Isometric abduction muscle activation in patients with rotator tendinosis of the shoulder

Experimentally Induced Pain Results in Reduced Activity of the Rotator Cuff Muscles in Healthy Subjects

Shoulder pain is a complex, prevalent problem that is multifactorial in nature. While there are many potential causes, one common suspect is the rotator cuff musculature. The purpose of the present study was to induce pain in the supraspinatus muscle of healthy subjects and observe the resulting changes in muscle activity. Eight muscles on 23 subjects were assessed using electromyography: anterior, middle, and posterior deltoid; pectoralis major; upper trapezius; latissimus dorsi; serratus anterior; supraspinatus; and infraspinatus. It was hypothesized that the rotator cuff muscles would display reduced activity during pain, and that reductions in activity would remain after the pain had dissipated. Both of the rotator cuff muscles measured did indeed display reduced activity in a majority of the dynamic, isometric, and maximal contractions. Many of those reductions remained after the pain had subsided.

Exercise for rotator cuff tendinopathy: Proposed mechanisms of recovery

Rotator cuff (RC) tendinopathy is a common recurrent cause of shoulder pain, and resistance exercise is the first-line recommended intervention. Proposed causal mechanisms of resistance exercise for patients with RC tendinopathy consist of four domains: tendon structure, neuromuscular factors, pain and sensorimotor processing, and psychosocial factors. Tendon structure plays a role in RC tendinopathy, with decreased stiffness, increased thickness, and collagen disorganization. Neuromuscular performance deficits of altered kinematics, muscle activation, and force are present in RC tendinopathy, but advanced methods of assessing muscle performance are needed to fully assess these factors. Psychological factors of depression, anxiety, pain catastrophizing, treatment expectations, and self-efficacy are present and predict patient-reported outcomes. Central nervous system dysfunctions also exist, specifically altered pain and sensorimotor processing. Resisted exercise may normalize these factors, but limited evidence exists to explain the relationship of the four proposed domains to trajectory of recovery and defining persistent deficits limiting outcomes. Clinicians and researchers can use this model to understand how exercise mediates change in patient outcomes, develop subgroups to deliver patient-specific approach for treatment and define metrics to track recovery over time. Supporting evidence is limited, indicating the need for future studies characterizing mechanisms of recovery with exercise for RC tendinopathy.

Self-efficacy and Emotional Distress in a Cohort With Patellofemoral Pain

Background:

Patellofemoral pain (PFP) is commonly described and approached in biomechanical terms despite strong evidence that psychosocial factors such as kinesiophobia, emotional distress, and self-efficacy are important in long-standing musculoskeletal pain.

Purpose:

To describe levels of self-efficacy, emotional distress, kinesiophobia, and widespread pain in a cohort with long-standing PFP and determine their association with measures of pain, function, and health-related quality of life.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Included were 112 patients with PFP (age range, 16-40 years) who had been recruited to a randomized controlled trial. Seven baseline factors (patient sex, pain duration, number of pain sites throughout the body, kinesiophobia [Tampa Scale of Kinesiophobia], emotional distress [Hopkins Symptom Checklist], self-efficacy, and knee extension strength) were investigated for associations with the following outcomes: symptoms of PFP (Anterior Knee Pain Scale), pain (worst and usual), and health-related quality of life (5-level EuroQol-5 Dimensions [EQ-5D-5L]). We used bivariate models and multivariable linear regression models with a stepwise backward removal method to find associations with the outcomes. Internal validation was conducted, and adjusted coefficients after shrinkage are presented.

Results:

Of the study patients, 28% reported emotional distress (Hopkins Symptom Checklist ≥1.75), 69% reported multiple pain sites, and 33% had widespread pain. The kinesiophobia score was elevated, with a mean score of 35.4 ± 8.2. Self-efficacy was strongly associated with better function (Anterior Knee Pain Scale) and health-related quality of life (EQ-5D-5L) as well as lower pain scores in bivariate and multivariable models. Self-efficacy and emotional distress explained 50% of the variance in health-related quality of life (EQ-5D-5L).

Conclusion:

Our findings support other studies of PFP suggesting elevated levels of kinesiophobia and emotional distress and higher rates of widespread pain compared with the general population or pain-free controls. Higher self-efficacy was associated with better function and health-related quality of life. Together with emotional distress, it explained half the variance of health-related life quality. The results underline the importance of approaching these patients in a biopsychosocial model.

Registration:

NCT02114294 ( ClinicalTrials.gov identifier).

High-Intensity Shoulder Abduction Exercise in Subacromial Pain Syndrome

Subacromial pain syndrome (SAPS) defined as pain of nontraumatic origin localized around the acromion, is a debilitating, common, and often chronic condition. Among many proposed underlying causes of SAPS, hypoperfusion and hypoxic conditions in and around the tendons may be an intrinsic cause of SAPS.

PURPOSE

This study aimed to determine if adding high-intensity aerobic interval training (HIIT) of the rotator cuff to usual care was feasible in SAPS and improved shoulder endurance more than usual care alone, as well as to examine the influence on shoulder pain and disability and the response of tendinous microcirculation after HIIT.

METHODS

Twenty-one subjects with chronic SAPS were randomized to two groups: experimental group (EG; n = 13) receiving HIIT in addition to treatment as usual and control group (CG; n = 8) receiving treatment as usual. Before and after 8 wk of exercise therapy, endurance performance was assessed by an incremental abduction exercise of the arm to exhaustion (TTE). Pain and disability was assessed by the shoulder pain and disability index (SPADI). Contrast-enhanced ultrasound of the musculus supraspinatus and tendon was utilized to indicate tendon blood flow.

RESULTS

Endurance in the TTE test improved by an estimated 233 s more on average in EG than in CG (P = 0.001; 95% confidence interval, 102 to 363). The SPADI score was reduced 22 points more on average in EG (P = 0.017; 95% confidence interval, -40 to -5). The change from pretest to posttest was significant in EG for both TTE test and SPADI improvement (P < 0.001). EG also experienced less pain during exercise after the intervention compared with CG (P < 0.001). Contrast-enhanced ultrasound indicated an increase in tendinous blood flow in EG (P = 0.019).

CONCLUSIONS

HIIT rotator cuff exercise seems to be a feasible intervention in SAPS, increasing endurance performance more than usual care alone.

Strength Reduction in Unilateral Shoulder Pain: Is the Healthy Side Really Healthy in Rotator Cuff Disease?

OBJECTIVE

The primary aim was to ascertain whether unilateral shoulder pain is implicated in strength reduction both on the ipsilateral and contralateral side. Secondarily, we aimed to determine whether strength was affected by sonographic tendon abnormalities.

DESIGN

A total of 122 subjects were evaluated. Sixty-six female subjects with unilateral shoulder pain in the dominant arm were recruited. Abduction strength was measured in both the dominant and nondominant arm. High-resolution ultrasonography was also conducted on both shoulders. A match-paired control group (n = 66) composed of healthy volunteers underwent the same strength and sonography tests. Subjects with any radiographic anomaly were excluded from the control group. A mixed analysis of variance was performed to test the effect of unilateral shoulder pain on abduction strength. The effect of tendinopathy on shoulder strength was investigated using a mixed 2 × 2 analysis of variance.

RESULTS

Analysis of variance showed that patients with dominant shoulder pain had lower shoulder strength (11.65 ± 4.05 kg) when compared with controls (14.37 ± 4.00 kg; F = 10.454, P = 0.002). No statistically significant effects were found when comparing subjects with and without tendinopathy among the study group.

CONCLUSIONS

In patients with unilateral shoulder pain, abduction strength was found to be lower both on the ipsilateral and contralateral side. The presence of tendinopathy did not affect the reduction in strength. Future research is needed to substantiate these findings.

Immediate and short-term effects of kinesiotaping on muscular activity, mobility, strength and pain after rotator cuff surgery: a crossover clinical trial

BACKGROUND

Kinesiotape (KT) is widely used in musculoskeletal rehabilitation as an adjuvant to treatment, but minimal evidence supports its use. The aim of this study is to determine the immediate and short-term effects of shoulder KT on muscular activity, mobility, strength and pain after rotator cuff surgery.

METHODS

Thirty-nine subjects who underwent shoulder rotator cuff surgery were tested 6 and 12 weeks post-surgery, without tape, with KT and with a sham tape (ST). KT and ST were applied in a randomized order. For each condition, the muscular activity of the upper trapezius, three parts of the deltoid and the infraspinatus were measured during shoulder flexion, and range of motion (ROM) and pain intensity were assessed. At 12 weeks, the isometric strength at 90° of shoulder flexion, related muscular activity and pain intensity were also measured. Subjects maintained the last tape that was applied for three days and recorded the pain intensity at waking up and during the day.

RESULTS

Modifications in muscle activity were observed with KT and with ST. Major changes in terms of decreased recruitment of the upper trapezius were observed with KT (P < 0.001). KT and ST also increased flexion ROM at 6 weeks (P = 0.004), but the differences with the no tape condition were insufficient to be clinically important. No other differences between conditions were found.

CONCLUSIONS

Shoulder taping has the potential to decrease over-activity of the upper trapezius, but no clinical benefits of KT on ROM, strength or pain were noted in a population of subjects who underwent rotator cuff surgery.

TRIAL REGISTRATION

The study was retrospectively registered on ClinicalTrials.gov PRS ( NCT03379636 ) on 21st December 2017.

Electromyographic analysis of rotator cuff muscles in patients with rotator cuff tendinopathy: A systematic review

The shoulder is inherently an unstable joint which heavily relies on the neuromuscular activation of the rotator cuff (RC) complex for stability during movement. Currently, there is no consensus regarding how the activity of RC muscles is affected among individuals with a RC tendinopathy (RCTe). This study reviewed the evidence of studies comparing the electromyographic (EMG) activity of any RC muscle of shoulders with a symptomatic RCTe to asymptomatic shoulders. Eight databases were searched. Data from 343 participants (201 symptomatic and 209 asymptomatic shoulders) were analyzed from 10 out of 402 included studies. Strong evidence for the infraspinatus and supraspinatus during isometric contractions and limited evidence for the supraspinatus and infraspinatus during isokinetic contractions suggest that the muscular activity is not altered among individuals with a RCTe during these types of contraction. Very limited evidence indicates reduced muscle activity for the infraspinatus and subscapularis in the presence of a RCTe during isotonic contractions, and no alterations for the supraspinatus or teres minor were identified. Lastly, conflicting to moderate evidence suggests alterations in RC muscle activity during unrestrained movements and swimming. These findings indicate that EMG deficits associated with a RCTe can best be appreciated during unrestrained movements.

Electromyographic activity of the shoulder muscles during rehabilitation exercises in subjects with and without subacromial pain syndrome: a systematic review

BACKGROUND

Subacromial pain syndrome (SPS) is a common cause of shoulder pain and muscle activity deficits are postulated to contribute to the development and progression of the disorder. The purpose of this systematic review was to definitively determine whether evidence exists of differences in electromyography (EMG) characteristics between subjects with and without SPS.

METHODS

Six key databases were searched: MEDLINE, EMBASE, CINAHL, SPORTdiscus, PEDro and The Cochrane Library (inception to May 2016). The search yielded 1414 records using terms relating to shoulder impingement, EMG, scapular and rotator cuff muscles. Twenty-two papers remained once duplicates were removed and selection criteria applied. Data extraction, quality assessment and data synthesis were performed. Effect sizes and 95% confidence intervals were calculated.

RESULTS

There was limited evidence that serratus anterior has lower amplitude, delayed activation and earlier termination in SPS participants. For the majority of muscles, regardless of task, load or arm position, significant differences were not demonstrated or results were contradictory.

CONCLUSIONS

The understanding of SPS is changing and EMG appears unable to capture the complexities associated with this condition. Addressing aberrant movement patterns and facilitating balanced activation of all shoulder muscles may be a more appropriate treatment direction for the future.

Tendon neuroplastic training: changing the way we think about tendon rehabilitation: a narrative review

Tendinopathy can be resistant to treatment and often recurs, implying that current treatment approaches are suboptimal. Rehabilitation programmes that have been successful in terms of pain reduction and return to sport outcomes usually include strength training. Muscle activation can induce analgesia, improving self-efficacy associated with reducing one's own pain. Furthermore, strength training is beneficial for tendon matrix structure, muscle properties and limb biomechanics. However, current tendon rehabilitation may not adequately address the corticospinal control of the muscle, which may result in altered control of muscle recruitment and the consequent tendon load, and this may contribute to recalcitrance or symptom recurrence. Outcomes of interest include the effect of strength training on tendon pain, corticospinal excitability and short interval cortical inhibition. The aims of this concept paper are to: (1) review what is known about changes to the primary motor cortex and motor control in tendinopathy, (2) identify the parameters shown to induce neuroplasticity in strength training and (3) align these principles with tendon rehabilitation loading protocols to introduce a combination approach termed as tendon neuroplastic training. Strength training is a powerful modulator of the central nervous system. In particular, corticospinal inputs are essential for motor unit recruitment and activation; however, specific strength training parameters are important for neuroplasticity. Strength training that is externally paced and akin to a skilled movement task has been shown to not only reduce tendon pain, but modulate excitatory and inhibitory control of the muscle and therefore, potentially tendon load. An improved understanding of the methods that maximise the opportunity for neuroplasticity may be an important progression in how we prescribe exercise-based rehabilitation in tendinopathy for pain modulation and potentially restoration of the corticospinal control of the muscle-tendon complex.

Shoulder muscle function in frozen shoulder syndrome patients following manipulation under anesthesia: a 6-month follow-up study

INTRODUCTION

The present study evaluates changes in shoulder muscle function in patients with frozen shoulder syndrome (FSS) following manipulation under general anesthesia (MUA).

PATIENTS AND METHODS

Fifteen FSS patients with mean (±SD) age of 53.6±9.7 years were included in this study. Isometric endurance of the shoulder muscles was characterized by time and net impulse (NI), which were assessed with the patient holding a weight in the hand until exhaustion. Fatigability of the deltoid and trapezius muscles during isometric endurance test was assessed by electromyogram power spectrum median frequency (MF) slope per minute. Patients were also screened for daytime pain. Data were collected before MUA, and at 1 and 6 months postoperatively.

RESULTS

Six months postoperatively, the MF slope for the trapezius and deltoid muscles of the involved and uninvolved shoulders did not differ (P>0.05), whereas NI remained lower and endurance time was longer (P<0.05). Shoulder pain was reduced as compared to preoperative levels (on visual analog scale) 1 and 6 months postoperatively (P<0.05).

DISCUSSION

In patients with FSS, the fastest improvements in shoulder muscle NI, fatigability and pain take place in the first month after MUA; 6 months after MUA, however, NI and endurance time remained impaired for the involved shoulder. Physiotherapy should pay more attention to muscle function recovery.

LEVEL OF EVIDENCE

Level III, prospective follow-up study.

Effect of brief daily resistance training on rapid force development in painful neck and shoulder muscles: randomized controlled trial

Objective: To determine the effect of small daily amounts of progressive resistance training on rapid force development of painful neck/shoulder muscles.

Methods: 198 generally healthy adults with frequent neck/shoulder muscle pain (mean: age 43·1 years, computer use 93% of work time, 88% women, duration of pain 186 day during the previous year) were randomly allocated to 2- or 12 min of daily progressive resistance training with elastic tubing or to a control group receiving weekly information on general health. A blinded assessor took measures at baseline and at 10-week follow-up; participants performed maximal voluntary contractions at a static 90-degree shoulder joint angle. Rapid force development was determined as the rate of torque development and maximal muscle strength was determined as the peak torque.

Results: Compared with the control group, rate of torque development increased 31·0 Nm s⁻¹ [95% confidence interval: (1·33–11·80)] in the 2-min group and 33·2 Nm s⁻¹ (1·66–12·33) in the 12-min group from baseline to 10-week follow-up, corresponding to an increase of 16·0% and 18·2% for the two groups, respectively. The increase was significantly different compared to controls (P<0·05) for both training groups. Maximal muscle strength increased only ∼5–6% [mean and 95% confidence interval for 2- and 12-min groups to control, respectively: 2·5 Nm (0·05–0·73) and 2·2 Nm (0·01–0·70)]. No significant differences between the 2- and 12-min groups were evident. A weak but significant relationship existed between changes in rapid force development and pain (r = 0·27, P<0·01), but not between changes in maximal muscle strength and pain.

Conclusion: Small daily amounts of progressive resistance training in adults with frequent neck/shoulder pain increases rapid force development and, to a less extent, maximal force capacity.

SHOULDER MUSCULOSKELETAL DISORDERS IN INDUSTRIAL AND OFFICE WORK

Although several studies addressed the work-related shoulder pathology, there is still a lack of knowledge regarding the causal relationship between different factors in industrial/office activities and shoulder musculoskeletal disorders. The goal of this review is to evaluate in a realistic manner the role of the factors implicated in the shoulder disorders development in high-risk activities. This article reviews the actual state of information regarding the etiological relationship between physical and psychosocial stress and occupational musculoskeletal problems in shoulder area, emphasizing the relationship between ergonomic interventions on musculoskeletal system. Secondly, a comprehensive presentation of the pathophysiology and etiology of shoulder muscle problems is provided. Critical factors such as arm elevation, lack of rest, overloading of several muscles and mental stress during performed tasks are discussed in relation to shoulder musculoskeletal disorders development. Finally, using the available data, the authors present a thorough recommendation of mandatory redesign interventions with suggestions for future research in this area.

Thigh and knee circumference, knee-extension strength, and functional performance after fast-track total hip arthroplasty

OBJECTIVE

To (1) quantify changes in knee-extension strength and functional-performance at discharge after fast-track total hip arthroplasty (THA) and (2) investigate whether these changes correlate to changes in thigh and knee circumference (ie, swelling) or pain.

DESIGN

A prospective, descriptive, hypothesis-generating study.

SETTING

A special unit for fast-track hip and knee arthroplasty operations at a university hospital.

PARTICIPANTS

Twenty-four patients (20 women and 4 men; ages 69 ± 6.1 years) scheduled for primary unilateral THA.

METHODS

All patients were evaluated before surgery and on the day of hospital discharge.

MAIN OUTCOME MEASURES

Knee-extension strength, thigh and knee joint circumference, hip pain, and functional performance (Timed Up & Go, 30-Second Chair Stand, and 10-Meter Walk tests).

RESULTS

All investigated variables changed significantly from before to after surgery, except for hip pain. The average loss in knee-extension strength after surgery (32%, P = .01) did not correlate with increased thigh circumference (6%, P < .01) or knee circumference (3%, P < .01) or with reductions in functional performance: Timed Up & Go test (114%, P = .01), 30-Second Chair Stand test (36%, P = .01), and 10-Meter Walk test (50%, P < .01). Only the increase in knee circumference correlated significantly with reduced performance in the 10-Meter Walk test time (R = -0.59, P < .01), explaining 34% of the variance in the 10-Meter Walk test. No correlations between changes in hip pain and functional performance or knee-extension strength were found. Mean postoperative hospital stay was 2.1 days.

CONCLUSIONS

Knee-extension strength is considerably reduced at discharge after THA, but the early strength reduction does not correlate with changes in thigh or knee circumferences. Because functional performance is also considerably reduced at discharge (unrelated to reduced knee-extension strength), other mechanisms such as fear, avoidance of movement, or decreased hip-muscle strength also may be involved.

Força do manguito rotador em indivíduos com síndrome do impacto comparado ao lado assintomático

OBJETIVO: Avaliar a força muscular de rotação interna, externa e elevação dos ombros sintomáticos comparado aos assintomáticos, associando a força muscular à função da articulação. MÉTODOS: Quarenta e oito indivíduos com diagnóstico de SIO unilateral foram avaliados quanto a força muscular isométrica do ombro sintomático e assintomático (utilizando um dinamômetro isométrico manual), além de serem avaliados quanto a função utilizando a escala de Constant-Murley. Os indivíduos foram distribuídos em 2 grupos: grupo 1 = 35 a 49 anos; grupo 2 = 50 a 65 anos. RESULTADOS: Foi encontrada redução da força de rotação interna, externa e elevação no ombro sintomático, comparado ao lado assintomáticos (p< 0,0001), mas não foi observada redução da força de rotação medial nos sujeitos do grupo 1. Também observamos que a força muscular é diretamente proporcional a função do ombro, onde indivíduos com pouca força do manguito rotador apresentam menor função. CONCLUSÃO: A SIO causa diminuição da força muscular de rotação interna, externa e elevação comparado ao lado assintomático, além de causar diminuição da função do ombro. A redução da função é proporcional a diminuição da força muscular do manguito rotador. Nível de Evidência III, Estudo analítico.

Exercise therapy after corticosteroid injection for moderate to severe shoulder pain: large pragmatic randomised trial

OBJECTIVE

To compare the effectiveness of subacromial corticosteroid injection combined with timely exercise and manual therapy (injection plus exercise) or exercise and manual therapy alone (exercise only) in patients with subacromial impingement syndrome.

DESIGN

Pragmatic randomised clinical trial.

SETTING

Primary care based musculoskeletal service. Patients Adults aged 40 or over with subacromial impingement syndrome with moderate or severe shoulder pain.

INTERVENTIONS

Injection plus exercise or exercise only.

MAIN OUTCOME MEASURES

Primary outcome was the difference in improvement in the total shoulder pain and disability index at 12 weeks.

RESULTS

232 participants were randomised (115 to injection plus exercise, 117 to exercise only). The mean age was 56 (range 40-78), 127 were women, and all had had a median of 16 weeks of shoulder pain (interquartile range 12-28). At week 12 there was no significant difference between the groups in change in total pain and disability index (mean difference between change in groups 3.26 (95% confidence interval -0.81 to 7.34), P=0.116). Improvement was significantly greater in the injection plus exercise group at week 1 (6.56, 4.30 to 8.82) and week 6 (7.37, 4.34 to 10.39) for the total pain and disability index (P<0.001), with no differences at week 24 (-2.26, -6.77 to 2.25, P=0.324).

CONCLUSIONS

In the treatment of patients with subacromial impingement syndrome, injection plus exercise and exercise only are similarly effective at 12 weeks. Trial registration ISRCT 25817033; EudraCT No 2005-003628-20.

The impact of subacromial impingement syndrome on muscle activity patterns of the shoulder complex: a systematic review of electromyographic studies

BACKGROUND

Subacromial impingement syndrome (SIS) is a commonly reported cause of shoulder pain. The purpose of this study was to systematically review the literature to examine whether a difference in electromyographic (EMG) activity of the shoulder complex exists between people with SIS and healthy controls.

METHODS

Medline, CINAHL, AMED, EMBASE, and grey literature databases were searched from their inception to November 2008. Inclusion, data extraction and trial quality were assessed in duplicate.

RESULTS

Nine studies documented in eleven papers, eight comparing EMG intensity and three comparing EMG onset timing, representing 141 people with SIS and 138 controls were included. Between one and five studies investigated each muscle totalling between 20 and 182 participants. The two highest quality studies of five report a significant increase in EMG intensity in upper trapezius during scaption in subjects with SIS. There was evidence from 2 studies of a delayed activation of lower trapezius in patients with SIS. There was otherwise no evidence of a consistent difference in EMG activity between the shoulders of subjects with painful SIS and healthy controls.

CONCLUSIONS

A difference may exist in EMG activity within some muscles, in particular upper and lower trapezius, between people with SIS and healthy controls. These muscles may be targets for clinical interventions aiding rehabilitation for people with SIS. These differences should be investigated in a larger, high quality survey and the effects of therapeutically targeting these muscles in a randomised controlled trial.

Voluntary activation of the infraspinatus muscle in nonfatigued and fatigued states

HYPOTHESIS

Failure of voluntary activation is an important source of weakness in several different muscles after injury or surgery. Despite the high prevalence of shoulder rotator cuff disorders and associated weakness, no test currently exists to identify voluntary activation deficits for the rotator cuff. The purpose of this study was to develop a test to quantify voluntary activation of the infraspinatus. We hypothesized that there would be a consistent relationship between the voluntary activation level and different force levels and that reduced voluntary activation would partially account for reduced force with fatigue.

MATERIALS AND METHODS

Twenty healthy volunteers underwent assessment of voluntary activation using an electrical stimulus applied to the infraspinatus muscle during active isometric external rotation. Voluntary activation was assessed across several levels of external rotation effort and during fatigue.

RESULTS

The voluntary activation-percent force relationship was best fit using a curvilinear model, and the fatigue test reduced both force and voluntary activation by 46%.

DISCUSSION

In the nonfatigued state, the voluntary activation-percent force relationship is similar to that reported for the quadriceps. After fatigue, however, greater failure of voluntary activation was observed compared with reported values for other upper and lower extremity muscles, which may have implications for the understanding and treatment of rotator cuff pathology.

CONCLUSION

A measure of voluntary activation for the infraspinatus varied with the percent maximum force in a predictable manner that is consistent with the literature. The infraspinatus may be more susceptible to failure of voluntary activation during fatigue than other muscles.

Endurance time is joint-specific: a modelling and meta-analysis investigation

Static task intensity-endurance time (ET) relationships (e.g. Rohmert's curve) were first reported decades ago. However, a comprehensive meta-analysis to compare experimentally-observed ETs across bodily regions has not been reported. We performed a systematic literature review of ETs for static contractions, developed joint-specific power and exponential models of the intensity-ET relationships, and compared these models between each joint (ankle, trunk, hand/grip, elbow, knee, and shoulder) and the pooled data (generalised curve). 194 publications were found, representing a total of 369 data points. The power model provided the best fit to the experimental data. Significant intensity-dependent ET differences were predicted between each pair of joints. Overall, the ankle was most fatigue-resistant, followed by the trunk, hand/grip, elbow, knee and finally the shoulder was most fatigable. We conclude ET varies systematically between joints, in some cases with large effect sizes. Thus, a single generalised ET model does not adequately represent fatigue across joints. STATEMENT OF RELEVANCE: Rohmert curves have been used in ergonomic analyses of fatigue, as there are limited tools available to accurately predict force decrements. This study provides updated endurance time-intensity curves using a large meta-analysis of fatigue data. Specific models derived for five distinct joint regions should further increase prediction accuracy.

Rapid muscle activation and force capacity in conditions of chronic musculoskeletal pain

BACKGROUND

The association between musculoskeletal pain and decreased maximal muscle strength capacity has been extensively studied, but knowledge about functional rapid force capacity in conditions of chronic musculoskeletal pain is lacking. The objective of this study is to investigate rapid muscle activation and force capacity of chronically painful muscles.

METHODS

Cross-sectional study with 42 women with chronic trapezius myalgia, and 20 healthy matched controls. Maximal capacity was determined as peak torque and peak EMG amplitude of the painful trapezius and painfree deltoid muscles during the stable high-force phase of maximal voluntary shoulder abduction, whereas rapid capacity was determined as the steepest slope of the torque-time and EMG-time curves, defined as rate of torque development and rate of EMG rise. Intensity of pain was registered prior to the test on a visual-analogue-scale.

FINDINGS

Peak torque was 18% lower at 115 degrees shoulder joint angle in women with myalgia compared with healthy controls (P<0.001), with a corresponding 29% lower level of peak EMG specifically of the painful trapezius muscle (P<0.001). Rate of torque development was 33-54% lower (P<0.001), with a corresponding 21-35% lower level of rate of EMG rise of both the painful trapezius and painfree deltoid (P<0.0001). Intensity of pain showed higher association with parameters of rapid capacity (R=-0.33 to -0.53, P<0.001-0.05) than with maximal capacity (R=-0.15 to -0.41, P<0.01-ns).

INTERPRETATION

In conditions of chronic musculoskeletal pain, the ability to rapidly activate painful and painfree synergistic muscles is more severely impaired than maximal muscle activation. These findings have clinical relevance for rehabilitation of chronically painful muscles.

Effect of physical training on function of chronically painful muscles: a randomized controlled trial

Pain and tenderness of the upper trapezius muscle is frequent in several occupational groups. The objective of this study is to investigate the effect of three contrasting interventions on muscle function and pain in women with trapezius myalgia. A group of employed women ( n = 42) with a clinical diagnosis of trapezius myalgia participated in a 10-wk randomized controlled intervention: specific strength training of the neck/shoulder muscles, general fitness training performed as leg bicycling, or a reference intervention without physical activity. Torque and electromyography (EMG) were recorded during maximal shoulder abductions in an isokinetic dynamometer at −60, 60, 0, and 180°/s. Furthermore, a submaximal reference contraction with only the load of the arms was performed. Significant changes were observed only in the specific strength training group. Pain decreased by 42–49% ( P < 0.01–0.05). Whereas the EMG activity of the unaffected deltoid remained unchanged during the maximal contractions, an increase in EMG amplitude (42–86%; P < 0.001–0.05) and median power frequency (19%; P < 0.001) were observed for the painful trapezius muscle. Correspondingly, torque increased by 18–53% ( P < 0.001–0.05). EMG during the reference contraction decreased significantly for both the trapezius and deltoid muscles ( P < 0.01). In conclusion, specific strength training relieves pain and increases maximal activity specifically of the painful trapezius muscle, leading to increased shoulder abduction strength in women with trapezius myalgia. Furthermore, decreased relative workload may indirectly augment pain reduction.

The validity of the lag signs in diagnosing full-thickness tears of the rotator cuff: a preliminary investigation

OBJECTIVE

To investigate whether the lag signs were valid tools in diagnosing full-thickness tears of the rotator cuff.

DESIGN

A same-subject, correlation, double-blinded design was used. The results of the external rotation lag sign, drop sign, and internal rotation lag sign were compared with the criterion standard of diagnostic ultrasound to establish their accuracy.

SETTING

A regional orthopedic hospital.

PARTICIPANTS

Consecutive subjects (N=37), 21 women and 16 men, with shoulder pain referred to a consultant orthopedic surgeon specializing in shoulder conditions were recruited for this investigation.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Sensitivity, specificity, and positive and negative likelihood ratios of the lag signs when using ultrasound as the reference test.

RESULTS

The specificities of the drop sign and internal rotation lag sign were 77% and 84%, respectively, which, together with low positive likelihood ratios 3.2 (95% confidence interval [CI], 1.5-6.7) and 6.2 (95% CI, 1.9-12.0), indicate that a positive result was poor at recognizing the presence of full-thickness tears. The drop sign had a sensitivity of 73% with a negative likelihood ratio of .34 (95% CI, 0.2-0.8), suggesting that a negative test was fair at ruling out the presence of full-thickness tears. The sensitivity of the internal rotation lag sign (100%) supported by the negative likelihood ratio of 0 (95% CI, 0.0-2.5) suggests that a negative test will effectively rule out the presence of full-thickness tears of the subscapularis. A positive external rotation lag sign is the clinical test most likely to indicate that full-thickness tears of the supraspinatus and infraspinatus are present (specificity, 94%). However, the external rotation lag sign did demonstrate a low sensitivity score of 46% and negative likelihood ratio of .57 (95% CI, 0.4-0.9), which means that a negative test will not rule out the presence of full-thickness tears.

CONCLUSIONS

The findings of this investigation suggest that a clinical diagnosis of a full-thickness tear of the rotator cuff cannot be conclusively reached using one or more of the lag signs.

Upper limb muscle imbalance in tennis elbow: a functional and electromyographic assessment

The purpose of this study was to investigate strength, fatigability, and activity of upper limb musculature to elucidate the role of muscular imbalance in the pathophysiology of tennis elbow. Sixteen patients clinically diagnosed with tennis elbow, recruited from a university hospital upper limb orthopedic clinic, were compared with 16 control subjects with no history of upper limb musculoskeletal problem, recruited from university students and staff. Muscle strength was measured for grip, metacarpophalangeal, wrist, and shoulder on both sides. Electromyographic activity (RMS amplitude) and fatigue characteristics (median frequency slope) of five forearm and two shoulder muscles were measured during isometric contraction at 50% maximum voluntary contraction. All strength measurements showed dominance difference in C, but none in TE. In tennis elbow compared to controls, hand/wrist and shoulder strength and extensor carpi radialis (ECR) activity were reduced (p < 0.05), while fatigue was normal. A global upper limb weakness exists in tennis elbow. This may be due to disuse and deconditioning syndrome caused by fear avoidance, and needs to be addressed in prevention and treatment. Activation imbalance among forearm muscles (reduced extensor carpi radialis activity) in tennis elbow, probably due to protective pain-related inhibition, could lead to a widespread upper limb muscle imbalance.

Exercise therapy for the conservative management of full thickness tears of the rotator cuff: a systematic review

PURPOSE

To review the evidence for the effectiveness of therapeutic exercise for the treatment of full thickness (including massive and inoperable) tears of the rotator cuff.

RELEVANCE

There is little consensus as to the most effective treatment of full thickness and massive tears of the rotator cuff. There is consensus that the outcome of rotator cuff tendon surgery in the elderly is generally very poor. As such, exercise therapy is usually recommended for this patient group. Although commonly prescribed, the evidence to support this approach is equivocal. The aim of this study was to conduct a systematic review of the literature to determine the efficacy of exercise therapy for the management of full thickness rotator cuff tears.

METHODS

A systematic review was conducted to synthesise the available research literature on the effectiveness of exercise therapy for full thickness tears of the rotator cuff.

DATA SOURCE

Reports up to and including September 2006 were located from MEDLINE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), AMED, EMBASE, the Cochrane Database of Systematic Reviews and the Physiotherapy Evidence Database (PEDro) using the terms "rotator cuff" and "tear/s" and "exercise" or "physiotherapy" or "physical therapy" or "rehabilitation".

STUDY SELECTION

Studies were included if they related to full thickness rotator cuff tears and exercise.

DATA EXTRACTION

Two independent reviewers assessed the methodological quality of the studies. Differences were resolved by consensus. ANALYSIS/DATA SYNTHESIS: Ten studies met the inclusion criteria: eight were observational case series and two were single case studies. There were no randomised clinical trials.

RESULTS

Four studies were specific to massive rotator cuff tears. One study had a sub-group with massive cuff tears and five studies were not specific as to the size of the full thickness tear. Due to the heterogeneity of outcome measures used, it was not possible to combine results. In all studies an improvement in outcome scores was reported. Exercise programmes were well documented in five studies.

CONCLUSIONS

No randomised controlled trials met the inclusion criteria and the evaluation has been based on observational studies of lower scientific merit. The findings suggest that some evidence exists to support the use of exercise in the management of full thickness rotator cuff tears. There is a definite need for well-planned randomised controlled trials investigating the efficacy of exercise in the management of full thickness and massive rotator cuff tears.

Force steadiness, muscle activity, and maximal muscle strength in subjects with subacromial impingement syndrome

We investigated the effects of the subacromial impingement syndrome (SIS) on shoulder sensory-motor control and maximal shoulder muscle strength. It was hypothesized that both would be impaired due to chronic shoulder pain associated with the syndrome. Nine subjects with unilateral SIS who remained physically active in spite of shoulder pain and nine healthy matched controls were examined to determine isometric and isokinetic submaximal shoulder-abduction force steadiness at target forces corresponding to 20%, 27.5%, and 35% of the maximal shoulder abductor torque, and maximal shoulder muscle strength (MVC). Electromyographic (EMG) activity was assessed using surface and intramuscular recordings from eight shoulder muscles. Force steadiness was impaired in SIS subjects during concentric contractions at the highest target force level only, with muscle activity largely unaffected. No between-group differences in shoulder MVC were observed. The present data suggest that shoulder sensory-motor control is only mildly impaired in subjects with SIS who are able to continue with upper body physical activity in spite of shoulder pain. Thus, physical activity should be continued by patients with SIS, if possible, to avoid the loss in neural and muscle functions associated with inactivity.

Long-term repeatability of force, endurance time and muscle activity during isometric contractions

We determined the repeatability and correlations between force, endurance and muscle activity during isometric contractions over three years. Twenty-six subjects, with and without complaints of the shoulder and neck, performed standardized maximal and submaximal shoulder-abduction contractions and wrist extension-contractions at yearly intervals from 1997 to 1999. Peak forces developed during maximal contraction and the endurance times of submaximal contractions during shoulder abduction and wrist extension were measured. Electromyography (EMG) of muscle activity was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles. Root mean square EMG amplitudes were calculated. We found statistically significant associations between peak forces developed during wrist extension and shoulder abduction, and between endurance times of submaximal wrist extension and shoulder abduction. No statistically significant changes in peak force and EMG(peak) were found over the measurement years. The responses were not statistically significantly influenced by gender, or neck and shoulder pain. However, we observed considerable intra-individual variation in the inter-year measurements particularly for the responses to submaximal contraction. Such large variations represent a challenge when attempting to use the responses to interpret the effects of therapies.

The effect of postural correction on muscle activation amplitudes recorded from the cervicobrachial region

In clinical practice, postural correction is a common treatment approach for individuals with neck and shoulder pain. As chronic static muscle use is thought to be associated with the onset of some neck and shoulder pain syndromes, it is important to understand the impact a postural correction program might have on muscle activation amplitudes in the neck and shoulder regions. Normalized surface electromyographic data were recorded from the levator scapulae, upper trapezius, supraspinatus, posterior deltoid, masseter, rhomboid major, cervical erector spinae, and sternocleidomastoid muscles of the dominant side of each of eighteen healthy subjects. Subjects performed five repetitions of each of four seated typing postures (habitual, corrected, head-forward and slouched) and four standing postures (habitual, corrected, and head-forward and slouched). Repeated-measures analysis of variance models (alpha=0.05) revealed that in sitting postural correction tended to decreased the level of muscle activation required in all muscles studied during seated computer work, however this finding was not statistically significant. Corrected posture in sitting did, however produce a statistically significant reduction in muscle activity compared to forward head posture. Corrected posture in standing required more muscle activity than habitual or forward head posture in the majority of cervicobrachial and jaw muscles, suggesting that a graduated approach to postural correction exercises might be required in order to train the muscles to appropriately withstand the requirements of the task. A surprising finding was that muscle activity levels and postural changes had the largest impact on the masseter muscle, which demonstrated activation levels in the order of 20% maximum voluntary electrical activation.

Análise cinemática tridimensional do manuseio de carga na construção civil

O presente estudo aborda a simulação da atividade de descarga manual de sacos de cimento (m = 50kg) sob o enfoque biomecânico do movimento com o objetivo de identificar as alturas de descarregamento mais favoráveis para a preservação das estruturas musculoesqueléticas do trabalhador. Foram realizados estudos preliminares com fotos e filmagens da situação real para então efetuar a simulação em laboratório utilizando procedimentos de cinemetria tridimensional. Alguns pontos são discutidos no artigo, como o posicionamento vertical do cotovelo, situações que apresentam maiores valores quanto à aceleração do movimento, inclinação da coluna vertebral e movimentação corporal durante o instante de recebimento das sacas. A análise dos resultados permite concluir que, das diferentes alturas de descarga que foram simuladas, a que se mostrou mais favorável foi a de 1,2 metro a partir do solo, em que a extensão do braço não ultrapassa a linha dos ombros.

Kinin peptides in human trapezius muscle during sustained isometric contraction and their relation to pain

To determine the muscular concentration of bradykinin and kallidin during static contraction, microdialysis probes were implanted bilaterally in the trapezius muscles of healthy women. Three hours after probe implantation, 200 μM of the angiotensin-converting enzyme (ACE) inhibitor enalaprilat were added to the perfusion solution in one of the sides for 30 min. Thirty minutes later, the subjects performed a sustained bilateral shoulder abduction at 10% of the maximal voluntary contraction until exhaustion. This protocol was repeated twice, with an interval of at least 17 days. High intersession repeatability was observed in the concentration of bradykinin but not of kallidin. Enalaprilat induced a significant increase in bradykinin levels in the dialysate, without affecting kallidin levels. The sustained contraction induced a significant increase in dialysate levels of both kinin peptides. The contraction also induced a significant increase in pain ratings, as measured by a visual analog scale. During contraction, positive correlations were found between pain ratings and levels of kinin peptides in dialysate, predominantly in the side previously perfused with enalaprilat. Subjects with the higher pain ratings also showed larger increases in kinin peptides in the side previously perfused with enalaprilat. The present results show that both plasma and tissue kinin-kallikrein are activated during muscle contraction, but that their metabolic pathways are differently regulated during rest and contraction, because they showed a different response to ACE inhibition. They also indicate that intramuscular kinin peptides levels, and ACE activity, may contribute to muscle pain.

Comparing the function of the upper and lower parts of the serratus anterior muscle using surface electromyography

STUDY DESIGN

Prospective single-group repeated-measures design.

OBJECTIVE

To use electromyographic (EMG) analysis during muscle testing to determine if there is a difference in function of the upper and lower parts of the serratus anterior (SA) muscle.

BACKGROUND

The SA muscle is a very important scapular protractor and upward rotator. Authors have anatomically described the muscle as being divided into 2 or 3 parts, and have suggested that the upper part is more suited for protraction and the lower part for upward rotation of the scapula.

METHODS AND MEASURES

Surface electrodes recorded EMG activity of the upper and lower parts of the SA muscle during 9 different muscle tests in 29 healthy subjects.

RESULTS

Three muscle tests demonstrated significantly greater (P<.05) EMG activity in the lower part of the SA as compared to the upper part. There was no significant difference in the EMG activity of the upper and lower parts of the SA when the other 6 muscle tests were analyzed.

CONCLUSION

When upward rotation was the primary position of the scapula during the muscle tests, the lower part of the SA was activated to a greater degree than the upper part. Muscle tests with maximum scapular protraction with varying degrees of upward rotation produced EMG activity with no significant difference when comparing the upper and lower parts of the SA. This information may be helpful for clinicians when muscle testing and developing exercise programs for the SA muscle.

Regional musculoskeletal conditions: shoulder pain

About half the population has at least one episode of shoulder pain yearly. History and clinical examination are cornerstones in the evaluation of the patient. Shoulder pain at the work place is associated with job strain: lack of control and work with elevated arms and hand tools. Clinical skills and knowledge about red and yellow flags and biomechanics are essential to perform a systematic and reliable evaluation. The diagnostic validity of clinical tests for rotator cuff tear, impingement syndrome and superior labral tears is equal or better than ultrasound and magnetic resonance imaging. Non-steroidal anti-inflammatory drugs and cortico-steroidal injections have documented short-term pain relief. Additionally, the physician should attempt to give the patient simple advice and reinforce active coping strategies. One randomized study suggests that a proper physiotherapy regimen and surgery are equally effective for the impingement syndrome. Further research should address the cost-effectiveness of diagnostic methods and treatments.

Cognitive performance and muscle activation in workers with chronic shoulder myalgia

The present study determined whether workers with chronic shoulder myalgia exhibit impaired cognitive performance and elevated muscle activation. Ten workers with and 10 without shoulder myalgia performed three sessions, each consisting of three different cognitive tasks. Subjective pain was reported on visual analogue scales (VAS). Surface electromyography was recorded bilaterally from the trapezius and forearm extensor muscles. Speed and error rates of the cognitive work were almost the same in the two groups, but the myalgia subjects reported more stress during the work. In two of the cognitive tasks, both groups increased their speed of performance to the same extent from the first to the third session, despite pain increase in the myalgia subjects. In the biomechanically demanding task, the speed fell from the first to the third session in both groups. Muscle activation was equal in the two groups and constant throughout the protocol despite changes in speed of performance and pain. It is concluded that localized chronic muscle pain does not significantly alter cognitive performance, or muscle activation level during cognitive work. However, the perceived burden of work is larger, as indicated by the higher stress reported during cognitive work in the myalgia subjects compared with their pain-free controls.

Minimal influence of facet joint anesthesia on isokinetic muscle performance in patients with chronic degenerative low back disorders

STUDY DESIGN

Experimental design.

OBJECTIVES

To examine the influence of pain reduction after facet joint injections on isokinetic back muscle performance.

SUMMARY OF BACKGROUND DATA

Methods for evaluating the effect of facet joint injections vary. Recent studies base their results solely on the patient's subjective opinion and suggest a need for more objective, concrete, and reliable measurements.

METHODS

Eighty-seven patients with a degenerative low back disorder (49 women and 38 men; mean age, 48 years; range, 22-79) who had facet joint injections as a part of preoperative evaluation participated. The mean duration of symptoms was 12.3 years (range, 1-45). The patients underwent isokinetic trunk flexor and extensor muscle strength testing at angular velocities of 60 deg/sec and 120 deg/sec. They performed two tests before the facet joint injections (to eliminate learning effect). All patients had bilateral facet joint injections at L5-S1. Those who did not report pain relief had additional injections at L4-L5. The flexion-extension test was repeated 15 minutes after each injection. Pain and fear were registered on visual analog scales.

RESULTS

All 87 patients could perform the isokinetic tests. For extension at 60 deg/sec, a significant improvement was found between the two pretests (P < 0.05). Pain increased significantly from the first to the second pretest (P = 0.02), and a significant decrease in pain was found after the first injection (P = 0.0001). Fear decreased between each test, with a significant decrease after the first injection. No significant change was found for the muscle strength measurements after facet joint anesthesia. There were only weak correlations between decrease in pain and alteration in muscle performance, ranging from 0.06 to 0.37.

CONCLUSION

Pain reduction after facet joint injections did not influence isokinetic muscle performance in patients with degenerative low back disorders.

Muscle activation in the contralateral passive shoulder during isometric shoulder abduction in patients with unilateral shoulder pain

Studies have shown an increased muscle activation at the opposite passive side during unilateral contractions. The purpose of the present study was to examine the influence of pain on muscle activation in the passive shoulder during unilateral shoulder abduction. Ten patients with unilateral rotator tendinosis of the shoulder and nine healthy controls performed unilateral maximal voluntary contractions (MVC) and sustained submaximal contractions with and without subacromial injections of local anaesthetics of the afflicted shoulder. Muscle activation was recorded by electromyography (EMG) from the trapezius, deltoid, infraspinatus and supraspinatus muscles in both shoulders. During MVCs, the EMG amplitude from muscles of the passive afflicted side was not different in patients and controls, and was not influenced by pain alterations. In contrast, the EMG amplitude from the muscles of the passive unafflicted side was lower in the patients and increased after pain reduction. During the sustained submaximal contraction the EMG amplitude increased gradually in the passive shoulder to 15-30% of the EMG amplitude observed during MVC. This response was not influenced by differences in pain. We conclude that muscle activation of the passive shoulder was closely related to the activation of the contracting muscles and thus related to central motor drive, and not directly influenced by changes in pain.

Muscle activation after supervised exercises in patients with rotator tendinosis

OBJECTIVE

To determine whether pain reduction induced by supervised exercises over several months results in increased maximal force and muscle activation.

DESIGN

Before-after trial.

PARTICIPANTS

Ten patients with unilateral rotator tendinosis and more than 3 months' duration of pain.

INTERVENTION

Supervised exercises for 3 to 6 months.

OUTCOME MEASURES

Maximal abduction force, muscle activation by surface electromyogram (EMG), and pain were assessed during brief maximal voluntary isometric contractions (MVC) before and after fatigue. EMG and pain were assessed during sustained submaximal contraction, performed with the shoulder 45 degrees abducted. The testing protocol was performed before and after supervised exercises.

RESULTS

In the afflicted shoulder, resting pain was reduced after supervised exercises and no longer differed from the unafflicted side. The increase in pain during contraction was almost the same before and after treatment. MVC force increased, but significant side differences remained. EMG increased for trapezius and deltoid muscles in both afflicted and unafflicted arms. Fatigue development and recovery was unaltered by the exercise regimen.

CONCLUSIONS

Pain reduction after supervised exercises was associated with an improved MVC force, but the side difference in maximal force generation was maintained. Muscle activity during maximal contraction increased in both the afflicted and unafflicted sides.

Phonophoresis versus ultrasound in the treatment of common musculoskeletal conditions

PURPOSE

The purpose of this study was to determine whether the pain response after phonophoresis (PH) differs from the pain response after ultrasound (US) alone.

METHODS

Forty-nine subjects with soft tissue injuries including epicondylitis, tendinitis, and tenosynovitis were randomly assigned (double blinded technique) to PH or US treatment groups. Both groups received 8 min of continuous US at 1.5 w x cm(-2), three times per week for 3 wk. For the PH group a gel containing 0.05% fluocinonide was used as a coupling agent. An identical gel absent the steroid was used for the US group. Subjects indicated their pain level by marking on a visual analog scale (VAS) at the start of treatment and at the end of weeks 1, 2, and 3. Pressure algometry was used to note tolerance to direct pressure over the target tissue. ANOVA for repeated measures was used to analyze data.

RESULTS

At the end of 3 wk of treatment, both groups combined showed a significant decrease in pain level and an increase in pressure tolerance (P < 0.05), but there were no differences between groups from the onset of treatment to the end of week 3 (VAS: US 5.5-1.9, PH 5.0-2.0; algometry (involved limb): US 4.7 lb-7.1 lb, PH 5.1 lb-6.6 lb).

CONCLUSIONS

We conclude that US results in decreased pain and increased pressure tolerance in these selected soft tissue injuries. The addition of PH with fluocinonide does not augment the benefits of US used alone.