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Kathleen A. Swanik, Kellie Huxel Bliven and Charles Buz Swanik

Context:

There are contradictory data on optimal muscle-activation strategies for restoring shoulder stability. Further investigation of neuromuscular-control strategies for glenohumeral-joint stability will guide clinicians in decisions regarding appropriate rehabilitation exercises.

Objectives:

To determine whether subscapularis, infraspinatus, and teres minor (anteroposterior force couple) muscle activation differ between 4 shoulder exercises and describe coactivation ratios and individual muscle-recruitment characteristics of rotator-cuff muscles throughout each shoulder exercise.

Design:

Crossover.

Setting:

Laboratory.

Participants:

healthy, physically active men, age 20.55 ± 2.0 y.

Interventions:

4 rehabilitation exercises: pitchback, PNF D2 pattern with tubing, push-up plus, and slide board.

Main Outcomes Measures:

Mean coactivation level, coactivation-ratio patterns, and level (area) of muscle-activation patterns of the subscapularis, infraspinatus, and teres minor throughout each exercise.

Results:

Coactivation levels varied throughout each exercise. Subscapularis activity was consistently higher than that of the infraspinatus and teres minor combined at the start of each exercise and in end ranges of motion. Individual muscle-recruitment levels in the subscapularis were also different between exercises.

Conclusion:

Results provide descriptive data for determining normative coactivation-ratio values for muscle recruitment for the functional exercises studied. Differences in subscapularis activation suggest a reliance to resist anteriorly directed forces.

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Ji-hyun Lee, Heon-seock Cynn, Sil-ah Choi, Tae-lim Yoon and Hyo-jung Jeong

Context:

Gluteus medius (Gmed) weakness is associated with some lower-extremity injuries. People with Gmed weakness might compensate by activating the tensor fasciae latae (TFL). Different hip rotations in the transverse plane may affect Gmed and TFL muscle activity during isometric side-lying hip abduction (SHA).

Objectives:

To compare Gmed and TFL muscle activity and the Gmed:TFL muscle-activity ratio during SHA exercise with 3 different hip rotations.

Design:

The effects of different hip rotations on Gmed, TFL, and the Gmed:TFL muscle-activity ratio during isometric SHA were analyzed with 1-way, repeated-measures analysis of variance.

Setting:

University research laboratory.

Participants:

20 healthy university students were recruited in this study.

Interventions:

Participants performed isometric SHA: frontal SHA with neutral hip (frontal SHAN), frontal SHA with hip medial rotation (frontal SHA-MR), and frontal SHA with hip lateral rotation (frontal SHA-LR).

Main Outcome Measures:

Surface electromyography measured the activity of the Gmed and the TFL. A 1-way repeated-measures analysis of variance assessed the statistical significance of Gmed and TFL muscle activity. When there was a significant difference, a Bonferroni adjustment was performed.

Results:

Frontal SHA-MR showed significantly greater Gmed muscle activation than frontal SHA-N (P = .000) or frontal SHA-LR (P = .015). Frontal SHA-LR showed significantly greater TFL muscle activation than frontal SHA-N (P = .002). Frontal SHA-MR also resulted in a significantly greater Gmed:TFL muscle-activity ratio than frontal SHA-N (P = .004) or frontal SHA-LR (P = .000), and frontal SHA-N was significantly greater than frontal SHA-LR (P = .000).

Conclusions:

Frontal SHA-MR results in greater Gmed muscle activation and a higher Gmed:TFL muscle ratio.

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Birgit Larsen, Michael Voigt and Michael J. Grey

The influence of pedaling frequency and crank load on the sensitivity of the soleus short latency stretch reflex (SLR) was examined in nine healthy subjects during pedaling by the use of a custom-built robotic actuator. The SLR decreased successively in downstroke when pedaling frequency increased from 20 to 40 and 60 revolutions per minute at a constant crank load (p = .005). The SLR was unchanged at crank load increases of 2.6 or 5.1 Nm at a constant pedaling frequency (p > .05). Accordingly, it was shown that increased muscle activation level as a consequence of added crank load and increased movement speed does not increase the sensitivity of the soleus SLR.

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Raffy Dotan

The current understanding of child-adult differences in muscular and neuromotor function will be reviewed while highlighting the gaps in our knowledge and raising research questions that could be addressed in the immediate or near future. Topics include muscle activation, muscle composition, strength attributes, strength- and aerobic-training, neuromotor development, where neuromuscular differences originate from, and the possible interrelationships between motor and cognitive function. The various differences will be discussed on their specific merits, but also as possible manifestations of a common underlying factor which, if true, could provide a more holistic view of child-adult functional differences.

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Jack M. Burns, Jeremiah J. Peiffer, Chris R. Abbiss, Greig Watson, Angus Burnett and Paul B. Laursen

Purpose:

Manufacturers of uncoupled cycling cranks claim that their use will increase economy of motion and gross efficiency. Purportedly, this occurs by altering the muscle-recruitment patterns contributing to the resistive forces occurring during the recovery phase of the pedal stroke. Uncoupled cranks use an independent-clutch design by which each leg cycles independently of the other (ie, the cranks are not fixed together). However, research examining the efficacy of training with uncoupled cranks is equivocal. The purpose of this study was to determine the effect of short-term training with uncoupled cranks on the performance-related variables economy of motion, gross efficiency, maximal oxygen uptake (VO2max), and muscle-activation patterns.

Methods:

Sixteen trained cyclists were matched-paired into either an uncoupled-crank or a normal-crank training group. Both groups performed 5 wk of training on their assigned cranks. Before and after training, participants completed a graded exercise test using normal cranks. Expired gases were collected to determine economy of motion, gross efficiency, and VO2max, while integrated electromyography (iEMG) was used to examine muscle-activation patterns of the vastus lateralis, biceps femoris, and gastrocnemius.

Results:

No significant changes between groups were observed for economy of motion, gross efficiency, VO2max, or iEMG in the uncoupled- or normal-crank group.

Conclusions:

Five weeks of training with uncoupled cycling cranks had no effect on economy of motion, gross efficiency, muscle recruitment, or VO2max compared with training on normal cranks.

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Se-yeon Park and Won-gyu Yoo

Objective:

The purpose of this study was to measure muscle activation during ascending and descending phases of the push-up exercise on both stable and unstable support surfaces.

Participants:

Fourteen asymptomatic male amateur badminton players. During push-up exercises on stable and unstable bases, muscle activation measurements were collected with phase divisions (ascending and descending phase).

Methods:

Electromyography (EMG) was utilized to measure activation of the upper trapezius (UT) and lower trapezius (LT), middle serratus anterior (MSA) and lower serratus anterior (LSA), pectoralis major (PM), and triceps brachii (TB) muscles.

Results:

An unstable support surface produced significantly greater activation of the UT, LT, LSA, and PM muscles than a stable support surface (p < 0.05). The MSA, LSA, TB, and PM muscles demonstrated greater activation during the ascending phase than the descending phase of the push-up exercise (p < 0.05).

Conclusions:

The unstable support surface appeared to produce relatively greater activation of the LSA than that of the MSA. The descending phase of the push-up did not demonstrate a higher level of activation for any of the muscles tested.

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Bart Van Gheluwe, Paul Huybrechts and Erik Deporte

This study evaluates the action of 20 selected arm and torso muscles. The subjects were 19 windsurfers of different skill levels. Muscular activity was recorded electromyographically, using surface electrodes. The subjects were standing on a specially devised windsurf simulator in order to keep the different surf postures as standardized as possible. Through two-way ANOVA techniques, the electromyographic activity relative to its maximal isometric value was compared for different muscles, surf postures, and skill levels. Also, differences between the left and right sides of the body were investigated. From the results, the following may be concluded: (a) As all muscles display rather low activity (an average of less than 20% of their maximal isometric values), windsurfing does not seem very demanding of muscular force. (b) The M. flexor carpi radialis, together with the M. erector spinae, tend to exhibit higher levels of activity for beginners, which suggests, respectively, a more rigid grip on the wishbone and stronger low back muscle activation in order to keep a correct posture, (c) Left–right asymmetries mainly occur for symmetrical body postures, especially for the M. flexor carpi radialis and the M. erector spinae. As for the M. trapezius (pars superior), experienced surfers tend to display a dominant right asymmetry, (d) Muscle activity does not exhibit significantly different values for various surf postures. However, typical deviating postures, as observed in beginners, may induce higher levels of muscle activation.

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Sabine Felser, Martin Behrens, Susanne Fischer, Mario Baeumler, Ralf Salomon and Sven Bruhn

Purpose:

To investigate differences in muscle activation of both legs between the straight and the curve and changes in muscle activity during a 1000-m time trial (TT) and their relationship to the change in skating velocity in 9 young short-track speed skaters. The authors recorded skating times and EMG data from different leg muscles during maximum-effort skating trials on the straight and in the curve, as well as during a 1000-m TT.

Results:

Muscle activation differs between the straight and the curves and between legs; ie, average activities of selected muscles of the right leg were significantly higher during skating through the curves than in the straights. This could not be observed for the left leg. The reduction in speed during the 1000-m TT highly correlates with the decrease in the muscle activity of both the tibialis anterior and the rectus femoris of the right leg. Muscle recruitment is different in relation to lap section (straight vs curve) and leg (right vs left leg). The decreased muscle activity of the tibialis anterior and rectus femoris of the right leg showed the highest relationships with the reduction in skating speed during the 1000-m TT.

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Sondra G. Siegel, T. Richard Nichols and Timothy C. Cope

Cutaneous reflexes have been described primarily according to their actions in the flexion/extension plane. It is shown here, by measuring electromyography and isometric force in decerebrate cats, that ankle muscles are activated in relation to their actions in the abduction/adduction plane during sural nerve (SNR) and crossed-extension (XER) reflexes. Ankle adductors (tibialis posterior, extensor digitorum longus, and flexors digitorum and hallucis longus) were active in XER, but not in SNR. Muscles producing ankle abduction (medial and lateral gastrocnemii and peroneus longus and brevis) were often activated in both reflexes, and medial gastrocnemius and peroneus longus were consistently more strongly activated in SNR than in XER. This differential pattern of muscle activation results in greater abduction torque at the ankle in SNR than in XER. These data demonstrate reflex organization in relation to the multidirectional torque generated by individual muscles.

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Nick Ball and Joanna Scurr

Electromyograms used to assess neuromuscular demand during high-velocity tasks require normalization to aid interpretation. This paper posits that, to date, methodological approaches to normalization have been ineffective and have limited the application of electromyography (EMG). There is minimal investigation seeking alternative normalization methods, which must be corrected to improve EMG application in sports. It is recognized that differing normalization methods will prevent cross-study comparisons. Users of EMG should aim to identify normalization methods that provide good reliability and a representative measure of muscle activation. The shortcomings of current normalization methods in high-velocity muscle actions assessment are evident. Advances in assessing alternate normalization methods have been done in cycling and sprinting. It is advised that when normalizing high-intensity muscle actions, isometric methods are used with caution and a dynamic alternative, where the muscle action is similar to that of the task is preferred. It is recognized that optimal normalization methods may be muscle and task dependent.