Shoulder kinematics during the wall push-up plus exercise.

BACKGROUND AND HYPOTHESIS: The push-up plus exercise is a common therapeutic exercise for improving shoulder function and treating shoulder pathology. To date, the kinematics of the push-up plus exercise have not been studied. Our hypothesis was that the wall push-up plus exercise would demonstrate increased scapular internal rotation and increased humeral anterior translation during the plus phase of the exercise, thereby potentially impacting the subacromial space. METHODS: Bone pins were inserted in the humerus and scapula in 12 healthy volunteers with no history of shoulder pathology. In vivo motion during the wall push-up plus exercise was tracked using an electromagnetic tracking system. RESULTS: During the wall push-up plus exercise, from a starting position to the push-up plus position, there was a significant increase in scapular downward rotation (P < .05) and internal rotation (P < .05). The pattern of glenohumeral motion was humeral elevation (P < .05) and movement anterior to the scapular plane (P < .05), with humeral external rotation remaining relatively constant. CONCLUSION: We found that during a wall push-up plus exercise in healthy volunteers, the scapula was placed in a position potentially associated with shoulder impingement. Because of the shoulder kinematics of the wall push-up plus exercise, utilization of this exercise without modification early on in shoulder rehabilitation, especially in patients with subacromial impingement, should be considered cautiously.

Three-dimensional acromioclavicular joint motions during elevation of the arm.

STUDY DESIGN: Descriptive laboratory study. OBJECTIVES: To determine the 3-dimensional motions occurring between the scapula relative to the clavicle at the acromioclavicular joint during humeral elevation in the scapular plane. BACKGROUND: Shoulder pathology is commonly treated through exercise programs aimed at correcting scapular motion abnormalities. However, little is known regarding how acromioclavicular joint motions contribute to normal and abnormal scapulothoracic motion. METHODS AND MEASURES: Thirty subjects (16 males, 14 females) participated. Subjects with positive symptoms on clinical exam or past history of shoulder pathology, trauma, or surgery were excluded. Electromagnetic surface motion analysis was performed tracking the thorax, clavicle, scapula, and humerus. Subjects performed 3 repetitions of scapular plane abduction. Passive motion data were also collected for scapular plane abduction from cadaver specimens. Data were analyzed using within-session reliability and descriptive statistics as well as repeated measures analyses of variance (ANOVAs) to determine the effect of elevation angle from rest to 90 masculine humeral elevation. Reliability was determined from repeated trials in the same session without removing sensors or redigitizing landmarks. RESULTS: Angular values were highly repeatable within session (ICC>0.94; SEM, < 2.3 degrees ). During active scapular plane abduction from rest to 90 degrees , average acromioclavicular joint angular values demonstrated increased internal rotation (approximately 4.3 degrees ), increased upward rotation (approximately 14.6 degrees ), and increased posterior tilting (approximately 6.7 degrees ) (P<.05). Passive motions on cadavers demonstrated similar kinematic patterns. CONCLUSIONS: Significant motion occurs at the acromioclavicular joint during active humeral elevation, contributing to scapular motion on the thorax. This information provides a foundation for understanding normal acromioclavicular joint motion as a basis for further investigation of pathology and rehabilitation approaches.

Effects of steroid hormones on spermatogenesis and GnRH release in male Leopard frogs, Rana pipiens.

Several lines of evidence suggest reproduction in the ranid frogs is potently regulated by the gonadal steroids, in particular 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E(2)), and a non-gonadal steroid, the stress hormone corticosterone (Cort). Little is known about how these steroid hormones act upon the GnRH system to regulate the downstream reproductive events. We address these gaps in our knowledge by investigating the effects of Cort, E(2), and DHT administration on the in vitro release of GnRH and on the spermatogenesis of adult male leopard frog, Rana pipiens. R. pipiens were implanted for 20 days with silastic capsules containing cholesterol (Ch; control), Cort, E(2), or DHT. Upon sacrifice, acute hypothalamic explants were cultured and measured for GnRH release, and testes processed for histological analysis. Although only E(2) implant significantly reduced the gonadosomatic index, all three steroid hormones altered spermatogenesis. Cort modestly but significantly reduced the presence of spermatids. The effects of E(2) and DHT were both stimulatory and inhibitory, depending on the stage of spermatogenesis. None of the steroid hormones altered baseline GnRH release. Interestingly, only E(2) significantly stimulated veratridine-induced GnRH release, suggesting E(2) treatment increased the releasable pool of GnRH and/or enhance the excitability of GnRH neurons. In sum, this is the first study to report the direct measurement of GnRH secretion in a poikilothermic tetrapod. Our results revealed potent but sometimes paradoxical effects of steroid hormones, especially E(2), on the reproductive regulation of the male R. pipiens.

Localization of gonadotropin-releasing hormone in the central nervous system and a peripheral chemosensory organ of Aplysia californica.

Gonadotropin-releasing hormone (GnRH) is a neurohormone crucial for the regulation of reproductive and neural functions in vertebrates. Recent discoveries of GnRH immunoreactivity (IR) in a number of invertebrates raised the possibility that GnRH may be an ancient molecule that had arisen before the emergence of Phylum Chordata. We previously demonstrated the presence of a GnRH IR similar to the mammalian (m) and tunicate I (tI) forms of GnRH in the hemolymph and ovotestis of an opisthobranch mollusk, Aplysia californica; however, the presence of GnRH in the central nervous system (CNS) of A. californica could not be detected with the available antisera against various forms of chordate GnRH. In the present study, we performed immunohistochemistry (IHC) to localize the presence of GnRH in the CNS and a peripheral chemosensory organ, the osphradium, of A. californica. A newly generated antiserum against tI-GnRH revealed the strong expression of GnRH IR in neurons of all CNS ganglia. A notable asymmetry in immunostaining was detected in the left and right abdominal hemiganglia. The CNS is rich in tI-GnRH immunoreactive neurons but lacks mGnRH IR, whereas the osphradium contains abundant mGnRH immunoreactive neurons but lacks tI-GnRH IR. The extract of CNS failed to stimulate the release of LH from mouse pituitary, demonstrating that the A. californica GnRH IR is structurally different from what is required to bind and activate mammalian GnRH receptor. Together, these results indicate the presence of at least two distinct GnRH systems in A. californica. The presence of GnRH in the osphradium is consistent with the long-standing anatomical relationship between GnRH and the chemosensory system observed in vertebrates.

Disruption of pubertal onset by exogenous testosterone and estrogen in two species of rodents.

The administration of adult physiological levels of testosterone (T) and 17beta-estradiol (E(2)) to male Siberian hamsters was previously shown to delay the onset of puberty. To examine whether this is a response common to other rodents, we investigated whether exogenous steroids also alter the onset of puberty in Syrian hamsters and mice. Juvenile male Syrian hamsters and mice were implanted with Silastic capsules containing T, E(2), or cholesterol control. After 15 days, plasma, pituitaries, and testes were processed for histological analysis or measurements of gonadotropins and circulating steroid hormones. T and E(2) implants reduced testis mass and gonadotropin stores in both species and arrested spermatogenesis in Syrian hamsters. In contrast, spermatogenesis in mice was unaffected by T and only modestly affected by E(2). Although E(2) inhibited circulating follicle-stimulating hormone (FSH) in both species, T inhibited circulating FSH in mice only. Overall, our results demonstrate that the hypothalamic-pituitary-gonadal axis of each rodent species responds uniquely to T and E(2) during the pubertal transition. Despite the highly varied effects of T and E(2) in these two species, the ability of steroid hormones to disrupt the onset of puberty appears to be a feature common to many rodents.