A Real-World High-Intensity Interval Training Protocol for Cardiorespiratory Fitness Improvement

Summary

This study presents a low-cost and easy-to-implement "real world" high-intensity interval training (HIIT) protocol for scientific research and discusses its efficiency for cardiorespiratory fitness.

Abstract

High-Intensity Interval Training (HIIT) has emerged as an interesting time-efficient approach to increase exercise adherence and improve health. However, few studies have tested the efficiency of HIIT protocols in a "real world" setting, e.g., HIIT protocols designed for outdoor spaces without specialized equipment. This study presents a "real world" training protocol, named "beep training", and compares the efficiency of a HIIT regiment versus a traditional long-duration Moderate-Intensity Continuous Training (MICT) regiment using this beep training protocol on VO₂ max of overweight untrained men. Twenty-two subjects performed outdoor running with MICT (n = 11) or HIIT (n = 11). Cardiorespiratory fitness was assessed before and after training protocols using a metabolic analyzer. Both training protocols were performed 3 days a week for 8 weeks using the Beep Test results. The MICT group performed the exercise program at 60%-75% of the maximum speed of the 20 m shuttle test (Vmax) and with a progression of the distance of 3,500-5,000 m. The HIIT group performed the interval exercise with 7-10 bouts of 200 m at 85%-100% of the maximum speed of the 20 m shuttle test (Vmax), interspersed with 1 min of passive recovery. Although the HIIT group presented a significantly lower training volume than the MICT group (p < 0.05) after 8 weeks of beep training, HIIT was superior to MICT in improving VO₂ max (MICT: ~4.1%; HIIT: ~7.3%; p < 0.05). The "real world" HIIT regiment based on beep training protocol is a time-efficient, low-cost, and easy-to-implement protocol for overweight untrained men.

Introduction

Robust evidence has shown that High-Intensity Interval Training (HIIT) induces similar or even superior positive physiological adaptations than a traditional long-duration Moderate-Intensity Continuous Training (MICT)^1,2,3. A HIIT session is composed of short bouts of high-intensity exercise interspersed with low-intensity exercise (active recovery) or rest (passive recovery). While a daily session with a MICT protocol lasts 30 to 60 min, on average, a daily session with HIIT may take half the time or less from a MICT session. Then, considering that sedentary individuals have indicated lack of time as the main barrier to engaging in a regular physical exercise program⁴, HIIT may be an interesting time-efficient approach to increase exercise adherence and improve health⁵.

However, despite the growing evidence pointing out the health benefits of HIIT, most studies have designed HIIT protocols for well-controlled laboratory environments using high-cost specialized equipment, such as treadmills and cycle ergometers. In the last 5 years, some studies have emphasized the importance of new studies confirming the health benefits of HIIT using exercise protocols for the real world, e.g., HIIT protocols performed in outdoor spaces without specialized equipment⁶. However, the difficulty in designing well-controlled studies to test HIIT protocols in non-laboratory environments has been the main challenge for researchers in this field.

In response to this challenge, a real-world HIIT protocol was developed here for scientific research and its efficiency in cardiorespiratory fitness was tested. A training protocol was developed using the shuttle test proposed by Leger et al.⁷ (named as Beep Training), and the effects of HIIT and MICT regiments based on this Beep training on VO₂ max were compared in overweight untrained men. Briefly, although the duration of daily sessions with HIIT was almost half of the duration of MICT protocol, the Beep Training with HIIT was superior to the Beep Training with MICT in increasing VO₂ max. Thus, Beep training with HIIT is a time-efficient and feasible approach to improve cardiorespiratory fitness in apparently healthy overweight/obese individuals. Moreover, general people may easily practice the beep training protocol as it is a low-cost and easy-to-implement physical training in a real-world scenario.

Protocol

This study was approved by the Federal University of the Jequitinhonha and Mucuri Valleys Ethics and Research Committee. All participants were informed of the study objectives and experimental procedures of the study and signed a written informed consent form before their participation.

1. Experimental design

1. Select individuals who meet the inclusion criteria: nonsmoking healthy individuals aged between 30 and 50 years with body mass index (BMI) of ≥25 kg·m^-2 and maximum oxygen consumption lesser than 50 mL O₂·kg^-1·min^-1 and engage them in regular physical exercise practices no more than 2 days a week for the past 3 months.
2. Apply the physical activity readiness questionnaire (PARq)⁸ to stratify signs or symptoms of cardiovascular disease, metabolic, or any other condition that impedes physical exercise practice.
3. Pair the participants firstly by BMI and secondly by maximal oxygen uptake (VO₂ max), and randomly divide them into one of the two groups, the Moderate-Intensity Continuous Training group (MICT; n = 11) and the High-Intensity Interval Training group (HIIT; n = 11).
4. Perform the MICT or HIIT protocol (Figure 1).
5. Record the VO₂ max before and after the exercise training protocols.

2. VO₂ max test (Ramp protocol)

1. Familiarize the participants with the treadmill and the mouthpiece used on the metabolic analyzer for at least 24 h before testing.
2. Calibrate the metabolic analyzer according to the manufacturers' recommendations.
3. Use a heart rate monitor to measure the participants' heart rate.
4. Place the non-rebreathing unilateral mouthpiece on the patient ensuring to cover the participant's mouth and nose completely.
5. Use the subject's physical activity level to program the speed and degree of maximal metabolic equivalent (MET) increments⁹.
6. Turn on the treadmill, select the Ramp protocol, and enter the subject's physical activity level (i.e., estimated maximal MET).
7. Press ON to start the Ramp protocol, which starts with a warm-up of 3 min at 5 km/h.
   NOTE: The ramp protocol estimates the progression of the test according to the informed subject's physical activity level and calculates an exercise test duration between 8 and 12 min.
8. Record heart rate (HR) and rating of perceived exertion (RPE) using the Borg scale 6-20 every min of the test.
9. Consider that VO₂ max is achieved when all the following criteria are met: respiratory exchange rate (RER) greater than 1.10; HR greater than 95% of the maximum HR predicted for the age (220-age); and RPE equal to or greater than 18.
10. Return the treadmill speed to 5 km/h (warm-up value) and remain on the treadmill for an additional 3 min.
11. Turn off the treadmill and remove the mouthpiece from the participant.

3. Beep test (Leger et al.⁷)

1. Choose a flat surface that allows placing two cones with 20 m of the distance between them.
2. Orient participants to run 20 m (marked by cones) within a predetermined period signaled by a beep sound produced by a specific software developed for this test.
3. Adjust the sound equipment connected to the computer with the software.
4. Familiarize the participants with the test.
5. Start the test.
   NOTE: The Beep Test software automatically reduces the timing of the beep sound so that the running speed increases by 0.5 km/h for every stage of the test.
6. End the test when the volunteer can no longer complete the 20 m run within the time stipulated by the beep sound.

4. Training protocols

NOTE: Table 1 summarizes the progression of the exercise protocols (MICT and HIIT) during the 8 weeks of training.

1. MICT protocol
   1. Orient each participant to maintain the running speed during the exercise sessions according to the GPS from the heart rate monitor.
   2. Instruct the participants to complete a 5 min warm-up by performing dynamic stretches and walking before each exercise session.
   3. Put on a heart rate (HR) monitor equipped with GPS tracking before each exercise session.
   4. Start the exercise session.
   5. Instruct the participants to maintain correct speed and distance by periodically checking the clock's speed and distance on the heart rate monitor.
   6. Train the participants for 2 weeks, three times a week (Monday, Wednesday, and Friday), once a day at 60% of the individual maximum speed achieved during the 20 m test (Vmax), covering a distance of 3,500 m per session in the first week and 4,000 m per session in the second week.
   7. Train the participants for 4 weeks, three times a week (Monday, Wednesday, and Friday), once a day at 65% of Vmax, covering a distance of 4,000 m per session in the third week, 4,500 m per session in the fourth and fifth week, and 5,000 m per session in the sixth week.
   8. Train the participants for 1 week, three times a week (Monday, Wednesday, and Friday), once a day at 70% of Vmax, covering a distance of 5,000 m per session in the seventh week.
   9. Train the participants for 1 week, three times a week (Monday, Wednesday, and Friday), once a day at 75% of Vmax, covering a distance of 5,000 m per session in the eighth week.
   10. Train the participants at 70% of Vmax, covering a daily distance of 5,000 m in the seventh week.
   11. Train the participants at 75% of Vmax, covering a daily distance of 5,000 m in the eighth week.
   12. Train the MICT group either in the morning or afternoon.
   13. Transfer the data recorded by the HR monitor to a computer after each exercise session to verify if the prescribed distance and running speed were reached.
   14. Exclude the participants who do not complete all the training sessions in the week.
   15. Analyze the data to ensure that each participant performs the respective training regimen according to the prescribed distance and speed.
2. HIIT protocol
   1. Calculate the time interval between beep sounds every 20 m according to the Vmax% prescribed for each exercise session.
   2. Open the Sound Forge PRO software.
   3. Enter the information such as how many seconds the beep sound must shoot, how many times the shoots must occur to complete each exercise sprint, and the interval period between the sprints (corresponding to passive recovery).
   4. Download the individual sound files in MP3 format.
   5. Send the beep sound file to the cell phone of each participant.
   6. Mark a lane with cones every 20 m.
   7. Instruct the participant to follow the command of the beep sounds (by listening to them through headphones), guiding the exact moment when each subject must reach the cone (placed every 20 m away).
   8. Instruct the participants to complete a 5 min warm-up by performing dynamic stretches and walking before each exercise session.
   9. Put on a heart rate (HR) monitor equipped with GPS tracking before each exercise session.
   10. Start the exercise session.
   11. Train the participants with seven sprints (first week) and eight sprints (second week) of 200 m at 85% of Vmax, interspersed by 1 min of passive recovery between sprints.
   12. Train the participants with eight sprints (third week), nine sprints (fourth and fifth week), and 10 sprints (sixth week) of 200 m at 90% of Vmax, interspersed by 1 min of passive recovery.
   13. Train the participants with 10 sprints (seventh week) of 200 m at 95% of Vmax interspersed by 1 min of passive recovery.
   14. Train the participants with 10 sprints (eighth week) of 200 m at 100% of Vmax interspersed by 1 min of passive recovery.
   15. Train the HIIT group once a day, three times a week (Monday, Wednesday, and Friday) in the morning or afternoon.
   16. Transfer the data recorded by the HR monitor to a computer after each exercise session.
   17. Exclude the participants who do not complete all the training sessions in the week.
   18. Analyze the data to ensure that each participant performs the respective training regimen according to the prescribed distance and speed.

5. Statistical analysis

1. Express all data as mean ± standard deviation.
2. Check the normality of data using the Shapiro-Wilk test.
3. Analyze the data using one or two-Way ANOVA followed by Tukey's post-hoc test; set the significance level at 5%.

Representative Results

Table 1 shows data of distance, speed, rest time, session duration, and mean heart rate from HIIT and MICT groups. During the 8 weeks of beep training, running distance and duration were higher in MICT than in the HIIT group (p < 0.05), while running velocity and heart rate were higher in HIIT than in the MICT group (p < 0.05). These data confirm the main differences between MICT and HIIT protocols, i.e., while MICT is characterized by long-duration moderate-intensity continuous exercises, HIIT is characterized by short-duration high-intensity interval exercises.

Figure 2 shows the effects of Beep training on VO₂ max. Before training, VO₂ max was similar between MICT and HIIT groups (MICT: 45.01 ± 4.12 mL O₂·Kg^-1·min^-1; HIIT: 46.16± 3.10 mL O₂·Kg^-1·min^-1; p = 0.98). After training, VO₂ max increased in both groups (MICT: 49.12 ± 5.26 mL O₂·Kg^-1·min^-1; HIIT: 53.47 ± 3.86 mL O₂·Kg^-1·min^-1; p < 0.05); however, increase in VO₂ max was superior in HIIT versus MICT group (MICT: ~4.1%; HIIT: ~7.3%; p < 0.5; Figure 2A,B).

MICT						HIIT
Week	Distance (m)	Velocity (Vmax)	Rest (min)	Duration (min)	Heart Rate (bpm)	Distance (m)	Velocity (Vmax)	Rest (min)	Duration (min)	Heart Rate (bpm)
1	3500	60%	--	27.8 ± 3.2	142 ± 11	7 x 200	85%	1	14.8 ± 0.7*	171 ± 11*
2	4000	60%	--	31.4 ± 4.2	145 ± 13	8 x 200	85%	1	16.7 ± 0.7*	170 ± 10*
3	4000	65%	--	29.4 ± 3.5	146 ± 10	8 x 200	90%	1	16.2 ± 0.7*	174 ± 11*
4	4500	65%	--	31.9 ± 3.4	147 ± 10	9 x 200	90%	1	18.2 ± 0.8*	173 ± 11*
5	4500	65%	--	31.2 ± 3.1	154 ± 9	9 x 200	90%	1	18.0 ± 0.9*	175 ± 10*
6	5000	65%	--	32.9 ± 3.3	151 ± 9	10 x 200	90%	1	19.9 ± 1.0*	174 ± 11*
7	5000	70%	--	33.4 ± 5.0	153 ± 10	10 x 200	95%	1	19.4 ± 0.8*	177 ± 10*
8	5000	75%	--	32.2 ± 4.0	156 ± 10	10 x 200	100%	1	19.1 ± 0.9*	178 ± 9*
Vmax: Maximum running velocity determined using a 20 m beep test.
*Significant difference between MICT and HIIT.

Table 1: Comparison of Distance, speed, rest time, session duration, and mean heart rate from HIIT and MICT groups during the 8 weeks of the training protocols. Adapted from Gripp et al.¹⁷.

Figure 1: Experimental design of MICT and HIIT protocols. Adapted from Gripp et al.¹⁷. Please click here to view a larger version of this figure.

Figure 2: VO₂ peak before and after the beep training from HIIT and MICT groups. (A) Pre-training and post-training VO₂ peak. (B) Delta (Δ) VO₂ peak (Post-training VO₂ peak - pre-training VO₂ peak). Different letters mean statistically significant differences within the same group. The asterisk denotes the statistically significant differences between groups. Data are presented as mean ± SD and p < 0.05. Adapted from Gripp et al.¹⁷. Please click here to view a larger version of this figure.

Discussion

HIIT has become a time-efficient alternative to the traditional MICT. This studypresents a low-cost, easy-to-implement HIIT protocol for a real-world setting. Most studies have proven the health benefits of HIIT using laboratory-based HIIT protocols^6,10, and, recently, few studies have investigated the effects of real-world HIIT protocols in overweight untrained individuals^10,14.

Roy et al.¹⁰ tested a home-based HIIT protocol consisting of multiple exercise types (the majority using only the body weight) in overweight individuals. The participants performed the home-based HIIT 3 days a week for 12 months. To reach high levels of exercise intensity targeting a Rating of Perceived Exertion (RPE) of 8-10 (10-point scale), the participants needed to progress to more challenging exercise options (e.g., a Wingate type HIIT protocol¹⁰) and were allowed to choose their exercise programs. No changes in VO₂ max were seen even after 1 year of the exercise program. One of the reasons for this result may be related to the low participant´s adherence (67%). Accordingly, some studies have argued that this type of home-based exercise has low long-term adherence as it is complex to perform for most people, especially sedentary individuals^11,12,13. In an approach more similar to the HIIT protocol proposed in this study, Lunt et al.¹⁴, tested a running outdoor HIIT protocol in overweight individuals. The participants performed HIIT 3 days a week for 4 months and the daily sessions lasted 15 min, on average, consisting of running for 4 min at 85%-95% HR followed by 3 min of active recovery (walking or jogging). After training, VO₂ max improved by ~10%; however, the participant's adherence was only 59% (still lower than the participant's adherence in Roy's study¹⁰).

This beep training protocol has important advantages to the HIIT protocols proposed by Roy et al.⁹ and Lunt et al.¹⁴ in the context of scientific research. While Roy et al.¹⁰ proposed a home-based HIIT protocol targeting an RPE of 8-10 (10-point scale), and Lunt et al.¹⁴ proposed an outdoor HIIT protocol targeting 85%-95% HR, a more reliable method of intensity control is created here, via easy-to-perform and enjoyable outdoor HIIT protocol.

The use of RPE and percentage of maximal heart rate (HRmax) for monitoring exercise intensity in scientific research using HIIT protocols have been criticized in recent studies^15,16. Although RPE use is encouraged to monitor exercise intensity in a clinical scenery due to its easy use, RPE use in research is questioned due to the difficulty of individuals reporting subjective perception of effort accurately¹⁵. Taylor et al.¹⁶ highlight that using % HRmax for exercise intensity prescription in HIIT protocols is also imprecise. Among the many reasons, they highlight the difficulty in estimating or even accurately measuring the individual´s HRmax in maximal exercise testing. Accordingly, the mean HR reached in clinical trials is usually lesser than the target HR prescribed for HIIT protocols.

The exercise intensity in the beep training protocol is prescribed according to the individual maximum velocity achieved during the 20 m shuttle test (Vmax), a test largely used for sports practices in children and adults⁸. During the 8 weeks of training, the run intensity was set progressively to 65%-75% and 85%-100% of Vmax for MICT and HIIT groups, respectively. Once an individual has the Vmax recorded, a trained instructor calculates the time interval between beep sounds every 20 m according to the Vmax% prescribed for each exercise session. Then, once familiarized with the beep training program, even a heart rate monitor is not necessary; just having a cell phone, a headset, and cones or similar objects to demarcate an area of 20 m is sufficient for the daily exercise practice.

Another highlight of the Beep training protocol compared with the HIIT protocols used by Roy et al.¹⁰ and Lunt et al.¹⁴ were the results of the Beep Training for cardiorespiratory fitness and adherence. All the studies had similar sample characteristics (i.e., overweight untrained individuals). The HIIT group from Roy's study had no change in VO₂ max and exhibited an exercise adherence of 67% while the HIIT group from Lunt´s study had a 10% increase in VO₂ max and an exercise adherence of 59%. In comparison with these results, in the present study, a 7.3% increase in VO₂ max and an exercise adherence of 81% are observed in the HIIT group.

The Beep training protocol has some limitations. First, a trained instructor must accompany the practitioners at least once a week for possible adjustments in the exercise prescription. Second, outdoor space and minimal equipment (cell phone, headset, and cones (or similar objects)) are also necessary. However, the use of remote monitoring by the instructor and adaptations of small outdoor spaces (e.g., 10 m spaces that allow the practitioner to go and come back to complete the 20 m required for the beep sound shot) may easily solve these limitations to allow the beep training practice. Moreover, several individuals may simultaneously exercise in the same spaces as they will use individual headphones with individual sounds for their exercise prescription. Finally, another limitation of the training protocol is that the speed of running used during the exercise sections is based on the beep test. In this test, the individual needs to decelerate every 20 m to turn out 180 degrees, resulting in some time being lost (maybe milliseconds). During the exercise sessions, if an individual will not need to turn out 180 degrees in the training track, the maximal velocity reached in the beep test would be underestimated compared with the real maximal velocity that would be reached in this training track.

In this study, a feasible, time-efficient, low-cost, and easy-to-implement HIIT regiment is proposed based on a beep training protocol designed to be practiced in a real-world setting. Future studies must be performed to test the efficiency and feasibility of beep training in healthy and unhealthy individuals of different ages.

Materials

Name	Company	Catalog Number	Comments
Beep Test software	Bitworks	N/A	version 2.0
Exercise Physiology Measurement & Analysis System	ADI INSTRUMENT	PL3508B80	PowerLab 8/35 and LabChart Pro software (which includes the Metabolic Module for calculating metabolic parameters such as VCO2, VO2, respiratory exchange ratio (RER) and minute ventilation) Bio Amp Gas Analyzer Gas Mixing Chamber Spirometer Thermistor Pod Exercise Physiology Accessory Kit
GraphPad Software	GraphPad Prism	N/A	version 7.00
Heart Rate monitor	Polar	N/A	RS800 Running Computer: The running computer displays and records your heartrate and other exercise data during exercise. 2. Polar WearLink W.I.N.D. transmitter: The transmitter sends the heart rate signal to the running computer. The transmitterconsists of a connector and a strap.
Sound Forge PRO software	Sound Forge	N/A	version 14.00
Treadmill	IMBRASPORT	N/A	Speed from 0 to 24 km/h. Elevation from 0 to 26%. Weight capacity for users up to 220 kg. 4 hp motor (220 v). Automatic lubrication system. With Safety Key and Emergency Stop Button. Runs 14 preset protocols: Bruce, Modified Bruce, mini Bruce, Naughton Ellestad, Balke, Balke-Ware, Astrand, Cooper, Kattus, Male Mader, Female Mader, Stanford and Modified Stanford. Run RAMP PROTOCOL.