BACKGROUND: Static stretching (SS) is widely used in warm-up as it is generally believed to increase mobility and reduce the risk of injury; however, SS has been shown to induce transient negative effects on subsequent muscle performance. Interestingly, recent studies have shown that sport specific exercise could restore SS-induced negative effects on certain sports, especially of explosive muscular performance. Whether sport specific exercise could restore SS-induced negative effects on isokinetic muscle performance remains unclear.

METHODS: The present study conducted two different warm-ups: 2-component warm-up and 3-component warm-up on 15 university students. Both protocols contained low intensity aerobic exercise and sport specific exercise, whereas the 3-component warm-up also contained SS which has been previously proven to induce negative effects on subsequent muscle performance. After the warm-ups, the subjects performed an isokinetic test on a Biodex. To make the sport specific exercise mimic the subsequent test, both included concentric isokinetic knee extension. During the tests, muscle performance of peak torque, mean power, and total work was recorded. Comparison of the measurements on each parameter between the two warm-ups was performed using paired t test.

RESULTS: The comparisons did not reveal any significant difference in the measurement of any parameter between the two different warm-up protocols, and calculation of Cohen's revealed small effect sizes on all of the three variables.

CONCLUSIONS: On basis of the present results and that the SS could induce transient negative effects on subsequent muscle performance, we concluded that the negative effects of the SS on the variables were restored by the isokinetic contractions.

The present work investigated serum vitamin D (25(OH)D) status in relation to bone and muscle qualities and functions in 19 female soccer players (13–16 years) resident at northern latitude with very low sun exposure (∼32–36 h/month) during winter season (late January to early March). Serum 25(OH)D, parathyroid hormone and bone turnover markers osteocalcin (OC) and beta carboxy-terminal collagen cross-links (β-Ctx), as well as body composition and muscle performance were examined. Hormones were tested using routine laboratory methods. Fat mass, lean mass, and bone mineral density in whole body, as well as femur and lumbar spine were evaluated with dual-energy X-ray absorptiometry. Muscle performance was assessed through isokinetic knee extension and flexion, countermovement jump, and sprint running. 25(OH)D was low (50.5 ± 12.8 nmol l−1), whereas the values of bone turnover markers were markedly high (OC: 59.4 ± 18.6 μg l−1; β-Ctx: 1075 ± 408 ng l−1). All bone and muscle measurements were normal or above normal. 25(OH) D was not significantly correlated with most of the parameters of bone and muscle quality or function, except the knee extension time to peak torque (r = −0.50, p = .03). In conclusion, the level of vitamin D is markedly low in adolescent female soccer players during the winter in Sweden. However, vitamin D levels did not significantly correlate with measures of bone and muscle except a moderate correlation in time to peak torque in the knee extensors. The practical implication of low vitamin D levels in young growing female athletes remains unclear.

The study aimed to evaluate the validity and reliability of a new automated pulmonary gas analysis system - Exercise Physiology System (EPS). The Oxycon Pro, a well-established automated pulmonary gas analysis system was used as a reference system. Six well-trained cyclists were recruited and performed two identical submaximal exercises on a cycle ergometer over one week interval. During the exercises, pulmonary gas exchange: ventilation (VE), oxygen consumption (VO2), elimination of carbon dioxide (VCO2), and ratio between carbon dioxide and oxygen (RER) was measured using both systems in randomized order. The exercise was composed of three incremental work-loads (Watt) of low, medium, and high load corresponding to 40%, 60%, and 80% of individual maximal work-load. Each work-load was performed twice so that pulmonary gas exchange was analyzed twice on each work-load using both systems. EPS validity was assessed by comparing the measurements from the two systems. For measurements presenting agreement between the systems, Bland-Altman plot analysis was performed to identify outlier. Reliability was evaluated by comparisons of measurements from repeated tests through each system, and by calculations of intra-class correlation coefficient (ICC) and standard error of measurement (SEM). Validity evaluations revealed that the majority of the measurements were in disagreements between the systems and most of them appeared at lower work-loads. The results indicated that at lower work-loads, EPS had lower validity than Oxycon Pro. At higher work-loads, ESP had high and comparable validity with Oxycon Pro. Reliability assessments revealed that agreements between repeated tests appeared in almost all measurements through both systems. Excellent agreements (very high ICC) in measurements between repeated tests were observed in VE, VO2, and VCO2 from both systems, and very small measurement errors (SEM), close to zero were observed in VO2, VCO2, and RER. The results suggested that the two systems had high and comparable reliability in measurement of pulmonary gas exchange.

The effects of long-term (over several years) anabolic androgen steroids (AAS) administration on human skeletal muscle are still unclear. In this study, seventeen strength training athletes were recruited and individually interviewed regarding self-administration of banned substances. Ten subjects admitted having taken AAS or AAS derivatives for the past 5 to 15 years (Doped) and the dosage and type of banned substances were recorded. The remaining seven subjects testified to having never used any banned substances (Clean). For all subjects, maximal muscle strength and body composition were tested, and biopsies from the vastus lateralis muscle were obtained. Using histochemistry and immunohistochemistry (IHC), muscle biopsies were evaluated for morphology including fiber type composition, fiber size, capillary variables and myonuclei. Compared with the Clean athletes, the Doped athletes had significantly higher lean leg mass, capillary per fibre and myonuclei per fiber. In contrast, the Doped athletes had significantly lower absolute value in maximal squat force and relative values in maximal squat force (relative to lean body mass, to lean leg mass and to muscle fiber area). Using multivariate statistics, an orthogonal projection of latent structure discriminant analysis (OPLS-DA) model was established, in which the maximal squat force relative to muscle mass and the maximal squat force relative to fiber area, together with capillary density and nuclei density were the most important variables for separating Doped from the Clean athletes (regression  =  0.93 and prediction  =  0.92, p<0.0001). In Doped athletes, AAS dose-dependent increases were observed in lean body mass, muscle fiber area, capillary density and myonuclei density. In conclusion, long term AAS supplementation led to increases in lean leg mass, muscle fiber size and a parallel improvement in muscle strength, and all were dose-dependent. Administration of AAS may induce sustained morphological changes in human skeletal muscle, leading to physical performance enhancement.

BACKGROUND: We have previously observed, in studies on an experimental overuse model, that the tachykinin system may be involved in the processes of muscle inflammation (myositis) and other muscle tissue alterations. To further evaluate the significance of tachykinins in these processes, we have used inhibitors of neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), substances which are known to terminate the activity of various endogenously produced substances, including tachykinins.

METHODS: Injections of inhibitors of NEP and ACE, as well as the tachykinin substance P (SP), were given locally outside the tendon of the triceps surae muscle of rabbits subjected to marked overuse of this muscle. A control group was given NaCl injections. Evaluations were made at 1 week, a timepoint of overuse when only mild inflammation and limited changes in the muscle structure are noted in animals not treated with inhibitors. Both the soleus and gastrocnemius muscles were examined morphologically and with immunohistochemistry and enzyme immunoassay (EIA).

RESULTS: A pronounced inflammation (myositis) and changes in the muscle fiber morphology, including muscle fiber necrosis, occurred in the overused muscles of animals given NEP and ACE inhibitors. The morphological changes were clearly more prominent than for animals subjected to overuse and NaCl injections (NaCl group). A marked SP-like expression, as well as a marked expression of the neurokinin-1 receptor (NK-1R) was found in the affected muscle tissue in response to injections of NEP and ACE inhibitors. The concentration of SP in the muscles was also higher than that for the NaCl group.

CONCLUSIONS: The observations show that the local injections of NEP and ACE inhibitors led to marked SP-like and NK-1R immunoreactions, increased SP concentrations, and an amplification of the morphological changes in the tissue. The injections of the inhibitors thus led to a more marked myositis process and an upregulation of the SP system. Endogenously produced substances, out of which the tachykinins conform to one substance family, may play a role in mediating effects in the tissue in a muscle that is subjected to pronounced overuse.

Unilateral strength training can cause cross-transfer strength effects to the homologous contralateral muscles. However, the impact of the cross-over effects on the muscle tissue is unclear. To test the hypothesis that unilateral muscle overuse causes bilateral alterations in muscle fiber composition and vascular supply, we have used an experimental rabbit model with unilateral unloaded overstrain exercise via electrical muscle stimulation (E/EMS). The soleus (SOL) and gastrocnemius (GA) muscles of both exercised (E) and contralateral non-exercised (NE) legs (n = 24) were morphologically analyzed after 1w, 3w and 6w of EMS. Non-exercised rabbits served as controls (n = 6). After unilateral intervention the muscles of both E and NE legs showed myositis and structural and molecular tissue changes that to various degrees mirrored each other. The fiber area was bilaterally smaller than in controls after 3w of E/EMS in both SOL (E 4420 and NE 4333 µm2 vs. 5183 µm2, p<0.05) and GA (E 3572 and NE 2983 µm2 vs. 4697 µm2, p<0.02) muscles. After 6w of E/EMS, the percentage of slow MyHCI fibers was lower than in controls in the NE legs of SOL (88.1% vs. 98.1%, p<0.009), while the percentage of fast MyHCIIa fibers was higher in the NE legs of GA (25.7% vs. 15.8%, p = 0.02). The number of capillaries around fibers in the E and NE legs was lower (SOL 13% and 15%, respectively, GA 25% and 23%, respectively, p<0.05) than in controls. The overall alterations were more marked in the fast GA muscle than in the slow SOL muscle, which on the other hand showed more histopathological muscle changes. We conclude that unilateral repetitive unloaded overuse exercise via EMS causes myositis and muscle changes in fiber type proportions, fiber area and fiber capillarization not only in the exercised leg, but also in the homologous muscles in the non-exercised leg.

Background: Tachykinins can have pro-inflammatory as well as healing effects during tissue reorganization and inflammation. Recent studies report an up-regulation in the expression of the substance P (SP)-preferred receptor, the neurokinin-1 receptor, in marked muscle inflammation (myositis). There is, however, only very little information on the expression patterns and levels of tachykinins in this situation.

Methods: The tachykinin system was analyzed using a rabbit experimental model of muscle overuse, whereby unilateral muscle exercise in combination with electrical stimulation led to muscle derangement and myositis in the triceps surae muscle (experimental length 1--6 weeks). Evaluations were made for both parts of the muscle (soleus and gastrocnemius muscles) in experimental and non-experimental (contralateral) sides. Morphologic evaluation, immunohistochemistry, in situ hybridization and enzyme immunoassay (EIA) analyses were applied.

Results: Myositis and muscle derangement occurred focally not only in the experimental side but also in the non-experimental side. In the inflammatory areas (focal myositis areas), there were frequent nerve fibers showing tachykinin-like immunoreactivity and which were parts of nerve fascicles and which were freely dispersed in the tissue. Cells in the inflammatory infiltrates showed tachykinin-like immunoreactivity and tachykinin mRNA expression. Specific immunoreactivity and mRNA expression were noted in blood vessel walls of both sides, especially in focally affected areas. With increasing experimental length, we observed an increase in the degree of immunoreactivity in the vessel walls. The EIA analyses showed that the concentration of tachykinin in the tissue on both sides increased in a time-dependent manner. There was a statistical correlation in the concentration of tachykinin and the level of tachykinin immunoreactivity in the blood vessel walls between experimental and non-experimental sides.

Conclusions: The observations show an up-regulation of the tachykinin system bilaterally during muscle derangement/myositis in response to pronounced unilateral muscle overuse. This up-regulation occurred in inflammatory areas and was related not only to increased tachykinin innervation but also to tachykinin expression in blood vessel walls and inflammatory cells. Importantly, the tachykinin system appears to be an important factor not only ipsilaterally but also contralaterally in these processes.

Nowadays professional soccer player trading between clubs/leagues is very common. Soccer players could be employed in foreign clubs/leagues, but when international competitive events come, the elite players are recruited to compose a national team. One can expect that the higher ranking of a national team, the more players are employed by the top soccer leagues. However, the relationship between the two issues has never been studied early. In the study, seven national soccer teams were selected from a list of the world top 35 soccer teams of year 2010[created by the Federation of International Football Association (FIFA)]. The 7 teams are Spain, England, Argentina, Germany, USA, Ghana and Sweden, across the full range of the list, thus, representing different levels of the world. On basis of the position of the 7 teams in the world ranking, an order ranking for the 7 teams was created. To identify player distribution of the 7 teams in different quality/level of soccer leagues, a league ranking including the top 25 soccer leagues in the world created by the International Federation of Football History and Statistics (IFFHS) was used. For each of the 7 teams, its player distribution in different soccer leagues was classified. On basis of the league ranking and the number of player(s) of each team in different leagues, calculated team point was calculated for each team. According to the amount of the calculated point, a calculated team ranking was obtained. Correlation analysis was performed between the two rankings: the order ranking and the calculated team ranking. The results showed a high and positive correlation between the two variables. We concluded that the more players are employed in higher ranking leagues the higher world ranking of a national team.

Muscle power is of great importance in most sports, and its development is one of the most fundamental physiological adaptations for improving physical performance. In order to optimize competition performance, athletes usually decrease training load before competition, the so-called tapering, to allow physiological and psychological recovery from accumulated training stress. Tapering could be conducted through changes in training volume, intensity and/or frequency, but training volume seems to be most effective in optimizing muscular power. There are two main types of tapering: progressive tapering and one-step tapering. Currently, there is no general conclusion on tapering duration. The physiological mechanisms regarding tapering effects on neuromuscular system are largely unknown. Generally, it is believed that sustained maximal muscular power after tapering is obtained through maintaining adaptations in muscle fiber size, fiber type and neural adaptations whereas increased maximal muscular power after tapering is assumed mainly through both physiological and psychological recovery. We believe that increased maximal muscular power after tapering may also rely on higher neural drive and increased muscle fiber cross sectional area (CSA), especially in type IIA muscle fibers. Complete rest is a special form of tapering and it usually only leads to sustained maximal power. This effect is believed to be associated with decreased muscle CSA and a transformation of muscle fibers from type IIA to type IIX.

Muscle injury and inflammation (myositis) in a rabbit model of an unilateral muscle overuse were examined. It is unknown if the tachykinin system has a functional role in this situation. In this study, therefore, the neurokinin-1 receptor (NK-1R) expression patterns were evaluated. White blood cells, nerve fascicles, fine nerve fibers, and blood vessel walls in myositis areas showed NK-1R immunoreaction. NK-1R mRNA reactions were observable for white blood cells and blood vessel walls of these areas. NK-1R immunoreaction and NK-1R mRNA reactions were also seen for muscle fibers showing degenerative and regenerative features. There were almost no NK-1R immunoreactions in normal muscle tissue. Interestingly, marked NK-1R expressions were seen for myositis areas of both the experimental side and the contralateral nonexperimental side. EIA analyses showed that the concentration of substance P in the muscle tissue was clearly increased bilaterally at the experimental end stage, as compared to the situation for normal muscle tissue. These observations show that the tachykinin system is very much involved in the processes that occur in muscle injury/myositis. The effects can be related to proinflammatory effects and/or tissue repair. The fact that there are also marked NK-1R expressions contralaterally indicate that the tachykinin system has crossover effects.