This is the first study to compare the response of three metabolic energy systems during sprint exercise as affected by training among athletes of different disciplines. The main findings are (i) significant differences between relative energy systems contribution and the energy expenditure depending on sport profile (endurance, speed-power, and mixed) and (ii) the lack of clear effects of ongoing training on the energy system contribution. Thus, the results indicate that specific long-term sport adaptations, rather than ongoing training stimuli determine energy systems contribution in highly trained athletic cohorts.
In earlier studies, the contribution of energy systems (phosphagen : glycolytic : aerobic) during the standard 30-s Wingate test was 31 : 50 : 18% and 32 : 45 : 23% among rugby players [29], and judo athletes [43], respectively. Despite the fact, that the duration of the Wingate test was longer compared to our investigation, the results of those studies were similar to our mixed and speed-power groups. The substantially lower contribution of the aerobic system in our athletes was arguably due to the shorter duration of the test. Nevertheless, the glycolytic system prevailed and the phosphagen system remained second in the speed-power or resistance groups, indicating specific training-related adaptations. The average contribution of the aerobic system was ranging from 8 to 12% among our participants, which is consistent with other studies that showed values in the range of 5‒18% during sprint exercise (6‒20 s of cycling) [44, 45]. In all our groups, the combined anaerobic energy contribution was about 90% (phosphagen + glycolytic). This corresponds with the results of an earlier study by Gastin [5], who reported that during maximal 15-second exercise about 88‒90% of energy was derived from anaerobic metabolism.
Differences between athletic groups
Paradoxically, we did not confirm that speed-power athletes use anaerobic metabolism to a greater extent than endurance athletes as it was hypothesized. In a certain sense, this finding may disrupt existing beliefs and stereotypes, that athletes with an endurance-type adaptation do not utilize the phosphagen system to such an extent as those with speed-power and mixed adaptations. Surprisingly, we observed that the endurance group showed a significantly higher contribution of the phosphagen system (both absolute and percentage) compared to the mixed and speed-power groups. To the best of our knowledge, there is only one former study on energy systems contribution in endurance athletes performing short-term maximal effort. Granier et al. [46] compared sprinters and middle-distance runners in the 30-s Wingate test. They estimated the anaerobic : aerobic systems ratio to be 55:45% for endurance runners and 72:28% for sprinters [46], whereas in our speed-power and endurance athletes the combined contribution of anaerobic metabolism was as high as ~ 91%. Also, in contrast to our study, they did not obtain significant differences between the athletic groups. This discrepancy may be due to, among other things, vastly different methods to estimate the energy systems contribution, with only two main systems available in research by Granier et al. According to Serresse et al. [6], it is essential to dissociate anaerobic lactic and alactic (phosphagen) metabolism indicators. Shimoyama et al. [26] examined endurance- and sprint-type swimmers, specializing in the distances of 100- and 200-meters, during continuous vs 10-second interval swimming with different recovery times. It was found that the anaerobic contribution of endurance-type athletes was significantly higher than those of sprint-type. These findings are in agreement with the study of Jannson et al. [47], who indicated that athletes with a higher aerobic capacity might have a better ability for phosphocreatine resynthesis during interval exercise. They concluded that athletes with lower aerobic capacity are more likely to rely upon anaerobic ATP resynthesis via glycolysis [47]. The above and our research suggests, thus, that endurance-type athletes tend to utilize the phosphagen system to a greater extent than the glycolytic system in maximal short-term exercise.
The contribution of the glycolytic energy was greater in speed-power and mixed (~ 50% and ~ 54%, respectively) athletes than in the endurance group (~ 38%). One explanation may be that, in general, speed-power and mixed athletes have a greater ability to produce higher exercise-induced blood lactate concentration [46, 48, 49]. In addition, a higher percentage of fast-twitch fibers, characteristic of sprinters, is associated with higher exercise-induced blood lactate concentrations [50]. The high level of lactate shows the ability to produce energy from anaerobic lactic metabolism via glycolysis [29, 51]. One can assume that, due to a lower capacity to produce and utilize lactate in the process of glycolysis, endurance athletes rely more on ATP resynthesis via the phosphagen system during sprint exercise. When glycolytic pathways are less developed, the phosphagen system ‘replaces’ them to some extent as more efficient and available during a very short exercise of maximum intensity.
The mixed and endurance groups showed discrepancies in the contributions of phosphagen and glycolytic systems. The glycolytic system dominated in the mixed group, whereas the contribution of the two systems remained similar in speed-power athletes. This indicates that the two components of the anaerobic metabolism are more balanced in the speed-power group. This may be related to specific long-term adaptation including sprint exercise of similar duration as the test we applied, most often interspersed by full recovery intervals. The mixed group consisted of soccer players, whose competitive match plays require the ability to perform repetitively high-intensity activities with recovery intervals of unpredictable (rather short) duration [52]. Thus, team game players are usually not able to quickly restore the phosphagen system. As a result, they rely more on the glycolytic system. In contrast, endurance training and competition is based more on continuous efforts, hence, ATP resynthesis via the glycolytic system is less utilized.
In addition, while absolute peak and average power differed significantly between speed-power and endurance athletes, the weight- and muscle mass-adjusted values showed no differences between the groups. This is consistent with the observations of Davies and Sandstorm [53], who observed that maximal power and capacity were determined by body size and muscularity. This suggests that the relative muscle mechanical efficiency is a rather constant value. Our study shows that the same mechanical efficiency per kg body mass or SMM can be achieved through considerably different contributions of energy systems.
The effect of training
The second hypothesis referred to the training effect as a key factor to determine the energy systems contribution. However, our data did not clearly indicate that athletes would change the proportions of energy systems with ongoing training. Several explanations for this observation are possible. First, one can speculate that after years of specific professional training, and reaching high levels of performance, energy system contributions are strongly fixed and do not respond to standard cyclic training stimuli. In support of this view, we observed a significant change in energy systems contribution only in our amateur soccer players (decrease in aerobic metabolism contribution), but not in our international-level athletes. It seems that an athlete's energy profile appears to be more resistant to change the longer the sports career and stronger training stimuli. Perhaps if we were to study untrained individuals, the energy systems contribution would change significantly with training. This requires further research.
Another explanation may be the nature of the training phase analyzed. i.e. general preparation period. In most sports, this period is focused on overall physical fitness, strength, and conditioning, with less emphasis on specialized training loads. In particular, endurance and resistance loads are used, rather than speed-power exercises that are the basis for Wingate test performance. Thus, the lack of adequate training loads would be the reason for unchanged energy systems contribution in our high-level endurance and speed-power athletes. However, our research team demonstrated in previous studies that the blood level of key biomarkers related to energy metabolism (e.g. hypoxanthine, ammonia, and hypoxanthine-guanine phosphoribosyl-transferase) changed significantly as early as in the period of general preparation in highly trained athletes [54–56]. Thus, it seems unlikely that the multi-week regular training we analyzed in this study did not result in any metabolic adaptations, regardless of the type of load.
Given the above, it is also important to note the limitations of the measurement method used. Oxygen uptake and lactate levels are the basis for calculating the energy expenditure and contribution of the three metabolic systems. The problem is that maximal oxygen uptake and peak lactate concentration usually do not change considerably with training phases in highly trained athletes[54, 57] which is consistent with this study. Consequently, these indicators cannot be considered sufficiently sensitive biomarkers of training adaptation in top-level athletes. Possibly, changes in the proportion of energy systems were not observed because these “secondary” parameters did not change significantly in our groups (Table 3). It seems that a method based on more sensitive physiological or biochemical indicators is needed to track changes in the contribution of energy systems in high-performance athletes. Calculating the energy systems contribution via the three-component method may be a useful tool to assess and compare well-established energy profiles of sprint- or endurance-type metabolism. However, this method may be less accurate in tracking changes in the training cycle of professional athletes. In addition, one cannot exclude that the energy profile is inherited to some extent and forms the basis of early selection for sports. If so, the energy metabolism profile may be relatively constant throughout the athletic career, and its “trainability” would be low.
Practical applications
In practical terms, since there exist individual profiles of energy metabolism that may be resistant to change, the picture of energy systems contribution obtained during the specific Wingate test may be used as a supplementary diagnostic tool in selecting for a given type of sport. However, the limitations of the measurement method probably do not allow tracking changes in energy profiles in high-level athletes. The findings may provide coaches and sport scientists with specific knowledge about classification athletes to choose adequate discipline at an early or later stage of sports training.
Limitations and strengths
The inference from our study is limited to male athletic groups in their preparatory period of the annual training cycle. In the future, data should be obtained from male and female athletic cohorts during competitive phase and from untrained individuals. The novelty of this study is the comparison of athletic groups with entirely different physiological adaptations and the attempt to determine the effect of training on energy systems contribution. The added value was the inclusion of three homogenous athletic groups, including two highly-trained and one amateur group.