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Concept: Gluteal muscles

169

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements.

Concepts: Gluteal muscles, Ligament, Electromyography, Muscular system, Anterior cruciate ligament injury, Cruciate ligament, Knee, Anterior cruciate ligament

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We investigated the neuromuscular contributions to kinematic variability and thus step to step adjustments in posture and foot placement across a range of walking speeds in response to optical flow perturbations of different amplitudes using a custom virtual environment. We found that perturbations significantly increased step width, decreased step length, and elicited larger trunk sway compared to normal walking. However, perturbation-induced effects on the corresponding variabilities of these measurements were much more profound. Consistent with our hypotheses, we found that: (1) perturbations increased EMG activity of the gluteus medius and postural control muscles during leg swing, and increased antagonist leg muscle coactivation during limb loading in early stance, and (2) changes in the magnitude of step to step adjustments in postural sway and lateral foot placement positively correlated with those of postural control and gluteus medius muscle activities, respectively, in response to perturbations. However, (3) interactions between walking speed and susceptibility to perturbations, when present, were more complex than anticipated. Our study provides important mechanistic neuromuscular insight into walking balance control and important reference values for the emergence of balance impairment.

Concepts: Locomotion, Leg, Length, Speed, Gluteal muscles, Electromyography, Foot, Gluteus medius muscle

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To determine how gluteus medius (Gmed) and maximus (Gmax) activate during closed-chain functional rehabilitative exercises in those with and without chronic ankle instability (CAI).

Concepts: Gluteal muscles, Gluteus medius muscle

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STUDY DESIGN: Controlled laboratory study, repeated measures design. OBJECTIVES: To compare hip abductor muscle activity during selected exercises using fine-wire electromyography (EMG), and determine which exercises are best for activating gluteus medius and the superior portion of gluteus maximus while minimizing activity of tensor fascia lata (TFL). BACKGROUND: Abnormal hip kinematics (i.e. excessive hip adduction and internal rotation) has been linked to certain musculoskeletal disorders. The TFL is a hip abductor but also internally rotates the hip. As such, it may be important to select exercises that activate the gluteal hip abductors while minimizing activation of TFL. METHODS: Twenty healthy persons participated. EMG signals were obtained from the gluteus medius, superior gluteus maximus, and TFL muscles using fine-wire electrodes as subjects performed 11 different exercises. Normalized EMG signal amplitude was compared among muscles for each exercise using multiple 1-way repeated measures analyses of variance (ANOVAs). A descriptive gluteal-to-TFL muscle activation (GTA) index was used to identify preferred exercises for recruiting the gluteal muscles while minimizing TFL activity. RESULTS: Both gluteal muscles were significantly (P<.05) more active than TFL in unilateral and bilateral bridging, quadruped hip extension (knee flexed and extending), the clam, side-stepping, and squatting. The GTA index ranged from 18 to 115, and was highest for the clam (115), side-step (64), unilateral bridge (59), and both quadruped exercises (50). CONCLUSION: If the goal of rehabilitation is to preferentially activate the gluteal muscles while minimizing TFL activation, then the clam, side-step, unilateral bridge, and both quadruped hip extension exercises would appear to be most appropriate.J Orthop Sports Phys Ther, Epub 16 November 2012. doi:10.2519/jospt.2013.4116.

Concepts: Extension, Adduction, Hip, Muscle, Gluteus maximus muscle, Gluteal muscles, Gluteus medius muscle, Electromyography

28

The purpose of this study was to determine the relationship between gluteal muscle activation and pelvis and trunk kinematics when catchers throw to second base. Forty-two baseball and softball catchers (14.74 ± 4.07 years; 161.85 ± 15.24 cm; 63.38 ± 19.98 kg) participated. Muscle activity of the bilateral gluteus maximus and medius were analyzed as well as pelvis and trunk kinematics throughout the throwing motion. It was discovered that at foot contact there were two significant inverse relationships between stride leg gluteus maximus activity and pelvis axial rotation (r = -0.31, r = 0.10, p = 0.05); and between trunk axial rotation and pelvis lateral flexion (r = -0.34, r = 0.12, p = 0.03). In addition, at foot contact, a significant positive relationship between the drive leg [throwing arm side] and trunk flexion (r = 0.33, r = 0.11, p = 0.04) was present. The results of this study provide evidence of gluteal activation both concentrically and eccentrically, in attempt to control the pelvis and trunk during the throwing motion of catchers. The gluteal muscles play a direct role in maintaining the stability of the pelvis and catchers should incorporate strengthening of the entire lumbo-pelvic hip complex into their training regimen. Incorporating concentric and eccentric gluteal exercises will help to improve musculoskeletal core stability thereby assisting in upper extremity injury prevention.

Concepts: Deadlift, Squat, Gluteus maximus muscle, Gluteus medius muscle, Gluteal muscles

28

Previous electromyographic (EMG) studies of gluteus medius (GMed) have not accurately quantified the function of the three proposed structurally and functionally unique segments (anterior, middle and posterior). Therefore this study used anatomically verified locations for intramuscular electrode recordings in three segments of GMed to determine whether the segments are functionally independent. Bipolar fine wire electrodes were inserted into each segment of GMed in 15 healthy individuals. Participants completed a series of four walking trials, followed by maximum voluntary isometric contractions (MVICs) in five different positions. Temporal and amplitude variables for each segment were compared across the gait cycle using ANOVA. The relative contributions of each segment to the MVIC trials were compared with non-parametric tests. All segments showed a biphasic response during the stance phase of gait. There were no differences in amplitude variables (% MVIC) between segments, but the anterior segment had a later peak during both the first and second bursts.For the MVIC trials, there were significant differences in amplitude between segments in four of the five test positions. These data indicate that GMed is composed of three functionally independent segments. This study contributes to the theoretical understanding of the role of GMed.

Concepts: Gluteal muscles, Electromyography, Electroencephalography, Isometric exercise, Non-parametric statistics, Electrode, Segment, Gluteus medius muscle

25

Background and purpose - There are no international guidelines to define adverse reaction to metal debris (ARMD). Muscle fatty atrophy has been reported to be common in patients with failing metal-on-metal (MoM) hip replacements. We assessed whether gluteal muscle fatty atrophy is associated with elevated blood metal ion levels and pseudotumors. Patients and methods - 263 consecutive patients with unilateral ASR XL total hip replacement using a posterior approach and with an unoperated contralateral hip were included in the study. All patients had undergone a standard screening program at our institution, including MRI and blood metal ion measurement. Muscle fatty atrophy was graded as being absent, mild, moderate, or severe in each of the gluteal muscles. Results - The prevalance of moderate-to-severe gluteal muscle atrophy was low (12% for gluteus minimus, 10% for gluteus medius, and 2% for gluteus maximus). Muscle atrophy was neither associated with elevated blood metal ion levels (> 5 ppb) nor with the presence of a clear (solid- or mixed-type) pseudotumor seen in MRI. A combination of moderate-to-severe atrophy in MRI, elevated blood metal ion levels, and MRI-confirmed mixed or solid pseudotumor was rare. Multivariable regression revealed that “preoperative diagnosis other than osteoarthrosis” was the strongest predictor of the presence of fatty atrophy. Interpretation - Gluteal muscle atrophy may be a clinically significant finding with influence on hip muscle strength in patients with MoM hip replacement. However, our results suggest that gluteal muscle atrophy seen in MRI is not associated with either the presence or severity of ARMD, at least not in patients who have been operated on using the posterior approach.

Concepts: Hip replacement, Squat, Solid, Gluteus maximus muscle, Gluteus minimus muscle, Muscle, Gluteus medius muscle, Gluteal muscles

12

The purpose of this study was to compare the neuromotor control of the Gluteus Medius (GMED) and Gluteus Maximus (GMAX) muscles in runners with Achilles tendinopathy to that of healthy controls.

Concepts: Squat, Gluteus maximus muscle, Gluteus medius muscle, Gluteal muscles

8

Background. The purpose of this study was to compare the peak electromyography (EMG) of the most commonly-used position in the literature, the prone bent-leg (90°) hip extension against manual resistance applied to the distal thigh (PRONE), to a novel position, the standing glute squeeze (SQUEEZE). Methods. Surface EMG electrodes were placed on the upper and lower gluteus maximus of thirteen recreationally active females (age = 28.9 years; height = 164 cm; body mass = 58.2 kg), before three maximum voluntary isometric contraction (MVIC) trials for each position were obtained in a randomized, counterbalanced fashion. Results. No statistically significant (p < 0.05) differences were observed between PRONE (upper: 91.94%; lower: 94.52%) and SQUEEZE (upper: 92.04%; lower: 85.12%) for both the upper and lower gluteus maximus. Neither the PRONE nor SQUEEZE was more effective between all subjects. Conclusions. In agreement with other studies, no single testing position is ideal for every participant. Therefore, it is recommended that investigators employ multiple MVIC positions, when possible, to ensure accuracy. Future research should investigate a variety of gluteus maximus MVIC positions in heterogeneous samples.

Concepts: Statistical significance, Isometric exercise, Mass, Comparison, Gluteal muscles, Electromyography, Gluteus maximus muscle, Extension

6

Study Design Observational prospective cohort study with 1-year follow-up. Objectives To investigate the relationship between eccentric hip abduction strength and the development of patellofemoral pain (PFP) in novice runners, during a self-structured running regime. Background Recent research indicates gluteal muscle weakness in individuals with PFP. However, current prospective research is limited to evaluation of isometric strength, producing inconsistent findings. Considering hip muscles including gluteus maximus and medius activate eccentrically to control hip and pelvic motion during weight-bearing activities such as running, evaluating the potential link between eccentric strength and PFP risk is needed. Methods 832 novice runners were included at baseline and 629 participants were included in the final analysis. Maximal eccentric hip abduction strength was measured using a handheld dynamometer prior to initiating a self-structured running program. The diagnostic criteria to classify knee pain as PFP were based on a thorough clinical examination. Participants were followed for 12 months and training characteristics was gathered with a Global Positioning System (GPS). Results Results from the unadjusted generalized linear regression model for the cumulative risk at 25 and 50 kilometres indicated differences in cumulative risk of PFP between high strength, normal strength, and low strength (P< 05), with higher strength associated with reduced risk. Conclusion Findings from this study indicate that among novice runners a level of peak eccentric hip abduction strength higher than normal reduces the risk of PFP during the first 50 kilometres of a self-structured running program. Level of Evidence Prognosis, level 1b-. J Orthop Sports Phys Ther, Epub 27 Jan 2015. doi:10.2519/jospt.2015.5091.

Concepts: Gluteus medius muscle, Gluteal muscles, Global Positioning System, Study design, Linear regression, Muscular system, Scientific method, Regression analysis