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Novel track field test to determine Vpeak, relationship with treadmill test and 10-km running performance in trained endurance runners

Objectives The aim of this study was to determine the peak running velocity on the track field (Vpeak_TF) based on the laboratory treadmill test (Vpeak_T), and relate the Vpeak values as well as their correlation with the 10-km running performance in trained endurance runners. Method Twenty male trained endurance runners (age: 29.5 ± 5.3 years; V̇O2max: 67.5±17.6 ml · kg-1·min-1) performed three maximum incremental tests to determine the Vpeak: one for Vpeak_T determination and two to obtain Vpeak_TF on the official track field (400 m), and a 10-km running performance. During the incremental tests, maximum heart rate (HRmax), maximal rating of perceived exertion (RPEmax), and peak lactate concentration (LApeak) were determined. Results The results showed significant difference between the Vpeak_TF and Vpeak_T (18.1 ± 1.2 vs. 19.2 ± 1.5 km·h-1, respectively), as well as the total time of the tests, the distance traveled and the RPEmax determined during the tests. A high correlation was observed between the Vpeak values (r = 0.94), and between Vpeak_TF and Vpeak_T with 10-km running performance (r = -0.95 vs. r = -0.89, respectively). Conclusions The good agreement and association with Vpeak_T and high correlation with 10-km running performance demonstrate that the novel track field test is efficient for Vpeak_TF determination.


Introduction
The assessment of aerobic variables for the prescription of endurance running is important when considering the training process [1,2], to determine possible adaptations and prescriptions of training intensities. Although these variables are generally determined in laboratories under controlled conditions [3,4], the applicability of the results in daily practice conditions is still questionable [5]. Therefore, it is more practical and ecological to determine the variables in an environment directly related to training practice using track field tests [5,6].
The peak running velocity (V peak ) is considered an indicator of aerobic fitness, is highly reproducible when determined on treadmill [7], has a high correlation with endurance running performance [8][9][10] and is sensitive to the training effects [11][12][13].
Despite the effectiveness of this test in determining Peak running velocity on the laboratory treadmill test V peak _ T , it is usually performed under laboratory conditions, which tend to relatively deviate from the reality of training and competition for runners [5,8,9]. Small differences in the V peak values could impair the entire training program and underestimate or overestimate the required exercise intensity [14][15][16]. However, some studies have not compared V peak _ T with the V peak obtained on the track field (V peak _ TF ) test based on this wellestablished laboratory treadmill test [8,9].
Previous studies have compared variables commonly used for endurance training prescription and monitoring (i.e., maximum aerobic speed-MAS, V peak ) which were determined during maximum incremental running tests performed on the treadmill and track field [6,17,18]. However, it should be noted that the studies mentioned above used different designs. Thus, the determination of the V peak_TF , as well as its relationship with V peak_T and endurance running performance, has not yet been determined using a well-established laboratory treadmill test. To the best of our knowledge, this is the first study that determined the V peak in trained endurance runners on the track field using the same protocol established for the treadmill in the design proposed by Machado et al. [9]. The result of the study will be important for coaches and athletes, because with the determination of this variable it is possible to prescribe training sessions both continuous and interval for endurance runners.
Therefore, the aim of this study was to determine the peak running velocity on the track field (V peak_TF ) based on the laboratory treadmill test (V peak_T ), and relate the V peak values as well as their correlation with the 10-km running performance in trained endurance runners. We hypothesized that although the V peak_TF is different from V peak_T , they have a good relationship; additionally, V peak_TF have a higher correlation to the 10-km running performance in trained endurance runners.

Participants
Twenty male trained endurance runners [mean ± SD (age: 29.5 ± 5.3 years, weight: 61.1 ± 6.9 kg, height: 174.6 ± 4.9 cm, V O 2max : 63.7 ± 14.5 ml�kg -1 �min -1 )] with 10-km time running performance of 35.2 ± 1.4 minutes, and mean velocity (MV) of 17.1 ± 0.9 km�h -1 (which represented ffi 74.6% of the MV of the World record, respectively) took place on this study. All participants were experience in competitive long-distance races with training frequency of 6 ± 1 days�wk -1 , and distance of 96.4 ± 23.4 km�wk -1 , who presented medical clearance to perform exhaustive physical tests. The article adheres to the ethical standards in sports and exercise science research, with the consent of the participant informed in writing to carry out the study and anonymity of its data [19]. The experimental protocol was approved by the University's Human Research Ethics Committee (#1.889.751/2017) and all participants learned information about a methodology of work, as well as risks and collateral.

Study design
After being familiarized with the rating of perceived exertion (RPE) scale and the equipment to be used in the evaluations (e.g., motorized treadmill), the participants performed one maximum incremental test on the treadmill under laboratory conditions (temperature = 21 ± 1˚C and relative humidity = 55-60%) and two maximum incremental tests on the official track field for V peak determination. The first test was carried out to adapt the participants to the track field test, and the second one was used to determine the V peak_TF . In addition, 10-km running performance was performed on the official track field. The tests were performed at the same time of the day (between 5:00 and 9:00 p.m.) under similar climatic conditions (temperature = 25-29˚C and relative humidity = 50-60%) and separated by 1-week interval. The total time, heart rate (HR), RPE and lactate concentrations ([La]) were monitored during all tests.

Determination of V peak on the treadmill (V peak_T )
To determine the V peak_T , a continuous and incremental test was used with velocity increments of 1 km�h −1 every 3-min without breaks between stages. The V peak_T was assessed on a motorized treadmill (Super ATL; Inbrasport 1 , Porto Alegre, Brazil) with a gradient set at 1% [20]. After 3-min warm-up walking at 6 km�h −1 , the test started with an initial velocity of 8 km�h −1 , followed by an increase of 1 km�h −1 every 3-min until volitional exhaustion (i.e., participant was unable to continue running) [9], and when at least two of the following criteria were met: (1) peak lactate concentration (LA peak ) � 8 mmol L −1 , (2) maximum HR (HR max ) � 100% of endurance-trained age-predicted HR max using the age-based "206-0.7 × age" equation [21] and (3) maximum RPE (RPE max ) � 18 in the 6-20 Borg scale. If the last stage was not completed, the V peak_T was calculated based on the partial time completed in the last stage achieved from the equation proposed by Kuipers et al. [22]: V peak_T = V complete + (Inc × t/T), in which V complete is the running velocity of the last complete stage, Inc is the velocity increment (i.e., 1 km�h −1 ), t is the number of seconds sustained during the incomplete stage, and T is the number of seconds required to complete a stage (i.e., 180 s).
HR was monitored during all tests (Polar 1 RS800sd; Kempele, Finland) and HR max was defined as the highest HR value recorded during the test. RPE was also monitored during all tests by using a 6-20 Borg scale [23], and the highest RPE value was adopted as the RPE max . Earlobe capillary blood samples (25 μl) were collected into a capillary tube at the end of the tests (time zero of recovery) and at the third, fifth, and seventh minutes of passive recovery with participants seated in a comfortable chair. The [La] was evaluated only at the end of the test and LA peak was defined for each participant as the highest post-exercise [La] value.
Determination of V peak on the track field (V peak_TF ). The test used to determine the V peak_TF was the same as the one used for the determination of V peak_T . The test was a continuous and incremental test was used with increments of 1 km�h -1 every 3-min without breaks between stages. The velocity during the test was controlled by sound signals. Participants should cross the lines marked by cones, which were distributed on the track field every 25 m, with at least one foot simultaneously to the beep [24]. The interval between the beeps at each stage decreased every three minutes, and the higher beep indicate that a new stage was starting. Each three minutes was a time reduction between beeps with the objective to increment the velocity, that is, at each velocity increment, the participants should exceed a greater number of cones (travel a greater distance) in the interval of 3-min compared to the previous velocity ( Table 1). The test was finished by voluntary exhaustion of the participant or when the evaluator identified that the participant failed to cross the reference lines with one of two feet for two consecutive times [24].

10-km running performance
Performance was undertaken on the track field preceded by 10-min warm-up. Participants were requested to run as fast as possible and the time was recorded every 400 m. Mineral water was provided ad libitum in cups throughout trials, so that participants could hydrate themselves as they were used to do in long-distance races. The 10-km mean velocity (MV) for each trial was calculated by dividing the total distance by the trial duration. Additionally, partial MVs were calculated in three phases: (1) start (first 400 m), (2) middle (400-9600 m) and (3) end (last 400 m), as previously reported [25,26].

Statistical analyses
All statistical analyses were performed using the software Statistical Package for the Social Sciences (SPSS 1 v.20, Inc., Chicago, IL, USA). Data normality was verified by the Shapiro-Wilk test. The variables are presented as mean ± standard deviation (SD). The comparisons between the V peak_TF and V peak_T tests were performed by the Student's paired t-test. To examine the correlation and confidence interval (CI) between both V peak and 10-km running performance, Pearson product-moment correlations were performed. Correlation coefficients (R) were interpreted using the following qualitative descriptors: trivial (< 0.1), small (< 0.3), moderate (0.3-0.5), large (0.5-0.7), very large (0.7-0.9), nearly perfect (> 0.9), and perfect (1.0) [27]. Simple linear regression analyses were used to generate a predictive equation V peak_TF and from V peak_T . The Bland-Altman analysis [28] was used to calculate the bias (difference between the means) between the V peak_TF and V peak_T with the respective limits of agreement for a 95% interval (LoA = bias ± 1.96 mean ± SD). Hopkins spreadsheets were used to calculate intraclass correlation coefficient (ICC). Results for MV recorded at the three different points during performances were compared using two-factor ANOVA for repeated measures followed by the LSD post hoc test for multiple comparisons. For all analyses a significance level of P < 0.05 was adopted.

Results
There was no significant difference between V peak_TF and V peak_T as well as for the total time of the tests, the distance travelled and RPE max determined during the tests, with higher values Table 1. Test characteristics for determination of V peak on the track field (V peak_TF ).

Number of cones traversed per stage
Interval between beeps (s)

Stages (km�h -1 ) Number of cones traversed per stage
Interval between beeps (s)

PLOS ONE
Determination of V peak on the track field (V peak_TF ) obtained on the treadmill test (Table 2). A higher ICC values was found for V peak values ( Table 2). Fig 1A shows the good agreement between the V peak values. Fig 1B demonstrates a significant and high linear correlation between the V peak_TF and V peak_T . Assuming a standard error of 0.36 km�h −1 , the resulting equation was:

PLOS ONE
Determination of V peak on the track field (V peak_TF )

Discussion
The aim of this study was to determine the peak running velocity on the track field based on the laboratory treadmill test, and relate the V peak values as well as their correlation with the 10-km running performance in trained endurance runners. The main findings were that despite the difference between V peak values both V peak values were associated and have good agreement, and V peak_TF had a higher correlation with the 10-km running performance than V peak_T , which confirm the initial hypothesis.

PLOS ONE
Determination of V peak on the track field (V peak_TF ) The results showed that V peak_TF was significantly lower compared to V peak_T . As demonstrated in the present study, some researchers compared incremental tests performed on the treadmill and track field and observed higher values for the variables (e.g., MAS and V peak ) determined on the treadmill [6,17,18]. Simillarly, Pallares et al. [6] showed that V peak and MAS obtained on the treadmill test (increments of 1 km�h -1 every 1-min) were similar when compared to the values measured in a new short track test (same treadmill protocol) performed in the field. Metsios et al. [18] observed that the MAS determined during the treadmill test (increments of 1 km�h -1 every 2-min) was overestimated by 8% when compared with the track field test (increments of 0.5 km�h -1 every 1-min), which is very similar to the present investigation (ffi 6%). However, previous studies [6,17,18] compared protocols in the treadmill and track field with different designs. According to Kuipers et al. [22], it is important to use the same test design for comparison and validation of a given variable, such as V peak , which is directly influenced by the protocol design [8,9,21].
Studies point out that there is a great difference between running on the treadmill and running in the field/track [29][30][31]. Considerable kinematic differences exist, and the mechanisms of the march are involved in the treadmill race different from those of the race on the track [32][33][34], as well as biomechanical differences (e.g., when running on a treadmill, the pass frequency is higher compared to the track, while the stride length is higher on the track) [29]. Although the study did not evaluate these factors, we consider that they may have contributed to the final differences found between the tests to determine. Furthermore, we highlight that the environmental conditions, which are variables that are better controlled when the tests are performed on the treadmill, contribute to the differences between V peak_TF and V peak_T (r = -0.95 � ) in the present study [35]. However, it is important to emphasize that the data obtained from the track field tests were closer to the competitive reality and training of the runners [36].
Despite the differences between both V peak tests, the ICC and Bland-Altman demonstrated that V peak_TF is highly associated with the well-established V peak_T ; however, the Bland-Altman demonstrated a bias of 1.1 km�h -1 and a percentage difference of 6.1% between the V peak values. In contrast, Pallarés et al. [6] with trained male athletes demonstrated that the V peak determined by the novel short track test had high ICC (0.96), low bias (-0.1) and a % Diff of -0.6% when related to the V peak obtained on the treadmill using the same protocol. This great similarity between the two protocols demonstrated by Pallarés et al. [6] can be related to the fact that the authors used a gas analyzer for the treadmill test. It is important to emphasize that the present study used clean protocols (i.e., without using gas analyzers in both tests), which contributed to the runners staying longer on the treadmill test and caused the difference between the V peak values.
In relation to other variables determined in the V peak tests, it was observed significant higher values for RPE max when determined on treadmill compared to track field. This can be justified by the fact that runners reach an extra stage during the treadmill test, in addition, runners have a perception of greater velocity on the treadmill due to the need for greater balance and coordination, the increased demand for attention and vision, and the fear of falling [37]. However, no significant difference was observed for the HR max and LA peak values, demonstrating that both incremental protocols attained similar maximal effort responses. The similar result was observed by Pallarés et al. [6] who also found no difference in HR max on comparing incremental tests on the track field and treadmill. It should be noted that these variables were used to identify the physiological responses generated by effort, in addition to being used as a parameter to identify the maximum effort during the incremental test [38,39].
Another important finding of the present study is that the V peak_TF showed a higher correlation with the 10-km running performance than the V peak_T (r = -0.95 vs. -0.89, respectively), demonstrating that improvements in the V peak_TF during a training period can directly reflect performance changes. Previous studies also observed high correlations (between -0.80 and -0.93) between V peak_T and performances ranging from 3 to 90 km [9,10,40], however, no study has demonstrated the correlation between V peak_TF and performance. It is suggested that the high correlation of V peak _ TF is because the test location (i.e., outdoor) was similar to that of the performance, and was where the runners usually compete. This result also reinforces the great practical application of V peak_TF as a training prescription variable.
To complete a 10 km performance, participants adopted the "U" strategy [41]. This strategy is commonly used by moderate and high-performance runners [26,42]. After assessing the contribution of some physiological and muscular variables to the rhythm strategy adopted during the 10 km running performance, Bertuzzi et al. [25] concluded that V peak , V O 2max and 1 maximum repetition are the variables that best explain the performance in the intermediate phase (0.4-9.6 km) and only V peak in the final phase (9.6-10 km), reaffirming its high performance prediction capacity for this type of test.
Despite the important findings, this study had some limitations such the absence of other test using the gas analyzer to obtain ventilatory parameters; however, future studies can investigate the relationship between V peak_TF and ventilatory parameters. Other limitation was the lack of a dietary recall to control and standardize the same diet before the testing sessions; however, it was recommended for the participants to maintain the same diet pattern before each test.
The results of this study have important practical implications for endurance coaches, practitioners, and runners in terms of the prescription of aerobic training loads on the track. This is because of the practicality and ecological validity of the V peak_TF test, which is determined in an environment directly related to the training location of runners. Further, this test is suitable for the simultaneous evaluation of several runners. In order to prescribe endurance training using the variable, it is suggested to use the intensity of 75 ± 4% of V peak for continuous training sessions and intensities of 100% ± 2% of V peak for long interval training session [11][12][13] and 120% ± 2% of V peak for short interval training session [13].

Conclusion
In conclusion, the good agreement and association with V peak_T and the high correlation with 10-km running performance demonstrate that the novel track field test is efficient for V peak_TF determination. Future studies should verify the reproducibility of this novel track field test in runners with different levels of performance.