Return to Sports Following Shoulder Injury: Clinical Evaluation, Isokinetic, and Functional Testing.

ABSTRACT: The shoulder is commonly injured in overhead sports. This is associated with a high degree of mobility at the expense of stability, sports specific demands, high volume or intensity of practice and competition, biomechanical deficits, and poor technique. Following injury, the return to competition process includes nonsurgical or surgical treatment, comprehensive rehabilitation, and a structured return to sports program. The return to sports continuum is divided into phases which include return to practice of the sport, return to competition at a lower level or with reduced performance, and return to expected performance. Components of the return to sports decision include clinical evaluation of physical and psychological readiness, measurement of muscle strength using isokinetic tests, evaluation of overhead functional tasks, and progression in a supervised interval throwing program. The evidence for the effectiveness of return to sports programs following shoulder injury is limited but evolving and is an area that will merit continued investigation.

Single skeletal muscle fiber mechanical properties: a muscle quality biomarker of human aging.

Skeletal muscle strength, mass, and function should be carefully monitored for signs of decline with advanced adult age. An understanding of the pathophysiology and severity of sarcopenia can be improved with the exploration of changes in muscle fiber properties. Furthermore, although functional decline with increase age is a well-known phenomenon, the mechanisms underlying this decline, and the features that characterize it, are complex and variable. The age-related decline of muscle function is a result of not only a decrease of muscle mass but also a decline in the intrinsic properties of muscle fibers that are independent of size. We believe it is important to understand changes in muscle quality (force adjusted for size), and not to focus solely on muscle mass, because muscle quality is closely related to measurements of function and could potentially predict clinical outcomes such as morbidity, disability, and mortality. Neurological and metabolic mechanisms contribute to muscle quality, but the intrinsic properties of muscle cells are central to the maintenance of force-generating capacity. Muscle quality can be evaluated with the assessment of morphological, physiological, and mechanical properties in single permeabilized or skinned fibers. This approach excludes the influence of the nervous system, tendons, and the extracellular matrix. In this review, we summarized the changes in active and passive mechanical properties at the single muscle cell level in older skeletal muscles. We argue that intrinsic mechanical changes in human single muscle fibers are useful biomarkers and indicators of muscle quality.

Rehabilitation Is a Global Health Priority.

Optimizing functioning at all ages is a major global public health goal. Rehabilitation is unique in its contribution to this public health agenda because of its focus on optimizing function. In this editorial, the editors of leading rehabilitation journals make the case for fully integrating rehabilitation into a nation's health system and strengthening it specifically at the primary care level to increase access and achieve its full potential. Authors submitting papers to rehabilitation journals are encouraged to consider the global health policy implications of their research when they prepare their research reports for publication and to make these implications explicit.

Passive force and viscoelastic properties of single fibers in human aging muscles.

PURPOSE: Changes in stiffness or extensibility of the muscle or muscle-tendon unit with aging could lead to impaired function and an increased vulnerability to injury. We aimed to investigate the passive force and viscoelastic properties of single muscle fibers in older adults. METHODS: Seven older adults (mean age 79.0 ± 3.8 years) and 10 young control (mean age 25.6 ± 4.5 years) were recruited. Biopsy specimens were obtained percutaneously from m. vastus lateralis and skinned single fibers were used for the experiments. Slack tests were performed to determine maximal force and maximal unloaded shortening velocity. Passive force was measured in pCa 9.0 solution using a stepwise stretch technique with increment of sarcomere length from 2.4 to 4.2 µm. Myosin heavy chain (MHC) isoform was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Specific force was calculated as maximal force divided by cross-sectional area. Passive force, peak passive force, time to half stress relaxation (T1/2) and force decay index (a force time integral under a stress relaxation curve) were measured. RESULTS: No difference between the groups were found in specific force and shortening velocity. Passive force and peak passive force were greater in both MHC I and IIa fibers of older adults (p < 0.001, p = 0.012, respectively, at 4.2 mm SL). Force decay index was higher in older adults. (p = 0.001 at 4.2 µm SL). There were no significant differences in passive force and viscoelastic properties between fiber types. CONCLUSION: We demonstrated greater passive force and viscoelastic properties at the level of single fibers in older adults.

Apoptosis in young and old denervated rat skeletal muscle.

INTRODUCTION: We investigated the apoptotic response to different degrees of denervation in young and older rats randomized into control (C), partial (PD), and complete denervation (CD) of muscles innervated by the sciatic nerve. METHODS: Muscle wet weight to body weight (MWW/BW), myosin heavy chain (MHC) isoforms, and fiber cross-sectional area were determined in gastrocnemius and soleus muscles. Apoptotic responses were determined by changes in myonuclei and expression of Bcl-2 and BAX. RESULTS: PD and CD resulted in significant reductions in MWW/BW and FCSA in both young and older rats. Older controls had greater apoptotic responses than young controls. Apoptotic responses were greater in PD and CD than in C in both age groups. No statistical interaction between denervation and age group was seen. CONCLUSIONS: Older age was associated with increased level of apoptosis, but older muscle was not more vulnerable to the effect of denervation. Muscle Nerve 55: 262-269, 2017.

Rehabilitation Research at the National Institutes of Health: Moving the Field Forward (Executive Summary).

Approximately 53 million Americans live with a disability. For decades, the National Institutes of Health (NIH) has been conducting and supporting research to discover new ways to minimize disability and enhance the quality of life of people with disabilities. After the passage of the Americans With Disabilities Act, NIH established the National Center for Medical Rehabilitation Research, with the goal of developing and implementing a rehabilitation research agenda. Currently, 17 institutes and centers at NIH invest more than $500 million per year in rehabilitation research. Recently, the director of NIH, Francis Collins, appointed a Blue Ribbon Panel to evaluate the status of rehabilitation research across institutes and centers. As a follow-up to the work of that panel, NIH recently organized a conference, "Rehabilitation Research at NIH: Moving the Field Forward." This report is a summary of the discussions and proposals that will help guide rehabilitation research at NIH in the near future.

Single muscle fiber contractile properties in diabetic RAT muscle.

INTRODUCTION: Diabetes is associated with accelerated loss of muscle mass and function. We compared the contractile properties of single muscle fibers in young rat soleus muscle of uncontrolled streptozotocin-induced diabetic animals (n = 10) and nondiabetic controls (n = 10). METHODS: Single fiber maximal force, shortening velocity, and power were assessed during maximal activation with calcium using the slack test 4 weeks after induction. Myosin heavy chain expression was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Oxidized myosin levels were detected by analyzing protein carbonyls in muscle homogenates. All fibers expressed the type I myosin heavy chain isoform. RESULTS: Diabetic rats had higher blood glucose (537 vs. 175 mg/dl; P < 0.001) and lower body weight (171 vs. 356 g; P < 0.001) than controls. Muscle fibers from diabetic rats showed smaller cross-sectional area (1128 vs. 1812 µm(2) ), lower maximal force (258 vs. 492 µN), and reduced absolute power (182 vs. 388 µN FL/s) (all P < 0.0001). No differences were seen in shortening velocity, specific force or specific power. Myosin carbonylation was higher (P < 0.01) in diabetic rats. CONCLUSIONS: After 4 weeks of untreated diabetes, there are significant alterations in muscle at the level of isolated single fibers and myosin protein, although some contractile properties seem to be protected. Muscle Nerve, 2015 Muscle Nerve 53: 958-964, 2016.

Skeletal muscle: a brief review of structure and function.

Skeletal muscle is one of the most dynamic and plastic tissues of the human body. In humans, skeletal muscle comprises approximately 40% of total body weight and contains 50-75% of all body proteins. In general, muscle mass depends on the balance between protein synthesis and degradation and both processes are sensitive to factors such as nutritional status, hormonal balance, physical activity/exercise, and injury or disease, among others. In this review, we discuss the various domains of muscle structure and function including its cytoskeletal architecture, excitation-contraction coupling, energy metabolism, and force and power generation. We will limit the discussion to human skeletal muscle and emphasize recent scientific literature on single muscle fibers.