training timing in order to increase the overall capacity of the body represents the main form which will influence the athlete s exercise capacity .
rowing is a sport whose practice depends on the environment conditions such as the temperature , humidity , rainfall and wind . at the same time
, other forms of activities can be developed in a special surrounding that will depend much less on the environment conditions , namely , indoor practice using concept 2 ergometer type .
such practice is considered an accurate method used in order to determine the athletes exercise capacity , based on minimizing the influence of external factors such as environment , and techniques factors .
in fact , numerous studies have examined through maximal vo2max test the energy systems contribution and lactate response correlated with the effort performed [ 24 ] .
an increased number of papers have studied the energy systems , starting with a research protocol whose activity and/or intensity have been established before testing .
few papers have studied these elements under specific activity without restricting the parameters mentioned [ 56 ] . thereby it should be noted that a high intensity effort will take place over a period of 18 minutes   being related to adenosine triphosphate ( atp ) released both by anaerobic and aerobic path .
however , it is suggested that within a period of activity 90 s , the anaerobic system will provide the energy needed , while a balance within the energy systems can be observed during an intensity effort that exceeds 90 s [ 89 ] .
establishing energy efficiency in an elite group of athletes will ensure metabolic efficiency during training , reported in aerobic and anaerobic effort zone and energy distribution .
energy input during exercise will be directly proportional to the total activity time , particularly in activity groups whose completion time does not exceed 365 seconds .
a cross - sectional study was conducted in february 2016 in bucharest , romania , on a group of 16 elite male athletes after receiving verbal acceptance , from the athletes , to participate in the study and written acceptance from the administration offices .
a total of 16 elite male athletes , international level , were included in the study .
only male athletes were included in the study due to hormonal influences reported in the case of female rowers associated in different stages of the menstrual cycle .
measurements were performed through cosmed quark cpet equipment ( rome , italy ) and concept 2 ergometer ( morrisville , united states ) , applying a maximal effort test ( vo2max ) over a standard distance of 2,000 m. the following parameters were monitored : heart rate ( hr -bpm ) , respiratory exchange ratio ( rer ) , minute ventilation ( ve -l / min ) , maximum rate of oxygen consumption ( vo2 -ml / min ) , carbon dioxide elimination rate ( vco2 -ml / min ) , metabolic equivalent ( mets ) , tidal ventilation ( vt -l ) , the amount of oxygen expired ( o2exp -ml ) , amount of carbon dioxide expired ( co2exp -ml ) , end - tidal oxygen tension ( peto2 -mmhg ) , end - tidal carbon dioxide tension ( petco2 -mmhg ) , partial pressure of carbon dioxide in the arterial blood ( paco2 -mmhg ) , partial pressure of oxygen in the arterial blood ( pao2 -mmhg ) , the ratio of physiologic dead space over tidal volume ( vd / vt ) , energy expenditure ( kcal / min ) , lipid consumption ( fat g% ) , carbohydrate consumption ( cho g/% ) in order to determine the ventilatory thresholds , and the energy systems contribution during specific 2,000 m rowing distance ( atp , atp+cp , muscle glycogen ) . the vo2max test was performed after a complementary activity conducted in order to adapt the body to exercise over a total time of 20 minutes , involving both basic elements in preparing the body for effort and ergometer specific activity at a predetermined intensity ( 5585% hr ) in order to simulate technically the effort to be performed .
the test was carried out over a distance of 2,000 m without imposing a time limit for completion , or an effort developed in different intensity stages .
vo2 value , along with respiratory and metabolic parameters were determined through cosmed quark cpet equipment , while the heart rate value , representing the only cardiovascular parameter analyzed , was determined through cosmed bluetooth strip with direct transmission to the main device .
statistical indicators used were : average value ( mean ) , median value ( median ) , standard deviation ( sd ) , standard error ( se ) , and coefficient of variation ( cv ) . for data normalization shapiro - wilk test ( w )
was used . at the same time , in order to demonstrate associations type hypothesis the pearson correlation ( r ) was applied , whereas in order to determine the differences between the study groups , we applied the student t - test ( unpaired ) .
level of significance , p<0.05 was considered statistically significant , while the obtained values illustration was conducted via mean value and standard deviation ( meansd ) .
the average age was 19.692.05 years , while the anthropometric data showed an average weight of 94.4410.15 kg , and 193.16.42 cm height .
the average 2,000 m completion time , in the study group , was 366.310.25 s. therefore , muscle atp was the main form of energy , on average , over a period of 12.815.70 s. a change in the energy system occurred at an average heart rate of 148.315.15 b / min , accounting for 3.491.55% of the total energy provided during exercise .
atp+cp was the main form of energy distribution during 66.0410.17 s , up to a heart rate value of 175.86.24 b / min accounting for 18.062.99% of the total energy provided .
at the same time , the stage of aerobic energy supply is associated with accessing 100% carbohydrate , through the muscle glycogen .
this source was the main energy form over an average period of 288.0210.2 s , while the end of the effort was achieved at a mean heart rate of 190.25.71 b / min .
muscle glycogen was equivalent to 77.943.39% of the total energy provided during the race ( figure 1 ) .
thereby the total energy consumption monitored during the 2,000 m race has reached 172.616.63 kcal , represented through 41.553.99 g cho , and 0.240.49 g fat . decreased exercise time by improving 2,000 m completion time ,
was associated with increased energy consumption over a minute ( 10.473.74 kcal ) , through p=0.0038 , r=0.6797 , ci95%=0.8792 to 0.2774 .
similar actions were identified in the case of elevated rer value ( 1.0 ) , which is associated with carbohydrate consumption , being highlighted an increased total energy consumption in association with a total 2,000 m completion time under 365 s , and an increased value of over 25 kcal / min energy consumption ( p=0.0105 , r=0.6194 , ci95%=0.8532 to 0.1784 ) .
more similar results are highlighted in table i. a short activity time was associated with a higher vo2 value ( 4.970.44 l / min ) .
also , parameters such as vt ( 3.1120.4819 l ) and o2exp ( 542.788.57 ml / min ) , by relating low determined values , along with an increase co2exp value ( 123.321.33 ml / min ) were associated with a reduced effort time .
muscle atp function ( 12.815.70 s ) indicated a direct proportional increase with the final value of carbohydrates consumption during the race ( 41.553.99 g ) .
muscle atp was associated with prolonged activity time in association with increased ve ( 17615.24 l / min ) , respectively vco2 ( 5559474 ml / min ) values ( figure 2 ) .
atp rephosphorylation function ( atp+cp ) , per time unit , indicates a decrease percentage of muscle glycogen contribution , during exercise , through increased atp+cp energy system action time ( p=0.0022 , r=0.7059 , ci95%=0.8902 to 0.3233 ) .
similar results regarding atp+cp , and rer where obtained , relating a decreased total activity time within the mentioned energy system associated to rer above 1.10 .
thus , the contribution of atp+cp ( 66.0410.17 s ) associates a directly proportional increase with parameters such as vt ( 3.110.48 l ) , and o2exp ( 542.788.57 ml / min ) . at the same time , increasing energy production through atp+cp system was associated with low vo2 , vco2 , co2exp values , while pao2 value ( 113.11.99 mmhg ) dropped by increasing the energy provided through atp+cp ( p=0.0333 , r=0.5336 , ci95%=0.8141 to 0.05144 ) .
furthermore , muscle glycogen has been identified as the main aerobic energy function ( 288.0210.2 s ) .
early work efficiency was determined by relating the carbohydrates accessing hr ( 175.86.24 b / min ) , and decreased total exercise time ( 366.310.25 s ) in direct correlation with decreased vt , o2exp and co2 values .
a low respiratory rate ( rf ) associates an increased vt value ( p=0.0002 , r=0.7948 , ci95%=0.9258 to 0.4934 ) .
similar data were identified within o2exp ( p=0.0004 ) and co2exp ( p=0.0001 ) parameters , while a growth in respiratory frequency was associated to a certain increase in paco2 ( p=0.0262 ) , and pao2 ( p=0.0093 ) .
increasing ve values were correlated to an elevated vo2 ( p=0.0012 , r=0.7356 , ci95%=0.3774 to 0.9023 ) , vco2 ( p=0.0012 , r=0.7327 , ci95%=0.3720 to 0.901 ) , vt ( p=0.0105 , r=0.6192 , ci95%=0.1780 to 0.8531 ) and o2exp value ( p=0.0086 , r=0.6319 , ci95%=0.1982 to 0.8587 ) .
during this study we differentiated the energy systems in a study group represented by elite rowers .
therefore the athletes adaptation , as well as metabolic changes , during 2,000 m completion time were associated with both respiratory and metabolic parameters through the energy systems . based on our knowledge ,
this is one of the only papers that recently have studied the energy systems evolution during indoor 2,000 m race simulation [ 34,1014 ] .
the obtained results indicate an anaerobic energy system contribution , through phosphates , atp , and phosphocreatine , to a total of 33% , and an aerobic energy system contribution of 77% from the total energy demands during the 2,000 m race simulation , represented by muscle glycogen degradation during exercise , accounting similar results to those identified in the literature [ 1314 ] .
the fastest energy source identified in the study group , during exercise was represented by adenosine triphosphate hydrolization ( atp ) , an action also reported in other papers .
however due to low concentration found in the body , different mechanisms are used to maintain muscle contraction [ 1516 ] .
the first phase of the energy system is considered to be the phosphates , phosphocreatine and atp use in order to sustain energy distribution during the beginning of the effort , which is characterized through high intensity activity , and oxygen debt , related in our study to a rer above 1.0 , and an elevated carbohydrate consumption .
the following energy process relies on aerobic degradation of carbohydrates , pyruvic acid or lactic acid via glycolysis , characterized in time unit to a total of 288.0210.2 s of carbohydrate distribution reported to a rer value above 1.0 , during the 2,000 m completion time .
the third energy distribution process is the anaerobic oxidative metabolism state as involving sources represented by carbohydrates , lipids , and in some cases , proteins , in the presence of oxygen , a process which is not reported during a maximal effort , either in literature or in our study . from a practical standpoint , relating to the study , the beginning of the effort is characterized by accessing carbohydrates , due to high rer , and oxygen debt .
however , sustenance of the effort , in energy terms , will be conducted through atp and cp , but the energetic value and its effectiveness appears to be inferior compared to the aerobic pathway , due to total activity time obtained in the study group , with a reported low 2,000 m completion time in association with high atp muscle energy and muscle glycogen energy contribution .
aerobic production of energy from sources such as carbohydrates and lipids is affected by vo2 value , representing the amount of oxygen taken up by the body , aspect which is reported through the paper due to high amount of oxygen used during the effort .
moreover , the determined amount of co2 produced by the body will be directly proportional to the use of macronutrient during exercise , as in the study conducted , being possible an association between co2 , and increasing proportion of carbohydrates . in terms of energy efficiency and the body s reaction
, energy release rate will be a basic element towards determining and maintaining a high level of force , expressed through watts ( w ) . during athletes maximal effort
, the rate of glycolysis may be increased by up to 100 times compared to the rest period , the actual period of energetic activity in this system being still low .
a reduction in ph will inhibit the activity of glycolytic enzymes , having a precisely effect on reducing the rate of atp resynthesize , which , based on the obtained results , will be associated to atp resynthesis ( 66.0410.17 s ) .
however , vo2 value , during the beginning of the effort would reflect the transport of oxygen and the body s metabolic evolution . as a result ,
an elevated contribution of the aerobic system is significant during specific activity that exceeds 90 seconds , being reported a decline in the importance of anaerobic system during increased total effort time , as shown in the conducted study with a proportion of 33% of the total energy demands .
it is also seen that the anaerobic energy system will support short duration activity , especially in the beginning of the effort and the end of the 2,000 m race , while the aerobic energy system will support the mentioned effort in a much smaller proportion , due to its ability to react in relationship with the requested effort intensity in the beginning and the end of the effort .
thus , parameters such as rf , o2exp , co2exp , and vt , parameters that are proportional with the race completion time , will be proportional to the effort volume and energy system efficiency during a maximal effort . as a result ,
increasing muscle atp activity time ( s ) is associated with increased vo2 , respectively vco2 values , while increased atp+cp total activation time is correlated with increased vt and o2 values , therefore , being identified an increasing proportion of fat used during high intensity physical effort [ 20 , 27 ] .
the results of the study groups indicated a decreased total activity time by increasing the proportion of energy from muscle glycogen , through increasing the anaerobic system efficiency , and the importance of aerobic system during an effort with total activity time between 320380 seconds .
therefore , in this paper , short 2,000 m completion time was associated with increased period of muscle atp ( % /s ) , as anaerobic energy system , along with high muscle glycogen energy contribution ( % /s ) , representing the aerobic energy system , associated to a reduced amount of fat consumed during maximal effort , due to metabolic adaptation .
 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 ( 180.24.80 b / min ) , and carbohydrate consumption during the sustained effort ( 41.553.99 g ) towards determining the energy systems involved : atp ( 3.491.55% ) , atp+cp ( 18.062.99% ) , muscle glycogen ( 77.93.39% ) . as a result , completion time ( 366.310.25 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 ( 12.815.70 s ) , atp+cp ( 66.0410.17 s , and muscle glycogen ( 2959.5 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 . 
Introduction
Hypothesis
Method
Results
Discussion
Conclusions