Cross-sectional study on exercise-related skin complaints among sports students at two German universities.

Sports activities can lead to exercise-related skin complaints. These include different symptoms (e.g. infections, mechanical injuries, contact dermatitis). Previous studies mostly focused only on skin infections and injuries in competitive athletes. The purpose of this study was to determine the frequency and characteristics of exercise-related skin complaints among sports students and to what extent these complaints influence physical fitness. We performed a self-administered online survey among 259 actively exercising sports students from two German universities. Descriptive analyses were conducted. The most common complaints were blistering (57.3%), dryness (56.7%), redness (44.7%), and chafing (34.0%). Hands and feet (78.0% each) were most frequently affected. Participants whose skin was particularly stressed (47.5%) had higher training duration (7.6 h/week, 95%-CI 6.8-8.3 h) than those without complaints (5.1 h/week, 95%-CI 5.5-6.7 h, p = 0.003). The students reported reduced intensity (34.7%) and frequency (22.7%) of training due to their skin complaints. A reduction in performance was reported by 32.0% of the students. Actively exercising sports students considered an intact skin as essential for their physical fitness. Reported impairments of the skin led to a reduced intensity and frequency of training. To enhance the awareness of exercise-related skin complaints, further research is necessary.

Tendon compliance and preload must be considered when determining the in vivo force-velocity relationship from the torque-angular velocity relation.

In vivo, the force-velocity relation (F-v-r) is typically derived from the torque-angular velocity relation (T-ω-r), which is subject to two factors that may influence resulting measurements: tendon compliance and preload prior to contraction. The in vivo plantar flexors' T-ω-r was determined during preloaded maximum voluntary shortening contractions at 0-200°/s. Additionally, we used a two factor block simulation study design to independently analyze the effects of preload and tendon compliance on the resulting T-ω-r. Therefore, we replicated the in vivo experiment using a Hill-type muscle model of the gastrocnemius medialis. The simulation results matched a key pattern observed in our recorded in vivo experimental data: during preloaded contractions, torque output of the muscle was increased when compared with non-preloaded contractions from literature. This effect increased with increasing contraction velocity and can be explained by a rapidly recoiling tendon, allowing the contractile element to contract more slowly, thus developing higher forces compared with non-preloaded contractions. Our simulation results also indicate that a more compliant tendon results in increased ankle joint torques. The simulation and the experimental data clearly show that the deduction of the in vivo F-v-r from the T-ω-r is compromised due to the two factors preloading and tendon compliance.

Validation of a new inertial measurement unit system based on different dynamic movements for future in-field applications.

Using inertial measurement units (IMUs) in monitoring and analysing sport movements has become popular in sports research since it avoids the laboratory limitation. However, the accuracy of modern IMU-systems (hardware combined with software) needs to be validated using gold-standard systems as baseline. In this study, we investigated the feasibility of the aktos-t IMU-system for in-field biomechanical research by comparing its outputs in various tasks (repetitive movements, gait and jumping) undertaken by 14 participants, with those of an optoelectronic system. The results showed that the accuracy of aktos-t varies according to the task performed. The accuracy of pelvis, hip and knee joints ranged between acceptable (root mean squared error (RMSE) < 5°) and tolerable (RMSE < 10°) in gait, while the upper limb joints showed inaccuracy (RMSE > 10°) and imprecision (coefficient of repeatability > 10°) during the repetitive movement test. Jump impact appeared not to influence the IMU outcomes (p > 0.05). The main sources of error could be related to the IMU-alignment during the reference T-pose. Finally, the study provides researchers the means for evaluating the accuracy of aktos-t (hardware, software and biomechanical model) as sufficiently precise for its application in their in-field investigations.

Residual force enhancement in humans: Is there a true non-responder?

When an active muscle is stretched and kept isometrically active, the resulting force is enhanced compared to a purely isometric reference contraction at the same muscle length and activity; a generally accepted muscle property called residual force enhancement (rFE). Interestingly, studies on voluntary muscle action regularly identify a significant number of participants not showing rFE. Therefore, the aim was to unmask possible confounders for this non-responsive behavior. Ten participants performed maximum voluntary isometric plantarflexion contractions with and without preceding stretch. Contractions were accompanied by the assessment of voluntary activation using the twitch-interpolation technique. The same test protocol was repeated four additional times with a least on day rest in-between. Additionally, at the first and fifth sessions, a submaximal tetanic muscle-stimulation condition was added. At both muscle-stimulation sessions mean rFE higher 10% (p < 0.028) was found. In contrast, during voluntary muscle action, individual participants showed inconsistent rFE across sessions and only one session (#3) had significant rFE (5%; p = 0.023) in group means. As all participants clearly had rFE in electrical stimulation conditions, structural deficits cannot explain the missing rFE in voluntary muscle action. However, we also did not find variability in voluntary activation levels or muscle activity as the confounding characteristics of "non-responders."

Effect of legroom proportions and individual factors for sitting with crossed legs: implications on the interior design of automated driving vehicles.

Sitting with crossed legs is a commonly adopted sitting posture in everyday situations. Yet, little is known about suitable design criteria to facilitate such a position inside a vehicle. This study is aimed at determining how much space is necessary for crossing the legs while considering legroom restrictions, anthropometric measures, and individual flexibility. More specifically, 3 D-kinematics of an ankle-on-knee leg-crossing task and the easiness to move ratings of 30 participants were assessed with restrictions of the legroom (2 heights × 3 distances) as well as without restrictions. Functional regression models revealed adaptations to a legroom restriction in the execution of movement, which occurred mainly in the knee joint and increased with more restricted legroom proportions. Therefore, the present study suggests a distance of 120% of the buttock-knee length between the dashboard and the occupant, as it requires only moderate adaptations and does not affect the perceived easiness of move. Practitioner Summary: This research investigated how much space is needed to cross the legs while sitting in a vehicle, finding that the movement execution is affected by legroom proportions, as well as individual anthropometry and flexibility. The study further presents the use of predicted motion traces to determine spatial requirements of movements. Abbreviations: BKL: buttock-knee length; H-point: hip point.

Automated driving: A biomechanical approach for sleeping positions.

Occupants of autonomous vehicle have frequently indicated the desire to sleep or rest while driving, yet little has been known regarding the suitable design criteria for a biomechanically reasoned in-vehicle sleeping position. This study was aimed at evaluating the biomechanical quality of different backrest and seat pan angle combinations, and at predicting the most favourable sleeping positions based on vehicle restriction. More specifically, the interface pressure distribution and subjective suitability rating of 23 subjects was assessed in a total of nine (3 × 3) combinations of seat pan (20°, 30°, 40°) and backrest (145°, 155°, 165°) angles. Biomechanical quality was evaluated with an interface pressure score (IPS) based on sensitivity weighted pressures and the total contact area. Two-way repeated measures ANOVA revealed that IPS significantly improves with increasing seat pan angle whereas backrest angles of 155° or 165° lead to significant better IPS compared to flatter ones (145°). The overall highest IPS was observed for a 40°-seat pan angle in combination with a 155°-backrest angle. Subjective suitability rating revealed that people prefer a combination of 165° backrest angle with a seat pan of 20°; however, eight of nine combinations can be considered as suitable for sleeping. Therefore, the combination of a 40°-seat pan angle and 155° backrest is recommended by the present study for an in-vehicle sleeping position due to the increased biomechanical quality.

Association of thigh and paraspinal muscle composition in young adults using chemical shift encoding-based water-fat MRI.

BACKGROUND: Paraspinal and thigh muscles comprise the major muscle groups of the body. We investigated the composition of the psoas, erector spinae, quadriceps femoris and hamstring muscle groups and their association to each other using chemical shift encoding-based water-fat magnetic resonance imaging (MRI) in adult volunteers. Our aim was to elucidate fat distribution patterns within these muscle groups. METHODS: Thirty volunteers [15 males, age: 30.5±4.9 years, body mass index (BMI): 27.6±2.8 kg/m2 and 15 females, age: 29.9±7.0 years, BMI: 25.8±1.4 kg/m2] were recruited for this study. A six-echo 3D spoiled gradient echo sequence was used for chemical shift encoding-based water-fat separation at the lumbar spine and bilateral thigh. Proton density fat fraction (PDFF), cross-sectional area (CSA) and contractile mass index (CMI) of the psoas, erector spinae, quadriceps femoris and hamstring muscle groups were determined bilaterally and averaged over both sides. RESULTS: CSA and CMI values calculated for the erector spinae, psoas, quadriceps and hamstring muscle groups showed significant differences between men and women (P<0.05). With regard to PDFF measurement only the erector spinae showed significant differences between men and women (9.5%±2.4% vs. 11.7%±2.8%, P=0.015). The CMI of the psoas muscle as well as the erector spinae muscle showed significant correlations with the quadriceps muscle (r=0.691, P<0.0001 and r=0.761, P<0.0001) and the hamstring group (r=0.588, P=0.001 and r=0.603, P<0.0001). CONCLUSIONS: CMI values of the erector spinae and psoas muscles were associated with those of the quadriceps femoris and hamstring musculature. These findings suggest a concordant spatial fat accumulation within the analyzed muscles in young adults and warrants further investigations in ageing and diseased muscle.

Correction to: Associations of thigh muscle fat infiltration with isometric strength measurements based on chemical shift encoding-based water-fat magnetic resonance imaging.

After publication of this article [1], it is noticed it contained some errors in the Methods section.

The Relationship between General Upper-Body Strength and Pole Force Measurements, and Their Predictive Power Regarding Double Poling Sprint Performance.

In recent years, there is an increasing importance of double poling (DP) performance regarding the outcome in classic cross-country skiing (XCS) races. So far, different approaches were used to predict DP performance but there is a lack of knowledge how general strength parameters are related to DP performance parameters gathered from in field-test situations. Therefore, the aim of this study was to determine the relationship between general strength measurements of different upper-body segments and pole force measurements during a DP sprint exercise. In addition, multiple linear regressions were calculated to determine the predictive power of theses variables regarding DP sprint performance, represented as maximum velocity. Thirteen none-elite cross-country skiers performed two 60 m DP sprints at maximal speed on a tartan track using roller skis. In addition, maximum isometric and concentric strength tests were performed on a motor-driven dynamometer with four major upper-body segments (trunk flexion / extension, shoulder / elbow extension). Especially the mean pole force and the strength test parameters correlated significantly (r ≥ 0.615) in all except one comparison. However, regression analyses revealed that neither pole force parameters (R² = 0.495) nor isometric (R² = 0.456) or dynamic (R² = 0.596) strength test parameters could predict the DP performance significantly. This study showed that standardized isokinetic strength tests could be used to estimate pole force capabilities of XCS athletes. However, pole-force and strength test parameters failed to predict significantly maximal velocity during a DP sprint exercise, which might be attributed to the non-elite subject group.

Associations of thigh muscle fat infiltration with isometric strength measurements based on chemical shift encoding-based water-fat magnetic resonance imaging.

BACKGROUND: Assessment of the thigh muscle fat composition using magnetic resonance imaging (MRI) can provide surrogate markers in subjects suffering from various musculoskeletal disorders including knee osteoarthritis or neuromuscular diseases. However, little is known about the relationship with muscle strength. Therefore, we investigated the associations of thigh muscle fat with isometric strength measurements. METHODS: Twenty healthy subjects (10 females; median age 27 years, range 22-41 years) underwent chemical shift encoding-based water-fat MRI, followed by bilateral extraction of the proton density fat fraction (PDFF) and calculation of relative cross-sectional area (relCSA) of quadriceps and ischiocrural muscles. Relative maximum voluntary isometric contraction (relMVIC) in knee extension and flexion was measured with a rotational dynamometer. Correlations between PDFF, relCSA, and relMVIC were evaluated, and multivariate regression was applied to identify significant predictors of muscle strength. RESULTS: Significant correlations between the PDFF and relMVIC were observed for quadriceps and ischiocrural muscles bilaterally (p = 0.001 to 0.049). PDFF, but not relCSA, was a statistically significant (p = 0.001 to 0.049) predictor of relMVIC in multivariate regression models, except for left-sided relMVIC in extension. In this case, PDFF (p = 0.005) and relCSA (p = 0.015) of quadriceps muscles significantly contributed to the statistical model with R2adj = 0.548. CONCLUSION: Chemical shift encoding-based water-fat MRI could detect changes in muscle composition by quantifying muscular fat that correlates well with both extensor and flexor relMVIC of the thigh. Our results help to initiate early, individualised treatments to maintain or improve muscle function in subjects who do not or not yet show pathological fatty muscle infiltration.

Ski Position during the Flight and Landing Preparation Phases in Ski Jumping Detected with Inertial Sensors.

Ski movement plays an important role during landing preparation, as well as in the whole ski jumping performance. Good landing preparation timing and correct ski position increase the jump length and reduce the impact forces. Inertial motion units (IMUs) placed on the skis could constitute a promising technology for analyzing the ski movements during training. During regular summer trainings, 10 elite athletes (17 ± 1 years) performed jumps while wearing IMUs and wireless force insoles. This set-up enabled the analysis of a possible correlation between ski movements and ground reaction force (GRF) during landing impact. The results showed that the pitch during the landing preparation is the most influential movement on the impact kinetic variables since it is related to the angle of attack, which affects the aerodynamics. The ski position at 0.16 s before landing did not influence the kinetics because the athlete was too close to the ground. During the impact, the roll angle did not correlate with GRF. Moreover, each athlete showed a different movement pattern during the flight phase. Concluding, the combination of IMUs and force insoles is a promising set-up to analyze ski jumping performance thanks to the fast placement, low weight, and high reliability.

Ground Reaction Forces and Kinematics of Ski Jump Landing Using Wearable Sensors.

In the past, technological issues limited research focused on ski jump landing. Today, thanks to the development of wearable sensors, it is possible to analyze the biomechanics of athletes without interfering with their movements. The aims of this study were twofold. Firstly, the quantification of the kinetic magnitude during landing is performed using wireless force insoles while 22 athletes jumped during summer training on the hill. In the second part, the insoles were combined with inertial motion units (IMUs) to determine the possible correlation between kinematics and kinetics during landing. The maximal normal ground reaction force (GRFmax) ranged between 1.1 and 5.3 body weight per foot independently when landing using the telemark or parallel leg technique. The GRFmax and impulse were correlated with flying time (p < 0.001). The hip flexions/extensions and the knee and hip rotations of the telemark front leg correlated with GRFmax (r = 0.689, p = 0.040; r = -0.670, p = 0.048; r = 0.820, p = 0.007; respectively). The force insoles and their combination with IMUs resulted in promising setups to analyze landing biomechanics and to provide in-field feedback to the athletes, being quick to place and light, without limiting movement.

Paraspinal Muscle DTI Metrics Predict Muscle Strength.

BACKGROUND: The paraspinal muscles play an important role in the onset and progression of lower back pain. It would be of clinical interest to identify imaging biomarkers of the paraspinal musculature that are related to muscle function and strength. Diffusion tensor imaging (DTI) enables the microstructural examination of muscle tissue and its pathological changes. PURPOSE: To investigate associations of DTI parameters of the lumbar paraspinal muscles with isometric strength measurements in healthy volunteers. STUDY TYPE: Prospective. SUBJECTS: Twenty-one healthy subjects (12 male, 9 female; age = 30.1 ± 5.6 years; body mass index [BMI] = 27.5 ± 2.6 kg/m2 ) were recruited. FIELD STRENGTH/SEQUENCE: 3 T/single-shot echo planar imaging (ss-EPI) DTI in 24 directions; six-echo 3D spoiled gradient echo sequence for chemical shift encoding-based water-fat separation. ASSESSMENT: Paraspinal muscles at the lumbar spine were examined. Erector spinae muscles were segmented bilaterally; cross-sectional area (CSA), proton density fat fraction (PDFF), and DTI parameters were calculated. Muscle flexion and extension maximum isometric torque values [Nm] at the back were measured with an isokinetic dynamometer and the ratio of extension to flexion strength (E/F) calculated. STATISTICAL TESTS: Pearson correlation coefficients; multivariate regression models. RESULTS: Significant positive correlations were found between the ratio of extension to flexion (E/F) strength and mean diffusivity (MD) (P = 0.019), RD (P = 0.02) and the eigenvalues (λ1: P = 0.026, λ2: P = 0.033, λ3: P = 0.014). In multivariate regression models λ3 of the erector spinae muscle λ3 and gender remained statistically significant predictors of E/F (R2adj = 0.42, P = 0.003). DATA CONCLUSION: DTI allowed the identification of muscle microstructure differences related to back muscle function that were not reflected by CSA and PDFF. DTI may potentially track subtle changes of back muscle tissue composition. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:816-823.

Association of paraspinal muscle water-fat MRI-based measurements with isometric strength measurements.

OBJECTIVES: Chemical shift encoding-based water-fat MRI derived proton density fat fraction (PDFF) of the paraspinal muscles has been emerging as a surrogate marker in subjects with sarcopenia, lower back pain, injuries and neuromuscular disorders. The present study investigates the performance of paraspinal muscle PDFF and cross-sectional area (CSA) in predicting isometric muscle strength. METHODS: Twenty-six healthy subjects (57.7% women; age: 30 ± 6 years) underwent 3T axial MRI of the lumbar spine using a six-echo 3D spoiled gradient echo sequence for chemical shift encoding-based water-fat separation. Erector spinae and psoas muscles were segmented bilaterally from L2 level to L5 level to determine CSA and PDFF. Muscle flexion and extension maximum isometric torque values [Nm] at the back were measured with an isokinetic dynamometer. RESULTS: Significant correlations between CSA and muscle strength measurements were observed for erector spinae muscle CSA (r = 0.40; p = 0.044) and psoas muscle CSA (r = 0.61; p = 0.001) with relative flexion strength. Erector spinae muscle PDFF correlated significantly with relative muscle strength (extension: r = -0.51; p = 0.008; flexion: r = -0.54; p = 0.005). Erector spinae muscle PDFF, but not CSA, remained a statistically significant (p < 0.05) predictor of relative extensor strength in multivariate regression models (R2adj = 0.34; p = 0.002). CONCLUSIONS: PDFF measurements improved the prediction of paraspinal muscle strength beyond CSA. Therefore, chemical shift encoding-based water-fat MRI may be used to detect subtle changes in the paraspinal muscle composition. KEY POINTS: • We investigated the association of paraspinal muscle fat fraction based on chemical shift encoding-based water-fat MRI with isometric strength measurements in healthy subjects. • Erector spinae muscle PDFF correlated significantly with relative muscle strength. • PDFF measurements improved prediction of paraspinal muscle strength beyond CSA.

Combined three-dimensional gait and plantar pressure analyses detecting significant functional deficits in children with juvenile idiopathic arthritis.

BACKGROUND: Children suffering from juvenile idiopathic arthritis (JIA), a heterogeneous group of chronic inflammatory joint diseases, adapt to individual gait patterns to avoid loading of inflamed, swollen and painful joints. As the interpretability of previous studies is limited, this study aims to assess the functional capacity, loads and plantar pressure distribution in the gait of a homogeneous JIA group. RESEARCH QUESTION: Does a symmetrical lower limb joint involvement influence the gait dynamics in JIA patients, and how are the results of three-dimensional gait analysis (3DGA) and pedobarography related? METHODS: Fifty JIA patients with symmetrical hip, knee and ankle joint arthritis and 27 healthy controls performed 3DGA and pedobarography at self-selected walking speeds. Kinematics and kinetics of lower limb joints were retrospectively compared in range of motion and in time-normalized waveforms. Plantar load was evaluated by measuring peak pressure, pressure-time integral and maximum force of the whole foot and ten selected foot regions. 1D-SPM analysis, parametric and non-parametric statistical significance tests and correlation coefficients were used for statistical analysis. RESULTS: JIA patients had a significantly slower walking speed with an anteriorly tilted pelvis and a reduced extension motion of all joints of the lower limb. The horizontal ground reaction forces and generated hip and ankle power during propulsion phase were small. Patients experienced reduced loading at toe regions, which correlated with limited ankle plantarflexion motion in the push-off phase. The total peak pressure was significantly increased and loads at lateral midfoot and metatarsal regions were higher in patients. SIGNIFICANCE: Symmetrical lower limb arthritis is linked to crouch-like gait and restricted gait dynamics with increased total peak pressure. The results confirm earlier results of 3DGA and provide new insights regarding waveform analysis and plantar loading in JIA patients. The used methods help to design individualized functional treatment of JIA patients.

Accuracy and precision of loadsol® insole force-sensors for the quantification of ground reaction force-based biomechanical running parameters.

Force plates represent the "gold standard" in measuring running kinetics to predict performance or to identify the sources of running-related injuries. As these measurements are generally limited to laboratory analyses, wireless high-quality sensors for measuring in the field are needed. This work analysed the accuracy and precision of a new wireless insole forcesensor for quantifying running-related kinetic parameters. Vertical ground reaction force (GRF) was simultaneously measured with pit-mounted force plates (1 kHz) and loadsol® sensors (100 Hz) under unshod forefoot and rearfoot running-step conditions. GRF data collections were repeated four times, each separated by 30 min treadmill running, to test influence of extended use. A repeated-measures ANOVA was used to identify differences between measurement devices. Additionally, mean bias and Bland-Altman limits of agreement (LoA) were calculated. We found a significant difference (p < .05) in ground contact time, peak force, and force rate, while there was no difference in parameters impulse, time to peak, and negative force rate. There was no influence of time point of measurement. The mean bias of ground contact time, impulse, peak force, and time to peak ranged between 0.6% and 3.4%, demonstrating high accuracy of loadsol® devices for these parameters. For these same parameters, the LoA analysis showed that 95% of all measurement differences between insole and force plate measurements were less than 12%, demonstrating high precision of the sensors. However, highly dynamic behaviour of GRF, such as force rate, is not yet sufficiently resolved by the insole devices, which is likely explained by the low sampling rate.

Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions.

Purpose: The aim of this study was to examine physiological responses to two different simulated firefighting exercises: a firefighting exercise with flashovers, smoke, poor visibility and extreme temperatures (300°) in a burning container and a standard firefighting exercise in temperate conditions. Furthermore, a second purpose of the study was to find out if the contribution of strength and endurance capacities to firefighting performance changes when the demands of the firefighting exercise change. Methods: Sixteen professional firefighters performed a maximum treadmill test, strength testing, a standard simulated firefighting exercise (SFE) without heat and flashovers and a firefighting exercise with a simulation of the flashover phenomenon in a burning container (FOT). The treadmill testing was used to determine peak oxygen uptake (VO2peak), ventilatory threshold (VT1) and respiratory compensation point (RCP). Three intensity zones were identified according to heart rate (HR) values corresponding to VT1 and RCP: zone 1-HR below VT1, zone 2-HR between VT1 and RCP, zone 3-HR above RCP. Firefighting performance was determined by a simple time-strain-air depletion model (TSA) taking the sum of z-transformed parameters of time to finish the exercise, strain in terms of mean heart rate, and air depletion from the breathing apparatus. Correlations were then established between TSA based firefighting performance parameters and fitness variables representing strength and endurance. Results: HR was significantly lower during SFE (79.9 ± 6.9%HRmax) compared to FOT (85.4 ± 5.2%HRmax). During SFE subjects spent 24.6 ± 30.2% of time in zone 1, 65.8 ± 28.1% in zone 2 and 9.7 ± 16.6% in zone 3. During FOT subjects spent 16.3 ± 12.8% in zone 1, 50.4 ± 13.2% in zone 2 and 33.3 ± 16.6% in zone 3. Out of all correlations, relative VO2peak showed the highest relation to mean HR during SFE (-0.593) as well as FOT (-0.693). Conclusions: Endurance in terms of VO2peak is an important prerequisite for both firefighting exercises. However, for standard simulated firefighting exercises it is important to work below VT1. For firefighting exercises in extreme temperatures with smoke, poor visibility and unexpected flashovers a high fitness level is required in order to keep the time spent above RCP as short as possible.

Relationships between strength and endurance parameters and air depletion rates in professional firefighters.

The aim of this study was to quantify the physical demands of a simulated firefighting circuit and to establish the relationship between job performance and endurance and strength fitness measurements. On four separate days 41 professional firefighters (39 ± 9 yr, 179.6 ± 2.3 cm, 84.4 ± 9.2 kg, BMI 26.1 ± 2.8 kg/m2) performed treadmill testing, fitness testing (strength, balance and flexibility) and a simulated firefighting exercise. The firefighting exercise included ladder climbing (20 m), treadmill walking (200 m), pulling a wire rope hoist (15 times) and crawling an orientation section (50 m). Firefighting performance during the simulated exercise was evaluated by a simple time-strain-air depletion model (TSA) taking the sum of z-transformed parameters of time to finish the exercise, strain in terms of mean heart rate, and air depletion from the breathing apparatus. Multiple regression analysis based on the TSA-model served for the identification of the physiological determinants most relevant for professional firefighting. Three main factors with great influence on firefighting performance were identified (70.1% of total explained variance): VO2peak, the time firefighter exercised below their individual ventilatory threshold and mean breathing frequency. Based on the identified main factors influencing firefighting performance we recommend a periodic preventive health screening for incumbents to monitor peak VO2 and individual ventilatory threshold.

Excellent balance skills despite active and inactive juvenile idiopathic arthritis - unexpected results of a cross-sectional study.

OBJECTIVES: Postural control (PC) is fundamental for human movements. Different factors, such as injuries or diseases, can adversely affect PC. The purpose of this study was to evaluate PC in juvenile idiopathic arthritis (JIA) patients with different disease activity levels in comparison to healthy peers. METHODS: JIA patients with active and inactive lower limb joints (n=36 each group) were examined. Both groups have been on medication and have had physiotherapy for at least 5 years. For comparison, an age- and gender-matched healthy control group (CG; n=36) participated. PC was measured bipedal on a balance-board (S3-Check, TST, Großhoeflein), with an instable tilting between left and right. The parameters of interest were the best results of Stability Index (STI), Sensorimotor Index (SMI) and Symmetry Index (SYI) out of 4 test trials as well as JIA disease-related variables. Data were analysed with descriptive statistics, comparison of averages, linear regression and correlations (p<0.05). RESULTS: The three groups showed no differences in anthropometric characteristics and SYI (p>0.05). In both JIA groups, STI and SMI were lower than indices of CG (p<0.05), indicating better stability and motor control. Balance indices did not differ between active and inactive JIA patients (p>0.05). CONCLUSIONS: JIA patients showed better PC than CG. Possible explanations are an increased body-awareness due to long-term physiotherapy and daily coordination training due to compensatory movements. The positive results highlight the success of individual, interdisciplinary treatment in JIA and can be used to promote recommendations for safe sport participation.

Association of Quadriceps Muscle Fat With Isometric Strength Measurements in Healthy Males Using Chemical Shift Encoding-Based Water-Fat Magnetic Resonance Imaging.

Magnetic resonance-based assessment of quadriceps muscle fat has been proposed as surrogate marker in sarcopenia, osteoarthritis, and neuromuscular disorders. We presently investigated the association of quadriceps muscle fat with isometric strength measurements in healthy males using chemical shift encoding-based water-fat magnetic resonance imaging. Intermuscular adipose tissue fraction and intramuscular proton density fat fraction correlated significantly (P < 0.05) with isometric strength (up to r = -0.83 and -0.87, respectively). Reproducibility of intermuscular adipose tissue fraction and intramuscular proton density fat fraction was 1.5% and 5.7%, respectively.