Effects of high-intense stimuli on continuous running exercise at the ventilatory threshold

Science & Sports (2011) 26, 292—297

ORIGINAL ARTICLE

Effects of high-intense stimuli on continuous running exercise at the ventilatory threshold Effets des stimuli d’une course de forte intensité sur un exercice de course continu au seuil anaérobie A.S. Oliveira a,c,∗, R.A. Tibana a, F. Aguiar a, H.B. Oliveira a, E.S. Barros b, P.B. Silva b a

Centro Universitário Unieuro, Brasilia, Distrito Federal, Brazil Universidade Católica de Brasilia, Distrito Federal, Brazil c Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7, DK 9220, Aalborg, Denmark b

Received 16 April 2010; accepted 29 September 2010 Available online 9 December 2010

KEYWORDS Exercise physiology; Fatigue; Maximal exercise; Interval training

∗

Summary Aims. — To verify the effects of previous interval training session on physiological and kinematic parameters during continuous running at ventilatory threshold. Methods. — Ten healthy male performed initially an incremental running test, in order to determine ventilatory threshold and maximal aerobic capacity. In another session, subjects performed three tasks as follows: (1) previous five-minute run at ventilatory threshold. After ten minutes rest: (2) interval training session (8 × 1-min at maximal velocity, alternated to one-minute at 50% maximal velocity). After 15 minutes rest: (3) posterior five-minute run at ventilatory threshold. Heart rate, ventilation, blood glucose and lactate concentrations, perceived exertion, stride frequency, stance period and swing period were compared before and after the interval training session. Results. — Significant increases were found in heart rate (∼12%), ventilation (∼23%), blood glucose (∼28%), blood lactate (230%), perceived exertion (∼25%) and stride frequency (∼5%) after interval training. Conclusion. — High-intense running stimuli affect physiological, perceptual and kinematics of a constant moderate intensity running, which could influence training session programmes, considering the impairment overall running performance. © 2010 Elsevier Masson SAS. All rights reserved.

Corresponding author. E-mail address: [email protected] (A.S. Oliveira).

0765-1597/$ – see front matter © 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.scispo.2010.09.011

Maximal stimuli affects continuous running exercises

MOTS CLÉS Exercice physiologie ; Fatigue ; Exercice maximal

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Résumé Objectifs. — Vérifier les effets d’une séance d’entraînement par intervalles sur des paramètres physiologiques et cinématiques lors d’une course continue réalisée au seuil anaérobie. Méthodes. — Dix sujets mâles sains ont initialement exécuté un test de course cumulatif afin de déterminer le seuil anaérobie et la vitesse aérobie maximale. Lors d’une autre séance, les sujets ont exécuté dans l’ordre les trois tâches suivantes : (1) précourse de cinq minutes au seuil anaérobie. Après dix minutes de repos, (2) séance d’entraînement par intervalles (8 × 1 minute à vélocité maximale, alternés avec une minute à 50 % de la vélocité maximale). Après 15 minutes de repos, (3) postcourse de cinq minutes au seuil anaérobie. Le rythme cardiaque, la ventilation, le taux de glucose dans le sang, la concentration d’acide lactique, la perception de l’effort, la fréquence de la marche, la phase d’appui et la phase oscillante ont été comparés avant et après la séance d’entraînement par intervalles. Résultats. — Des augmentations significatives ont été trouvées, après l’entraînement par intervalles, pour le taux de glucose dans le sang (∼23 %), la ventilation (∼12 %), le rythme cardiaque (∼28 %), la concentration d’acide lactique (230 %), la perception de l’effort (∼25 %), ainsi que la fréquence de la marche (∼5 %). Conclusion. — Les stimuli induits par une course de forte intensité affectent la physiologie, la perception et la cinématique d’une course constante d’intensité modérée. Ces observations pourraient influer sur les programmes d’entraînement en considérant l’altération globale de la performance de la course. © 2010 Elsevier Masson SAS. Tous droits réservés.

1. Introduction Running exercises have been widely investigated concerning health benefits, kinematic influence on performance [1,2], metabolic and neuromuscular adaptations to training [3,4], musculoskeletal injuries [4] and muscle fatigue [5]. Especially interval training (INTTR ) has been used to promote both velocity and endurance, by its nature intimately linked to constant changes in short-term metabolic responses. It is possible to maintain running technique along the training session by using active rest intervals [3]. These stimuli induce loss of homeostasis, requiring more energy expenditure and muscular activation [6,7]. Usually, an INTTR session has short-time and intense running stimulus (above the anaerobic threshold or the second ventilatory threshold [VT2 ]), followed by a recovery, which may be smaller, equal or even longer than the active period of running [3]. A proper motor gesture is essential during high-intense running, since its optimization may increase running economy [8—10], and consequently performance. Increases in running speed are related to kinematics changes, such as range of motion in the knee and hip joints [11], higher stride length and stride frequency [9,10,12]. Despite the fact that higher speeds demand higher activation of some lower limb muscles [12], impaired running technique may promote undesirable muscle activations, and braking forces which eventually increase metabolic cost [2,9]. The accumulation of metabolites, such as blood lactate concentration [LAC] and extracellular K+ is natural during INTTR sessions by the high participation of the anaerobic metabolism. As consequence of this accumulation, muscle fatigue decreases the energy offer, impairs muscle activation, excitation—contraction coupling and pacing [3,6,13]. These changes during INTTR sessions differ from those found during continuous running exercise [14], since high intensity stimuli require higher metabolic demands. In theory, INTTR may provide improvement of running technique and conditioning at the same time, however, to our knowledge, there

is a lack of information about how the performance of running exercises at preestablished indexes (as the VT2 ) may be affected by high-demanding stimuli, as found during INTTR sessions. Once INTTR aims to promote maintenance of proper technique, it seems relevant to analyze INTTR at the maximal velocity stimuli, for which the effects of fatigue are not entirely explored in terms of biomechanics and physiology after this type of task. We hypothesized that an INTTR session will strongly affect the performance of a short period of continuous running exercise at the VT2 . Physiological parameters (HR, ventilation [VE], [LAC], blood glucose concentration [GLU], perceived exertion [PE]), and kinematic parameters (as SF, stance phase duration [STA], swing phase duration [SWI]) will be affected when constant running is compared before and after the INTTR session. Possibly, higher HR, VE, LAC, GLU, PE, STA, CP, and lower SWI may be found as consequence of the neurophysiological effects of the INTTR session. In this way, the main objective of the present study was to verify the effects of an INTTR session on physiological and kinematic parameters during continuous running at VT2 before and after INTTR session.

2. Methods Ten healthy male, recreational running practitioners, without musculoskeletal disorders at lower limbs and back within the last 12 months, participated in this study (anthropometric parameters are showed in Table 1). They gave informed consent to participate in the study. The study was approved by the Institutional Research Ethics Committee.

2.1. Experimental design Subjects were tested in two different days:

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Table 1 General, anthropometric and physiological parameters (mean ± SD), speed corresponding to anaerobic threshold (AT), heart rate corresponding to the AT (HRAT), ventilation corresponding to the AT (VEAT) and maximal speed reached during incremental running test; N = 10.

Mean ± SD

Age (years)

Mass (kg)

Height (cm)

Body fat (%)

AT (km.h−1 )

HRAT (bpm)

VEAT (/min)

vMAX (km.h−1 )

25 5

74 9

173 5

11.6 4.7

11.8 1.9

163.3 8.6

65.3 10.4

15.4 1.0

• they were submitted to anthropometric measurements, percentage of body fat calculation [15] and performed an incremental running test on a treadmill in order to determine maximal aerobic velocity (vMAX) and VT2 ; • performed a five-minute run at VT2 intensity (PRE), followed by an INTTR session (8 × 1 min at vMAX, one minute at 50% vMAX for recovery); with 15 minutes interval between them. Immediately after the INTTR session, a new five minutes run at the VT2 intensity was performed (POST), in order to verify INTTR effect on constant run. These two sessions were separated by, at least, 48 hours between them.

2.2. Determination of the second ventilatory threshold (VT2 ) vMAX and VT2 were determined using an incremental protocol performed on a motorized treadmill (Micromed, Centurion, Brasilia, Brazil) with the gradient set at 1% [16]. Initial speed was set at 8 km.h.−1 for three minutes, with 1 km.h−1 increments every three-minutes, until volitional exhaustion. During tests, HR and VE were monitored by specific software (Micromed, FlowMet, Brasilia, Brazil). A ventilometer (Micromed, Centurion, Brasilia, Brazil) was used to monitor VE. VT2 was defined as the second inflexion of the VE curve [17]. Estimation based on VE has been described and validated previously on literature, in which there is similarity to the gas exchange determination (second inflexion of the VE/VO2 curve) [17,18].

2.3. Running exercise at second ventilatory threshold and interval training Passive reflexive markers were placed on right ankle (lateral maleolus), calcaneous and fifth metatarsal head. A fiveminute warm-up was conduced on treadmill at 1 km.h−1 below the VT2 , followed by five-minutes at VT2 (PRE-INT) velocity. Thus, data obtained from PRE-INT are not influenced by INTTR session. After 15 minutes rest, subjects performed INTTR session: three-minute run at VT2 (a second warm-up), and immediately after this, subjects performed eight sets of one-minute run at the vMAX, followed by oneminute run at 50% vMAX. After the INTTR session, there was three-minute recovery at rest, and a second five-minute run at VT2 was required (POST-INT). This way, comparing PREINT to POST-INT allowed to verify the effect of INTTR on constant run at moderate intensity.

2.4. Kinematic measurements Kinematic data was collected by using 2D movement analyses at 60 Hz sample rate. A camera (Sony, DCR-TRV351, Tokyo, Japan) was placed 1.20 m high, and 6 m at the sagittal plane of the subject. Images were recorded during the last 20 seconds of the PRE-INT and POST-INT running efforts. Motion Analysis Tools® six, free-software, was used to verify SF, STA and SWI in six complete cycles during the last 20 seconds running [2]. Stride cycle was determined as two consecutive heel contacts and SF was determined based on stride cycle duration and expressed as strides per minute. STA was determined considering the foot contact duration (ms), from heel contact to subsequent fifth metatarsal off, and SWI was determined considering air phase duration (ms), from fifth metatarsal off to subsequent heel contact.

2.5. Physiological measurements Blood samples were collected by asepsis of the index finger to evaluate LAC (Roche, Accu-Check Performa, Brazil) and GLU (Roche, Accu-Check Advantage, Brazil) [19]. These samples were collected just before PRE-INT (RESTPRE ), three-minute after PRE-INT, just before POST-INT (RESTPOST ) and three-minute after POST-INT. HR and PE measurements were recorded during same period of kinematic parameters of PRE-INT and POST-INT. PE scale used was Borg CR-20 [20] ranged from 6 (least perceived exertion) to 20 (maximum perceived exertion). Subjects were asked to give a number that would describe how they felt during running, using a PE scale as a guide, while placed in front of the subject, on the control panel of the treadmill. During all running exercises, examiners strongly encouraged the subjects to execute the tasks.

2.6. Data processing and statistical analyses Kinematic data of STA and SWI from six complete cycles were averaged to a single representative value for each parameter. All measurements are described mean ± standard deviation. To verify the differences between RESTPRE vs RESTPOST (HR, [LAC] and [GLU]), and PRE-INT vs POST-INT in the HR, VE, LAC, GLU, PE, SF, STA, and SWI, paired samples Student’s t-tests were used. The significance level was set at P < 0.05.

3. Results Table 1 summarizes anthropometric and metabolic characteristics of subjects. VT2 was reached at 76 ± 9% vMAX.

Maximal stimuli affects continuous running exercises

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Table 2 Mean ± SD heart rate (HR), blood lactate concentration [LAC] and blood glucose concentration [GLU] at rest immediately before PRE-INT (RESTPRE) and immediately before POST-INT (RESTPOST).

RESTPRE RESTPOST

HR (bpm)

[LAC]mmol/L

[GLU]mg/dL

82.5 ± 14.3 135.4 ± 14.4a

2.8 ± 0.9 10.5 ± 3.5a

95.6 ± 10.5 133.5 ± 19.6a

a

Denotes significant difference in relation to RESTPRE (P < 0.001).

Table 3 Mean ± SD stride frequency (SF), stance phase duration (STA) and swing phase duration (SWI) at the intensity of the anaerobic threshold before (PRE-INT) and after (POST-INT) an interval training session.

PRE-INT POST-INT a

SF (/min)

STA (ms)

SWI (ms)

82.3 ± 3.9 85.5 ± 4.7a

225 ± 0.26 227 ± 029

502 ± 0.24 495 ± 0.20

Denotes significant difference in relation to PRE-INT.

Physiological parameters collected just before PRE-INT and POST-INT were presented in the Table 2. HR, LAC and GLU presented significantly lower at RESTPRE in comparison to RESTPOST (P < 0.001). In general, physiological parameters (Fig. 1) were more affected than kinematic parameters by INTTR running session. There were found significant increases after the INTTR session in blood LAC (231 ± 197% change, P < 0.01) and GLU (28.3 ± 26% change, P < 0.001). In the same way, during last 20 seconds of POST-INT, significantly higher HR (12 ± 3% change, P < 0.01), VE (23 ± 15% change, P < 0.01), and PE (25 ± 20% change, P < 0.01) were found in comparison to PREINT. Kinematic parameters presented influence of INTTR on SF, which presented significant increase between PRE and POST conditions (P < 0.05). However, STA and SWI (Table 3) presented no changes when PRE-INT and POST-INT were compared (P > 0.05).

4. Discussion Running exercise is often characterized by high demands for human physiology, specially under maximal conditions. Impaired homeostasis leads to unbearable metabolical and mechanical imbalances which determines the end of session by exhaustion [3,5,6]. In this way, the main findings in the present investigation are global changes in physiological responses, and just one local biomechanical effect, when the same condition is repeated before and after an INTTR session. These results are relevant to describe the exact extent of changes related to maximal running stimulus under normal running conditions. In practical terms, it is more difficult to run just after a short but high-intense running INTTR session. These overall changes may be also present in other conditions which involve short and high-intense stimuli, such as soccer, basketball etc., in which the different intensities may even be related to injuries [4].

Figure 1 Mean ± SD heart rate (HR), ventilation (VE), rate of perceived exertion (PE), blood lactate [LAC] and blood glucose [GLU] at the intensity of the anaerobic threshold before (PREINT) and after (POST-INT) an interval training session. * Denotes significant difference in relation to PRE-INT (P < 0.05).

296 Since running speed alters physiological demand [3] and kinematic behavior [9,10,12], the same intensity (VT2 ) has been used in PRE-INT and POST-INT. Although physiological changes related to fatigue during running affect the VT2 determination, in the present study, we have used a fixed threshold to evaluate the same velocity and its respective changes related to the exercise. Increases in physiological parameters during running exercises are common, depending on running intensity, duration and subject’s status of training [3]. It is important to state that only by maintaining a constant velocity (avoiding the interval exercise) there are also changes in some of the investigated parameters, as increases in HR, VE and LAC [3,14]. However, these published increases are not as high as for our results. For instance, the LAC relative to a continuous running exercise around 30—40 minutes at 95% of onset of blood lactate accumulation (OBLA) is ∼3.5 mmol/L [21], and at the maximal lactate steady state is around 4.3 mmol/L [14] in the end of the exercise. These cited results were substantially lower than the changes during the present investigation (10.5 ± 3.5 mmol/L just after the INTTR ), even in a shorter session period (16 minutes) involving maximal stimuli. Runners face a high effort along INTTR with effects on physiological parameters remaining even after the end of the exercise. HR and VE during POST-INT were higher than PRE-INT, possibly by the incomplete recovery from the maximal exercise, as verified in our results (RESTPRE vs RESTPOST ). During running oxygen consumption increases, and to assure oxygen delivery, and CO2 re-uptake to all active tissues, blood must circulate faster, consequently there is a higher heart rate [5,22]. Beside this, lower vagal tonus and increases in the sympathetic component during this workout may increase HR [19]. In the same way, VE must increase during exercise, to maintain gas exchanges and O2 offer [5,6]. An important issue related to maximal exercises is that recovery of both HR and VE may be delayed under maximal and supramaximal conditions [6]. During INTTR exercises, an incomplete recovery may occur caused by the cumulative effect of multiple maximal stimuli [6,23]. In the present study, as a result of the running intensity and its cumulative effect, HR was ∼12% higher and ventilation was ∼23% higher during running at the VT2 , after the INTTR session, showing that metabolic demand was high enough to lead to aerobic conditioning. Previous studies have demonstrated that effects of INTTR session are related to increases in blood glucose release during exercise. The increased GLU may be associated with high intensities and/or long exercise durations [22]. Specifically, during INTTR session, there are transitions between aerobic and anaerobic metabolisms, with a predominant anaerobic component [3]. The present study verified ∼28% increase in the GLU after INTTR session, as a consequence of the high-energy costs and slow GLU re-uptake. As expected, LAC was affected by the INTTR session, once it is related to running intensity and blood glucose availability [3]. Before the running session, LAC at the ANTH was ∼2.8 mmol/L, demonstrating the effectiveness of our protocol in determining intensities below the well referenced 3.5—4.0 mmol/L [13]. After an intense running exercise, usually LAC samples are collected from three to five minutes after test/session, allowing determination of a peak in LAC [24]. In the present study, LAC was 10.5 ± 3.5 mmol/L just three minutes after

A.S. Oliveira et al. the exercise, and significantly higher (P < 0.05, t-Student test) than after the second run at VT2 (8.41 ± 3.31 mmol/L after the INTTR session, Fig. 1), indicating the re-uptaking of the metabolites, or even its use as energy [6] until eight to ten minutes after INTTR . Thus, in general, INTTR exercise affects metabolites, (LAC) and energy substrates (GLU) re-uptake, delaying mechanisms responsible to reestablish homeostasis. One interesting result in the present study was the increased PE after the INTT . Conversely to other measurements, PE represents a global effort sensation during exercise performance, being affected by muscular fatigue. Eston et al. [25] investigated submaximal cycling exercises (75% VO2 peak) performed in two different conditions — just after an incremental test, and under fresh condition few days after the first test. These authors found increases in PE and HR under fatigued conditions (after the incremental test), possibly explained by physiological regulation of effort from the central nervous system and peripheral influences [25,26]. We found increases ∼25% for PE after INTTR , what in practical terms was a change in perception from ‘‘fairly light’’ or ‘‘somewhat hard’’ (∼11 in the scale), to a ‘‘hard’’ or ‘‘very hard’’ exercise (∼14 on the scale), respectively for PRE and POST conditions. The only kinematic parameter affected by the INTTR exercise was the SF. Previous studies presented effects of the exercise intensity [12] and duration [9,11,27] on running kinematics, commonly affected by the fatigue process. Generally, muscular fatigue impairs the EC coupling (consequently the force output) and increases metabolite accumulation (such as [LAC], K+ , H+ ) [6,23,28]. SF may present different results, depending on the running task. Long-term running may induce higher contact phase duration due to decrements on joint stiffness caused by muscle fatigue, which leads to decreased contact periods [9,10,28]. On the other hand, short-term and high-intense running with recovery periods may present decreased stride length [29], explained by activation of fast twitch fibers to shorten contact duration and use of storage elastic energy, decreasing energy expenditure. Long-term running have showed the same decreased stride length in function of time, possibly due to and decrement of muscle force and causing the SF increase at the same speed [27]. Our designed fatiguing protocol was intense and may have caused loss of muscle force not allowing stride length maintenance, showing that threeminute recovery was not enough for maintenance of running technique, since SF was increased to keep running performance on a treadmill [27]. Thus, INTTR sessions targeting higher demand stimuli, for biomechanical gesture maintenance, may have longer recovery periods between bouts in order to achieve running technique improvement.

4.1. Limitations of the study Measurements of anaerobic threshold were made by using a ventilometer, and its index was extract without a gas exchange analysis. However, the technique applied in this investigation has validity tested by previous studies [18]. In this way, the absence of traditional parameters as the VO2 , and maximal VO2 was a limitation in this study, and should not be ignored, being purposed for further studies the inclu-

Maximal stimuli affects continuous running exercises sion of gas exchanges measurements, in order to improve the knowledge. However, speculations about increases in these measurements are reasonable, just like for the HR and VE, since during fatiguing exercises, their increases are concomitant [6]. The use of gas exchange measurements to determine VT2 may not have influenced the results, because there are studies correlating this direct determination to the second curve inflexion [17]. In summary, running INTTR exercise at maximal intensity affected in physiological ([LAC] [GLU], HR and VE) and kinematic parameters (SF), when two identical conditions (running at the VT2 ) were performed before and after it. These global changes are linked by the high-demanded INTTR exercise, which was barely recovered prior to the last running. At the same time, the sensation during the exercise is affected, raising the difficulty for the same task, caused by interactions between physiological and psychological systems during running exercises.

Conflict of interest None.

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