suggested that kinematic and kinetic adaptations occurred to reduce the biomechanical loading on the fatigued shoulder region. In addition, the kinematic and kinetic responses at the elbow and wrist joints also changed, possibly to compensate for the increased variability caused by the shoulder joint while still maintaining task requirements. These motion strategies in responses to muscle fatigue were similar between two age groups although the older group showed more effort in adaptation than the younger in terms of magnitude and affected body parts.     

Working hours and fatigue of Japanese flight attendants (FA).

There have been some reports concerning high complaint rates of fatigue or fatigue-related symptoms including lower back pain in flight attendants (FA). Thus, the relations of working conditions with work stress and fatigue symptoms were studied chiefly by focusing on working hours. From analysis of the time-table and fatigue symptoms of workers on international flights, it was suspected that there were some work-related factors jointly causing serious FA fatigue symptoms; night time and early morning work, long flight hours and a large time difference, thus disturbing their biological rhythms. On domestic flights, showing up early in the morning and debriefing late in the night were often observed together with a highly irregular FA time schedule. By statistical analyses, some factors including long working hours, frequent landing and late debriefing hours were considered to contribute significantly to the high fatigue complaint rates. Thus, it should be emphasized that many countermeasures are necessary to improve FA working conditions including working hours, rest on the airplane (ONO et al., 1990) and sleep during layover, in order to reduce their work stress and fatigue symptoms.     

EMG scanning in the diagnosis of chronic pain

A surface EMG diagnostic protocol was developed to assess the neuromuscular/postural contributions to pain states. The EMG activity of the right and left aspects of 11 muscle groups were monitored while the patient was in the sitting and standing positions. The diagnostic protocol was evaluated by comparing the patterns of EMG activity in four diagnostic groups: headache only, neck/shoulder/upper back pain only, low back pain only, and mixed pain states. The results suggest that (1) bilateral levels of EMG activity in the frontalis and masseter groups are of primary importance for the headache patients, (2) the discrepancy between the right and left EMG activity in the lumbar and cervical paraspinal muscle groups are of primary importance for low back pain patients, (3) position (sit/stand) may provide important diagnostic information, and (4) the data appear to support the notion of a postural disturbance as a contributing factor in low back pain.     

Changes in EMG activity in the upper trapezius muscle due to local vibration exposure

Exposure to vibration is suggested as a risk factor for developing neck and shoulder disorders in working life. Mechanical vibration applied to a muscle belly or a tendon can elicit a reflex muscle contraction, also called tonic vibration reflex, but the mechanisms behind how vibration could cause musculoskeletal disorders has not yet been described. One suggestion has been that the vibration causes muscular fatigue. This study investigates whether vibration exposure changes the development of muscular fatigue in the trapezius muscle. Thirty-seven volunteers (men and women) performed a sub-maximal isometric shoulder elevation for 3 min. This was repeated four times, two times with induced vibration and two times without. Muscle activity was measured before and after each 3-min period to look at changes in the electromyography parameters. The result showed a significantly smaller mean frequency decrease when performing the shoulder elevation with vibration (?2.51 Hz) compared to without vibration (?4.04 Hz). There was also a slightly higher increase in the root mean square when exposed to vibration (5.7% of maximal voluntary contraction) compared to without (3.8% of maximal voluntary contraction); however, this was not statistically significant. The results of the present study indicate that short-time exposure to vibration has no negative acute effects on the fatiguing of upper trapezius muscle.     

Quantitative Estimation of Muscle Shear Elastic Modulus of the Upper Trapezius with Supersonic Shear Imaging during Arm Positioning

Pain and tenderness of the upper trapezius are the major complaints among people with chronic neck and shoulder disorders. Hyper-activation and increased muscle tension of the upper trapezius during arm elevation will cause imbalance of the scapular muscle force and contribute to neck and shoulder disorders. Assessing the elasticity of the upper trapezius in different arm positions is therefore important for identifying people at risk so as to give preventive programmes or for monitoring the effectiveness of the intervention programmes for these disorders. This study aimed to establish the reliability of supersonic shear imaging (SSI) in quantifying upper trapezius elasticity/shear elastic modulus and its ability to measure the modulation of muscle elasticity during arm elevation. Twenty-eight healthy adults (15 males, 13 females; mean age = 29.6 years) were recruited to participate in the study. In each participant, the shear elastic modulus of the upper trapezius while the arm was at rest and at 30° abduction was measured by two operators and twice by operator 1 with a time interval between the measurements. The results showed excellent within- and between-session intra-operator (ICC = 0.87–0.97) and inter-observer (ICC = 0.78–0.83) reliability for the upper trapezius elasticity with the arm at rest and at 30° abduction. An increase of 55.23% of shear elastic modulus from resting to 30° abduction was observed. Our findings demonstrate the possibilities for using SSI to quantify muscle elasticity and its potential role in delineating the modulation of upper trapezius elasticity, which is essential for future studies to compare the differences in shear elastic modulus between normal elasticity and that of individuals with neck and shoulder disorders.     

EMG median frequency changes in the neck–shoulder stabilizers of symptomatic office workers when challenged by different physical stressors

The problem of work-related neck and upper limb disorders among computer users has been reported extensively in the literature, and commonly cited risk factors include static posture, speed and force of keyboard operation. The present study examined changes in median frequency (MF) of the neck–shoulder muscles in symptomatic and asymptomatic office workers when they were exposed to these three physical stressors.

A quasi-experimental Case–Control design was used to examine MF changes in two groups of female office workers when they were subjected to controlled doses of computer work involving prolonged static posture, increased typing speed and increased typing force. The MF of four major neck–shoulder muscles were examined bilaterally and compared between groups.

The MF changes over time-at-task did not clearly illustrate any muscle fatigue mechanism. However, Case Group consistently showed trends for higher MF than the Control Group, and this pattern was observed in response to all three physical stressors. The consistent group differences in MF suggest different muscle recruitment strategies between symptomatic and asymptomatic office workers. These results implied that symptomatic individuals had altered motor control, which may have important implications in understanding the etiology of work-related musculoskeletal disorders.     

Sex-specific myoelectric manifestations of localized fatigue during a multi-joint repetitive task

We have previously demonstrated that fatigue at different locations impacts joint angles, angular variability, and coordination variability differently. However, the neuromuscular control aspects underlying these kinematic changes have never been demonstrated. Seventeen young adults (8 males) were recruited. Electromyographic electrodes were placed on: upper trapezius, pectoralis major, anterior and middle deltoid, biceps and triceps brachii, and left and right erector spinae. Subjects performed the repetitive pointing task (RPT) at 1 Hz for 30 s before and after localized fatigue tasks, which consisted of one shoulder, one elbow and one lower back isometric fatiguing protocols until exhaustion in randomized order. Electromyographic amplitude (RMS), variability (SD) and mean power frequency (MnPF) were calculated for each of the pre-fatigue and post-fatigue RPT trials. There were sex × fatigue location interaction effects on upper trapezius RMS (p = 0.038) with males’ values increasing the most after shoulder fatigue. Females’ triceps brachii RMS was greater compared to males after shoulder, elbow, and trunk fatigue (p = 0.003, p = 0.001 and p = 0.007 respectively). There were sex × fatigue location effects on left erector spinae MnPF (p = 0.011) with males and females’ values decreasing the most after trunk fatigue, but more so in males. Results demonstrate that males and females compensate differently during a repetitive pointing task when their elbows, shoulders and trunks are locally fatigued, which could have implications on sex-specific workplace injury risks. See Table 1 for acronyms.     

The effect of prolonged isometric contractions on muscle fluid balance

Ultrasound scanning was performed at three sites above the fossa supraspinata on nine healthy subjects and five patients with myofascial shoulder pain. This method produced a well-defined depiction of the soft tissue layers above the fossa supraspinata and reproducible muscle thickness measurements. In the healthy subjects the average distance from the skin surface to the trapezius muscle was 7.7 mm and the average thickness of the trapezius muscle was 5.3 mm, and the average thickness of supraspinatus muscle was 20.0 mm. The supraspinatus muscle was thinner at the medial measuring site than at the other two sites. In contrast, a tendency towards a larger distance was seen from the skin to trapezius muscle at the medial measuring site than at the other two sites. No statistical differences were found between the two groups of subjects either at rest or during brief shoulder abductions. All the subjects performed a 30° unilateral isometric shoulder abduction test to exhaustion. The median endurance time was 33 min for the healthy subjects and only 5 min for the patients. The ratings of perceived exertion (RPE) were in line with this, since the increment in RPE with time was larger for the patients than for the healthy group. The reduced shoulder abduction endurance time in the patient group may have been related to impaired muscle function and/or pain development. During the 33-min shoulder abduction in the healthy subjects, the thickness of supraspinatus muscle increased by 14%, indicating muscle swelling, whereas the thickness of trapezius muscle remained constant. The fluid imbalance in the supraspinatus muscle compartment may well play a role in the development of muscle fatigue and the disorders found in industry resulting from prolonged work with arms elevated.     

A method to quantify frequency and duration of sustained low-level muscle activity as a risk factor for musculoskeletal discomfort

AimThe purpose of this paper was to describe and evaluate different aspects of muscle activity patterns associated with musculoskeletal discomfort/pain.MethodSurface electromyography (sEMG) of the right upper trapezius and the right extensor digitorum muscles was conducted continuously during one working day in 19 male forest machine operators driving harvesters, 20 driving forwarders and 20 researchers at the Forest Research Institute.Perceived discomfort/pain in the right side of the neck and the right forearm was rated morning, noon and afternoon with Borg’s CR-10 scale. Static, median and peak levels of muscle activity were analyzed and the number and total duration of EMG gaps (muscular rest) were calculated. Sustained low-level muscle activity (SULMA) was defined as continuous muscle activity above 0.5% of the maximal EMG activity quantified into 10 periods of predetermined duration intervals from 1.6 to 5 s up to above 20 min. The number of SULMA periods is presented within each interval and as cumulative periods above the already determined levels. The operators handled control levers seated in a fixed position while the researchers performed mainly PC work and other varied tasks.ResultsA positive correlation was found between discomfort/pain in the right upper trapezius muscle region in the afternoon and cumulative SULMA periods above 10 min duration, and a negative correlation to cumulative SULMA periods also including the short durations. No specified patterns were found for discomfort/pain in the right extensor digitorum or for the other EMG measurements. All EMG measurements distinguished to some extent between the occupational groups, especially between machine operators driving harvesters and researchers.ConclusionsNumber of SULMA periods longer than 10 min per hour was positively correlated, and predominantly short periods were negatively correlated, to complaints in the neck region. This seems promising in order to find duration limits for sustained low-level muscle activity as a risk factor for musculoskeletal disorders.     

A systematic review of 3D scapular kinematics and muscle activity during elevation in stroke subjects and controls

Through the onset of post-stroke motor disorders, the normal scapular function is compromised. As a result, shoulder pain and associated upper limb dysfunctions frequently arise after stroke.This review aimed to provide a systematic overview of available literature on scapular function, i.e. scapular three-dimensional (3D) kinematics and muscle activity during elevation, in healthy persons, persons with primary shoulder disorders and post-stroke patients. 3D scapular kinematics have been widely reported in healthy persons and persons with primary shoulder disorders, whereby a general pattern of upward rotation and posterior tilt during elevation has been agreed upon. Results on scapular internal/external rotation are inconsistent. In a post-stroke population, 3D scapular kinematics are less frequently reported. Scapular muscle activity has thus far been studied to very limited extend and firm conclusions could not be drawn.Although 3D scapular kinematics and muscle activity registrations are being increasingly used, some general methodological aspects should be considered. While the International Society of Biomechanics already proposed recommendations on the definition of upper limb joint coordinate systems and rotation sequences, proper result comparison necessitates further guidelines on other methodological aspects, i.e. data collection, processing, analyzing, and reporting.     

Effect of training and lifting equipment for preventing back pain in lifting and handling: systematic review

Objectives To determine whether advice and training on working techniques and lifting equipment prevent back pain in jobs that involve heavy lifting.Data sources Medline, Embase, CENTRAL, Cochrane Back Group’s specialised register, CINAHL, Nioshtic, CISdoc, Science Citation Index, and PsychLIT were searched up to September-November 2005.Review methods The primary search focused on randomised controlled trials and the secondary search on cohort studies with a concurrent control group. Interventions aimed to modify techniques for lifting and handling heavy objects or patients and including measurements for back pain, consequent disability, or sick leave as the main outcome were considered for the review. Two authors independently assessed eligibility of the studies and methodological quality of those included. For data synthesis, we summarised the results of studies comparing similar interventions. We used odds ratios and effect sizes to combine the results in a meta-analysis. Finally, we compared the conclusions of the primary and secondary analyses.Results Six randomised trials and five cohort studies met the inclusion criteria. Two randomised trials and all cohort studies were labelled as high quality. Eight studies looked at lifting and moving patients, and three studies were conducted among baggage handlers or postal workers. Those in control groups received no intervention or minimal training, physical exercise, or use of back belts. None of the comparisons in randomised trials (17 720 participants) yielded significant differences. In the secondary analysis, none of the cohort studies (772 participants) had significant results, which supports the results of the randomised trials.Conclusions There is no evidence to support use of advice or training in working techniques with or without lifting equipment for preventing back pain or consequent disability. The findings challenge current widespread practice of advising workers on correct lifting technique.     

Interrelated hypoalgesia,creep, and muscle fatigue following a repetitive trunk flexion exposure

Repetitive trunk flexion can damage spinal tissues, however its association with low back pain in the workplace may be confounded by factors related to pain sensitivity. Muscle fatigue, exercise-induced hypoalgesia, and creep-induced neuromuscular changes following repetitive trunk flexion may all affect this assumed exposure-pain relationship. This study’s purpose was to determine how mechanical pain sensitivity in the low back is affected by a repetitive trunk flexion exposure and identify factors associated with changes in low back pain sensitivity. Pressure pain thresholds, perceptions of sub-threshold stimuli, and muscle fatigue in the trunk and tibia, as well as lumbar spine creep were tracked in 37 young healthy adults before and up to 40 min after a 10-min repetitive trunk flexion exposure. Pressure pain thresholds (p = 0.033), but not perceptions of sub-threshold stimuli (p > 0.102) were associated with approximately a 12.5% reduction in pain sensitivity 10 min after completing the exposure, while creep and local muscle fatigue effects were only observed immediately following the exposure. Creep and fatigue interactions and the corresponding tibial measure co-varied with individual low back pressure pain thresholds. The net hypoalgesic effects of repetitive trunk flexion have the potential to partially mask possibly injurious loads, which could contribute to the severity or incidence of lower back injuries related to these exposures.     

Using biofeedback to optimize scapular muscle activation ratios during a seated resisted scaption exercise

Impairments in muscle activation have been linked to increased risk of developing shoulder pathologies such as subacromial impingement syndrome (SIS) and associated rotator cuff injuries. Individuals with SIS have demonstrated increased upper trapezius (UT) muscle activation and reduced serratus anterior (SA) and lower trapezius (LT) muscle activation, which can be collectively represented as ratios (UT/SA and UT/LT). Targeted exercise is an important component of shoulder rehabilitation programs to re-establish optimal muscle activation and ratios. Electromyography (EMG) biofeedback during exercise has been shown to reduce UT activation and favorably alter scapular muscle activation ratios, however, a literature gap exists regarding the efficacy of other types of biofeedback. Therefore, we compared the effects of three types of biofeedback (visual EMG, auditory, verbal cues) on UT/SA and UT/LT ratios during a seated resisted scaption exercise in fifteen subjects without shoulder pain. Baseline muscle activation was recorded and compared to real-time muscle activation during each randomized biofeedback trial. All biofeedback types showed improvements in the UT/SA and UT/LT ratios, with visual EMG demonstrating a significant change in UT/LT ratio (p < 0.05). These results suggest that biofeedback could be utilized as a component of rehabilitation programs to prevent or treat shoulder pain.