Isokinetic strength relationships in shoulder muscles

Residual kinematic deviations of the shoulder during humeral elevation after conservative treatment for mid-shaft clavicle fractures

Despite residual functional deficits clinically observed in conservatively treated mid-shaft clavicle fractures, no study has reported a quantitative assessment of the treatment effects on the kinematics of the shoulder complex during functional movement. Using computerised motion analysis, the current study quantified the 3D residual kinematic deviations or strategies of the shoulder complex bones during multi-plane elevations in fifteen patients with conservatively treated mid-shaft clavicle fractures and fifteen healthy controls. Despite residual clavicular malunion, the patients recovered normal shoulder kinematics for arm elevations up to 60° in all three tested planes. For elevations beyond 60°, normal clavicle kinematics but significantly increased scapular posterior tilt relative to the trunk was observed in the patient group, leading to significantly increased clavicular protraction and posterior tilt relative to the scapula (i.e., AC joint). Slightly different changes were found in the sagittal plane, showing additional changes of increased scapular upward rotations at 90° and 120° elevations. Similar kinematic changes were also found on the unaffected side, indicating a trend of symmetrical bilateral adaptation. The current results suggest that shoulder kinematics in multi-plane arm elevations should be monitored for any compromised integrated motions of the individual bones following conservative treatment. Rehabilitation strategies, including muscle strengthening and synergy stability training, should also consider compensatory kinematic changes on the unaffected side to improve the bilateral movement control of the shoulder complex during humeral elevation.

Sex differences in strength at the shoulder: a systematic review

Background

Understanding differential strength capability between sexes is critical in ergonomics and task design. Variations in study designs and outcome measures generates challenges in establishing workplace guidelines for strength requirements to minimize upper extremity risk for workers. The purpose of this systematic review was to collate and summarize sex differences in strength at the shoulder across movement directions and contraction types.

Methods

A total of 3,294 articles were screened from four databases (Embase, Medline, SCOPUS, and Web of Science). Eligibility criteria included observational studies, direct measurement of muscular joint, and healthy adult participants (18-65 years old). Strength outcome measures were normalized to percentages of male outputs to allow comparisons across articles.

Results

A total of 63 studies were included within the final review. Majority of articles observed increased strength in males; the gap between male-female strength was greater in flexion and internal/external rotation, with females generating ~30% of male strength; scaption strength ratios were most consistent of the movement groups, with females generating 55-62% of male strength.

Conclusion

Sex strength differences should be considered as an important factor for workplace task design as women are more at risk for occupational-related injuries than men in equivalent strength requirements. Differences in strength were not synonymous across motions; females demonstrated increased disparity relative to male strength in horizontal flexion/extension, forward flexion and internal/external rotation. Some movements had an extremely limited pool of available studies for examination which identified critical research gaps within the literature. Collating and quantifying strength differences is critical for effective workstation design with a range of users to mitigate potential overexertion risk and musculoskeletal injury.

Assessment of shoulder rotation strength, muscle co-activation and shoulder pain in tetraplegic wheelchair athletes - A methodological study

Objective: To develop a feasible protocol for testing maximum shoulder rotation strength in tetraplegic wheelchair athletes, and investigate concurrent validity of maximum isometric handheld dynamometer (HHD) towards maximum isokinetic dynamometer (ID) strength measurements; secondly, to study shoulder muscle activation during maximum shoulder rotation measurements, and the association between shoulder strength and shoulder pain.Design: Descriptive methodological.Setting: Danish Wheelchair Rugby (WCR) association for WCR tetraplegic athletes from local WCR-clubs.Participants: Twelve adult tetraplegics.Interventions: N/A.Outcome measures: Wheelchair User's Shoulder Pain Index (WUSPI) and Visual Analog Scale (VAS) measured shoulder pain, isometric HHD and ID (60°/s) measured maximum internal (IR) and external (ER) shoulder rotation strength. Surface Electromyography normalized to maximum EMG measured muscle activity (mm Infraspinatus and Latissimus Dorsi) during maximum shoulder rotation strength.Results: Concurrent validity of isometric HHD towards ID showed Concordance Correlation Coefficients of left and right arms 0.90 and 0.86 (IR), and 0.89 and 0.91 (ER), with no difference in muscle activity between isometric HHD and ID, but larger co-activation during ER. There was no association between shoulder strength and pain, except for significantly weak negative associations between ID and pain during ER for left and right arms (P = 0.03; P = 0.04).Conclusion: Standardized feasible protocol for tetraplegic wheelchair athletes for measuring maximum shoulder rotation strength was established. Isometric HHD is comparable with ID on normalized peak torques and muscle activity, but with larger co-activation. Strength was not clearly associated with shoulder pain.

Comparing in vivo three-dimensional shoulder elevation kinematics between standing and supine postures

Background

It is often assumed that body posture, standing vs. supine, changes shoulder muscle activation and range of motion, but these altered shoulder mechanics have not been objectively assessed. We expected the supine posture might facilitate scapular rotation and change subacromial pressure. The purpose of this study is to evaluate the influence of body posture on shoulder kinematics during arm elevation.

Methods

Ten males and eight females with a mean age of 33 years participated in this study. Shoulder kinematics were assessed during scapular plane elevation in the standing and supine postures by using single-plane fluoroscopic images. Kinematics were measured using 3-dimensional to 2-dimensional model-image registration techniques: matching the 3-dimensional bone model derived from computed tomography onto each fluoroscopic image. Glenohumeral superior/inferior translation, acromiohumeral distance, and scapular rotations were compared between the postures. The effect of sex also was evaluated.

Results

With the arm at the side position, the humeral head in the supine posture was located 0.5 mm superior compared to the standing posture (P < .001). During humeral elevation, the humeral head significantly shifted more inferiorly in the supine posture than in standing; the biggest mean difference was 0.6 mm, P = .003. But acromiohumeral distance during elevation was not significantly affected by the body posture (P = .05). Scapular upward rotation and posterior tilt were significantly different between the postures (P < .001). Sex had statistically significant, but quantitatively small, effects on shoulder kinematics.

Conclusions

Body postures affect shoulder kinematics during humeral elevation. This knowledge will be useful to optimize rehabilitation exercises and for diagnostic insight.

Effect of hand loads on upper extremity muscle activity during pushing and pulling motions

Manual pushing or pulling with a hand tool is a coordinated action by various upper extremity muscles. The objective of this experimental study was to examine the effects of horizontal and vertical hand loads on upper extremity muscle activity during concentric pushing and pulling exertions. Twenty young female participants conducted repetitive pushing and pulling trials with three horizontal loads (1 kg, 2 kg, 3 kg) and two vertical loads (0.6 kg, 1.3 kg) in a seated posture, while the myoelectric activity of seven upper extremity and shoulder muscles were quantified. Study results indicate that the shoulder flexor and extensor muscles were more strongly associated with horizontal load, and elbow flexors were more sensitive to vertical load. The empirical data from this systematic evaluation can offer initial insights for ergonomic design and evaluation of hand tools or occupational tasks that involve repetitive pushing or pulling.

Preseason shoulder rotational isokinetic strength and shoulder injuries in volleyball players

BACKGROUND: Rotator cuff weakness is considered an important risk factor for shoulder injuries in volleyball. OBJECTIVE: To evaluate association of shoulder preseason strength status with shoulder injury occurrence in subsequent season. METHODS: Volleyball players (N= 181; 99 men) from Slovenian 1st and 2nd national league volunteered to participate in this prospective cohort study. Preseason isokinetic testing of the shoulder was conducted at 60∘/s in the concentric mode of contraction over a RoM of 60∘ with five repetitions of internal (IR) and external (ER) rotation. During the subsequent season the players reported shoulders injuries through a weekly questionnaire. RESULTS: During the season we have registered 14 (7.7%) shoulder injuries (10 in men). All injuries affected the dominant shoulder. There was significant preseason weakness of ER and lower ER/IR strength ratio in players with shoulder injury. Normal strength ratio ER/IR was a significant protective factor (Exp (B) = 0.217, 95% C.I. 0.058–0.811) for shoulder injury occurrence when controlled for sex and previous injury. CONCLUSIONS: The inclusion of systematic strengthening of the external rotators of the shoulder is necessary, especially for male volleyball players, as part of preventive measures for the prevention of shoulder injuries.

Dynamic and static shoulder strength relationship and predictive model

Static strength is typically used to standardize occupational tasks in an effort to limit over-exertion injuries; however, workplace tasks are commonly dynamic in nature. The purpose of this investigation was to assess factors influencing isokinetic shoulder strength and to develop predictive equations for isokinetic shoulder flexion and extension strength using isometric strength. Fifteen women performed a set of concentric isokinetic and isometric shoulder flexion and extension maximal exertions across a series of movement planes, angular velocities, and grip types. Data were used to generate two stepwise multiple regression models for predicting isokinetic shoulder flexion and exertion strength across the various exertion parameters. The final regression models explained a high degree of variance in predicting isokinetic shoulder flexion (R² = 0.59) and extension (R² = 0.67) with a subset of four and five inputs, respectively. The predictive equations can help establish acceptable force limits for workplace tasks requiring dynamic actions using more easily attainable static forces.

The centre of rotation of the shoulder complex and the effect of normalisation

Shoulder motions consist of a composite movement of three joints and one pseudo-joint, which together dictate the humerothoracic motion. The purpose of this work was to quantify the location of the centre of rotation (CoR) of the shoulder complex as a whole. Dynamic motion of 12 participants was recorded using optical motion tracking during coronal, scapular and sagittal plane elevation. The instantaneous CoR was found for each angle of elevation using helical axes projected onto the three planes of motion. The location of an average CoR for each plane was evaluated using digitised and anthropometric measures for normalisation. When conducting motion in the coronal, scapular, and sagittal planes, respectively, the coefficients for locating the CoRs of the shoulder complex are −61%, −61%, and −65% of the anterior–posterior dimension – the vector between the midpoint of the incisura jugularis and the xiphoid process and the midpoint of the seventh cervical vertebra and the eighth thoracic vertebra; 0%, −1%, and −2% of the superior–inferior dimension – the vector between the midpoint of the acromioclavicular joints and the midpoint of the anterior superior iliac spines; and 57%, 57%, and 78% of the medial–lateral dimension −0.129 times the height of the participant. Knowing the location of the CoR of the shoulder complex as a whole enables improved participant positioning for evaluation and rehabilitation activities that involve movement of the hand with a fixed radius, such as those that employ isokinetic dynamometers.

Evaluation of rotator cuff muscle strength in healthy individuals

OBJECTIVE:

To compare the strength generated by the rotator muscles of the shoulder joint between the right upper limb and left upper limb among healthy individuals.

METHODS:

To evaluate the muscle strength of upper limbs from isometric contractions in the horizontal direction (rotation) an isometric dynamometer was used, equipped with transducers, signal conditioning, a data acquisition board, and finally, a computer. Study participants were 22 male military subjects, aged between 18 and 19 years old, body mass between 57.7 and 93.0 kg (71.8 ± 9.45 kg) and height between 1.67 and 1.90 m (1.75 ± 0.06 m), healthy and without clinical diseases or any type of orthopedic injury in the muscle skeletal system.

RESULTS:

The internal rotation in the right upper limb (RUL) was higher than the average strength of internal rotation in the left upper limb (LUL) (p = 0.723). The external rotation strength in RUL was lower than the average strength of external rotation in the LUL (p=0.788). No statistical difference was observed by comparing the strength values of all isometric strength tests.

CONCLUSION:

For the sample and methodology used to assess muscle strength, there was no statistical difference between the strength generated by the muscles of the rotator cuff of the right and left upper limbs. Experimental Study.

Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations

BACKGROUND

The contralateral shoulder is often used as a reference when evaluating a pathologic shoulder. However, the literature provides contradictory results regarding the symmetry of the scapular pattern in a healthy population. We assume that several factors including gender and type of motion may influence the bilateral symmetry of the scapulae.

MATERIALS AND METHODS

The dominant and nondominant shoulders of 2 populations of men and women comprising 11 subjects each were evaluated for 3 distinct motions: flexion in the sagittal plane, abduction in the frontal plane, and glenohumeral internal/external rotation with the arm abducted at 90°. Posture, kinematics, and range of motion were studied separately.

RESULTS

Asymmetries are observed for motions performed in the frontal and sagittal plane but not for internal/external rotation with the arm abducted at 90°. For both male and female populations, multiplanar asymmetries are observed and the dominant scapula has a larger upward rotation. The asymmetries mainly originate in the scapula's kinematics and not in its original posture.

CONCLUSION

Small but significant asymmetries exist between the dominant and nondominant shoulders in terms of kinematics. One should be aware of these differences when using the contralateral shoulder as a reference.

LEVEL OF EVIDENCE

Basic science study, kinematics

Long-term clinical outcomes, motion, strength, and function after total claviculectomy

BACKGROUND

Total excision of the clavicle is rarely performed. No previous study has documented long-term outcomes with objective measurements of strength, motion, and patient-centered outcomes. We present the long-term consequences of total claviculectomy on shoulder girdle function, global upper extremity function, and overall general health.

METHODS

Five total claviculectomy patients were evaluated at 2 time points (2005 and 2010, mean 4.8 and 9.4 years postoperatively) by use of the DASH, SF-36, Simple Shoulder Test, ASES, UCLA, HSS, and Constant shoulder scores. Isokinetic strength, clinical range of motion, and kinematic analysis were performed on each limb pair.

RESULTS

All clinical scores allowing side-to-side comparison were poorer for the aclaviculate side, with significance reached for 2005 ASES scores and 2010 ASES, UCLA, HSS, and Constant scores. DASH scores and SF-36 scores were not significantly inferior to age- and sex-matched population norms. Deficits in strength were present in the aclaviculate limbs, with significance reached for adduction in 2005 and for forward flexion and external rotation in 2010. Kinematic and clinical range of motion analysis revealed scapular dyskinesis and significant deficits in external rotation in the aclaviculate limb.

CONCLUSIONS

We found that the clavicle contributes to the strength, coordinated scapulohumeral rhythm, and overall range of motion of the shoulder girdle. Patients compensate for loss of the clavicle with minimal functional deficit. With time, patients gradually lose some compensatory ability as evidenced by deteriorating limb-specific, patient-centered outcome measures, diminished strength in certain planes of shoulder motion, and scapular dyskinesis at long-term follow-up. Despite objective deficits, these patients continue to have normal self-perceptions of overall health and global upper extremity function.

Analysis of continuous steering movement using a motor-based quantification system

Continuous steering movement (CSM) of the upper extremity (UE) is an essential component of steering movement during vehicle driving. This study presents an integrated approach to examine the force exertion and movement pattern during CSM. We utilized a concept similar to the isokinetic dynamometer to measure the torque profiles during 180°/s constant-velocity CSM. During a steering cycle, the extremity movement can be divided into stance and swing phases based upon the hand contact information measured from the hand switch devices. Data from twelve normal young adults (six males and six females) showed that there are three typical profiles of force exertion. The two hands exhibit similar time expenditures but with asymmetric force exertions and contact times in both the clockwise (CW) and counterclockwise (CCW) steering cycles. Both hands contribute more force but with less contact time in their outward CSM directions (i.e., CW for the right hand and CCW for the left hand). These findings help us to further understand CSM and have a number of important implications for future practice in clinical training. Considerably more research is required to determine the roles of the various shoulder muscles during CSM at various speeds.

Applicability and test-retest reliability of isokinetic shoulder abduction and adduction in women fibromyalgia patients

OBJECTIVE

To investigate the applicability and reliability of isokinetic strength measurements during concentric and eccentric actions of the shoulder muscles in fibromyalgia (FM) patients.

DESIGN

Test-retest reliability study.

SETTING

University laboratory.

PARTICIPANTS

Women with FM (N=25) aged 37 to 69.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Two isokinetic tests of the shoulder were repeated after an interval of 7 days. Each test involved 3 repetitions of abduction and adduction performed at a rate of 60°/s. The first test involved 2 concentric muscle actions (concentric/concentric test). The second test involved concentric abduction followed by eccentric adduction (concentric/eccentric test). Unilateral peak torque (Nm) and average work (J) were measured. Applicability was calculated as the proportion of participants who were able to complete every test. Reliability was analyzed by intraclass coefficient (ICC), standard error of measurement, and smallest real difference (SRD).

RESULTS

Applicability was 84% for the concentric/concentric test and 52% for the concentric/eccentric test. The main factor influencing applicability was age. In the concentric/eccentric test, measurement of peak torque showed high reliability for the abduction (ICC=.88; standard error of measurement=1.82; SRD=5.05) and adduction (ICC=.89; standard error of measurement=3.83; SRD=10.62) phases. In the concentric/concentric test, measurement of peak torque showed low reliability in the abduction phase (ICC=.29; standard error of measurement=6.45; SRD=17.87) and excellent reliability in the adduction phase (ICC=.92; standard error of measurement=5.95; SRD=16.50).

CONCLUSIONS

The applicability of shoulder isokinetic tests in FM patients who are women may be affected by age. In comparison, the concentric/concentric test was more applicable and less reliable than the concentric/eccentric test during abduction and adduction. These findings will facilitate the clinical interpretation of changes in isometric and isokinetic shoulder adduction and abduction tests in women with FM.

Isokinetic muscle assessment after treatment of pectoralis major muscle rupture using surgical or non-surgical procedures

INTRODUCTION

Rupture of the pectoralis major muscle appears to be increasing in athletes. However, the optimal treatment strategy has not yet been established.

OBJECTIVES

To compare the isokinetic shoulder performance after surgical treatment to that after non-surgical treatment for pectoralis major muscle rupture.

METHODS

We assessed 33 pectoralis major muscle ruptures (18 treated non-surgically and 15 treated surgically). Horizontal abduction and adduction as well as external and internal rotation at 60 and 120 degrees/s were tested in both upper limbs. Peak torque, total work, contralateral deficiency, and the peak torque agonist-to-antagonist ratio were measured.

RESULTS

Contralateral muscular deficiency did not differ between the surgical and non-surgical treatment modalities. However, the surgical group presented twice the number of athletes with clinically acceptable contralateral deficiency (<20%) for internal rotators compared to the non-surgical group. The peak torque ratio between the external and internal rotator muscles revealed a similar deficit of the external rotation in both groups and on both sides (surgical, 61.60% and 57.80% and non-surgical, 62.06% and 54.06%, for the dominant and non-dominant sides, respectively). The peak torque ratio revealed that the horizontal adduction muscles on the injured side showed similar weakness in both groups (surgical, 86.27%; non-surgical, 98.61%).

CONCLUSIONS

This study included the largest single series of athletes reported to date for this type of injury. A comparative analysis of muscular strength and balance showed no differences between the treatment modalities for pectoralis major muscle rupture. However, the number of significant clinical deficiencies was lower in the surgical group than in the non-surgical group, and both treatment modalities require greater attention to the rehabilitation process, especially for the recovery of muscle strength and balance.

Abnormal isokinetic time-to-peak torque of the medial rotators of the shoulder in subjects with impingement syndrome

The time-to-peak torque (TPT) and the peak torque ratio of the lateral to medial rotators (LR/MR) during isokinetic lateral and medial rotation of the shoulder were evaluated in patients with shoulder impingement and in healthy subjects. Fifteen patients with shoulder impingement on the dominant side and 9 healthy subjects were evaluated. TPT and LR/MR were measured bilaterally during isokinetic concentric lateral and medial rotation at 60 degrees/s and 180 degrees/s. The impingement group showed a bilateral decrease in the TPT during medial rotation for both 60 degrees/s and 180 degrees/s. No differences were found in the LR/MR between the groups. It is proposed that decreased (TPT) of the medial rotators can be used as a tool for early detection of shoulder impingement. Notably, the decreased time-to-peak torque of the medial rotators may occur before the alteration in the peak torque ratio.

Normalization of the Constant score

The strength of the normal shoulder may differ by gender and deteriorate with age. Thus, the Constant score may also decrease in absolute value while still reflecting a normal score. To account for age- and gender-related differences, normal results for this scale must be determined across a population of patients without shoulder disease. Patients presenting for evaluation of nonshoulder conditions participated. A subjective questionnaire was completed. Range of motion and strength were measured. This analysis includes the data of 441 patients. The mean Constant score for men was significantly greater than that for women in each age group ( P < .05). Significant age-related differences were noted in each group ( P < .05). Normative values for the Constant score based on age and gender were determined. The adjusted score represents the gender- and age-matched function of the shoulder and is useful in the evaluation of shoulder outcomes.

Pouring liquid from a pot-kinematics of an everyday task

An experiment was carried out to investigate the effects of handle design on postures in the use of pots. Six combinations of handle (sloping, vertical and curved) and spout designs (long and short) were tested during grasping, lifting and pouring. The fill load was 1000 ml of water at the prevailing room temperature (about 20 degrees C) and three males and three females were involved as subjects. Measurements were made of x- (horizontal), y- (lateral) and z- (vertical) co-ordinates of the wrist, elbow shoulder and hip joints in space throughout the motions, using a CODA MPX30 optical 3D measurement system and both linear and angular displacements of the arm joints and trunk were computed. Very different configurations of arm posture were found to be adopted at the moment of pot lift, and when pouring commences and the subjects' movement patterns during transfer of the pot to fill vessel showed to be influenced by the configuration of arm posture adopted at the moment of pot lift. For lifting the pot, the vertical handle design proved to be more desirable than either the curved or sloping design, while for pouring from the pot the short spout proved to be more desirable than the long spout, at least when the pot was full. The results are however, not clear on which handle or spout design is best for transferring the pot.

The Effect of Functional Training on the Incidence of Shoulder Pain and Strength in Intercollegiate Swimmers

Objective:

To determine whether functional training reduces the incidence of shoulder pain and increases strength in intercollegiate swimmers.

Design:

Pretest–posttest.

Setting:

Laboratory and weight room.

Participants:

26 intercollegiate swimmers (13 men, 13 women).

Intervention:

6-wk functional training program.

Main Outcome Measures:

Incidence of shoulder pain was recorded throughout the study. Isokinetic shoulder strength was assessed before and after training.

Results:

Attest showed significant differences (P< .05) for the incidence of shoulder pain between the experimental (mean episodes = 1.8 ± 2.1) and control (mean episodes = 4.6 ± 4.7) groups. ANOVA with repeated measures revealed no significant strength differences between groups but exhibited significant within-group increases.

Conclusions:

Incorporating functional exercises might reduce incidence of shoulder pain in swimmers. The results also validate the need to modify preventive programs as the demands of the sport change throughout the season.

EMG and strength correlates of selected shoulder muscles during rotations of the glenohumeral joint

OBJECTIVE

To identify activation patterns of several muscles acting on the shoulder joint during isokinetic internal and external rotation.

DESIGN

Combined EMG and isokinetic strength analysis in healthy subjects.

BACKGROUND

EMG studies of the shoulder region revealed intricate muscular activation patterns during elevation of the arm but no parallel studies regarding pure rotations of the joint could be located.

METHODS

Fifteen (n=30 shoulders) young, asymptomatic male subjects participated in the study. Strength production during isokinetic concentric and eccentric internal and external rotations at 60 and 180 degrees /s was correlated with the EMG activity of the rotator cuff, biceps, deltoid and pectoralis major. Analysis of the smoothed EMG related to the timing of onset of the signal and to the normalized activity at the angle of the peak moment. Determination of the association between the EMG and the moment was based on strength ratios.

RESULTS

Findings indicated that for both types of rotations, the rotator cuff and biceps were active 0.092+/-0.038-0.215+/-0.045 s prior to the initiation of the actual movement and 0.112-0.034 s prior to onset of deltoid and pectoralis major activity. These differences were significant in all of the eight conditions (P<0.05). In terms of the strength ratios, strong association was found between electrical activity and moment production in the subscapularis and infraspinatus (r(2)=0.95 and 0. 72, respectively) at the low and high angular velocities.

CONCLUSIONS

Prior to actual rotation of the shoulder joint, normal recruitment of the rotator cuff and biceps is characterized by a non-specific presetting phase which is mainly directed at enhancing the joint 'stiffness' and hence its stability. Once movement is in progress, the EMG patterns of these muscles become movement specific and are correlated with the resultant moment.

RELEVANCE

Muscular dysfunction relating to delayed onset activity or altered activation patterns, due to pain, perturbed mechanics or disturbed neural activation have been implicated as concomitant factors in other joint associated pathologies. Through highlighting the role of the rotator cuff in shoulder joint rotations, this study lends further support to the argument that a parallel situation may prevail with respect to shoulder joint dysfunction. This could lead to the development of rehabilitation protocols aimed specifically at redressing such dysfunction.

Differentiation of submaximal from maximal trunk extension effort: an isokinetic study using a new testing protocol

STUDY DESIGN

An evaluation of the relations between concentric and eccentric contractions of the trunk extensors and extension effort performed at maximal and submaximal levels.

OBJECTIVE

To define quantitative parameter(s) derivable from isokinetic dynamometry that may differentiate submaximal from maximal trunk extension moment.

SUMMARY OF BACKGROUND DATA

Using various consistency-related parameters, researchers in previous studies have not been able confirm the potential of isokinetic dynamometry for identifying submaximal effort during trunk extension.

METHODS

Twenty healthy subjects, 8 women and 12 men without low back pain history, aged 21 to 30 years, took part in this study. Testing consisted of three experimental conditions using four intermittent concentric and eccentric contractions at 20 degrees and 60 degrees/second. The first condition, in which subjects were asked to exert maximal concentric and eccentric effort, served as the baseline. In the second condition, subjects were asked to exert 50% of the force measured in the first condition. In the third condition, subjects repeated the second condition but were asked to exert the best reproducible level of force.

RESULTS

The highest differentiating power among the experimental conditions was attributed to the intervelocity difference between the concentric and eccentric contractions (P < 0.0001).

CONCLUSIONS

This protocol effectively differentiates submaximal from maximal trunk extension effort in normal subjects.

Grade 4 in manual muscle testing: the problem with submaximal strength assessment

OBJECTIVE

To compare the static moment of force required for a muscle group to support a limb segment against gravity with the maximal dynamic moment it can generate.

DESIGN

Based on anthropometric measures of both sexes and theoretical calculations, the estimated anti-gravity static muscular moments (MGM) at the shoulder, elbow, hip and knee joints were compared with published data relating to the isokinetic strength (MIM) of the same muscle groups.

RESULTS

The ratio of static to dynamic moment, MGM/MIM, was drastically higher in muscles operating on the proximal compared with the more distal joints. In women, the values of this ratio in the shoulder, hip, elbow and knee muscles were 7-27%, 5-65%, 7% and 5-10% respectively. The corresponding figures in men were 7-21%, 4-44%, 8-10% and 5-8%. The ratios relating to the abductors, flexors and extensors of the hip joint were substantially higher in women than in men.

CONCLUSIONS

Since MGM and MIM correspond to grades 3 and 5 in manual muscle testing, the findings of this theoretical analysis indicate that elbow and knee muscles assessed as having grade 4 may generate as low as 10% of their maximal strength. With regard to shoulder and hip muscles the corresponding values are typically around 20% and 30-40% Coupled with the very limited human precision in sensing of force, these findings indicate that where quantitative targets in muscle strength conditioning are set or when an accurate measure of impairment is being sought, grade 4 cannot and should not serve as a valid criterion.