Peak velocity and its time limit are as good as the velocity associated with VO_2max for training prescription in runners

Abstract

This study compared the effects of 4 weeks of training prescribed by peak velocity (V_peak) or velocity associated with maximum oxygen uptake (vVO_2max) in moderately trained endurance runners. Study participants were 14 runners (18–35 years) randomized into 2 groups, named group VO₂ (GVO₂) and group V_peak (GVP). The GVO₂ had training prescribed by vVO_2max and its time limit (t_lim), whereas the GVP had training prescribed by V_peak and its t_lim. Four tests were performed on a treadmill: 2 maximum incremental for V_peak and vVO_2max and 2 for their t_lim. Performance (10 km) was evaluated on a 400 m track. Evaluations were repeated after 4 weeks of endurance training. The results showed a significant effect of training on V_peak [GVP (16.7±1.2–17.6±1.5 km^.h⁻¹), GVO₂ (17.1±1.9–17.7±1.6 km·h⁻¹)]; vVO_2max [GVP (16.4±1.4–17.0±1.3 km·h⁻¹), GVO₂ (17.2±1.7–17.5±1.9 km·h⁻¹)]; and 10 km performance [GVP (41.3±2.4–39.9±2.7 min), GVO₂ (40.1±3.4–39.2±2.9 min)]. The V_peak highly correlated with performance in both pre- and post-training in GVP (–0.97;–0.86) and GVO₂ (–0.95;–0.94), as well as with vVO_2max in GVP (–0.82;–0.88) and GVO₂ (–0.99; –0.98). It is concluded that training prescribed by V_peak promoted similar improvements compared to training prescribed by vVO_2max. The use of V_peak is recommended due to its practical application and the low cost of determination.

Key words

training programs - effort testing - athletic performance - running

Introduction

Success in endurance racing depends on an elaborate training prescription utilizing appropriate loads and recovery periods. Such prescriptions should be planned according to the needs of the individual athlete for achieving the highest level of adaptation possible prior to the competition [16] [22] [29]. For proper training prescription, it is necessary to use variables that control and monitor the intensity of effort and possible physiological adaptations resulting from this practice and, most importantly, that show a correlation with performance [7].

Currently, the velocity associated with the occurrence of maximum oxygen uptake (vVO_2max) is considered a good variable to predict performance and to monitor and prescribe endurance running training [2] [9] [27]. In addition, the application of its time limit (t_lim) may improve the prescription of the most adequate set duration for high-intensity interval workouts [2]. Previous studies show that training prescribed by vVO_2max and its respective t_lim promoted improvements in performance of 3, 5 and 10 km [9] [13] [34]. In addition, the training prescribed by these variables can promote improvements in VO_2max, running speed at the lactate threshold, and parameters related to heart rate (HR) among others [9] [13] [34]. However, the vVO_2max determination requires the use and handling of expensive and delicate equipment, as well as the interpretation of data, limiting its use to only a few research laboratories, coaches, and athletes. Moreover, the vVO_2max refers to estimating the minimum speed required to achieve VO_2max, as a result of calculating vVO_2max based on VO_2max determination, whereas the peak velocity (V_peak) is the maximum speed directly measured and associated with VO_2max [26].

Thus, V_peak is an attractive variable that has been gaining attention among researchers, trainers, and endurance runners due to its practicality and financial accessibility. Despite the fact that V_peak is associated with vVO_2max and is a great predictor of endurance performance in tests 3–90 km [25] [26] [30], it is necessary to test its applicability to endurance training prescription as well as the applicability of its t_lim to determine duration of high-intensity interval sets. Although the intra-individual differences between V_peak and vVO_2max might be very small, the t_lim differences may be large, which would meaningfully change the duration of high-intensity interval sets.

Given that, as far as it is known, V_peak based training prescription for moderate intensity continuous training and high-intensity interval training has not been tested yet, the aim of this study was to evaluate the effect of 4 weeks of training prescribed by V_peak, vVO_2max, and their respective t_lim in moderately trained endurance runners. Our hypothesis was that both training models would improve aerobic, anaerobic, and performance parameters of moderately trained runners in a similar manner. We also hypothesized that V_peak would demonstrate a higher correlation with the 10 km performance than the vVO_2max before and after training, given that V_peak is the ‘measured’ speed associated with VO_2max, and vVO_2max is the ‘estimated’ speed associated with VO_2max [11] [26]. Should this be shown, it would demonstrate that the V_peak was a more sensitive variable to the effects of training for moderately trained runners.

Methods

Participants

Fourteen moderately trained endurance runners were recruited for participation in this study and showed average speed (AS) between 14 and 16 km·h⁻¹ (≅ 62–71% of the world record). They performed at least 5 training sessions per week. Their average training distance during the study was 40.9±4.5 km ∙ week⁻¹, which was similar to their training distance before the study. Subjects had the following characteristics: (mean±SD, age 29.2±5.3 years, weight 71.9±11.0 kg, height 175.1±4.3 cm) with a minimum of 1 year of experience in competitive long distance races. Before the study, the subjects were informed about the testing and training and possible risks involved and provided written informed consent. This study was approved by the University’s Human Research Ethics Committee (#1.022.468). All research was conducted ethically according to international standards and as required by the International Journal of Sports Medicine [15].

Experimental design

Runners were randomized into 2 groups using random numbers. One group was trained by V_peak (GVP; n=8) and the other group by vVO_2max (GVO₂; n=6). The experiment involved the implementation of 2 different endurance running training programs (GVP vs. GVO₂) using the prescribed external workload (%V_peak or %vVO_2max) for 5 sessions per week over a 4 week period, for a total of 20 sessions. Before and after the training intervention, in a counterbalanced order, the subjects were evaluated using 2 incremental tests on a treadmill to measure VO_2max and V_peak and 2 to determine their t_lim. Performance (10 km) was evaluated on an official running track (400 m). In addition, variables such as heart rate (HR), blood lactate concentration [LA], and rating of perceived exertion (RPE) were also evaluated during the tests. The tests were performed over 2 weeks, with a period of at least 48 h separating each of them.

Determination of V_peak and its t_lim

The V_peak was assessed on a motorized treadmill (Super ATL; Inbrasport, Porto Alegre, Brazil) (with the gradient set at 1% [21]. After a 3 min warm-up walking at 8 km·h⁻¹, the protocol started with an initial velocity of 10 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). If the last stage was not completed, the V_peak was calculated on the partial time remaining in the last stage using the equation proposed by Kuipers et al. [23]: V+(t/180×1.0), where V was the last completed velocity (km·h⁻¹) and t, the time (s) of the uncompleted step (180 s). The t_lim at V_peak was assessed after a 15 min warm-up at 60% V_peak, when velocity was increased to V_peak. The subjects were verbally encouraged to run to volitional exhaustion [4].

Determination of VO_2max and its t_lim

The protocol used for determining the VO_2max was the same as that used for the determination of V_peak; additionally, exhaled gas was collected to determine the VO_2max using a portable gas analyzer (k4b^2, Cosmed, Roma, Italy). The VO_2max was regarded as the maximum value obtained during the test, measured at an average of 15-s intervals, and when at last 2 of the following criteria were met: (1) LA_peak≥8 mmol·L⁻¹, (2) HR_max≥100% of endurance-trained age-predicted HR_max using the age-based “206–0.7×age” equation [37] and (3) RPE_max≥18 in the 6–20 Borg scale [6]. The vVO_2max was the minimal velocity at which the athlete was running when VO_2max occurred [2] [4]. To determine t_lim at vVO_2max, the same protocol was applied as that used for determining the t_lim at V_peak using the values of vVO_2max as parameters.

Time trials of 10 km

Participants undertook 10 km time trials on a 400 m outdoor running track at 6:00 pm. The trial was preceded by a self-selected pace warm-up of 10 min duration. A hydration station was set up on the track with natural water. The participants were encouraged to achieve their best performance. Split times were registered at each 400 m and the average velocity of each section was calculated.

Determination [LA], HR, and RPE

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. From these samples, [LA] was subsequently determined by electroenzymatic methods using an automated analyzer (YSI 2300 STAT, Yellow Springs, Ohio, USA). Peak [LA] (LA_peak) was defined for each participant as the highest post-exercise [LA] value. RPE was also monitored during all tests by using a 6–20 Borg scale [6], and the highest RPE value was adopted as the peak RPE (RPE_peak). HR was monitored during all tests (Polar RS800sd; Kempele, Finland) and HR_max was defined as the highest HR value recorded during the test.

Training programs

All training sessions were held on a 400 m outdoor running track, between 5:00 and 9:00 pm hours due to the availability of participants and the fact that their performance would be better in the evening [10]. The training protocol consisted of 2 types of running training: continuous moderate-intensity and high-intensity interval training (short interval and long interval). The running intensity was prescribed based on the V_peak and t_lim for the GVP group, and the vVO_2max and t_lim for the GVO₂ group ([Table 1]).

Table 1 Continuous and interval training prescribed for GVP and GVO₂ groups.

GVP and GVO2
Continuous training	45*±2.5 min at 75±4% of Vpeak or vVO2max. (weeks 1 & 2) 60±2.5 min at 75±4% of Vpeak or vVO2max. (weeks 3 & 4)
Short interval training	X* # sets at 120±2% of Vpeak or vVO2max with duration 10% their respective tlim and intervals (passive) with duration 30% of tlim at Vpeak or vVO2max.
Long interval training	X* # sets at 100±2% of Vpeak or vVO2max with duration 60% their respective tlim and intervals (passive) with duration 60% of tlim at Vpeak or vVO2max.

# The number of series performed by each participant was adjusted so that the total duration of interval training session corresponded to 30±2.5 min

* The intensity and duration of training was the same for both groups with differences only in the prescription variable: the GVO₂ had the training prescribed by vVO_2max and its respective t_lim and GVP had training prescribed by V_peak and its respective t_lim

Training was based on studies by Buchheit et al. [9]; Esfarjani and Laursen [13]; Smith; Coombes, and Geraghty, [34]; Billat et al. [2]

The GVO₂ and GVP training sessions were preceded by a 15 min warm-up consisting of 5 min of low intensity running at a self-selected velocity, 5 min of stretching, and 5 min of running at 60% of V_peak or vVO_2max [35]. After the warm-up, the main training session (continuous or interval training) was conducted, followed by a cool-down comprised of self-selected low-intensity running and stretching.

The training participants of both groups were trained 5 times per week for 4 weeks. They performed 10 sessions of continuous training and 10 of interval training. During the odd weeks, participants performed 3 sessions of continuous training and 2 sessions of interval training; and the reverse during even weeks. The training sessions of the groups were differentiated by the prescription method (V_peak and their respective t_lim to GVP and vVO_2max and their respective t_lim to GVO₂). The intensity and volume of training were maintained throughout the protocol, except for continuous training in weeks 3 and 4 when the duration was increased from 45 to 60 min for both groups.

Statistical analyses

All statistical analyses were performed using the SPSS software (v.20, SPSS Inc., Chicago, IL, USA). The variables are presented as mean±standard deviation (SD). Data normality was verified by the Shapiro-Wilk test. The comparison between the pre- and post-training for the 2 groups was made by mixed ANOVA for repeated measures. Correlations between aerobic and anaerobic parameters with 10 km running performance were performed using the Pearson correlation coefficient. The differences (i. e., effect size [ES]) were considered small when ES≤0.2, moderate when ES≤0.5 and large when ES>0.8. Furthermore, magnitude-based inferences were applied to estimate the chances of a true observed effect being positive, trivial or negative, considering the smallest worthwhile change per Hopkins et al. [18]. The probability of a positive/trivial/negative effect of the training programs was interpreted following the recommendations of Hopkins et al. [18]; effect: <1% almost certainly not; 1–5% very unlikely; 5–25% unlikely; 25–75% possibly; 75–95% likely; 95–99% very likely;>99% almost certainly. When the chance of having positive or negative effects in an outcome were both above 10%, the qualitative inference result was considered as unclear.

Results

The results show V_peak improvement in both groups after the 4 week training period: GVP=0.9 [0.4–1.4] km·h⁻¹ (p=0.01) and GVO₂=0.6 [0.2–1.0] km·h⁻¹ (p=0.03) ([Table 2]). A significant increase in the total duration of the incremental test was observed in both groups: GVP=2.8 [1.5–4.1] min (p=0.01) and GVO₂=2.2 [0.4–3.9] min (p=0.06) ([Table 2]).

Table 2 Mean±standard deviation (SD) difference (90% CI), magnitude of inference, and significance level for group×time interaction (P) for the variables: V_peak, (km ^. h⁻¹) Total time of the incremental test (min), HR_max (bpm) RPE_max (AU), LA_peak (mmol ^. L⁻¹) and t_lim at V_peak (min) obtained from the experimental protocol for determining the V_peak.

	GVP (n=8)				GVO2 (n=6)
Variable	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Group×time interaction (P)
Vpeak (km·h−1)	16.7±1.2	17.6±1.5*	0.9 [0.4–1.4]	Very likely 98/2/0	17.1±1.9	17.7±1.6*	0.6 [0.2–1.0]	Possible 72/28/0	0.352
Duration (min)	23.0±3.7	25.8±4.4*	2.8 [1.5–4.1]	Very likely 99/1/0	24.3±5.7	26.4±4.7*	2.2 [0.4–3.9]	Likely 81/19/0	0.566
HRmax (bpm)	189±5.0	191±6.0	1.6 [−0.6–3.8]	Possible 66/32/2	183±10.0	184±12.0	1.8 [−4.1–7.7]	Unclear 42/48/10	0.943
RPEmax (AU)	19.9±0,4	19.9±0.4	−0.1 [−0.6–0.3]	Unclear 20/23/57	19.7±0.5	19.8±0.4	0.2 [−0.5–0.8]	Unclear 55/25/20	0.449
LApeak (mmol·L−1)	9.3±0.6	10.3±0.8	0,9 [−0.2–2.1]	Likely 81/15/3	8.0±0.6	9.0±1.0	1.1 [−1.0–3.1]	Unclear 74/15/11	0.914
tlim (min)	6.8±1.6	6.7±1.3	−0.1 [−0.6–0.4]	Unlikely 7/72/21	7.7±1.8	6.8±2.3	−0.9 [−1.7- −0.1]	Likely 1/14/85	0.130

*P<0.05 in relation to pre moment to the same group. Dif=Difference; (P/T/N)=Positive/Trivial/Negative

No significant differences were observed in either group between pre- and post-training for HR_max, RPE_max, t_lim at V_peak, t_lim at vVO_2max, and LA_peak.

After 4 weeks of training, we observed a significant improvement in vVO_2max only in the GVP group: 0.6 [–2.2–1.8] km·h⁻¹; (p=0.01). In relation to the total duration of the test, a significant increase was observed in both groups: GVP=1.7 [0.4–3.0] min (p=0.036) and GVO₂=1.2 [0.2–2.2] min (p=0.047) ([Table 3]).

Table 3 Mean±standard deviation (SD) difference (90% CI), magnitude of inference, and significance level for group×time interaction (P) for the variables: VO_2max (ml·kg⁻¹·min⁻¹), vVO_2max (km·h⁻¹), total duration of incremental test (min) HR_max (bpm) RPE_max (AU), LA_peak (mmol·L⁻¹) and t_lim at vVO_2max (min) obtained from the determination of the protocol vVO_2max

	GVP (n=8)				GVO2 (n=6)
Variable	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Group×time interaction (P)
VO2max (ml.kg−1·min−1)	50.2±3.5	50.0±2.3	−0.2 [−2.2–1.8]	Unclear 19/52/29	49.0±6.9	48.9±6.1	−0.1 [−1.7–1.6]	Unlikely 4/90/6	0.957
vVO2max (km·h−1)	16.4±1,4	17.0±1.3*	0.6 [0.3–1.0]	Likely 93/7/0	17.2±1.7	17.5±1.9	0.3 [−0.1–0.8]	Possible 37/62/1	0.317
Duration (min)	21.6±4.8	23.3±4.2*	1.7 [0.4–3.0]	Likely 81/19/0	23.7±5.9	24.9±5.2*	1.2 [0.2–2.2]	Possible 36/64/0	0.601
HRmax (bpm)	193±11.0	190±6.0	−2.9 [−9.0–3.3]	Possible 7/37/54	183±8.0	182±7.0	−0.8 [−4.2–2.5]	Possible 8/65/27	0.623
RPEmax (AU)	18.8±2.1	19.5±1.1	0.8 [0.0–1.5]	Possible 75/24/1	19.0±1.7	19.3±1.3	0.3 [−0.3–1.0]	Possible 43/53/4	0.470
LApeak (mmol·L−1)	9.1±1.9	8.8±1.3	0.5 [−0.5–1.5]	Possible 67/24/9	8.4±1.1	8.0±2.5	−0.8 [−1.6–0.1]	Possible 1/28/71	0.911
tlim (min)	7.5±1.7	6.7±1.1	−0.8 [−2.3–0.6]	Possible 8/21/72	6.3±1.4	6.1±2.1	0.5 [−0.8–1.7]	Unclear 57/30/13	0.225

*P<0.05 in relation to pre moment to the same group. Dif=Difference; (P/T/N)=Positive/Trivial/Negative

[Table 4] shows the values of the variables both pre- and post-training obtained in the 10 km performance. In both groups, there was a significant reduction in the time it took to run a 10 km distance after the training program (GVP (– 1.4 [−2.5 to −0.3] min; p=0.04) and GVO₂ (– 0.9 [–1.6–0.2] min; p=0.048)). Furthermore, there was a significant increase in the AS after 4 weeks of training (0.6 [0.1–1.0] km·h⁻¹ for GVP (p=0.04) and 0.4 [0.1–0.6] km·h⁻¹ for GVO₂ (p=0.036)). The runners’ AS was between 14 and 16 km·h⁻¹ (≅62–71% of the world record).

Table 4 Mean±standard deviation (SD), difference (90% CI), magnitude of inference, and significance level for group×time interaction (P) for the variables in the time trial of 10 km (min), average speed (AS) 10 km (km ^. h⁻¹) HR_max (bpm), RPE_max (AU) and LA_peak (mmol·L⁻¹), obtained from the 10 km track performance.

	GVP (n=8)				GVO2 (n=6)
Variable	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Pre	Post	Dif. (90% CI)	Inference (P/T/N)	Group×time interaction (P)
Time (min)	41.3±2.4	39.9±2.7*	−1.4 [−2.5- −0.3]	Likely 1/8/91	40.1±3.4	39.2±2.9*	−0.9 [−1.6–0.2]	Possible 0/37/63	0.517
AS 10-km	14.6±0.9	15.1±1.1*	0.6 [0.1–1.0]	Likely 92/7/1	15.1±1.3	15.4±1.2*	0.4 [0.1–0.6]	Possible 60/40/0	0.478
HRmax (bpm)	179±8.0	179±5.0	2.9 [−1.5–7.3]	Possible 58/39/3	171±10.0	173±8.0	6.5 [−1.0–14.0]	Likely 86/11/3	0.404
RPEmax (AU)	18.8±1.9	18.8±1.9	−0.1 [−0.8–0.5]	Unclear 15/49/35	18±2.8	17.0±2.6	0.0 [−0.5–0.5]	Unclear 15/70/15	0.792
LApeak (mmol·L−1)	7.8±2.0	7.7±1.7	−0.1 [−1.7–1.5]	Unclear 27/39/34	6.7±0.6	7.4±0.8	0.7 [−0.2–1.6]	Likely 85/9/6	0.486

* P<0.05 in relation to pre moment to the same group. Dif=Difference; (P/T/N)=Positive/Trivial/Negative

The effect size for the comparison between GVP and GVO₂ for the percentage variation after the 4 week running training period revealed a small effect for V_peak and 10 km time and a moderate effect for vVO_2max, all favorable to GVP ([Fig. 1]).

Fig. 1 Effect sizes of the comparison between GVP and GVO₂ for the variation (%) of vVO_2max (km·h⁻¹) V_peak (km ^. h⁻¹) and the 10 km time after the 4 week running training period.

The V_peak and vVO_2max were significantly correlated with the 10 km performance in both pre- and post-training time in both groups ([Table 5]). The VO_2max, however, did not correlate with the 10 km performance at any time ([Table 5]).

Table 5 Correlation between the performances of 10 km before and after 4 weeks of training with the variables: V_peak (km ^. h⁻¹), VO_2max (ml·kg⁻¹·min⁻¹), vVO_2max (km·h⁻¹).

	GVP (n=8)		GVO2 (n=6)
Variable (Pre and Post)	Performance Pre	Performance Post	Performance Pre	Performance Post
Vpeak (km·h−1)	−0.97*	−0.86*	−0.95*	−0.94*
VO2max (ml·kg−1min−1)	−0.35	0.03	−0.64	−0.70
vVO2max (km·h−1)	−0.82*	−0.88*	−0.99*	−0.98*

* P<0.05

Discussion

The aim of the study was to evaluate the effect of 4 weeks of training prescribed by V_peak, vVO_2max, and their respective t_lim in moderately trained endurance runners.

The main finding of the study was that the training prescribed by V_peak or by vVO_2max promoted similar improvements for moderately trained endurance runners, which confirmed a previous hypothesis. Effect size analysis showed slightly favorable changes for GVP. A significant correlation was observed between the 10 km performance and the V_peak and vVO_2max, but our hypothesis was disproven because only in the pre-training time, the GVP showed a higher correlation of the V_peak with the 10 km performance compared with the vVO_2max.

For proper training prescription, it is necessary to use variables that can control and monitor the intensity of effort and possible physiological adaptations resulting from this practice and, most importantly, show a correlation with performance [7].

In our review, we found no previous studies that had used V_peak in the prescription of individualized endurance training. The GVP showed improvement in 10 km performance after 4 weeks of training, suggesting that V_peak is an effective variable for prescribing training and is able to promote improvements in performance after a period of training. The improvements found in performance caused by the training prescribed by V_peak were similar to those described by studies that used vVO_2max for training prescription [13] [35]. As for GVO₂, the improvements in the 10 km performance were similar to those observed for GVP after 4 weeks of training. This improvement in performance is in line with previous studies that used the same variable for training prescription [13] [35]. Esfarjani and Laursen [13] observed improvements in 3 000 m performance after applying a 10 week training in 17 moderately trained runners whose training sessions were prescribed by vVO_2max and their respective t_lim. Similar improvements observed in the 10 km performance by both prescription variables (V_peak and vVO_2max) can be explained by the fact that both variables are highly interrelated, as well as related to endurance performance [12] [25] [32]. This similarity is of great interest to coaches, athletes, and researchers, because currently vVO_2max is widely known as a variable to predict performance, monitoring, and training prescription [9] [24] [27]. However because it requires the use of expensive equipment, its use is limited to only a few research laboratories, coaches, and athletes. Thus, the V_peak is an attractive alternative variable because of its practicality and low financial cost.

Both the V_peak and vVO_2max groups showed improvement after the training program. This improvement is mainly associated with the prescription model used in the study for interval training sessions. The intensity of the V_peak and vVO_2max were related to VO_2max, which is considered the ideal intensity to utilize the maximum aerobic production system energy and maintain it as long as possible [31]. Moreover, the stimuli had a duration of 60% of t_lim at V_peak and vVO_2max, which is considered the time required to achieve and maintain the VO_2max, resulting in an improvement in the prescription variable [5] [31]. No evidence was provided, however, about the existence of a limit to the improvement in prescription variables with training, or if they might be bettered by improving the performance test.

The improved V_peak demonstrates the sensitivity of this variable in that it is capable of accurately monitoring the changes caused by this type of training, which is one of the main requirements for an athletic training prescription variable [7]. Regarding vVO_2max, improvement was observed for post-training GVP, but no difference was found in the GVO₂ after the 4 weeks of training. It is noteworthy that even without a statistical difference in vVO_2max, there was significant improvement in the total duration of the incremental test when we observe the pre- and post-training duration (23.7±5.9 vs. 24.9±5.2 min, respectively). The improvement in test time and the absence of improvement in vVO_2max may be related to the methodology for its determination, which is to record the minimum intensity at which the occurrence of VO_2max was observed [2] [4]. In addition to being dependent on VO_2max, this estimation is not considered the total period of the test; therefore, even with the improvement in test duration, the occurrence of VO_2max can be observed at similar intensities between the pre- and post-training, with no change in vVO_2max. This does not occur with the V_peak when the Kuipers et al. [23] adjustment (which takes into account the precise length of the incomplete stage) is applied. This result shows that vVO_2max determined by this protocol is a less accurate alternative variable for monitoring training when possible adaptations are small. It also supports the use of V_peak as a variable for monitoring and training prescription because it is sensitive to small changes caused by training. This sensitivity is of great interest since the more highly trained the athletes, the smaller the improvements will be. Even detection of these small gains would warrant a new training protocol.

As for t_lim at V_peak and vVO_2max, no difference was found for these variables after the 4 week training program. This result deserves further consideration, however, because after the training program the participants have managed to remain at t_lim the same amount of time while exercising at higher intensities. These results were similar to those of Billat et al. [2], who also found no difference at t_lim after a 4 week training protocol. The t_lim seems to be a variable that does not follow the changes caused by training [24]. Despite that, the application of t_lim for prescribing interval training favors greater individualization of the duration of each high-intensity effort, given the large variation between subjects at t_lim, even if V_peak or vVO_2max do not show major differences between the subjects.

No improvements were seen at VO_2max in either group after the training program. Results from previous studies observed the effect of a training program on VO_2max in trained endurance runners with similar training prescriptions to those used in our study [2] [31] [35]. Even without changes in VO_2max, these studies have in common a significant improvement in performance, demonstrating that VO_2max seems to be a less sensitive training variable, which in turn suggests that the use of other variables for monitoring adaptations may be warranted [8] [20] [26].

No changes were observed in variables HR_max·LA_peak, or RPE_max, either in the treadmill test or in track performance. The absence of change to these variables after training was expected because they are routinely used for the identification of physiological responses generated by the effort [17]. They serve as a parameter for identifying the maximum effort during the incremental test [14]. Thus, for already moderately trained runners such as our participants, the 4 week training period is a short time to promote changes in the said variables, especially in HR.

The correlation among V_peak, vVO_2max, and performance in the present study was also observed in previous studies [3] [26]. In the present study, the GVO₂ presented higher correlation of the performance with vVO_2max than with V_peak. The ability to predict performance by vVO_2max is related to the fact that it is a variable that shows the interaction between VO_2max and running economy (RE) [3] [12] [26], which are important variables for predicting performance. However, they are not able to predict the performance as isolated variables [19], especially in individuals with similar VO_2max and/or who have a high level of training [28]. Unlike the GVO₂, the GVP group showed a higher correlation between V_peak and 10 km performance in the pre-training time. Previous studies have also shown high correlations between V_peak and performance [11] [36]. Noakes et al. [30], in a study on expert runners over long distances (20 marathoners and 23 ultra-marathoners) with different performances, found that V_peak determined on a treadmill and lactate threshold (LT) were the 2 best performance predictors from 10- to 90 km running performances, concluding that V_peak is a great predictor of performance. Even in groups presenting different correlations of each variable (V_peak and vVO_2max) with performance, it was observed that both were able to predict performance, justified by the fact the 2 variables are highly interrelated [26].

Although studies show that VO_2max has a great capacity for performance prediction in races ranging from 3 km through ultramarathons [1] [26] [28], in this study no correlation was found between VO_2max and 10 km performance in either the pre-training time or post-training time in either group. The fact that the runners present a similar VO_2max may indicate that the VO_2max is not as efficient a variable to predict the performance when individuals have similar VO_2max [12]. The results demonstrated in this study have important practical implications for teams, coaches, and athletes in obtaining information about the adaptations induced by training, especially its effects on performance, given that the V_peak is a variable of great practicality and low financial cost because it does not require expensive equipment (gas analyzer).

Based on the results of this study, it was concluded that the training prescribed by V_peak promoted improvements similar to the training prescribed by vVO_2max in moderately trained endurance runners. Therefore, we recommend the additional use of V_peak associated with its time limit for endurance training prescription in recreational runners with a similar training level to that of the study participants.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES, Brazil

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