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A trend in large yellow croaker (Larimichthys crocea) aquaculture is to establish production sites suitable for extreme weather conditions. However, continuous and strong currents can harm fish welfare. To determine a suitable site location, the swimming ability of large yellow croakers must be assessed. This study aims to provide novel insights into the physiological characteristics of large yellow croaker swimming and a reference for fishing and cage site selection. Currently, research on large yellow croakers has focused on behavior analysis. Herein, we investigate the effects of swimming on large yellow croakers' metabolites by examining the preferred speed of the group and the sustained swimming ability of single-tailed fish. We evaluated factors that influence the large yellow croaker's swimming fatigue by quantifying the metabolite contents and constructing a sustained swimming model. The results showed that large yellow croaker populations tend to grow in low-velocity environments, similar to their traditional habitat. The samples were taken at different swimming times at a flow velocity of 0.35 m/s. According to the results of the metabolite content analysis, blood glucose levels are closely associated with the swimming ability in large yellow croakers. The content of liver glycogen, which regulates blood glucose concentration, decreased in a certain linear relationship. The sustained swimming model of the large yellow croaker was constructed according to the changes in liver glycogen content. Based on our findings, we recommend the following: (1) for large yellow croakers with a size of approximately 13.5 cm (approximately 1 year old), the water velocity inside the cage should not exceed 2.6 BL/s; (2) the concentration of liver glycogen limits the sustained swimming ability of the large yellow croaker, providing a reference for studying the swimming ability of other fish. [ABSTRACT FROM AUTHOR]

Aquaculture has greater potential for seafood production than wild capture fisheries. To meet the growing demand for seafood, China's marine aquaculture industry has begun building deep-water cages in the open sea. However, under these conditions, fish encounter strong currents and waves, and ensuring their healthy growth is key to the farming process. To address these issues, it is necessary to study the sustained swimming abilities of cultured fish species. Blackhead seabream (Acanthopagrus schlegelii) and red drum (Sciaenops ocellatus) are traditional economic fish species in China; however, their sustained swimming ability under a constant current has been underexplored. Therefore, we examined the endurance swimming ability of three size classes of blackhead seabream and red drum at 20 °C. The fish were then subjected to swimming tests of 0, 30, 60, 90, 120, and 150 min at a constant swimming speed of 0.55 m/s (0.80 m/s), 0.65 m/s (0.90 m/s), and 0.70 m/s (0.98 m/s). The fish were then dissected to obtain muscle, blood, and liver samples; sample metabolite concentrations were measured at six time points, each of which guaranteed five sets of valid data. The results indicated that red drum has a significantly stronger swimming ability, and can be cultured in waters with a short-term flow rate not exceeding 0.75 m/s or 3.5 BL/s. Further, blackhead seabream can be cultured in waters with a flow velocity lower than 0.55 m/s or 2.5 BL/s. The species-related metabolic differences were mainly reflected in the hepatic glycogen and blood glucose concentrations, and those in swimming ability caused by body length were mainly reflected by the hepatic glycogen concentration. The hepatic glycogen concentration had the most significant effect on fish with body lengths >28 cm (P < 0.05). Overall, the experimental results indicated that the liver plays a major role in the physiological level of fish swimming fatigue, providing a direction for further research. • Red drum swimming ability is significantly stronger than Blackhead seabream. • The swimming ability of blackhead seabream and red drum is positively correlated with size. • The extent of the effect of hepatic glycogen concentration on swimming ability is positively correlated with body length. • Blackhead seabream is more adaptable to the changes in metabolite concentration than red drum. [ABSTRACT FROM AUTHOR]

Glycogen particles are situated in key areas of the muscle cell in the vicinity of the main energy‐consumption sites and may be utilised heterogeneously dependent on the nature of the metabolic demands. The present study aimed to investigate the time course of fibre type‐specific utilisation of muscle glycogen in three distinct subcellular fractions (intermyofibrillar, IMF; intramyofibrillar, Intra; and subsarcolemmal, SS) during repeated high‐intensity intermittent exercise. Eighteen moderately to well‐trained male participants performed three periods of 10 × 45 s cycling at ∼105% watt max (EX1–EX3) coupled with 5 × 6 s maximal sprints at baseline and after each period. Muscle biopsies were sampled at baseline and after EX1 and EX3. A higher glycogen breakdown rate in type 2 compared to type 1 fibres was found during EX1 for the Intra (−72 vs. −45%) and IMF (−59 vs. −35%) glycogen fractions (P < 0.001) but with no differences for SS glycogen (−52 vs. −40%). In contrast, no fibre type differences were observed during EX2–EX3, where the utilisation of Intra and IMF glycogen in type 2 fibres was reduced, resulting in depletion of all three subcellular fractions to very low levels post‐exercise within both fibre types. Importantly, large heterogeneity in single‐fibre glycogen utilisation was present with an early depletion of especially Intra glycogen in individual type 2 fibres. In conclusion, there is a clear fibre type‐ and localisation‐specific glycogen utilisation during high‐intensity intermittent exercise, which varies with time course of exercise and is characterised by exacerbated pool‐specific glycogen depletion at the single‐fibre level. Key points: Muscle glycogen is the major fuel during high‐intensity exercise and is stored in distinct subcellular areas of the muscle cell in close vicinity to the main energy consumption sites.In the present study quantitative electron microscopy imaging was used to investigate the utilisation pattern of three distinct subcellular muscle glycogen fractions during repeated high‐intensity intermittent exercise.It is shown that the utilisation differs dependent on fibre type, subcellular localisation and time course of exercise and with large single‐fibre heterogeneity.These findings expand on our understanding of subcellular muscle glycogen metabolism during exercise and may help us explain how reductions in muscle glycogen can attenuate muscle function even at only moderately lowered whole‐muscle glycogen concentrations. [ABSTRACT FROM AUTHOR]

Previous work has shown that poorer mitochondrial function is associated with age-related perceived fatigability. However, whether glucose oxidation and anaerobic metabolism are intermediate factors underlying this association remains unclear. We examined the total cross-sectional association between mitochondrial function and perceived fatigability in 554 adults aged 22-99 years. Mitochondrial function was assessed by skeletal muscle oxidative capacity (kPCr) using 31P magnetic resonance spectroscopy. Perceived fatigability was measured by rating of perceived exertion after a 5-minute (0.67 m/s) treadmill walk. The intermediate role of glucose oxidation (measured by the rate of change of respiratory exchange ratio [RER change rate] during the 5-minute treadmill walk) and anaerobic metabolism (measured by ventilatory threshold [VeT] during a maximal treadmill test) was evaluated by examining their cross-sectional associations with kPCr and perceived exertion. For each 0.01/s lower kPCr, perceived fatigability was 0.47 points higher (p = .002). A 0.01/s lower kPCr was also associated with 8.3 L/min lower VeT (p < .001). Lower VeT was associated with higher fatigability at lower levels of kPCr but not at higher kPCr levels (β for interaction = 0.017, p = .002). kPCr and RER change rate were not significantly associated (p = .341), but a 0.01/min higher RER change rate was associated with 0.12-point higher fatigability (p = .001). Poorer mitochondrial function potentially contributes to higher perceived fatigability through higher glucose oxidation and higher anaerobic metabolism. Future studies to further explore the longitudinal mechanisms between these metabolic changes and fatigability are warranted. [ABSTRACT FROM AUTHOR]

Nowadays, compression garments (CGs) are widely used in winter racing sports, such as speed skating, short-track speed skating, alpine skiing, and cross-country skiing. However, the effect of wearing CGs on athletic performance in these specific sports is still not fully examined. Thus, the aim of this narrative review is to summarize the research and application of CGs in winter racing sports and to discuss how the CGs help athletes improve their performance in an integrative manner (i.e., physiology, aerodynamics, and biomechanics). A total of 18 experimental studies dedicated to CGs in winter racing sports were identified from the peer-review scientific literature. The main findings are as follows. (1) Currently, CG studies have mainly focused on drag reduction, metabolism, muscle function, strength performance, and fatigue recovery. (2) The results of most studies conducted in wind tunnels showed that, for cylindrical structures similar to the human body, clothing with rough surfaces can reduce air drag. Notably, the effect of CGs on drag reduction in real competition has not been fully explored in the literature. (3) Compression can reduce muscle vibrations at high impact and help athletes control the center of pressure movement, a function that is important for alpine skiing. Future studies are needed to improve current understanding of the effects of compression clothing microstructure on drag reduction and their stretching in different parts of the body. Furthermore, the design of experimental protocol must be consistent with those during the competition, thus providing a full discussion on energy metabolism, fatigue, and recovery affected by CGs. [ABSTRACT FROM AUTHOR]

We tested the hypotheses that the parameters of the power-duration relationship, estimated as the end-test power (EP) and work done above EP (WEP) during a 3-min all-out exercise test (3MT), would be reduced progressively after 40 min, 80 min, and 2 h of heavy-intensity cycling and that carbohydrate (CHO) ingestion would attenuate the reduction in EP and WEP. Sixteen participants completed a 3MT without prior exercise (control), immediately after 40 min, 80 min, and 2 h of heavyintensity exercise while consuming a placebo beverage, and also after 2 h of heavy-intensity exercise while consuming a CHO supplement (60 g/h CHO). There was no difference in EP measured without prior exercise (260 ± 37 W) compared with EP after 40 min (268 ± 39 W) or 80 min (260 ± 40 W) of heavy-intensity exercise; however, after 2 h EP was 9% lower compared with control (236 ± 47 W; P < 0.05). There was no difference in WEP measured without prior exercise (17.9 ± 3.3 kJ) compared with after 40 min of heavy-intensity exercise (16.1 ± 3.3 kJ), but WEP was lower (P < 0.05) than control after 80 min (14.7 ± 2.9 kJ) and 2 h (13.8 ± 2.7 kJ). Compared with placebo, CHO ingestion negated the reduction of EP following 2 h of heavy-intensity exercise (254 ± 49 W) but had no effect on WEP (13.5 ± 3.4 kJ). These results reveal a different time course for the deterioration of EP and WEP during prolonged endurance exercise and indicate that EP is sensitive to CHO availability. NEW & NOTEWORTHY The parameters of the power-duration relationship [critical power (CP) and the curvature constant (W=)] have typically been considered to be static. Here we report the time course for reductions in CP and W=, as estimated with the 3-min all-out cycle test, during 2 h of heavy-intensity exercise. We also show that carbohydrate ingestion during exercise preserves CP, but not W=, without altering muscle glycogen depletion. These results provide new mechanistic and practical insight into the power-duration curve and its relationship to exercise-related fatigue development. [ABSTRACT FROM AUTHOR]

It is not clear how the parameters of the power-duration relationship [critical power (CP) and W=] are influenced by the performance of prolonged endurance exercise. We used severe-intensity prediction trials (conventional protocol) and the 3-min all-out test (3MT) to measure CP and W= following 2 h of heavy-intensity cycling exercise and took muscle biopsies to investigate possible relationships to changes in muscle glycogen concentration ([glycogen]). Fourteen participants completed a rested 3MT to establish end-test power (Control-EP) and work done above EP (Control-WEP). Subsequently, on separate days, immediately following 2 h of heavy-intensity exercise, participants completed a 3MT to establish Fatigued-EP and Fatigued-WEP and three severe-intensity prediction trials to the limit of tolerance (Tlim) to establish Fatigued-CP and Fatigued-W=. A muscle biopsy was collected immediately before and after one of the 2-h exercise bouts. Fatigued-CP (256 ± 41 W) and Fatigued-EP (256 ± 52 W), and Fatigued-W= (15.3 ± 5.0 kJ) and Fatigued-WEP (14.6 ± 5.3 kJ), were not different (P > 0.05) but were ~11% and ~20% lower than Control-EP (287 ± 46 W) and Control-WEP (18.7 ± 4.7 kJ), respectively (P < 0.05). The change in muscle [glycogen] was not significantly correlated with the changes in either EP (r = 0.19) or WEP (r = 0.07). The power-duration relationship is adversely impacted by prolonged endurance exercise. The 3MT provides valid estimates of CP and W= following 2 h of heavy-intensity exercise, but the changes in these parameters are not primarily determined by changes in muscle [glycogen]. [ABSTRACT FROM AUTHOR]

The goal of this randomized, double-blind, cross-over study was to assess the acute effects of caffeine ingestion on muscular strength and power, muscular endurance, rate of perceived exertion (RPE), and pain perception (PP) in resistance-trained men. Seventeen volunteers (mean ± SD: age = 26 ± 6 years, stature = 182 ± 9 cm, body mass = 84 ± 9 kg, resistance training experience = 7 ± 3 years) consumed placebo or 6 mg kg−1of anhydrous caffeine 1 h before testing. Muscular power was assessed with seated medicine ball throw and vertical jump exercises, muscular strength with one-repetition maximum (1RM) barbell back squat and bench press exercises, and muscular endurance with repetitions of back squat and bench press exercises (load corresponding to 60% of 1RM) to momentary muscular failure. RPE and PP were assessed immediately after the completion of the back squat and bench press exercises. Compared to placebo, caffeine intake enhanced 1RM back squat performance (+2.8%; effect size [ES] = 0.19;p = .016), which was accompanied by a reduced RPE (+7%; ES = 0.53;p = .037), and seated medicine ball throw performance (+4.3%, ES = 0.32;p = .009). Improvements in 1RM bench press were not noted although there were significant (p = .029) decreases in PP related to this exercise when participants ingested caffeine. The results point to an acute benefit of caffeine intake in enhancing lower-body strength, likely due to a decrease in RPE; upper-, but not lower-body power; and no effects on muscular endurance, in resistance-trained men. Individuals competing in events in which strength and power are important performance-related factors may consider taking 6 mg kg−1of caffeine pre-training/competition for performance enhancement. [ABSTRACT FROM PUBLISHER]

This study compared the effect of counter-movement-jump (CMJ)-based recovery on repeated-sprint-ability (RSA). Eighteen male footballers (16 ± 0 years, 65 ± 10 kg, 1.74 ± 0.10 m)performed three RSA-tests. RSA-1/-3 were performed according to standard procedures, while three CMJs (over 10″) – as a potential fatigue-determinant and/or running mechanics interference – were administered during RSA-2 recoveries. RSA performance, exercise effort (fatigue index [FI], rating of perceived exertion [RPE], blood lactate concentration [BLa]), simple kinematics (steps number), vertical-jump characteristics (stretch-shortening-cycle-efficiency [SSCE] assessed before/after RSA) were investigated. ANOVA showed no differences between RSA-1,-3. During RSA-2, performance was lower than RSA-1/-3, while steps number did not change. During RSA-2, FI, BLa, RPE were higher than RSA-1/-3 (FI +21.10/+20.43%, P<0.05; BLa +16.25/+13.34%, P<0.05; RPE +12.50/+9.57%, P<0.05). During RSA-2, SSCE, as the CMJ/squat-jump-height-ratio, was not significantly different from RSA-1/-3. Passive recovery RSA allows better performance. Yet, RSA CMJ-based recovery is effective in increasing training load (FI, BLa, RPE) without perturbing running mechanics (simple kinematics, SSCE). [ABSTRACT FROM PUBLISHER]

The purpose of this study was to compare the effect on strength gains of two isoinertial resistance training (RT) programmes that only differed in actual concentric velocity: maximal (MaxV) vs. half-maximal (HalfV) velocity. Twenty participants were assigned to a MaxV (n = 9) or HalfV (n = 11) group and trained 3 times per week during 6 weeks using the bench press (BP). Repetition velocity was controlled using a linear velocity transducer. A complementary study (n = 10) aimed to analyse whether the acute metabolic (blood lactate and ammonia) and mechanical response (velocity loss) was different between the MaxV and HalfV protocols used. Both groups improved strength performance from pre- to post-training, but MaxV resulted in significantly greater gains than HalfV in all variables analysed: one-repetition maximum (1RM) strength (18.2 vs. 9.7%), velocity developed against all (20.8 vs. 10.0%), light (11.5 vs. 4.5%) and heavy (36.2 vs. 17.3%) loads common to pre- and post-tests. Light and heavy loads were identified with those moved faster or slower than 0.80 m·s−1 (∼60% 1RM in BP). Lactate tended to be significantly higher for MaxV vs. HalfV, with no differences observed for ammonia which was within resting values. Both groups obtained the greatest improvements at the training velocities (≤0.80 m·s−1). Movement velocity can be considered a fundamental component of RT intensity, since, for a given %1RM, the velocity at which loads are lifted largely determines the resulting training effect. BP strength gains can be maximised when repetitions are performed at maximal intended velocity. [ABSTRACT FROM AUTHOR]

This study examined the acute effects of a single dose of an antioxidant (AO; Lactaway®containing pycnogenol) on time to fatigue (TTF). Nine trained cyclists [mean ± SD age 35 ± 10 yrs; body mass 71.6 ± 10.2 kg; VO2peak 63 ± 11 ml/kg/min] performed on two separate occasions a continuous protocol of 5 min at 50% of peak power output (PPO), 8 min at 70% of PPO, and then cycled to fatigue at 95% PPO. Four hours prior to the exercise protocol, the subjects consumed the supplement or a placebo (counterbalanced, double blind protocol). Cyclists, on average, rode for 80 s more in the Lactaway trial than they did in the placebo trial. There was considerable evidence (chances ≥94.5%) for substantial positive treatment effects for TTF and the other performance-related variables (excluding [BLa] at 95% PPO). Other studies are necessary to confirm these results and identify the mechanisms underlying the observed effects. [ABSTRACT FROM AUTHOR]

A spinal cord injury usually leads to an increase in contractile speed and fatigability of the paralysed quadriceps muscles, which is probably due to an increased expression of fast myosin heavy chain (MHC) isoforms and reduced oxidative capacity. Sometimes, however, fatigue resistance is maintained in these muscles and also contractile speed is slower than expected. To obtain a better understanding of the diversity of these quadriceps muscles and to determine the effects of training on characteristics of paralysed muscles, fibre characteristics and whole muscle function were assessed in six subjects with spinal cord lesions before and after a 12-week period of daily low-frequency electrical stimulation. Relatively high levels of MHC type I were found in three subjects and this corresponded with a high degree of fusion in 10-Hz force responses (r=0.88). Fatigability was related to the activity of succinate dehydrogenase (SDH) (r=0.79). Furthermore, some differentiation between fibre types in terms of metabolic properties were present, with type I fibres expressing the highest levels of SDH and lowest levels of α-glycerophosphate dehydrogenase. After training, SDH activity increased by 76±26% but fibre diameter and MHC expression remained unchanged. The results indicate that expression of contractile proteins and metabolic properties seem to underlie the relatively normal functional muscle characteristics observed in some paralysed muscles. Furthermore, training-induced changes in fatigue resistance seem to arise, in part, from an improved oxidative capacity. [ABSTRACT FROM AUTHOR]

The maximal lactate steady state (MLSS) and the critical power (CP) are two widely used indices of the highest oxidative metabolic rate that can be sustained during continuous exercise and are often considered to be synonymous. However, while perhaps having similarities in principle, methodological differences in the assessment of these parameters typically result in MLSS occurring at a somewhat lower power output or running speed and exercise at CP being sustainable for no more than approximately 20–30 min. This has led to the view that CP overestimates the 'actual' maximal metabolic steady state and that MLSS should be considered the 'gold standard' metric for the evaluation of endurance exercise capacity. In this article we will present evidence consistent with the contrary conclusion: i.e., that (1) as presently defined, MLSS naturally underestimates the actual maximal metabolic steady state; and (2) CP alone represents the boundary between discrete exercise intensity domains within which the dynamic cardiorespiratory and muscle metabolic responses to exercise differ profoundly. While both MLSS and CP may have relevance for athletic training and performance, we urge that the distinction between the two concepts/metrics be better appreciated and that comparisons between MLSS and CP, undertaken in the mistaken belief that they are theoretically synonymous, is discontinued. CP represents the genuine boundary separating exercise in which physiological homeostasis can be maintained from exercise in which it cannot, and should be considered the gold standard when the goal is to determine the maximal metabolic steady state. [ABSTRACT FROM AUTHOR]