Energy System Contribution Research Articles

Energy systems efficiency influences the results of 2,000 m race simulation among elite rowers.

HypothesisEnergy efficiency within an elite group of athletes will ensure metabolic adaptation during training.ObjectivesTo identify energy system efficiency and contribution according to exercise intensity, and performance obtained during a 2,000 m race simulation in an elite group of rowers.MethodAn observational cross-sectional study was conducted in February 2016 in Bucharest, Romania, on a group of 16 elite rowers. Measurements were performed through Cosmed Quark CPET equipment, and Concept 2 ergometer, by conducting a VO2max test over a standard rowing distance of 2,000 m. The analyzed parameters during the test were: HR (bpm), Rf (b/min), VE (l/min), VO2 (ml/min), VCO2 (ml/min), VT (l), O2exp (ml), CO2exp (ml), RER, PaCO2 (mmHg), PaO2 (mmHg), Kcal/min, FAT (g), CHO (g), from which we determined the ventilatory thresholds, and the energy resource used during the specific 2,000 m rowing distance (ATP, ATP+CP, muscle glycogen).ResultsWe performed an association between HR (180.2±4.80 b/min), and carbohydrate consumption during the sustained effort (41.55±3.99 g) towards determining the energy systems involved: ATP (3.49±1.55%), ATP+CP (18.06±2.99%), muscle glycogen (77.9±3.39%). As a result, completion time (366.3±10.25 s) was significantly correlated with both Rf (p=0.0024), and VO2 (p=0.0166) being also pointed out that ≥5 l VO2 value is associated with an effort time of ≤360 s. (p=0.040, RR=3.50, CI95%=1.02 to 11.96). Thus, the average activation time among muscle ATP (12.81±5.70 s), ATP+CP (66.04±10.17 s, and muscle glycogen (295±9.5 s) are interrelated, and significantly correlated with respiratory parameters.ConclusionsDecreased total activity time was associated with accessing primary energy source in less time, during effort, improving the body energy power. Its effectiveness was recorded by early carbohydrates access, as a primary energy source, during specific activity performed up to 366 seconds.

Results of intensity variable effort on condition of Polish National Team cross country MTB cyclists

Introduction Selection of endurance test for cyclist, which reflects most precisely training or starting is very complicated. Accurate evaluation of endurance warrants pricise indication of training load (Lucia et all 2004). Alteration of training load is pricesly correlated with periodization of training load (RA¸nnestad, Hansen 2014) and is result of various training goals set for respective traning periods (RA¸nnestad et all 2014). Purpose of this study was establishing training load during general and special preparatory periods in cross country cyclists. Double testing procedurA™ for endurance testing was used to verify different intensity zone parameters.  Methods Subjects for this study were cyclits MTB Cross Country team. Women (n=3), age: 28,5±2,3 years old, body mass: 54,1±2,2 kg, body height: 171,8±2,4 cm and men cyclists (n=5), age: 29,3±4,8 years old, body weight: 64,1±4,7 kg, body height: 178,6±3,4 cm, All studies were medalists of Olimpic Games, World and Europe Championships Test were performed at the beginning of 12-week general and special preparatory period. The participants of the study performer graded incremental exercise test (GXTs). The GXTs test was executed on ergometer Cyclus 2 (RBM, Germany). The I-st step was 1Wxkg-1 b.m. and increased every 3 minutes by 0,5 Wxkg-1 b.m. In last 30 the seconds of every exercise grade was taken 20 µl of arterialized blood to the sign LA (Biosen S-line, EKF, Germany). In the course of effort VO2, VE, VCO2 was measured by means of K4b2 analyser. The heart rate monitor, Polar V650 (Polar Finland ) measured HR during GXTs. At the level of aerobic threshold (LT) (Farell et al. 1979), anaerobic threshold (AT) (Powers et al. 1983) i VO2max. the power value was set. After this subjects performer 60-minute effort characterized by: 10minutes at 50% PVO2max, 5 minutes at 75% PVO2max, 5 minutes at 90% PVO2max, 10 minutes at 50% PVO2max, 10 minutes at 75% PVO2max, 5 minutes at 90% PVO2max, 6 minutes at 75% PVO2max, 5 minutes 50% PVO2max and 4 minutes at 100% PVO2max.  Results In table 1 presented are results of graded incremental endurance test. Table 2 presents results of 60-minutes variable-intensity endurance test. This efforts reflects loads of special training based on intensity and proportions which is used in cross country cycling. It allows to evaluate changes in endurance as results of applied training load. In both tested groups it was observed during graded test statistically significant increase (p≤ .001 - 0.005) of VO2max induced during preparatory period. Other parameters i.e. HRmax and HR at aerobic and anaerobic threshold has not been changed significantly. Analysis of maximal values obtained during 60-minute test revealed reduced values of maximal LA, VE and HR after general preparatory period. With constant intensity in each preparatory period it was observed adaptation of energy system contribution to performer affort. Partially anaerobic effort was replaced by aerobic effort. Results of this study shown that first 6 weeks of preparatory period improved aerobic capacity and follwoing 6-week period increased level of anaerobic values.  Conclusions 60-minute variable effort has served 2 planned in this study purposes. It has evaluated direction and range of changes in subsequent preparatory periods on following values: VO 2 max, VEmax i HRmax. Intensity zones after general preparatory period are too low to evaluate effectivness of training for general and special preparatory period. Training efforts lasting 60 minutes consisting of: 21 minutes at 50% PCr, 26 minutes at 75% PCr, 10 minutes at 90% PCr and 3 minutes at intensity of 100% PCr allows to observe effort which reflects specific cross country cycling effort. It also allows observe changes in endurance parameters during preparatory period. In order to use this test for purpiose of verification of training intensity zones, it is required to performing test and establishing parameters used in graded endurance test.

Performance and energy systems contributions during upper-body sprint interval exercise.

The main purpose of this study was to investigate the performance and energy systems contribution during four upper-body Wingate tests interspersed by 3-min intervals. Fourteen well-trained male adult Judo athletes voluntarily took part in the present study. These athletes were from state to national level, were in their competitive period, but not engaged in any weight loss procedure. Energy systems contributions were estimated using oxygen uptake and blood lactate measurements. The main results indicated that there was higher glycolytic contribution compared to oxidative (P<0.001) during bout 1, but lower glycolytic contribution was observed compared to the phosphagen system (adenosine triphosphate-creatine phosphate, ATP-PCr) contribution during bout 3 (P<0.001), lower glycolytic contribution compared to oxidative and ATP-PCr (P<0.001 for both comparisons) contributions during bout 4 and lower oxidative compared to ATP-PCr during bout 4 (P=0.040). For the energy system contribution across Wingate bouts, the ATP-PCr contribution during bout 1 was lower than that observed during bout 4 (P=0.005), and the glycolytic system presented higher percentage contribution in the first bout compared to the third and fourth bouts (P<0.001 for both comparisons), and higher percentage participation in the second compared to the fourth bout (P<0.001). These results suggest that absolute oxidative and ATP-PCr participations were kept constant across Wingate tests, but there was an increase in relative participation of ATP-PCr in bout 4 compared to bout 1, probably due to the partial phosphocreatine resynthesis during intervals and to the decreased glycolytic activity.

Karate Kumite: How to Optimize Performance - Análisis de libro

&lt;p&gt;This work reviews the book entitled &lt;em&gt;Karate Kumite: How to Optimize Performance&lt;/em&gt;, edited in English by Helmi Chaabane, PhD., in 2015. The book is composed of five chapters and a total of seven authors participate in it. The first chapter, “Performance Analysis in Karate”, analyzes the temporal structure of combat. The second chapter, “Physiological Characteristics of Karate Athletes and Karate-Specific Tasks” describes the cost and contribution of energy systems, cardiovascular response, blood lactate and hormonal response to combat. The third chapter, “Physical Determinants of Karate Kumite”, analyzes the muscular power, maximum strength, acceleration, speed, reaction time and flexibility of karate. The fourth chapter, “Training Load Monitoring”, describes different methods for monitoring the internal load. Finally the last chapter, “Physical and Physiological Assessment”, presents general and specific tests used in karate. The sound research background of the authors, as well as the extensive use of up to date literature, results in a book of high scientific value. In addition, this is a digital, open-access book that can be accessed without restriction. In conclusion, this is a highly recommended book for coaches, practitioners and professionals related to karate.&lt;/p&gt;

Correction: Caffeine Ingestion Increases Estimated Glycolytic Metabolism during Taekwondo Combat Simulation but Does Not Improve Performance or Parasympathetic Reactivation

[This corrects the article DOI: 10.1371/journal.pone.0142078.].

The Effects of Recovery Frequency On V[Combining Dot Above]O2, Muscle Deoxygenation, And Energy System Contribution During Intermittent Work

The Effects of Recovery Frequency On V[Combining Dot Above]O2, Muscle Deoxygenation, And Energy System Contribution During Intermittent Work

RESIDENTIAL SOLAR ENERGY POTENTIAL FOR PUBLIC DISSEMINATION: A CASE STUDY IN CONCEPCIÓN, CHILE

This paper presents a method for estimating the solar capture capacity of dwellings using the central urban area of Concepción, Chile, as a case study in order to promote self-generation of energy by residents. The method takes into account the growing domestic energy demand and the possibility of meeting this demand through integrated solar energy collection into buildings using different systems. The methodology considers a study of the potential incoming solar radiation on buildings according to their geographical location and the surrounding buildings. The capacity for solar capture is then estimated for different dwelling types according to their morphology. Subsequently, the energy contribution provided by different technologies (solar thermal, photovoltaic and hybrid) is identified in relation to the main average energy demands for electricity, water and space heating. Finally, systems for each dwelling are recommended in an urban map available online. The development is based on climate information, cartography, aerial photographs, surveys, housing models, technical standards, standardised calculations and dynamic simulations, implemented according to building layouts from an online Geographic Information System (GIS). The housing types are categorised in an urban map that relates household demands and the contribution of different solar energy systems. According to the estimates calculated, the residential units in the study offer sufficient solar capacity to supply between 40 and 60% of their energy consumption, especially in detached houses using roof-mounted hybrid systems.

Energy system contributions and determinants of performance in sprint cross-country skiing.

To improve current understanding of energy contributions and determinants of sprint-skiing performance, 11 well-trained male cross-country skiers were tested in the laboratory for VO2max , submaximal gross efficiency (GE), maximal roller skiing velocity, and sprint time-trial (STT) performance. The STT was repeated four times on a 1300-m simulated sprint course including three flat (1°) double poling (DP) sections interspersed with two uphill (7°) diagonal stride (DS) sections. Treadmill velocity and VO2 were monitored continuously during the four STTs and data were averaged. Supramaximal GE during the STT was predicted from the submaximal relationships for GE against velocity and incline, allowing computation of metabolic rate and O2 deficit. The skiers completed the STT in 232±10s (distributed as 55±3% DP and 45±3% DS) with a mean power output of 324±26W. The anaerobic energy contribution was 18±5%, with an accumulated O2 deficit of 45±13mL/kg. Block-wise multiple regression revealed that VO2 , O2 deficit, and GE explained 30%, 15%, and 53% of the variance in STT time, respectively (all P<0.05). This novel GE-based method of estimating the O2 deficit in simulated sprint-skiing has demonstrated an anaerobic energy contribution of 18%, with GE being the strongest predictor of performance.

GEDAE-LaB: A Free Software to Calculate the Energy System Contributions during Exercise.

PurposeThe aim of the current study is to describe the functionality of free software developed for energy system contributions and energy expenditure calculation during exercise, namely GEDAE-LaB.MethodsEleven participants performed the following tests: 1) a maximal cycling incremental test to measure the ventilatory threshold and maximal oxygen uptake (O2max); 2) a cycling workload constant test at moderate domain (90% ventilatory threshold); 3) a cycling workload constant test at severe domain (110% O2max). Oxygen uptake and plasma lactate were measured during the tests. The contributions of the aerobic (AMET), anaerobic lactic (LAMET), and anaerobic alactic (ALMET) systems were calculated based on the oxygen uptake during exercise, the oxygen energy equivalents provided by lactate accumulation, and the fast component of excess post-exercise oxygen consumption, respectively. In order to assess the intra-investigator variation, four different investigators performed the analyses independently using GEDAE-LaB. A direct comparison with commercial software was also provided.ResultsAll subjects completed 10 min of exercise at moderate domain, while the time to exhaustion at severe domain was 144 ± 65 s. The AMET, LAMET, and ALMET contributions during moderate domain were about 93, 2, and 5%, respectively. The AMET, LAMET, and ALMET contributions during severe domain were about 66, 21, and 13%, respectively. No statistical differences were found between the energy system contributions and energy expenditure obtained by GEDAE-LaB and commercial software for both moderate and severe domains (P > 0.05). The ICC revealed that these estimates were highly reliable among the four investigators for both moderate and severe domains (all ICC ≥ 0.94).ConclusionThese findings suggest that GEDAE-LaB is a free software easily comprehended by users minimally familiarized with adopted procedures for calculations of energetic profile using oxygen uptake and lactate accumulation during exercise. By providing availability of the software and its source code we hope to facilitate future related research.

Oxygen Uptake, Acid-Base Balance and Anaerobic Energy System Contribution in Maximal 300 – 400 M Running In Child, Adolescent and Adult Athletes

1.1 Objective: The purpose of this study was to investigate oxygen uptake, acid-base balance and energy system contributions during and after short maximal running in adult (n = 8), adolescent (n = 8) and child (n = 8) male athletes. 1.2 Methods: The tests included a maximal time trial of 400 m, 350 m and 300 m for different age groups respectively and a VO2max running test on a 200 m indoor track. Capillary blood samples to analyse pH and lactate were taken before and after the time trial. Energy system contributions were estimated using the accumulated oxygen deficit (AOD) method. 1.3 Results: Peak oxygen uptake (VO2peak) during the time trial was the lowest in children (53.1 ± 4.6 ml/kg/min) compared to adolescents (59.9 ± 3.7 ml/kg/min, P < 0.01) and to adults (60.7 ± 2.4 ml/kg/min, P < 0.01). After the time trial minimal blood pH was the lowest in adults (6.97 ± 0.06) compared to adolescents (7.14 ± 0.07, P < 0.05) and children (7.18 ± 0.03, P < 0.001) and maximal blood lactate was the greatest in adults (17.4 ± 1.8 mmol/l) compared to adolescents (13.3 ± 3.7 mmol/l, P < 0.05) and children (10.2 ± 1.1mmol/l, P < 0.01). The estimated anaerobic energy percentage during the time trial was the greatest in adults (53 ± 5 %) compared to adolescents (44 ± 7 %, P < 0.05) and children (45 ± 5 %, P < 0.05). 1.4 Conclusion: The present data demonstrated that adult and adolescent male athletes achieved greater oxygen uptake than child athletes during maximal 52–54 s running and adult athletes used mainly anaerobic energy and achieved greater acidosis than adolescents and children, who used mainly aerobic energy.

Caffeine Ingestion Increases Estimated Glycolytic Metabolism during Taekwondo Combat Simulation but Does Not Improve Performance or Parasympathetic Reactivation.

ObjectivesThe aim of this study was to evaluate the effect of caffeine ingestion on performance and estimated energy system contribution during simulated taekwondo combat and on post-exercise parasympathetic reactivation.MethodsTen taekwondo athletes completed two experimental sessions separated by at least 48 hours. Athletes consumed a capsule containing either caffeine (5 mg∙kg-1) or placebo (cellulose) one hour before the combat simulation (3 rounds of 2 min separated by 1 min passive recovery), in a double-blind, randomized, repeated-measures crossover design. All simulated combat was filmed to quantify the time spent fighting in each round. Lactate concentration and rating of perceived exertion were measured before and after each round, while heart rate (HR) and the estimated contribution of the oxidative (WAER), ATP-PCr (WPCR), and glycolytic (W[La-]) systems were calculated during the combat simulation. Furthermore, parasympathetic reactivation after the combat simulation was evaluated through 1) taking absolute difference between the final HR observed at the end of third round and the HR recorded 60-s after (HRR60s), 2) taking the time constant of HR decay obtained by fitting the 6-min post-exercise HRR into a first-order exponential decay curve (HRRτ), or by 3) analyzing the first 30-s via logarithmic regression analysis (T30).ResultsCaffeine ingestion increased estimated glycolytic energy contribution in relation to placebo (12.5 ± 1.7 kJ and 8.9 ± 1.2 kJ, P = 0.04). However, caffeine did not improve performance as measured by attack number (CAF: 26. 7 ± 1.9; PLA: 27.3 ± 2.1, P = 0.48) or attack time (CAF: 33.8 ± 1.9 s; PLA: 36.6 ± 4.5 s, P = 0.58). Similarly, RPE (CAF: 11.7 ± 0.4 a.u.; PLA: 11.5 ± 0.3 a.u., P = 0.62), HR (CAF: 170 ± 3.5 bpm; PLA: 174.2 bpm, P = 0.12), oxidative (CAF: 109.3 ± 4.5 kJ; PLA: 107.9 kJ, P = 0.61) and ATP-PCr energy contributions (CAF: 45.3 ± 3.4 kJ; PLA: 46.8 ± 3.6 kJ, P = 0.72) during the combat simulation were unaffected. Furthermore, T30 (CAF: 869.1 ± 323.2 s; PLA: 735.5 ± 232.2 s, P = 0.58), HRR60s (CAF: 34 ± 8 bpm; PLA: 38 ± 9 bpm, P = 0.44), HRRτ (CAF: 182.9 ± 40.5 s, PLA: 160.3 ± 62.2 s, P = 0.23) and HRRamp (CAF: 70.2 ± 17.4 bpm; PLA: 79.2 ± 17.4 bpm, P = 0.16) were not affected by caffeine ingestion.ConclusionsCaffeine ingestion increased the estimated glycolytic contribution during taekwondo combat simulation, but this did not result in any changes in performance, perceived exertion or parasympathetic reactivation.

The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution.

We examined the effects of inserting 3-s recovery periods during high-intensity cycling exercise at 25-s and 10-s intervals on pulmonary oxygen uptake (V̇o2p), muscle deoxygenation [deoxyhemoglobin (HHb)], their associated kinetics (τ), and energy system contributions. Eleven men (24 ± 3 yr) completed two trials of three cycling protocols: an 8-min continuous protocol (CONT) and two 8-min intermittent exercise protocols with work-to-rest periods of 25 s to 3 s (25INT) and 10 s to 3 s (10INT). Each protocol began with a step-transition from a 20-W baseline to a power output (PO) of 60% between lactate threshold and maximal V̇o2p (Δ60). This PO was maintained for 8 min in CONT, whereas 3-s periods of 20-W cycling were inserted every 10 s and 25 s after the transition to Δ60 in 10INT and 25INT, respectively. Breath-by-breath gas exchange measured by mass spectrometry and turbine and vastus lateralis [HHb] measured by near-infrared spectroscopy were recorded throughout. Arterialized-capillary lactate concentration ([Lac-]) was obtained before and 2 min postexercise. The τV̇o2p was lowest (P < 0.05) for 10INT (24 ± 4 s) and 25INT (23 ± 5 s) compared with CONT (28 ± 4 s), whereas HHb kinetics did not differ (P > 0.05) between conditions. Postexercise [Lac-] was lowest (P < 0.05) for 10INT (7.0 ± 1.7 mM), was higher for 25INT (10.3 ± 1.9 mM), and was greatest in CONT (14.3 ± 3.1 mM). Inserting 3-s recovery periods during heavy-intensity exercise speeded V̇o2p kinetics and reduced overall V̇o2p, suggesting an increased reliance on PCr-derived phosphorylation during the work period of INT compared with an identical PO performed continuously.NEW & NOTEWORTHY We report novel observations on the effects of differing heavy-intensity work durations between 3-s recovery periods on pulmonary oxygen uptake (V̇o2p) kinetics, muscle deoxygenation, and energy system contributions. Relative to continuous exercise, V̇o2p kinetics are faster in intermittent exercise, and increased frequency of 3-s recovery periods improves microvascular O2 delivery and reduces V̇o2p and arterialized-capillary lactate concentration. The metabolic burden of identical intensity work is altered when performed intermittently vs. continuously.

Energy System Contribution During Maximal Incremental Test as an Indicator of Endurance Performance

Energy System Contribution During Maximal Incremental Test as an Indicator of Endurance Performance

Physiological responses to karate specific activities

Summary Objectives The aim of this critical review was to discuss performance analysis characteristics and particular physiological demands related to karate kata and kumite. News The intermittent nature of karate has been revealed via kumite's time-motion analysis, with a 1:1.5 effort-pause ratio during official competition. Karate combat is mainly dependent on the aerobic metabolism. However, decisive actions’ energy is provided by the anaerobic system. Concerning kata, it seems that the fraction of the energy supply is mainly a function of kata's duration. The high-energy phosphate seems to be the major contributors while the aerobic energy system’ participation rises with the increased kata's duration. Prospects and projects Future investigations in an ecologically valid environment are needed to support the findings presented in the current review. Conclusion Irrespective of karate's discipline, the aerobic system represents the main energy system, especially in longer kata. Kumite appears to demand much higher metabolic power than kata, regardless of gender, while kata appears to require more ATP-PCr energy system contribution than kumite.

Aerobic and anaerobic determinants of repeated sprint ability in team sports athletes.

The aim of this study was to examine in team sports athletes the relationship between repeated sprint ability (RSA) indices and both aerobic and anaerobic fitness components. Sixteen team-sport players were included (age, 23.4 ± 2.3 years; weight, 71.2 ± 8.3 kg; height, 178 ± 7 cm; body mass index, 22.4 ± 2 kg · m−2; estimated VO2max, 54.16 ± 3.5 mL · kg−1 · min−1). Subjects were licensed in various team sports: soccer (n = 8), basketball (n = 5), and handball (n = 3). They performed 4 tests: the 20 m multi-stage shuttle run test (MSRT), the 30-s Wingate test (WingT), the Maximal Anaerobic Shuttle Running Test (MASRT), and the RSA test (10 repetitions of 30 m shuttle sprints (15 + 15 m with 180° change of direction) with 30 s passive recovery in between). Pearson's product moment of correlation among the different physical tests was performed. No significant correlations were found between any RSA test indices and WingT. However, negative correlations were found between MASRT and RSA total sprint time (TT) and fatigue index (FI) (r = -0.53, p < 0.05 and r = -0.65, p < 0.01, respectively). No significant relationship between VO2max and RSA peak sprint time (PT) and total sprint time (TT) was found. Nevertheless, VO2max was significantly correlated with the RSA FI (r = -0.57, p < 0.05). In conclusion, aerobic fitness is an important factor influencing the ability to resist fatigue during RSA exercise. Our results highlighted the usefulness of MASRT, in contrast to WingT, as a specific anaerobic testing procedure to identify the anaerobic energy system contribution during RSA.

VO₂ kinetics and metabolic contributions during full and upper body extreme swimming intensity.

Our purpose was to characterize the oxygen uptake ([Formula: see text]) kinetics, assess the energy systems contributions and determine the energy cost when swimming front crawl at extreme intensity. Complementarily, we compared swimming full body with upper body only. Seventeen swimmers performed a 100 m maximal front crawl in two conditions: once swimming with full body and other using only the upper propulsive segments. The [Formula: see text] was continuously measured using a telemetric portable gas analyser (connected to a respiratory snorkel), and the capillary blood samples for lactate concentration analysis were collected. A sudden increase in [Formula: see text] in the beginning of exercise, which continuously rose until the end of the bout (time: 63.82 ± 3.38 s; [Formula: see text]: 56.07 ± 5.19 ml min(-1) kg(-1); [Formula: see text] amplitude: 41.88 ± 4.74 ml min(-1) kg(-1); time constant: 12.73 ± 3.09 s), was observed. Aerobic, anaerobic lactic and alactic pathways were estimated and accounted for 43.4, 33.1 and 23.5 % of energy contribution and 1.16 ± 0.10 kJ m(-1) was the energy cost. Complementarily, the absence of lower limbs lead to a longer time to cover 100 m (71.96 ± 5.13 s), slower [Formula: see text] kinetics, lower aerobic and anaerobic (lactic and alactic) energy production and lower energy cost. Despite the short duration of the event, the aerobic energy contribution covers about 50 % of total metabolic energy liberation, highlighting that both aerobic and anaerobic energy processes should be developed to improve the 100 m swimming performance. Lower limbs action provided an important contribution in the energy availability in working muscles being advised its full use in this short duration and very high-intensity event.

Prior low- or high-intensity exercise alters pacing strategy, energy system contribution and performance during a 4-km cycling time trial.

We analyzed the influence of prior exercise designed to reduce predominantly muscle glycogen in either type I or II fibers on pacing and performance during a 4-km cycling time trial (TT). After preliminary and familiarization trials, in a randomized, repeated-measures crossover design, ten amateur cyclists performed: 1) an exercise designed to reduce glycogen of type I muscle fibers, followed by a 4-km TT (EX-FIB I); 2) an exercise designed to reduce glycogen of type II muscle fibers, followed by a 4-km TT (EX-FIB II) and; 3) a 4-km TT, without the prior exercise (CONT). The muscle-glycogen-reducing exercise in both EX-FIB I and EX-FIB II was performed in the evening, ∼12 h before the 4-km TT. Performance time was increased and power output (PO) was reduced in EX-FIB I (432.8±8.3 s and 204.9±10.9 W) and EX-FIB II (428.7±6.7 s and 207.5±9.1 W) compared to CONT (420.8±6.4 s and 218.4±9.3 W; P<0.01), without a difference between EX-FIB I and EX-FIB II (P>0.05). The PO was lower in EX-FIB I than in CONT at the beginning and middle of the trial (P<0.05). The mean aerobic contribution during EX-FIB I was also significantly lower than in CONT (P<0.05), but there was no difference between CONT and EX-FIB II or between EX-FIB I and EX-FIB II (P>0.05). The integrated electromyography was unchanged between conditions (P>0.05). Performance may have been impaired in EX-FIB I due a more conservative pacing at the beginning and middle, which was associated with a reduced aerobic contribution. In turn, the PO profile adopted in EX-FIB II was also reduced throughout the trial, but the impairment in performance may be attributed to a reduced glycolytic contribution (i.e. reduced lactate accumulation).

Energy system contribution and correlates to performance in a 2000 m rowing ergometry time trial in South African rowers

Energy system contribution and correlates to performance in a 2000 m rowing ergometry time trial in South African rowers Exercise physiologists and coaches frequently base training objectives on physical and physiological demands of sports, including relative contributions of energy supply mechanisms during the activity. Oxidative and non-oxidative metabolic contributions to 2000 m rowing ergometry have been studied previously in rowers of various abilities and using different methods, but never on a group of elite athletes. The results of this study have practical implications for athlete profiling, sport classification and time trial performance interpretation.

Assessment of reactive power contribution of photovoltaic energy systems on voltage profile and stability of distribution systems

This paper studies the impact of large-scale photovoltaic (PV) generation, up to 50% penetration level, on distribution system voltage regulation and voltage stability. The system voltage profiles are computed using power-flow calculations with load variation of a 24-h time scale. The steady-state voltage stability is examined at different times of the day using a developed continuation power-flow method with demand as continuation parameter and up to the maximum loading conditions. The load-flow analysis, implemented for both voltage regulation and voltage stability analysis, is performed by using the forward/backward sweep method. The secant predictor technique is developed for predicting the node voltages which are then corrected using the load flow solver. Three models of the PV interface inverter are implemented in this study with full set of data representing environmental conditions. The voltage profiles are regulated using the PV interface inverters, where the available inverter capacity is utilized for regulating the system node voltages. The most possible scenarios of system voltage collapse are investigated at different times of the study period. The developed methods and models are used to assess the performance of a 33-bus radial distribution feeder which operates with a high level of PV penetration. The results show that the PV interface inverters operate for reactive power support in distribution system resulting in improved voltage profile, secure power systems operation, and increasing the lifetime of the online tap changing transformers due to minimizing the total number of switching operations.

Comparison Between Swimming VO2peak and VO2max at Different Time Intervals

Accepting that the evaluation of the aerobic energy system contribution is very important for swimming training diagnostics purposes and that oxygen uptake kinetics (VO2) is one of the most used parameters in that task, we purposed to assess the variability of the peak VO2 and VO2max values obtained in a 200 m front crawl effort, using five different presentation intervals: breath-by-breath and average of 5, 10, 15, and 20 s. Ten male high-level swimmers performed a 200 m front crawl effort at maximal velocity being attached to a respiratory valve that allowed to directly measure the breath-by-breath VO2 kinetics. VO2 peak was accepted as the highest single value on breath-by-breath sampling and VO2max was considered as the average values of the 5, 10, 15 and 20 s sampling obtained during the test. The obtained VO2peak and VO2max mean values in breath-by-breath and averaged 5 s sampling were similar to those described in the literature for experienced male competitive swimmers. Higher VO2 values were observed for breath-by-breath sampling, being observed differences between that data acquisition method and all the other time intervals (5, 10, 15 and 20 s). Differences were also visible between the 5 s averaging and the other less frequent data acquisitions considered (10, 15 and 20 s), evidencing that less frequent sampling frequencies underestimate the VO2max values. More future research about this topic, also conducted in real competition conditions, i.e., in swimming-pool (not in running or cycle ergometers) is needed.