Authors: Shane S. Robinson1, Jason C. Casey2, Gregory Palevo3
1GME Senior Research Project Manager, Northeast Georgia Medical Center, Gainesville, GA, USA
2Associate Professor, Metropolitan State University of Denver, Denver, CO, USA
3Assistant Professor, Albany State University, Albany, GA, USA
Shane S. Robinson, MS, CSCS
549 Paxton LN
Jefferson, Georgia 30549
Shane Robinson, MS, CSCS is a Senior Research Project Manager for Graduate Medical Education at Northeast Georgia Medical Center and Adjunct Faculty for Kinesiology at the University of North Georgia. His research interests include acute cardiovascular and metabolic responses to high-intensity exercise and adaptations to resistance training and cardiovascular disease.
Jason Casey, Ph.D., CSCS*D, ACSM-EP, is an Associate Professor of Exercise Science at Metropolitan State University of Denver, CO. His research interests focus on fatigue and recovery associated with exercise, athlete monitoring, and sport-related measurement issues.
Gregory Palevo, PhD, ACSM-EP, AACVPR Fellow, is an Assistant Professor of Exercise Science at Albany State University in Albany, GA. He continues to pursue his research interests in heart failure patients, studying the effects of nitric oxide supplementation and exercise.
Comparing Cardiovascular and Metabolic Demands between Two Bouts of High-Intensity Functional Training (HIFT)
Purpose: The overall objective of this study is to determine if the wide variety of exercise selections in High-Intensity Functional Training (HIFT) affects the metabolic demands between each workout. Methods: A crossover design with six experienced participants were used to compare the mean and maximum values of heart rate, oxygen consumption, the difference between post-exercise and resting blood lactate accumulation, immediate post-exercise rating of perceived exertion, and total caloric expenditure from exercise and 15-minute post-exercise oxygen consumption between a seven-minute workout of burpees and an eight-minute workout box jumps and ascending weight and repetitions of the barbell deadlift. An independent T-test was used to compare the outcome variables between the two workouts. Results: Mean and maximal oxygen consumption was significantly greater in the seven minutes of maximum burpees compared to the eight minutes of box jumps and deadlifts. There was no significant difference in mean and maximal heart rate, blood lactate accumulation, rating of perceived exertion, and total caloric expenditure between the two workouts. Conclusion: Both bouts of HIFT were executed to complete as many repetitions as possible, which lead to similar cardiovascular and metabolic measures except for the participants’ oxygen consumption. This difference was primarily due to the ascending weights and the repetitions of the deadlift. All participants’ average repetitions completed per minute decreased significantly when they came across the 275-pound barbell for 25 repetitions. Applications in Sport: These findings show that even though all HIFT workouts are performed at high intensity, the variance in exercise selection can impact the participant and how they respond to each workout requires further research into how these different modalities and variations can impact exercise participants and their limitations to better understand HIFT and how it can compare to other forms of exercise.
Keywords: HIFT, metabolic demands, AMRAP, burpees, box jumps, deadlifts, EPOC, intermittent exercise, body composition
High-Intensity Functional Training (HIFT) is a new way of exercise that consists of gymnastics, Olympic lifting, powerlifting, and cyclical conditioning (rowing, biking, and running) (3). As a result, we still need an understanding of what makes HIFT a favored option in improving health and fitness for the vast majority. This style of fitness is unique as it combines a high-intensity philosophy similar to other types of high-intensity training, but another key component is the complete variance of movements and structure that makes it difficult to compare with other forms of exercise to gain a better understanding.
HIFT is a form of concurrent training, that experiences a blend of endurance and resistance training, that experiences longitudinal improvements in both strength and endurance (9). HIFT’s popularity is due to the constant variety of exercises to avoid burnout and its health-related success (3,4,12). Over the course of 16 weeks, nine men and sixteen women went through high-intensity functional training to find significant improvements in body composition and maximal strength in the front squat (7) (13). Unlike High-Intensity Interval Training (HIIT), HIFT is consistently made of workouts titled “For Time” and “As Many Reps As Possible (AMRAP) within an allotted time. This is significant from HIIT’s interval format as these types of HIFT only have rest intervals that are chosen by the participant that is completing the workout because it is up to them on how fast they go. Compared to HIIT, the heavier resistance from the Olympic lifts and the power lifts increases the motor unit recruitment and the overall intensity of effort needed to execute the work required in the training sessions (11). There have been comparisons of cardiorespiratory and muscular fitness adaptations between unimodal HIIT interval training versus a replicated version of HIFT called mixed modal HIIT (2) and comparing the oxidative stress during checkpoints of bodyweight HIFT workout “Cindy” (20:00 as many rounds as possible of 5 pullups, 10 pushups, and 15 air squats) to 20:00 of high-intensity treadmill running at 90% of max heart rate (8). We are beginning to take steps toward understanding the responses and adaptations that occur with HIFT compared to different styles of exercise, but this understanding will be limited without understanding that all bouts of HIFT may not be the same.
HIFT has many different variations and styles of workouts. There are heavy-resistant workouts that have a shorter duration and there are workouts that consist of only bodyweight movements that can last for longer periods of time. Before we continue to keep comparing different bouts of HIFT to other types of exercise, we need to gain a better understanding of different bouts of HIFT between themselves. We can best do this by comparing commonly used HIFT workouts and isolating variables to measure the metabolic responses to further find why it is a superior exercise philosophy. Therefore, the aim of this study is to compare the cardiovascular and metabolic demands between two well-known bouts of HIFT that are carried out at similar intensities and time duration but with varied exercises selected.
Each participant (N = 6) that completed the study were experienced in HIFT with a minimum experience of three times a week for a minimum of 6 months. All participants signed informed consent and a PARQ before beginning any measurement of the study. To ensure consistency in work capacity between participants in the intervention, all male participants were required to be able to complete six unbroken deadlifts at 315 pounds and eight burpees every minute for 7 consecutive minutes.
Each participant will have signed a PARQ and informed consent before beginning any portion of the study. All participants will have the right to back out of the study if they no longer can or feel comfortable undergoing either of the bouts of HIFT. All subjects agreed to participate by signing their informed consent and the study was approved by the University of North Georgia’s Institutional Review Board (IRB). Each participant will have a rep counter and bystander that is CPR and AED certified in case of emergency. The primary investigator is level 1 CrossFit certified and provides specific requirements for all movements to ensure a consistent range of motion for the consistency and safety of the participants.
Every participant will be wearing a K5 portable military-grade metabolic analyzer to report VO2 for pre-workout, during a workout, and 15-minute EPOC after completing each workout. To measure oxygen consumption, we will be using breath-by-breath analyses (Perez-Suarez, et al., 2018). This happens with an assessment of the tidal volume of each breath with the fractions of expired oxygen and carbon dioxide (1). 15 minutes of post-oxygen consumption will also be analyzed to calculate the complete thermic effect of exercise and rephosphorylation from oxygen debt following high-intensity exercise (6). A blood lactate accumulator will also be used for resting measures during pre-workout and five-minute post-workout. In trained subjects, peak blood lactate concentration appears between four to six minutes post-workout with inactive recovery (5). The Borg scale will be used to analyze levels of perceived exertion (12). The Borg scale for perceived exertion has a great correlation with reported heat rate and blood lactate accumulation during exercise (12). The seven-minute AMRAP of Burpees will require a target that is six inches above the subject’s reach to touch so that we make sure that everyone is reaching the full range of motion that is fair. A 24” box and a barbell with 3 pairs of 45lb plates and 1 pair of 25lb plates will be required for the deadlift and box jump workout. We used a rogue plyo box, a rogue ohio barbell, and rogue weights for all participants executing the eight-minute AMRAP of box jumps and ascending weight and repetitions of the deadlift.
To compare the metabolic demands between the two exercises we conducted a crossover study. Each subject completed a familiarization session and two experimental sessions. All subjects were randomized after the familiarization session where half started with the seven-minute AMRAP of burpees and the other half started with the eight-minute AMRAP of box jumps and ascending weight and repetitions of the deadlift.
To make sure that all participants are completely recovered from the first AMRAP before completing the second one we had a five-day period in between both workouts. There was also a required 48 hours with no strenuous activity outside of the study before completing either of the AMRAPs.
At first, resting measures of blood lactate and current VO2 measures were taken while the participant was seated. For each session, each participant completed a warmup prior to the workout. The warmup had a 10:00 timer where each participant completed: ten calories on the Concept 2 rower, 8 pushups, 10 air squats, 10 barbell RDL at 45 pounds for both workouts at a moderate warmup pace. There was a five-minute transition period between the warmup and the start of the workout.
In the familiarization session, each participant began by filling out an informed consent form and a Par-Q questionnaire. The body composition of each participant was evaluated using a three-site skinfold assessment of the pectoralis, umbilical, and quadriceps. Following body composition, participants were sized for their oxygen consumption masks for the use of the K5 metabolic analyzer. Once they were sized, they began the same warmup that was completed for the experimental sessions before completing the familiarization workouts. For the seven-minute AMRAP of burpees, the participant needed to perform the burpee by dropping down to where the chest is on the floor then pushing themselves up to full extension and jumping up to touch a target that is six inches above their reach. Once the clock started, each subject had seven minutes to perform as many burpees as possible. They were equipped with a judge to count their reps and to critique their movement if needed to make sure everyone followed the same protocol. The second workout had the same warmup as the seven-minute AMRAP of burpees that was followed by taking the resting measures of blood lactate and resting VO2. Once the clock started, each subject had eight minutes to do as many repetitions as possible of a ladder of deadlifts starting at ten repetitions at 135 pounds and increases five repetitions each round as the weight goes up in an increasing fashion (135, 185, 225, 275, 315, 365 pounds). After each round of deadlifts, each participant completed 15 box jumps. There was a judge to count the repetitions being done as well as someone to load the barbell throughout the workout so that each participant could fully focus on performing as many repetitions as possible during the workout.
Following the completion of each session, the subject’s 15-minute measurement of EPOC began while continuing to wear the K5 portable metabolic analyzer. Data continued to be recorded every five minutes. At five minutes post-workout, the subject’s post-workout blood lactate and blood glucose levels were taken to compare the difference from their resting measures. VO2 was also monitored and recorded every two minutes during the workouts.
To compare the means of the variables being measured between the two different bouts of HIFT, a Student’s T-test was conducted a for the statistical analysis. The chosen level of significance was set at p < 0.05. The mean values of the six participants between the burpee trial and the deadlift box jump trial were compared.
All participants completed both the seven minutes of burpees and the eight minutes of deadlift and box jumps Mean and maximum values of oxygen consumption, heart rate (HR), ratings of perceived exertion (RPE), difference of 5:00 post-workout blood lactate concentration to pre-resting measures, total caloric expenditure of each workout, and 15-minute excessive post oxygen consumption (EPOC) were recorded and shown in table 1.
The average and maximum VO2 were recorded using the mix method from the Cosmed K5 portable metabolic analyzer. Each measure was recorded every 10 seconds and then was collected to find the mean and the max recorded VO2 for the duration of the workout. The seven minutes of burpees required a significantly higher average Burpee and maximum VO2 than the eight minutes of deadlifts and box jumps.
Average and max heart rate was collected using a Garmin heart rate monitor that was connected to the K5 via Bluetooth. Heart rate was recorded every 10 seconds like theVO2 measures. The data was collected and transferred where the average and maximum heart rate was found for the duration of the workout. There was no significant difference between average heart rate (p = 0.167) and maximum heart rate (p = 0.282).
RPE was measured using the Borg scale from 6-20. A visual chart was used for the athletes once they completed the workout and sat down immediately after the workout for them tostate their RPE. Immediate post RPE for both workouts were very similar with an average of 16 ± 1for the burpee workout and an average of 16 ± 1 for the deadlift and box jump workout. With very similar averages within the five participants, there was no significant difference between the two (p = 0.389).
Blood lactate was measured as the difference between the five-minute post workout blood lactate reading and the one that was taken for pre-resting measures when the participant was sitting in a back supported chair for five minutes. The blood lactate difference was very close between the burpee and the deadlift box jump workout. The average difference of blood lactate for the burpee workout was 11.08 ± 2.5 mmol/L and the difference of blood lactate for the deadlift and box jump workout was 10.92 ±2.6 mmol/L. There was no significant difference in the difference of blood lactate between these two workouts (p = 0.77).
Total caloric expenditure for both workouts were measured during the duration of the workout and 15 minutes post workout. Total caloric expenditure for the burpee workout was 205.6 ± 16 calories and the expenditure for the deadlift and box jump workout was 213.2 ± 20 calories. There were more calories from the deadlift and box jump workout, but it was a minute longer than the burpee workout that had a higher average VO2. Even with the difference, there was no significant difference between the two workouts (p = 0.227).
All sessions performed were completed in the summer of 2021 to avoid any significant changes in environmental temperature that could affect the physiological responses to both exercises. All three sessions were performed within three weeks’ time to ensure the participants were at the same work capacity and not undertrained to avoid unlikely responses to skew any results. The requirement was to avoid any high-intensity exercise within 48 hours before the experimental session and 24 hours of no exercise at all. To avoid any participants suffering from pre-existing fatigue and soreness, a recovery questionnaire was completed as a screening tool before beginning the experimental session.
HIFT is well known for its constantly varied movements that are executed at a high intensity (3). People are drawn to HIFT from its significant results that bring improvements in body composition, flexibility, muscular strength, muscular endurance, and cardiorespiratory endurance (2,7,10). The purpose of this study was to see what was more significant between the high intensity or the constantly varied modalities and movements that are in HIFT to keep members from hitting a fitness plateau to better understand this form of high-intensity training. The seven-minute workout of burpees and the eight-minute workout of deadlifts and box jumps have been two famous and widely used workouts in HIFT with similar times and both have the goal of executing the greatest number of repetitions possible, but the movements are very different. The findings showed that executing HIFT workouts at a high intensity seems to be more significant than the constant changes in variance.
APPLICATION TO SPORT
Although the other values remained similar with no significance, the oxygen consumption was affected towards the end of the eight minutes of deadlifts and box jumps. Once the participants began to lift the heavier barbells, the average cadence of repetitions per minute began to slow down. Due to the combination with the box jumps, the participants began executing smaller sets and even singles in order to keep moving as quickly as they could, but the movement speed couldn’t be performed at a continuous rate like the burpees were. The burpees only had the physical limitation of the participant’s aerobic capacity to be able to sustain a consecutive pace whereas the increasing weight and volume of the deadlift caused more limitations associated with muscle fatigue that required chosen breaks to avoid failing repetitions.
High intensity might be a primary indicator of the physiological demands in HIFT, but variability can cause changes that can significantly impact the intended stimulus of each workout. HIFT contains many complex movements in gymnastics and weightlifting that require breaks to remain consistent.
The observed markers symbolizing the metabolic demands needed to execute each of the two workouts showed very similar results. The only marker of VO2 values showed a significant increase with the burpee workout compared to the deadlift and box jump workout. The study shows that you can burn the same calories doing a minute less of burpees compared to doing a workout with heavy deadlifts and box jumps with a very similar RPE was between the two workouts.
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