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Jennifer Erin Earl and Jay Hertel

Objective:

To identify integrated EMG (I-EMG) activity of 6 lower-extremity muscles during the 8 Star Excursion Balance Tests (SEBTs).

Design and Setting:

Repeated measures, laboratory setting.

Subjects:

10 healthy young adults.

Interventions:

The SEBTs require the subject to balance on the stance leg and maximally reach with the contralateral foot along each of 8 lines extending from a common axis at 45° intervals.

Measures:

I-EMG activity of the vastus medialis obliquus (VMO), vastus lateralis (VL), medial hamstring (MH), biceps femoris (BF), anterior tibialis (AT), and gas-trocnemius.

Results:

Significant differences were found in all muscles (P < .05) except the gastrocnemius (P = .08). VMO and VL activity tended to be greatest with anteriorly directed excursions, whereas the MH and BF activity were greatest with posteriorly directed excursions. AT activity was lowest with the lateral excursion.

Conclusions:

Performance of the different SEBTs results in different lower-extremity muscle-activation patterns.

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Catriona O’Dwyer, David Sainsbury and Kieran O’Sullivan

Context:

Functional subdivisions are proposed to exist in the gluteus medius (GM) muscle. Dysfunction of the GM, in particular its functional subdivisions, is commonly implicated in lower limb pathologies. However, there is a lack of empirical evidence examining the role of the subdivisions of the GM.

Objectives:

To compare the activation of the functional subdivisions of the GM (anterior, middle, and posterior) during isometric hip contractions.

Design:

Single-session, repeated-measures observational study.

Setting:

University research laboratory.

Participants:

Convenience sample of 15 healthy, pain-free subjects.

Intervention:

Subjects performed 3 maximal voluntary isometric contractions for hip abduction and internal and external rotation on an isokinetic dynamometer with simultaneous recording of surface electromyography (sEMG) activity of the GM subdivisions.

Main Outcome Measures:

sEMG muscle activity for each functional subdivision of the GM during each hip movement was analyzed using a 1-way repeated-measures ANOVA (post hoc Bonferroni).

Results:

The response of GM subdivisions during the 3 different isometric contractions was significantly different (interaction effect; P = .003). The anterior GM displayed significantly higher activation across all 3 isometric contractions than the middle and posterior subdivisions (main effect; both P < .001). The middle GM also demonstrated significantly higher activation than the posterior GM across all 3 isometric contractions (main effect; P = .027). There was also significantly higher activation of all 3 subdivisions during both abduction and internal rotation than during external rotation (main effect; both P < .001).

Conclusions:

The existence of functional subdivisions in the GM appears to be supported by the findings. Muscle activation was not homogeneous throughout the entire muscle. The highest GM activation was found in the anterior GM subdivision and during abduction and internal rotation. Future studies should examine the role of GM functional subdivisions in subjects with lower limb pathologies.

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Gretchen D. Oliver, Audrey Stone and Jessica Washington

Recently, sports medicine professionals have shown interest in using dynamic movement assessments to help identify biomechanical risk factors for musculoskeletal injury. Thus the purpose of this study was to propose two movements (single leg step down and single leg lateral hop) that could predict injury and determine if these proposed movements elicited muscle activation of the hamstrings and gluteals. Surface electromyography was employed and muscle activations of the hamstrings and gluteus medius muscles were classified as strong during both the single leg step down (SLSD) and single leg lateral hop (SLLH). Both the hamstrings and gluteus medius muscles are associated with musculoskeletal injury. The SLSD and SLLH cause significantly high muscle activation of both these muscle groups and should be considered for use in dynamic movement assessments.

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Ralf Roth, Lars Donath, Lukas Zahner and Oliver Faude

For performance and injury prevention in sport, core strength and endurance are focused prerequisites. Therefore we evaluated characteristics of trunk muscle activation and performance during strength-endurance related trunk field tests. Strength-endurance ability, as total time to failure, and activation of trunk muscles was measured in 39 football players of the highest German female football league (Bundesliga) (N = 18, age: 20.7 y [SD 4.4]) and the highest national male under-19 league (N = 21, age: 17.9 y [0.7]) in prone plank, side plank, and dorsal position. Maximal isometric force was assessed during trunk extension and flexion, rotation, and lateral flexion to normalize EMG and to compare with the results of strength-endurance tests. For all positions of endurance strength tests, a continuous increase in normalized EMG activation was observed (P < .001). Muscle activation of the rectus abdominis and external oblique in prone plank position exceeded the maximal voluntary isometric contraction activation, with a significantly higher activation in females (P = .02). We conclude, that in the applied strength-endurance testing, the activation of trunk muscles was high, especially in females. As high trunk muscle activation can infer fatigue, limb strength can limit performance in prone and side plank position, particularly during high trunk muscle activation.

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Peter R. Blanpied

Closed kinetic chain exercises are commonly used in strengthening and rehabilitation programs. Altering positions of body segments and supports might affect the way these exercises are performed. The purpose of this study was to compare gluteal, quadriceps, hamstring, and plantar flexor muscle activations during wall-slide (WS) vs. squat-machine (SM) exercise. In addition, the effects of support location and foot position were investigated. Twenty women performed 8 exercises, to 60° of knee flexion. Results indicated that placing the foot forward caused an increase in all muscle activations except in the plantar flexors, which showed an increase with the foot placed in line with the hip. This effect was exaggerated during WS for the plantar flexors and quadriceps and during SM for the hamstrings. When the support was located at the scapular level, hamstring and gluteal activations were greater, and quadriceps activity was less during SM than during WS. These results could be used to target specific muscle groups during strengthening exercise.

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Mark A. Sutherlin and Joseph M. Hart

Context:

Individuals with a history of low back pain (LBP) may present with decreased hip-abduction strength and increased trunk or gluteus maximus (GMax) fatigability. However, the effect of hip-abduction exercise on hip-muscle function has not been previously reported.

Objective:

To compare hip-abduction torque and muscle activation of the hip, thigh, and trunk between individuals with and without a history of LBP during repeated bouts of side-lying hip-abduction exercise.

Design:

Repeated measures.

Setting:

Clinical laboratory.

Participants:

12 individuals with a history of LBP and 12 controls.

Intervention:

Repeated 30-s hip-abduction contractions.

Main Outcome Measures:

Hip-abduction torque, normalized root-mean-squared (RMS) muscle activation, percent RMS muscle activation, and forward general linear regression.

Results:

Hip-abduction torque reduced in all participants as a result of exercise (1.57 ± 0.36 Nm/kg, 1.12 ± 0.36 Nm/kg; P < .001), but there were no group differences (F = 0.129, P = .723) or group-by-time interactions (F = 1.098, P = .358). All participants had increased GMax activation during the first bout of exercise (0.96 ± 1.00, 1.18 ± 1.03; P = .038). Individuals with a history of LBP had significantly greater GMax activation at multiple points during repeated exercise (P < .05) and a significantly lower percent of muscle activation for the GMax (P = .050) at the start of the third bout of exercise and for the biceps femoris (P = .039) at the end of exercise. The gluteal muscles best predicted hip-abduction torque in controls, while no consistent muscles were identified for individuals with a history of LBP.

Conclusions:

Hip-abduction torque decreased in all individuals after hip-abduction exercise, although individuals with a history of LBP had increased GMax activation during exercise. Gluteal muscle activity explained hip-abduction torque in healthy individuals but not in those with a history of LBP. Alterations in hip-muscle function may exist in individuals with a history of LBP.

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Cindy Y. Lin, Liang-Ching Tsai, Joel Press, Yupeng Ren, Sun G. Chung and Li-Qun Zhang

Context:

Gluteal-muscle strength has been identified as an important component of injury prevention and rehabilitation in several common knee injuries. However, many conventionally prescribed gluteal-strengthening exercises are not performed during dynamic weight-bearing activities, which is when most injuries occur.

Objectives:

To compare lower-limb muscle-activation patterns between conventional gluteal-strengthening exercises and off-axis elliptical exercises with motorized foot-plate perturbations designed to activate gluteal muscles during dynamic exercise.

Evidence Acquisition:

Twelve healthy volunteers (26.1 ± 4.7 y) participated in the study. They performed 3 conventional exercises (single-leg squat, forward lunge, and clamshell) and 3 elliptical exercises (regular, while resisting an adduction force, and while resisting an internal-rotation torque). Gluteus medius (GMed) and maximus (GMax), quadriceps, hamstrings, and gastrocnemius muscle activations during each exercise were recorded using surface electromyography (EMG) and normalized to maximal voluntary isometric contraction (MVIC).

Evidence Synthesis:

Normalized GMed EMG was the highest during the adduction-resistance elliptical exercise (22.4% ± 14.8% MVIC), significantly greater than forward lunge (8.2% ± 3.8% MVIC) and regular elliptical (6.4% ± 2.5% MVIC) and similar to clamshell (19.1% ± 8.8% MVIC) and single-leg squat (18.4% ± 7.9% MVIC). Normalized GMax EMG during adduction-resistance (11.1% ± 7.6% MVIC) and internal-rotation-resistance elliptical (7.4% ± 3.8% MVIC) was significantly greater than regular elliptical (4.4% ± 2.4% MVIC) and was similar to conventional exercises. The single-leg squat required more muscle activation from the quadriceps and gastrocnemius than the elliptical exercises.

Conclusions:

Off-axis elliptical exercise while resisting an adduction force or internal-rotation torque activates gluteal muscles dynamically while avoiding excessive quadriceps activation during a functional weight-bearing activity compared with conventional gluteal-strengthening exercises.

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Bjørn Harald Olstad, Christoph Zinner, João Rocha Vaz, Jan M.H. Cabri and Per-Ludvik Kjendlie

Purpose:

To investigate the muscle-activation patterns and coactivation with the support of kinematics in some of the world’s best breaststrokers and identify performance discriminants related to national elites at maximal effort.

Methods:

Surface electromyography was collected in 8 muscles from 4 world-class (including 2 world champions) and 4 national elite breaststroke swimmers during a 25-m breaststroke at maximal effort.

Results:

World-class spent less time during the leg recovery (P = .043), began this phase with a smaller knee angle (154.6° vs 161.8°), and had a higher median velocity of 0.18 m/s during the leg glide than national elites. Compared with national elites, world-class swimmers showed a difference in the muscle-activation patterns for all 8 muscles. In the leg-propulsion phase, there was less triceps brachii activation (1 swimmer 6% vs median 23.0% [8.8]). In the leg-glide phase, there was activation in rectus femoris and gastrocnemius during the beginning of this phase (all world-class vs only 1 national elite) and a longer activation in pectoralis major (world champions 71% [0.5] vs 50.0 [4.3]) (propulsive phase of the arms). In the leg-recovery phase, there was more activation in biceps femoris (50.0% [15.0] vs 20.0% [14.0]) and a later and quicker activation in tibialis anterior (40.0% [7.8] vs 52.0% [6.0]). In the stroke cycle, there was no coactivation in tibialis anterior and gastrocnemius for world champions.

Conclusion:

These components are important performance discriminants. They can be used to improve muscle-activation patterns and kinematics through the different breaststroke phases. Furthermore, they can be used as focus points for teaching breaststroke to beginners.

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Isabelle Rogowski, David Rouffet, Frédéric Lambalot, Olivier Brosseau and Christophe Hautier

This study compared EMG activity of young tennis players’ muscles during forehand drives in two groups, GD—those able to raise by more than 150% the vertical velocity of racket-face at impact from flat to topspin forehand drives, and GND, those not able to increase their vertical velocity to the same extent. Upper limb joint angles, racket-face velocities, and average EMGrms values, were studied. At similar joint angles, a fall in horizontal velocity and a rise in racket-face vertical velocity from flat to topspin forehand drives were observed. Shoulder muscle activity rose from flat to topspin forehand drives in GND, but not for drives in GD. Forearm muscle activity reduced from flat to topspin forehand drives in GD, but muscle activation was similar in GND. The results show that radial deviation increased racket-face vertical velocity more at impact from the flat to topspin forehand drives than shoulder abduction.

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Beth Norris and Elaine Trudelle-Jackson

Context:

The Star Excursion Balance Test (SEBT) is often used to train and assess dynamic balance and neuromuscular control. Few studies have examined hip- and thigh-muscle activation during the SEBT.

Objective:

To quantify hip- and thigh-muscle activity during the SEBT.

Design:

Repeated measures.

Setting:

Laboratory.

Participants:

22 healthy individuals, 11 men and 11 women.

Methods:

EMG measurements were taken as participants completed 3 trials of the anterior (A), medial (M), and posteromedial (PM) reach directions of the SEBT.

Main Outcome Measures:

Mean EMG data (% maximal voluntary isometric contraction) from the gluteus medius (Gmed), gluteus maximus (Gmax), and vastus medialis (VM) were measured during the eccentric phase of each SEBT reach direction. Test–retest reliability of EMG data across the 3 trials in each direction was calculated. EMG data from each muscle were compared across the 3 reach directions.

Results:

Test–retest reliability ranged from ICC3,1 values of .91 to .99. A 2-way repeated-measure ANOVA revealed a significant interaction between muscle activation and reach direction. One-way ANOVAs showed no difference in GMed activity between the A and M directions. GMed activity in the A and M directions was greater than in the PM direction. There was no difference in GMax and VM activity across the 3 directions.

Conclusion:

GMed was recruited most effectively when reaching was performed in the A and M directions. The A, M, and PM directions elicited similar patterns of muscle recruitment for the GMax and VM. During all 3 SEBT directions, VM activation exceeded the 40–60% threshold suggested for strengthening effects. GMed activity also exceeded the threshold in the M direction. GMax activation, however, was below the 40% threshold for all 3 reach directions, suggesting that performing dynamic lower extremity reaching in the A, M, and PM directions may not elicit strengthening effects for the GMax.