A Longitudinal Study of Quantitative Muscle Strength and Functional Motor Ability in Ambulatory Boys with Duchenne Muscular Dystrophy

Background: Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder, that is characterized by progressive muscle degeneration and loss of ambulation between 7–13 years of age. Novel pharmacological agents targeting the genetic defects and disease mechanisms are becoming available; however, corticosteroid (CS) therapy remains the standard of care. Objective: The purpose of this longitudinal study was to elucidate the effect of CS therapy on the rate of muscle strength and gross motor skill decline in boys with DMD and assess the sensitivity of selected outcome measures. Methods: Eighty-four ambulatory boys with DMD (49–180 months), 70 on CS, 14 corticosteroid naïve (NCS), participated in this 8-year multi-site study. Outcomes included; isokinetic dynamometry, the Standing (STD) and Walking/Running/jumping (WRJ) dimensions of the Gross Motor Function Measure (GMFM), and Timed Function Tests (TFTs). Nonlinear mixed modeling procedures determined the rate of change with age and the influence of steroids. Results: Despite CS therapy the rate of decline in strength with age was significant in all muscle groups assessed. CS therapy significantly slowed decline in knee extensor strength, as the NCS group declined at 3x the rate of the CS group. Concurrently, WRJ skills declined in the NCS group at twice the rate of the CS group. 4-stair climb and 10 meter walk/run performance was superior in the boys on CS therapy. Conclusion: CS therapy slowed the rate of muscle strength decline and afforded longer retention of select gross motor skills in boys on CS compared to boys who were NCS. Isokinetic dynamometry, Walk/Run/Jump skills, and select TFTs may prove informative in assessing the efficacy of new therapeutics in ambulatory boys with DMD.

ASSESSMENT OF KNEE JOINT POSITION SENSE IN PATIENTS WITH MULTIPLE SCLEROSIS

Purpose: Multiple sclerosis (MS) disrupts joint position sense (JPS). The aims were: - to assess the JPS of knee extensors, using three target angles in MS patients and in healthy; - to estimate the changes in reproducing the joint position by using absolute (AE), constant (CE) and variable error (VE) and the effect of sex on knee JPS acuity. Subjects and Methods: Twenty MS patients and twenty healthy were tested, by knee joint angle reproduction with three targets (20o, 60o, 75o), by passive and active mode, without visual and verbal feedback. JPS measurement was done using isokinetic dynamometry. Deviations from the targets were calculated as AE, VE and CE, which correspond to accuracy, precision and direction of the bias, respectively. Results: Increased values of AE and sex differences in JPS accuracy in MS individuals, as compared with healthy, were: - at targets 20o and 60o in females in passive mode in both legs; - at 60o in the involved leg in males (more pronounced as compared with females); and – at 75o in the less involved leg, in passive reproduction in women and active in men. The significantly increased negative CE indicates a more pronounced deficit in males with MS at 60o in the involved leg and at 75o in less involved leg. Increased VE in passive repositioning was also proved (p<0.05) in females with MS at 20o and 60o. Conclusion: These results suggest impaired proprioceptive performance and sex differences in MS individuals. The findings provide information to recommend appropriate strategies for the evaluation and treatment of proprioceptive deficits.

Rate of torque development and striatal shape in individuals with prodromal Huntington's disease

The aim of the present study was to quantify explosive joint torque or the ability to develop joint torque rapidly, typically measured as the rate of torque development, in individuals with prodromal Huntington’s disease and healthy controls and its associations with measures of disease burden and striatal pathology. Twenty prodromal Huntington’s disease and 19 healthy control individuals volunteered for this study. Plantar flexor isometric rate of torque development values were evaluated using isokinetic dynamometry. Pathological changes in striatal shape were evaluated using magnetic resonance imaging. Disease burden was evaluated using the disease burden score and cytosine-adenine-guanine age product score. No statistical differences in the rate of torque development were observed between individuals with prodromal Huntington’s disease and healthy controls. However, significant associations were observed between the rate of torque development values and measures of disease burden (r = −0.42 to −0.69) and striatal pathology (r = 0.71–0.60) in individuals with prodromal Huntington’s disease. We found significant associations between lower rate of torque development values and greater striatal shape deflation and disease burden and striatal pathology in individuals with prodromal Huntington’s disease. While no significant differences in the rate of torque development were found between prodromal Huntington’s disease and healthy controls, the noted associations suggest that differences may emerge as the disease advances, which should be investigated longitudinally in future studies.

Isokinetic Dynamometry as a Tool to Predict Shoulder Injury in an Overhead Athlete Population: A Systematic Review

Prospective and cross-sectional studies have used pre-season isokinetic dynamometry strength and endurance measurements of shoulder internal rotation (IR) and external rotation (ER) to determine if they can be correlated to injury. However, to date, no review has provided a synthesis of all available literature on this topic. The aim of this systematic review was to identify isokinetic dynamometry studies that assess shoulder IR and ER strength and endurance in the overhead athletic population in relation to shoulder injury. Electronic databases (PubMed, CINAHL, and SportDiscus) were searched through September 2019 using pre-determined search terms. Both prospective and cross-sectional studies were included in this review. Studies were assessed for quality using either Appraisal Tool for Cross-sectional Studies (AXIS) or Critical Appraisal Skills Programme (CASP). Data on outcome measures of strength and endurance peak torque (PT) and ratios (ER:IR) were extracted and further analysed using a best evidence synthesis approach. A total of 13 articles met the inclusion criteria. Conflicting evidence was found when reviewing all studies without differentiating by study type. Prospective study designs revealed strong evidence that reduced IR endurance and reduced strength ratios are predictive of shoulder injury. Cross-sectional literature showed only conflicting and limited evidence for all outcome measures. At this stage, more research is needed in individual sporting populations using prospective cohort designs.