A Randomized Factorial Feasibility Study of High-Resistance Circuit Training and Strength Training Intervention in Untrained Adolescents: A Mixed Methods Approach
Phase: NA
Conditions: Feasibility Studies
Sponsor: University of Utah

 
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A Randomized Factorial Feasibility Study of High-Resistance Circuit Training and 
Strength Training Intervention in Untrained Adolescents: A Mixed Methods Approach 
 
Mitchell Wyatt1, Leslie Podlog2, Ryan Burns1, Bradley King1, Kristin Heumann3, and Timothy 
Brusseau Jr.1 
 
NCT: TBA 
11/20/24 
 
 
 
Correspondence: 
Mitchell Wyatt 
mitch.wyatt@utah.edu 
1Department of Health and Kinesiology, University of Utah, Salt Lake, Utah.  
2School of Kinesiology and Physical Activity Sciences, University of Montreal, Montreal, 
Quebec.  
3Department of Kinesiology, Colorado Mesa University, Grand Junction, Colorado.  

 
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Methods 
Experimental design  
This study used an explanatory sequential design by collecting quantitative data first, 
then qualitative data to expand understanding of participant experience. After receiving 
University of Utah IRB and Murray School District Board approval, a cohort of participants 
were recruited for a before-school trial. Due to low enrollment of the before-school trial, another 
cohort of participants were recruited for an after-school trial following the conclusion of the 
before-school trial. Before-school sessions were conducted October 23rd to November 17th at 
6:30 AM to 7:50 AM. After-school sessions were conducted November 27th to December 14th at 
2:40 PM to 4:00 PM. After obtaining parental consent and participant assent, participants 
completed a pre-intervention testing session. Using randomizing software from randomizer.org, 
participants were randomized and stratified by sex into the high-resistance circuit training group 
(HRC) or traditional strength training group (ST). A waitlist control group was part of the 
original experimental design, however due the small sample, it was removed. The training 
section below contains details on the training protocols for the different groups. Concluding the 
intervention, subjects completed post-intervention testing. Primary feasibility outcomes included: 
consent rate, fidelity, participant attendance, study retention, adverse events, and participant 
experience. Secondary outcomes included measures of strength, body composition and aerobic 
fitness. After the conclusion of the intervention and quantitative data analysis, participants were 
invited for a one month follow up interview assessing their motivation to join the study, barriers 
and experiences partaking in the study.   
Participants 

 
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Seven healthy untrained adolescents (16.9 ± .7 years old, 4 males and 3 females) from a 
northern Utah high school participated. The high school had 1,500 students across 10th, 11th and 
12th grades. For the purpose of this study, untrained participants were defined as participants who 
reported being physically inactive with no regular participation in physical activity for the past 
month prior to the intervention. Participants were recruited through posted flyers and table events 
during lunch periods. Exclusion criteria included recent injuries or medical conditions that may 
influence high-intensity performance, currently enrolled in another training program including 
resistance, cardiovascular, or sports-based program, uninsured participants, drastically altering 
diet and use of performance-enhancing substances (i.e., creatine, pre-workout, post-workout 
supplements). Prior to the start of the study, participants and respective guardians read and 
signed informed consent, parent permission and assent documents. The 2023 PAR-Q + form and 
modified Copper Institute Fitnessgram and Activitygram questionnaires were used to screen 
participants.  
Table 1. Summary Table of Participants  
Category 
Frequency 
Percent 
Sex 
Male 
4 
57% 
Female 
3 
43% 
Ethnicity 
Non-Hispanic 
7 
100% 
Race 
White 
7 
100% 
 

 
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Category 
Mean 
Standard Deviation 
Age 
16.9 
0.7 
BMI 
24.4 
5.8 
Body Fat Percentage 
25.3 
8.9 
Table 1 shows the baseline participant characteristics.  
Protocol 
Participants performed 1-1 ½ hour sessions three times a week for four weeks under the 
supervision of the primary researcher. Participants followed the weekly progression adapted 
from Alcarez [32]. Exercises were adapted to fit the facility’s equipment by prioritizing free 
weight compound movements over single joint machine exercises. In addition, instead of 
prescribing 6RM (85% of 1RM) to untrained participants, an autoregulatory approach using rate 
of perceived exertion (RPE) was prescribed (Figure 2). To simplify RPE use, participants used 
whole numbers such as 8 RPE which lowers the intensity from HRC’s traditional intensity of 
85% of 1RM to 80% 1RM. Literature supports the use of RPE-based loading as an effective 
alternative to prescribing percentages of 1RM for improving strength [39]. Use of RPE-based 
loading negated a safety concern with untrained participants conducting 1RM testing.  
Figure 2. Equivalent Intensity Prescriptions of Traditional Percentage Based and RPE 
Targeted strength 
quality 
Percent of 1RM 
Rate of perceived 
exertion 
Reps left in reserve 
Maximal strength 
85% 
8.5 
1-2 
Strength-speed 
80% 
8 
2 
Figure 2 shows the equivalent values for percent of 1RM loading vs RPE-based loading adapted 
from Shattock & Tee [40].   

 
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The following four-week progression was developed to help participants become familiar 
with basic weightlifting movements in addition to appropriately increase intensity of sessions 
(Figure 3). In the first week of the intervention, ST and HRC groups completed 4 sets of each 
exercise at 6 RPE on the 1-10 modified Borg Scale. During this time, emphasis was given to 
proper weightlifting technique over the amount of weight being used. In the second week, 
participants completed 2 sets of 6 RPE, then 2 sets of 7 RPE. In the third week, participants 
increased intensity to 2 sets of 7 RPE and 2 sets of 8 RPE. In the fourth week, participants 
increased intensity to 4 sets of 8 RPE. Participants were expected to complete the workouts and 
appropriately increase the difficulty of resistance used if movements were performed correctly. 
Lifts were performed at a tempo with a 3 second eccentric phase, 2 second isometric pause, 
followed by a concentric phase at maximum velocity. Participants were able to adjust resistance 
by 2-5% each set based on RPE.  
Figure 3. Periodization of Training Volume  
Week 1 
Week 2 
Week 3 
Week 4 
4 sets at 6 RPE 
2 sets at 6 RPE 
2 sets of 7 RPE 
2 sets at 7 RPE 
2 sets of 8 RPE 
4 sets at 8 RPE 
Figure 3 shows the progression of prescribed sets across weeks. 
Training 
Warm Up. Participants in ST and HRC groups engaged in a 5 min warm-up specific to 
the first block followed by 5 min of dynamic stretching and mobility. Participants then 
performed 2 sets of the first three exercises using the following sequence; 10 reps at 5 RPE with 
30 sec - 1 min rest, 8 reps at 6-7 RPE with 30 sec - 1 min rest, then participants started target sets 
of 6 reps at the prescribed RPE.  

 
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Strength Training. Once the warm-up was completed, ST participants performed the 6 
reps of the first exercise at the prescribed RPE then rested 1 minute. Participants then completed 
another set of their first exercise with the required rest until the prescribed sets were completed. 
Participants performed the second and third exercise in the same fashion. Once the first block 
was completed, participants rested 5 min, then completed the second block with the same warm 
up sequence.   
High-Resistance Circuit Training. An adapted version of Alcaraz’s HRC was utilized in 
the intervention. Exercises and intensities used by ST was the same for HRC except HRC 
participants performed the first three exercises as a circuit with 35 seconds rest between 
exercises (Figure 4).  
Figure 4. Protocols for the ST and HRC Training Groups 
 
Figure 4 shows the Traditional Strength Training (ST) and High-Resistance Circuit Training 
(HRC) interventions at week 4 of the intervention. ST participants performed four sets of six reps 
of a single exercise with 1 minute rest between sets. HRC performed the same exercises in a 
circuit fashion rotating from one exercise to another with 35 sec rest between sets.  
RDL
Bench Press
Core
Knee Flexion
Elbow Extension
Core
5 Min Rest
4 x 6
4 x 6
4 x 6
4 x 6
4 x 6
4 x 6
RPE 8
RPE 8
RPE 8
RPE 8
RPE 8
RPE 8
RDL
(35 sec rest)
Bench Press
(35 sec rest)
Core
(35 sec rest)
Knee Flexion
(35 sec rest)
Elbow Extension
(35 sec rest)
Core
(35 sec rest)
5 Min Rest
4 x 6
4 x 6
RPE 8
RPE 8
1 min rest between sets
ST Training Group
HRC Training Group

 
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Feasibility outcomes  
Primary feasibility outcomes included recruitment process, sample size, consent rate, 
retention rate, fidelity, attendance, participant experience, and adverse events.  
Recruitment process. The recruitment process refers to the protocols used to find, select, 
and enroll participants into a study [41]. The recruitment process for this study was represented 
by reporting the total number of unique QR code scans from posted flyers and tabling events, the 
number of completed interest forms, the number of eligible participants and the number of 
consented participants. A recruitment period of 3 weeks was given for the before and after-
school trials.    
Sample size. Sample size was used as another key feasibility marker and refers to the total 
number of individuals used in the intervention. A sample size of 30 participants per trial with 15 
participants in each treatment group was established based on previous literature examining the 
difference between resistance training groups [32], suggestions of 12 participants minimum per 
group in feasibility trials from Julious [42], and practicality how many participants could receive 
intervention treatment with proper supervision. While larger sample sizes would be ideal for 
secondary fitness outcomes, the primary purpose of this study was to assess feasibility outcomes 
and not report statically powered differences.  
Consent rate. Consent rate is often referred to as the percentage of participants enrolled 
divided by the number of eligible participants [43]. For this study, consent rate was calculated by 
taking the total number of participants that consented and were randomized divided by the 
number of eligible students. An acceptable consent rate was set at 80% based on findings from 
Jacques [43].   

 
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Retention rate. Retention rate is defined as the percentage of the total number of 
randomized participants assessed for primary outcomes and used in the primary outcome 
analysis [43]. For the purpose of this study, researchers were interested in retention for both 
primary and secondary outcomes meaning researchers tracked retention from pre-intervention 
fitness testing, through treatments, and post-intervention fitness testing sessions. The follow up 
interview was not included in calculating the retention rate. Only participants that withdrew from 
the study or were not included in the primary and secondary outcome analysis influenced the 
retention rate. Thus, retention was calculated as the percentage of participants that completed pre 
and post-intervention fitness assessments and intervention treatment divided by the number of 
participants randomized into treatment groups. Participants that withdrew (i.e., stopped 
attending) from the study were tracked by the investigator. Based on prior literature, 80% 
retention rate was used as an acceptable threshold [44]. 
Fidelity. Fidelity is referred to how well an intervention was delivered as intended and is 
measured at the participant, deliverer or setting level [41]. For this study, fidelity was assessed at 
the instructor (deliverer) and participant level. Instructor fidelity was measured as a percentage 
by totaling the provided sessions divided by the total number of planned sessions. An acceptable 
percentage was set at 80% due to conflicts with events such as holiday breaks or parent teacher 
conferences. To assess participant fidelity, the primary researcher and participants recorded 
session durations, completed sets and intensity along with activity and diet audits at weeks 2, and 
4 of the intervention. The activity and diet audit included a modified Copper Institute 
Fitnessgram and Activitygram questionnaire (Figure 5). If participants recorded additional days 
of aerobic, muscular strength and muscular endurance activities and/or a dramatic change in diet, 

 
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resulting post-intervention data was excluded in the secondary performance outcomes data 
analysis. 
Figure 5. Modified Fitnessgram Physical Activity and Diet Audit Questions 
Aerobic 
Outside of the intervention with the researcher, how many of the past 7 days 
did you participate in any physical activity for a total of 30 to 60 minutes or 
over the course of a day? This includes moderate to vigorous activities 
(walking, slow bicycling, or outdoor play) as well as vigorous activities 
(jogging, active games, or active sports such as basketball, tennis, or soccer). 
(0, 1, 2, 3, 4, 5, 6, 7 days) 
Muscular 
strength and 
endurance 
Outside of the intervention with the researcher. how many of the past days 
did you exercise to strengthen or tone your muscles? This includes exercises 
such as push-ups, sit-ups, or weightlifting. (0, 1, 2, 3 ,4 ,5 ,6 ,7 days) 
Diet 
Have you changed your diet in the past 7 days? If so, please describe.  
Figure 5 is a modified physical activity and diet questionnaire from the Cooper Institute’s 
Fitnessgram and Activitygram assessment manual to investigate additional activity and diet 
changes outside of the investigation [45]. 
Participant attendance. Participant attendance was observed by the researcher and 
measured as attended sessions divided by total sessions offered. Based on systematic reviews and 
meta-analyses [46, 47], 80% was selected as an acceptable attendance threshold.  
Adverse events. Adverse events were recorded during the intervention by the participants 
on workout documents and by observations from the primary researcher. The primary researcher 
used no adverse events as an acceptable threshold.  

 
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Participant experience. Participant experience was assessed by utilizing the validated 
short form 4 item Physical Activity Enjoyment Scale (PACES-S) survey for adolescents [48]. 
Participants answered 4 items including: “I enjoyed it; I find it pleasurable; It is very pleasant; 
and It feels good” by responding with the five-point Likert scale ranging from 1= “strongly 
disagree” to 5 = “strongly agree”. To further investigators’ depth of understanding, participant 
experience was also assessed by a follow up interview concluding the intervention. Please see 
qualitative assumptions, interview process and qualitative data analysis section below for further 
details. 
Progression criteria  
 
Of the above feasibility measures, selected outcomes were used as key markers to assess 
if further investigations were warranted for the future. The following criteria for evaluating 
feasibility are below:  
1. No adverse events related to the intervention treatment.  
2. Sample size of 30 participants per trial. 
3. Consent rate no less than 80%. 
4. Retention rate no less than 80%. 
5. Attendance rates no less than 80%. 
If all five criteria were met, then further investigations can continue without modification. 
If three to four criteria were met, then further investigations can continue with modifications. If 
two or less criteria were met, the study is assessed as not feasible.   
Secondary outcomes 
All secondary outcome assessments were taken pre and post-intervention. Testing 
protocols required participants to avoid strenuous physical activity 48 hours prior to testing days. 

 
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Assessments took a single session to complete and all participants were tested within similar 
time periods.   
Bioelectric Impedance Analyzer. In a separate private room, one participant at a time 
weighed themselves on a certified scale. Participants used the handheld Omron model HBF-306 
to enter their weight, age, sex and activity level. Resulting BMI and body fat percentage data was 
recorded. Omron HBF-306 has been shown to be a reliable tool to track body composition over 
time [49]. 
Isometric lower body pull. Using the Baseline 12-0400 Back-Leg-Chest dynamometer 
participants stood up-right and feet hip width apart on the dynamometer platform with the chain 
adjusted so the handle was at the intra-articular space of the knee joint. Participants were 
instructed to grip the handle evenly at the center then produce a maximal 5 sec pull keeping the 
back from bending and arms straight. Participants were allowed to rest 30 sec between attempts. 
Participants had one practice attempt for familiarization purposes and then the best score of the 
three following attempts were recorded. Prior research has established reasonable test-retest 
reproducibility of the Baseline 12-0400 Back-Leg-Chest dynamometer in adolescent populations 
[50].  
90° push-up. Participants were paired; participant 1 performed the test while participant 2 
recorded the number of push-ups. Participants performed the assessment in accordance with the 
Cooper Institute’s procedures [45]. Participant 1 assumed a prone plank position with hands 
slightly outside of shoulders, fingers stretched out and legs straight with a slight gap. While 
performing push-ups, the participants’ back maintained a straight line from head to ankles. 
Participants started by lowering their body until the upper arms became parallel to the ground. 
The participant then extended their arms straight pushing their body up. This movement was 

 
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performed every three seconds by metronome and repeated until failure. Participants were 
allowed one form correction and two form corrections resulted in test termination. Form 
corrections included participants stopping to rest, a failure to maintain a straight back, achieving 
proper depth or fully extending the arms. Prior research notes the acceptable reliability of the 
push-up assessment in males and females [51]. 
Modified Pull-up. Participants performed the modified pull-up test in accordance with 
Cooper Institute’s procedure [45]. Participants placed a barbell in a squat rack so that the barbell 
was one to two inches away from participant’s reach while supine on the ground. A band was 
then placed seven to eight inches below the barbell. Participants started the assessment by 
overhand gripping the barbell and creating a straight line from head to heels so that only the 
heels were in ground contact. Participants then pulled their body toward the barbell until the chin 
was above the band. This movement was performed every three seconds by metronome and 
repeated until failure. Participants were allowed one form of correction and two form corrections 
would result in test termination. Form corrections included participants stopping to rest, failure 
to maintain a straight line, achieve proper depth and fully extending the arms.  
PACER. To assess cardiovascular fitness, the Progressive Aerobic Cardiovascular 
Endurance Run (PACER) assessment was used. Prior to the start of assessment, the primary 
investigator measured and marked a designated 20-meter distance in the gymnasium for testing. 
Participants were briefed on the assessment guidelines and participated in one practice 
opportunity prior to the official assessment. Once familiarized, participants ran the 20-meter 
distance in accordance to PACER cadences from the Cooper Institute for as long as possible. The 
test was terminated when the participant voluntarily stopped due to fatigue or when two laps 
were missed. The primary researcher recorded total number of successful levels. Once 

 
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completed, the primary researcher computed predicted peak VO2 by using VO2peak = 
0.353(Laps) – 1.121(Age) + 45.619. This equation has been shown to have moderately strong 
linear relationships compared to measured VO2 peak of adolescents [52].  
Quantitative data analysis  
Non-parametric analyses of primary and secondary outcomes were used due to the small 
sample size. Wilcoxon signed rank tests were used to test significance of pre and post-
intervention data within treatment groups. Reports of Wilcoxon signed rank included medians, 
inner quartile ranges, z scores and p-values. Two sample Wilcoxon rank sum (Mann-Whitney) 
tests were used to test significance between treatment group differences. Reports of Wilcoxon 
rank-sum (Mann-Whitney) tests included medians, inner quartile ranges, U statistic and p-values. 
Due to an underpowered sample, effect sizes were calculated for all secondary outcome 
statistical tests. Given the exploratory nature of this study and the small sample, effect sizes may 
be more useful in guiding future research. Effect sizes were interpreted as small if r = 0.2 - 0.5, 
medium if r = 0.5 - 0.8 medium and large if r > 0.8. Statistical package STATA (version; BE 
18.0, StataCorp, College Station, Texas, USA) was used and Alpha level was set at P< 0.05.  
Qualitative assumptions   
Following quantitative data analysis, a constructivist paradigm was utilized for the 
qualitative phase. Hatch [53] depicts the ontological assumption (nature of reality) in a 
constructivist paradigm as “multiple realities are constructed”. In a constructivist paradigm the 
epistemological assumption (nature of data) is that data is collected in close, personal and 
interactive settings. Researchers in this paradigm let the participants drive the investigation to 
explain their perceived reality without the addition of the researcher’s influence. Thus, the 

 
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axiological assumption (value of data) is subjective and relative to the participant. These realities 
are important to consider as perceptions may influence how the participant behaves.  
Interview methods  
Participants were invited to a recorded interview for 30 min on Zoom. The interview 
followed a piloted semi-structured interview guide (Figure 6) created by the primary researcher 
to further understand participant experiences of the training protocols. Participants were given 
pseudonyms to protect their identity.  
Figure 6. Interview Guide 
Background info  
Do you enjoy being active, if so why?  
What about weightlifting do you find appealing?  
Explain to me why you wanted to sign up for this study. 
Participant experience 
Did the timing of the workout sessions work well for you? Why or why not?  
Tell me about some of the factors, if any, that made it difficult to attend.  
Were there aspects of the workout sessions that you enjoyed and if so why?  
Were there aspects of the workout sessions that you disliked and if so why? 
In what ways did participating in this study benefit you?  
In what ways did participation in this study not benefit you?  
Tell me about some parts of the program, if any, that made it challenging to complete as 
directed.   
If anything, what would you change regarding the workout sessions?  
In general, how would you describe your experience participating in this study?  

 
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Figure 6 shows the semi-structured follow up interview guide. 
Qualitative data analysis 
Once interviews were concluded, thematic analysis as described by Terry and colleagues 
[54] was conducted to analyze data. The primary researcher familiarized himself with the data by 
viewing recorded interviews and checking transcripts for correct transcription. Initial codes were 
then generated by highlighting test segments relevant to the study aims examining participant 
experiences. Codes were grouped into initial themes based on their underlying conceptual 
similarities. Themes were then reviewed and revised to generate three final themes: “It was a 
positive experience”, “workout difficulty and duration”, and “barriers”. Extracts of interviews 
were used to support reported themes.     
 
 
 
 
 
 
 
 
 
 
 
 
 

 
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