Effects of marathon running on running economy and kinematics

The present study was designed to investigate interactions between running economy and mechanics before, during, and after an individually run marathon. Seven experienced triathletes performed a 5-min submaximal running test on a treadmill at an individual constant marathon speed. Heart rate was monitored and the expired respiratory gas was analyzed. Blood samples were drawn to analyze serum creatine kinase activity (S-CK), skeletal troponin I (sTnI), and blood lactate (B-La). A video analysis was performed (200 frames · s⁻¹) to investigate running mechanics. A kinematic arm was used to determine the external work of each subject. The results of the present study demonstrate that after the marathon, a standardized 5-min submaximal running test resulted in an increase in oxygen consumption, ventilation, and heart rate (P < 0.05), with a simultaneous decrease in the oxygen difference (%) between inspired and expired air, and respiratory exchange ratio (P < 0.05). B-La did not change during the marathon, while sTnI and S-CK values increased (P < 0.05), peaking 2 h and 2 days after the marathon, respectively. With regard to the running kinematics, a minor increase in stride frequency and a similar decrease in stride length were observed (P < 0.01). These results demonstrate clearly that weakened running economy cannot be explained by changes in running mechanics. Therefore, it is suggested that the increased physiological loading is due to several mechanisms: increased utilization of fat as an energy substrate, increased demands of body temperature regulation, and possible muscle damage. Accepted: 20 March 2000     

The distribution of quick phase interval durations in human optokinetic nystagmus

There is an interesting dichotomy between models that predict the quick phase interval durations (QPIDs) of human optokinetic nystagmus (OKN). Accumulator models describe a stochastic signal in a neural network that triggers a response once the signal reaches a fixed threshold value. However, it is also possible that quick phases are triggered after eye position reaches a variable amplitude threshold. In this study, we fitted a range of probability density functions previously predicted by stochastic models of OKN (including those of the reciprocal truncated Normal, inverse Gaussian, gamma, lognormal and the mixture of two reciprocal truncated Normal distributions) to individual QPID histograms. We compared the goodness of fit between these models, and a model where the distribution of QPIDs is determined by the ratio of two correlated and truncated Normal random variables. The ratio distribution gave the best fit to the data, and we propose this is due to the approximately linear trajectory of slow phases (SPs) and that QPIDs are given by the ratio of a variable SP amplitude threshold and variable SP velocity.     

Use of recoveryVO2 to predict running economy

Summary The purpose of this study was to determine whether running economy. (RE) could be predicted accurately using recoveryVO₂ values. Twelve runners (VO_2max=61.9, SD 4.9 ml·kg^–1·min^–1) completed three treadmill RE sessions over a 2-week period. During each session, subjects performed three 6-min runs at 69%, 78%, and 87%VO_2max. RE was calculated from a single 2-min gas collection during the last 2 min of running. Immediately following each run, recoveryVO₂ data obtained during randomly assigned 15-s, 20-s, or 25-s gas collections were used to predict exerciseVO₂. Correlations and mean absolute percentage variation (%VAR) between actual and predictedVO₂ at each relative intensity and recovery period are reported. Although the relationship between actual and predictedVO₂ was significant and more pronounced at higher exercise intensities, the overall magnitude of the association was low to moderate (r range= 0.50–0.81). The range of % VAR between actual and predicted aerobic demands also obscured marked underprediction (–6.5% to –12.5%) and overprediction (+ 10.1% to + 17.4%) of actualVO₂ in some subjects. These data suggest that 15-, 20-, and 25-s recoveryVO₂ values do not correlate strongly with steady-stateVO₂, nor do they adequately account for variation in individual economy profiles.     

Heritability of running economy: a study made on twin brothers

Running economy (RE), defined as the steady-state of oxygen uptake (V˙O₂) for a given running velocity, is a factor of sports performance the genetic component of which has seldom been reported to date. We studied this component using a heritability index (HI) in a group of 32 male twins, 8 monozygotic (MZ) and 8 dizygotic (DZ) pairs, all sportsmen with similar perinatal and environmental backgrounds. Zygocity was determined by the identity of erythrocytic antigenic, protein and enzymatic polymorphism, and human leucocyte antigen serologic types between co-twins. The subjects exercised twice on a treadmill, once until exhaustion and again at submaximal intensities. Pulmonary gas exchange was measured continuously using an automatic analyser system during both tests. Blood samples were obtained during the recovery period to determine lactate concentrations. No significant differences were observed between MZ and DZ, in respect of RE at any speed or in maximal V˙O₂ relative to body mass. Nevertheless, significant HI (P??1 (HI?=?0.71) and 8?km?·?h^?1 (HI?=?0.79), differences which probably suggest that there are differences in RE. In conclusion, we did not detect a genetic component in RE or in maximal oxygen uptake, but a genetic component for markers of anaerobic metabolism was present.     

影响跑步运动耐力的生理学与生物力学因素

文题释义：跑步经济性：是与运动成绩具有高度相关的评测指标,通过检验跑步速度与能量消耗之间的关系,来体现运动员有氧代谢能力的一种指标,跑步经济性的单位与最大摄氧量类似,是mL/(kg·min)。 最大摄氧量：人体在进行有大量肌肉群参与且长时间的剧烈运动时,当心肺功能和肌肉利用氧的能力达到人体极限水平时,单位时间内(每分钟)所能摄取的氧量称为最大摄氧量,其单位为mL/(kg·min)。 背景：跑步经济性被认为是反映耐力运动员尤其是长跑运动员性能的重要指标,通常定义为在给定速度下跑步的能量需求,表示为给定速度下的摄氧量。 目的：综述现有的影响跑步性能的生理学与生物力学因素。 方法：以“running economy,physiological factors,biomechanical and neuromuscular characteristics,spatiotemporal factors,lower Limb kinematic factors,kinetic factors,nutritional interventions”为检索词,检索PubMed数据库(1960至2018年)中与跑步性能、急性或慢性干预措施和其他影响因素等相关的内容。 结果与结论：共得到113篇文献,根据纳入排除标准,对其中58篇文献进行分析。①目前证据表明心肺功能、肌纤维类型、肌肉力量、腿部刚度等生理因素与跑步经济性的改善有关,而跑步者的体温变化和弹性势能与跑步经济性的关系目前没有统一结论;②有利于改善跑步经济性的生物力学因素是步幅频率或长度、垂直振荡、下肢惯性力矩、脚趾离地时腿部伸展以及手臂摆动,而足部与地面的接触时间、躯干倾斜等因素与跑步经济性之间呈现出不一致的关系;③其他的影响因素中,高海拔适应可改善跑步经济性;伸展性和灵活性与跑步经济性之间的关系仍待确定;一些营养干预也受到关注,最明显的是膳食硝酸盐;④尽管该文章已经总结了影响跑步经济性的大部分因素,但未来可以专注于研究个体跑步者,以便确定跑步者的结构和功能能力如何影响跑步经济性,以及后续表现和运动伤害的情况。 ORCID: 0000-0002-0077-6904(徐盛嘉) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Effects of menstrual phase on performance and recovery in intense intermittent activity

Game sport and training require repeated high intensity bursts. This study examined differences between high intensity, intermittent work in two phases of the menstrual cycle. Six physically active young women (age 19–29) performed 10 6-s sprints on a cycle ergometer in both the mid-follicular (FP) (days 6–10) and late-luteal phases (LP) (days 20–24) of the menstrual cycle. Work, power, oxygen intake parameters, and capillarized blood lactate were measured. Data are analyzed using the Friedman and Wilcoxon matched pairs tests. There was no difference between menstrual phases in peak 6-s power (6.8(0.6) W kg⁻¹ in FP, 6.9(0.6) W kg⁻¹ in LP), the drop off in work (1.2(3.5) J kg⁻¹ in FP and 1.0(2.7) J kg⁻¹ in LP), or in the sprint (23.7 (1.5) mL kg⁻¹ min⁻¹ in LP and 24.3(2.4) mL kg⁻¹ min⁻¹ in FP). Capillarized blood lactate was also similar in both phases of the menstrual cycle both at 1 min (9.2 (2.7) mmol L⁻¹ in FP, 9.2 (3.1) mmol L⁻¹) and at 3 min (9.0 (2.2) mmol L⁻¹ in FP, 9.2 (2.2) mmol L⁻¹ in LP). However, the average 6-s work was greater in the LP (39.3 (3.4) J kg⁻¹) than during the FP (38.3 (3.1) J kg⁻¹) (P=0.023). The recovery was also greater in the LP than the FP (26.3 (2.4) mL kg⁻¹ min⁻¹ in LP, 25.0 (2.6) mL kg⁻¹ min⁻¹ in FP, P=0.023). Average work over a series of sprints and the consumed between sprints may be slightly greater during the LP than the FP of the menstrual cycle.     

Oxidative stress after three different intensities of running.

In 8 trained subjects (T) and 9 untrained subjects (UT), lipid peroxidation (LPO), total antioxidant capacity (TRAP), superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities were measured in the blood before and after three different intensities of exercise on the treadmill, determined from ventilatory threshold and maximal oxygen uptake data, obtained from a maximal aerobic power test. In plasma, LPO decreased from 3589 +/- 193 to 3274 +/- 223 cps x mg Hb(-1) (p < 0.05), and TRAP increased from 304 +/- 45 to 384 +/- 57 micromol x L(-1) trolox (p < 0.05) after high intensity exercise in T. GPx activity increased in the T group as compared to the UT group, after exercise in moderate (25.90 +/- 3.79 to 15.05 +/- 3.23 nM x min(-1) x mg protein(-1)) and high (21.75 +/- 4.91 to 12.1 +/- 2.46 nM x min(-1) x mg protein(-1)) intensities (p < 0.05). Superoxide dismutase activity increased after exercise at low (8.35 +/- 0.85 to 9.23 +/- 1.03 U SOD x mg protein(-1)) and moderate (8.89 +/- 0.98 to 10.44 +/- 0.86 U SOD x mg protein(-1)) intensity in UT (p < 0.05). There were no changes in catalase activity. These findings indicate that exercise in this model did not increase lipid peroxidation, probably because of the alterations in TRAP and enzymatic antioxidants.     

The effects of a single bout of downhill running and ensuing delayed onset of muscle soreness on running economy performed 48 h later

Delayed onset of muscle soreness (DOMS) is a common response to exercise involving significant eccentric loading. Symptoms of DOMS vary widely and may include reduced force generating capacity, significant alterations in biochemical indices of muscle and connective tissue health, alteration of neuromuscular function, and changes in mechanical performance. The purpose of the investigation was to examine the effects of downhill running and ensuing DOMS on running economy and stride mechanics. Nine, well-trained distance runners and triathletes participated in the study. Running economy was measured at three relative intensities [65, 75, and 85% of maximal aerobic capacity (V̇O_2peak)] before (RE1) and 48 h after (RE2) a 30-min downhill run (−10%) at 70% V̇O_2peak. Dependent variables included leg muscle soreness, rate of oxygen consumption (V̇O₂), minute ventilation, respiratory exchange ratio, lactate, heart rate, and stride length. These measurements were entered into a two-factor multivariate analysis of variance (MANOVA). The analysis revealed a significant time effect for all variables and a significant interaction (time × intensity) for lactate. The energy cost of locomotion was elevated at RE2 by an average of 3.2%. This was coupled with a significant reduction in stride length. The change in V̇O₂ was inversely correlated with the change in stride length (r= −0.535). Lactate was significantly elevated at RE2 for each run intensity, with a mean increase of 0.61 mmol l⁻¹. Based on these findings, it is suggested that muscle damage led to changes in stride mechanics and a greater reliance on anaerobic methods of energy production, contributing to the change in running economy during DOMS.     

Effect of different durations of overdistention on rat bladder function and morphology

We investigated the contribution of the duration of overdistention (DOD) to rat bladder function and morphology and explored its possible molecular mechanisms. Bladder overdistention was induced in male Sprague-Dawley rats (200-250 g) by an infusion of saline. Forty rats were divided into 5 groups submitted to different DOD, i.e., 1, 2, 4, and 8 h, and control. Bladder function was evaluated by cystometry. Morphological changes were observed by light and transmission electron microscopy. Compared to control (44.567 ± 3.472 cmH₂O), the maximum detrusor pressure of groups with 2-, 4- and 8-h DOD decreased significantly (means ± SEM): 32.774 ± 3.726, 31.321 ± 2.847, and 29.238 ± 3.724 cmH₂O. With the increase of DOD, inflammatory infiltration and impairment of ultrastructure were more obvious in bladder tissue. Compared to control (1.90 ± 0.77), the apoptotic indexes of groups with 1-, 2-, 4-, and 8-h DOD increased significantly (6.47 ± 2.10, 10.66 ± 1.97, 13.91 ± 2.69, and 18.33 ± 3.28%). Compared to control (0.147 ± 0.031/0.234 ± 0.038 caspase 3/β-actin and Bax/Bcl-2 ratios), both caspase 3/β-actin and Bax/Bcl-2 ratios of 1-, 2-, 4-, and 8-h DOD increased significantly (0.292 ± 0.037/0.508 ± 0.174, 0.723 ± 0.173/1.745 ± 0.471, 1.104 ± 0.245/4.000 ± 1.048, and 1.345 ± 0.409/8.398 ± 3.332). DOD plays an important role in impairment of vesical function and structure. With DOD, pro-apoptotic factors increase and anti-apoptotic factors decrease, possibly contributing to the functional deterioration and morphological changes of the bladder.     

Learning and generalization of time production in humans: rules of transfer across modalities and interval durations

This article investigated both the ability of naive human subjects to learn interval production, as well as the properties of learning generalization across modalities and interval durations that varied systematically from the over-trained interval. Human subjects trained on a 450-, 650-, or 850-ms single-interval production task, using auditory stimuli to define the intervals, showed a significant decrease in performance variability with intensive training. This learning generalized to the visual modality and to non-trained durations following a Gaussian transfer pattern. However, the learning carryover followed different rules, depending on the duration of the trained interval as follows: (1) the dispersion of the generalization curve increased as a function of the trained interval, (2) the generalization pattern was tilted to the right in the visual condition, and (3) the transfer magnitude for 650 ms was less prominent than for the other two intervals. These findings suggest the existence of neural circuits that are tuned to specific time lengths and that show different temporal processing properties depending on their preferred interval duration. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of two durations of short-term intermittent hypoxia on ventilatory chemosensitivity in humans

The purpose of this study was to clarify the influence of duration of intermittent hypoxia per day on ventilatory chemosensitivity. Subjects were assigned to three different groups according to the duration of exposure to intermittent hypoxia (12.3 ± 0.2% O₂): a first group (H-1, n = 6) was exposed to hypoxia for 1 h per day, the second group (H-2, n = 6) was exposed for 3 h per day, and the third (C, n = 7) was used as control. Hypoxic and hypercapnic ventilatory responses (HVR and HCVR) were determined before and after 1 week of intermittent hypoxia. HVR was increased significantly (P < 0.05) after intermittent hypoxia in both the H-1 and H-2 groups. However, there was no significant difference in magnitude of increased HVR between H-1 and H-2 groups. HCVR did not show any changes in all groups after intermittent hypoxia. These results suggest that 1 h of daily exposure is as equally effective as 3 h of daily exposure to severe hypoxia for a short period for enhancing ventilatory chemosensitivity to hypoxia.     

c-Fos expression in the supraoptic nucleus is the most intense during different durations of restraint water-immersion stress in the rat

Restraint water-immersion stress (RWIS) can induce anxiety, hypothermia, and severe vagally-mediated gastric dysfunction. The present work explored the effects of different durations of RWIS on neuronal activities of the forebrain by c-Fos expression in conscious rats exposed to RWIS for 0, 30, 60, 120, or 180 min. The peak of c-Fos induction was distinct for different forebrain regions. The most intense c-Fos induction was always observed in the supraoptic nucleus (SON), and then in the hypothalamic paraventricular nucleus (PVN), posterior cortical amygdaloid nucleus (PCoA), central amygdaloid nucleus (CeA), and medial prefrontal cortex (mPFC). Moreover, body temperature was reduced to the lowest degree after 60 min of RWIS, and the gastric lesions tended to gradually worsen with the prolonging of RWIS duration. These data strongly suggest that these nuclei participate in the organismal response to RWIS to different degrees, and may be involved in the hypothermia and gastric lesions induced by RWIS.     

Oxygen uptake during high-intensity running: response following a single bout of interval training

Elevated oxygen uptake (V˙O₂) during moderate-intensity running following a bout of interval running training has been studied previously. To further investigate this phenomenon, the V˙O₂ response to high-intensity exercise was examined following a bout of interval running. Well-trained endurance runners were split into an experimental group [maximum oxygen uptake, V˙O_{2 max} 4.73 (0.39) l?·?min^?1] and a reliability group [V˙O_{2 max} 4.77 (0.26) l?·?min^?1]. The experimental group completed a training session (4?×?800?m at 1?km?·?h^?1 below speed at V˙O_{2 max} , with 3?min rest between each 800-m interval). Five minutes prior to, and 1?h following the training session, subjects completed 6?min 30?s of constant speed, high-intensity running designed to elicit 40% Δ (where Δ is the difference between V˙O₂ at ventilatory threshold and V˙O_{2 max} ; tests 1 and 2, respectively). The slow component of V˙O₂ kinetics was quantified as the difference between the V˙O₂ at 6?min and the V˙O₂ at 3?min of exercise, i.e. ΔV˙O₂₍₆₃₎. The ΔV˙O₂₍₆₃₎ was the same in two identical conditions in the reliability group [mean (SD): 0.30 (0.10) l?·?min^?1 vs 0.32 (0.13) l?·?min^?1]. In the experimental group, the magnitude of the slow component of V˙O₂ kinetics was increased in test 2 compared with test 1 by 24.9% [0.27 (0.14) l?·?min^?1 vs 0.34 (0.08)?l?·?min^?1, P?V˙O₂₍₆₃₎ in the experimental group was observed in the absence of any significant change in body mass, core temperature or blood lactate concentration, either at the start or end of tests 1 or 2. It is concluded that similar mechanisms may be responsible for the slow component of V˙O₂ kinetics and for the fatigue following the training session. It has been suggested previously that this mechanism may be linked primarily to changes within the active limb, with the recruitment of alternative and/or additional less efficient fibres.     

Assessment of middle-distance running performance in sub-elite young runners using energy cost of running

The purpose of this study was to assess the validity of v _amax as an indicator of middle-distance running performance in sub-elite young runners, _amax being defined as the quotient maximal oxygen uptake (V˙O _2max) divided by the net energy cost of running (C _r) on a treadmill at a submaximal running velocity (280?m?·?min^?1). The V˙O _2max, ventilatory threshold, _amax, and C _r were assessed in 39 young male sub-elite runners having only small variations in performance level. The relationship between each variable and running performance (at 1500?m, 3000?m, and 5000?m) was evaluated. A trend toward a negative correlation existed between C _r and performance although this was not significant. The V˙O _2max and _amax were significantly related to performance. The _amax accounted for around 50% of the variability in performance whereas other physiological variables selected in this study were responsible, at best, for approximately 39%. The results presented in this study suggested that _amax was a useful indicator of middle-distance running performance in sub-elite young runners with similar performance levels as well as in top elite athletes.     

Effect of the interval between pregnancies on perinatal outcomes

BACKGROUND: A short interval between pregnancies has been associated with adverse perinatal outcomes. Whether that association is due to confounding by other risk factors, such as maternal age, socioeconomic status, and reproductive history, is unknown. METHODS: We evaluated the interpregnancy interval in relation to low birth weight, preterm birth, and small size for gestational age by analyzing data from the birth certificates of 173,205 singleton infants born alive to multiparous mothers in Utah from 1989 to 1996. RESULTS: Infants conceived 18 to 23 months after a previous live birth had the lowest risks of adverse perinatal outcomes; shorter and longer interpregnancy intervals were associated with higher risks. These associations persisted when the data were stratified according to and controlled for 16 biologic, sociodemographic, and behavioral risk factors. As compared with infants conceived 18 to 23 months after a live birth, infants conceived less than 6 months after a live birth had odds ratios of 1.4 (95 percent confidence interval, 1.3 to 1.6) for low birth weight, 1.4 (95 percent confidence interval, 1.3 to 1.5) for preterm birth, and 1.3 (95 percent confidence interval, 1.2 to 1.4) for small size for gestational age; infants conceived 120 months or more after a live birth had odds ratios of 2.0 (95 percent confidence interval, 1.7 to 2.4);1.5 (95 percent confidence interval, 1.3 to 1.7), and 1.8 (95 percent confidence interval, 1.6 to 2.0) for these three adverse outcomes, respectively, when we controlled for all 16 risk factors with logistic regression. CONCLUSIONS: The optimal interpregnancy interval for preventing adverse perinatal outcomes is 18 to 23 months.