This study detected no significant variation in muscle strength and muscle endurance during the menstrual cycle. In contrast to other studies showing variations in strength and endurance during the menstrual cycle, the present study was hormonally validated and was repeated in 2 consecutive menstrual cycles. However, it is unknown whether these data in moderately active university students would be relevant to the highly trained woman athlete.

ObjectiveSkeletal muscle weakness is a prominent clinical feature in patients with rheumatoid arthritis (RA), but the underlying mechanism(s) is unknown. Here we investigate the mechanisms behind arthritis-induced skeletal muscle weakness with special focus on the role of nitrosative stress on intracellular Ca2+ handling and specific force production.MethodsNitric oxide synthase (NOS) expression, degree of nitrosative stress and composition of the major intracellular Ca2+ release channel (ryanodine receptor 1, RyR1) complex were measured in muscle. Changes in cytosolic free Ca2+ concentration ([Ca2+]i) and force production were assessed in single-muscle fibres and isolated myofibrils using atomic force cantilevers.ResultsThe total neuronal NOS (nNOS) levels were increased in muscles both from collagen-induced arthritis (CIA) mice and patients with RA. The nNOS associated with RyR1 was increased and accompanied by increased [Ca2+]i during contractions of muscles from CIA mice. A marker of peroxynitrite-derived nitrosative stress (3-nitrotyrosine, 3-NT) was increased on the RyR1 complex and on actin of muscles from CIA mice. Despite increased [Ca2+]i, individual CIA muscle fibres were weaker than in healthy controls, that is, force per cross-sectional area was decreased. Furthermore, force and kinetics were impaired in CIA myofibrils, hence actin and myosin showed decreased ability to interact, which could be a result of increased 3-NT content on actin.ConclusionsArthritis-induced muscle weakness is linked to nitrosative modifications of the RyR1 protein complex and actin, which are driven by increased nNOS associated with RyR1 and progressively increasing Ca2+ activation.

We found no support for any significant influence of OC use on muscle strength and hop performance in healthy moderately active women.

Many risk factors for injury are presented in the literature, few of those are however consistent and the majority is associated with adult and not adolescent elite athletes. The aim was to identify risk factors for injury in adolescent elite athletes, by applying a biopsychosocial approach. A total of 496 adolescent elite athletes (age range 15-19), participating in 16 different sports, were monitored repeatedly over 52 weeks using a valid questionnaire about injuries, training exposure, sleep, stress, nutrition, and competence-based self-esteem. Univariate and multiple Cox regression analyses were used to calculate hazard ratios (HR) for risk factors for first reported injury. The main finding was that an increase in training load, training intensity, and at the same time decreasing the sleep volume resulted in a higher risk for injury compared to no change in these variables (HR 2.25, 95% CI, 1.46-3.45, P<.01), which was the strongest risk factor identified. In addition, an increase by one score of competence-based self-esteem increased the hazard for injury with 1.02 (HR 95% CI, 1.00-1.04, P=.01). Based on the multiple Cox regression analysis, an athlete having the identified risk factors (Risk Index, competence-based self-esteem), with an average competence-based self-esteem score, had more than a threefold increased risk for injury (HR 3.35), compared to an athlete with a low competence-based self-esteem and no change in sleep or training volume. Our findings confirm injury occurrence as a result of multiple risk factors interacting in complex ways.

Little is known about health variables and if these variables could increase the risk of injuries among adolescent elite athletes. The primary aim was to present overall data on self-perceived stress, nutrition intake, self-esteem, and sleep, as well as gender and age differences, on two occasions among adolescent elite athletes. A secondary aim was to study these health variables as potential risk factors on injury incidence. A questionnaire was e-mailed to 340 adolescent elite athletes on two occasions during a single school year: autumn semester and spring semester. The results show that during autumn semester, the recommended intake of fruits, vegetables, and fish was not met for 20%, 39%, and 43% of the adolescent elite athletes, respectively. The recommended amount of sleep during weekdays was not obtained by 19%. Multiple logistic regression showed that athletes sleeping more than 8 h of sleep during weekdays reduced the odds of injury with 61% (OR, 0.39; 95% CI, 0.16-0.99) and athletes reaching the recommended nutrition intake reduced the odds with 64% (OR, 0.36; 95% CI, 0.14-0.91). Our findings suggest that nutrition intake and sleep volume are of importance in understanding injury incidence.