The Kerlan-Jobe Orthopaedic Clinic Shoulder & Elbow Score used as a Patient-Reported Outcome Measure for the Youth and High School Aged Baseball Athlete.

Background: The Kerlan-Jobe Orthopaedic Clinic Shoulder & Elbow Score (KJOC) provides questions for the overhead athlete that can aid with determining if someone is throwing with or without pain. However, this scale was initially created for the adult baseball athlete and has not been validated for younger male demographics. Hypothesis/Purpose: To (1) determine if the scores on the KJOC are different between those throwing with and without pain in male youth and high school-aged baseball athletes, and (2) establish a prediction score for whether a young baseball athlete is throwing with symptoms. Methods: The KJOC questionnaire was used to compare scores in male baseball players between the ages of 10 through 18. This questionnaire consists of 10 questions that each contain a 10-point visual analogue scale (VAS). When all questions are added together the highest possible score is 100 points, with a higher score equating to a better outcome of throwing without symptoms. Retrospective data from 28 subjects with throwing arm pain were compared to 28 prospective subjects actively participating in baseball with no pain. A Mann Whitney-U test was used to compare the mean scores, and regression analysis was used to establish a threshold score between those throwing with and without pain. Results: Significant differences were found between the groups (U = 698.5, p < .001) with capability to discriminate those throwing with pain versus those throwing without pain (Area Under Curve (AUC) .891). Results indicate this discriminating threshold score to be at 68.6 points, which signifies anyone scoring above this threshold would be throwing with no pain and a score below this number indicating throwing with pain. Conclusion: The KJOC can differentiate between younger baseball athletes throwing with and without pain. The predictive threshold score can be used in a clinical setting to aid with determining if a youth or high school-aged athlete is suffering from pain while participating in overhead throwing, and to guide rehabilitation management. Level of Evidence: Level III.

Stride Length and Torso Biomechanics As They Relate To Medial Elbow Injuries In Adolescent Aged Baseball pitchers: A Clinical Commentary.

There is a limited amount of literature examining torso biomechanics and stride length while addressing their relationship to medial elbow injuries in the adolescent baseball pitcher. Anatomical changes, growth, early sport specialization, multiple team participation, mound distance, mound height, and high pitch counts place adolescent pitchers at an exceptionally higher risk for medial elbow injuries. Existing evidence indicates that decreased stride length and altered trunk rotation is correlated with increased medial elbow loading for the adolescent overhead athlete. Further research is required to quantify adequate parameters for torso kinematics, control, and their correlation to stride length, in order to positively affect the biomechanical transfer of energy and potentially prevent injuries during the overhead throwing motion. The purpose of this clinical commentary is to examine and summarize the role of torso biomechanics and stride length in relation to medial elbow injuries in adolescent baseball pitchers. Level of Evidence: 5.

An Anterior Cruciate Ligament (ACL) Injury Risk Screening and Reduction Program for High School Female Athletes: A Pilot Study.

Background: Anterior cruciate ligament (ACL) injury causes physical, mental, and financial burdens. Therefore, it is imperative to screen, identify, and educate athletes who are at high-risk. The combination of screening and education could identify those at risk and potentially reduce future injuries. Purpose: The purpose was to conduct a feasible community pre-season screening program for high school female athletes for the presence of known modifiable risk factors that predispose them to sustaining a non-contact ACL injury. Study Design: Non-experimental prospective study. Methods: A convenience sample of 15 healthy female athletes were recruited from local high schools, consisting of 11 soccer players and four basketball players.  A pre-season screening program was designed encompassing four stations that addressed modifiable neuromuscular and biomechanical risk factors including range of motion (ROM), jump-landing technique, strength, and balance. Athletes were categorized into high-risk versus low-risk groups based on cutoff scores previously established in the literature. Results: Every athlete met the high-risk cutoff score for at least one extremity during the ROM screening, and some met high-risk cutoff scores for more than one ROM. Out of all four categories tested, lower extremity ROM demonstrated the greatest deficits. Conclusion: This study identified athletes as having multiple modifiable risk factors that can be addressed with training and exercises. This supports implementing a pre-season program aimed at screening for injury risk factors. Level of Evidence: Level 3.

Selectively reshaping a muscle phenotype: functional overload of cat plantaris.

INTRODUCTION: Functional overload (FO) of the fast plantaris muscle was studied in treadmill-exercised (FO-Ex) or sedentary (FO-Sed) adult cats. METHODS: Mechanical, phenotype, and kinematics analyses were performed. RESULTS: Plantigrade vs. normal digitigrade posture was observed early post-FO. Relative plantaris mass was greater in FO-Sed (10%) and FO-Ex (60%) cats than in controls 12 weeks post-FO. Specific tension was similar across groups, indicating functional hypertrophy. Fiber size was greater, percent slow fibers higher, percent IIa myosin heavy chain (MHC) higher, and IIx MHC lower in FO-Ex than controls. Twitch and half-relaxation times were longer, and the frequency-tension curve shifted toward that observed in slow muscles. Electromyography (EMG) and tendon force amplitudes during stepping were larger, and the yield (lengthening) phase occurred at a longer muscle length before compared with after FO. DISCUSSION: Reshaping the plantaris phenotype was highly dependent on the overload stimulus, indicating that electrical stimulation paradigms used during rehabilitation should be performed with the muscles under "loaded" conditions.

Geniohyoid muscle properties and myosin heavy chain composition are altered after short-term intermittent hypoxic exposure.

Patients with obstructive sleep apnea (OSA) often exhibit fatigued or inefficient upper airway dilator and constrictor muscles; an upper airway dilator, the geniohyoid (GH) muscle, is a particular example. Intermittent hypoxia (IH) is a frequent concomitant of OSA, and it may trigger muscle fiber composition changes that are characteristic of a fatigable nature. We examined effects of short-term IH on diaphragmatic and GH muscle fiber composition and fatigue properties by exposing 24 rats to alternating 10.3% O(2)-balance N(2) and room air every 480 s (240 s duty cycle) for a total duration of 5, 10, 15, 20, or 30 h. Sternohyoid fiber composition was also examined. Control animals were exposed to room air on the same schedule. Single-fiber analyses showed that GH muscle fiber types changed completely from myosin heavy chain (MHC) type 2A to MHC type 2B after 10 h of exposure, and the conversion was maintained for at least 30 h. Sternohyoid muscle fibers showed a delayed transition from MHC type 2A/2B to MHC type 2B. In contrast, major fiber types of the diaphragm were not significantly altered. The GH muscles showed similar tension-frequency relationships in all groups, but an increased fatigability developed, proportional to the duration of IH treatment. We conclude that short-term IH exposure alters GH muscle composition and physical properties toward more fatigable, fast-twitch types and that it may account for the fatigable upper airway fiber types found in sleep-disturbed breathing.

RETURN TO HITTING: AN INTERVAL HITTING PROGRESSION AND OVERVIEW OF HITTING MECHANICS FOLLOWING INJURY.

BACKGROUND AND PURPOSE: Participation in baseball is prevalent across all age groups. Baseball injuries are common and can impact a player's ability to participate. An injury to any region can influence the player's ability to swing the bat. As a part of the athlete's rehabilitation, a sports-specific program should be implemented re-introducing the hitting cycle that addresses proper biomechanics as well as providing a progressive atmosphere to return to hitting. Although there are several return to throwing progression programs in the literature, to the author's knowledge no published hitting progression programs exist. Thus, the purpose of this clinical commentary is to propose a progressive return to hitting program that emphasizes proper mechanics for ballplayers who have sustained an injury. DESCRIPTION OF TOPIC: This return to hitting program describes in detail the phases of the baseball hitting cycle. Proper biomechanical information is provided on each phase that can be used to assist the clinician in injury prevention. This article gives the healthcare professional guidance for assessment for appropriate readiness for return to sport using impairment measures, patient-report measures, and physical performance measures. The purpose of this hitting progression is to provide a safe, gradual increase in hitting intensity by moving from a fixed position to soft toss and finally to increasing pitch velocity. DISCUSSION: This interval hitting program guides the clinician from when the patient is ready to begin hitting through a full return to sport. Use of appropriate hitting mechanics must be ensured during rehabilitation to avoid compensation. Similar to the return to throwing programs that exist, this interval hitting progression program can provide a framework to quantify progression and reduce the chance of re-injury from occurring during the return to sport phase of rehab. LEVEL OF EVIDENCE: Level 5.

Does daily activity level determine muscle phenotype?

The activation level of a muscle is presumed to be a major determinant of many mechanical and phenotypic properties of its muscle fibers. However, the relationship between the daily activation levels of a muscle and these properties has not been well defined, largely because of the lack of accurate and sustained assessments of the spontaneous activity levels of the muscle. Therefore, we determined the daily activity levels of selected rat hindlimb muscles using intramuscular EMG recordings. To allow comparisons across muscles having varying activity levels and/or muscle fiber type compositions, we recorded EMG activity in a predominantly slow plantarflexor (soleus), a predominantly fast plantarflexor (medial gastrocnemius, MG), a predominantly fast ankle dorsiflexor (tibialis anterior, TA) and a predominantly fast knee extensor (vastus lateralis, VL) in six unanesthetized rats for periods of 24 h. EMG activity levels were correlated with the light:dark cycle, with peak activity levels occurring during the dark period. The soleus was the most active and the TA the least active muscle in all rats. Daily EMG durations were highest for soleus (11-15 h), intermediate for MG (5-9 h) and VL (3-14 h) and lowest for TA (2-3 h). Daily mean EMG amplitudes and integrated EMG levels in the soleus were two- to threefold higher than in the MG and VL and seven- to eightfold higher than in the TA. Despite the three- to fourfold difference in activation levels of the MG and VL vs the TA, all three predominantly fast muscles have been reported to have a similar, very low percentage of slow fibers. Comparing these relative EMG levels to the published fiber type profiles of these muscles yields a very poor relationship between daily activity level and fiber type composition in the same muscles across several species. Although it is clear that changing the levels of activity can modulate the expression of the myosin phenotype, these results indicate that factors other than activation must play critical roles in determining and maintaining normal phenotypic properties of skeletal muscle fibers.

Mechanical properties of rat soleus aponeurosis and tendon during variable recruitment in situ.

The in vitro mechanical properties of tendons are well described, whereas little data exist for conditions mimicking those found in vivo. Descriptions of the in situ mechanical properties of aponeuroses are more common, but the results are variable. Our goal was to examine the mechanical properties of these tissues under conditions mimicking the in vivo state. Tissue strains were measured in the rat (Rattus norvegicus) soleus muscle directly from the spacing of metal markers implanted within the tissues of interest using an X-ray video microscope. Strains were measured for the tendon and three regions (proximal, middle and distal) of the aponeurosis. Muscle stimulation was accomplished through isolated ventral rootlets, allowing force to be graded in seven repeatable increments independent of muscle-tendon unit length. Peak strains (during maximal tetanic contraction at optimum length; P(o)) were approximately 5% in tendon and approximately 12% in all regions of the aponeurosis. At forces above 50% of P(o), tissue stiffness was nearly constant in all regions, and a pronounced toe region was observed only at forces below approximately 25% of P(o). Stiffness increased in all regions as the muscle-tendon unit was lengthened. These results suggest that using mechanical properties measured ex vivo or during single contractile events in situ to estimate the in vivo behavior of tendon and aponeurosis may lead to errors in estimating the distribution of strain among the contractile and series elastic elements of the muscle.

Mechanical properties of the electrically silent adult rat soleus muscle.

The isometric and isotonic in situ mechanical properties of the soleus muscle of adult female rats were determined after 60 days of inactivity induced by spinal cord isolation (SI). Compared to control, the absolute muscle mass, physiological cross-sectional area, and maximum tetanic tension of the soleus in SI rats were reduced by 69%, 66%, and 77%, respectively. Isometric twitch time-to-peak-tension and half-relaxation times were 41% and 60% shorter in SI than control rats. The maximum velocity of shortening (mm/s), as determined using the afterloaded technique, was 66% faster in SI than control rats, whereas unloaded shortening velocity was similar in the two groups (9% faster in SI rats). Peak power was 48% lower in SI than control rats. The SI soleus was 39% more fatigable than control. Thus, the soleus became a smaller, faster, and more fatigable muscle following 60 days of inactivity. In general, the results indicate that the adaptations are of a lesser magnitude than those reported previously following denervation for the same duration. These data provide a baseline for future efforts to experimentally define the mechanisms of neurally mediated, but activity-independent, regulation of the mechanical properties of the rat soleus muscle.

Adaptations in skeletal muscle disuse or decreased-use atrophy.

Those factors that seem to play some role in inducing adaptations of skeletal muscle in vivo are discussed. The role of myogenesis in maintaining and repairing muscle during atrophic and hypertrophic states is discussed, including pointing out that the modulation of myonuclear number is one means of adapting to varying chronic levels of neuromuscular activity. Finally, we point out the potential consequences of muscle atrophy on the control of movement and the susceptibility to fatigue.