Circulatory effects of fluid loss and fluid intake during exercise

Abstract

Cardiorespiratory responses to two levels of exercise (133 and 200 W) on a bicycle ergometer were measured in nine subjects before and after a 1‐h outdoor run of 12.8 km completed in ambient temperatures of 20–25° C. After the run, the subjects showed a mean weight loss of 1.49 kg; the laboratory exercises produced higher mean levels of O2 consumption than before the run (1.91 and 2.66 1 min‐1 compared with 1.80 and 2.46 1 min‐1) and higher mean heart rates (141 and 158 beats min‐1 compared with 115 and 140 beats min‐1); and lower levels of stroke volume (83 and 85 ml compared with 109 and 101 ml) and of cardiac output (11.6 and 13.3 1 min‐1 compared with 12.6 and 14.1 1 min‐1). Five subjects were studied in a similar way on a second occasion when they consumed 1.25 1 of a dextrose‐electrolyte solution during the first 45 min of the outdoor run. Differences in the exercise variables measured before and after the outdoor run were now small or insignificant. It is postulated that in the first study uncompensated loss of body water reduced plasma volume and cardiac filling, thus reducing stroke volume and cardiac output. Such changes jeopardize body temperature regulation during exercise.     

The effect of shoe type on gait in forefoot strike runners during a 50-km run

PurposeTo observe the relative change in foot-strike pattern, pressure characteristics, surface electromyography (sEMG) recordings, and stride characteristics in forefoot strike runners wearing both minimalist and traditional shoes during a 50-km run.MethodsFour experienced minimalist runners were enrolled in this study. Each runner ran a 50-km simulated run in both minimalist shoes and traditional shoes. Pressure data, sEMG recordings, and limited 3D motion capture data were collected during the initial 0.8 km and final 0.8 km for each trial.ResultsThree runners in the traditional shoe type condition and one runner in the minimalist shoe type condition demonstrated a more posterior initial contact area (midfoot strike (MFS) pattern) after the 50-km run, which was supported by increased activity of the tibialis anterior in the pre-contact phase (as per root mean square (RMS) values). In addition, in both pre- and post-run conditions, there were increased peak pressures in the minimalist shoe type, specifically in the medial forefoot. Muscle fatigue as defined by a decreased median frequency observed in isometric, constant force contractions did not correspond with our hypothesis in relation to the observed foot strike change pattern. Finally, step rate increased and step length decreased after the 50-km run in both shoe type conditions.ConclusionMore runners adopted a more posterior initial contact area after the 50-km run in the traditional shoe type than in the minimalist shoe type. The runners who adopted a more posterior initial contact area were more closely associated with an increased median frequency of the medial gastrocnemius, which suggests there may be a change in motor unit recruitment pattern during long-distance, sustained velocity running. The increased peak pressures observed in the medial forefoot in the minimalist shoe type may predispose to metatarsal stress fractures in the setting of improper training.     

Perceived life stress and anxiety correlate with chronic gastrointestinal symptoms in runners

Numerous causes of exercise-related gastrointestinal (GI) distress exist but scarce research has evaluated potential psychological causes. Runners (74 men, 76 women) prospectively recorded running duration, intensity (Rating of Perceived Exertion [RPE]), and GI symptoms for 30 days. Six GI symptoms were rated on a 0–10 scale. The percentage of runs over 30 days that participants reported at least one upper, lower, or any GI symptom ≥3 was calculated. After 30 days, participants completed a questionnaire on GI distress triggers (demographics, anthropometrics, experience, analgesic use, antibiotic use, probiotic consumption, fluid/food intake, stress, anxiety). Stress and anxiety were measured via the Perceived Stress Scale (PSS) and Beck Anxiety Inventory (BAI). The median percentage of runs that participants experienced at least one GI symptom ≥3 was 45.6% (interquartile range [IQR], 16.6–67.3%). Age and running experience negatively correlated with GI distress occurrence (rho = ?0.17 to ?0.34; p < 0.05). Run RPE, probiotic food consumption, PSS scores, and BAI scores positively correlated with GI distress occurrence (rho = 0.18 to 0.36; p < 0.05). Associations between GI distress, stress and anxiety remained significant after adjustment for covariates, except for lower GI symptoms. This study suggests that stress and anxiety contribute to running-related GI distress.     

Relationship between physiological parameters and performance during a half-ironman triathlon in the heat

Abstract

Triathlon is a popular outdoor endurance sport performed under a variety of environmental conditions. The aim of this study was to assess physiological variables before and after a half-ironman triathlon in the heat and to analyse their relationship with performance. Thirty-four well-trained triathletes completed a half-ironman triathlon in a mean dry temperature of 29 ± 3ºC. Before and within 1 min after the end of the race, body mass, core temperature, maximal jump height and venous blood samples were obtained. Mean race time was 315 ± 40 min, with swimming (11 ± 1%), cycling (49 ± 2%) and running (40 ± 3%) representing different amounts of the total race time. At the end of the competition, body mass changed by ?3.8 ± 1.6% and the change in body mass correlated positively with race time (r = 0.64; P < 0.001). Core temperature increased from 37.5 ± 0.6ºC to 38.8 ± 0.7ºC (P < 0.001) and post-race core temperature correlated negatively with race time (r = ?0.47; P = 0.007). Race time correlated positively with the decrease in jump height (r = 0.38; P = 0.043), post-race serum creatine kinase (r = 0.55; P = 0.001) and myoglobin concentrations (r = 0.39; P = 0.022). In a half-ironman triathlon in the heat, greater reductions in body mass and higher post-competition core temperatures were present in faster triathletes. In contrast, slower triathletes presented higher levels of muscle damage and decreased muscle performance.     

Redox status and antioxidant response in professional cyclists during training

Abstract

The aim of this study was to investigate whether different phases of training affect oxidative stress and antioxidant defences in professional cyclists. Ten professional cyclists, aged 21.8 ± 2.5 years, were enrolled in the study. They were classified into two groups of five athletes each one with similar nutritional intake excepting for the overload of vitamin C (1000 mg day^?1) and E (400 mg day^?1) supplementation in one of them. The cyclists of both groups performed the same exercise design, consisting of hard, tapering and recovery training periods. Total antioxidant capacity (TAC) of the diet, plasma oxygen radical absorption capacity (ORAC), lipid peroxidation (LPO), DNA damage (8-OHdG) and erythrocyte glutathione disulfide/glutathione ratio (GSSG:GSH^?1) were measured. During the intense exercise trainings, the cyclists without vitamin supplements had the TAC of diet significantly lower than the supplemented group. Plasma ORAC, LPO and 8-OHdG were similar in both groups of athletes. Athletes with supplements had a basal LPO:ORAC^?1 ratio lower than that without supplements, but this ratio converged to the same level at the end of the training in both groups of cyclists. Both groups of cyclists showed similar changes in GSSG:GSH^?1 ratio and in GSSG and GSH levels along the study. The data suggest that well-trained athletes with suitable ultra-endurance training volume and intensity do not require antioxidant vitamin supplements to adapt their endogenous antioxidant defenses to exercise-induced ROS.     

Carbohydrate gel ingestion during running in the heat on markers of gastrointestinal distress

The purpose of this study is to measure the effects of carbohydrate ingestion during exercise in the heat by measuring markers of gastrointestinal damage and inflammation. Methods: Active subjects (n?=?7) completed two 60-min running trials in a heated environment (70% VO₂max, 30°C). At minute 20 of exercise, subjects consumed a carbohydrate gel (Cho) (27?g), or a non-carbohydrate placebo (nCho). Plasma endotoxin, I-FABP, TNF-α, IL-6, IL-1β, IL-10, and MCP-1 were measured pre-exercise, 20-min post-exercise, and again 2-h, and 4-h post-exercise. Results: Endotoxin increased 20-min post-exercise compared to pre in the Cho trial only (p?=?.03). I-FABP levels increased 20-min post-exercise in the Cho trial only compared to pre-exercise (p?=?.003). I-FABP levels were also increased in Cho trial 20-min post-exercise when compared to same time point in the nCho trial (p?=?.032). TNF-α increased 20-min post-exercise in the Cho trial only compared to pre (p?=?.03). Plasma IL-6 concentration increased 20-min post-exercise when compared to pre in both the Cho (p?=?.002) and nCho (p?=?.009), but remained elevated at the 2-h time point in the nCho trial (p?=?.03). I-FABP and several plasma cytokines (TNF-α, MCP-1, Il-6) returned to baseline sooner in the Cho trial. Conclusions: Ingestion of carbohydrate gel during exercise in the heat enhances markers of gastrointestinal wall damage.     

Perception of effort in Exercise Science: Definition,measurement and perspectives

Perception of effort, also known as perceived exertion or sense of effort, can be described as a cognitive feeling of work associated with voluntary actions. The aim of the present review is to provide an overview of what is perception of effort in Exercise Science. Due to the addition of sensations other than effort in its definition, the neurophysiology of perceived exertion remains poorly understood. As humans have the ability to dissociate effort from other sensations related to physical exercise, the need to use a narrower definition is emphasised. Consequently, a definition and some brief guidelines for its measurement are provided. Finally, an overview of the models present in the literature aiming to explain its neurophysiology, and some perspectives for future research are offered.     

The menstrual cycle and its effect on the immune status of female endurance runners

Twenty highly trained, eumenorrhoeic female endurance runners were studied over three consecutive menstrual cycles. Average training distance per week, total years training and mood states were recorded throughout the three cycles. Salivary progesterone and menstrual cycle diaries were recorded over the first two cycles to identify luteal phase onset and the presence of any menstrual irregularities. Saliva samples were collected daily over the third cycle for analysis of immunoglobulin A (IgA) concentration and secretion and saliva flow rate. Twoway analysis of variance (ANOVA) revealed no significant differences in mood states across the phases of the menstrual cycle ( P > 0.05). Training logs indicated that training did not alter throughout the 3 month study. One-way ANOVArevealed no significant differences in IgA concentration ( P = 0.92), secretion rate ( P = 0.84) or saliva flow rate ( P = 0.95) across the phases of the menstrual cycle. Pearson's product-moment correlation revealed no relationship between IgA concentration and progesterone between the phases of the cycle ( r = 0.39). We conclude that, in ovulatory female endurance runners whose physical and emotional stress are stable, IgA concentration is not significantly affected by fluctuations in progesterone during the menstrual cycle.     

A prospective examination of the impact of high levels of exercise training on sedentary behaviour

The aim of this study is to determine changes in sedentary behaviour in response to extensive aerobic exercise training. Participants included adults who self-selected to run a marathon. Sedentary behaviour, total activity counts and physical activity (PA) intensity were assessed (Actigraph GT3X) for seven consecutive days during seven assessment periods (?3, ?2, and ?1 month prior to the marathon, within 2 weeks of the marathon, and +1, +2, and +3 months after the marathon). Models were fitted with multiple imputation data using the STATA mi module. Random intercept generalized least squares (GLS) regression models were used to determine change in sedentary behaviour with seven waves of repeated measures. Results: Twenty-three individuals (mean?±?S_x: 34.4?±?2.1y, 23.0?±?1.9% fat, 15 women, 8 men) completed the study. Marathon finishing times ranged from 185 to 344 minutes (253.2?±?9.6 minutes). Total counts in the vertical axis were 1,729,414 lower one month after the race, compared with two months prior to the race (peak training). Furthermore, counts per minute decreased by 252.7 counts·minute^?1 during that same time period. Daily sedentary behaviour did not change over the seven assessment periods, after accounting for age, gender, per cent body fat, wear time, marathon finishing time, and previous marathon experience. This prospective study supports the notion that PA and sedentary behaviours are distinct, showing that sedentary behaviour was not impacted by high levels of aerobic training.     

Effects of inertia correction and resistive load on fatigue during repeated sprints on a friction-loaded cycle ergometer

Abstract

Seven 6 s sprints with 30 s recovery between sprints were performed against two resistive loads: 50 (L50) and 100 (L100) g · kg^?1 body mass. Inertia-corrected and -uncorrected peak and mean power output were calculated. Corrected peak power output in corresponding sprints and the drop in peak power output relative to sprint 1 were not different in the two conditions, despite the fact that mean power output was 15–20% higher in L100 (P < 0.01). The effect of inertia correction on power output was more pronounced for the lighter load (L50), with uncorrected peak power output in sprint 1 being 42% lower than the corresponding corrected peak power output, while this was only 16% in L100. Fatigue assessed by the drop in uncorrected peak and mean power output in sprint 7 relative to sprint 1 was less compared with that obtained by corrected power values, especially in L50 (drop in uncorrected vs. corrected peak power output: 13.3 ± 2.2% vs. 23.1 ± 4.1%, P < 0.01). However, in L100, the difference between the drop in corrected and uncorrected mean power output in sprint 7 was much smaller (24.2 ± 3.1% and 21.2 ± 2.7%, P < 0.01), indicating that fatigue may be safely assessed even without inertia correction when a heavy load is used. In conclusion, when inertia correction is performed, fatigue during repeated sprints is unaffected by resistive load. When inertia correction is omitted, both power output and the fatigue profile are underestimated by an amount dependent on resistive load. In cases where inertia correction is not possible during a repeated sprints test, a heavy load may be preferable.     

Psychophysiological effects of audiovisual stimuli during cycle exercise

Immersive environments induced by audiovisual stimuli are hypothesised to facilitate the control of movements and ameliorate fatigue-related symptoms during exercise. The objective of the present study was to investigate the effects of pleasant and unpleasant audiovisual stimuli on perceptual and psychophysiological responses during moderate-intensity exercises performed on an electromagnetically braked cycle ergometer. Twenty young adults were administered three experimental conditions in a randomised and counterbalanced order: unpleasant stimulus (US; e.g. images depicting laboured breathing); pleasant stimulus (PS; e.g. images depicting pleasant emotions); and neutral stimulus (NS; e.g. neutral facial expressions). The exercise had 10 min of duration (2 min of warm-up?+?6 min of exercise?+?2 min of warm-down). During all conditions, the rate of perceived exertion and heart rate variability were monitored to further understanding of the moderating influence of audiovisual stimuli on perceptual and psychophysiological responses, respectively. The results of the present study indicate that PS ameliorated fatigue-related symptoms and reduced the physiological stress imposed by the exercise bout. Conversely, US increased the global activity of the autonomic nervous system and increased exertional responses to a greater degree when compared to PS. Accordingly, audiovisual stimuli appear to induce a psychophysiological response in which individuals visualise themselves within the story presented in the video. In such instances, individuals appear to copy the behaviour observed in the videos as if the situation was real. This mirroring mechanism has the potential to up-/down-regulate the cardiac work as if in fact the exercise intensities were different in each condition.     

Iron balance and iron supplementation for the female athlete: A practical approach

Maintaining a positive iron balance is essential for female athletes to avoid the effects of iron deficiency and anaemia and to maintain or improve performance. A major function of iron is in the production of the oxygen and carbon dioxide carrying molecule, haemoglobin, via erythropoiesis. Iron balance is under the control of a number of factors including the peptide hormone hepcidin, dietary iron intake and absorption, environmental stressors (e.g. altitude), exercise, menstrual blood loss and genetics. Menstruating females, particularly those with heavy menstrual bleeding are at an elevated risk of iron deficiency. Haemoglobin concentration [Hb] and serum ferritin (sFer) are traditionally used to identify iron deficiency, however, in isolation these may have limited value in athletes due to: (1) the effects of fluctuations in plasma volume in response to training or the environment on [Hb], (2) the influence of inflammation on sFer and (3) the absence of sport, gender and individually specific normative data. A more detailed and longitudinal examination of haematology, menstrual cycle pattern, biochemistry, exercise physiology, environmental factors and training load can offer a superior characterisation of iron status and help to direct appropriate interventions that will avoid iron deficiency or iron overload. Supplementation is often required in iron deficiency; however, nutritional strategies to increase iron intake, rest and descent from altitude can also be effective and will help to prevent future iron deficient episodes. In severe cases or where there is a time-critical need, such as major championships, iron injections may be appropriate.     

The effects of prior incremental cycle exercise on the physiological responses during incremental running to exhaustion: relevance for sprint triathlon performance

It is common for the physiological working capacity of a triathlete when cycling and running to be assessed on two separate days. The aim of this study was to establish whether an incremental running test to exhaustion has a negative effect after a 5 h recovery from an incremental cycling test. Eight moderately trained triathletes (age, 26.2 +/- 3.4 years; body mass, 67.3 +/- 9.1 kg; VO2max when cycling, 59 +/- 13 ml x kg x min(-1); mean +/- s) completed an incremental running test 5 h after an incremental cycling test (fatigue) as well as an incremental running test without previous activity (control). Maximum running speed, maximal oxygen uptake (VO2max) and the lactate threshold were determined for each incremental running test and correlated with the average speed during a 5 km run, which was performed immediately after a 20 km cycling time-trial, as in a sprint triathlon. There were no significant differences in maximum running speed, VO2max or the lactate threshold in either incremental running test (control or fatigue). Furthermore, good agreement was found for each physiological variable in both the control and fatigue tests. For the fatigue test, there were significant correlations between the average speed during a 5 km run and both VO2max expressed in absolute terms (r = 0.83) and the lactate threshold (r = 0.88). However, maximum running speed correlated most strongly with the average speed during a 5 km run (r = 0.96). The results of this study indicate that, under controlled conditions, an incremental running test can be performed successfully 5 h after an incremental cycling test to exhaustion. Also, the maximum running speed achieved during an incremental running test is the variable that correlates most strongly with the average running speed during a 5 km run after a 20 km cycling time-trial in well-trained triathletes.     

营养与体能和健康的研究进展

营养是影响竞技能力、机能状态、体力适应和恢复的一个主要因素,而且可以操作。营养结合科学训练可明显提高运动能力。任何营养素的缺乏或过度都会影响到人体的健康、生理、机能和竞技状态,从而影响到运动能力的发挥。缺乏体力活动和膳食营养不当是引起慢性病的主要风险。适量运动与合理营养结合有益于各年龄组人群的健康、体能和防治慢性病,这种非药物、经济、有效又无副作用的防治措施尤其适用于我国国情。     

The use of individualized speed and intensity thresholds for determining the distance run at high-intensity in professional soccer

Abstract

As with other match analysis systems, ProZone® uses an absolute speed threshold to identify running speeds at “high-intensity”. In this study, we examined the use of an individualized high-intensity speed threshold based on the speed at the second ventilatory threshold (VT_2speed) for assessment of the distance run at high-intensity during matches. Ten professional soccer players completed a maximal treadmill test to determine VT_2speed. Match data were identified by means of the ProZone® match analysis system. The distances run at high-intensity during matches were calculated using the default value (19.8 km · h^?1) and VT_2speed. Differences between VT_2speed and the default were analysed using a non-parametric median sign test. The distances run at high-intensity were compared with a paired t-test. The median VT_2speed was 15 km · h^?1 (range 14–16 km · h^?1), which was less than the default (P < 0.01). Mean distance run at high-intensity based on the default and VT_2speed was 845 m (s = 296) and 2258 m (s = 707), respectively [mean difference 1413 m; P < 0.001 (95% CI: 1037–1789 m)]. The high-intensity running speeds based on the second ventilatory threshold are substantially less than that used as the default within the ProZone® match analysis system, thus the distance run at high-intensity can be substantially underestimated.     

提倡运动加营养，创建健康生活方式

阐述了不同人群的亚健康问题及其危害,并就规律运动和合理营养在远离亚健康,防治疾病和抗衰老等方面的作用进行了深入的介绍。为使运动加营养真正成为健康生活方式,在运动的科学安排和营养的合理化方面进行了叙述和指导。     

Changes in blood lactate and pyruvate concentrations and the lactate-to-pyruvate ratio during the lactate minimum speed test

The aim of this study was to assess the responses of blood lactate and pyruvate during the lactate minimum speed test. Ten participants (5 males, 5 females; mean +/- s: age 27.1 +/- 6.7 years, VO 2max 52.0 +/- 7.9 ml kg -1 min -1 ) completed: (1) the lactate minimum speed test, which involved supramaximal sprint exercise to invoke a metabolic acidosis before the completion of an incremental treadmill test (this results in a ‘U-shaped’ blood lactate profile with the lactate minimum speed being defined as the minimum point on the curve); (2) a standard incremental exercise test without prior sprint exercise for determination of the lactate threshold; and (3) the sprint exercise followed by a passive recovery. The lactate minimum speed (12.0 +/- 1.4 km h -1 ) was significantly slower than running speed at the lactate threshold (12.4 +/- 1.7 km h -1 ) (P < 0.05), but there were no significant differences in VO 2 , heart rate or blood lactate concentration between the lactate minimum speed and running speed at the lactate threshold. During the standard incremental test, blood lactate and the lactate-topyruvate ratio increased above baseline values at the same time, with pyruvate increasing above baseline at a higher running speed. The rate of lactate, but not pyruvate, disappearance was increased during exercising recovery (early stages of the lactate minimum speed incremental test) compared with passive recovery. This caused the lactate-to-pyruvate ratio to fall during the early stages of the lactate minimum speed test, to reach a minimum point at a running speed that coincided with the lactate minimum speed and that was similar to the point at which the lactate-to-pyruvate ratio increased above baseline in the standard incremental test. Although these results suggest that the mechanism for blood lactate accumulation at the lactate minimum speed and the lactate threshold may be the same, disruption to normal submaximal exercise metabolism as a result of the preceding sprint exercise, including a three- to five-fold elevation of plasma pyruvate concentration, makes it difficult to interpret the blood lactate response to the lactate minimum speed test. Caution should be exercised in the use of this test for the assessment of endurance capacity.     

抗阻运动与肌肉减少症的防治

肌肉减少症又称肌少症(sarcopenia),是一种近来备受关注的老年综合征,泛指随着年龄的增长,人体出现肌量减少和肌力下降等改变。肌少症的特点是骨骼肌肌量减低并且肌肉内脂肪堆积,导致肌肉力量减低和肌肉功能下降,进而导致躯体残疾、生活质量降低,甚至死亡等。抗阻运动或称力量训练(strength training),是指肌肉主动收缩对抗阻力的一种运动形式,在通常情况下,这种运动的负荷远高于肌肉在有氧状态下的能力,具有强度大、持续时间短、力竭性等特征。肌肉是产生人体自主运动的动力源泉,而肌肉运动,特别是抗阻运动可使肌肉产生很多生理生化的变化。文章回顾了近年来不同学者和临床工作者针对抗阻运动改善肌肉减少症的数据,论述了抗阻运动防治肌肉减少症的机理,强调了抗阻运动和有针对性的营养调理对肌肉减少症的有效改善,对未来肌少症的治疗研究提供更清晰的方向。     

大学生冬季体育锻炼的营养补充

冬季体育锻炼能促进身体健康和身体素质的提高。通过调查发现,很多大学生在运动后,缺乏对合理饮食及营养补充重要性的认识,针对这一问题,本文提出了冬季体育锻炼、营养代谢特点及营养补充的必要性,提出了推广合理膳食,科学进行营养补充的实施建议。