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Momoko Yamagata, Ali Falaki and Mark L. Latash

Simultaneous activation of muscles with opposing actions, addressed as agonist–antagonist muscle coactivation, is a very common phenomenon, which has been studied across species, effectors, and behaviors (reviewed in Latash, 2018 ; Smith, 1981 ; Tilney & Pike, 1925 ). There is, however, no clear

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Harsh H. Buddhadev and Philip E. Martin

Higher aerobic demand or energy expenditure of locomotion is a commonly reported change associated with advancing age ( Hortobágyi, Finch, Solnik, Rider, & DeVita, 2011 ; Mian, Thom, Ardigo, Narici, & Minetti, 2006 ; Peterson & Martin, 2010 ). Greater coactivation of antagonist muscles has also

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Rachael D. Seidler-Dobrin, jiping He and George E. Stelmach

The aim of this experiment was to determine whether elderly persons exhibit reciprocal phasing of muscle activity and scale EMG burst amplitude in the same manner as young people. Seven young and 7 elderly adults performed 30° elbow flexion movements at 800 ms duration to a visual target against varying inertial loads. The elderly were not able to achieve the required movement duration as frequently and spent a greater portion of the movement accelerating than the young. The young and the elderly subjects scaled EMG burst amplitude to the increasing loads in the same fashion, although the elderly subjects coactivated the agonisthtagonist muscles more than did the young subjects and thus did not accelerate the limb as rapidly. We hypothesized that the elderly used coactivation to reduce movement variability, and we developed a single-joint model with two muscles to examine this hypothesis. The model simulation correctly predicted the variability reduction due to coactivation. It appears, however, that this reduces the capability to accelerate rapidly.

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Nahid Tahan, Amir Massoud Arab, Bita Vaseghi and Khosro Khademi

Context:

Coactivation of abdominal and pelvic-floor muscles (PFM) is an issue considered by researchers recently. Electromyography (EMG) studies have shown that the abdominal-muscle activity is a normal response to PFM activity, and increase in EMG activity of the PFM concomitant with abdominal-muscle contraction was also reported.

Objective:

The purpose of this study was to compare the changes in EMG activity of the deep abdominal muscles during abdominal-muscle contraction (abdominal hollowing and bracing) with and without concomitant PFM contraction in healthy and low-back-pain (LBP) subjects.

Design:

A 2 × 2 repeated-measures design.

Setting:

Laboratory.

Participants:

30 subjects (15 with LBP, 15 without LBP).

Main Outcome Measures:

Peak rectified EMG of abdominal muscles.

Results:

No difference in EMG of abdominal muscles with and without concomitant PFM contraction in abdominal hollowing (P = .84) and abdominal bracing (P = .53). No difference in EMG signal of abdominal muscles with and without PFM contraction between LBP and healthy subjects in both abdominal hollowing (P = .88) and abdominal bracing (P = .98) maneuvers.

Conclusion:

Adding PFM contraction had no significant effect on abdominal-muscle contraction in subjects with and without LBP.

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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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John P. Miller and Ronald V. Croce

Context:

Researchers have postulated that coactivation of the hamstrings during active knee extension assists the anterior cruciate ligament in maintaining knee joint stability by exerting an opposing force to anterior tibial translation.

Objective:

To compare the reciprocal coactivation of the hamstrings while performing low and high velocity isokinetic movements and two closed chain movements.

Design:

Within subject’s comparison of isokinetic and closed chain exercises.

Setting:

Biomechanics laboratory utilizing a Cybex norm isokinetic dynamometer and Biopac Data Collection system.

Participants:

12 healthy women.

Main Outcome Measures:

The root mean square of the Electromyogram (rmsEMG) was used as a measure of overall muscle activity.

Results:

The rmsEMG for hamstring coactivation during knee extension showed significant differences between the isokinetic movements and the closed chain exercises with greater coactivation when performing the isokinetic movements. In addition, greater activity was seen at the higher isokinetic velocity and during the one legged squat.

Conclusions:

These results suggest isokinetic movements, particularly at high speed, can more effectively increase the coactivation activity of the hamstrings when compared to two closed chain activities.

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Joanne N. Hodder, Tova E. Plashkes, Regan A. Franklin, Heather K. Hickey and Monica R. Maly

Coactivation of the knee extensors and flexors increases knee joint contact forces, which may lead to degradation of the articular surfaces. This study investigated the effect of neuromuscular fatigue induced by submaximal, repetitive, dynamic contractions on coactivation of knee musculature in young and middle-aged women. Data from 10 young women (24.6 ± 1.8 years) and 8 middle-aged women (55.4 ± 4.2 years) were analyzed. Measures included peak knee extension and flexion torques and the average amplitude of surface electromyography of rectus femoris and biceps femoris. Coactivation ratios were calculated from these activations. To induce fatigue, participants completed up to ten sets of 50 concentric knee extension and flexion contractions at 60°/s. A two-factor analysis of variance was used to determine the effect of age and fatigue. The young group showed higher peak torque compared with the middle-aged group (P < .001). During flexion, biceps femoris activity increased after fatigue when both groups were considered together (P = .018). During extension, biceps femoris activity was higher in the middle-aged than young group (P = .043). Middle-aged women exhibited a trend for greater coactivation during knee extension compared with young women (P = .066). This coactivation likely contributed to extension torque decrements in middle-aged women.

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Tania Suarez, Luca Laudani, Arrigo Giombini, Vincenzo Maria Saraceni, Pier Paolo Mariani, Fabio Pigozzi and Andrea Macaluso

Context:

Tearing of the anterior cruciate ligament (ACL) may disrupt the ability to recognize the knee position in space during limb-repositioning tasks, which is referred to as joint-position sense (JPS). Impairments in JPS have been shown to be lower during active than passive repositioning tasks, thus suggesting that coactivation patterns of the muscles surrounding the knee might compensate for the disrupted JPS and ensure accurate limb repositioning in ACL-deficient individuals.

Objective:

To investigate muscle coactivation patterns during JPS repositioning tasks in ACL-deficient and healthy individuals.

Design:

Prospective observational study.

Setting:

Functional assessment laboratory.

Participants:

8 men age 25 ± 8 y with isolated ACL rupture and 10 men age 30 ± 4 y with no history of knee injury.

Intervention:

JPS was evaluated by means of an electrogoniometer in a sitting position during either passive or active joint-positioning and -repositioning tasks with a 40° target knee angle.

Main Outcome Measures:

Root mean square (RMS) of the surface electromyogram from the vastus lateralis and biceps femoris muscles was measured during active joint positioning and repositioning.

Results:

Healthy participants showed a significant decrease in vastus lateralis RMS (−19%) and an increase in biceps femoris RMS (+26%) during joint repositioning compared with positioning. In contrast, ACL-deficient patients showed no modulation in muscle coactivation between joint positioning and repositioning, although they exhibited significantly lower RMS of the vastus lateralis (injured limb, −28%; uninjured limb, −21%) and higher RMS of the biceps femoris (injured limb, +19%; uninjured limb, +30%) than the healthy participants during joint positioning.

Conclusions:

The lack of modulation in muscle coactivation patterns between joint positioning and repositioning in ACL-deficient patients might be attributed to disrupted neural control after the injury-related loss of proprioceptive information. These results should be taken into account in the design of rehabilitation protocols with emphasis on muscle coactivation and JPS.

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Gulcan Harput, A. Ruhi Soylu, Hayri Ertan, Nevin Ergun and Carl G. Mattacola

Context:

Coactivation ratio of quadriceps to hamstring muscles (Q:H) and medial to lateral knee muscles (M:L) contributes to the dynamic stability of the knee joint during movement patterns recommended during rehabilitation and important for daily function.

Objective:

To compare the quadriceps-to-hamstring and medial-to-lateral knee muscles' coactivation ratios between men and women during the following closed kinetic chain exercises performed on a balance board: forward lunge, side lunge, single-leg stance, and single-leg squat.

Design:

Cross-sectional.

Participants:

20 healthy subjects (10 female and 10 male).

Main Outcome Measures:

Surface electromyography was used to measure the activation level of quadriceps (vastus lateralis and medialis) and hamstrings (biceps femoris and medial hamstrings) during forward- and side-lunge, single-leg-stance, and single-leg-squat exercises. Subjects were instructed during each exercise to move into the test position and to hold that position for 15 s. EMG was recorded during the 15-s isometric period where subjects tried to maintain a “set” position while the foot was on a balance board. Analysis of variance was used for statistical analysis.

Results:

There was a significant exercise-by-gender interaction for Q:H ratio (F 3,48 = 6.63, P = .001), but the exercise-by-gender interaction for M:L ratio was not significant (F 3,48 = 1.67, P = .18). Women showed larger Q:H ratio in side-lunge exercises than men (P = .002). Both genders showed larger M:L and lower Q:H ratio in a single-leg-stance exercise than in the other exercises.

Conclusions:

The results indicate that the forward- and side-lunge and single-leg-squat exercises should not be recommended as exercise where a balanced coactivation between quadriceps and hamstring muscles is warranted. Single-leg-stance exercise could be used when seeking an exercise where the ratio is balanced for both women and men.

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Ronald V. Croce, John P. Miller, Robert Confessore and James C. Vailas

The purpose of this study was to examine coactivation patterns of the lateral and medial quadriceps and the lateral and medial hamstrings during low- and moderate-speed isokinetic movements. Twelve female athletes performed isokinetic knee assessments at 60 and 180°/s. Root mean square electromyographic (rmsEMG) activity and the median frequency of the EMG (mfEMG) were determined by placing bipolar surface electrodes on the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and medial hamstrings (MH). Results of rmsEMG indicated that the VM showed almost twice the coactivation of the VL (p < .05), and that the BF showed almost four times the coactivation of the MH (p < .05). Finally, differences were noted in the mfEMG (p < .05), with the VM displaying different recruitment patterns at 180°/s as an agonist compared to that as an antagonist. Results indicated that when acting as antagonists, the VM and BE display the greatest EMG patterns during isokinetic knee joint movement.