Gluteus minimus: an intramuscular EMG investigation of anterior and posterior segments during gait

Gluteus minimus is believed to consist of two structurally and functionally unique segments (anterior and posterior); however there is a lack of electromyography (EMG) research that attempts to verify current theoretical knowledge of this muscle. The purpose of this study was therefore to evaluate the function of gluteus minimus during gait, and to determine whether anterior and posterior segments are functionally independent. Bipolar fine wire intramuscular EMG electrodes were inserted into anterior and posterior gluteus minimus segments of fifteen healthy volunteers (9 males) according to previously verified guidelines. Participants completed a series of four walking trials, followed by maximum voluntary isometric contractions in five different positions. Temporal and amplitude variables for each segment were compared across the gait cycle with independent t-tests. The relative contribution of each segment to the maximum resisted trials was compared with Mann-Whitney U tests (α = 0.05). Anterior and posterior segments were contracting at different relative intensities for three of the five maximum resisted trials (effect size = 0.39 to 0.62, P < 0.037). The posterior segment was larger in EMG amplitude (peak and average) during the first 20% of the gait cycle (effect size = 0.96 to 1.03, P < 0.02), while the anterior segment peaked later in the stance phase (effect size = 0.83, P = 0.034). Gluteus minimus is therefore composed of functionally independent segments. These results build on contemporary theoretical knowledge and may signify hip stabilising roles for each segment across different phases of the gait cycle.

Modifying a shrug exercise can facilitate the upward rotator muscles of the scapula

BACKGROUND

Scapular dyskinesis, characterised by drooping scapulae and reduced upward rotation, has been implicated in the presentation of a number of shoulder disorders. Traditionally, in shoulder rehabilitation programmes, the shrug exercise has been prescribed to facilitate upward rotation of the scapula by strengthening the upper trapezius muscle. The aim of this research was to compare muscle activation levels during the standard shrug and the upward rotation shrug in a normal and pathological population.

METHODS

Surface electrodes recorded electromyographical activity from upper trapezius, middle trapezius, lower trapezius and serratus anterior muscles in 23 normal participants and 14 participants with multi-directional shoulder instability. Participants completed 10 trials of the standard shrug exercise at 0° of shoulder abduction and the upward rotation shrug exercise at 30° of shoulder abduction in the coronal plane. Muscle activity was expressed as a percentage of maximum voluntary isometric contraction.

FINDINGS

The four muscles tested performed at a higher intensity during the modified shrug than the standard shrug. Upper trapezius and lower trapezius activity was significantly greater (P < 0.05) in both populations. Though for middle trapezius and serratus anterior muscles, the modified shrug was statistically significant only in the normal population, P = 0.031 and P = <0.001 respectively.

INTERPRETATION

The upward rotation shrug is a more effective exercise for eliciting muscle activity of the upper and lower trapezius than the standard shrug in a normal and multi-directional instability population. Clinically, the upward rotation shrug might be useful to address scapular dyskinesis involving drooping shoulders and reduced scapula upward rotation.

The effect of exercise-based management for multidirectional instability of the glenohumeral joint: a systematic review

BACKGROUND

The most commonly recommended treatment for multidirectional instability (MDI) of the glenohumeral joint is exercise-based management. The primary objective of this review was to evaluate the effectiveness of exercise-based management in patients with MDI. The secondary aim was to observe the types of exercise protocols and outcomes used, as well as any adverse results associated with exercise.

METHODS

The Cochrane Database of Systematic Reviews, Medline, Embase, CINAHL (Cumulative Index to Nursing and Allied Health Literature), PEDro, Current Contents, Allied and Complementary Medicine (AMED), Australasian Medical Index (AMI), Ausport, and Clinical Trials Registers were searched for published and unpublished studies from the inception date to June 2012 using the keywords multidirectional instability, glenohumeral, and exercise. Selection criteria included all study designs (except case reports and case series) and participants with clinically diagnosed MDI using exercise-based management. Inclusion criteria were not limited by outcomes. The authors' own risk-of-bias tool was used for quality assessment of studies. The GRADE approach (Grading of Recommendations, Assessment, Development and Evaluation) was used to synthesize the evidence.

RESULTS

The risk of bias was high in all 7 included studies. For before-and-after comparisons of exercise-based management, GRADE assessment showed very low-quality evidence for improvements in shoulder kinematics, the Rowe score, overall status rating, and peak muscle strength.

CONCLUSIONS

The effect of exercise-based management on MDI was variable across the included studies because of study heterogeneity and a high level of bias. There is a need for high-quality intervention studies to be undertaken to validate the effect of exercise for MDI.

The predictive validity of a single leg bridge test for hamstring injuries in Australian Rules Football Players

BACKGROUND

Hamstring muscle strain injuries (HMSI) are the greatest injury problem in kicking sports such as Australian Rules Football. Reduced hamstring muscle strength is commonly perceived to be a risk factor for hamstring injury; however, evidence is inconclusive. Testing hamstring strength with the hip and knee at functional angles and assessing endurance parameters may be more relevant for examining the risk of hamstring injury.

OBJECTIVE

The primary aim of this prospective study was to examine if reduced hamstring muscle strength assessed with the single leg hamstring bridge (SLHB) was a risk factor for hamstring injury.

METHODS

Hamstring muscle strength of 482 amateur and semielite players from 16 football clubs, mean age 20.7 (range 16-34 years), was tested during the 2011 preseason. Players were then monitored throughout the 2011 playing season for HMSI.

RESULTS

A total of 28 hamstring injuries, 16 right and 12 left, were recorded. Players who sustained a right HMSI during the season had a significantly lower mean right SLHB score (p=0.029), were older (p=0.002) and were more likely to have sustained a past right hamstring injury (p=0.02) or right knee injury (p=0.035). For left-sided hamstring injury, the injured group was more likely to be left leg dominant (p=0.001), older athletes (p=0.002) and there was a trend towards a history of left hamstring injury (p=0.07).

CONCLUSIONS

This study demonstrated a significant deficit in preseason SLHB scores on the right leg of players that subsequently sustained a right-sided hamstring injury. Age, previous knee injury and a history of hamstring injury were other risk factors supported in this study. Low hamstring strength appears to be a risk factor for hamstring injury; however, due to the confounding variables and low injury rate in this study, further studies are required.

Technical application and the level of discomfort associated with an intramuscular electromyographic investigation into gluteus minimus and gluteus medius

Our current theoretical understanding of gluteus minimus (GMin) and gluteus medius (GMed) function is primarily based on cadaveric studies and biomechanical modelling. There is an absence of electromyographic (EMG) research that aims to verify this understanding, particularly in relation to the potentially unique functional roles of structurally distinct segments within GMin (anterior and posterior) and GMed (anterior, middle and posterior). The aim of this paper is to provide a comprehensive technical description for inserting intramuscular EMG electrodes into uniquely oriented segments of GMin and GMed; and to report the levels of discomfort associated with gluteal intramuscular electrode insertions. Fifteen healthy volunteers took part in a series of walking trials after intramuscular EMG electrodes were inserted into segments of GMin (×2) and GMed (×3) according to previously verified guidelines. Visual analogue scores following walking trials at comfortable and fast speed indicate that discomfort levels associated with these insertions were low (2.4±1.4 and 1.6±0.7 respectively). The technical descriptions and illustrations provided in this paper will allow trained intramuscular electromyographers to insert electrodes into these muscle segments with confidence.

A Systematic Literature Review of the Resistance Exercises That Promote Maximal Muscle Activity of the Rotator Cuff in Normal Shoulders

Background

There are numerous resistance exercises that can be used to activate the rotator cuff. However, the optimal exercises to achieve maximal muscle activation in supraspinatus, infraspinatus, subscapularis and teres minor remain unclear. Thus, the aim of this systematic review is to identify the optimal resistance exercises for producing maximal muscle activation of the rotator cuff in normal shoulders. Methods A literature search was completed using six key databases - MEDLINE, EMBASE, CINAHL, PEDro, SPORTdiscus and Cochrane Library (from inception to January 2012). The search yielded 452 records using terms relating to rotator cuff, exercise, and electromyography. Eighteen papers remained after duplicates were removed and selection criteria applied. Quality assessment, data extraction and data synthesis of included papers was undertaken.

Results

Prone horizontal abduction at 90–100° with external rotation, push-up-plus, empty can and full can produced greatest activity in supraspinatus; prone horizontal abduction at 90–100° with full external rotation, standing external rotation at 0° abduction and the push-up-plus exercise produced greatest activity in infraspinatus and push-up-plus and shoulder flexion exercise in subscapularis. There was limited data for teres minor.

Discussion

Exercises to elicit maximal activity of supraspinatus, infraspinatus and subscapularis in normal shoulders were identified.

Onset of sexual maturity in female chickens is genetically linked to loci associated with fecundity and a sexual ornament

Onset of sexual maturation is a trait of extreme importance both evolutionarily and economically. Unsurprisingly therefore, domestication has acted to reduce the time to sexual maturation in a variety of animals, including the chicken. In comparison with wild progenitor chickens [the Red Junglefowl (RJF)], domestic layer hens attain maturity approximately 20% earlier. In addition, domestic layers also possess larger combs (a sexual ornament), produce more eggs and have denser bones. A large quantitative trait loci (QTL) analysis (n=377) was performed using an F(2) intercross between a White Leghorn layer breed and a RJF population, with onset of sexual maturity measured and mapped to three separate loci. This cross has already been analysed for comb mass, egg production and bone allocation. Onset of sexual maturity significantly correlated with comb mass, whilst the genetic architecture for sexual maturity and comb mass overlapped at all three loci. For two of these loci, the QTL for sexual maturity and comb mass were statistically indistinguishable from pleiotropy, suggesting that the alleles that increase comb mass also decrease onset of sexual maturity.

Development of clinical rating criteria for tests of lumbopelvic stability

Background. Lumbopelvic stability (LPS) is regarded as important for injury prevention, yet there are few reliable or valid tests that can be used in the clinical assessment of LPS. Three dynamic functional tests were identified that assess LPS in multiple planes of motion: dip test (DT), single leg squat (SLS), and runner pose test (RPT). Existing rating criteria for SLS have limited reliability and rating criteria for DT and RPT have not been established. Objective. To develop rating criteria for three clinical tests of LPS. Design. Qualitative research: focus group. Method. A focus group of five expert physiotherapists used qualitative methods to develop rating criteria for the three clinical tests. Results. Detailed rating criteria were established for the three tests. Each key factor considered important for LPS had characteristics described that represented both good and poor LPS. Conclusion. This study established rating criteria that may be used to clinically assess LPS.

Groin pain and hip range of motion is different in Indigenous compared to non-indigenous young Australian football players

OBJECTIVES

Hip and groin pain are common problems in Australian football. Although indigenous (I) players are at greater risk of soft tissue injury than their non-indigenous (non-I) counterparts, Aboriginal descent has not previously been identified as a risk factor for hip and groin injury. The aim of this study was to investigate if hip and groin screening tests would demonstrate differences between indigenous and non-indigenous junior elite AF players.

DESIGN

Cross-sectional study.

METHOD

Two hundred and seventy elite junior Australian football players were screened using five hip and groin musculoskeletal tests.

RESULTS

Thirty-three players (12%) were indigenous. Differences were demonstrated between the two groups for right prone hip internal rotation (I X = 27.60 ± 9.16, non-I X = 33.39 ± 8.88, p < 0.001) and left prone hip internal rotation (I X = 25.83 ± 10.25, non-I X = 31.36 ± 8.75, p < 0.001), pressure on squeeze test with knees at 90° (I X = 165.71 ± 40.32, non-I X = 188.17 ± 62.32, p = 0.001) and pressure on squeeze tests with knees at 0° (I X = 172.57 ± 35.98, non-I X = 202.57 ± 49.14, p = 0.049), and pain provocation during squeeze test with knees at 90° (I X = 3.19 ± 2.26, non-I X = 1.03 ± 1.78, p > 0.001).

CONCLUSIONS

The indigenous players displayed less range of passive hip internal rotation with the hip in neutral, reduced adductor squeeze force and higher levels of groin pain with the squeeze test at 90°. The differences observed between indigenous and non-indigenous players suggest indigenous players are at greater risk of hip and groin injuries in Australian football.