We examined the relationship between grip strength declines and muscle-tendon responses induced by long-term performance of a high-repetition, low-force (HRLF) reaching task in rats. We hypothesized that grip strength declines would correlate with inflammation, fibrosis and degradation in flexor digitorum muscles and tendons. Grip strength declined after training, and further in weeks 18 and 24, in reach limbs of HRLF rats. Flexor digitorum tissues of reach limbs showed low-grade increases in inflammatory cytokines: IL-1beta after training and in week 18, IL-1alpha in week 18, TNF-alpha and IL-6 after training and in week 24, and IL-10 in week 24, with greater increases in tendons than muscles. Similar cytokine increases were detected in serum with HRLF: IL-1alpha and IL-10 in week 18, and TNF-alpha and IL-6 in week 24. Grip strength correlated inversely with IL-6 in muscles, tendons and serum, and TNF-alpha in muscles and serum. Four fibrogenic proteins, TGFB1, CTGF, PDGFab and PDGFbb, and hydroxyproline, a marker of collagen synthesis, increased in serum in HRLF weeks 18 or 24, concomitant with epitendon thickening, increased muscle and tendon TGFB1 and CTGF. A collagenolytic gelatinase, MMP2, increased by week 18 in serum, tendons and muscles of HRLF rats. Grip strength correlated inversely with TGFB1 in muscles, tendons and serum; with CTGF-immunoreactive fibroblasts in tendons; and with MMP2 in tendons and serum. Thus, motor declines correlated with low-grade systemic and musculotendinous inflammation throughout task performance, and increased fibrogenic and degradative proteins with prolonged task performance. Serum TNF-alpha, IL-6, TGFB1, CTGF and MMP2 may serve as serum biomarkers of work-related musculoskeletal disorders, although further studies in humans are needed. / Biomedical Sciences

Injuries of the hands and wrist are prevalent in many occupations requiring repetitive tasks and may be further aggravated by advancing age; these injuries are termed work related musculoskeletal disorders (WMSDs). Prior studies using an innovative operant rat model of reaching and grasping as a model of WMSDs demonstrated exposure dependent changes in forelimb bones of young adult rats performing repetitive tasks ≤ 3 months. No one has yet to examine if aging enhances forelimb bone degradative changes occurring with WMSDs, or if forelimb bones adapt or degrade further in response to moderate versus high demand repetitive tasks performed for prolonged time periods (up to 24 months). Bone remodeling is a normal biological process that allows bones to adjust to strains. Unfortunately, both aging and inflammation can deregulate the balance between bone resorption and formation. Aging mammals display increased baseline inflammatory-cytokine levels, both systemically and at the tissue level. Several inflammatory cytokines have been shown to stimulate osteoclastogenesis leading to bone resorption and reduced bone formation. We have reported increased production of inflammatory cytokines in serum and musculotendinous tissues of aged animals performing a repetitive reaching and grasping tasks for up to 12 weeks, warranting further examination of whether aged rats performing these tasks have increased bone resorptive changes, compared to young adult rats. We hypothesized that aging would enhance bone degradative changes in our model as a consequence of increased bone inflammatory responses to a moderate demand repetitive task. Therefore, our first aim was to examine forearm grip strength, trabecular and cortical bone quality, and inflammatory cytokine levels in radii of mature (14-18 mo of age) and young adult (2.5-6.5 mo of age) female Sprague Dawley rats after performance of a high repetition low force (HRLF) task for 12 weeks, compared to each other and age-matched controls. We found that mature rats performing a moderate demand repetitive task for 12 weeks had decreased bone formation and quality, particularly cortical bone quality, compared to young adult rats performing the same task, with increased inflammatory and decreased anti-inflammatory responses, and perhaps lower grip strength, as likely contributors. An adaptive bone response was observed in young adult animals performing a moderate level task of high repetition low force for 12 weeks. In contrast, a previous study showed bone degradative changes in young adult rats performing a high demand task of high repetition high force task for 12 weeks. Osteocytes are the mechanosensing cells of bones, and disruption or changes to their environment can lead to apoptosis or molecular changes. In models of forced bone loading to bone fatigue, osteocyte apoptosis increases sclerostin levels and osteoclast recruitment. Increased sclerostin also leads to increased RANKL production. In contrast, low level loading for a short period reduces sclerostin levels and encourages bone formation. We hypothesized that long-term muscle loading at high repetition low force loads would induce further bone adaptation, but that long-term high repetition high force muscle loading would result in detrimental bone loss, as well as alterations in these two bone remodeling proteins, RANKL and sclerostin. Therefore, our second aim was to determine if prolonged performance of a moderate demand upper extremity reaching and grasping task by young adult rats would continue to enhance forelimb bone formation and quality. We hypothesized that continued performance of a high repetition low force (HRLF) task for 24 weeks would lead to increased bone formation. We also hypothesized that RANKL and sclerostin, two proteins that have not been investigated in our rat model of WMSDs, would be reduced in rats performing a HRLF task for 24 weeks, as the bones reach adaptation. We found that 24 week HRLF rats showed several indices of bone formation and adaptation to the task; as well as reduced sclerostin immunoexpression, compared to controls, a reduction that likely contributed to the enhanced bone formation. To expand on this investigation, in our third aim, we investigated the impact of performance of a high repetition high force (HRHF) task for 18 weeks on young adult rat forelimb bones, and on sclerostin and RANKL levels. We observed detrimental trabecular bone remodeling in the radius, including decreased trabeculae bone volume, number and thickness, increased trabecular separation and anisotropy, and a transition to rod-shaped trabeculae in 18-week HRHF task animals, compared to food restricted control rats. In the 18-week HRHF rats, osteoclast numbers increased and osteoblast numbers decreased, concomitant with increased osteocyte apoptosis and empty lacunae, compared to control rats. Also, mRNA and protein levels of RANKL increased and sclerostin decreased in the 18-week HRHF rats, compared to to control rats. Thus, prolonged performance of a high demand task of high repetition high force induced detrimental trabecular bone changes. The increased RANKL likely contributed to these changes, and although sclerostin level decreased, a change that should contribute to enhanced osteoblast activity, bone formation was not rescued. In conclusion, prolonged performance of a HRLF task by young adult rats leads to reduced sclerostin levels and increased bone formation and bone quality. Aged rats performing the same HRLF task showed increased bone degradative changes that might increase fracture risk. In contrast, prolonged performance of a HRHF task by young adult rats leads to increased bone resorption and degradation, changes associated with RANKL expression. Sclerostin levels were reduced by the HRHF task, but failed to rescue bone formation. / Cell Biology

Background: Overuse injuries (OI) account for a substantial part of sport injury incidence among athletes of various sports and levels. They lead to serious consequences for athletes’ physical and mental health, as well as athletic performance. Despite the gradual onset of symptoms, athletes often persevere in training and competing. The present study aimed to identify psychological risk profiles suggested to explain maladaptive behaviors prior or in response to first signs of overuse injuries. Design: Prospective cohort study. Methods: 149 athletes representing 10 individual and team sports responded to a range of questionnaires regarding personal (athletic identity, perfectionistic concerns, grit and negative life stress) and interpersonal (coach-athlete relationship) psychological traits. By using the mobile application Briteback®, participants subsequently answered the OSTRC Overuse Injury Questionnaire on a weekly basis during a 10 weeks period. A latent profile analysis was used in order to identify different psychological profiles. Results: Athletes were classified into 3 latent profiles regarding their psychological characteristics: profile 1 was labelled a “perfectionistic OI risk profile”, profile 2 a “negative stress OI risk profile” whereas profile 3 was called a “low risk profile for OI”. Indeed, athletes in profile 1 and 2 were found to be significantly more often affected by overuse problems than individuals in profile 3 (71% of the time, χ² (2) = 9.62, Hedges’ g = (0.71), p < .01 and 70% of the time χ² (2) = 9.13, Hedges’ g = (0.68), p < .01 vs 45% of the time), with athletes in profile 1 also experiencing more substantial overuse problems than for profile 3 (35% vs 21% of the time; χ² (2) = 4.12, Hedges’ g = (0.50), p < .05). Conclusions: Our findings support the existence of two “risk profiles” in which athletes are characterized either by elevated perfectionistic concerns or by high negative stress. These findings could be explained by the perseverative and rigid personality of perfectionistic concerns individuals and by the hypothesis of a synergy between psychological and physiological stress for negative stressed athletes. Coaches should pay particular attention to the psychological characteristics of their athletes in order to prevent overuse injury occurrence and worsening, especially those with high perfectionistic concerns and negative life stress. Cognitive behavioral interventions supporting at-risk athletes in reframing their rule-governed behaviors might decrease the risk of overuse problems.

Psychological factors specific to overuse injury pain in physical activity contexts were explored within a social identity theoretical framework. Study 1 involved development of a method for designating overuse injury pain occurrence of hikers (N = 751), along with exploration of relationships between psychological measures, overuse injury pain occurrence, and effort levels. The findings of this cross-sectional, mixed-methods investigation revealed that social identification, social identity content, and mental toughness differentiated hikers who incurred overuse injury pain or selected a higher-effort behaviour from those who did not. From qualitative analysis, several social identity constructs (i.e., group member's presence, in-group status, social creativity, additional social identity content) emerged as contributors to overuse injury occurrence. The focus of Study 2 was a prospective examination of the aforementioned psychological factors in relation to overuse injury severity of hikers (N = 283). Additionally, the Test of Intentions to Reduce Effort (TIRE) was developed to identify individuals with susceptibility to higher overuse injury severity. Results provided evidence of factorial, construct, and predictive validity of TIRE factor scores. TIRE factors and social identity content significantly predicted higher severity of hikers' overuse injury pain. Mental toughness scores moderated the relationship between social identification and overuse injury severity. Study 3 consisted of a qualitative examination of social identity mechanisms of overuse injury pain in a physical activity context, CrossFit®, involving the presence of group leaders, and in which group members view each other. Findings revealed mechanisms pertaining to social identity content, in-group status, and social threats. Overall, the findings support a new means for assessing overuse injury occurrence and susceptibility to higher overuse injury severity, whilst demonstrating the potential applicability of social identity theory to the study of overuse injury. Knowledge gained may ultimately aid development of interventions to reduce overuse injury occurrence and severity of physical activity participants.

Problemområdet som det här examensarbetet undersöker är frekvensen av överbelastningsskador inom ishockey genom en casestudie med ishockeyklubben ’Malmö Redhawks’. Tidigare forskning har visat att det finns en samband mellan asymmetrisk effektutveckling och överbelastningsskador i andra sporter och den nuvarande studien avser att förtydliga dess roll inom ishockey. Syftet med studien är att undersöka om det finns ett samband mellan asymmetrisk effektutveckling vid tävlingsprestation och frekvensen av överbelastningsskador inom ishockey, och föreslå strategier gällande hur man kan minska skadefrekvensen genom preventivt arbete. Forskningsfrågorna som ligger till grund för studien är: ”Hur har asymmetrisk effektutveckling påverkat de överbelastningsskador som inträffat under säsongen?”; och ”Vilka fysiologiska faktorer är relevanta när man utvecklar riktlinjer för skadepreventivt arbetet med överbelastningsskador inom ishockey?”. För att undersöka syftet genomfördes en sammanställning av tillgänglig empiri från säsongens matcher genom kvantitativ metod som sedan analyserades statistiskt i SPSS genom variansanalysen ’ANOVA’. Resultaten visar att det på gruppnivå inte finns en signifikant korrelation mellan effektutveckling (F=2,554, sig.=0,11), asymmetri (F=0,003, sig.=0,96) och överbelastningsskador. Det finns inte heller någon påvisbar trend när man undersöker skadetillfällena på matchnivå, och en mer komplett förklaringsmodell behöver undersökas i framtida forskningsprojekt med större omfattning. Slutsatsen är att det inte går att använda de generella riktlinjerna för att uppskatta atleters risk för överbelastningsskador. Det finns dock underlag i den tidigare forskningen för att anta att individuella riktlinjer har en relevans vid skadepreventivt arbete inom ishockey som en atlets nuläge kan jämföras med för att belysa avvikelser. Mer forskning krävs för att fastställa vilka fysiologiska faktorer som är relevanta för ishockey och hur idrotten förhåller sig till den tidigare forskningen inom området. / There has been speculations in the scientific community that the frequency of overuse injuries in ice hockey can be attributed in part to asymmetrical power development. Research has shown a correlation between more than ten percent asymmetrical power development and increased injury frequency in several other sports. This phenomenon will be examined through a case study with the elite ice hockey team ‘Malmö Redhawks’. The purpose of this study is to examine if there is a significant correlation between the occurrence of asymmetrical differences and the frequency of overuse injuries in ice hockey, and propose strategies for injury prevention. A quantitative method was used to summarize the empirical data from the previous season, which was then analysed through an ‘ANOVA’ test of variance. The results of the study shows that there is no significant correlation between power development (F=2,554, sig.=0,11), asymmetry (F=0,003, sig.=0,96) and injury frequency at the group level. There is no clear tendencies when examining the individual games either. The conclusion is that general guidelines are rough instruments for assessing an athletes risk of overuse injury in ice hockey. There is some basis in the scientific community for assuming that individual guidelines could be effective as injury prevention, but more research is needed to determine its correlations and which physiological variables that are relevant.

Text in English / Regular exercise has significant physical and psychological health benefits yet, paradoxically, may also have harmful effects. The purpose of this study was to investigate the physical and psychological health risks of distance running, a popular participation sport in South Africa. Structural equation modelling was employed to examine the personality and motivational antecedents of running addiction and its influence, in turn, on self-reported overuse injuries and upper respiratory tract infections in 220 athletic club members. The predictors and physical health effects of customary training load were also assessed. It was found that perfectionistic concerns, Type A behaviour pattern, and task goal orientation had a direct, positive impact on running addiction, which predicted higher running injury scores. In contrast, training workload (Volume × Intensity) was inversely related to injury risk. Neither running addiction nor any training load variables influenced infectious illness susceptibility. The findings of this study indicate that maladaptive perfectionism, Type A behaviour, and achievement goal orientation may be risk factors for running addiction, which may, in turn, contribute to increased injury incidence in South African distance runners. Conversely, heavier training loads may be protective against injury occurrences in this population. The results of this research may help to enhance current understanding of the possible health hazards of distance running. This knowledge may have practical implications for the health and well-being of runners of diverse levels of ability and experience. / Psychology / D.Litt. et Phil. (Psychology)