Changes in EMG characteristics and metabolic energy cost during 90-min prolonged running

This study quantified the interaction of integrated electromyography (iEMG) obtained from the vastus lateralis and the metabolic energy cost of running (C_r), an index to assess running economy, during 90-min prolonged running. The iEMG during running was divided into eccentric (ECC) and concentric (CON) phases using a force platform and a knee-joint goniometer. The ratio of ECC to CON (ECC/CON ratio) significantly decreased during 90-min prolonged running in novice distance runners, which would be explained by an increase in muscle activity during the CON phase of running. The average C_r value significantly increased during 90-min prolonged running. The individual's C_r values significantly correlated with the ECC/CON ratio (r = −0.702, P < 0.05). These results suggest that changes in the ECC/CON ratio and C_r value during prolonged running are associated.     

Does cost of running depend on speed?

Abstract Two series of experiments were carried out with similar techniques to assess the gross cost of running (CR), i.e. the ratio between O₂ demand and speed. The two groups of male subjects differed in average maximal O₂ uptake and variation coefficient (V̇O₂ max = 70.9 ± 4.7 ml O₂ • min ^–1 • kg^–1 , VC = 6.6%; and 61.1±10.1 ml O₂ • min^–1 • kg^–1, VC =16.5%). In the first series the O² demand (VO₂, mlO₂ • min^–1 • kg^–1) was measured in the final 30 s of 4-min runs at 7 treadmill speeds (V, 166.7 to 366.7 m • min^–1) in 12 well trained male marathon runners. After having added the anaerobic component of O₂ demand, a mean linear regression was computed: VO₂ = -11.5±4.0 + 0.232±0.018 * V , R² = 0.992±0.004 (mean ± standard deviation). The intercepts (i.e. the apparent VO₂ corresponding to V=0 or VO_{2 V0}) were linearly related to the slopes (ΔVO₂/ΔV; R=-0.71, p=0.0007). CR increased on average from 0.163±0.013 to 0.198±0.010 mlO₂ • kg^–1 • m^–1 in the range of 166.7–333.3 m • min^–1. The percent increase ranked from 10.1% to 37.4%. In the second series of experiments (18 subjects), VO_{2 V0} was inversely related to VO₂ max while the opposite was true for ΔVO₂/ΔV. Subjects with the lowest (VO₂ max) presented positive values of VO_{2 V0}. In conclusion, the widespread idea that gross CR is speed independent does not apply to all distance runners. Therefore, gross CR should be measured at race speed whenever gross CR is utilized to predict running performance.     

Maximal and submaximal oxygen uptake during running: how should body mass be accounted for?

Oxygen uptake during running, i.e., the running economy, is an important factor in determining running performance in endurance events. The relation to performance is particularly strong when the aerobic running capacity is calculated, i.e., when running economy is related to the maximal oxygen uptake. There is considerable interindividual variation in running economy, and the reason for this is only partly understood. To some extent, this may be due to the way in which the oxygen uptake during running is usually expressed. This may expecially be true when subjects with different or changing body masses are compared. Several lines of evidence, including earlier animal studies as well as more recent human studies, favor the expression of submaximal and maximal oxygen uptake during running in terms of ml · kg^−0.75· min⁻¹ rather than as ml · kg⁻¹· min^−1.     

Effects of a 30-min running performed daily after downhill running on recovery of muscle function and running economy

This study investigated the effects of a 30-min level running performed daily for 6 days after downhill running (DHR) on indicators of muscle damage and running economy (RE). Fifty men were placed into five groups – control (CON), 40%, 50%, 60% and 70% (10 subjects per group) – by matching the baseline maximal oxygen consumption () among the groups. Subjects in the 40%, 50%, 60% and 70% groups had a treadmill (0°) run for 30 min at 40%, 50%, 60% and 70% of the pre-determined , respectively, at 1–6 days after a bout of 30-min DHR at −15% (−8.5°). Maximal voluntary isometric strength of the knee extensors, muscle soreness, plasma creatine kinase and lactate dehydrogenase activities were measured before, immediately after and every day for 7 days after DHR. RE was assessed by oxygen consumption, minute ventilation, respiratory exchange ratio, lactate, heart rate and rating of perceived exertion during a 5-min level running at 85% performed before and at 2, 5 and 7 days after DHR. All muscle damage markers changed significantly (P < 0.05) after DHR without significant differences among the groups. The RE parameters showed a significant decrease in RE for 7 days after DHR, but no significant differences in the changes were evident among the groups. These results suggest that the daily running performed after DHR did not have any beneficial or adverse effects on recovery of muscle damage and RE regardless of the intensity.     

Relation of speed of a mile run, maximum energy cost of running, and maximum oxygen consumption: a field study.

OBJECTIVE: To compare the maximum energy cost of running (MECR) estimated from the speed of a mile run and the maximum oxygen consumption (VO2max) with a field step test. METHODS: MECR was defined as the maximum VO2, derived from the equation VO2 = 5.3 mph + 3.9 (ml.min-1.kg-1), when the subject performs a maximal, exhausting run and attains maximum speed. The equation is based on a straight line relation between speed and VO2. In this study MECR was obtained from a mile run and was compared with VO2max by extrapolation using a step test. Both tests were performed in the field. RESULTS AND CONCLUSIONS: The variation in the MECR with VO2max was within +/- 10%. It therefore appears that the speed of a mile run is a good criterion of VO2max or estimated MECR for the measurement of physical fitness, and for the selection, recruitment, and assignment of an individual in field sports.     

Real-time measurements of cellular oxygen consumption, pH, and energy metabolism using nuclear magnetic resonance spectroscopy.

Changes in molecular expression or apoptotic behavior, induced by malignant transformation or anticancer treatment, are frequently reflected in cellular metabolism and oxygen consumption. A technique to monitor oxygen consumption, cell physiology, and metabolism noninvasively would provide a better understanding of interactions between molecular changes and metabolism in malignant transformation and following cancer treatment. Such a system was developed in this study by adapting multinuclear MRI and spectroscopic techniques to an isolated cell perfusion system. The system was evaluated by studying the effects of two agents, carbonyl cyanide m-chlorophenylhydrazone (CCCP) which is an uncoupler of oxidative phosphorylation, and antimycin, an inhibitor of oxidative phosphorylation, on the oxygen consumption and metabolism of MCF-7 and MatLyLu cancer cell lines.     

Investigation of treadmill and overground running: Implications for the measurement of oxygen cost in children with developmental coordination disorder

Differences in the kinematics and kinetics of overground running have been reported between boys with and without developmental coordination disorder (DCD). This study compared the kinematics of overground and treadmill running in children with and without DCD to determine whether any differences in technique are maintained, as this may influence the outcome of laboratory treadmill studies of running economy in this population. Nine boys with DCD (10.3 ± 1.1 year) and 10 typically developing (TD) controls (9.7 ± 1 year) ran on a treadmill and overground at a matched velocity (8.8 ± 0.9 km/h). Kinematic data of the trunk and lower limb were obtained for both conditions using a 12-camera Vicon MX system. Both groups displayed an increase in stance time (p < 0.001), shorter stride length (p < 0.001), higher cadence (p < 0.001) and reduced ankle plantar flexion immediately after toe-off (p < 0.05) when running on the treadmill compared with overground. The DCD group had longer stance time (p < 0.009) and decreased knee flexion at mid-swing (p = 0.04) while running overground compared to their peers, but these differences were maintained when running on the treadmill. Treadmill running improved ankle joint symmetry in the DCD group compared with running overground (p = 0.019). Overall, these findings suggest that there are limited differences in joint kinematics and lower limb symmetry between overground and treadmill running in this population. Accordingly, laboratory studies of treadmill running in children with DCD are likely representative of the energy demands of running.     

Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study

This pilot study investigated whether a 10‐week running program (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics, and gear ratios. Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption () during steady‐state running, were recorded pre‐ and post‐10wkRP. decreased (8%) from pre‐10wkRP to post‐10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post‐10wkRP compared with pre‐10wkRP (10.8 ± 4.9 vs 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (P = 0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post‐10wkRP. The change in was associated with the change in alignment of the resultant GRF and leg axis (r_s = 0.88, P = 0.003). As runners became more economical, they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self‐optimization strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.     

The association between gait variability with the energy cost of walking depends on the fall status in people with multiple sclerosis without mobility aids

BackgroundFalls, gait variability and increased energy cost of walking are common in people with multiple sclerosis (PwMS). However, no studies have as yet examined this triple association in PwMS or in other neurological populations.Research questionDoes a relationship exist between gait variability, falls and the energy cost of gait in PwMS?MethodsThis cross sectional study included 88 PwMS (50 women), mean age 39.8 (S.D = 13.0) and mean disease duration of 6.2 (SD = 8.2) years since diagnosis. Energy expenditure during walking was collected via a portable metabolic device (COSMED K5, COSMED Srl, Roma, Italy). Gait variability was measured by an electronic walkway (GAITRite™). Participants were divided into groups based on fall history (fallers and non-fallers). Differences between groups in terms of energy expenditure measures and gait variability metrics were determined by the analysis of variance test. The relationship between gait variability and energy cost of walking was examined by the Pearson's correlation coefficient test.ResultsThirty-three PwMS were classified as fallers and 55 as non-fallers. Non-significant differences between groups were observed in the energy expenditure measures, including cost of walking. Fallers demonstrated higher step length variability compared with non-fallers (4.58 (S.D. = 2.42 vs. 3.40 (S.D. = 1.40); p-value = 0.005). According to the Pearson's correlation coefficient analysis, a significant relationship was found between step length variability and energy cost of walking in the non-fallers group (Rho = 0.372, P-value = 0.006) and the total group (Rho = 0.296, p-value = 0.005), but not in those PwMS with a history of falls.SignificanceWe demonstrated a significant relationship between increased gait variability and energy expenditure while walking only in MS patients without a history of falls. This is important as there is evidence of the clinical relevance of increased gait variability, poor fitness level and high risk of falling in the MS population.     

Energy cost of gait in children and the effect of speed,age, and body size

BackgroundEnergy cost (EC) of comfortable walking is often used in clinical evaluation of children with altered gait function. EC is presented as energy expenditure per kg bodyweight per meter, either in total (grossEC) or in addition to resting energy expenditure (netEC). GrossEC is considered more reliable and netEC less affected by between-subject variations in speed, age, and body size. However, the effect of the individual child’s speed on EC is rarely considered, while altered gait function may affect both speed and EC.Research questionTo what extent are grossEC and netEC affected by within-subject variation in speed and between-subject variations in speed, age, and body size?MethodsForty-two typically developing children (7–15 y) were included in this cross-sectional study. Age, height, and bodyweight were obtained. Breath-to-breath gas-exchange measures of VO₂ and VCO₂ were conducted during rest and five over-ground gait conditions: walking at slow, comfortable, and fast speed, jogging and running. All conditions lasted 3–5 min. Body surface area, non-dimensional speed, grossEC, and netEC were calculated. Regression analyses and mixed model analyses were conducted to explain the effect of speed, age, and body size on variations in EC.ResultsGrossEC showed a non-significant, concave up relation to within-subject variation in speed, with a minimum around comfortable/fast walking speed. NetEC had a strong positive linear relation to within-subject variation in speed. For each gait condition, grossEC was more affected by between-subject variations in speed, age, and body size compared to netEC. However, the effect of age and body size was not eliminated for netEC but was quadratic.SignificanceAlthough normalised to speed and bodyweight, grossEC and netEC are still affected by those factors. However, they are affected differently for within- and between-subject variations. This must be considered when interpreting EC in children in relation to gait function.     

The energy cost of level walking before and after hydro-kinesi therapy in patients with spastic paresis

In this study the energy cost of level walking was measured in 23 patients with stationary spastic paresis before and after a two-week treatment (45 min daily) of hydro-kinesi therapy, the latter consisting of passive and active movements in warm (32°C) sea water, free swimming and water immersion walking. Among the subjects (80.2±13.2 kg body mass; 56.0±14.6 years of age; 10.7±6.6 years of duration of spasticity), 12 were affected by hemiparesis, 4 by multiple sclerosis and 7 by spinal cord injury. The energy cost of level walking (C_w) was measured before and after therapy from the ratio of the overall steady-state oxygen consumption to the effective speed of progression. The differences in C_w due to the treatment, at matched speeds, were found to be negligible at speeds higher than 0.75 m · s⁻¹ (less than 5%) but to increase, with decreasing speed, up to about 17% at 0.1 m · s⁻¹. The treatment was therefore effective in improving the gait characteristics of the subjects, through a decrease of their C_w, mainly at low speeds of progression.     

急性一氧化碳中毒大鼠血小板活性的变化及其高压氧暴露的影响

目的观察急性一氧化碳中毒(ACOP)大鼠血小板活性的变化及其高压氧(HBO)暴露的影响。方法将实验动物Wistar大鼠共128只随机分成正常对照组(NC组)、一氧化碳中毒组(COP组)、一氧化碳中毒+高气压组(HPT组)及一氧化碳中毒+高压氧组(HBO组)。测定COP后1,5,10,15,20d大鼠血小板平均相对体积及血小板CD61的动态变化。结果COP后,血小板平均相对体积及血小板CD61的表达均显著升高(P<0.05),而且持续15d以上。HBO组较COP组血小板平均相对体积及血小板CD61的表达较快恢复正常(P<0.05)。HPT组与COP组相比高气压对血小板平均相对体积及血小板CD61的表达均无显著影响(P>0.05)。结论ACOP可导致血小板活性增加并持续。HBO治疗可以使其较快恢复正常。     

Measurement of pulmonary partial pressure of oxygen and oxygen depletion rate with hyperpolarized helium-3 MRI: a preliminary reproducibility study on pig model

RATIONAL AND OBJECTIVES: Pulmonary partial pressure of oxygen (pO(2)) and oxygen depletion rate (R) are two important parameters of lung function. The dependence of hyperpolarized (3)He (HP (3)He) T(1) on local oxygen concentration provides the basis for high-resolution mapping of the regional distributions of pO(2) and R in the lung. Although the oxygen-sensitive HP (3)He magnetic resonance imaging technique has been applied in human subjects and several animal species, reproducibility studies are rarely reported in the literature. This work presents a preliminary reproducibility study on a pig model. In this study, important scan parameters, such as measurement timing and flip angle, are optimized to minimize the noise-induced measurement uncertainty. MATERIALS AND METHODS: In the in vivo study, five normal pigs and one diseased pig with simulated pulmonary emboli were scanned with a small flip angle gradient echo sequence. The pulmonary oxygen measurement was repeated two to four times in each pig. In each measurement, a series of six images were acquired with optimal timing and flip angle. The parametric maps were generated using a bin-based data processing procedure that applied the multiple regression fitting method to extract the pO(2) and R. Variations of global mean, percentiles, and regions of interest were calculated from the maps to analyze reproducibility. RESULTS: The global statistical analyses show that average variation of global mean is 10.7% for pO(2) and 23.8% for R, and that the average variation of percentiles (10th, 25th, 50th, 75th, and 90th) and interquartile range is 14.8% for pO(2) and 30.4% for R. The region-of-interest analysis on the manually selected regions shows that the average variation of mean is 12.6% for pO(2) and 21.9% for R. CONCLUSION: In this work, a preliminary study on the reproducibility of measuring pO(2) and R with HP (3)He magnetic resonance imaging on a pig model is presented.     

高压氧综合治疗对颅内动脉瘤术后神经功能障碍和生活能力的康复作用

目的 观察高压氧综合康复治疗对颅内动脉瘤术后患者的神经功能缺损(NFI)和日常牛活活动能力(ADL)的影响,方法术后患者平均分为对照组和高压氧组(每组40例),对照组予常规药物和理疗、针灸治疗;高压氧组在上述治疗基础上加用高压氧治疗,观察治疗前后临床疗效、神经功能缺损评分和Barthel的ADL评分.结果 2组治疗后神经功能缺损评分较治疗前明显降低,治疗后高压氧组与对照组比较,NFI评分差异有统计学意义(分别为7.4±6.0和9.8±4.5,P<0.05);2组治疗后Barthel评分较治疗前有提高,治疗后高压氧组与对照组比较,Barthel评分差异亦有统计学意义(分别为42.7±11.6和35.3±10.4,P<0.01).高压氧治疗的疗效与开始治疗时间和Hunt-Hess动脉瘤分级有关.结论 术后早期积极地运用高压氧综合康复治疗,可使颅内动脉瘤患者神经功能和生活活动能力得到明显改善,生活质量得以提高.     

Database of normal human cerebral blood flow, cerebral blood volume, cerebral oxygen extraction fraction and cerebral metabolic rate of oxygen measured by positron emission tomography with 15O-labelled carbon dioxide or water, carbon monoxide and oxygen: a multicentre study in Japan

Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂) by positron emission tomography (PET) with oxygen-15 labelled carbon dioxide (C¹⁵O₂) or ¹⁵O-labelled water (H₂ ¹⁵O), ¹⁵O-labelled carbon monoxide (C¹⁵O) and ¹⁵O-labelled oxygen (¹⁵O₂) is useful for diagnosis and treatment planning in cases of cerebrovascular disease. The measured values theoretically depend on various factors, which may differ between PET centres. This study explored the applicability of a database of ¹⁵O-PET by examining between-centre and within-centre variation in values. Eleven PET centres participated in this multicentre study; seven used the steady-state inhalation method, one used build-up inhalation and three used bolus administration of C¹⁵O₂ (or H₂ ¹⁵O) and ¹⁵O₂. All used C¹⁵O for measurement of CBV. Subjects comprised 70 healthy volunteers (43 men and 27 women; mean age 51.8±15.1 years). Overall mean±SD values for cerebral cortical regions were: CBF=44.4±6.5 ml 100 ml^–1 min^–1; CBV=3.8±0.7 ml 100 ml^–1; OEF=0.44±0.06; CMRO₂=3.3±0.5 ml 100 ml^–1 min^–1. Significant between-centre variation was observed in CBV, OEF and CMRO₂ by one-way analysis of variance. However, the overall inter-individual variation in CBF, CBV, OEF and CMRO₂ was acceptably small. Building a database of normal cerebral haemodynamics obtained by the¹⁵O-PET methods may be practicable.     

Metabolic and vascular origins of the BOLD effect: Implications for imaging pathology and resting‐state brain function

The blood oxygenation level‐dependent (BOLD) phenomenon has profoundly revolutionized neuroscience, with applications ranging from normal brain development and aging, to brain disorders and diseases. While the BOLD effect represents an invaluable tool to map brain function, it does not measure neural activity directly; rather, it reflects changes in blood oxygenation resulting from the relative balance between cerebral oxygen metabolism (through neural activity) and oxygen supply (through cerebral blood flow and volume). As such, there are cases in which BOLD signals might be dissociated from neural activity, leading to misleading results. The emphasis of this review is to develop a critical perspective for interpreting BOLD results, through a comprehensive consideration of BOLD's metabolic and vascular underpinnings. We demonstrate that such an understanding is especially important under disease or resting conditions. We also describe state‐of‐the‐art acquisition and analytical techniques to reveal physiological information on the mechanisms underlying measured BOLD signals. With these goals in mind, this review is structured to provide a fundamental understanding of: 1) the physiological and physical sources of the BOLD contrast; 2) the extraction of information regarding oxidative metabolism and cerebrovascular reactivity from the BOLD signal, critical to investigating neuropathology; and 3) the fundamental importance of metabolic and vascular mechanisms for interpreting resting‐state BOLD measurements. J. Magn. Reson. Imaging 2015;42:231–246.