Abstract
impact of six high-intensity interval training (HIIT) running sessions on 1% or 10% slopes on various physiological and performance parameters in 25 men. The participants underwent assessments of VO 2max, time to exhaustion on 1% slope (TLim1%), and time to exhaustion on 10% slope (TLim10%) in the initial three visits. They were then randomly assigned to control (CON), HIIT on 1% slope (GT1%), or HIIT on 10% slope (GT10%) groups. Over three weeks, participants performed six HIIT sessions with equalized workload based on their individual maximal oxygen uptake (vVO 2max). The
to exhaustion on 1% slope (TLim1%), and time to exhaustion on 10% slope (TLim10%) in the initial three visits. They were then randomly assigned to control (CON), HIIT on 1% slope (GT1%), or HIIT on 10% slope (GT10%) groups. Over three weeks, participants performed six HIIT sessions with equalized workload based on their individual maximal oxygen uptake (vVO 2max). The sessions comprised 50% of TLim, with a 1:1 ratio of exercise to recovery at 50% vVO 2max. The results indicated significant improvements in VO 2maxand peak velocity (VPeak) after HIIT on both slopes. Heart rate (HR) differed between sessions for GT1%, while no significant differences were observed for GT10%. Ratings of perceived exertion (RPE) were significantly reduced for GT1% after the third session, with a similar trend for GT10%. In summary, six HIIT sessions on a 1% or 10% slope effectively enhanced VO 2maxand VPeak, but there was no improvement in TLim performance, suggesting no adaptive transfer between training groups. Keywords:anaerobic threshold; running speed; oxygen consumption; exercise test; physical endurance 1. Introduction Significant adaptations are observed in maximal oxygen uptake (VO2max) and aerobic performance after a few short sessions of high-intensity interval training (HIIT) performed at speeds close to VO2max(vVO2max) [1,2] and/or above maximum speed [3,4]. There is substantial evidence supporting the benefits of HIIT in competitive runners [5], highlighting that this high-intensity protocol, executed in brief periods, elicits physiological responses comparable to those achieved by continuous programs of prolonged exercise [6–8]. These adaptations establish a favorable relationship between training time and ef- fectiveness [9–11] for the HIIT training model, regardless of the sport in focus, athlete’s experience, and fitness level [4]. In addition to the intensification proposed by HIIT, the vari- ation of training stimuli emerges as a potential strategy for metabolic and neuromuscular enhancements [12], beyond adaptations related to running performance. Appl. Sci.2024,14, 9699.
Appl. Sci.2024,14, 9699 2 of 12 In a competitive running scenario, physiological and mechanical changes resulting from alterations in terrain (horizontal vs. inclined vs. declined) influence the dynam- ics of the stretching–shortening cycle and, consequently, the energy cost [13,14]. In this sense, uphill running, for example, demonstrates an increase in neuromuscular [15] and metabolic [16] overload compared to horizontal running, resulting in a higher perception of effort. Studies indicate an increase in muscle activation and a predominance of concentric overload during uphill running [17], possibly explaining the increase in energy cost and the reduction in acute performance [18]. Currently, there is substantial evidence supporting the effectiveness of different train- ing programs for runners, aiming to minimize disparities caused by variations in inclination and optimize results [19]. Traditional approaches, such as continuous training at different intensities and resistance training regimens, have been widely studied and associated with improvements in endurance, metabolic efficiency, and aerobic performance in runners [20]. However, there is a current gap in specific evidence regarding the effects of HIIT on run- ners, especially concerning different inclinations. While HIIT is recognized for its general benefits, the specific application of these principles in varied uphill contexts in running still seems to lack investigations to establish clear and direct evidence on acute responses in variables of interest of aerobic performance [21]. Although previous studies have addressed the effects of HIIT in different sports con- texts, there is a scarcity of research specifically focused on runners and their response to HIIT at different slope percentages [22,23]. In addition to methodological limitations, available studies have not adequately explored the complexity of the relationship between HIIT and uphill running. Furthermore, the lack of experimental research hinders a com- prehensive understanding of adaptations over time [24]. This study aimed to investigate the impact of six sessions of HIIT running on 1% and 10% slopes on key physiological parameters, including VO2max, peak velocity (VPeak), heart rate (HR), rate of perceived exertion (RPE), and time to exhaustion (TLim). Given the higher neuromuscular demand associated with a 10% slope, our hypotheses were as follows: (a) running on a
[24]. This study aimed to investigate the impact of six sessions of HIIT running on 1% and 10% slopes on key physiological parameters, including VO2max, peak velocity (VPeak), heart rate (HR), rate of perceived exertion (RPE), and time to exhaustion (TLim). Given the higher neuromuscular demand associated with a 10% slope, our hypotheses were as follows: (a) running on a 10% slope will result in more substantial adaptive improvements compared to a 1% slope (H1); (b) HR and RPE will show equal adaptation patterns over time; and (c) training on a 10% slope will lead to significant performance gains for both TLim1% and TLim10% (H3—adaptive transfer hypotheses), while training on a 1% slope will generate specific improvements, primarily in flat terrain performance. 2. Materials and Methods 2.1. Study Design and Registration This study followed all the items proposed in the guidelines of CONSORT for reporting parallel group randomized trials. All procedures were performed in accordance with the Declaration of Helsinki and included in the clinical trial registration of the U.S. National Institutes of Health (ClinicalTrials.gov; NCT02511964). This research analyzed the effect of HIIT with different slope programs (1% slope or uphill running on 10% slope) on aerobic performance in healthy people, using a randomized, between-group design (experimental group [EG] and control group [CG], respectively). The primary outcomes of this study involve the dependent variables: VO2max, total time of protocol (TTotal), peak of velocity (VPeak), metabolic demands, and absolute time values (min) of time to exhaustion for the 1% slope and uphill running on the 10% slope (TLim1% and TLim10%). As a secondary outcome, HR and RPE were observed, as well as whether there was a possible transfer of adaptations between the training group, measured based on TLim performance. Scheme presents the entry and exclusion of participants and the primary and secondary outcomes.
Appl. Sci.2024,14, 9699 3 of 12Appl. Sci. 2024, 14, x FOR PEER REVIEW 3 of 13 possible transfer of adaptations between the training group, measured based on TLim performance. Chart 1 presents the entry and exclusion of participants and the primary and secondary outcomes. Chart 1. Entry flow and exclusion of participants. 2.2. Subjects Twenty-five male college students, physically active and familiar with aerobic activities on a treadmill, participated in this study. Individuals were invited through announcements made at the university and in a fitness center where the study was conducted over the course of six months. As inclusion criteria, participants needed to have a minimum of 2 years of aerobic training experience and perform high-intensity exercises a minimum of twice a week, with at least 150 min of moderate or vigorous aerobic activities executed. This study excluded those with a recent history of injury due to the potential interference on running performance, low adherence to the exercise program (i.e., an interval of more than three days between sessions), or the use of any ergogenic substance that could potentially interfere with the study results. All individuals were invited to have their questions clarified after signing the consent form. This study was approved by the ethics committee of the university (#045.2010). Using the statistical package G-Power (Free Version 3.0.5) for analysis, “ANOVA Repeated Measures Between Factors”, with two measures and three groups, the sample size considered an error of 5%, statistic power of 80%, and an effect size of 0.60 (moderate) (19), resulting in 24 participants. Considering sample loss and significant abandonment when conducting chronic experimental models, a greater number of participants were recruited, expecting a loss of around 20% to 30%. Table 1 contains the anthropometry, body composition, physiological parameters, and performance of the groups investigated. Table 1. Average (SD) of the subjects’ characteristics, training sessions, physiological parameters, and performance. Variables GT 1% GT 10% CON (n = 9) (n = 8) (n = 8) Age years (SD) 26 (5) 28 (3) 26 (3) Anthropometry and Body Composition Body mass kg (SD) 79.5 (9.8) 84.0 (13.6) 82.2 (10.5) Height cm
and performance of the groups investigated. Table 1. Average (SD) of the subjects’ characteristics, training sessions, physiological parameters, and performance. Variables GT 1% GT 10% CON (n = 9) (n = 8) (n = 8) Age years (SD) 26 (5) 28 (3) 26 (3) Anthropometry and Body Composition Body mass kg (SD) 79.5 (9.8) 84.0 (13.6) 82.2 (10.5) Height cm (SD) 178.0 (7.4) 175.1 (5.9) 177.3 (6.5) Scheme 1.Entry flow and exclusion of participants. 2.2. Subjects Twenty-five male college students, physically active and familiar with aerobic activities on a treadmill, participated in this study. Individuals were invited through announcements made at the university and in a fitness center where the study was conducted over the course of six months. As inclusion criteria, participants needed to have a minimum of 2 years of aerobic training experience and perform high-intensity exercises a minimum of twice a week, with at least 150 min of moderate or vigorous aerobic activities executed. This study excluded those with a recent history of injury due to the potential interference on running performance, low adherence to the exercise program (i.e., an interval of more than three days between sessions), or the use of any ergogenic substance that could potentially interfere with the study results. All individuals were invited to have their questions clarified after signing the consent form. This study was approved by the ethics committee of the university (#045.2010). Using the statistical package G-Power (Free Version 3.0.5) for analysis, “ANOVA Repeated Mea- sures Between Factors”, with two measures and three groups, the sample size considered an error of 5%, statistic power of 80%, and an effect size of 0.60 (moderate) (19), resulting in 24 participants. Considering sample loss and significant abandonment when conducting chronic experimental models, a greater number of participants were recruited, expecting a loss of around 20% to 30%. Table physiological parameters, and performance of the groups investigated. Table 1.Average (SD) of the subjects’ characteristics, training sessions, physiological parameters, and performance. Variables GT 1% GT 10% CON (n = 9) (n = 8) (n = 8) Age years (SD) 26 (5) 28 (3) 26 (3)
greater number of participants were recruited, expecting a loss of around 20% to 30%. Table physiological parameters, and performance of the groups investigated. Table 1.Average (SD) of the subjects’ characteristics, training sessions, physiological parameters, and performance. Variables GT 1% GT 10% CON (n = 9) (n = 8) (n = 8) Age years (SD) 26 (5) 28 (3) 26 (3) Anthropometry and Body Composition Body mass kg (SD) 79.5 (9.8) 84.0 (13.6) 82.2 (10.5) Height cm (SD) 178.0 (7.4) 175.1 (5.9) 177.3 (6.5) BF % (SD) 13.5 (4.3) 14.7 (3.6) 12.5 (4.2) Physiologic variables VO 2maxmL·kg −1 ·min −1 (SD) 52.6 (4.4) 54.1 (4.1) 54.7 (5.6) HRmaxbpm (SD) 193 (7) 191 (10) 193 (10) Subtitle: GT1%—running group on 1% slope; GT10%—running group on 10% slope; CON—control group; SD— standard deviation; HRmax—maximum heart rate; BF—body fat.
Appl. Sci.2024,14, 9699 4 of 12 2.3. Withdrawal Criteria Participants were automatically removed from this study if they did not fully comply with the evaluation processes within a period of two weeks or did not complete the six training sessions exactly twice a week. Participants were instructed in such cases to abandon the experiment and were free to withdraw, without harm, at any time. 2.4. Experimental Approach The comparison between running programs was carried out using a randomized clinical trial composed of three groups (i.e., HIIT on 1% slope (GT1%) [n = 9], HIIT on 10% slope (GT10%) [n = 8], and control (CON) [n = 8]). The allocation was given a random strategy conducted by a researcher not involved in the experiment (described in specific sessions). The different groups (GT1%, GT10%, and CON) before the start of the experimental sessions, that is, pre-intervention, did not present significant differences for the TLim1% variable (p= 0.632). The GT1% and GT10% groups underwent a training program with six sessions, while the control group did not train. The pre- and post-training sessions were performed in three visits, as described in Figure. All training sessions were carried out at the same time of day with the temperature controlled between 21 and 23 degrees and a relative humidity of ~60%. All participants were instructed not to eat in the three hours preceding the tests and not to perform physical activity in the 24 h before the evaluations. The protocol to evaluate VO2maxand the time to exhaustion evaluation were performed on different days, with 48 h in between.Appl. Sci. 2024, 14, x FOR PEER REVIEW 4 of 13 BF % (SD) 13.5 (4.3) 14.7 (3.6) 12.5 (4.2) Physiologic variables VO 2max mL∙kg −1 ∙min −1 (SD) 52.6 (4.4) 54.1 (4.1) 54.7 (5.6) HR max bpm (SD) 193 (7) 191 (10) 193 (10) Subtitle: GT1%—running group on 1% slope; GT10%—running group on 10% slope; CON—control group; SD—standard deviation; HR max—maximum heart rate; BF—body fat. 2.3. Withdrawal Criteria Participants were automatically removed from this study if they did not fully comply with the evaluation processes within a period
52.6 (4.4) 54.1 (4.1) 54.7 (5.6) HR max bpm (SD) 193 (7) 191 (10) 193 (10) Subtitle: GT1%—running group on 1% slope; GT10%—running group on 10% slope; CON—control group; SD—standard deviation; HR max—maximum heart rate; BF—body fat. 2.3. Withdrawal Criteria Participants were automatically removed from this study if they did not fully comply with the evaluation processes within a period of two weeks or did not complete the six training sessions exactly twice a week. Participants were instructed in such cases to abandon the experiment and were free to withdraw, without harm, at any time. 2.4. Experimental Approach The comparison between running programs was carried out using a randomized clinical trial composed of three groups (i.e., HIIT on 1% slope (GT1%) [n = 9], HIIT on 10% slope (GT10%) [n = 8], and control (CON) [n = 8]). The allocation was given a random strategy conducted by a researcher not involved in the experiment (described in specific sessions). The different groups (GT1%, GT10%, and CON) before the start of the experimental sessions, that is, pre-intervention, did not present significant differences for the TLim1% variable (p = 0.632). The GT1% and GT10% groups underwent a training program with six sessions, while the control group did not train. The pre- and post- training sessions were performed in three visits, as described in Figure 1. All training sessions were carried out at the same time of day with the temperature controlled between 21 and 23 degrees and a relative humidity of ~60%. All participants were instructed not to eat in the three hours preceding the tests and not to perform physical activity in the 24 h before the evaluations. The protocol to evaluate VO 2max and the time to exhaustion evaluation were performed on different days, with 48 h in between. Figure 1. Visual representation of the entry and exclusion flow of participants until the collection of the primary and secondary outcomes. 2.5. Procedures 2.5.1. Anthropometry and Body Composition Standard measurements established by the International Society for the Advancement of Kinanthropometry (ISAK) were used, consisting of the following indicators: body weight, height, and
on different days, with 48 h in between. Figure 1. Visual representation of the entry and exclusion flow of participants until the collection of the primary and secondary outcomes. 2.5. Procedures 2.5.1. Anthropometry and Body Composition Standard measurements established by the International Society for the Advancement of Kinanthropometry (ISAK) were used, consisting of the following indicators: body weight, height, and skinfold. Height was measured with the volunteer in a standing position and barefoot, with the ankles, calves, buttocks, scapula, and head leaning on a wall. The position of the head followed Frankfurt’s plan, and stature was measured at the moment of inhaling air. Body mass was measured while the participants wore light clothes (Mechanic, Filizola, Brazil). The relative body fat was estimated using Figure 1.Visual representation of the entry and exclusion flow of participants until the collection of the primary and secondary outcomes. 2.5. Procedures 2.5.1. Anthropometry and Body Composition Standard measurements established by the International Society for the Advancement of Kinanthropometry (ISAK) were used, consisting of the following indicators: body weight, height, and skinfold. Height was measured with the volunteer in a standing position and barefoot, with the ankles, calves, buttocks, scapula, and head leaning on a wall. The position of the head followed Frankfurt’s plan, and stature was measured at the moment of inhaling air. Body mass was measured while the participants wore light clothes (Mechanic, Filizola, Brazil). The relative body fat was estimated using the skinfold technique, in which body density is calculated using the seven-fold protocol proposed by Jackson and Pollock [25] where values are collected at each point in a rotational sequence on the right side of the body and the average value of three measures is recorded. The measurements were performed by a single investigator using a skinfold compass (Slim Guide, Rosscraft, Canada). After calculating the body density, it was converted to a percentage of body fat using the equation proposed by Siri [26].
investigator using a skinfold compass (Slim Guide, Rosscraft, Canada). After calculating the body density, it was converted to a percentage of body fat using the equation proposed by Siri [26].
Appl. Sci.2024,14, 9699 5 of 12 2.5.2. Estimation of VO2maxand vVO2max After a 6 to 10 min rest in the supine position and a subsequent assessment of HR and blood pressure, participants commenced walking on a treadmill at 5 km/h with a 1% inclination. The speed was incrementally increased by 1.0 km/h per minute until reaching 65% of heart rate reserve (HRRes), at which point, the speed was maintained for 6 min. HR and RPE were recorded every minute. Subsequently, additional increments of 1.0 km/h were introduced every minute until participants could no longer sustain running, at which point, the actual maximum HR (HRmaxR) and VPeak were recorded. Verbal encouragement was given to participants to achieve maximum performance. The VO2maxand vVO2max(velocity associated with VO2max) were predicted from the equations for running proposed by ACSM and the reserve method proposed by Swain et al. [27]. The reliability of the method using running provided a typical measurement error of 2.4 mL −1 ·kg −1 ·min −1 (4.9%) and an intraclass correlation coefficient of 0.864 [28]. 2.5.3. Time to Exhaustion (TLim) After a 6 min warm-up at 50% of vVO2max, participants underwent a time to exhaus- tion test on a treadmill with inclinations of either 1% or 10%, randomly determined. The test aimed to determine the maximum duration achievable at vVO2max. HR and RPE were closely monitored at 15 s intervals. In the post-training test, a new vVO2maxwas established based on the achieved VO2max. Given the variations in speed between pre- and post-training, we utilized the metabolic demand (mL·kg −1 · min −1 ) estimated at the training speed (pre and post) for each gradient, multiplied by the duration in minutes achieved in the time to exhaustion test (TLim), as the primary outcome under investigation. 2.5.4. Training Program Participants completed a total of six training sessions over three weeks (two sessions per week), with an interval of exactly three days between each session. The running sessions began with a 6 min warm-up to 60% vVO2max. The stimuli were administered in vVO2max, with equalized workloads calculated by the ACSM running equation for the two
Description
The study examines the effects of HIIT on aerobic performance across different slopes.