Thyroid hormones are widely studied for their involvement in energy metabolism and thermogenesis. However, their role on muscle fibers and the structure and organelles of this tissue has yet to be reviewed. This mini-review aims to show the involvement of thyroid hormone signalings in the function of muscle fibers. Serum levels of thyroid hormones depend on the hypothalamic–pituitary–thyroid axis, which, in turn, acts depending on changes in homeostasis and the environment. In skeletal muscle, thyroxine (T4) and triiodothyronine (T3) participate in contractile function, metabolism, myogenesis, and regeneration. T3 regulates skeletal muscle gene expression through the interaction with the specific nuclear isoforms receptors for thyroid hormones: α (THRA) and β (THRB). In addition, T3 activates phosphoinositide 3-kinase (PI3K), which ultimately increases the transcription of hypoxia-inducible factor 1-alpha (HIF-1α). They can bind to a membrane integrin, Alpha-5 beta-3 integrin (αvβ3), and activate the PI3K and mitogen-activated protein kinase (MAPK) signal transduction pathways. T3 and T4 also increase Fibroblast Growth Factor 2 (FGF2) gene transcription. These initially nongenomic, nonclassical actions serve as additional interfaces for transcriptional regulation by thyroid hormones. In addition, di-iodine (T2), the thyroid hormone metabolite, has been shown to play a role in this process.
To examine the micro-pacing (within-lap) strategies during biathlon skiing with and without the biathlon rifle.
Twenty biathletes (7 women, 13 men) performed two cross-country skiing time-trials on a ≈2300 m course, once with and once without the biathlon rifle. During time-trials, biathletes wore a sensor that recorded position, distance and skiing-speed. A trajectory correction and statistical parametric mapping procedure determined the course positions (clusters) where instantaneous skiing-speed was significantly related to time-trial performance. The time differences between the fastest and slowest skier in these clusters were calculated.
The fastest biathletes skied with greater instantaneous speeds in specific clusters, which included both uphill and downhill sections. The clusters represented time gains for the fastest skier over the slowest skier of between 16.1 and 25.8 s for the women and between 18.9 and 21.9 s for the men. The largest time gains between the fastest and slowest biathletes were observed in a downhill section that was preceded by a 180° turn, where time gains were between 2.9 and 4.1 s in clusters of between just 12 to 62 m. In biathlon skiing with-rifle, there were more clusters that were not present during without-rifle. When skiing with-rifle, there were additional clusters in the uphill sections that represented time gains of 5.2 s and 2.3 s for the women and men, respectively.
Statistical parametric mapping can be used in biathlon to provide pacing and performance feedback to athletes and coaches.
The mechanisms that underpin exercise-induced muscle damage and recovery are believed to be mediated, in part, by immune cells recruited to the site of injury. The aim of this study was to characterise the effects of muscle damage from bench-stepping on circulating cytokine and immune cell populations post-exercise and during recovery.
Ten untrained, healthy male volunteers completed 30 min of bench-stepping exercise to induce muscle damage to the eccentrically exercised leg. Muscle function, muscle pain and soreness were measured before, immediately after and 24, 48 and 72 h after exercise. Plasma creatine kinase, cartilage oligomeric matrix protein, cytokines and circulating immune cell phenotyping were also measured at these timepoints.
Significant decreases occurred in eccentric, isometric and concentric (P=0.018, 0.047 and 0.003, respectively) muscle function in eccentrically, but not concentrically, exercised quadriceps post-exercise. Plasma monocyte chemoattractant protein (MCP)-1 concentrations significantly increased immediately after exercise (69.0±5.8 to 89.5±10.0 pg/mL), then declined to below pre-exercise concentrations (58.8±6.3 pg/mL) 72 h after exercise. These changes corresponded with the significant decrease of circulating CD45+CD16− CD14+monocytes (5.8%±1.5% to 1.9%±0.5%; Pre-exercise vs. 48 h) and increase of CD45+CD3+CD56− T-cells (60.5%±2.2% to 66.1%±2.1%; Pre-exercise vs. 72 h) during recovery.
Bench-stepping induced muscle damage to the quadriceps, which mediated systemic changes in MCP-1, monocytes and T-cells immediately post-exercise and during recovery. Further research is needed to clarify how modulations in immune subpopulations facilitate muscle recovery and adaptation following muscle damage.
(i) To investigate the correlation between sleep complaints and history of musculoskeletal injuries in adolescent track athletes; (ii) to characterize the prevalence of sleep complaints; and (iii) to investigate the correlation between sleep complaints and age.
This was a cross-sectional study with 19 male and 11 female adolescent track athletes (mean age 16.5 years). The participants answered the sleep complaints questionnaire and retrospective musculoskeletal injuries data were collected by the physical therapy department, considering the previous 6 months. Spearman’s correlation coefficient was used to verify the correlation between variables. The significance level was set at 0.05.
Correlations between sleep complaints and history of injuries were found for the following variables: frequency of insufficient sleep and previous re-injuries (rs = 0.687, P=0.028), somnambulism and severity of previous injuries (rs = 0.577, P=0.006), frequency of somnambulism and previous injuries (rs = 1.000, P=0.010), frequency of kicking legs and previous injuries (rs = 0.736, P=0.010), frequency of breathing complaints and previous re-injuries (rs = 0.889, P=0.044). The most prevalent sleep complaint was moving a lot during sleep (60%). The mean total sleep time was 7 h and 37 min. Age positively correlated with frequency of insufficient sleep (rs = 0.555, P=0.032), frequency of somnambulism (rs = 1.000, P=0.010), and negatively with breathing complaints (rs = − 0.382, P=0.037).
Some complaints may be associated with a history of occurrence, re-occurrence, and severity of injuries in adolescent athletes and they tend to sleep less than the recommended total sleep time. Longitudinal studies should be carried out to confirm whether these sleep complaints are risk factors for sports injuries.
Resistance training volume is one of the most important variables to induce muscular adaptations. However, high-volume training can be exhausting and cause prior knowledge of training volume in a session to negatively affect the total number of repetitions performed, thus reducing the overall training effect. This study was designed to determine the influence of prior knowledge of the number of sets to be performed on total training volume.
Eleven men with previous resistance training experience (≥12 months) performed six sets of bench press under three different conditions: a control trial (CL) where participants were informed that they would perform six sets and complete six sets; a deception trial (DC) where participants were informed they would perform three sets but had an additional three sets added after completing the first three sets, and an unknown trial (UN) in which participants received no information about how many sets would be performed but actually completed six sets. Conditions were randomized among all participants. All sets were performed to momentary concentric failure using 70% of one-repetition maximum.
Results showed no significant difference among the three conditions for the total number of repetitions (CL=62.4±8.5, DC=61.1±13.2, UN=62.2±2.8, P=0 .94).
These results suggest that prior knowledge of the number of sets to be performed in a training session has no significant effect on total training volume achieved in resistance-trained men.
To identify predictors of soccer injuries’ severity among professional soccer teams.
At the end of soccer season 2019, 152 professional soccer players (premier league and division-I teams) participated in this study. Players and teams’ medical staff provided demographics information, previous soccer injuries, current soccer injury profile, playing surface when they were injured. Further, they indicated the medical treatment and time-loss from soccer participation since injury (mild: 4–7, moderate: 8–28, severe:>28 days). Player’s sex, previous soccer injuries, playing factors (team division and playing surfaces), and mechanism of injury were entered into multinomial regression model, with severe injury was reference group.
Sixty-eight out of 152 players (44.73%) sustained soccer injuries [mild: 30.8% (n=21), moderate: 33.8% (n=23), severe: 35.4% (n=24)]. Player’s sex (Men-vs.-Women: OR: 0.2, R2:9.9%), mechanism of injury (Contact-vs.-Non-contact: OR: 3.12, R2: 6.9%), playing surfaces (Synthetic-vs.-Natural grass: OR: 1.91, R2: 13.8%), and having previous injury (Yes-vs.-No: OR: 0.13, R2: 11.9%) were significant predictors of severity of soccer injuries (moderate vs. sever injuries).
Players’ sex, mechanism of injury, playing surfaces, and having previous soccer injury predicted the soccer injuries’ severity. Men players and those with previous soccer injury were less likely to have moderate verses sever injuries compared to women and players without previous injury. Players with contact injuries and who were injured on synthetic surface were more likely to have moderate versus severe injuries compared to players with non-contact injury and who were injured on natural grass. These factors may be taking in consideration to implement personalized rehabilitation program, reduce soccer injuries’ severity, and to develop tailored injury preventive strategies.
Researchers have predicted body fat percentage (BF%), as indicated by dual energy X-ray absorptiometry (DXA), from skinfold thicknesses in North American and European athletes, but not athletes from other regions. We sought to estimate an equation to predict BF% in elite Asian athletes from their skinfold thickness and girth measurements, with DXA as a reference method.
We collected data from two samples of athletes on Singaporean national teams. With the first sample (n=95), we developed an equation to predict BF%, and then tested the equation in the second sample (n=21). We used backward stepwise regression and the Akaike information criteria (AIC) to determine the final equation.
Triceps, subscapular, front thigh, and (natural log of) abdominal skinfold thicknesses, waist circumference, and female sex were positively associated with BF% (P<0.05).
Our equation for predicting BF% from anthropometric measurements is the first one based on Asian athletes. This equation could help practitioners estimate BF% of Asian athletes if DXA is unavailable.
Post-activation potentiation has been considered an effective intervention in relation to improving sports performance in several modalities. Specifically, indoor soccer studies have shown significant gains in muscle strength and physical capabilities. The aim of the present study was to evaluate the effects of two neuromuscular training, pre- and post-8 weeks, with and without induction of post-activation potentiation. All participants were submitted to the counter movement jump protocols, maximum voluntary isometric contraction, three maximum repetitions of knee extensors, 20 m maximum horizontal speed, and Illinois agility test. Significant acute effect was found only at the height of the experimental group, pre- and post-training (0.40±0.04 m and 0.45±0.05 m; P=0.035). Significant chronic effects were observed only at the height (Control: 0.39±0.05 m and 0.45±0.05 m; P=0.002) and at maximum strength in three maximum repetitions (Experimental: 112±17 kg and 130±17 kg; P=0.032), pre- and post-training. Therefore, the 8-week neuromuscular training, with post-activation potentiation induction, results in acute and chronic improvements, and can be adopted as an effective alternative method for the improvement in sports performance.
Shoulder strength evaluation is a recommended procedure in musculoskeletal rehabilitation.
To examine hand-held sphygmomanometer (HHS) and hand-held dynamometer (HHD) intra- and inter-rater reliability during isometric shoulder external and internal rotation strength testing in prone rotation position in asymptomatic participants, and to compare these two testing modalities.
Reliability study.
A total of 20 asymptomatic participants (27.7±7.4 years; 77.1±10.1 kg) attended a strength assessment consisting of HHS and HHD tests. Reliability was assessed using the intra-class correlation coefficient (ICC) with 95% confidence intervals (CI), coefficient of variation (CV) with 95%CI, and standard error of measurement (SEM). Pearson correlation and linear regression analysis were used to compare HHS and HHD testing modalities.
“Good” to “excellent” intra (ICC range=0.896 to 0.979) and inter-rater reliability scores (ICC range=0.850 to 0.978) were displayed during both HHS and HHD tests during internal and external rotation strength assessments. Linear relationships between HHS and HHD measures were found, with coefficients of determination (R2) ranging between 0.60 and 0.79.
HHS and HHD resulted to be reliable strength assessment modalities for clinical practice. These assessment modes can be equally valid in assessing intra and inter-limb asymmetries in isometric shoulder rotation strength. The affordability and availability of HHS in ordinary clinical settings can facilitate its implementation in musculoskeletal practice.
Research findings are typically reported at the group level but applied to individuals. However, an emerging issue in sports science concerns nonergodicity—whereby group-level data cannot be generalized to individuals. The purpose of this study was to determine if the relationship between daily carbohydrate intake and perceived recovery status displays nonergodicity.
Fifty-five endurance athletes recorded daily measures of self-selected dietary intake, training, sleep, and subjective wellbeing for 12 weeks. We constructed linear models to measure the influence of daily carbohydrate intake on perceived recovery status while accounting for training load, sleep duration, sleep quality, and muscle soreness. Using linear model coefficients for carbohydrate intake we tested whether the distributions (mean and SD) differed at the group and individual levels (indicating nonergodicity). Additionally, a decision tree was created to explore factors that could provide an indication of an individual athlete’s relationship between carbohydrate intake and perceived recovery status.
Mean values were not different between group- and individual-level analyses, but SDs at the individual level were ~2.4 times larger than at the group level, indicating nonergodicity. Model coefficients for carbohydrate intake were negative for three participants, positive for four participants, and non-significant for 37 participants. The κ value measuring accuracy of the decision tree was 0.52, indicating moderate prediction accuracy.
For most individuals, carbohydrate intake did not influence recovery status. However, the influence of dietary carbohydrate intake on daily recovery differs at the group and individual level. Therefore, practical recommendations should be based on individual-level analysis.
Exercise has well-documented effects on immune function with both positive and negative sequelae dependent on intensity, volume, and duration. The immunosuppressive effects of exercise are mediated, in part, by the complex interaction of cytokines, catecholamines, and nutrition. Caffeine has been reported to modulate immune function; however, the interaction with brief exhaustive exercise is not well characterized. It was hypothesized that caffeine would upregulate the cytokine response to intense exercise. Seven male students volunteered to participate in a randomized, double-blinded crossover study where they ingested either caffeine (6 mg/kg) or a maltodextrin placebo (6 mg/kg) 1 h prior to a cycling exercise. The exercise protocol started at 100 W and the intensity was increased by 50 W every two minutes until exhaustion. Serum samples were collected pre-, post-, and 1-h post-exercise and analyzed for IL-4, IL-10, and TGF-β1. Caffeine ingestion increased time to exhaustion (P=0.005; Effect Size [ES]=1.33), IL-4 (P=0.004; ES=2.34), IL-10 (P=0.047; ES=0.41±0.57), and TGF-β1 (P=0.013; ES=0.76). The accentuated response of the cytokines may have important ramifications due to their potent anti-inflammatory and immunoregulatory properties. Specifically, the 6 mg/kg caffeine dose not only improved exercise performance but the cytokine data is indicative of an upregulated inflammatory response and an enhancement of the anti-inflammatory benefits of exercise.