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Dean C. Hay, Mark P. Wachowiak and Ryan B. Graham

Advances in time-frequency analysis can provide new insights into the important, yet complex relationship between muscle activation (ie, electromyography [EMG]) and motion during dynamic tasks. We use wavelet coherence to compare a fundamental cyclical movement (lumbar spine flexion and extension) to the surface EMG linear envelope of 2 trunk muscles (lumbar erector spinae and internal oblique). Both muscles cohere to the spine kinematics at the main cyclic frequency, but lumbar erector spinae exhibits significantly greater coherence than internal oblique to kinematics at 0.25, 0.5, and 1.0 Hz. Coherence phase plots of the 2 muscles exhibit different characteristics. The lumbar erector spinae precedes trunk extension at 0.25 Hz, whereas internal oblique is in phase with spine kinematics. These differences may be due to their proposed contrasting functions as a primary spine mover (lumbar erector spinae) versus a spine stabilizer (internal oblique). We believe that this method will be useful in evaluating how a variety of factors (eg, pain, dysfunction, pathology, fatigue) affect the relationship between muscles’ motor inputs (ie, activation measured using EMG) and outputs (ie, the resulting joint motion patterns).

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David Hawkins and Mark Smeulders

The purpose of this study was to determine if the characteristic Hill model, used to describe me force–velocity relationship for isolated tetanically stimulated muscle, could be modified and used to describe me torque–velocity behavior of me hip for maximally and submaximally stimulated hip extensor muscles. Fourteen subjects performed hip extension movements at effort levels of 100%, 70%, and 40% of a maximum isometric effort. A solenoid provided isometric resistance to hip extension. Once the desired effort level was achieved, as indicated by me isometric force, the solenoid released and me hip moved against an opposing elastic resistance equal to 75%, 50%, 25%, and 0% of the specified effort level. An electrogoniometer quantified hip angle. Hip velocity was determined by numerically differentiating the angle data. Torque-velocity-activation (or effort level) data were determined for each trial. Model parameters were determined to give me best fit to the data for each subject. Average parameter values were determined for each gender and for the entire group. The modified Hill-type model, T m = (T max · AK 1 · ω)/(K2 · ω + 1), accurately describes me relationship between joint torque (T m), maximum isometric joint torque (T max), joint velocity (ω), and muscle activation level (A) for subject-specific parameters (K 1 and K 2), but not for parameters averaged across genders or the entire group. Values for T max, K 1, and K 2 ranged from 90 to 385 Nm, 6.1 to 47.9 Nms, and 0.030 to 0.716 s, respectively.

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Chia-Wei Lin, Fong-Chin Su and Cheng-Feng Lin

Ballet deep squat with legs rotated externally (grand plié) is a fundamental movement for dancers. However, performing this task is a challenge to ankle control, particularly for those with ankle injury. Thus, the purpose of this study was to investigate how ankle sprains affect the ability of postural and muscular control during grand plié in ballet dancers. Thirteen injured dancers and 20 uninjured dancers performed a 15 second grand plié consisting of lowering, squatting, and rising phases. The lower extremity motion patterns and muscle activities, pelvic orientation, and center of pressure (COP) excursion were measured. In addition, a principal component analysis was applied to analyze waveforms of muscle activity in bilateral medial gastrocnemius, peroneus longus, and tibialis anterior. Our findings showed that the injured dancers had smaller pelvic motions and COP excursions, greater maximum angles of knee flexion and ankle dorsiflexion as well as different temporal activation patterns of the medial gastrocnemius and tibialis anterior. These findings suggested that the injured dancers coped with postural challenges by changing lower extremity motions and temporal muscle activation patterns.

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Vinícius Yan Santos Nascimento, Rafaela Joyce Barbosa Torres, Natália Barros Beltrão, Priscila Soares dos Santos, André Luiz Torres Pirauá, Valéria Mayaly Alves de Oliveira, Ana Carolina Rodarti Pitangui and Rodrigo Cappato de Araújo

This study evaluated the effects of instability on the EMG activity of scapular stabilizing and upper limb muscles during exercises with axial and rotational load. Twenty male volunteers (20.9 ± 1.8 years, 174.1 ± 0.04 cm, 73.17 ± 8.77 kg) experienced in strength training participated in a crossover design. Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major (PM), biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) were determined on both conditions. Participants performed a single series of 10 repetitions of bench press and fly exercises on stable (bench) and unstable (proprioceptive disc) conditions at 60% of 1-RM. The Friedman test and post hoc Dunn’s indicated that the unstable condition showed greater EMG activity for AD (P = .001) and BB (P = .002) on the fly exercise, SA (P = .001) and LT (P = .048) on the bench press, and PM (P ≤ .002) on both exercises. These results show that using an unstable surface in exercises with rotational load provides superior EMG activity of the agonist muscles, while in exercise with axial load, the instability favors EMG activity of the scapular stabilizing muscles.

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Brian Caulfield, Tara Crammond, Angela O’Sullivan, Susan Reynolds and Tomas Ward

Context:

Identification of motor control deficit associated with Functional Instability (FI) of the ankle joint.

Objective:

T o compare patterns of ankle muscle activation during jump landing in participants with FI and a control group.

Design:

Cross-sectional comparison.

Setting:

Research laboratory.

Participants:

Twelve participants with FI (6 m, 6 f; age, 26.4 ± 4.6 years) and 10 control subjects (5 m, 5 f; age 24.9 ± 2.5 years).

Main Outcome Measures:

Integrated electromyographic (IEMG) activity of ankle musculature in the 150-millisecond period immediately prior to and post impact during 2 different jump landing activities.

Results:

Participants with FI demonstrated a significant reduction in pre-impact peroneus longus IEMG activity during both jumping activities compared to controls (P < .05). There were no significant differences between the groups’ soleus or tibialis anterior IEMG activity during the pre- or post-impact periods.

Conclusions:

These results help to further our understanding of changes in control of ankle movement during dynamic activity in participants with FI.

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David Hawkins and Mark Smeulders

The purpose of this study was to determine if the Hill model, used to describe the force-velocity relationship for isolated tetanically stimulated muscle, could be modified and used to describe the torque-velocity behavior of the knee for maximally and submaximally stimulated quadriceps and hamstrings muscles. Fourteen subjects performed both knee flexion and extension movements at 100%, 70%, and 40% of maximum isometric effort. For each effort level, the knee was allowed to move against resistances equal to 75%, 50%, 25%, and 0% of the specified effort level. An electrogoniometer quantified knee angle. Knee velocity was determined by numerically differentiating the joint angle data. Torque-velocity-activation (or effort level) data were determined for each trial. Model parameters were determined to give the best fit to the data for each subject. Average parameter values were determined for each gender and for the entire group. The modified Hill-type model accurately described the relationship between torque, velocity, and muscle activation level for subject-specific parameters but not for parameters averaged across genders or the entire group.

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Rafaela J.B. Torres, André L.T. Pirauá, Vinícius Y.S. Nascimento, Priscila S. dos Santos, Natália B. Beltrão, Valéria M.A. de Oliveira, Ana Carolina R. Pitangui and Rodrigo C. de Araújo

The aim of this study was to evaluate the acute effect of the use of stable and unstable surfaces on electromyography (EMG) activity and coactivation of the scapular and upper-limb muscles during the push-up plus (with full protraction of the scapula). Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major, biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) levels and coactivation index were determined by surface EMG in 20 young men during push-up plus performed on a stable and unstable condition (2 unstable devices applied to hands and feet). The paired t test and Cohen d were used for statistical analysis. The results showed that during the execution of the push-up plus on the unstable surface an increased EMG activity of the scapular stabilizing muscles (SA, MT, and LT) was observed, while AD and PD muscles showed a decrease. During exercise execution on the unstable surface there was a higher index of coactivation of the scapular muscles (SA–MT and UT–LT pairs). No significant differences were observed in TB–BB and AD–PD pairs. These results suggest that the push-up-plus exercise associated with unstable surfaces produced greater EMG activity levels and coactivation index of the scapular stabilizing muscle. On the other hand, the use of an unstable surface does not promote the same effect for the shoulder muscles.

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Samantha N. Boudreau, Maureen K. Dwyer, Carl G. Mattacola, Christian Lattermann, Tim L. Uhl and Jennifer Medina McKeon

Context:

Functional exercises are often used in strengthening programs after lower extremity injury. Activation levels of the stabilizing hip muscles have not been documented.

Objective:

To document the progression of hip-muscle activation levels during 3 lower extremity functional exercises.

Design:

Cross-sectional.

Setting:

Laboratory.

Participants:

44 healthy individuals, 22 women and 22 men.

Intervention:

Subjects, in 1 testing session, completed 3 trials each of the lunge (LUN), single-leg squat (SLSQ), and step-up-and-over (SUO) exercise.

Main Outcome Measures:

Root-mean-square muscle amplitude (% reference voluntary muscle contraction) was measured for 5 muscles during the 3 exercises: rectus femoris (RF), dominant and nondominant gluteus medius (GMed_D and GMed_ND), adductor longus (ADD), and gluteus maximus (GMX).

Results:

The RF, GMAX, and GMed_D were activated in a progression from least to greatest during the SUO, LUN, and SLSQ. The progression for the GMed_ND activation was from least to greatest during the SLSQ, SUO, and then LUN. Activation levels of the ADD showed no progression.

Conclusion:

Progressive activation levels were documented for muscles acting on the hip joint during 3 functional lower extremity exercises. The authors recommend using this exercise progression when targeting the hip muscles during lower extremity strengthening.

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Jennifer E. Earl, Jay Hertel and Craig R. Denegar

Context:

Dynamic malalignment (DM), abnormal muscle activation, and static malalignments all might lead to patellofemoral pain (PFP) but have not been examined using a multifactorial approach.

Objective:

To determine which measures of static malalignment, DM, and muscle-onset times best predict PFP.

Design and Setting:

Between-subjects, laboratory.

Subjects:

2 groups (PFP and uninjured) of 16 subjects each.

Interventions:

EMG and 3-D kinematic data were recorded during a step-down. Five static-alignment assessments were performed.

Measurements:

Three discriminant analyses using injury as the grouping variable and static measures, joint angles, and EMG onsets as the predictor variables. A final combined discriminant analysis using the most predictive variables from each set.

Results:

The static-alignment discriminant function was most predictive (81.3% correct), followed by the kinematic (69%) and the EMG (67%) functions. The final discriminant function included iliotibial-band flexibility, navicular drop, pronation, knee flexion, hip adduction, gluteus medius, and vastus medialis obliquus onset time and correctly classified 92.3% of PFP subjects.

Conclusions:

PFP can most accurately be predicted when multiple measures of lower extremity function are considered together.

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Joseph S. Parry, Rachel Straub and Daniel J. Cipriani

Context:

The Bodyblade Pro is used for shoulder rehabilitation after injury. Resistance is provided by blade oscillations—faster oscillations or higher speeds correspond to greater resistance. However, research supporting the Bodyblade Pro’s use is scarce, particularly in comparison with dumbbell training.

Objective:

To compare muscle activity, using electromyography (EMG), in the back and shoulder regions during shoulder exercises with the Bodyblade Pro vs dumbbells.

Design:

Randomized crossover study.

Setting:

San Diego State University biomechanics laboratory.

Participants:

11 healthy male subjects age 19–32 y.

Intervention:

Subjects performed shoulder-flexion and -abduction exercises using a Bodyblade Pro and dumbbells (5, 8, and 10 lb) while EMG recorded activity of the deltoid, pectoralis major, infraspinatus, serratus anterior, and erector spinae.

Main Outcome Measures:

Average peak muscle activity (% maximum voluntary isometric contraction) was separately measured for shoulder abduction and flexion in the range of 85° to 95°. Differences among exercise devices were separately analyzed for the flexed and abducted positions using 1-way repeated-measures ANOVA.

Results:

The Bodyblade Pro produced greater muscle activity than all the dumbbell trials. Differences were significant for all muscles measured (all P < .01) except for the erector spinae during shoulder flexion with a 10-lb dumbbell. EMG activity for the Bodyblade Pro exceeded 50% of the MVIC during both shoulder flexion and abduction. For the dumbbell conditions, only the 10-lb trials approached this effect.

Conclusions:

Using a Bodyblade during shoulder exercises results in greater shoulder- and back-muscle recruitment than dumbbells. The Bodyblade Pro can activate multiple muscles in a single exercise and thereby minimize the need for multiple dumbbell exercises. The Bodyblade Pro is an effective device for shoulder- and back-muscle activation that warrants further use by clinicians interested in its use for rehabilitation.