Should Exercises be Painful or not? Effects on Clinical and Experimental Pain in Individuals with Shoulder Pain

Exercise can reduce pain, however the effect of painful versus non-painful exercises is uncertain. The primary aim of this randomized crossover study was to compare the effect of painful versus nonpainful isometric shoulder exercises on pain intensity after exercise in individuals with rotator cuff-related shoulder pain. Secondary exploratory aims were to describe the effects on pressure pain thresholds (PPTs), conditioned pain modulation (CPM) and muscle strength. On separate days, 35 individuals performed painful isometric shoulder exercises (external rotation; 20% above pain threshold), nonpainful isometric shoulder exercises (external rotation; 20% below pain threshold), and a rest condition, in randomised order. Shoulder pain intensity, PPTs, CPM, and external rotation strength were assessed before, immediately after and 45 minutes after conditions. No significant differences were observed between painful and nonpainful exercises. Visual analogue scale scores increased immediately after both painful and non-painful exercises compared with rest (P = .047, partial ƞ² = .07), but were similar to preexercise levels after 45 minutes. No changes in PPTs, CPM, or muscle strength after exercises compared with rest were observed. Painful and non-painful isometric exercises caused a moderate but short-lasting increase in shoulder pain in individuals with RCRSP. Isometric exercises had no effect on pain sensitivity and shoulder muscle strength or CPM.PerspectiveThis study evaluated for the first time in individuals with rotator cuff-related shoulder pain the effects of painful versus non-painful isometric exercises on different pain-related outcome measures. Both painful and non-painful isometric exercises caused a moderate but relatively short-lasting increase in shoulder pain in individuals with rotator cuff-related shoulder pain.Trial registration number: (ClinicalTrials.gov) NCT03675399     

Shoulder function after latissimus dorsi transfer in breast reconstruction

Background/Aims: Latissimus dorsi (LD) transfer in the case of breast reconstruction remains frequently used because this muscle provides a good size source of tissue in reconstructive surgery. Given that, the consequences of the LD removal on shoulder function and the actual loss of maximal strength developed must be investigated. Methods: Twenty women (50 ± 7·5 years old) were evaluated before surgery, 3 and 6 months after an unilateral transfer of a pedicle flap of LD muscle used for breast reconstruction. Women performed a bilateral shoulder isokinetic assessment [for the internal rotators (IRs) and external rotators and for the abductor and adductor (ADD) muscles] allowing the establishment of bilateral muscular deficit status and the study of agonist/antagonist muscle ratios. The algofunctional and clinical status of the shoulders was analysed by the means of Constant score and specific shoulder clinical tests. The women did not perform any specific strengthening of muscle shoulder after surgery. Results: The isokinetic assessment showed a muscle weakness 3 and 6 months after LD transfer, mainly on the ADDs (33 ± 9% at 6 months) and on the IRs (16 ± 11% at 6 months). The Constant score significantly decreased after surgery on the operated shoulder. Women with a Constant score impairment showed pain during specific shoulder clinical tests. We also found a correlation between Constant score impairment and internal rotators weakness or rotator muscle imbalance. Conclusion: Given those results, we could advocate a specific shoulder strengthening after LD transfer, focused mainly on the IRs and ADDs.     

Relationship between strength and functional indexes (Rowe and Walch-Duplay scores) after shoulder surgical stabilization by the Latarjet technique

IntroductionThe rotator cuff muscles help stabilize the glenohumeral joint. Postoperative recovery of rotator cuff muscle strength appears to be an important factor for optimal joint stabilization and the resumption of professional and/or sports activities.ObjectiveTo study the relationship between internal rotator (IR) and external rotator (ER) muscle strength, shoulder function and the resumption of sports activities (as typically evaluated with functional scores) following surgical stabilization with the Bristow-Latarjet procedure in cases of chronic shoulder instability.Patients and methodsTwenty patients with anterior, post-traumatic, chronic shoulder instability were included prospectively in a cohort study. The Rowe and Walch-Duplay functional scores were rated for the operated shoulder and the isokinetic IR and ER peak torque values were evaluated with a Con-Trex^® dynamometer before surgery and then 3, 6 and 21 months afterwards. The isokinetic evaluation was performed (at 180°/s, 120°/s and 60°/s) in the seated position, with the arms in 45° of abduction and 30° of antepulsion in the plane of the scapula.ResultsThere were no significant postoperative correlations between shoulder function (as judged by the Rowe and Walch-Duplay scores) and IR or ER muscle strength.ConclusionThis study did not provide evidence for a correlation between IR and ER muscle strength and functional scores after surgical stabilization of the shoulder. However, it is necessary to objectively measure the rotator cuff strength recovery to adequate the strengthening of rotator muscle prior to the resumption of sports activities. Isokinetic strength assessment may thus be a valuable decision support tool for the resumption of sports activities and would complement the functional scores studied here.     

The impact of recurrent dislocation on shoulder rotator muscle balance (a prospective study of 102 male patients)

Purpose of the studyWe performed an isokinetic analysis of both shoulders in 102 male patients suffering from shoulder instability after several trauma-related anterior or anterior-inferior dislocations. The analysis was part of a comprehensive medical and radiological assessment (with standard X-rays and cross-sectional imaging) prior to surgery. The study's objective was to measure the strength of the patients’ internal and external rotators after recurrent dislocations (by comparing injured and healthy sides) and to evaluate the dislocations’ impact on the muscles on the injured side.Materials and methodsThe mean patient age was 24.8 (range: 16–47). We analysed the impact of instability on rotator muscle performance according to the side (dominant or non-dominant), the number of dislocations and the severity of any associated bone damage. The isokinetic analysis was performed at least one month after the last shoulder dislocation. The same operator performed all procedures. The modified Davies position was adopted, in order to record the peak torque of the internal and external rotators during concentric contractions at 60° and 180° per second. Means and standard deviations for peak torque to body weight ratios and external/internal rotator peak torque ratios were reported.ResultsAfter several anterior or anterior-inferior shoulder dislocations, there was a non-significant difference in the external rotator/internal rotator ratio when comparing injured and healthy sides - regardless of whether the injured side was dominant or not, the number of dislocations and the severity of bone damage.ConclusionSystematic, presurgical, isokinetic testing of the shoulder does not appear to be of value in post-traumatic instability in male patients.     

The stabilizing role of the rotator cuff at the shoulder--responses to external perturbations

Background

The rotator cuff has been hypothesized as a dynamic stabilizer at the shoulder joint yet evidence supporting this role remains inconclusive. We aimed to investigate the activity levels and recruitment patterns between the rotator cuff and superficial shoulder muscles in response to external perturbations to provide insight into the stabilizing role of the rotator cuff.

Methods

Surface and intramuscular electromyography (EMG) were used to measure timing of onset and level of activation (EMG amplitude as a percentage of maximum voluntary isometric contraction, % MVIC) of rotator cuff (supraspinatus, infraspinatus and subscapularis) and superficial muscles (anterior and posterior deltoid) on 19 healthy participants. Participants received expected and unexpected externally applied perturbations in directions of internal and external rotation at the glenohumeral joint.

Findings

All three rotator cuff muscles demonstrated pre-activation in anticipation of the perturbation prior to their representative global synergists, anterior and posterior deltoid (P < 0.05). Subscapularis and infraspinatus were activated prior to all other muscles during external rotation and internal rotation perturbation trials respectively (P < 0.01). Direction specific activation levels were observed; subscapularis was moderately strongly active (37% MVIC) in response to an external rotation perturbation and infraspinatus was moderately active (28% MVIC) in response to an internal rotation perturbation. No muscle was activated > 10% MVIC when not acting as the main muscle opposing the movement.

Interpretation

The rotator cuff may function in part as a dynamic stabilizing unit of the shoulder demonstrating a feedforward muscle activation pattern. These results may assist in improving assessment and treatment of shoulder dysfunction.     

等速肌力训练在肩袖修补术后康复中的作用

目的 探讨等速肌力训练在关节镜下肩袖修补术后康复治疗中的作用。 方法 选取关节镜下小肩袖损伤修复术后3个月、患侧肩关节活动度正常且肩袖肌力达到3级及以上的患者共40例,按随机数字表法分为对照组（采用常规肌力训练治疗）和训练组（采用等速训练方法治疗）,每组20例。2组患者均行Thera-Band弹力带肩关节内外旋肌力训练,每组10～20个,每日3次;训练组在常规肌力训练的基础上,增加肩关节内外旋等速肌力训练,每次15～20 min,每周2次。分别于术后3个月（训练前）和术后6个月（训练后）,对2组患者均行等速肌力测试,测试速度分别为60°/s和180°/s。并分别对2组患者的患侧肩关节内外旋峰力矩、峰力矩体重比、患侧与健侧峰力矩差值比、训练前后患侧峰力矩差值和训练前后患侧峰力矩体重比差值等评定指标进行评估和比较。 结果 训练后,训练组60°/s时外旋峰力矩［（15.56±5.03）N·m］、内旋峰力矩［（22.03±6.18）N·m］,外旋峰力矩体重比［（22.12±4.63）%］、内旋峰力矩体重比［（31.62±6.42）%］,180°/s时外旋峰力矩［（10.60±5.71）N·m］、内旋峰力矩［（19.13±5.62）N·m］,外旋峰力矩体重比［（14.90±6.34）%］、内旋峰力矩体重比［（27.83±6.04）%］,以及对照组60°/s时外旋峰力矩［（13.30±4.07）N·m］、内旋峰力矩［（20.07±6.95）N·m］,外旋峰力矩体重比［（20.27±5.93）%］、内旋峰力矩体重比［（29.75±10.52）%］,180°/s时外旋峰力矩［（7.15±5.43）N·m］、内旋峰力矩［（16.14±6.03）N·m］,外旋峰力矩体重比［（11.19±8.49）%］、内旋峰力矩体重比［（24.75±8.80）%］,均明显优于组内训练前,各项指标差异有统计学意义（P<0.05）。此外,训练后,训练组180°/s时患侧与健侧外旋峰力矩差值比［（15.58±41.76）%］、60°/s和180°/s时训练前后患侧外旋峰力矩差值［（5.04±1.88）N·m、（5.04±2.47）N·m］、60°/s和180°/s时训练前后患侧外旋峰力矩体重比差值［（7.02±2.14）%、（7.90±4.69）%］均明显优于对照组,差异有统计学意义（P<0.05）。 结论 等速肌力训练有助于恢复关节镜下肩袖损伤修复术后患者的肩袖力量,尤其是快速外旋肌力。     

Resistance training is accompanied by increases in hip strength and changes in lower extremity biomechanics during running

Background

Movement and muscle activity of the hip have been shown to affect movement of the lower extremity, and been related to injury. The purpose of this study was to determine if increased hip strength affects lower extremity mechanics during running.

Methods

Within subject, repeated measures design. Fifteen healthy women volunteered. Hip abduction and external rotation strength were measured using a hand-held dynamometer. Three-dimensional biomechanical data of the lower extremity were collected during running using a high-speed motion capture system. Measurements were made before, at the mid-point, and after a 6-week strengthening program using closed-chain hip rotation exercises. Joint range of motion (rearfoot eversion, knee abduction, hip adduction, and internal rotation), eversion velocity, eversion angle at heel strike, and peak joint moments (rearfoot inversion, knee abduction, hip abduction, and external rotation) were analyzed using repeated measures analysis of variance (P ? 0.05). The independent variable was time (pre-, week 3, and week 6). A separate analysis of variance was conducted with the dependent variables of peak hip abduction and external rotation strength.

Findings

Hip abduction (P = 0.009) and external rotation strength (P < 0.0005) increased by 13% and 23%, respectively. Eversion range of motion decreased (P = 0.05), hip adduction range of motion increased (P = 0.05), and a trend of decreased hip internal rotation range of motion (P = 0.08) were found. Rearfoot inversion moment (P = 0.02) and knee abduction moment (P = 0.05) decreased by 57% and 10%, respectively.

Interpretation

The hip abductors and external rotators were strengthened, leading to an alteration of lower extremity joint loading which may reduce injury risk. These exercises could be used in the rehabilitation, or prevention, of lower extremity injuries.     

Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: The effects of Latent Myofascial Trigger Points

BackgroundLatent Myofascial Trigger Points are pain-free neuromuscular lesions that have been found to affect muscle activation patterns in the unloaded state. The aim was to extend these observations to loaded motion by investigating muscle activation patterns in upward scapular rotator muscles (upper and lower trapezius and serratus anterior) hosting Latent Myofascial Trigger Points simultaneously with lesion-free synergists for shoulder abduction (infraspinatus and middle deltoid). This approach allowed examination of the effects of these lesions on both their hosts and their lesion-free synergists in order to understand their effects on the performance of shoulder abduction.MethodsSurface electromyography was employed to measure the timing of onset of muscle activation of the upper and lower trapezius and serratus anterior (upward scapular rotators), infraspinatus (rotator cuff) and middle deltoid (abductor of the arm) initially without load and then with light (1–4 kg) dumbbells. Comparisons were made between control (no Latent Trigger Points; n = 14) and Latent Trigger Point (n = 28) groups.FindingsThe control group displayed a relatively stable sequence of muscle activation that was significantly different in timing and variability to that of the Latent Trigger Point group in all muscles except middle deltoid (all P < 0.05). The Latent Trigger Point group muscle activation pattern under load was inconsistent, with the only common feature being the early activation of the infraspinatus.InterpretationThe presence of Latent Trigger Points in upward scapular rotators alters the muscle activation pattern during scapular plane elevation, potentially predisposing to overuse conditions including impingement syndrome, rotator cuff pathology and myofascial pain.     

The dependence of muscle strength in the shoulder rotators on the shoulder abduction angle

Background. The shoulder joint has a very complex structure. Normal shoulder function is dependent on joint stability and proper neuromuscular control. Given its anatomical structure and range of movement, this joint is highly susceptible to numerous disorders and injuries. Normal stability of the shoulder guarantees physiological function, and is also the most important element of injury prevention. Disturbances of the strength and reciprocal proportions of the inner and outer rotator muscles, as well as the shoulder abductors, can be a mechanism leading to shoulder instability. The goal of our study was to evaluate the muscle strength of the shoulder rotators in terms of the abduction angle in healthy individuals. Material and methods. We examined 100 healthy volunteers (200 shoulders), 50 men and 50 women. Each subject enrolled in the study performed 32 measurements of muscle strength in the shoulder rotators, for a grand total of 3200 measurements, performed in alternation (outward and inward rotation) at various angles of shoulder abduction. Results. The strength of the muscles responsible for inward and outward rotation in persons without shoulder injury rose along with shoulder abduction, from 0 degrees to 70 degrees . When the shoulder was abducted to 70 degrees , the strength of the inner rotators was the highest, significantly higher than that of the outer rotators. When the shoulder was abducted to 90 degrees , there was relative equilibrium of muscle strength (N) between the inner and outer rotators. Conclusions. 1. Muscle strength in the outer and inner shoulder rotators in healthy individuals was dependent on the abduction angle. 2. The overall strength was higher in the men than in the women, but there were no significant differences in the direction of changes in strength at various angles of abduction. 3. The results obtained here in persons without shoulder injury can serve as norms for evaluating progress in physiotherapy in 20-30-year-old patients with shoulder injuries.     

Isokinetic assessment of shoulder complex strength in adolescent elite synchronized swimmers

Children and adolescent participation in sport has increased in recent years. Synchronized swimming requires correct muscle balance in the shoulder complex. The purpose of this study was to establish isokinetic strength profiles and peak torque ratios of shoulder internal and external rotator muscles in a female high-level synchronized swimming team. Twenty-six adolescent female high-level synchronized swimmers, aged 12–14, participated in this study. Maximal bilateral shoulder concentric external and internal rotation force was measured at 60°/s (5 repetitions) and 180°/s (15 repetitions). The isokinetic concentric strength generated by the internal rotator muscles was significantly higher (p?<?0.05) than by the external rotators in both limbs and at both velocities. Significant bilateral differences in the external rotation (ER):internal rotation (IR) strength ratio were noted at 60°/s. Isokinetic assessment is essential in sports medicine, since it is the only test capable of diagnosing any shoulder strength deficit.     

Changes in infraspinatus cross-sectional area and shoulder range of motion with repetitive eccentric external rotator contraction

Background

Repetitive eccentric loading results in muscle damage and subsequent changes in muscle stiffness and edema accumulation, which manifest as reduced joint range of motion and increased muscle cross-sectional area. The purpose of the study was to evaluate changes in shoulder range of motion and the infraspinatus cross-sectional area with repetitive eccentric contraction.

Methods

Twenty physically active participants performed 9 sets of 25 repetitions of eccentric external rotator contractions. The ultrasonographic measurement of the infraspinatus cross-sectional area, and shoulder internal/external rotation and horizontal adduction range of motion were measured before, immediately after, and 24 h after the intervention.

Findings

Infraspinatus cross-sectional area significantly increased from baseline immediately after exercise (P < 0.001), and remained elevated from baseline at the 24-hour follow up (P < 0.001). Internal rotation and horizontal adduction range of motion did not change significantly between baseline and post-exercise (P > 0.05), but were significantly decreased at the 24-hour follow up from the baseline (internal rotation: P < 0.001, horizontal adduction: P < 0.001) and the immediate post-exercise (internal rotation: P = 1.012, horizontal adduction: P = 0.016).

Interpretation

These changes observed after the eccentric contractions may have implications for injury development in pitchers, because 1) the infraspinatus endures repetitive eccentric loading with pitching and 2) decreased internal rotation and horizontal adduction range of motion have been linked to upper extremity injuries. However, since the muscle response after eccentric loading varies by the task and previous exposure to similar stress, future study needs to investigate the time course of recovery of the muscle cross-sectional area and range of motion after pitching in competitive pitchers.     

Relationship between single-leg stance test with light touch and hip muscle strength in healthy young adults

[Purpose] This study investigated the relationship between the single-leg stance test with light touch and hip rotator muscle strength. [Participants and Methods] Thirty-one healthy young adults participated in the study. A single leg stance test with light touch was performed to evaluate the participants’ static balance ability. The duration that an individual could successfully perform the single leg stance test with light touch in the eyes open was measured. The participants were instructed to slightly touch their right index fingertip on the digital scale. The hip muscle strength of the internal rotators and external rotators were measured by the isometric peak torque. The internal/external rotator strength ratio was calculated by dividing the strength of the internal rotator by that of the external rotator. [Results] The hip external rotator muscle strength was higher in males than in females. Moreover, there was a significant correlation between the single-leg stance test with light touch and hip external rotator muscle strength in males and between the single leg stance test with light touch and hip internal rotator muscle strength in females. Furthermore, a significant positive correlation was found between the single leg stance test with light touch and hip internal rotator/external rotator ratio in males. [Conclusion] We concluded that the single leg stance test with light touch is a useful tool to evaluate static hip muscle strength.Key words: Hip rotator cuff, Hip stability, LT-SLST     

Effects of humeral head compression taping on the isokinetic strength of the shoulder external rotator muscle in patients with rotator cuff tendinitis

[Purpose] The purpose of this study was to examine the effects of humeral head compression taping (HHCT) on the strength of the shoulder external rotator muscle in patients with rotator cuff tendinitis. [Subjects and Methods] Twenty patients with rotator cuff tendinitis were recruited. The shoulder external rotator strength was measured using a Biodex isokinetic dynamometer system. A paired t-test was performed to evaluate within-group differences in the strength of the shoulder external rotator muscle. [Results] Significantly higher shoulder external rotator peak torque and peak torque per body weight were found in the HHCT condition than in the no-taping condition. [Conclusion] HHCT may effectively increase the shoulder external rotator muscle strength in patients with rotator cuff tendinitis.Key words: Shoulder external rotator, Taping, Rotator cuff tendinitis     

The influence of muscle length on one-joint shoulder internal and external rotator muscle strength

Abstract

Background and purpose: Kendall suggests testing the rotator cuff muscles in their maximally shortened position, since one-joint muscles are thought to be strongest. We found little evidence to support this concept. The purpose of this study was to determine if the shoulder internal rotator (IR) and external rotator (ER) muscles are strongest when placed in their shortened length position. Methods: Fifty-three subjects participated. Glenohumeral joint internal rotation and external rotation motion was measured. Muscle strength was then tested using a hand-held dynamometer in four positions: (1) end-range ER; (2) neutral 0°; (3) glenohumeral joint mid-range and (4) end-range IR. Data were analyzed using two repeated measures ANOVA’s. Results: The results suggest that rotator muscle strength is dependent on muscle length. IR strength was weakest at end-range IR in its shortest length; ER muscle strength was weakest at end-range ER in its shortest length. Muscle strength of the IR or ER was not significantly different when comparing neutral 0° to the mid-range position and at their most lengthened position. Conclusion: The IR and ER muscles were found to be weakest when placed in a position of shortest muscle length, while the neutral 0° and mid-range positions were the strongest positions.     

Robotic-Assisted Shoulder Rehabilitation Therapy Effectively Improved Poststroke Hemiplegic Shoulder Pain: A Randomized Controlled Trial

ObjectiveThe purpose of this study was to investigate the therapeutic effects of a newly developed shoulder robot on poststroke hemiplegic shoulder pain.DesignProspective, single-blind randomized controlled trial.SettingInpatient department of a tertiary university hospital.ParticipantsHemiplegic shoulder pain patients (N=38) were consecutively recruited and randomly assigned to an intervention or control group.InterventionsA newly developed robot was designed to perform joint mobilization and stretching exercises with patients lying in the supine position. Conventional physical therapy directed at both improving upper extremity mechanics and reducing neurologic injury was performed twice per day in both groups. In the intervention group, additional robotic-assisted shoulder rehabilitation therapy was administered for 30 minutes per day, 5 times per week for 4 weeks.Main Outcome MeasuresThe visual analog scale was the primary outcome, and the pain-free passive range of motion of the shoulder joint, the Korean version of the Shoulder Disability Questionnaire, and ultrasonographic grades were the secondary outcomes. The outcomes were evaluated at baseline (T0), postintervention (T1), and a 4-week follow-up (T2).ResultsSignificant time and group interaction effects were found on the visual analog scale, in the abduction passive range of motion, and on the Shoulder Disability Questionnaire (F_2,33=16.384, P=.002; F_2,33=10.609, P=.012; F_2,33=32.650, P=.008, respectively). Significantly higher improvements in these outcome measures were observed in the intervention group than in the control group at T1 after post hoc analysis (P<0.05, all). These improvements were sustained at T2 when the intervention group was compared with the control group (P<.05, all).ConclusionsA prototype shoulder rehabilitation robot as an adjuvant therapy improves hemiplegic shoulder pain and self-reported shoulder-related disability.     

Shoulder Rotational Strength Profiles of Danish National Level Badminton Players

BackgroundIncreased age has been shown to be associated with weaker external rotators and stronger internal rotators of the shoulder in pitchers and tennis players. Whether this age-associated change is present in elite badminton players is unknown.PurposeTo compare the internal and external rotation strength of the shoulder in adolescent and adult elite badminton players.Study designCross-sectional.MethodsThirty-one adolescent (12 females aged 16.8 ± 1.6 years and 19 males aged 17.1 ± 1.6 years) and 29 adult (10 females aged 25 ± 2.9 years and 19 males aged 26.2 ± 4.6 years) national level badminton players were tested pre-seasonally for external rotation (ER) and internal rotation (IR) isometric muscle strength bilaterally, using a hand-held dynamometer. Within-group ER to IR strength ratios were calculated (ER/IR×100%).ResultsThe adolescents had stronger shoulder ER than the adults on both sides (p < 0.05). The adult males tended to have stronger IR of the dominant shoulder than the adolescent males (p = 0.071). In the dominant shoulders, the strength ratios for adult females and males were 77% and 78%, respectively, while the same ratio for adolescent females and males were 85% and 99%, respectively. In the non-dominant shoulders, the ER/IR strength ratios for adult females and males were 90% and 87%, respectively, while the ratios for adolescent females and males were 116% and 102%, respectively.ConclusionThis study is the first to demonstrate that in shoulder injury-free national team badminton players, adolescents have stronger shoulder ER than adults on both sides. Therefore, increased age appears to be associated with weaker shoulder ER muscles in elite badminton players.Level of evidence3b.     

Anterior glenohumeral force/translation behavior with and without rotator cuff contraction during clinical stability testing

OBJECTIVE: Measure stiffness of the glenohumeral joint during clinical laxity testing with and without muscular contraction of the Internal rotators. DESIGN: Cross-sectional study of normal shoulders. BACKGROUND: Clinical examination for shoulder instability is based on subjective impression, and is only performed passively. Our study presents a method for quantitative clinical examination of the shoulder under both passive and active muscle contraction conditions. We hypothesized that in a normal shoulder, contraction of the internal rotators will increase the stiffness of the glenohumeral joint, effectively constraining the head of the humerus against anterior directed forces. METHODS: Ten subjects were instrumented with electromagnetic sensors to record glenohumeral linear displacements. A mini-force transducer recorded forces applied to subjects during anterior drawer testing (forced anterior glenohumeral displacement), which was performed passively, and during isometric contraction of internal rotators. RESULTS: Only mild contraction of the internal rotators is needed to significantly increase the stiffness to anterior directed forces. Greater muscular activation does not result in further increased stiffness. CONCLUSION: Objective measurement of glenohumeral stiffness during passive and active muscular contraction may be useful for evaluating the capacity of rotator cuff muscles to stabilize the shoulder. The concept of more strength is better, for rotator cuff strengthen programs is questioned.     

The strength of the ankle dorsiflexors has a significant contribution to walking speed in people who can walk independently after stroke: an observational study

Dorsch S, Ada L, Canning CG, Al-Zharani M, Dean C. The strength of the ankle dorsiflexors has a significant contribution to walking speed in people who can walk independently after stroke: an observational study.ObjectiveTo investigate the relationship between the strength of muscles of the affected lower limb and walking speed after stroke.DesignA cross-sectional observational study.SettingUniversity laboratory.ParticipantsStroke survivors (N=60; mean age ± SD, 69±11y) 1 to 6 years poststroke, able to walk 10m independently without aids.InterventionsNot applicable.Main Outcome MeasuresMaximum isometric strength of 12 muscle groups (hip flexors/extensors, adductors/abductors, internal/external rotators, knee flexors/extensors, ankle dorsiflexors/plantarflexors, invertors/evertors) of the affected lower limb was measured using hand-held dynamometry. Comfortable walking speed was measured using the ten-meter walk test.ResultsUnivariate analysis revealed that strength of the hip flexors (r=.35, P=.01), hip extensors (r=.29, P=.03), hip internal rotators (r=.30, P=.02), hip adductors (r=.29, P=.03), knee extensors (r=.27, P=.03), knee flexors (r=.30, P=.02), ankle dorsiflexors (r=.50, P=.00), ankle plantarflexors (r=.29, P=.03), and ankle evertors (r=.33, P=.01) were all positively associated with walking speed. Multivariate analysis (n=58) revealed that the combined strength of the ankle dorsiflexors and the hip flexors accounted for 34% of the variance in walking speed (P<.001). The ankle dorsiflexors accounted for 31% of the variance (P<.001).ConclusionsThe strength of muscle groups other than the lower limb extensors, particularly the ankle dorsiflexors, has an important role in determining walking speed after stroke.     

Modeling a rotator cuff tear: Individualized shoulder muscle forces influence glenohumeral joint contact force predictions

BackgroundRotator cuff tears in older individuals may result in decreased muscle forces and changes to force distribution across the glenohumeral joint. Reduced muscle forces may impact functional task performance, altering glenohumeral joint contact forces, potentially contributing to instability or joint damage risk. Our objective was to evaluate the influence of rotator cuff muscle force distribution on glenohumeral joint contact force during functional pull and axilla wash tasks using individualized computational models.MethodsFourteen older individuals (age 63.4 yrs. (SD 1.8)) were studied; 7 with rotator cuff tear, 7 matched controls. Muscle volume measurements were used to scale a nominal upper limb model's muscle forces to develop individualized models and perform dynamic simulations of movement tracking participant-derived kinematics. Peak resultant glenohumeral joint contact force, and direction and magnitude of force components were compared between groups using ANCOVA.FindingsResults show individualized muscle force distributions for rotator cuff tear participants had reduced peak resultant joint contact force for pull and axilla wash (P ≤ 0.0456), with smaller compressive components of peak resultant force for pull (P = 0.0248). Peak forces for pull were within the glenoid. For axilla wash, peak joint contact was directed near/outside the glenoid rim for three participants; predictions required individualized muscle forces since nominal muscle forces did not affect joint force location.InterpretationOlder adults with rotator cuff tear had smaller peak resultant and compressive forces, possibly indicating increased instability or secondary joint damage risk. Outcomes suggest predicted joint contact force following rotator cuff tear is sensitive to including individualized muscle forces.