MUSCLE ACTIVITY DURING KNEE‐EXTENSION STRENGTHENING EXERCISE PERFORMED WITH ELASTIC TUBING AND ISOTONIC RESISTANCE

Background/Purpose:

While elastic resistance training, targeting the upper body is effective for strength training, the effect of elastic resistance training on lower body muscle activity remains questionable. The purpose of this study was to evaluate the EMG‐angle relationship of the quadriceps muscle during 10‐RM knee‐extensions performed with elastic tubing and an isotonic strength training machine.

Methods:

7 women and 9 men aged 28‐67 years (mean age 44 and 41 years, respectively) participated. Electromyographic (EMG) activity was recorded in 10 muscles during the concentric and eccentric contraction phase of a knee extension exercise performed with elastic tubing and in training machine and normalized to maximal voluntary isometric contraction (MVC) EMG (nEMG). Knee joint angle was measured during the exercises using electronic inclinometers (range of motion 0‐90°).

Results:

When comparing the machine and elastic resistance exercises there were no significant differences in peak EMG of the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) during the concentric contraction phase. However, during the eccentric phase, peak EMG was significantly higher (p<0.01) in RF and VM when performing knee extensions using the training machine. In VL and VM the EMG‐angle pattern was different between the two training modalities (significant angle by exercise interaction). When using elastic resistance, the EMG‐angle pattern peaked towards full knee extension (0°), whereas angle at peak EMG occurred closer to knee flexion position (90°) during the machine exercise. Perceived loading (Borg CR10) was similar during knee extensions performed with elastic tubing (5.7±0.6) compared with knee extensions performed in training machine (5.9±0.5).

Conclusion:

Knee extensions performed with elastic tubing induces similar high (>70% nEMG) quadriceps muscle activity during the concentric contraction phase, but slightly lower during the eccentric contraction phase, as knee extensions performed using an isotonic training machine. During the concentric contraction phase the two different conditions displayed reciprocal EMG‐angle patterns during the range of motion.

Level of Evidence:

5     

EFFECT OF RESTRICTED HIP FLEXOR MUSCLE LENGTH ON HIP EXTENSOR MUSCLE ACTIVITY AND LOWER EXTREMITY BIOMECHANICS IN COLLEGE‐AGED FEMALE SOCCER PLAYERS

Background

Hip flexor tightness is theorized to alter antagonist muscle function through reciprocal inhibition and synergistic dominance mechanisms. Synergistic dominance may result in altered movement patterns and increased risk of lower extremity injury.

Hypothesis/Purpose

To compare hip extensor muscle activation, internal hip and knee extension moments during double‐leg squatting, and gluteus maximus strength in those with and without clinically restricted hip flexor muscle length.

Design

Causal‐comparative cross‐sectional laboratory study.

Method

Using a modified Thomas Test, female soccer athletes were assigned to a restricted (>0 ° of sagittal plane hip motion above the horizontal; n=20, age=19.9 ± 1 years, ht=167.1 ± 6.4 cm, mass=64.7 ± 8.2kg) or normal (>15 ° of sagittal plane hip motion below horizontal; n=20, age=19.4 ± 1 years, ht=167.2 ± 5.5 cm, mass=61.2 ± 8.6 kg) hip flexor muscle length group. Surface electromyographic (sEMG) activity of the gluteus maximus and biceps femoris, and net internal hip and knee extension moments were measured between groups during a double‐leg squat. Isometric gluteus maximus strength was assessed using handheld dynamometry.

Results

Individuals with restricted hip flexor muscle length demonstrated less gluteus maximus activation (p=0.008) and a lower gluteus maximus : biceps femoris co‐activation ratio (p=0.004). There were no significant differences (p>0.05) in hip or knee extension moments, isometric gluteus maximus strength, or biceps femoris activation between groups.

Conclusions

Female soccer athletes with hip flexor muscle tightness exhibit less gluteus maximus activation and lower gluteus maximus : biceps femoris co‐activation while producing similar net hip and knee extension moments. Thus, individuals with hip flexor muscle tightness appear to utilize different neuromuscular strategies to control lower extremity motion.

Level of Evidence

3     

TRUNK AND HIP ELECTROMYOGRAPHIC ACTIVITY DURING SINGLE LEG SQUAT EXERCISES DO SEX DIFFERENCES EXIST?

Purpose/Background:

Researchers have identified sex‐differences in lower extremity muscle activation during functional activities that involve landing and cutting maneuvers. However, less research has been conducted to determine if muscle activation differences occur during rehabilitation exercises. The purpose of this investigation was to determine if sex‐differences exist for activation amplitudes of the trunk and hip muscles during four single leg squat (SLS) exercises.

Methods:

Eighteen males and 16 females participated. Surface electromyography (EMG) was used to determine muscle activity of the abdominal obliques (AO), lumbar extensors (LE), gluteus maximus (GMX), and gluteus medius (GM) during four SLS exercises. Data were expressed as a percentage of a maximum voluntary isometric contraction (% MVIC). A 2 X 4 mixed‐model analysis of variance with repeated measures was used to determine the interaction between sex and exercise on each muscle''s activity.

Results:

No interaction effect existed between sex and exercise. A main effect for sex existed for the GM and LE. On average, females generated 39% greater GM (27.6 ± 10.4 % MVIC versus 19.8 ± 10.5 % MVIC) and 40% greater LE (8.0 ± 2.8 % MVIC versus 5.7 ± 2.8 % MVIC) activity than males. All subjects, regardless of sex, demonstrated similar GMX and AO activity. Overall EMG values ranged from 11.0 % MVIC to 14.7 % MVIC for the GMX and 5.7 % MVIC to 8.8 % MVIC for the AO.

Conclusions:

None of the subjects generated sufficient EMG activity for strength gains. Females generated a moderate level of GM activity appropriate for neuromuscular re‐education/endurance. Males generated a low level of GM activity that may not necessarily be sufficient to improve GM function. Subjects exhibited low levels of EMG activity for the other muscles. These findings suggest that clinicians modify and/or prescribe different exercises than those studied herein for the purpose of improving GM, GMX, AO, and LE function.

Level of Evidence:

3b     

THE RELIABILITY OF REHABILITATIVE ULTRASOUND IMAGING IN THE MEASUREMENT OF INFRASPINATUS MUSCLE FUNCTION IN THE SYMPTOMATIC AND ASYMPTOMATIC SHOULDERS OF PATIENTS WITH UNILATERAL SHOULDER IMPINGEMENT SYNDROME

Background:

Rehabilitative ultrasound Imaging (RUSI) is increasingly used in the management of musculoskeletal conditions as it provides an objective measure of muscle function while being less invasive than needle electromyography. While research has documented the ability to reliably measure trunk muscles in patients with back pain, no study to date has used RUSI to quantify infraspinatus muscle function in patients with shoulder impingement syndrome (SIS).

Hypothesis/Purpose:

The purpose of this study was to examine the intra‐rater and inter‐rater reliability of measuring infraspinatus muscle thickness with RUSI and to compare such measures during resting versus contracted muscle states and in the symptomatic versus asymptomatic shoulders in patients with SIS.

Study Design:

Cross‐sectional, measurement study

Methods:

Fifty‐two participants with unilateral SIS underwent a standard baseline examination to include RUSI of the infraspinatus muscle bilaterally. Images were acquired at rest and during a submaximal isometric contraction, by two novice examiners. The isometric contraction was elicited by having prone participants externally rotate their shoulder from a position of 90° abduction into a dynamometer and hold a static force of 20 mmHg (approximately 20‐30% maximal voluntary contraction). Images were captured using a standardized placement of the transducer placed just inferior to the spine of the scapula along the medial scapular border and measured off‐line using Image J software (V1.38t, National Institutes of Health, Bethesda, Maryland).

Results:

Estimates (ICCs) for thickness measurements ranged between 0.96 and 0.98 for intra‐rater reliability and between 0.87 and 0.92 for inter‐rater reliability. Reliability was substantially lower (ICC = 0.43 to 0.79) for calculations of percent thickness change. The infraspinatus muscle was significantly thicker when contracted (19.1mm) than during rest (16.2mm) in both shoulders (p < 0.001). There was also a statistically significant interaction between contraction state and shoulder (p = 0.026), indicating that the change in thickness that occurred during contraction was significantly smaller in the symptomatic shoulder than in the asymptomatic shoulder.

Conclusion:

RUSI measurements of infraspinatus muscle thickness appear to be highly reliable, both within the same examiner and between different examiners, in patients with SIS. Moreover, such measurements were different in rested and contracted states of the infraspinatus, as well as, between the symptomatic and asymptomatic shoulders of patients with unilateral SIS.

Level of evidence:

Level 2     

EMG Analysis and Sagittal Plane Kinematics of the Two‐Handed and Single‐Handed Kettlebell Swing: A Descriptive Study

Introduction

Kettlebell (KB) swing exercises have been proposed as a possible method to improve hip and spinal motor control as well as improve power, strength, and endurance.

Purpose

To describe electromyographic (EMG) and sagittal plane kinematics during two KB exercises: the two‐handed KB swing (THKS) and the single‐handed KB swing (SHKS). In addition, the authors sought to investigate whether or not hip flexor length related to the muscular activity or the kinematics of the exercise.

Methods

Twenty‐three healthy college age subjects participated in this study. Demographic information and passive hip flexor length were recorded for each subject. A maximum voluntary isometric contraction (MVIC) of bilateral gluteus maximus (GMAX), gluteus medius (GMED), and biceps femoris (BF) muscles was recorded. EMG activity and sagittal plane video was recorded during both the THKS and SHKS in a randomized order. Normalized muscular activation of the three studied muscles was calculated from EMG data.

Results

During both SHKS and THKS, the average percent of peak MVIC for GMAX was 75.02% ± 55.38, GMED 55.47% ± 26.33, and BF 78.95% ± 53.29. Comparisons of the mean time to peak activation (TTP) for each muscle showed that the biceps femoris was the first muscle to activate during the swings. Statistically significant (p < .05), moderately positive correlations (r = .483 and .417) were found between passive hip flexor length and % MVIC for the GMax during the SHKS and THKS, respectively.

Conclusions

The THKS and SHKS provide sufficient muscular recruitment for strengthening of all of the muscles explored. This is the first study to show significant correlations between passive hip flexor length and muscular activation of hip extensors, particularly the GMax. Finally, the BF consistently reached peak activity before the GMax and GMed during the SHKS.

Level of Evidence

Level 3     

AN ELECTROMYOGRAPHIC STUDY OF THE VASTII MUSCLES DURING OPEN AND CLOSED KINETIC CHAIN SUBMAXIMAL ISOMETRIC EXERCISES

Background:

Rehabilitation programs for patients with patellofemoral dysfunction aim to recruit the vastus medialis obliquus muscle (VMO) in an attempt to reduce pain and to improve patellar tracking.

Objectives:

The aim of the present study was to use surface EMG to assess the effectiveness of two isometric submaximal contractions (10% and 60% of maximal voluntary contraction, MVC) in promoting preferential activation of VMO over vastus medialis longus (VML) and vastus lateralis (VL) in open and closed kinetic chain isometric exercises with the knee joint fixed at 30, 60 and 90 degrees of flexion.

Methods and Measures:

Surface electromyography (EMG) signals were recorded with linear adhesive arrays of four electrodes from fourteen healthy young men (age 23.5±3.2, mean±SD) during isometric knee extension contractions at 10% and 60% of the maximum voluntary contraction (MVC) for 1 min and 20 s respectively at 30, 60 and 90 degrees of knee flexion. Initial values and rate of change (slope) of mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) of the EMG signal were calculated.

Results:

Comparisons between the force levels produced at 10% and 60% MVC revealed that the initial values of ARV and CV for the VL, VML and VMO muscle were greater at 60% MVC compared to 10% MVC (3‐way ANOVA; F=536; p<0.001, F=49: p<0.01 for ARV and CV respectively). Comparisons between the different muscles demonstrated lower initial values of CV for VMO compared to VL and VLM at 10% and 60% of MVC (F=15; p<0.05). In addition, initial estimates of ARV were higher for VMO compared to VML at both force levels (F=66; p<0.05). Comparisons between open and closed kinetic chain exercises revealed higher initial estimates of ARV for open kinetic chain knee extension at both force levels (F=62; p<0.01). In addition, the absolute value of MNF slope appeared to increase at higher angles for closed kinetic chain at 60% MVC while it was minimum at 60° degrees for open kinetic chain. No significant differences were observed in the rate of change of CV and MNF among the three muscles.

Conclusions:

Based on the results of this study, both open and closed kinetic chain exercise similarly activate the three portions of the quadriceps muscle, suggesting that selective training of the vastii muscle is not achievable in these conditions.     

THE IMPACT OF SAGITTAL PLANE HIP POSITION ON ISOMETRIC FORCE OF HIP EXTERNAL ROTATOR AND INTERNAL ROTATOR MUSCLES IN HEALTHY YOUNG ADULTS

Purpose/Background:

Hip external rotator (ER) and internal rotator (IR) muscle weakness is theorized to be associated with lower extremity injury in athletes including knee ligament tears and patellofemoral pain. Previous studies investigating hip musculature strength have utilized various sagittal plane hip positions for testing. The relationship between results at these different positions is unknown.

Methods:

Eighty healthy, pain‐free young adults participated in the study: 40 female, mean age 22.90 (± 2.32) years, and 40 male, mean age 23.50 (± 2.15) years. Peak isometric torque of bilateral hip ER and IR were tested at 90° and 0° of hip flexion with an instrumented dynamometer. Peak muscle forces were calculated. Peak forces were normalized by body mass. Mean normalized force was calculated for dominant and non‐dominant limbs for ER and IR in both positions. Male and female data were analyzed separately with paired t‐tests (2‐tailed). Reference values for average muscle force and torque were calculated for dominant and non‐dominant limbs for both hip positions.

Results:

Hip IR normalized peak force was greater at 90° compared to 0° flexion position bilaterally in both genders (p < .01). Hip ER normalized peak force was greater at 90° compared to 0° flexion in dominant limbs of both genders and in non‐dominant limbs of males (p < .01). Non‐dominant hip ER normalized force in females was greater at 90° versus 0° flexion; however, it was not significant (p = .092). Post hoc analysis of normalized average force (average over 5‐second contraction) yielded similar results.

Conclusion:

Clinicians and researchers should use consistent positioning for testing of hip ER and IR strength. This will improve certainty of determining if a patient’s strength has changed or if differences between groups are present. Reference values reported will be useful in order to determine if weakness is present and to set goals, particularly in cases of bilateral involvement.

Level of Evidence:

2b     

Hand‐held Dynamometer Positioning Impacts Discomfort During Quadriceps Strength Testing: A Validity and Reliability Study

Purpose/Background

A belt‐stabilized hand‐held dynamometer (HHD) offers the ability to quantify quadriceps muscle strength in a clinical environment, but a limitation is participant discomfort at the interface between the HHD and the tibia. The purpose of this study was to quantify the level of discomfort associated with a modified belt‐stabilized HHD configuration compared to a standard belt‐stabilized configuration and an isokinetic dynamometer. The secondary purpose of this study was to determine the validity and reliability of a modified configuration used to measure quadriceps strength compared to the “gold‐standard” isokinetic dynamometer.

Methods

Twenty healthy participants (5 males, 15 females; age=24.7±2.2 years, height=171.1±8.8 cm, mass=72.0±18.7 kg) performed maximal knee extension isometric contractions during each of three testing conditions: isokinetic dynamometer, standard configuration with HHD placement on the tibia, and an alternative configuration with the HHD interfaced with the leg of a table. Discomfort was quantified using a Visual Analog Scale (VAS). Differences in discomfort and torque (N•m) associated with the testing positions were determined using Friedman test or repeated measures analysis of variance. Validity was quantified using Pearson correlations and within‐session intrarater reliability was determined using an intraclass correlation coefficient (ICC2,1) and associated confidence intervals (95% CI).

Results

The isokinetic dynamometer configuration resulted in the least discomfort (p< .01) and the modified configuration was more comfortable than the standard configuration (p= .003). There was a significant correlation between measures from the isokinetic dynamometer and the standard configuration (r=.87) and modified configuration (r=.93). Within‐session intrarater reliability was good for both the standard configuration (ICC_2,1=0.93) and modified configuration (ICC_2,1=0.93) conditions.

Conclusions

The use of the modified belt‐stabilized HHD configuration, where the HHD was interfaced with the leg of a table, offers a more comfortable alternative compared to the standard belt‐stabilized configuration to obtain isometric quadriceps strength measures in a clinical environment. This configuration is also a valid and reliable alternative to the “gold standard” isokinetic dynamometer when testing isometric quadriceps strength at 90° of knee flexion.

Level of Evidence

Diagnostic, Level 3     

MUSCLE ACTIVATION OF THE TORSO DURING THE MODIFIED RAZOR CURL HAMSTRING EXERCISE

Purpose/Background:

The RAZOR curl has been introduced as a hamstring exercise. However, modifications to the exercise have been developed which are proposed to utilize some of the muscles of the lumbo-pelvic-hip complex. Thus, it was the purpose of this study to quantitatively examine the modified RAZOR curl using surface electromyography (sEMG), as an exercise that may recruit the trunk muscles of the lumbo-pelvic-hip complex.

Methods:

Twenty-eight active male and female graduate students (24.2±1.3 years; 174.8±9.9 cm; 74.9±14.9 kg), consented to participate. Dependent variables were muscle activation of trunk musculature (dominant side gluteus medius, gluteus maximus, multifidus, longissimus, lower rectus abdominis, upper rectus abdominis, external obliques) reported as percent of maximum voluntary isometric contraction (%MVIC) during the exercise while the independent variable was the muscle selected.

Results:

The multifidus and longissimus demonstrated moderately strong activation (35-50%MVIC) while the upper rectus abdominis demonstrated strong activation (20-35%MVIC) and the gluteus medius, gluteus maximus, lower rectus abdominis, and external obliques had minimal activation.

Conclusions:

These findings allow the practitioner to utilize an exercise that provides a functional training stimulus that activates not only the hamstrings but also some musculature of the trunk muscles of the lumbopelvic-hip complex at strong to moderately strong levels.

Level of Evidence:

5     

EVIDENCE FOR ISOKINETIC KNEE TORQUE ASYMMETRIES IN MALE LONG DISTANCE‐TRAINED RUNNERS

Purpose/Background

Strength asymmetries are related to knee injuries and such injuries are frequently observed among runners. The purpose of this study was to examine whether long‐distance runners have symmetric performance during knee isokinetic testing at two angular velocities.

Methods

Twenty‐three healthy and well‐trained male long‐distance runners performed open‐chain isokinetic trials for assessment of concentric quadriceps and hamstrings contractions at velocities of 60 °·s^‐1 and 240 °·s^‐1. Data were compared between the lower limbs at different velocities.

Results

Peak torque and total work were similar between the limbs. Asymmetry was observed for knee flexor power at 240 °·s^‐1 (237 ± 45 W and 205 ± 53 W, in the preferred and non‐preferred limb, respectively). Asymmetry indexes for flexor power were different between the velocities tested (13.1% and 2.21% for 240 °·s^‐1 and 60 °·s^‐1, respectively).

Conclusion

A limb asymmetry was observed among runners for knee flexor power, mainly at higher angular velocities (240 °·s^‐1). In addition, H/Q ratios were observed to be contraction velocity dependent.

Level of Evidence

3     

THE RELATIONSHIP BETWEEN PASSIVE GLENOHUMERAL TOTAL ROTATION AND THE STRENGTH OF THE INTERNAL AND EXTERNAL ROTATOR MUSCLES,A PRELIMINARY STUDY

Background

There is little research on how the amount of shoulder joint range of motion, specifically glenohumeral rotation, may be related to the muscle strength of the rotator cuff muscles. A long held belief is that a joint with excessive range of motion needs sufficient muscular strength for stability. However, no studies have examined this concept.

Purpose

The purpose of this study was to see if total arc of glenohumeral joint rotation (External rotation [ER]+Internal rotation [IR]) could predict peak isometric muscle strength of the IR or ER muscles of the shoulder.

Study Design

Cross‐sectional study design

Methods

Fifty‐three participants (41 females, 12 males) participated in the study. Passive glenohumeral joint internal rotation and external rotation motion was measured for each participant with a standard goniometer. Isometric muscle force of the ER and IR muscles were tested using a handheld dynamometer in three positions: end range ER, neutral 0°, and end range IR. Data were analyzed using a non‐parametric tree based regression method (CART) and then cross‐validated.

Results

The results showed that those with an increased total arc of motion of glenohumeral rotation (greater than 165.0°) had less muscle isometric muscle strength in all tests positions than those with less glenohumeral rotation.

Conclusion

Decreased force of the ER and IR muscles of the shoulder was noted in those with increased total arc glenohumeral rotation ( > 165.0°), specifically those with increased glenohumeral internal rotation ( > 80.0°) when compared to those with glenohumeral rotation ( < 165.0°) and glenohumeral internal rotation ( < 80.0°). Future studies should include more males and attempt to develop strategies to assist those with larger excursions of shoulder rotation who may be at risk of developing shoulder problems.

Level of Evidence

Level 2     

GLUTEAL MUSCLE ACTIVITY DURING WEIGHTBEARING AND NON‐WEIGHTBEARING EXERCISE

Background:

Researchers suggest that decreased strength of the gluteus medius (GMed) and the gluteus maximus (GMax) muscles contributes to the etiology of various orthopedic pathologies of the knee. Currently, equivocal evidence exists regarding Electromyography (EMG) activity of gluteal musculature during weightbearing (WB) and non‐weightbearing (NWB) exercise. The purpose of this study was to compare GMed and GMax muscle activation during WB functional exercise and NWB 10 repetition maximum (RM) exercises.

Methods:

Surface EMG electrodes recorded the muscle activity of the GMax and GMed as subjects performed three sets of 10 repetitions of the following exercises: (1) forward step‐up, (2) lateral step‐up, (3) 10 repetition maximum (10 RM) side‐lying hip abduction and (4) 10 RM prone hip extension. The 10 RM resistances were determined one week prior to data collection.

Results:

The GMed was recruited significantly more during side‐lying 10 RM than the remaining exercises (side‐lying, 99.9±17% vs. lateral step‐up, 61±20%; Forward step‐up, 62.7±18.2%; prone, 38±22.2%)(p<0.001). The GMax was recruited to the greatest extent during prone 10 RM hip extension (prone, 100.7±14.5% vs. forward step‐up, 28.7±18.7%; lateral step‐up, 31±19.9%; side‐lying, 38±23.3%)(p<0.001).

Discussion:

These results suggest that performing a 10 RM NWB exercise results in greater muscle activation than two functional WB exercise without load in young, healthy individuals. In addition, forward and lateral step‐ups failed to effectively recruit the GMax at a high enough level to achieve a strengthening stimulus. The GMed was recruited to a higher extent than the GMax during the stepping tasks which might be further augmented if the activity is performed with an additional external load.

Level of Evidence:

III     

SUSTAINED ISOMETRIC SHOULDER CONTRACTION ON MUSCULAR STRENGTH AND ENDURANCE: A RANDOMIZED CLINICAL TRIAL

Background

The Advanced Throwers Ten Exercise Program incorporates sustained isometric contractions in conjunction with dynamic shoulder movements. It has been suggested that incorporating isometric holds may facilitate greater increases in muscular strength and endurance. However, no objective evidence currently exists to support this claim.

Hypothesis/Purpose

The purpose of this research was to compare the effects of a sustained muscle contraction resistive training program (Advanced Throwers Ten Program) to a more traditional exercise training protocol to determine if increases in shoulder muscular strength and endurance occur in an otherwise healthy population. It was hypothesized that utilizing a sustained isometric hold during a shoulder scaption exercise from the Advanced Throwers Ten would produce greater increases in shoulder strength and endurance as compared to a traditional training program incorporating a isotonic scapular plane abduction (scaption) exercise.

Study Design

Randomized Clinical Trial.

Method

Fifty healthy participants were enrolled in this study, of which 25 were randomized into the traditional training group (age: 26 ± 8, height:172 ± 10 cm, weight: 73 ± 13 kg, Marx Activity Scale: 11 ± 4) and 25 were randomized to the Advanced Throwers Ten group (age: 28 ± 9, height: 169 ± 23 cm, weight: 74 ± 16 kg, Marx Activity Scale: 11 ± 5). No pre‐intervention differences existed between the groups (P>0.05). Arm endurance and strength data were collected pre and post intervention using a portable load cell (BTE Evaluator, Hanover, MD). Both within and between group analyses were done in order to investigate average torque (strength) and angular impulse (endurance) changes.

Results

The traditional and Advanced Throwers Ten groups both significantly improved torque and angular impulse on both the dominant and non‐dominant arms by 10–14%. There were no differences in strength or endurance following the interventions between the two training groups (p>0.75).

Conclusions;

Both training approaches increased strength and endurance as the muscle loads were consistent between protocols indicating that either approach will have positive effects.

Level of Evidence

Level 2     

EFFECTS OF LOWER EXTREMITY AND TRUNK MUSCLES RECRUITMENT ON SERRATUS ANTERIOR MUSCLE ACTIVATION IN HEALTHY MALE ADULTS

Background:

Poor activation of the serratus anterior (SA) muscle may result in abnormal shoulder rhythm, and secondarily contribute to impingement and rotator cuff tears. Sequential activation of the trunk, pelvis, and lower extremity (LE) muscles is required to facilitate the transfer of appropriate forces from these body segments to the upper extremity. Myofascial connections that exist in the body, and LE and trunk muscles (TM) activity may influence scapular and upper limb activity. The purpose of this study was to investigate the effect of simultaneous recruitment of the LE muscles and TM on the SA muscle activation when performing a forward punch plus (FPP) and six variations of the FPP exercise.

Study Design:

Experimental, within‐subject repeated measures.

Methods:

Surface electromyographic (EMG) activity of the SA, latissimus dorsi, and external oblique muscles on the dominant side, bilateral gluteus maximus muscles, and contra‐lateral femoral adductor muscles were analyzed in forward punch plus (FPP) movement and six variations in twenty one healthy male adults. The percentage of maximum voluntary isometric contraction (%MVIC) for each muscle was compared across various exercises using a 1‐way repeated –measures analysis of variance with Sidak pair wise comparison as post‐hoc test (p < 0.05).

Results:

Pairwise comparisons found that the EMG activity of the serratus anterior (SA) during the FPP with contralateral closed chain leg extension (CCLE), FPP with ipsilateral closed chain leg extension (ICLE), FPP with closed chain serape effect (CS), and FPP with open chain serape effect (OS) showed significantly higher EMG activity than the FPP.

Conclusions:

Simultaneous recruitment of the lower extremity and trunk muscles increases the activation of the SA muscle during the FPP exercise.

Clinical Relevance:

Rehabilitation clinicians should have understanding of the kinetic chain relationships between the LE, the trunk, and the upper extremity while prescribing exercises. The results of this study may improve clinicians'' ability to integrate the kinetic chain model in a shoulder rehabilitation program.

Level of Evidence:

2b     

A COMPARISON OF CHANGE IN 3D SCAPULAR KINEMATICS WITH MAXIMAL CONTRACTIONS AND FORCE PRODUCTION WITH SCAPULAR MUSCLE TESTS BETWEEN ASYMPTOMATIC OVERHEAD ATHLETES WITH AND WITHOUT SCAPULAR DYSKINESIS

Background

The significance of scapular dyskinesis is being challenged due to a lack of the association with pain and ability to predict injury in athletic populations. However, it is unknown whether asymptomatic overhead athletes with dyskinesis cope by normalizing scapular position with higher demand activities.

Hypothesis/Purpose

The purpose of this study was to compare change in scapular kinematics from an active unweighted contraction to a maximal isometric contraction in asymptomatic overhead athletes with and without scapular dyskinesis. Secondarily, force generated with manual muscle tests were explored for differences and relationships with kinematics.

Study Design

Cross‐sectional laboratory study

Methods

Twenty‐five matched asymptomatic overhead athletes with (n=14) and without (n=11) scapular dyskinesis, defined with a reliable and validated clinical method, participated in this study. Three‐dimensional scapular kinematics were evaluated in an active unweighted condition, and during maximal isometric contractions at 90 ° of shoulder flexion. Isometric force produced with lower trapezius and serratus anterior manual muscle tests were assessed with a dynamometer. Changes in scapular kinematics were compared between groups. Differences in force generated with manual muscle tests between groups and relationships with kinematics were explored.

Results

Athletes with dyskinesis demonstrated greater deficits in scapular upward rotation with maximal contraction (p=<0.001), less external rotation (p=0.036) and weaker lower trapezius manual muscle test strength (p=0.031). Lower trapezius (p=0.003;r=0.57) and serratus anterior (p=0.042;r=0.41) manual muscle test strength deficits were fair to moderately associated with a lack of scapular upward rotation during maximal contraction.

Conclusion

Small to moderate changes in scapular kinematics are normal responses to a maximal contraction, but with scapular dyskinesis this response is accentuated. Athletes with dyskinesis generate less force with lower trapezius manual muscle testing compared to athletes without dyskinesis. Decreased strength with lower trapezius and serratus anterior manual muscle testing was also related to a lack of upward rotation in all athletes.

Level of Evidence

3     

SWISS BALL ABDOMINAL CRUNCH WITH ADDED ELASTIC RESISTANCE IS AN EFFECTIVE ALTERNATIVE TO TRAINING MACHINES

Background:

Swiss ball training is recommended as a low intensity modality to improve joint position, posture, balance, and neural feedback. However, proper training intensity is difficult to obtain during Swiss ball exercises whereas strengthening exercises on machines usually are performed to induce high level of muscle activation.

Purpose:

To compare muscle activation as measured by electromyography (EMG) of global core and thigh muscles during abdominal crunches performed on Swiss ball with elastic resistance or on an isotonic training machine when normalized for training intensity.

Methods:

42 untrained individuals (18 men and 24 women) aged 28–67 years participated in the study. EMG activity was measured in 13 muscles during 3 repetitions with a 10 RM load during both abdominal crunches on training ball with elastic resistance and in the same movement utilizing a training machine (seated crunch, Technogym, Cesena, Italy). The order of performance of the exercises was randomized, and EMG amplitude was normalized to maximum voluntary isometric contraction (MVIC) EMG.

Results:

When comparing between muscles, normalized EMG was highest in the rectus abdominis (P<0.01) and the external obliques (P<0.01). However, crunches on Swiss ball with elastic resistance showed higher activity of the rectus abdominis than crunches performed on the machine (104±3.8 vs 84±3.8% nEMG respectively, P<0.0001). By contrast, crunches performed on Swiss ball induced lower activity of the rectus femoris than crunches in training machine (27±3.7 vs 65±3.8% nEMG respectively, P<0.0001) Further, gender, age and musculoskeletal pain did not significantly influence the findings.

Conclusion:

Crunches on a Swiss ball with added elastic resistance induces high rectus abdominis activity accompanied by low hip flexor activity which could be beneficial for individuals with low back pain. In opposition, the lower rectus abdominis activity and higher rectus femoris activity observed in machine warrant caution for individuals with lumbar pain. Importantly, both men and women, younger and elderly, and individuals with and without pain benefitted equally from the exercises.     

BASEBALL PLAYERS WITH ULNAR COLLATERAL LIGAMENT TEARS DEMONSTRATE DECREASED ROTATOR CUFF STRENGTH COMPARED TO HEALTHY CONTROLS

Background

Ulnar Collateral Ligament (UCL) tears are common in baseball players. Alterations in rotator cuff strength are believed to be associated with injury to the shoulder and/or elbow in baseball players.

Hypothesis/Purpose

Baseball players diagnosed with a UCL tear will demonstrate decreased internal (IR) and external rotation (ER) force as an indication of isometric muscular strength in the throwing arm compared to IR and ER force of the throwing arm in healthy baseball players. The purpose of this study was to examine isometric IR and ER strength of the shoulder in baseball players with UCL tears at the time of injury compared to healthy baseball players.

Study Design

Case‐control study design

Methods

Thirty‐three of the participants were diagnosed with a UCL tear and thirty‐three were healthy, age‐ and positioned‐matched controls. All of the participants played baseball at either the high school or collegiate level and volunteered for the study. Isometric rotator cuff strength measurements for internal (IR) and external rotation (ER) were performed with the arm held to the side at 0 ° of shoulder abduction. All measurements were taken bilaterally and the means of the throwing and non‐throwing arms for IR and ER in the UCL group were compared to the means of the throwing and non‐throwing arms in the healthy group. One‐way ANOVAs were used to calculate differences between groups (p < 0.05).

Results

Baseball players with UCL tears demonstrated significant rotator cuff strength deficits on their throwing arm IR (p < .001) and ER (p < .001) compared to throwing arm IR and ER in the Healthy (UCL IR = 131.3 ± 31.6 N; Healthy IR = 174.9 ± 20.7 N) (UCL ER = 86.4 ± 18.3 N; Healthy ER = 122.3 ± 18.3 N). On the non‐throwing arm, the UCL group was weaker in both IR (135.0 ± 31.1 N; p < .001) and ER (93.4 ± 22.8 N; p < .001) than IR (172.1 ± 24.1 N) and ER (122.3 ± 19.1 N) in the Healthy group.

Conclusion

Participants with a UCL tear exhibit lower force values as an indication of isometric rotator cuff strength in both the throwing and non‐throwing arms than a healthy cohort.

Level of Evidence

Level 4