Energy system contribution in track running

[Nick]

Energy system contribution in track running Part 1

By Rob Duffield, Brian Dawson



ABSTRACT

   As a wide range of values have been suggested the relative energetics of track running events, this collection of studies aimed to quantify the respective aerobic and anaerobic energy system contribution during actual track running. Subjects performed (on separate days) a laboratory graded test and multiple race time trials. The relative energy system contribution was calculated based upon measures of race VO2 and accumulated oxygen deficit. Aerobic - anaerobic energy system contributions for male track athletes were 3000m; 86% - 14%, 1500m; 77% - 23%, 800m; 60% - 40%, 400m; 47% - 59%, 200m; 28%-72% and 100m; 20% - 80%. This data, collected during specific track running events, compares well with previous estimates of relative energy system contributions. Additionally, the relative importance and speed of interaction of the respective metabolic pathways has implications to training for these events.



Introduction

   This paper serves to review a series of studies re-investigating the relative energy system contribution to track running events between 100m and 3000m.
   The relative contribution and interaction of the respective energy systems for the provision of Adenosine tri-phosphate (ATP) during track running is of importance in order to understand the metabolic demands of an athletic event. This knowledge is useful for aiding the correct implementation of training programmes designed to optimise the metabolic production of ATP and hence achieve peak performance.
   Knowledge of energy system contribution and interaction particularly applies to events that fall within exercise durations relying heavily upon both anaerobic and aerobic metabolism. Despite near maximal or maximal utilisation of anaerobic glycolytic and phosphorylative pathways, the provision of considerable aerobic energy is also required to perform these sustained high intensity efforts. Events such as 400m, 800m and to a lesser extent 1500m track races, lasting from approximately 45 sec to 5 min (depending on ability), fall within the category of demanding heavy reliance on all three energy pathways. Furthermore, while previous research (1) may have described little involvement of aerobic metabolism in events of short durations (up to 400m), recent data has shown that the speed of the interaction of oxidative processes to the overall metabolic supply is faster than previously described (2). Hence, an understanding of the energetics of these athletic events, particularly from actual track running data, is important for evaluating the contribution of the respective energy systems involved.
   Two factors have hindered the previous quantification of the relative energy system contrib?tion to track running events. Firstly, the use of outdated methods for the measurement of anaerobic metabolism and secondly, the lack of specific data measured during track running. While early research (3) reported energy system interaction to exercise of varying durations, methods used to quantify the anaerobic energy system contribution, including O2 debt and blood lactate ([La-]B ) methods, have since been shown to be inaccurate, hence casting doubt on the reported values (see Gastin (2) for a review). Recent research has utilised the more popular (although not universally accepted) accumulated oxygen deficit (AOD) method to measure anaerobic metabolism (4), which accordingly has been applied to the measurement of energy system contribution in track running (5). However, much of the recent literature reporting the energetics of track running has measured oxygen consumption (V02) during constant-velocity treadmill running, attempting to simulate the duration of the respective track events (5,6,7). To date, no literature has reported the energy system contribution to track running events utilising direct measurement of V02 during track running events, where velocity will not be constant.
   Table 1 presents a review of the research reporting the results of aerobic and anaerobic energy system contributions to track running events from 100m to 5000m. Apart from research which has mathematically modeled energy system interaction, results in Table 1 were based on the measurement of VO2 during treadmill running, while anaerobic metabolism was measured using either the AOD or [La-]b methods. As seen, the range of percent contributions presented for the respective energy systems to track running is relatively large for most events. Disagreement between coaches, sports scientists and athletes over energy system contribution (16) is probably a result of the wide range of data available in textbooks and coaching manuals.
   Thus, while individual athletic ability (performance) may alter the measured energetics of an event, the large range in estimated values currently makes it difficult to advise coaches and athletes on the likely aerobic! anaerobic energetics of these events. Combined with this range of estimates is also the lack of data collected during actual track running events. Hence, the aim of this series of studies was to quantify the relative aerobic and anaerobic energy system contribution to track running events between 100m and 3000m, during actual simulation of races on a synthetic athletics track. The principal objective of this research was to gauge the energetic contributions from as much 'in-race' data as possible.

[Nick]

Part 2


Methods
   Ten 3000m (8 male, 2 female), 14  1500m (10 male, 4 female), 11  800m (9 male, 2 female), 16  400m (11 male, 5 female). 13  200m (8 male, 5 female) and 15  100m (9 male, 6 female) athletes were recruited as subjects for these studies. Participants were trained track athletes, ranging from club to national level, who were specialists in the event/s they acted as subjects in. Testing was performed in the Exercise Physiology Laboratory at the School of Human Movement and Exercise Science (HM and ES), University of Western Australia (UWA) and on an outdoor synthetic rubber (Rekortan) 400m athletic track.


Procedure Overview:
   All subjects performed four testing sessions, separated by at lea?t 48 hours and no more than 7 days, with time of day kept constant between testing sessions for each participant. Following initial familiarisation (test 1) with both the exercise protocol and Cosmed K4b2 measuring equipment, a second testing session involved a graded incremental (motorised) treadmill test and a run to volitional exhaustion. The final two testing sessions involved participants performing a solo time trial run over their chosen athletic distance on an outdoor 400m synthetic athletics track. Subjects were asked to refrain from the ingestion of food or caffeine 2 hours prior to all testing sessions and from engaging in physical exercise in the 24 hours prior to testing. All testing took place during the competition phase of the local athletic season. Outdoor track testing sessions were postponed if climatic conditions were too extreme (40Ã,°C < Temp < 15Ã,°C, wind> 4 m/s-l or raining).


Graded Exercise Test (GXT):
   Following a standardised warm up of 5 min treadmill running (9 -10 km/h-1) and a 5 min stretching period, subjects performed 6 - 9 stages of 4.5 - 7 min duration, separated by increasing recovery periods for each step of 4 - 7 min(5)). The treadmill was maintained at a constant 1% gradient in order to account for the energy cost involved in over ground running(17), with initial velocities of 10 - 12 km/h-1 and final velocities of 16 - 18 km/h-l (30% - 90% peak VO2). During the exercise test, expired air was analysed with a breath-by-breath portable gas analyser (Cosmed K4b2, Rome, Italy). Calibration of ventilation and fractional gas concentration measures was performed prior to each test in line with manufacturer's instructions. Following a 10 - 15 min recovery after the GXT, subjects completed an incremental run to volitional exhaustion, in order to elicit peak VO2.This run began at the penultimate treadmill velocity achieved by the subject during the previous step test and the velocity was increased by 1 km/h-1 each min until the subject reached volitional exhaustion. An average of the highest values attained over any rolling one minute period was used as the peak VO2 value.


Track sessions:
   On arrival, the subject engaged in a standardised warm up consisting of several laps jogging and 10 - 20 min stretching. Following stretching, the Polar Heart rate monitor, Cosmed K4b2 base harness and Cosmed K4b2 system were attached to the subjects' torso. The subject then performed 3 - 4 x 90-100m "run throughs" at increasing speeds before calibration procedures were employed (as previously described for the GXT). Before commencement of the time trial, a pre-race capillary blood sample from an ear lobe was obtained for the measurement of [La-]b- (Accusport blood lactate analyser, Boehringer Mannheim, Mannheim, Germany)(18). Once the subject was prepared, measurement of VO2 commenced and the subject proceeded to the start line where he/she was given standard starting commands, at which point the time trial began. Electronic infra-red timing systems (customised system, School of HM and ES, UWA, Perth, Australia) were located at the 400m (or start and finish line) and 200m (half lap) line and movement of the subject through the starting infra-red beam initiated the timing mechanism. The timing system enabled the measurement of split times and calculation of speed for each 200m as well as for the whole trial. Following completion of the time trial, Cosmed K4b2 measurement was ceased and 1,3, 5 and 7 min capillary blood samples from the ear lobe were obtained for the measurement of post exercise [La-]b' Finally, the Cosmed K4b2 system was detached from the subject and gentle cool down exercise was allowed.



Calculation of relative energy expenditure: graded step test

   For each subject, steady state (breath by breath) VO2 data were averaged over the final minute of each step (Excel 10.0). A linear regression analysis was used on the collected step test data to determine the individual VO2-velocity relationship for each subject, using custom written AOD determination software (Labview 5.1 National Instruments). This analysis allowed for the calculation of AOD (measured in ml O2 equivalents/kg-') for each time trial from calculating the difference between the O2 demand for the respective speed (from extrapolation of the calculated relationship) and the measured O2 cost.


Calculation of relative energy expenditure: track session
   For each subject, data from the fastest time trial were used in subsequent analysis. Cosmed K4b2 breath by breath data was aligned to time trial start time in order to exclude data that were not collected during the time trial. Based on the predicted VO2 from the individual VO2 - velocity relationship determined from the GXT, VO2, speed and time (over each 200m) were then used to calculate the AOD of each 200m component of the time trial. This allowed for a measurement of anaerobic (AOD) and aerobic (VO2) energy contribution for each 200m throughout the run and a total contribution over the whole time trial. Gastin et al. (19) provided support for the application of AOD methodology to non-constant, all-out supra-maximal exercise, demonstrating no differences in the calculation of AOD between all out supra- maximal and constant intensity exercise.

Statistical Analysis:
   Comparison across event distance and within event comparison of relative anaerobic energy percentage contributions, AOD, [La-]b and peak race VO2 were analysed by a two-way ANOVA. Significance was set a priori at the 0.05 level and all statistical analysis was conducted on SPSS statistical software (Version 10).

Results
   Mean (+SD) and range of values for the aerobic and anaerobic energy contribution to all time trials is presented in Table 2. Mean (+SD) values for race time, peak race VO2, peak [La-]b and AOD for all trials respectively are presented in Table 3. The interaction and change of the relative contribution by the anaerobic energy system throughout the duration of each trial is presented in Figure 1.



Conclusion
   In conclusion, this series of studies determined the aerobic - anaerobic energy system contribution to track running events (for males and females) of 3000m as 86% - 14% and 94% - 6% respectively, 1500m as 77% - 23% and 86% - 14%, 800m events as 60% - 40% and 70 - 30%, 400m as 41 % - 59% and 45% - 55%, 200m as 28% - 72% and 33% - 67% and finally 100m as 20% - 80% and 25% - .75%. This data fits well with recent previous research into the energetics of track events of these distances and provides specific applied information as to both the role and interaction of the respective metabolic pathways throughout track events from 100m to 3000m. While training status, performance and ability of an athlete may alter the energetics of any event, the use of specific track run data allows for a more relevant measurement of the relative energy system contributions to these events. Also, these studies highlight and confirm previous research outlining both the significance of and speed at which the aerobic energy system becomes involved in maximal exercise between 11 sec and 10 min. This information may be helpful to coaches and sports scientists alike for the further understanding of event energetics and it's application in the correct planning and implementation of training programmes to achieve peak athletic performance.



THE AUTHORS



Rob Duffield is a final year PhD student at the School of Human Movement and Exercise Science and is the Co-ordinator of the Centre for Athletic Testing at the University of Western Australia. He is involved in track and field i? both competitive and administrative roles.


Associate Professor Brian Dawson teaches and conducts research in exercise physiology in the School of Human Movement and Exercise Science at the University of Western Australia. He is also Research Co-ordinator for the West Coast Eagles (Australian Football League) Football Club.