Paul B. Gastin

Energy System Interaction and Relative Contribution During Maximal Exercise

AbstractThere are 3 distinct yet closely integrated processes that operate together to satisfy the energy requirements of muscle. The anaerobic energy systemis divided into alactic and lactic components, referring to the processes involved in the splitting of the stored phosphagens, ATP and phosphocreatine (PCr), and the nonaerobic breakdown of carbohydrate to lactic acid through glycolysis. The aerobic energy system refers to the combustion of carbohydrates and fats in the presence of oxygen. The anaerobic pathways are capable of regenerating ATP at high rates yet are limited by the amount of energy that can be released in a single bout of intense exercise. In contrast, the aerobic system has an enormous capacity yet is somewhat hampered in its ability to delivery energy quickly. The focus of this review is on the interaction and relative contribution of the energy systems during single bouts of maximal exercise. A particular emphasis has been placed on the role of the aerobic energy system during high intensity exercise.Attempts to depict the interaction and relative contribution of the energy systems during maximal exercise first appeared in the 1960s and 1970s. While insightful at the time, these representations were based on calculations of anaerobic energy release that now appear questionable. Given repeated reproduction over the years, these early attempts have lead to 2 common misconceptions in the exercise science and coaching professions. First, that the energy systems respond to the demands of intense exercise in an almost sequential manner, and secondly, that the aerobic system responds slowly to these energy demands, thereby playing little role in determining performance over short durations. More recent research suggests that energy is derived from each of the energy-producing pathways during almost all exercise activities. The duration of maximal exercise at which equal contributions are derived from the anaerobic and aerobic energy systems appears to occur between 1 to 2 minutes and most probably around 75 seconds, a time that is considerably earlier than has traditionally been suggested.

Energy system contribution during 200- to 1500-m running in highly trained athletes.

PURPOSE The purpose of the present study was to profile the aerobic and anaerobic energy system contribution during high-speed treadmill exercise that simulated 200-, 400-, 800-, and 1500-m track running events. METHODS Twenty highly trained athletes (Australian National Standard) participated in the study, specializing in either the 200-m (N = 3), 400-m (N = 6), 800-m (N = 5), or 1500-m (N = 6) event (mean VO2 peak [mL x kg(-1)-min(-1)] +/- SD = 56+/-2, 59+/-1, 67+/-1, and 72+/-2, respectively). The relative aerobic and anaerobic energy system contribution was calculated using the accumulated oxygen deficit (AOD) method. RESULTS The relative contribution of the aerobic energy system to the 200-, 400-, 800-, and 1500-m events was 29+/-4, 43+/-1, 66+/-2, and 84+/-1%+/-SD, respectively. The size of the AOD increased with event duration during the 200-, 400-, and 800-m events (30.4+/-2.3, 41.3+/-1.0, and 48.1+/-4.5 mL x kg(-1), respectively), but no further increase was seen in the 1500-m event (47.1+/-3.8 mL x kg(-1)). The crossover to predominantly aerobic energy system supply occurred between 15 and 30 s for the 400-, 800-, and 1500-m events. CONCLUSIONS These results suggest that the relative contribution of the aerobic energy system during track running events is considerable and greater than traditionally thought.

Monitoring the athlete training response: subjective self-reported measures trump commonly used objective measures: a systematic review

Background Monitoring athlete well-being is essential to guide training and to detect any progression towards negative health outcomes and associated poor performance. Objective (performance, physiological, biochemical) and subjective measures are all options for athlete monitoring. Objective We systematically reviewed objective and subjective measures of athlete well-being. Objective measures, including those taken at rest (eg, blood markers, heart rate) and during exercise (eg, oxygen consumption, heart rate response), were compared against subjective measures (eg, mood, perceived stress). All measures were also evaluated for their response to acute and chronic training load. Methods The databases Academic search complete, MEDLINE, PsycINFO, SPORTDiscus and PubMed were searched in May 2014. Fifty-six original studies reported concurrent subjective and objective measures of athlete well-being. The quality and strength of findings of each study were evaluated to determine overall levels of evidence. Results Subjective and objective measures of athlete well-being generally did not correlate. Subjective measures reflected acute and chronic training loads with superior sensitivity and consistency than objective measures. Subjective well-being was typically impaired with an acute increase in training load, and also with chronic training, while an acute decrease in training load improved subjective well-being. Summary This review provides further support for practitioners to use subjective measures to monitor changes in athlete well-being in response to training. Subjective measures may stand alone, or be incorporated into a mixed methods approach to athlete monitoring, as is current practice in many sport settings.

Accumulated oxygen deficit during supramaximal all-out and constant intensity exercise

Two studies were conducted to test the validity of an all-out procedure for the assessment of the maximal accumulated oxygen deficit (AOD). Subjects in study 1 (N = 9; VO2max = 57 +/- 3 ml.kg-1.min-1 [+/- SEM]) completed three supramaximal efforts on a cycle ergometer. Exhaustive exercise during an all-out isokinetic procedure (mean intensity of 149% VO2max) was compared with constant intensity exercise at approximately 110% and 125% VO2max. Subjects in study 2 (N = 12; VO2max = 55 +/- 3 ml.kg-1.min-1) completed a constant intensity test to exhaustion at approximately 110% VO2max and a 90 s all-out test on a Monark friction loaded cycle ergometer (mean intensity of 143% VO2max). The AOD within each study were not significantly different (study 1:43.9, 44.1, and 42.0 ml.kg-1 for the 110%, 125%, and all-out tests; study 2: 52.1 and 51.2 ml.kg-1 for the 110% and all-out tests, respectively; P > 0.05). The total amount of work was significantly greater the longer the test, the additional work being attributed to aerobic processes. The rate of both aerobic and anaerobic energy production in the first 30 s of exercise was directly related to exercise intensity and the protocol used. The results indicate that an all-out procedure provides a valid estimate of the maximal AOD and shows potential for a more complete assessment of anaerobic ability as traditional indices of high intensity exercise performance are also obtained.

Quantification of anaerobic capacity

Anaerobic capacity may be defined as the maximal amount of ATP formed by the anaerobic processes during a single bout of maximal exercise. While several methods have been presented to measure a persons anaerobic capacity, none have become universally accepted. The muscle biopsy technique provides information on the anaerobic energy release from direct measures of ATP and CP breakdown and muscle lactate concentrations. As a practical measure of anaerobic capacity, the method may be limited, as it is an invasive, skilled technique. Furthermore, it has the limitation of measuring relative changes in concentrations, not amounts, such that the anaerobic contribution is estimated from estimates of the active muscle mass involvement. Measurement of lactate in blood after exhaustive exercise has frequently been used, but several factors suggest that, while it provides an indication of the extent of anaerobic glycolysis, it cannot be used as a quantitative measure of the anaerobic energy yield. The mean power during an all‐out effort on a bicycle ergometer has also been assumed to be a measure of anaerobic capacity, yet it provides only an indication of the ability to maintain high power outputs. Concerns over the duration of the test, the protocol and type of ergometer used and the contribution of the aerobic energy system to the energy supply also limit its validity as a measure of anaerobic capacity. The oxygen debt, defined as the recovery oxygen uptake above resting metabolic rates, has been discredited as a valid and reliable measure of the anaerobic capacity, as it is generally acknowledged that mechanisms other than the metabolism of lactate also contribute to the post‐exercise oxygen uptake. The recent work of Medbø et al. in re‐examining the issue of oxygen deficit has created considerable interest in its use as a measure of anaerobic capacity. The measurement of oxygen deficit directly depends on the accurate assessment of the energy cost of the work completed. This is not difficult during submaximal exercise, as the steady‐state oxygen uptake represents the energy costs. During exhaustive supramaximal exercise, the validity of the maximal accumulated oxygen deficit as a measure of the anaerobic capacity has been questioned, as the energy cost is estimated and not measured, either by assuming a given mechanical efficiency or by extrapolating the submaximal relationship between work intensity and oxygen uptake to supramaximal levels. Despite these theoretical objections, the maximal accumuiated oxygen deficit method remains a promising measure of the anaerobic capacity, as it provides a non‐invasive means of quantifying the anaerobic energy release during exhaustive exercise.

Influence of training status on maximal accumulated oxygen deficit during all-out cycle exercise.

AbstractThe influence of training status on the maximal accumulated oxygen deficit (MAOD) was used to assess the validity of the MAOD method during supramaximal all-out cycle exercise. Sprint trained (ST; n = 6), endurance trained (ET; n = 8), and active untrained controls (UT; n = 8) completed a 90 s all-out variable resistance test on a modified Monark cycle ergometer. Pretests included the determination of peak oxygen uptake (

Biological maturity influences running performance in junior Australian football

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Variable resistance all-out test to generate accumulated oxygen deficit and predict anaerobic capacity

O2peak) and a series (5–8) of 5-min discontinuous rides at submaximal exercise intensities. The regression of steady-state oxygen uptake on power output to establish individual efficiency relationships was extrapolated to determine the theoretical oxygen cost of the supramaximal power output achieved in the 90 s all-out test. Total work output in 90 s was significantly greater in the trained groups (P<0.05), although no differences existed between ET and ST. Anaerobic capacity, as assessed by MAOD, was larger in ST compared to ET and UT. While the relative contributions of the aerobic and anaerobic energy systems were not significantly different among the groups, ET were able to achieve significantly more aerobic work than the other two groups, while ST were able to achieve significantly more anaerobic work. Peak power and peak pedalling rate were significantly higher in ST. The results suggested that MAOD determined during all-out exercise was sensitive to training status and provided a useful assessment of anaerobic capacity. In our study sprint training, compared with endurance training, appeared to enhance significantly power output and high intensity performance over brief periods (up to 60 s), yet few overall differences in performance (i.e. total work) existed during 90 s of all-out exercise.