Surgeons' posture and muscle strain during laparoscopic and robotic surgery.

BACKGROUND: It is assumed that conventional laparoscopy (LAP) and robotic-assisted laparoscopic surgery (RALS) differ in terms of the surgeon's comfort. This study compared muscle workload, work posture and perceived physical exertion of surgeons performing LAP or RALS. METHODS: Colorectal surgeons with experience in advanced LAP and RALS performed one of each operation. Bipolar surface electromyography (EMG) recordings were made from forearm, shoulder and neck muscles, and expressed relative to EMG maximum (%EMGmax ). The static, median and peak levels of muscle activity were calculated, and an exposure variation analysis undertaken. Postural observations were carried out every 10 min, and ratings of perceived physical exertion before and after surgery were recorded. RESULTS: The study included 13 surgeons. Surgeons performing LAP showed higher static, median, and peak forearm muscle activity than those undertaking RALS. Muscle activity at peak level was higher during RALS than LAP. Exposure variation analysis demonstrated long-lasting periods of low-level intensity muscle activity in the shoulders for LAP, in the forearms for RALS, and in the neck for both procedures. Postural observations revealed a greater need for a change in work posture when performing LAP compared with RALS. Perceived physical exertion was no different between the surgical modalities. CONCLUSION: Minimally invasive surgery requires long-term static muscle activity with a high physical workload for surgeons. RALS is less demanding on posture.

ANTECEDENTES: Se asume que la cirugía laparoscópica (laparoscopic, LAP) y la cirugía laparoscópica asistida por robot (robotic-assisted laparoscopic surgery, RALS) difieren en cuanto a la comodidad del cirujano. En este estudio se comparó la carga de trabajo muscular, la postura de trabajo y el esfuerzo físico percibido por los cirujanos al realizar LAP o RALS. MÉTODOS: Trece cirujanos colorrectales con experiencia en LAP avanzada y RALS realizaron una operación con cada uno de los abordajes. Se registró la electromiografía de superficie bipolar en los músculos del antebrazo, del hombro y del cuello, y se expresó en relación con el EMG máximo (% EMGmax). Se calculó el nivel de actividad muscular estático, mediano y pico, y se realizó un análisis de variación de la exposición. Las observaciones posturales se llevaron a cabo cada diez minutos y se registraron las valoraciones del esfuerzo físico percibido antes y después de la cirugía. RESULTADOS: La práctica de LAP mostró una mayor actividad muscular estática, mediana y pico del antebrazo en comparación con la práctica de RALS. El hombro izquierdo mostró la mayor actividad muscular en RALS a nivel máximo. El análisis de variación de exposición demostró periodos prolongados de actividad muscular de baja intensidad para LAP en los hombros, para RALS en los antebrazos y para ambos en el cuello. Las observaciones posturales mostraron una mayor necesidad de un cambio en la postura de trabajo al realizar LAP en comparación con RALS. El esfuerzo físico percibido no fue diferente entre ambas modalidades quirúrgicas. CONCLUSIÓN: La cirugía mínimamente invasiva requiere una actividad muscular estática prolongada con una alta carga de trabajo físico para los cirujanos. RALS es menos exigente en el aspecto postural.

Calcium Fluxes in Work-Related Muscle Disorder: Implications from a Rat Model.

INTRODUCTION: Ca2+ regulatory excitation-contraction coupling properties are key topics of interest in the development of work-related muscle myalgia and may constitute an underlying cause of muscle pain and loss of force generating capacity. METHOD: A well-established rat model of high repetition high force (HRHF) work was used to investigate if such exposure leads to an increase in cytosolic Ca2+ concentration ([Ca2+]i) and changes in sarcoplasmic reticulum (SR) vesicle Ca2+ uptake and release rates. RESULT: Six weeks exposure of rats to HRHF increased indicators of fatigue, pain behaviors, and [Ca2+]i, the latter implied by around 50-100% increases in pCam, as well as in the Ca2+ handling proteins RyR1 and Casq1 accompanied by an ∼10% increased SR Ca2+ uptake rate in extensor and flexor muscles compared to those of control rats. This demonstrated a work-related altered myocellular Ca2+ regulation, SR Ca2+ handling, and SR protein expression. DISCUSSION: These disturbances may mirror intracellular changes in early stages of human work-related myalgic muscle. Increased uptake of Ca2+ into the SR may reflect an early adaptation to avoid a sustained detrimental increase in [Ca2+]i similar to the previous findings of deteriorated Ca2+ regulation and impaired function in fatigued human muscle.

Surgeons' muscle load during robotic-assisted laparoscopy performed with a regular office chair and the preferred of two ergonomic chairs: A pilot study.

Surgeons work in awkward work postures and have high precision demands - well-known risk factors for musculoskeletal pain. Robotic-assisted laparoscopy is expected to be less demanding compared to conventional laparoscopy; however, studies indicate that robotic-assisted laparoscopy is also associated with poor ergonomics and musculoskeletal pain. The ergonomic condition in the robotic console is partially dependent upon the chair provided, which often is a regular office chair. Our study quantified and compared the muscular load during robotic-assisted laparoscopy using one of two custom built ergonomic chairs and a regular office chair. The results demonstrated no differences that could be considered clinically relevant. Overall, the study showed high levels of static and mean muscular activity, increased perceived physical exertion from pre-to-post surgery, and moderate to high risk for musculoskeletal injuries measured by the Rapid Upper Limb Assessment worksheet. Authors advocate for further investigation in surgeons' ergonomics and physical work demands in robotic surgery.

Pyelonephritis in persons after age 50 as a clinical marker of urogenital cancer.

OBJECTIVES: Urinary tract infections have been linked with urinary tract cancer, but the association remains controversial. We examined whether pyelonephritis is a clinical marker of urogenital cancer. METHODS: We used Danish medical databases to create a population-based cohort of patients with an incident hospital-based pyelonephritis diagnosis during 1994-2013. Follow-up for cancer began at pyelonephritis diagnosis and ended on 30 November 2013. We restricted the cohort to patients older than 50 years, as urogenital cancer risk in the younger population is low. We calculated the absolute risk of urogenital cancer and the standardized incidence ratio (SIR) comparing risk observed in pyelonephritis patients to risk expected in the general population of Denmark. RESULTS: Among 15 070 patients with pyelonephritis, we observed 197 urinary tract cancers and 374 genital organ cancers over a 20-year follow-up period. The absolute risk of urogenital cancer was 1.5% 6 months after a pyelonephritis diagnosis, and the cumulative risk was 3.0% at 5 years. During the first 6 months following a pyelonephritis diagnosis, the SIR of urogenital cancer was 8.56 (95% CI 7.49-9.75). Between 6 and 12 months following this diagnosis, the SIR was 1.75 (95% CI 1.26-2.35), and beyond 1 year the SIR was approximately unity for most cancers. Notably, the SIR for bladder cancer among women remained elevated beyond 1 year of follow-up. CONCLUSIONS: Patients presenting with a hospital-based diagnosis of pyelonephritis had a higher 6-month risk of urogenital cancer than expected. However, causation cannot be inferred because of the study design.

Does a combination of physical training, specific exercises and pain education improve health-related quality of life in patients with chronic neck pain? A randomised control trial with a 4-month follow up.

AIM: To investigate the effect of combining pain education, specific exercises and graded physical activity training (exercise) compared with pain education alone (control) on physical health-related quality of life (HR-QoL) in chronic neck pain patients. METHODS: A multicentre randomised controlled trial of 200 neck pain patients receiving pain education. The exercise group received additional exercises for neck/shoulder, balance and oculomotor function, plus graded physical activity training. Patient-reported outcome measures (Short Form-36 Physical and Mental component summary scores, EuroQol-5D, Beck Depression Inventory-II, Neck Disability Index, Pain Bothersomeness, Patient-Specific Functioning Scale, Tampa Scale of Kinesiophobia, Global Perceived Effect) and clinical tests (Aastrand Physical Fitness, cervical Range of Motion, Pressure Pain Threshold at infraspinatus, tibialis anterior and cervical spine, Cranio-cervical Flexion, Cervical Extension muscle function, and oculomotion) were recorded at baseline and after 4 months. RESULTS: The exercise group showed statistically significant improvement in physical HR-QoL, mental HR-QoL, depression, cervical pressure pain threshold, cervical extension movement, muscle function, and oculomotion. Per protocol analyses confirmed these results with additional significant improvements in the exercise group compared with controls. CONCLUSIONS: This multimodal intervention may be an effective intervention for chronic neck pain patients. TRIAL REGISTRATION: The trial was registered on www.ClinicalTrials.govNCT01431261 and at the Regional Scientific Ethics Committee of Southern Denmark S-20100069.

Occupational and leisure-time physical activity and workload among construction workers - a randomized control study.

BACKGROUND: There is a lack of quantification of occupational physical activity (OPA) and leisure time physical activity (LTPA) among construction workers. OBJECTIVES: To describe physical activity energy expenditure (PAEE), physical workload, and the effect of a PA-intervention among construction workers. METHODS: Sixty-seven Construction workers self-reported their physical activity (PA), had PA assessed directly (PAEE), and observed OPA using the tool "Posture, Activity, Tools and Handling." The PA-intervention (Intervention; n = 29, Controls; n = 24) included 3x20-min training/week for 12 weeks. RESULTS: Baseline median OPA was 5036 MET-min/week and LTPA 2842 MET-min/week, p < 0.01. OPA directly recorded was (mean ± SE): 56.6 ± 3.2 J/kg/min and LTPA was: 35.7 ± 2.2 J/kg/min (p < 0.001). Manual material handling was performed for ≥ 25% of working time by more than 50% of the participants. Post-intervention, the training group reduced overall PAEE compared to the control group but not specifically during work. CONCLUSIONS: OPA was within the maximum recommended level of 1/3 proposed in consensus guidelines but did not decrease with PA-intervention.

Pain education combined with neck- and aerobic training is more effective at relieving chronic neck pain than pain education alone--A preliminary randomized controlled trial.

OBJECTIVE: To evaluate the effect of training and pain education vs pain education alone, on neck pain, neck muscle activity and postural sway in patients with chronic neck pain. METHODS: Twenty women with chronic neck pain were randomized to receive pain education and specific training (neck-shoulder exercises, balance and aerobic training) (INV), or pain education alone (CTRL). Effect on neck pain, function and Global Perceived Effect (GPE) were measured. Surface electromyography (EMG) was recorded from neck flexor and extensor muscles during performance of the Cranio-Cervical Flexion Test (CCFT) and three postural control tests (two-legged: eyes open and closed, one-legged: eyes open). Sway parameters were calculated. RESULTS: Fifteen participants (CTRL: eight; INV: seven) completed the study. Per protocol analyses showed a larger pain reduction (p = 0.002) for the INV group with tendencies for increased GPE (p = 0.06), reduced sternocleidomastoid activity during the CCFT (p = 0.09), reduced sway length (p = 0.09), and increased neck extensor activity (p = 0.02) during sway compared to the CTRL group. CONCLUSION: Pain education and specific training reduce neck pain more than pain education alone in patients with chronic neck pain. These results provide encouragement for a larger clinical trial to corroborate these observations.

Properties of the Tampa Scale for Kinesiophobia across Workers with Different Pain Experiences and Cultural Backgrounds: A Rasch Analysis.

The main aim of this study was to evaluate whether the construct validity of the Tampa Scale for Kinesiophobia (TSK) is consistent with respect to its scaling properties, unidimensionality and targeting among workers with different levels of pain. The 311 participating Danish workers reported kinesiophobia by TSK (13 statement version) and number of days with pain during the past year (less than 8 days, less than 90 days and greater than 90 days). A Rasch analysis was used to evaluate the measurement properties of the TSK in the workers across pain levels, ages, genders and ethnicities. The TSK did not fit the Rasch model, but removing one item solved the poorness of fit. Invariance was found across the pain levels, ages and genders. Thus, with a few modifications, the TSK was shown to capture a unidimensional construct of fear of movement in workers with different pain levels, ages, and genders.

Pneumonia and the incidence of cancer: a Danish nationwide cohort study.

OBJECTIVES: To examine the risk of a subsequent pulmonary or extra-pulmonary cancer diagnosis following a first-time hospital-based diagnosis of pneumonia. DESIGN: Population-based cohort study using Danish medical registries. SETTING: All hospitals in Denmark. SUBJECTS: A total of 342,609 patients with a first-time hospital-based (inpatient, emergency room or outpatient clinic) diagnosis of pneumonia between 1995 and 2011. MAIN OUTCOME MEASURES: We quantified the excess risk of various cancers amongst pneumonia patients compared to the expected risk in the general population, using relative [standardised incidence ratios (SIRs)] and absolute risk calculations. Follow-up started 1 month after a hospital-based diagnosis of pneumonia and ended on 31 December 2011. RESULTS: A total of 28,496 cancers were observed, compared with 21,625 expected, amongst 342,609 pneumonia patients followed for a median of 4.2 years. The absolute risk of a cancer diagnosis 1 to <6 months following a pneumonia diagnosis was 1.4%, with a corresponding SIR of 2.48 [95% confidence interval (CI) 2.41-2.55]. This was mainly due to an increased risk of lung cancer (eightfold) and haematological cancers (fourfold). The SIR for any cancer remained increased at 1.35 (95% CI 1.30-1.40) during 6-12 months of follow-up, and 1.20 (95% CI 1.18-1.22) during 1-5 years of follow-up. Beyond 5 years, an increased risk was maintained for lung, oesophageal, liver and bladder cancers, squamous cell carcinoma of the skin, lymphoma and multiple myeloma. CONCLUSIONS: A hospital-based pneumonia diagnosis was associated with an increased risk of a cancer diagnosis, especially in the ensuing months, but the absolute risk was small.

The interactions between pain, pain-related fear of movement and productivity.

BACKGROUND: Employees with physically heavy work have an increased risk of musculoskeletal disorders leading to reduced work ability. AIMS: To investigate if a high level of musculoskeletal pain or pain-related fear of movement was associated with low productivity among employees with physically heavy work and differing work ability levels. METHODS: The study was conducted at a Danish production site and employees with physically heavy work in the production line were included in the study. Work ability was assessed with the Work Ability Index (WAI), pain-related fear of movement with the Tampa Scale for Kinesiophobia and productivity and musculoskeletal pain by self-reported measures. Sickness absence records for construction of WAI were obtained from the workplace. RESULTS: There was a 77% response rate with 350 employees included in the final analysis. Among employees with only moderate work ability, there was neither an association between pain and productivity nor between pain-related fear of movement and productivity. For employees with good work ability, higher levels of pain and higher levels of pain-related fear of movement both raised the odds of low productivity significantly. CONCLUSIONS: Despite the fact that musculoskeletal pain increases the risk of reduced work ability significantly, musculoskeletal pain and pain-related fear of movement were associated with low productivity only among employees with good work ability.

Comparison of objectively measured and self-reported time spent sitting.

Until recently, methods for objective quantification of sitting time have been lacking. The aim of this study was to validate self-reported measures against objectively measured total sitting time and longest continuous time with uninterrupted sitting during working hours, leisure time on workdays and leisuredays. Objective diurnal measurement of sitting time was obtained among 26 office workers with 2 accelerometers (ActiGraph GT3X+) for a 7-day period. Customized software (Acti4) was used to identify sitting time separated from other sedentary behaviours. Self-reported sitting time was obtained from a retrospective 7-day questionnaire. A generalized linear model showed the difference between the methods. No significant correlations were found between objective and self-reported sitting time (r<0.315). Total sitting time was significantly underestimated (2.4 h) on a leisureday (p<0.001) and uninterrupted sitting time was in all 3 time settings significantly overestimated (0.4-0.5 h) (p<0.045). Poor agreement (mean difference between 0.5 to -2.4 h) between objectively measured and self-reported sitting time was shown in Bland-Altman plots with wide (3.3-10.8 h) limits of agreement. This study showed a great individual variation and a general lack of agreement between self-reported vs. objectively measured total and uninterrupted sitting time. Objective measures are recommended for determining sitting time.

Selective activation of intra-muscular compartments within the trapezius muscle in subjects with Subacromial Impingement Syndrome. A case-control study.

Neuromuscular control of the scapular muscles is important in the etiology of shoulder pain. Electromyographical (EMG) biofeedback in healthy people has been shown to support a selective activation of the lower compartment of the trapezius muscle, specifically. The aim of the present paper was to investigate whether patients with Subacromial Impingement Syndrome (SIS) were able to selectively activate the individual compartments within the trapezius muscle, with and without EMG biofeedback to the same extent as healthy controls (No-SIS). Fifteen SIS and 15 No-SIS participated in the study. Sessions with and without visual biofeedback were conducted. Surface EMG was recorded from four compartments of the trapezius muscle. Selective activation was defined as activation above 12% with other muscle parts below 1.5% or activation ratio at or above 95% of the total activation. Without biofeedback significantly fewer SIS subjects than No-SIS achieved selective activation (p=0.02-0.03). The findings of the study show that without biofeedback No-SIS had a superior scapular muscle control. However, when provided with visual EMG feedback the SIS group performed equally well as the No-SIS group. This indicated that individuals with SIS may benefit from biofeedback training to gain control of the neuromuscular function of the scapular muscle.

Neuromuscular control of scapula muscles during a voluntary task in subjects with Subacromial Impingement Syndrome. A case-control study.

Imbalance of neuromuscular activity in the scapula stabilizers in subjects with Subacromial Impingement Syndrome (SIS) is described in restricted tasks and specific populations. Our aim was to compare the scapular muscle activity during a voluntary movement task in a general population with and without SIS (n=16, No-SIS=15). Surface electromyography was measured from Serratus anterior (SA) and Trapezius during bilateral arm elevation (no-load, 1kg, 3kg). Mean relative muscle activity was calculated for SA and the upper (UT) and lower part of trapezius (LWT), in addition to activation ratio and time to activity onset. In spite of a tendency to higher activity among SIS 0.10-0.30 between-group differences were not significant neither in ratio of muscle activation 0.80-0.98 nor time to activity onset 0.53-0.98. The hypothesized between-group differences in neuromuscular activity of Trapezius and Serratus was not confirmed. The tendency to a higher relative muscle activity in SIS could be due to a pain-related increase in co-activation or a decrease in maximal activation. The negative findings may display the variation in the specific muscle activation patterns depending on the criteria used to define the population of impingement patients, as well as the methodological procedure being used, and the shoulder movement investigated.

Patterns of musculoskeletal pain in the population: a latent class analysis using a nationally representative interviewer-based survey of 4817 Danes.

BACKGROUND: Pain from the musculoskeletal system often occurs in more than one site. This appears to affect prognosis negatively. Knowledge about specific pain patterns is lacking. OBJECTIVES: To define specific patterns of musculoskeletal co-complaints occurring alongside a primary musculoskeletal complaint. METHODS: Using data from an interview-based health survey of a nationally representative sample of the adult Danish population in 1991 (n = 4817), we describe the co-occurrence of musculoskeletal complaints. Using latent class analysis, we identify clusters of musculoskeletal complaints. RESULTS: Forty percent reported a complaint during a 2-week period; the most common being the low back, neck, shoulder, and knee, and 40% reported more than one complaint. Two latent classes were found for each of the nine primary pain sites except for the low back where three were found. For all primary pain areas, the largest class had site-specific pain only, whereas the smallest class had diffuse pain covering large parts of the body. For participants with a primary musculoskeletal complaint in the spine, the highest probabilities for co-complaints were at other sites in the spine. For primary complaints in the extremities, co-complaints occurred most commonly at adjacent areas. One noticeable exception was a primary complaint of knee pain where co-complaints were found in more remote areas as the neck and low back. CONCLUSIONS: Unique clusters of musculoskeletal co-complaints can be determined based on primary pain site. These patterns are different for persons with a primary complaint in the spine compared with persons with a primary complaint in the extremities.

Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion.

Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software "Daisy". DR was lower in OLD in RECR-10% (17.9%, p < 0.001), RECR-20% (15.8%, p < 0.05), ISO-10% (17.7%, p < 0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p < 0.001) and ISO-20% (55.2%, p < 0.05) which were accompanied with a slight increase in DR variation (n.s.). The observed lower DR in OLD is in line with earlier findings in small distal muscles. Also the larger force fluctuation in OLD was in line with previous studies with smaller hand muscles. These findings suggest that the age-related changes in MU control do exist also in large leg extensors that play an important role in human locomotion and balance control.

Does muscle strength predict future musculoskeletal disorders and sickness absence?

BACKGROUND: High muscle strength is considered relevant for preventing musculoskeletal disorders and long-term sickness absence. However, prospective studies on the association between muscle strength and future musculoskeletal disorders and long-term sickness absence are few and show contrasting results. AIMS: To investigate the association between low muscle strength and future musculoskeletal disorders and long-term sickness absence. METHODS: Muscle strength in trunk flexion and extension, shoulder elevation and abduction as well as handgrip was recorded from a representative sample of Danish workers (n = 421) in 1995. Musculoskeletal disorders were reported 5 years later (in 2000). Information on long-term sickness absence was retrieved from a register of social transfer payments in the period 1996-2007. RESULTS: Regression analyses adjusted for age, gender, smoking, body mass index and physical work demands showed that workers with low muscle strength (the lowest quartile) of trunk extension and flexion, shoulder elevation and abduction and handgrip did not have a significantly increased risk for future musculoskeletal disorders or long term sickness absence compared with stronger workers. CONCLUSIONS: Low muscle strength does not seem to be a good predictor for musculoskeletal disorders and long-term sickness absence in the general working population.

The health paradox of occupational and leisure-time physical activity.

BACKGROUND: Occupational and leisure-time physical activity are considered to provide similar health benefits. The authors tested this hypothesis. METHODS: A representative sample of Danish employees (n=7144, 52% females) reported levels of occupational and leisure-time physical activity in 2005. Long-term sickness absence (LTSA) spells of ≥3 consecutive weeks were retrieved from a social-transfer payment register from 2005 to 2007. RESULTS: 341 men and 620 females experienced a spell of LTSA during the period. Cox analyses adjusted for age, gender, smoking, alcohol, body mass index, chronic disease, social support from immediate superior, emotional demands, social class and occupational or leisure-time physical activity showed a decreased risk for LTSA among workers with moderate (HR 0.85, CI 0.72 to 1.01) and high (HR 0.77, CI 0.62 to 0.95) leisure-time physical activity in reference to those with low leisure-time physical activity. In contrast, an increased risk for LTSA was shown among workers with moderate (HR 1.59, CI 1.35 to 1.88) and high (HR 1.84, CI 1.55 to 2.18) occupational physical activity referencing those with low occupational physical activity. CONCLUSION: The hypothesis was rejected. In a dose-response manner, occupational physical activity increased the risk for LTSA, while leisure-time physical activity decreased the risk for LTSA. The findings indicate opposing effects of occupational and leisure-time physical activity on global health.

Hypercoagulability in cirrhosis: causes and consequences.

Decreased levels of most coagulation factors and thrombocytopenia are the main haemostatic abnormalities of cirrhosis. As a consequence, this condition was, until recently, considered as the prototype acquired coagulopathy responsible for bleeding. However, recent evidence suggests that it should, rather, be regarded as a condition associated with normal or even increased thrombin generation. The bleeding events that occur in these patients should, therefore, be explained by the superimposed conditions that frequently occur in this setting. Due to elevated levels of factor VIII (procoagulant driver) in combination with decreased protein C (anticoagulant driver), which are typically found in patients with cirrhosis, a procoagulant imbalance, defined as a partial resistance to the in vitro anticoagulant action of thrombomodulin, can be demonstrated. Whether this in vitro hypercoagulability is truly representative of what occurs in vivo remains to be established. However, the hypothesis that it may have clinical consequences is attractive and deserves attention. The possible consequences that we discuss herein include whether (i) cirrhosis is a condition associated with increased risk of venous thromboembolism or portal vein thrombosis; (ii) the hypercoagulability associated with cirrhosis has any other role outside coagulation (i.e. progression of liver fibrosis); and (iii) anticoagulation should be used in cirrhosis. Although apparently provocative, considering anticoagulation as a therapeutic option in patients with cirrhosis is now supported by a rationale of increasing strength. There may be subgroups of patients who benefit from anticoagulation to treat or prevent thrombosis and to slow hepatic fibrosis. Clinical studies are warranted to explore these therapeutic options.

The use of EMG biofeedback for learning of selective activation of intra-muscular parts within the serratus anterior muscle: a novel approach for rehabilitation of scapular muscle imbalance.

Motor control and learning possibilities of scapular muscles are of clinical interest for restoring scapular muscle balance in patients with neck and shoulder disorders. The aim of the study was to investigate whether selective voluntary activation of intra-muscular parts within the serratus anterior can be learned with electromyographical (EMG) biofeedback, and whether the lower serratus anterior and the lower trapezius muscle comprise the lower scapula rotation force couple by synergistic activation. Nine healthy males practiced selective activation of intra-muscular parts within the serratus anterior with visual EMG biofeedback, while the activity of four parts of the serratus anterior and four parts of the trapezius muscle was recorded. One subject was able to selectively activate both the upper and the lower serratus anterior respectively. Moreover, three subjects managed to selectively activate the lower serratus anterior, and two subjects learned to selectively activate the upper serratus anterior. During selective activation of the lower serratus anterior, the activity of this muscle part was 14.4+/-10.3 times higher than the upper serratus anterior activity (P<0.05). The corresponding ratio for selective upper serratus vs. lower serratus anterior activity was 6.4+/-1.7 (P<0.05). Moreover, selective activation of the lower parts of the serratus anterior evoked 7.7+/-8.5 times higher synergistic activity of the lower trapezius compared with the upper trapezius (P<0.05). The learning of complete selective activation of both the lower and the upper serratus anterior of one subject, and selective activation of either the upper or lower serratus anterior by five subjects designates the promising clinical application of EMG biofeedback for restoring scapular muscle balance. The synergistic activation between the lower serratus anterior and the lower trapezius muscle was observed in only a few subjects, and future studies including more subjects are required before conclusions of a lower scapula rotation couple can be drawn.