Thermal Strain During Open-Water Swimming Competition in Warm Water Environments

Open-water swim racing in warm water is associated with significant physiological strain. However, existing international policy that governs safe participation during competition relies only on a fixed water temperature threshold for event cancellation and has an unclear biophysical rationale. The current policy does not factor other environmental factors or race distance, nor provide a stratification of risk (low, moderate, high, or extreme) prior to the threshold for cancellation. Therefore, the primary aim of this Perspectives article is to highlight considerations for the development of modernized warm-water competition policies. We highlight current accounts (or lack thereof) of thermal strain, cooling interventions, and performance in warm-water swimming and opportunities for advancement of knowledge. Further work is needed that systematically evaluate real-world thermal strain and performance during warm water competition (alongside reports of environmental conditions), novel preparatory strategies, and in-race cooling strategies. This could ultimately form a basis for future development of modernized policies for athlete cohorts that stratifies risk and mitigation strategies according to important environmental factors and race-specific factors (distance).

Impact of DanceSport on General Fitness from the Perspective of Chinese Athletes

Energy metabolism and motion are the essence of dance. Scientific training of athletes involves theoretical guidance in terms of fitness, talent-based selection, and high-performance practice. However, limited research work is carried out on the physiological strain of DanceSport competitions. Therefore, proper channel needs to be established for aerobic-based exercise on participant’s performance and general fitness. Competition simulation is used to collect personal data from real-time experimentations. Database gathers athlete information based on age, gender, and performance. Furthermore, results are obtained from experiment, record, and simulation in comparison to evaluate athlete performance. Main purpose of this article is to discover the characteristics of DanceSport from the perspectives of energetics in 32 domestic elite. Finally, World DanceSport Federation Judging System 2.1 “WFJS2.1” strategy is utilized for international game challenges.

Effects of Half-Time Cooling Using a Fan with Skin Wetting on Thermal Response During Intermittent Cycling Exercise in the Heat

The present study investigated the effects of half-time (HT) break cooling using a fan and damp sponge on physiological and perceptual responses during the 2nd half of a repeated-sprint exercise in a hot environment. Eight physically active men performed a familiarization trial and two experimental trials of a 2×30-min intermittent cycling exercise protocol with a 15-min HT break in hot conditions (35°C, 50% relative humidity). Two experimental trials were conducted in random order: skin wetting with a fan (FANwet) and no cooling (CON). During the 2nd half, a repeated-sprint cycling exercise was performed: i. e., 5 s of maximal pedaling (body weight×0.075 kp) every minute, separated by 25 s of unloaded pedaling (80 rpm) and 30 s of rest. Rectal temperature, skin temperature (chest, forearm, thigh, and calf), heart rate, physiological strain index, rating of perceived exertion, thermal sensation, and comfort were significantly improved in the FANwet condition (P<0.05). There was no significant difference in the repeated-sprint cycling exercise performance between conditions. The results suggest that skin wetting with a fan during the HT break is a practical and effective cooling strategy for mitigating physiological and perceptual strain during the 2nd half in hot conditions.

Effect of Pre-Exercise Caffeine Intake on Endurance Performance and Core Temperature Regulation During Exercise in the Heat: A Systematic Review with Meta-Analysis

Background: Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat. Objective: Use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat. Design: Systematic review with meta-analysis. Data sources: Four databases and cross-referencing. Data analysis: Weighted mean effect summaries using random-effects models for EP and CT, as well as meta regressions with robust standard errors to explore confounders. Study selection: Placebo-controlled, randomized studies in adults (≥ 18 yrs old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27°C. Results: Respectively 6 and 12 studies examined caffeine's impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of 70 min conducted at 34°C and 47% relative humidity. Caffeine supplementation improved EP by 2.0 +/- 0.7% (95% CI: 0.6 to 3.5%) and increased the rate of change in CT by 0.10 +/- 0.04°C/h (95% CI: 0.03 to 0.16°C/h), compared with the ingestion of a placebo. Conclusion: Caffeine ingestion of 6 mg/kg body mass 1 h before an exercise in the heat provides a worthwhile improvement in EP of 2%, while trivially increasing the rate of change in CT by 0.10°C/h.

A Novel Push-pull Central-lever Mechanism Reduces Peak Forces and Energy-cost Compared to Hand-rim Wheelchair Propulsion During a Controlled Lab-based Experiment

Background: Hand-rim wheelchair propulsion is straining and mechanically inefficient, often leading to upper limb complaints. Previous push-pull lever propulsion mechanisms have shown to perform better or equal in efficiency and physiological strain. Propulsion biomechanics have not been evaluated thus far. A novel push-pull central-lever propulsion mechanism is compared to conventional hand-rim wheelchair propulsion, using both physiological and biomechanical outcomes under low-intensity steady-state conditions on a motor driven treadmill. Methods: In this 5-day (distributed over a maximum of 21 days) between-group experiment, 30 able-bodied novices performed 60 minutes (5x3x4 min) of practice in either the push-pull central lever wheelchair (n=15) or the hand-rim wheelchair (n=15). At the first and final sessions cardiopulmonary strain, propulsion kinematics and force production were determined in both instrumented propulsion mechanisms. Repeated measures ANOVA evaluated between (propulsion mechanism type), within (over practice) and interaction effects. Results: Over practice, both groups significantly improved on all outcome measures. After practice the peak forces during the push and pull phase of lever propulsion were considerably lower compared to those in the handrim push phase (42±10 & 46±10 vs 63±21 N). Concomitantly, energy expenditure was found to be lower as well (263±45 vs 298±59 W), on the other hand gross mechanical efficiency (6.4±1.5 vs 5.9±1.3 %), heart-rate (97±10 vs 98±10 bpm) and perceived exertion (9±2 vs 10±1) were not significantly different between modes.Conclusion: The current study shows the potential benefits of the newly designed push-pull central-lever propulsion mechanism over regular hand rim wheelchair propulsion. The much lower forces and energy expenditure might help to reduce the strain on the upper extremities and thus prevent the development of overuse injury. This proof of concept in a controlled laboratory experiment warrants continued experimental research in wheelchair-users during daily life.

Effects of Hot and Humid Environments on Thermoregulation and Aerobic Endurance Capacity of Laser Sailors

The purpose was to investigate the effects of hot and humid environments on thermoregulation and aerobic endurance capacity of Laser sailors. A randomized cross-over design was applied to this study, in which nine Laser sailors performed the 6 km rowing test (6 km test) in both a warm (ambient temperature: 23±1.4 °C; relative humidity: 60.5±0.7 %; wind speed: 0 km/h; WARM) and hot environment (ambient temperature: 31.8±1.1 °C; relative humidity: 63.5 ± 4.9 %; wind speed: 3.5±0.7 km/h; HOT). The time for completing 6 km test of HOT group was significantly longer than that of WARM group (P=0.0014). Mean power of 3-4 km, 4-5 km and 5-6 km were significant lower in HOT group (P=0.014, P=0.02, P=0.003). Gastrointestinal temperature and skin temperature were significantly higher in HOT group during the 6 km test (P=0.016, P=0.04). Heat storage at 5 min and 15 min of HOT group were significantly higher than that of WARM group (P=0.0036; P=0.0018). Heart rate and physiological strain index of HOT group were significantly higher than that of WARM group during the 6 km test (P=0.01, P<0.01). The increase magnitude of skin temperature was more obvious than the changes of core temperature during exercise in hot and humid environments. The higher skin temperature narrowed the core to skin temperature gradient and skin to ambient temperature gradient, which may result in greater accumulation of heat storage. The greater heat storage led to the lower muscle power output, which contributed to the reduction of the heat production.

Need for Speed: The Importance of Physiological Strain Rates in Determining Myocardial Stiffness

The heart is viscoelastic, meaning its compliance is inversely proportional to the speed at which it stretches. During diastolic filling, the left ventricle rapidly expands at rates where viscoelastic forces impact ventricular compliance. In heart disease, myocardial viscoelasticity is often increased and can directly impede diastolic filling to reduce cardiac output. Thus, treatments that reduce myocardial viscoelasticity may provide benefit in heart failure, particularly for patients with diastolic heart failure. Yet, many experimental techniques either cannot or do not characterize myocardial viscoelasticity, and our understanding of the molecular regulators of viscoelasticity and its impact on cardiac performance is lacking. Much of this may stem from a reliance on techniques that either do not interrogate viscoelasticity (i.e., use non-physiological rates of strain) or techniques that compromise elements that contribute to viscoelasticity (i.e., skinned or permeabilized muscle preparations that compromise cytoskeletal integrity). Clinically, cardiac viscoelastic characterization is challenging, requiring the addition of strain-rate modulation during invasive hemodynamics. Despite these challenges, data continues to emerge demonstrating a meaningful contribution of viscoelasticity to cardiac physiology and pathology, and thus innovative approaches to characterize viscoelasticity stand to illuminate fundamental properties of myocardial mechanics and facilitate the development of novel therapeutic strategies.