Non-traditional HIIT-style ROTC training elicits positive bone quality and performance adaptations

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Non-traditional HIIT-style ROTC training
elicits positive bone quality and performance
adaptations
Allen L. Redinger, Shawn M. F. Allen, Samuel R. Buchanan, Christopher D.
Black & Breanne S. Baker
To cite this article: Allen L. Redinger, Shawn M. F. Allen, Samuel R. Buchanan, Christopher
D. Black & Breanne S. Baker (2023) Non-traditional HIIT-style ROTC training elicits positive
bone quality and performance adaptations, Journal of Sports Sciences, 41:17, 1587-1595, DOI:
10.1080/02640414.2023.2283998
To link to this article: https://doi.org/10.1080/02640414.2023.2283998
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PHYSICAL ACTIVITY, HEALTH AND EXERCISE
Non-traditional HIIT-style ROTC training elicits positive bone quality and
performance adaptations
Allen L. Redinger
a
, Shawn M. F. Allen
a
, Samuel R. Buchanan
b,c
, Christopher D. Black
c
and Breanne S. Baker
a,c
a
Musculoskeletal Adaptations to Aging and eXercise (MAAX) Lab, Oklahoma State University, Stillwater, OK, USA;
b
Department of Health and Human
Performance, University of Texas Rio Grande Valley, Edinburg, TX, USA;
c
Department of Health and Exercise Science, University of Oklahoma, Norman,
OK, USA
ABSTRACT
Military personnel experience elevated bone injury incidence, partly due to arduous and repetitive
training. Non-traditional High-Intensity Interval Training-style (HIIT) may benet pre-enlisted Reserve
Ocer Training Corps (ROTC) cadet’s musculoskeletal health and performance prior to military service.
This study investigated 16 ROTC (n = 12 males; n = 4 females) and 15 physically active sex-, age-, and body
mass-matched Controls’ musculoskeletal health and performance from November to April. Total body,
lumbar spine, and dual- hip dual-energy X-ray absorptiometry scans and 4%, 38%, 66% tibial peripheral
quantitative computed tomography scans, blood draws (serum sclerostin and parathyroid hormone), and
maximal muscle strength and aerobic capacity testing were completed. From November to April, ROTC
improved bone density (DXA) of the dominant total hip and greater trochanter and non-dominant
greater trochanter and 38% and 66% tibial total volumetric and cortical bone density (pQCT) similarly
or more than Controls (all p ≤ 0.049). From November to April, ROTC also improved bench and leg press,
and peak aerobic capacity (all p ≤ 0.013). From November to January, serum sclerostin increased (p ≤
0.007) and remained elevated through April, while parathyroid hormone was unchanged. HIIT-style
training induced positive musculoskeletal adaptations, suggesting it may be an excellent pre-service
training modality for this injury prone group.
ARTICLE HISTORY
Received 12 December 2022
Accepted 9 November 2023
KEYWORDS
High-intensity interval
training; reserve officers
training corps; skeletal
health; DXA; pQCT; sclerostin
Introduction
The dynamic nature of bone turnover induced by exercise or
physical training consists of skeletal and endocrine responses to
internal and external loading stimuli (Pro & Römer, 2009; Smith
et al., 2021) and is often assessed using skeletal imaging tech-
nologies and serum biomarkers. Specic imaging systems such
as dual-energy X-ray absorptiometry (DXA) and peripheral quan-
titative computed tomography (pQCT) measure bone density,
content, and geometric characteristics at a macro-level. DXA also
can provide information regarding bone-free lean body mass
and fat mass, oering an encompassing assessment of bone
health and body composition for whole body and segmental
regions (Varela & Jolette, 2018). Bone geometric properties can
be measured by pQCT, providing estimations of bones’ morphol-
ogy and structural integrity (Varela & Jolette, 2018). At a micro-
level, many biomarkers are used to understand rates of bone
turnover; these are called bone turnover markers (BTMs). For
instance, cross-linked C telopeptide of type I collagen, parathyr-
oid hormone (PTH), and sclerostin indicate resorptive processes
while N-terminal propeptide of type I procollagen (PINP), osteo-
calcin (OC), and bone-specic alkaline phosphatase (BAP) indi-
cate formative processes (Varela & Jolette, 2018). A multi-faceted
approach to analysing skeletal health utilizing both imaging
devices and biomarkers allows for a systematic and dynamic
assessment of skeletal responses to exercise or physical training.
Exercise is often considered an osteogenic stimuli; however,
inadequate rest between vigorous bouts, consistently elevated
training volumes, and low energy availability may lead to
chronic elevation of resorptive cues, and amplifying negative
skeletal characteristics (O’Leary et al., 2020; Yanovich et al.,
2015). This has been researched extensively in traditional ath-
letes such as cyclists (Baker & Reiser, 2017; Sherk et al., 2014),
runners (Beermann et al., 2020; Warden et al., 2021), and rowers
(Lundy et al., 2022; Baker et al., 2020), with collegiate athletes
suering from 5.7 bone stress injuries at a rate of 100,000 per
exposures (Hoenig et al., 2022). Military personnel also fre-
quently conduct repetitive and arduous physical training with
inadequate rest periods that may reduce bone density and
quality (Armstrong et al., 2004; Hauschild et al., 2016). These
individuals can suer from high injury rates, with 5–10% of new
Army, Navy, and Marine recruits developing a bone stress injury
within the rst 3 months of basic training, in large part due to
lower baseline physical tness levels prior to enlistment
(Kardouni et al., 2021; Lee & Center AFHS, 2011; Waterman
et al., 2016). Previous epidemiological research from
Waterman and colleagues (Waterman et al., 2016) indicated
that 77.5% of diagnosed stress injuries during military training
and deployment occurred in junior enlisted members (<25
years old) spanning all U.S. military branches between 2009
and 2012. For instance, Armstrong et al., (2004), evaluated 31
U.S. Naval Academy midshipman aged 18–19 years old with
CONTACT Allen L. Redinger allen.redinger@okstate.edu MAAX Lab (Musculoskeletal Adaptations to Aging and eXercise), School of Kinesiology, Applied
Health, and Recreation, Oklahoma State University, 190 Colvin Recreation Center, Stillwater, OK 74078
Supplemental data for this article can be accessed online https://doi.org/10.1080/02640414.2023.2283998.
JOURNAL OF SPORTS SCIENCES
2023, VOL. 41, NO. 17, 1587–1595
https://doi.org/10.1080/02640414.2023.2283998
© 2023 Informa UK Limited, trading as Taylor & Francis Group

stress fractures compared to matched controls throughout
introductory summer training. They found those that suered
from a fracture, lost more body mass and had reduced bone
mineral content (BMC) and bone strength compared to non-
fracture controls throughout the study duration. It would be
benecial to gain an understanding of training-related bone
changes in those who have yet to start military training such as
college-aged Reserve Ocers Training Corps (ROTC) cadets, in
an eort to reduce bone injury risk during service.
ROTC cadets can begin preliminary military training and
studies during their collegiate career, with the option to com-
mission as ocers after graduation. Traditional ROTC training
programmes often mimic exercises they will encounter during
service, such as running, marching/rucking, push-ups/pull-ups,
and crunches. If these programmes are completed at similarly
high volumes and intensities, they could result in similar bone
injury patterns. An additional factor to consider is the develop-
mental age of cadets. Those between the ages of 18–25 can still
experience skeletal geometric adaptations to training and are
in a key period of bone mineral content accrual. Training pro-
grammes which negatively alter bone morphology and meta-
bolism could have lasting detriments to bone injury risk. Key
factors to consider include technical experience, training his-
tory, physical tness, auxiliary exercise engagement, previous
injury history, body composition, and nutritional factors (Jacobs
et al., 2014; Scott et al., 2015). For instance, Scott et al., (2015)
evaluated 195 cadets aged 18–33 years, throughout 16 months
of traditional ROTC training, nding that lower Military Science
class rank and higher physical training exposure were strong
predictors of lower extremity injury. While Crombie et al., (2012)
found that over 6 months, collegiate-level ROTC training did
not inhibit an accumulation of body fat which is also predictor
of injury in military personnel; potentially further increasing
bone injury risk once enlisted. Traditional training programmes
have been under scrutiny for increasing injury risk while pro-
viding lacklustre improvements in military physical readiness
over the past decade, but the extent to which an updated ROTC
training programme might alter bone and improve physical
tness is lacking (Nindl et al., 2015).
The primary aim of this study was to examine changes in
bone density and quality, serum sclerostin and PTH responses,
body composition, muscle strength, and aerobic capacity in
ROTC cadets who engaged in an updated training programme
utilizing a High-Intensity Interval Training-style (HIIT) as com-
pared to physically active matched controls. We hypothesized
ROTC cadets would exhibit improvements in all skeletal, body
composition, and performance metrics post 6 months com-
pared to their baseline values and demonstrate similar or
greater improvements than physically active matched controls.
Materials and methods
Subjects
Approval for this study was granted by University of Oklahoma
Institutional Review Board (#8338 and 8600) and was in accor-
dance with the Declaration of Helsinki and its amendments.
Methods have been described elsewhere (Baker et al., 2021) but
in brief, voluntary written informed consent was obtained from
all subjects. ROTC inclusion criteria included males and females
between 18 and 30 years old who were an active member of
either the Army or Navy college ROTC programme for at least
1 year. Inclusion criteria for Controls were males and females
who were physically active ≥3×/week and were matched for
sex, age (±2 yrs), and body mass (±2.5 kg) to an enrolled ROTC
participant. Exclusion criteria for both ROTC and Controls con-
sisted of having a reported history of musculoskeletal diseases,
current or past smoking, metal implants, pregnancy, and sec-
ondary amenorrhoea, which was dened as having no menses
for more than three consecutive months, without contraceptive
use (Elliott-Sale et al., 2021).
Research design
This prospective study was split into three phases (Figure 1).
Phase one occurred in late November, concluding the Fall
semester eight-week ROTC training block. Phase two started
in late January after a four-week winter break for college stu-
dents and marked the beginning of a new Spring semester
ROTC eight-week training block. Phase three ended the study
in early April, marking the end of the Spring ROTC training
block. Controls were tested ±12 days to their ROTC match
across the entire six-month study and maintained their activity
levels.
Training and activity
Both Army and Navy ROTC cadets completed identical training
protocols during both fall and spring semesters. The traditional
ROTC training programme, consisting of long-distance runs,
rucking and marching, pull-ups, push-ups, and curl-ups, was
replaced with a HIIT programme, which aimed to incorporate
Figure 1. Phases and tests completed throughout the six-month evaluation period. Abbreviations include DXA: dual-energy X-ray Absorptiometry; pQCT: peripheral
quantitative computed tomography; 1RM: 1 repetition maximum; peak VO
2
: peak amount of oxygen consumption during the maximal aerobic capacity treadmill tests.
1588 A. L. REDINGER ET AL.

both resistance training and aerobic training within each ses-
sion. All the exercise sessions (two sessions per week for 8
weeks, equating to 16 training hours) incorporated speed,
agility, strength, and power movements. HIIT sessions and
circuits were often followed by additional strength or endur-
ance focused movements such as bench press, squat, runs, or
cycling, providing a more comprehensive exercise programme.
Control participants reported exercising ≥3×/week, with char-
acterization of frequency and type indicated through self-
reported training logs. Neither the ROTC or Controls exercise
regimens were administered or altered by the research team in
any way throughout the study.
Questionnaires
All subjects completed questionnaires regarding general health
status, exercise and training logs, calcium intake (Musgrave
et al., 1989), and bone-specic physical activity (BPAQ) (Weeks
& Beck, 2008). Training logs included type, frequency, intensity,
duration, and time of exercise. Questions specic to ROTC
subjects included auxiliary exercise and physical activity out-
side of ROTC mandated training sessions and injury history
such as stress fractures. The BPAQ was administered to quantify
past, current, and total levels of osteogenic physical activity and
has been shown to be positively correlated with bone geome-
try (Baker et al., 2020). All female subjects also completed an in-
house menstrual history questionnaire to obtain information
on cycle characteristics in the past 12 months such as contra-
ceptive use, age at menarche, and symptoms of menstrual
cycle and hormonal disturbances.
Bone and biomarkers
Subjects underwent DXA and pQCT scans for the assessment of
body composition and bone measures (Baker et al., 2020, 2021).
Urine samples were collected to ensure proper hydration
1.004–1.028 USG and conrmation of negative pregnancy sta-
tus in females prior to scans. DXA (Lunar Prodigy, enCORE 16,
GE Healthcare, Madison, WI) was used to measure total body fat
mass (FM; g), % fat mass (BF%), bone-free lean body mass
(BFLBM; g), and bone mineral content (BMC; g). Areal bone
mineral density (aBMD; g/cm
2
) was calculated for total body,
lumbar spine (L1-L4), and proximal femora (femoral neck,
greater trochanter, total hip) scans. Automated DXA data
extraction was completed using the DXA Data Xtraction
Assistant (DXA
2
) programme (Baker et al., 2021). Additionally,
a pQCT scanner (XCT 3000, v.6.00, Stratec Medizintechnik
GmbH, Pforzheim, Germany) was used to measure non-
dominant 4%, 38%, and 66% tibial characteristics. At the distal
tibia (4%), measures included total and trabecular measures of
volumetric bone mineral density (vBMD; mg/cm
3
), bone area
(mm
2
), periosteal circumference (mm), and estimated bone
strength index (BSI; mg/mm
4
). At the 38% and 66% tibia sites,
variables included total and cortical measures of vBMD (mg/
cm
3
) and bone area (mm
2
), cortical thickness (mm), polar
moment of inertia (Ipolar; mm
4
), periosteal and endosteal cir-
cumference (mm), and polar strength for strength-strain index
(pSSI; mm
3
). Muscle cross-sectional area (mCSA; mm
2
) was also
calculated for the 66% tibia site. All scans were visually rated as
a two or below and the average pMovement was 45.9 indicat-
ing scans with little to no movement as described by Blew et al.,
(2014). In our laboratory, the coecient of variance percentage
for all DXA and pQCT measurements ranges from 0.3% to 2.7%
and the same qualied and trained technicians performed all
quality assurance tests, scans, and analyses.
Enzyme-linked immunosorbent assays (ELISAs) for serum
PTH and sclerostin were completed for all time points.
Subjects were instructed to not exercise or eat for 24 and 8
hours, respectively, prior to blood draws. Approximately 10 mL
were collected via venipuncture between 8:00 and 9:00 am.
Clotted samples were centrifuged, aliquoted, and stored at
−80°C. All samples were assayed in duplicate using DRG
International Inc., Springeld, NJ. (Cat# EIA3645) for PTH and
TECO medical Quidel Corp., Santa Clara, CA and Sissach,
Switzerland (Cat# TE1023-HS) for sclerostin. For all assays, the
intra- and inter-assay coecient of variance percentage ranged
from 0.2 to 9.4% and 4.7% to 8.5%, respectively.
Physical performance testing
All subjects completed upper and lower body assessments of
maximal muscle strength and peak aerobic capacity tests. One
repetition maximum (1RM) testing for bench press (Cybex,
Medway, MA) and leg press (Body Solid, Forest Park, IL) fol-
lowed National Strength and Conditioning Association recom-
mendations (Miller, 2012); with interclass correlation
coecients for 1RM testing in our laboratory being above
0.990. Peak aerobic capacity (VO
2
peak) was measured using
a modied Balke (Baker et al., 2021) treadmill protocol with
open-circuit spirometry (ParvoMedics; Sandy, UT) and heart
rate was monitored continuously using a coded transmitter
worn around the chest (Polar T31, Bethpage, NY). Prior to the
end of each stage, subjects were asked their Rating of
Perceived Exertion (RPE) using the 15 point (6-20) Borg Scale
(30). Four criteria were used to identify maximal oxygen uptake;
a plateau in oxygen consumption despite an increased work-
load, Respiratory Exchange Ratio (RER) values over 1.10, RPE
values 18 or over, and maximal Heart Rate (HR) within 10 bpm
of the age predicted max HR. VO
2
peak was calculated as the
average of the two highest consecutive 30-second VO
2
measurements.
Statistical analysis
An a priori power analysis using results from Janik et al., (2018),
for serum sclerostin concentration, Vaara et al., (2015), for 1 RM
bench press, and O’leary et al., (2021), for total body aBMD,
were conducted. At 80% power, eect sizes were indicated as
0.6, 0.5, and 0.2 for each metric, respectively, suggesting
a sample size of between 6 and 28 for 80% power. All statistical
procedures were performed using IBM SPSS (v26, Armonk,
New York), and signicance was set at p ≤ 0.05. All data were
normally distributed based on the Shapiro–Wilks test and are
reported as unadjusted means ± standard deviations (SD) in
tables and means ± standard errors (SE) in gures. Baseline
dierences in physical characteristics between ROTC and
Controls were examined using independent t-tests. A 2 × 3
repeated measures analysis of variance (RMANOVA) was used
JOURNAL OF SPORTS SCIENCES 1589

to determine group (ROTC, Controls) and time (Nov, Jan, Apr)
main eects and group by time interactions. Signicant inter-
actions were decomposed using one-way ANOVAs with Fisher’s
Least Signicant Dierence post-hocs for each time point.
Results
Participant descriptives
Initially, 36 subjects (ROTC n = 18, Controls n = 18) were screened
for the study. Two ROTC were excluded prior to participation,
one for prolonged illnesses and another withdrew after visit one,
so their respective controls were also excluded. One more con-
trol was excluded after the winter break for not being able to
maintain matching criteria. In total, 31 subjects (ROTC n = 16;
Controls n = 15) were included in the nal analysis. Females
comprised 22% of the sample (n = 8) and 50% of females
reported using oral contraceptives, while an additional 13%
reported using an implant contraceptive method. No signicant
dierences were found between ROTC and Controls’ baseline
data for all anthropometrics, questionnaire responses, calcium
intake, exercise volumes, or BPAQ scores (all p ≥ 0.062; Table 1).
Calcium intake was not signicantly dierent between groups (p
= 0.062); however, ROTC were meeting the recommended daily
intake (Insitutue of Medicine US, 2000), while Controls were not,
so an exploratory analysis included it as a potential covariate.
This analysis did not change any statistical outcomes, so only
RMANOVA data are reported. Additionally, there were no signi-
cant dierences between groups at baseline for bone (all p ≥
0.111; Tables 2 and 3) or biomarker and performance variables
(all p ≥ 0.052; Table 4).
Changes over time
Multiple signicant group by time interactions and main eects
for time were observed for DXA measures of the total hip aBMD
and BMC (all p ≤ 0.050; Table 2, Figure 2, Supplemental Digital
Content - Table 1). Model decomposition via one-way ANOVAs
and post hoc analyses revealed a signicant increase in domi-
nant total hip aBMD and non-dominant femoral neck BMC in
ROTC from November to April (all p ≤ 0.030). However, ROTC
demonstrated a signicant decrease in dominant and non-
dominant greater trochanter from November to April (both p
< 0.050). It should be noted that despite reaching statistical
signicance, this decrease did not exceed the least signicant
change of the DXA machine and should not be considered.
Additionally, ROTC dominant total hip BMC signicantly
increased from November to April (post hoc p = 0.047).
Signicant group by time interactions and main eects for
time were observed for pQCT measures at all sites (all p ≤ 0.038;
Table 3, Supplemental Digital Content - Table 2). At the 4% site,
signicant interactions were found for total and trabecular
vBMD and area and periosteal circumference (all p ≤ 0.034);
however, after post hoc analyses no signicant group or time
eects remained (all p ≥ 0.054). At the 38% and 66% sites total
vBMD and content, and cortical vBMD all signicantly increased
from November to April in ROTC (all p ≤ 0.029). Lastly, 66%
cortical area, thickness, and mCSA all increased from
November to April in ROTC (all p ≤ 0.025).
Sclerostin signicantly increased from November to January
in ROTC (p < 0.001) and remained elevated by April (p = 0.278),
while PTH did not change in either group (Table 4 and Figure 3).
When considering physical performance improvements
(Table 4), leg press signicantly increased during each testing
phase similarly between groups (all post hoc p ≤ 0.040), while
bench press increased from November to April for both groups
(p = 0.013). Peak VO
2
was signicantly greater in ROTC compared
to Controls at all time points (group eect p = 0.020) but both
groups improved their aerobic capacity during each testing
phase to a similar extent (all time main eect post hocs p ≤
0.022).
Table 1. Participant characteristics at baseline testing, data are shown as mean (SD).
Measures
ROTC
(n = 16)
Controls
(n = 15)
Independent
t-test p
Age (years) 20.4 (2.5) 21.2 (1.9) 0.445
Height (m) 1.76 (0.10) 1.79 (0.07) 0.325
Body Mass (kg) 74.4 (11.1) 76.8 (10.1) 0.543
Calcium Intake (mg/day) 1118 (668) 737 (378) 0.062
Total PA (days/wk) 5.0 (1.4) 5.0 (1.0) 0.996
Total RT (days/wk) 4.2 (1.5) 4.0 (1.4) 0.726
Total ET (days/wk) 3.3 (1.7) 2.3 (1.9) 0.130
BPAQ – Total 21.7 (14.4) 33.6 (22.0) 0.084
BPAQ – Past 38.3 (28.7) 62.8 (43.4) 0.072
BPAQ – Current 5.1 (1.7) 4.4 (2.6) 0.368
No significant differences were found between groups. Abbreviations: SD:
Standard Deviation; 1RM: one repetition maximum; PA: Physical Activity; RT:
Resistance Training; ET: Endurance Training, BPAQ: Bone-specific Physical
Activity Questionnaire.
Table 2. DXA measures of body composition and bone over time, data are shown as mean (SD).
Measures
ROTC (n = 16) Controls (n = 15)
November January April November January April
Total Body Fat % 19.48 (6.01) 20.27 (5.51) 19.83 (5.81) 20.07 (5.38) 20.12 (5.72) 19.83 (5.54)
Lean Mass:Fat Mass 4.34 (1.52) 4.04 (1.26) 4.23 (1.52) 4.10 (1.31) 4.16 (1.49) 4.21 (1.52)
Total aBMD (g/cm
2
) 1.34 (0.12) 1.34 (0.11) 1.33 (0.12) 1.36 (0.12) 1.37 (0.12) 1.36 (0.11)
L1-L4 aBMD (g/cm
2
) 1.36 (0.21) 1.31 (0.12) 1.32 (0.12) 1.34 (0.17) 1.35 (0.17) 1.35 (0.15)
Dom Hip aBMD (g/cm2)
Femoral Neck 1.24 (0.14) 1.24 (0.14) 1.28 (0.15) 1.28 (0.13) 1.28 (0.14) 1.26 (0.14)
Greater Trochanter 1.00 (0.12) 0.99 (0.13) * 0.99 (0.12) ‡ 1.00 (0.14) 0.99 (0.14) * 0.98 (0.14) ‡
Total Hip 1.22 (0.13) 1.22 (0.14) * 1.22 (0.13) ‡ 1.24 (0.14) 1.23 (0.14) * 1.23 (0.14) ‡
ND Hip aBMD (g/cm2)
Femoral Neck 1.24 (0.13) 1.24 (0.13) 1.24 (0.13) 1.29 (0.13) 1.28 (0.14) 1.28 (0.14)
Greater Trochanter 1.00 (0.13) 0.99 (0.12) 0.99 (0.13) ‡ 1.02 (0.15) 1.02 (0.17) 1.00 (0.15) ‡
Total Hip 1.22 (0.13) 1.22 (0.13) 1.22 (0.13) 1.24 (0.15) 1.23 (0.15) 1.23 (0.15)
Significance set at p ≤ 0.05; * significant time effect from November to January; † significant time effect from January to April; ‡ significant time effect from November
to April. Abbreviations: SD: Standard Deviation; aBMD: areal Bone Mineral Density; L1-L4: lumbar spine 1–4; Dom: dominant; ND: non-dominant.
1590 A. L. REDINGER ET AL.

Table 3. pQCT measures of bone and muscle over time, data are shown as mean (SD).
Measures
ROTC (n = 16) Controls (n = 15)
November January April November January April
4% Tibia
Tot vBMD (mg/cm
3
) 345.9 (29) 346.2 (27) 346.5 (27) 365.3 (36) 363.6 (37) 361.1 (38)
Tot Area (mm
2
) 1175.6 (182) 1171.4 (180) 1170.7 (177) 1137.1 (206) 1149.0 (206) 1155.4 (209)
Tot BSI (mg
2
/mm
4
) 140.6 (27) 140.4 (27) 140.6 (27) 151.5 (34) 151.5 (34) 150.3 (35)
Trab vBMD (mg/cm
3
) 310.2 (27) 310.5 (27) 310.8 (26) 317.4 (33) 317.1 (34) 315.4 (35)
Trab Area (mm
2)
1074.1 (177) 1071.9 (176) 1070.5 (171) 1020.6 (204) 1033.0 (205) 1041.5 (207)
Trab BSI (mg
2
/mm
4
) 103.8 (24) 103.9 (24) 103.9 (24) 103.5 (30) 104.4 (30) 104.2 (30)
38% Tibia
Tot vBMD (mg/cm
3
) 933.5 (57) 935.4 (58) * 937.1 (57) ‡ 937.1 (67) 940.3 (69) * 939.6 (68) ‡
Tot Cont (mg/mm) 399.5 (55) 400.5 (55) 402.0 (56) ‡ 425.6 (65) 425.9 (64) 426.0 (64) ‡
Cort vBMD (mg/cm
3
) 1174.2 (26) 1175.8 (27) * 1176.3 (26) ‡ 1162.0 (28) 1166.6 (29) * 1165.5 (28) ‡
Cort Cont (mg/mm) 384.7 (52) 385.5 (51) 407.9 (59) 407.5 (60) 407.8 (60) 407.9 (59)
Cort Thickness (mm) 6.0 (0.6) 6.0 (0.6) 6.0 (0.7) 6.3 (0.7) 6.3 (0.7) 6.3 (0.7)
EndoCirc (mm) 35.3 (5.2) 35.3 (5.2) 35.3 (5.2) 35.9 (7.3) 35.9 (7.2) 35.9 (7.2)
66% Tibia
Tot vBMD (mg/cm
3
) 694.5 (52) 716.9 (92) 698.5 (52) ‡ 723.7 (71) 728.0 (71) 728.4 (71) ‡
Tot Cont (mg/mm) 439.6 (61) 440.6 (63) * 441.8 (63) † ‡ 464.8 (71) 466.3 (70) * 466.8 (70) † ‡
Cort vBMD (mg/cm
3
) 1134.4 (23) 1137.5 (27) 1136.9 (23) ‡ 1130.4 (26) 1131.3 (24) 1133.6 (26) ‡
Cort Cont (mg/mm) 399.8 (56) 401.7 (55) * 402.4 (58) ‡ 420.1 (61) 451.6 (61) * 422.7 (61) ‡
Cort Thickness (mm) 4.7 (0.5) 4.9 (0.5) 4.8 (0.5) ‡ 5.0 (0.6) 5.0 (0.6) 5.1 (0.6) ‡
EndoCirc (mm) 59.3 (6.9) 57.6 (10.5) 59.1 (6.7) ‡ 58.3 (8.5) 58.1 (8.5) 58.0 (8.4) ‡
mCSA (mm
2
) 7874.9 (1005.9) 7716.4 (928.3) 7931.5 (920.8) † 8332.4 (1379.6) 8417.6 (1512.3) 8471.8 (1611.7) †
Significance set at p ≤ 0.05; * significant time effect from November to January; † significant time effect from January to April; ‡ significant time effect from November
to April. Abbreviations: SD: Standard Deviation; Tot: Total; vBMD: volumetric Bone Mineral Density; Trab: Trabecular; BSI: Bone Strength Indices; Cort: Cortical; Endo
Circ: Endosteal Circumference; mCSA: muscle Cross-Sectional Area.
Table 4. Changes in serum biomarkers and performance measures over time, data are shown as mean (SD).
Measures
ROTC (n = 16) Controls (n = 15)
November January April November January April
Biomarkers
Sclerostin (ng/mL) 0.38 (0.09) 0.44 (0.14) * 0.42 (0.12) ‡ 0.37 (0.09) 0.42 (0.09) * 0.14 (0.11) ‡
Parathyroid Hormone (U/L) 45.95 (12.47) 39.03 (20.87) 43.98 (21.68) 40.68 (12.27) 41.90 (14.43) 42.95 (16.12)
Performance
1RM Leg Press (kg) 242 (83) 266 (75) * 292 (82) † ‡ 280 (89) 289 (89) * 315 (97) † ‡
1RM Bench Press (kg) 83 (29) 84 (29) 87 (29) ‡ 87 (33) 87 (32) 89 (32) ‡
VO
2
Peak (ml/kg/min) 51.4 (7.1) # 53.3 (7.9) *# 54.3 (8.4) † ‡ # 46.8 (5.4) 47.7 (5.0) * 49.4 (5.6) † ‡
Respiratory Exchange Ratio 1.21 (0.06) 1.15 (0.06) 1.13 (0.07) 1.18 (0.06) 1.17 (0.07) 1.12 (0.04)
Maximal Heart Rate (bpm) 199 (6) 197 (6) 196 (6) 199 (7) 195 (6) 196 (8)
Rate of Perceived Exertion 17 (1) 18 (1) 18 (1) 18 (1) 18 (1) 19 (1)
Significance set at p ≤ 0.05; * significant time effect from November to January; † significant time effect from January to April; ‡ significant time effect from November
to April; # significant group effect. Abbreviations: SD: Standard Deviation; 1RM: one repetition maximum.
Figure 2. Dominant femoral neck, greater trochanter, and total hip aBMD throughout the six-month evaluation period are shown, from left to right respectively. ROTC
data is in the grey bars while control data is in the white bars. Greater trochanter and total hip aBMD significantly increased from November to January (* both p ≤
0.009) and remained significantly elevated in April (‡ both p ≤ 0.016) for both groups. Abbreviations included Dom: dominant limb; aBMD: areal bone mineral density.
JOURNAL OF SPORTS SCIENCES 1591

Discussion
Due to the physically arduous nature of military training and high
injury incidence, longitudinal evaluation of musculoskeletal
health and performance is critical (Armstrong et al., 2004; Popp
et al., 2021). This study temporally evaluated skeletal health,
biomarker responses, and physical performance changes in col-
lege-aged ROTC cadets over 6 months, nding an updated ROTC
training programme based on HIIT principles elicited positive
musculoskeletal adaptations which, if maintained, would be ske-
letally protective during their future military training.
Just 5 years ago, overuse injuries accounted for nearly 70% of
all reported musculoskeletal injuries among active-duty Army
personnel (Molloy et al., 2020), costing over $115 million
(Forrest et al., 2021). These bone stress injuries are often
characterized as either mineral insuciency or fatigue-derived
overuse fractures and the risk of either type may be reduced by
implementing the HIIT style training. First, the new programme
eectively deviates from traditional endurance-based pro-
grammes (Scoeld & Kardouni, 2015) by including many func-
tional, multi-vector loading-based circuits. The improvements in
ROTC bone density and content of the total hip and bone
geometry at both 38% and 66% tibial sites most likely beneted
from the introduction of these multi-directional loading patterns,
eectively increasing load resistance and reducing insucient
fracture risk. Our results support those of Hughes et al., (2018)
and O’Leary et al., (2019) who both assessed bone quality and
strength in 91 female U.S. Army recruits and 43 male British Army
recruits, respectively. Both studies noted positive tibial bone
geometry adaptations similar to the current study and noted
Figure 3. Serum concentrations of sclerostin and PTH throughout the six-month evaluation period are shown in the top and bottom panels, respectively. Sclerostin
significantly increased from November to January (* p < 0.001) and remained significantly elevated in April (‡ p = 0.007). PTH did not change over time (p = 0.342) and
no group effects were found for either biomarker (p = 0.744). ROTC data is in the grey bars while control data is in the white bars. Exclusion of outliers (greater than two
standard deviations) did not change statistical findings and thus all the data are included.
1592 A. L. REDINGER ET AL.

these improvements were most likely attributed to participants’
exposure to novel loading patterns. These improvements in
ROTC may be especially important due to the developmental
age of the cadets as positive bone adaptations now can have
lasting benet to the skeleton and potentially reduce future
injury risk.
Fatigue fracture risk may also be reduced in new ROTC training
programmes due to the adoption of HIIT foundations. During HIIT
training, ROTC may be able to see performance improvements
that meet or exceed those of a traditional programme, while
engaging in reduced training volumes. For instance, Gist et al.,
(2015), compared the ecacy of 4 weeks of HIIT training versus
the traditional ROTC training programme in 26 college-aged
cadets. HIIT training required less than half of the same training
time and volume compared to the traditional training, but Army
Physical Fitness Test performance was similar. Using HIIT reduced
the overall training volume, shifted the loading prole from repe-
titive to novel, and increased the rest periods, all of which can be
substantial stimuli for positive bone growth. HIIT has also been
shown to improve bone more than traditional training pro-
grammes in adolescents (Julian et al., 2022) and college-aged
adults (Lu et al., 2022). Taken together, it appears that this updated
training programme which utilized HIIT as the foundation has the
ability to reduce risk of both insuciency and fatigue fractures by
improving bone content, density, and geometry while also redu-
cing training volumes and increasing rest periods.
The updated ROTC programme also positively impacted
many factors that are indirectly associated with bone injuries.
For instance, Beck et al., (2000) reported military recruits suer-
ing from stress injuries demonstrated poorer tness levels,
smaller mid-thigh mCSA, and reduced estimated thigh and
tibiae bone strength compared to their injury-free counter-
parts. These ndings were corroborated by Homan et al.,
(1999) who found 18-year-old army recruits with lower extre-
mity strength greater than one standard deviation below the
population mean were at a signicantly greater estimated risk
for stress fractures. Beck et al., (2000) hypothesized that those
with reduced muscle strength and size would not be able to
adequately dissipate ground reaction forces during training,
leading to increased localized skeletal loading, and the accu-
mulation of microtrauma resulting in bone injury. Our ndings
support those of Beck et al., (2000) and Homan et al., (1999) as
ROTC from the current study signicantly improved their mus-
cle strength and mCSA, which coincided with improved bone
geometry. Furthermore, Armstrong et al., (2004) evaluated
bone health using DXA in 31 Naval Academy cadets aged
18.7 years over the summer months. They found cadets who
suered a stress fracture had greater reductions in body mass
and BMC compared to those who did not fracture throughout
a traditional training regimen, suggesting weight maintenance
to be a key factor. In the current study, ROTC participants-
maintained body mass and BMC while reporting no fractures
during the intervention period. Taken together, these data
suggest that the newly adapted ROTC training programme
also improved many indirect correlates of bone injury, poten-
tially further reducing future risk.
The biomarkers sclerostin and PTH were included in this study
to provide a metabolic indicator of bone metabolism over time.
PTH did not change, and the literature surrounding this biomar-
ker’s response to military training is mixed as previously noted.
However, sclerostin signicantly increased during the winter
break and remained elevated for the remainder of the study,
posing some interesting questions. As sclerostin is a potent inhi-
bitor of bone formation, high serum concentrations are often
linked with periods of physical inactivity. At rst, our data con-
rmed this relationship as sclerostin increased during the winter
break, when training was not mandated. However, activity levels
as estimated via BPAQ show no dierence in activity from
November to January suggesting a maintenance in activity.
Additionally, these high serum sclerostin values remained ele-
vated during the second eight-week training period from
January to April. These data suggest high rates of bone resorp-
tion; however, bone loss was not observed from DXA or pQCT
measures. We hypothesize that during the intervention period
participants were indeed experiencing increased rates of bone
resorption as evidenced by the elevated sclerostin concentra-
tions; however, bone formation outpaced this catabolic activity
to result in the observed increases in bone mineral deposition.
Without denitive assessments of bone formation from biomar-
kers, such as PINP, OC, or BAP, this is purely speculative.
This study presents several strengths and limitations to
consider. First, this study assessed ROTC’s bone health and
performance using DXA, pQCT, serum biomarkers, 1RM, and
peak VO
2
testing across multiple training interventions. And
while these data are valid, reliable, and precise, they are not
tools that can always be easily utilized in the eld with
hundreds of young military personnel engaging in basic
training blocks, reducing the potential generalizability of
these data. Second, as previously noted, measures of both
bone resorption and formation must be included in future
research to have a better understanding of the magnitude
of metabolic shifts that may occur in response to training.
Third, although physical activity frequency was collected,
resistance and endurance training intensity were not
recorded which may inuence the magnitude of musculos-
keletal adaptation to training and should serve as
a pertinent measure for future investigations. Finally, our
cohort was comprised almost entirely of male cadets and
future research needs to consist of a more diverse cohort,
especially since women now make up a larger proportion of
enlisted military than ever before.
In conclusion, a non-traditional HIIT-style ROTC training regi-
men elicited positive skeletal adaptations which coincided with
improved muscle size and strength. These ndings indicate
collegiate ROTC cadets should perhaps engage in more HIIT-
style training programmes prior to service to reduce the risk of
bone injury.
Acknowledgments
The authors would like to thank all participants and Dr. D. Bemben and Dr.
M. Bemben for their time, eort, and essential contribution to this study.
Disclosure statement
No potential conict of interest was reported by the author(s).
JOURNAL OF SPORTS SCIENCES 1593

Funding
The author(s) reported that there is no funding associated with the work
featured in this article.
ORCID
Allen L. Redinger http://orcid.org/0000-0001-7152-6067
Shawn M. F. Allen http://orcid.org/0000-0002-6367-2600
Samuel R. Buchanan http://orcid.org/0000-0003-3606-3786
Christopher D. Black http://orcid.org/0000-0003-2662-8341
Breanne S. Baker http://orcid.org/0000-0002-0098-149X
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