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Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer
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similarly to the deadlift
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Daniel L. Plotkin1,*, Merlina A. Rodas2, Andrew D. Vigotsky3,4, Mason C. McIntosh1, Emma
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Breeze1, Rachel Ubrik1, Cole Robitzsch1, Anthony Agyin-Birikorang1, Madison L. Mattingly1, J.
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Max Michel1, Nicholas J. Kontos1, Andrew D. Frugé5, Christopher M. Wilburn1, Wendi H.
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Weimar1, Adil Bashir6, Ronald J. Beyers6, Menno Henselmans7, Bret M. Contreras8, Michael D.
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Roberts1,*
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Affiliations: 1School of Kinesiology, Auburn University, Auburn, AL, USA; 2Department of
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Psychological Sciences, Auburn, AL, USA; 3Departments of Biomedical Engineering and
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Statistics, Evanston, IL, USA; 4Department of Neuroscience, Northwestern University, Chicago,
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IL, USA; 5College of Nursing, Auburn University, Auburn, AL, USA; 6MRI Research Center,
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Auburn University, Auburn AL, USA; 7International Scientific Research Foundation for Fitness
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and Nutrition, Amsterdam, Netherlands; 8BC Strength, San Diego, CA, USA
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*Co-correspondence to:
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Daniel L. Plotkin, MS
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PhD student, School of Kinesiology
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Auburn University
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E-mail: dzp0092@auburn.edu
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Michael D. Roberts, PhD
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Professor, School of Kinesiology
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Auburn University
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E-mail: mdr0024@auburn.edu
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ABSTRACT
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Purpose: We examined how set-volume equated resistance training using either the back squat
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(SQ) or hip thrust (HT) affected hypertrophy and various strength outcomes.
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Methods: Untrained college-aged participants were randomized into HT (n=18) or SQ (n=16)
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groups. Surface electromyograms (sEMG) from the right gluteus maximus and medius muscles
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were obtained during the first training session. Participants completed nine weeks of supervised
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training (15–17 sessions), before and after which we assessed muscle cross-sectional area (mCSA)
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via magnetic resonance imaging and strength via three-repetition maximum (3RM) testing and an
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isometric wall push test.
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Results: Glutei mCSA growth was similar across both groups. Estimates [(−) favors HT; (+) favors
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SQ] modestly favored the HT compared to SQ for lower [effect ± SE, −1.6 ± 2.1 cm2], mid [−0.5
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± 1.7 cm2], and upper [−0.5 ± 2.6 cm2], but with appreciable variance. Gluteus medius+minimus
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[−1.8 ± 1.5 cm2] and hamstrings [0.1 ± 0.6 cm2] mCSA demonstrated little to no growth with small
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differences between groups. Thigh mCSA changes were greater in SQ for the quadriceps [3.6 ± 1.5
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cm2] and adductors [2.5 ± 0.7 cm2]. Squat 3RM increases favored SQ [14 ± 2.5 kg] and hip thrust
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3RM favored HT [−26 ± 5 kg]. 3RM deadlift [0 ± 2 kg] and wall push strength [−7 ± 13 N]
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similarly improved. All measured gluteal sites showed greater mean sEMG amplitudes during the
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first bout hip thrust versus squat set, but this did not consistently predict gluteal hypertrophy
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outcomes.
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Conclusion: Nine weeks of squat versus hip thrust training elicited similar gluteal hypertrophy,
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greater thigh hypertrophy in SQ, strength increases that favored exercise allocation, and similar
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strength transfers to the deadlift and wall push.
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Keywords: Hip thrust, back squat, gluteus maximus, strength
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INTRODUCTION
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Resistance training (RT) presents potent mechanical stimuli that produce robust biological
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responses (1). However, RT responses vary considerably depending on several training variables.
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One such variable is exercise selection; specifically, different exercises have varying mechanical
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demands that can lead to differences in muscle growth, strength, and other related outcomes (2-5).
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Practitioners and researchers often rely on functional anatomy, basic biomechanics, and acute
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physiological measurements to surmise what adaptations different exercises may elicit. The degree
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to which such surmises can meaningfully predict outcomes remains an open question, and recent
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work casts some doubt on their fidelity.
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The reliance on theory and acute measures to guide exercise selection is especially evident
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in the hip extension exercise literature, an area of particular interest with applications in
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rehabilitation, performance, injury prevention, and bodybuilding. The roles of various hip extensor
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muscles during different hip extension tasks have been studied in several ways, including surface
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electromyography (sEMG), nerve blocks, and musculoskeletal modeling (6-8). Based on these
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acute measures, investigators infer stimulus potency or exercise superiority. For instance, previous
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work investigated sEMG amplitudes during two common and contentiously contrasted hip
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extension exercises—the hip thrust and squat—to compare muscle function, implying that this
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relates to subsequent adaptations (9-11). Although mean and peak sEMG amplitudes favored hip
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thrusts, sEMG’s ability to predict longitudinal strength and hypertrophy outcomes from resistance
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training interventions was recently challenged (12). To help overcome some sEMG limitations,
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more sophisticated investigations integrate excitation into musculoskeletal models (8). Yet, more
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comprehensive analyses of muscle contributions are still limited by their underlying assumptions
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(13), and even perfect modeling of muscle contributions presumes a one-to-one relationship
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between tension and adaptations.
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Muscle tension is the primary driver of muscle hypertrophy but is unlikely to be its sole
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determinant. Recent evidence demonstrates that RT at long muscle lengths and long-duration static
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stretching can augment hypertrophic outcomes (14, 15), suggesting other factors may modulate
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anabolic signaling. It is unknown to what extent muscle tension may interact with position-specific
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anabolic signaling and other variables to contribute to the anabolic response and how this
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interaction may change under different conditions. Regarding the squat and hip thrust, the former
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has a steeper hip extension resistance curve with a relatively greater emphasis in hip flexion(7,
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16), which may confer a more potent gluteal training stimulus. However, this notion assumes
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proportional force sharing among the hip extensors, but contributions shift throughout the range
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of motion, clouding inferences (17). This highlights that longitudinal predictions necessitate
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assumptions about how motor systems satisfy the mechanical constraints imposed by each exercise
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and subsequent biological responses, it is difficult to infer the potency of the hypertrophic stimulus
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using indirect measures. We ultimately need longitudinal data to understand and accurately
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forecast longitudinal outcomes from individual movements.
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Direct evidence is presently needed to compare the outcomes of various exercises.
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Therefore, the purpose of this study was to examine how RT using either the barbell squat or
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barbell hip thrust on a set-volume equated basis affected gluteus maximus, medius, and minimus
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muscle hypertrophy (determined by MRI) and various strength outcomes including the back squat,
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hip thrust, deadlift, and isometric wall push. As a secondary outcome, we sought to determine how
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We acknowledge but will not further discuss the squat versus hip thrust paper by Barbalho et al.(18). These and
other data from this laboratory were scrutinized and retracted for being improbable(19)
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these exercises affected gluteus maximus/medius muscle excitation patterns using sEMG and if
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sEMG amplitudes forecasted hypertrophy.
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METHODS
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Ethical considerations and participant recruitment
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Before commencing study procedures with human participants, this study was approved by the
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Auburn University Institutional Review Board (protocol #: 22-588). All approved study
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procedures followed the latest revisions to the Declaration of Helsinki (2013) except for being pre-
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registered as a clinical trial on an online repository. Inclusion criteria were as follows: (a) between
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the ages of 18-30 years old with a body mass index (body mass/height2) of less than 30 kg/m2; (b)
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have minimal experience with resistance training, averaging less than or equivalent to one day per
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week for the last five years; (c) have not been actively participating in any structured endurance
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training program (e.g. running or cycling) for more than two days per week over the past six
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months; (d) free of any known overt cardiovascular or metabolic disease; (e) have not consumed
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supplemental creatine, and/or agents that affect hormones (testosterone boosters, growth hormone
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boosters, etc.) within the past two months, (f) free of any medical condition that would
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contraindicate participation in an exercise program, (g) do not have conditions which preclude
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performing an MRI scan (e.g., medically-implanted devices), (h) and free of allergies to lactose or
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intolerances to milk derived products that would contraindicate ingestion of whey protein. Eligible
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participants who provided verbal and written consent partook in the testing and training procedures
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outlined in the following paragraphs.
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Study design overview
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An overview of the study design can be found in Figure 1. Participants performed two pre-
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intervention testing visits, one in a fasted state for body composition and MRI assessments and the
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other in a non-fasted state for strength assessments. These visits occurred in this sequence ~48
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hours apart; after the pre-intervention strength visit, participants were randomly assigned to one of
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two experimental groups, including the barbell back squat (SQ) or barbell hip thrust (HT) groups.
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Two days following the pre-intervention strength testing, all participants partook in their first
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workout, which served to record right gluteal muscle excitation via sEMG during one set of 10
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repetitions for both the SQ and HT exercises. Thereafter, participants engaged in 9 weeks of
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resistance training (two days per week). Seventy-two hours following the last training bout,
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participants performed two post-intervention testing visits with identical timing and protocols as
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pre-testing.
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Figure 1. Study design overview
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Legend: Figure depicts study design overview described in-text. Abbreviations: PRE, pre-intervention testing visit;
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POST, post-intervention testing visit; HT, barbell hip thrust; SQ, barbell squat; body comp., body composition testing
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using bioelectrical impedance spectroscopy; MRI, magnetic resonance imaging; sEMG, electromyography.
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Body composition and MRI assessments
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Body composition. Participants were told to refrain from eating for 8 h prior to testing,
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eliminate alcohol consumption for 24 h, abstain from strenuous exercise for 24 h, and to be well
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hydrated for testing. Upon arrival participants submitted a urine sample (~50 mL) for urine specific
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gravity assessment (USG). Measurements were performed using a handheld refractometer
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(ATAGO; Bellevue, WA, USA), and USG levels in all participants were ≤ 1.020, indicating
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sufficient hydration. Participants’ heights were measured using a stadiometer and body mass was
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assessed using a calibrated scale (Seca 769; Hanover, MD, USA) with body mass being collected
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to the nearest 0.1 kg and height to the nearest 0.5 cm. Body composition was then measured by
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bioelectrical impedance spectroscopy (BIS) using a 4-lead (two hands, two feet) SOZO device
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(ImpediMed Limited, Queensland, Australia) according to the methods described by Moon et al.
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(20). Our laboratory has previously shown these methods to produce test-retest intraclass
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correlation coefficients (ICC3,1) >0.990 for whole body intracellular and extracellular water
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metrics on 24 participants (21), and this device provided estimates of fat free mass, skeletal muscle
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mass, and fat mass.
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MRI Measurements. MRI testing assessed the muscle cross-sectional area (mCSA) of both
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glutei maximi. Upon arriving to the Auburn University MRI Research Center, participants were
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placed onto the patient table of the MRI scanner (3T SkyraFit system; Siemens, Erlangen,
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Germany) in a prone position with a ~5-minute latency period before scanning was implemented.
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A T1-weighted turbo spin echo pulse sequence (1400 ms repetition time, 23 ms echo time, in-
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plane resolution of 0.9 × 0.9 mm2) was used to obtain transverse image sets. 71 slices were obtained
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with a slice thickness of 4 mm with no gap between slices. Measurements were taken by the same
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investigator (R.J.B.) for all scans who did not possess knowledge of the training conditions for
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each participant.
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Following the conclusion of the study, MRI DICOM files were preprocessed using Osirix
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MD software (Pixmeo, Geneva, Switzerland), and these images were imported into ImageJ
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(National Institutes of Health; Bethesda, MD, USA) whereby the polygon function was used to
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manually trace the borders of muscles of interest to obtain mCSA. For all participants, image
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standardization was as follows: (a) the middle of the gluteus maximus was standardized at the
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image revealing the top of the femur, (b) the image that was 10 slices upward from this mark was
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considered to be the upper gluteus maximus, (c) the image that was 18 slices downward from the
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top of the femur was considered lower gluteus maximus, (d) gluteus medius and minimus mCSAs
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were ascertained at the upper gluteus maximus image, and (e) combined quadriceps (vastii and
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rectus femoris), adductors (brevis, longus, and magnus), and combined hamstrings (biceps
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femoris, semitendinosus, semimembranosus) mCSAs were ascertained at the first transverse slice
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distal to the last portion of the lower gluteus maximus. When drawing borders to quantify muscles
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of interest, care was taken to avoid fat and connective tissue. Certain muscles were grouped (i.e.,
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gluteus medius + minimus, combined quadriceps muscles, combined adductor muscles, combined
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hamstrings muscles) due to inconsistent and poorly delineated muscle borders within participants.
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All left- and right-side gluteus muscles were summed to provide bilateral mCSA values at each
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site. Alternatively, thigh musculature mCSA values were yielded from the averages of the left and
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right legs. This method was performed on the thigh because ~10% of participants yielded either
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left or right thigh images that presented visual artifacts from the edge of the MRI receiving coil.
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In these situations, thigh musculature from only one of the two legs was quantified.
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Strength assessments
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Isometric muscle strength (wall push). Participants reported to the laboratory (non-fasted)
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having refrained from any exercise other than activities of daily living for at least 48 h before
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baseline testing. A tri-axial force plate (Bertec FP4060-10-2000; Columbus, OH, USA) with an
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accompanying amplifier (Bertec model # AM6800) sampling at 1000 Hz was used to measure
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horizontal force production in newtons (N) during a wall push test. The distance from the force
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plate to the wall was positioned such that when the subjects’ forearms parallel with the ground,
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the torso was at a ~45º angle with the ground, and one rear foot was in contact with the force plate.
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Hand placement was standardized by distance from the ground and foot placement was
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standardized by distance from the wall. The subject was instructed to push, using the dominant
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leg, as hard as possible into the wall while keeping the torso at 45º (Figure 2). Two wall pushes
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were performed for three seconds each, with each repetition being separated by two minutes of
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rest. The highest peak horizontal force from these two tests was used for analysis.
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Figure 2. Wall push demonstration
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Legend: Figure depicts the wall push test with one of the co-authors (M.D.R.) and shows force tracing.
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Horizontal force (N)
Start Stop
Peak value
Time (s)
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Dynamic muscle strength. Following wall push testing, dynamic lower body strength was
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assessed by three-repetition maximum (3RM) testing for the barbell back squat, barbell hip thrust,
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and barbell deadlift exercises. Notably, our laboratory has extensively performed 3RM dynamic
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strength testing on numerous occasions in untrained and trained participants (22-25). Briefly,
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specific warm-up sets for each exercise consisted of coaching participants through the movement
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patterns and gauging comfort and movement proficiency. Subsequent warm-ups for each exercise
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were chosen with an attempt at approximating 5 repetitions at ~50% 1RM for one set and 2–3
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repetitions at ~60–80% 1RM for two additional sets. Participants then performed sets of three
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repetitions with incremental increases in load for 3RM determinations for each exercise and three
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minutes of rest was given between each successive attempt. For all exercises, participants were
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instructed to perform repetitions in a controlled fashion, with a concentric action of approximately
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1 s and an eccentric action of approximately 2 s. All three exercises were performed with feet
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spaced 1–1.5-times shoulder width apart. For the barbell squat, depth was set to when the femur
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was parallel to the floor, with all but one participant achieving a depth at or below this point. For
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the barbell hip thrust, the hip thrust apparatus (Thruster 3.0, BC Strength; San Diego, CA, USA)
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was set to a height at which participants could make brief contact with the ground with the weight
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plate (21”) and hips at the bottom of each repetition. Repetitions were considered properly
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executed when the participant’s tibia was perpendicular to the floor and the femur was parallel to
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the floor. Torso position was sufficiently maintained to avoid excessive motion through the pelvis.
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For the barbell deadlift, participants began repetitions from the floor and were prompted to
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maintain the torso position throughout the execution of the lift. A lift was deemed successful once
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participants stood upright with full knee and hip extensions.
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sEMG measurements during the first training bout
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Subjects were asked to wear loose athletic attire to access the EMG electrode placement sites.
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Before placing the electrodes on the skin, if necessary, excess hair was removed with a razor, and
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the skin was cleaned and abraded using an alcohol swab. After preparation, double-sided adhesives
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were attached to wireless sEMG electrodes (Trigno system; Delsys, Natick, MA, USA), where
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were placed in parallel to the fibers of the right upper gluteus maximus, mid gluteus maximus,
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lower gluteus maximus, and gluteus medius (see Fig. 4a in Results). Upper and middle gluteus
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maximus electrodes were placed based on the recommendations of Fujisawa and colleagues (26),
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albeit we considered the lower gluteus maximus as middle. The upper gluteus maximus electrodes
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were placed superior and lateral to the shortest distance between the posterior superior iliac spine
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(PSIS) and the posterior greater trochanter, and the middle gluteus maximus electrodes were
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placed inferior and medial to the shortest distance between the PSIS and the posterior greater
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trochanter. Lower gluteus maximus electrodes were placed one inch (2.54 cm) above the most
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medial presentation of the gluteal fold. If it was ambiguous as to whether an appreciable amount
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of muscle tissue existed in this lower region, the participant was asked to contract the area and
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palpation was used to confirm proper placement. Gluteus medius electrodes were placed over the
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proximal third of the distance between the iliac crest and the greater trochanter. After the electrodes
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were secured, a quality check was performed to ensure sEMG signal validity. Following electrode
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placement, maximum voluntary isometric contraction (MVIC) testing was performed immediately
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prior to 10RM testing. For the gluteus maximus, the MVIC reference was a prone bent-leg hip
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extension against manual resistance applied to the distal thigh, as used by Boren and colleagues
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(6). For the gluteus medius MVIC, participants laid on their side with a straight leg and abducted
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against manual resistance. Care was taken not to depress the joint of interest during manual testing.
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In all MVIC positions, participants were instructed to contract the tested muscle as hard as
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possible. After five minutes of rest following MVIC testing, all participants performed one set of
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ten repetitions utilizing estimated 10RM loads for both the barbell back squat and the barbell hip
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thrust exercises. The exercise form and tempo used were the same as described in the strength
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testing section above. During both sets, muscle excitation of the upper/middle/lower gluteus
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maximus and gluteus medius were recorded with the wireless sEMG system whereby electrodes
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were sampled at 1000 Hz. Participants allocated to HT training performed the squat set first
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followed by the hip thrust set. Participants allocated to SQ training performed the hip thrust set
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first followed by the back squat set. Following these two sEMG sets, the wireless sEMG electrodes
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were removed. Participants finished the session with two more sets of 8–12 repetitions using the
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calculated 10RM load for the exercise allocated to them for the intervention.
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Signal processing was performed using software associated with the sEMG system (Delsys
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EMGworks Analysis v4.7.3.0; Delsys). sEMG signals from the MVICs and 10RM sets of back
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squat and hip thrust were first rectified. Signals were then processed with a second-order digital
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low-pass Butterworth filter, with a cutoff frequency of 10 Hz, and further smoothed using a root
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mean square moving window of 250 ms. The average of the middle 3 seconds of the filtered MVIC
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time series was then used to normalize the squat and hip thrust data for each site. Data were then
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visually inspected for fidelity before calculating the mean and peak sEMG values. Partial
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sequences of sEMG data were removed in the rare event that tempo was irregular or not
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maintained, or if a brief artifact was introduced. Final EMG data are presented as mean and peak
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sEMG amplitudes during the hip thrust and back squat 10RM sets. sEMG issues were only evident
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for a small portion (see Results) of the 34 participants who finished the intervention. Data were
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dropped from analyses due to artifacts produced through either electrode slippage or sEMG
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electrode jarring during the 10RM sets, leading to persistent clipping. In this regard, sample sizes
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for each muscle site are presented in the results section.
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Resistance training procedures
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The RT protocol consisted of 3–6 sets per session of barbell hip thrusts for HT participants or
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barbell back squats for SQ participants. Excluding the first week, which consisted of one session,
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all remaining weeks consisted of two sessions per week on non-consecutive days for 9 weeks.
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Week-to-week set schemes per session were as follows: week 1, 3 sets; week 2, 4 sets; weeks 3–
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6, 5 sets; weeks 7–9, 6 sets. The repetition range was set to 8–12 repetitions; if a participant
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performed less than 8 repetitions or more than 12 repetitions, the load was adjusted accordingly.
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D.L.P. and 1–2 other co-authors supervised all sessions, during which participants were verbally
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encouraged to perform all sets to the point of volitional muscular failure, herein defined as the
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participants being unable to volitionally perform another concentric repetition while maintaining
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proper form. Again, the exercise form and tempo used were the same as described in the strength
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testing section above; however, squat repetitions were not limited to a depth corresponding to the
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femur parallel to the floor but rather the lowest depth achievable. Outside of these supervised
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training sessions, participants were instructed to refrain from performing any other lower-body RT
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for the duration of the study. Participants could miss a maximum of 2 sessions and still be included
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in the analysis.
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Dietary instructions during the study
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Participants were given containers of a whey protein supplement (Built with Science; Richmond,
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BC, Canada) and were instructed to consume one serving per day (per serving: 29 g protein, 1 g
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carbohydrate, 0.5 g fat, 130 kcal). This was done in the hope of diminishing inadequate protein
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intake as a confounding variable. Other than this guidance, participants were advised to maintain
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their customary nutritional regimens to avoid other potential dietary confounders.
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Notes on randomization and blinding
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Investigators were blinded to group allocation during the MRI scan and its analysis. Participants
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were not blinded to group allocation as exercise comparisons were not amenable to blinding. Due
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to logistical constraints investigators were not blinded to group allocation during strength testing
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and, thus, bias cannot be completely ruled out in this context. Randomization into SQ and HT
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groups was performed via a random number generator in blocks of 2 or 4 as participants consented.
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Statistics and figure construction
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Data were analyzed in Jamovi v2.3 (https://www.jamovi.org) and R (version 4.3.0). We performed
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three different sets of analyses. First, we compared mean and peak HT and SQ sEMG amplitudes
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from the first training session, for which we performed paired t-tests.
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Second, we compared the longitudinal effects of HT and SQ training on mCSA and
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strength. Notably, baseline and within-group inferential statistics were not calculated, as baseline
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significance testing is inconsequential (27) and within-group outcomes are not the subject of our
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research question (28). However, we descriptively present within-group changes to help
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contextualize our findings. The effect of group (SQ versus HT) on each outcome variable was
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estimated using linear regression, in which post-intervention scores were the response variable,
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group was dummy-coded 0 for SQ and 1 for HT, and the pre-intervention score was included as a
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covariate of no interest (29). The model output can thus be interpreted as the expected difference
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in post-intervention (or mathematically equivalently, change) scores between the SQ and HT
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groups for a given pre-intervention score. We used the bias-corrected and accelerated stratified
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bootstrap with 10,000 replicates to calculate 95% compatibility intervals (CIs).
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Third, we investigated the extent to which sEMG amplitudes from the first session
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forecasted growth. There are multiple ways this question could be posed, and since claims
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surrounding sEMG amplitude’s predictive power are ambiguous, we addressed each of the
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following questions: i) Do individuals with greater sEMG amplitudes grow more than individuals
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with lower sEMG amplitudes? For this, we calculated a Pearson correlation for each muscle using
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changes in mCSA and the sEMG amplitudes. ii) Do regions or muscles with greater sEMG
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amplitudes grow more than regions or muscles with lower sEMG amplitudes? For this, we used a
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linear mixed-effects model in which ln(mCSApost/mCSApre) was the response variable; sEMG
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amplitude, group, and their interaction were fixed effects; and we permitted intercepts and slopes
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for sEMG amplitude to vary across subjects. Since we are interested in generalizable predictions,
333
we calculated prediction intervals for the slopes by calculating a Wald interval using the sum of
334
the parameter variance and random effects variance. iii) Can the differences in growth elicited
335
from different exercises be accounted for by sEMG amplitude? For this, we calculated the so-
336
called “indirect effect” of sEMG amplitude, which represents the extent to which the group effect
337
on hypertrophy can be explained by sEMG amplitudes. This was done the same way a typical
338
“mediation analysis” is done (although, this should not be viewed as causal here)—we
339
bootstrapped the difference between the group effect (SQ vs. HT) when sEMG was not in the
340
model and when sEMG was added to the model. If group-based sEMG differences accounted for
341
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10
group-based hypertrophy differences, then the effect of group on growth would shrink towards 0
342
and sEMG would absorb the variance in growth.
343
Figures were constructed using Microsoft PowerPoint and through paid site licenses for
344
BioRender (https://www.biorender.com), GraphPad Prism v9.2.0 (San Diego, CA, USA), and
345
ggplot2.
346
347
RESULTS
348
CONSORT and general baseline participant characteristics
349
The CONSORT diagram is presented in Figure 3. In total, 18 HT and 16 SQ participants completed
350
the study and were included in data analyses unless there were technical issues precluding the
351
inclusion of data (e.g., sEMG clipping).
352
General baseline characteristics of the 18 HT participants who finished the intervention
353
were as follows: age: 22 ± 3 years old, 24 ± 3 kg/m2, 5 M and 13 F. Baseline characteristics of the
354
16 SQ participants who finished the intervention were as follows: age: 24 ± 4 years old, 23 ± 3
355
kg/m2, 6 M and 10 F. Also notable, the HT participants missed an average of 0.8 ± 0.4 workouts
356
during the study, and the SQ participants missed 0.8 ± 0.5.
357
358
359
Figure 3. CONSORT diagram
360
Figure depicts participant numbers through various stages of the intervention. All participants were included in data
361
analysis unless there were technical issues precluding the inclusion of data (e.g., EMG clipping).
362
363
First bout sEMG results
364
sEMG data obtained from the right gluteus muscles during the first workout bout, based on one
365
set of 10RM hip thrust and one set of 10RM sqaut, are presented in Figure 4. All sites showed
366
greater mean sEMG values during the hip thrust versus squat set (p < 0.01 for all; Fig. 4b). Peak
367
sEMG values were greater for the upper and middle gluteus maximus (p < 0.001 and p = 0.015,
368
respectively), whereas small differences existed for the lower gluteus maximus or gluteus medius
369
sites (Fig. 4b). The number of repetitions completed during the 10RM sets used for sEMG
370
recordings were not different between exercises (back squat: 9±1 repetitions, hip thrust: 9±2
371
repetitions).
372
373
39 eligible participants signed up for study
35 participants completed PRE testing
Randomization
4 participants dropped due to
not returning for PRE testing
18 HT participants 17 SQ participants
Enrollment and pre-data collection scheduling
Intervention
18 finishers 16 finishers
1 participant dropped
due to non-study-related
health reasons
18 participants 16 participants
Data analysis
Recruitment and consenting
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374
Figure 4. Surface electromyogram (sEMG) amplitudes during the back squat and barbell hip thrust
375
Legend: During the first session, all participants performed both back squats and barbell hip thrusts while we recorded
376
sEMG amplitudes. (a) Representative sEMG electrode placement is depicted on a co-author in panel. (b) Data depict
377
mean (left) and peak (right) sEMG amplitudes during one 10RM set of hip thrusts and one 10RM set of back squats.
378
As 34 participants partook in this test, sample sizes vary due to incomplete data from electrode slippage or clipping.
379
Bars are mean ± SD, and individual participant values are depicted as dots. (c) Representative data from one
380
participant.
381
382
383
Gluteus musculature mCSAs according to MRI
384
The effect of SQ relative to HT for left+right mCSA was negligible across gluteal muscles. Point
385
estimates modestly favored HT for lower [effect ± SE, −1.6 ± 2.1 cm2; CI95% (−6.1, 2.0)], mid
386
[−0.5 ± 1.7 cm2; CI95% (−4.0, 2.6)], and upper [−0.5 ± 2.6 cm2; CI95% (−5.8, 4.1)] gluteal mCSAs;
387
these point estimates were dwarfed by the variance. Left+right mCSA values for the gluteus
388
medius + minimus demonstrated a lesser magnitude of growth (see Table 1), with a point estimate
389
that also modestly favored HT albeit with appreciable variance [−1.8 ± 1.5 cm2; CI95% (−4.6, 1.4)].
390
391
Upper glut. max. Mid glut. max.
Lower glut. max. Glut. medius
a b
c
Upper glute Middle glute Lower glute Glute medius
0
50
100
150
200
Mean EMG during first training set
(norm. to % MVIC)
Back squat
Hip thrust
p<0.001
(n=31) (n=31) (n=26) (n=32)
p=0.005
p=0.008 p<0.001
1.1
2.6
4.0
5.5
7.0
8.5
10.0
11.5
13.0
14.5
16.0
17.5
19.0
20.5
22.0
23.5
25.0
26.5
0
50
100
150
200
Rep-by-rep EMG signal
(norm. to % MVIC)
Squat (8 reps)
Hip thrust (9 reps)
seconds
Upper gluteus maximus
1.1
2.6
4.0
5.5
7.0
8.5
10.0
11.5
13.0
14.5
16.0
17.5
19.0
20.5
22.0
23.5
25.0
26.5
0
50
100
150
200
seconds
Middle gluteus maximus
1.1
2.6
4.0
5.5
7.0
8.5
10.0
11.5
13.0
14.5
16.0
17.5
19.0
20.5
22.0
23.5
25.0
26.5
0
50
100
150
200
seconds
Lower gluteus maximus
1.1
2.6
4.0
5.5
7.0
8.5
10.0
11.5
13.0
14.5
16.0
17.5
19.0
20.5
22.0
23.5
25.0
26.5
0
50
100
150
200
seconds
Gluteus medius
Upper glute Middle glute Lower glute Glute medius
1
10
100
1000
10000
Peak EMG during first training set
(norm. to % MVIC)
p<0.001
(n=31) (n=31) (n=26) (n=32)
p=0.015
p=0.180
p=0.051
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12
392
Figure 6. Gluteus musculature mCSA changes following back squat and barbell hip thrust training, assessed
393
using MRI
394
Legend: Figure depicts change adjusted for pre-intervention scores for MRI-derived muscle cross-sectional area
395
(mCSA). (a) left + right (L+R) upper gluteus maximus, (b) L+R middle gluteus maximus, (c) L+R lower gluteus
396
maximus, and (d) L+R gluteus medius+minimus. Data include 18 participants in the hip thrust group and 16
397
participants in the back squat group. Graphs contain change scores with individual participant values depicted as dots.
398
(e) Three pre and post representative MRI images are presented from the same participant with white polygon tracings
399
of the L+R upper gluteus maximus and gluteus medius+minimus (top), L+R middle gluteus maximus (middle), and
400
L+R lower gluteus maximus (bottom).
401
402
Thigh musculature mCSAs according to MRI
403
Compared to HT, SQ produced greater mCSA growth for quadriceps [3.6 ± 1.5 cm2; CI95% (0.7,
404
6.4)] and adductors [2.5 ± 0.7 cm2; CI95% (1.2, 3.9)]. However, hamstrings growth was equivocal
405
across both conditions, yielding negligible between-group effects [0.1 ± 0.6 cm2; CI95% (−0.9,
406
1.4)].
407
408
upper
middle
lower
Pre Post
e
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409
Figure 7. Thigh musculature mCSA changes following back squat and barbell hip thrust training, assessed
410
using MRI
411
Legend: Figure depicts change adjusted for pre-intervention scores for MRI-derived muscle cross-sectional area
412
(mCSA). Left and/or right (a) quadriceps, (b) adductors, and (c) hamstrings. Data include 18 participants in the hip
413
thrust group and 16 participants in the back squat group. Bar graphs contain change scores with individual participant
414
values depicted as dots. (d) A representative pre- and post-intervention MRI image is presented with white polygon
415
tracings of the quadriceps (denoted as Q), adductors (denoted as ADD), and hamstrings (denoted as H).
416
417
Strength outcomes
418
Strength outcomes of SQ relative to HT favored respective group allocation for specific lift 3RM
419
values. Specifically, Squat 3RM favored SQ [14 ± 2 kg; CI95% (9, 18)], and hip thrust 3RM favored
420
HT [−26 ± 5 kg; CI95% (−34, −16)]. Results were more equivocal for the deadlift 3RM [0 ± 2 kg;
421
CI95% (−4, 3)] and wall push [−7 ± 12 N; CI95% (−32, 17)].
422
423
Pre Post
Q
ADD
H
d
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424
Figure 8. Strength outcomes following back squat and barbell hip thrust training
425
Legend: Figure depicts change adjusted for pre-intervention scores for (a) 3RM barbell back squat values, (b) 3RM
426
barbell hip thrust values, (c) 3RM barbell deadlift values, and (d) wall push as demonstrated in Figure 2. Data include
427
18 participants in the hip thrust group and 16 participants in the back squat group.
428
429
Forecasting training-induced gluteus muscle mCSA changes with sEMG amplitudes
430
across-subject correlations. sEMG amplitude’s ability to forecast muscle growth across-subjects
431
was generally poor and variable. Mean sEMG amplitudes produce negligible to moderate
432
correlations for lower [r = 0.18 (−0.30, 0.57)], middle, [r = −0.03 (−0.32, 0.25)], upper [r = 0.50
433
(0.03, 0.81)], and medius+minimus [r = 0.28 (0, 0.53)]. We observed similar results for peak
434
sEMG amplitudes from the lower [r = 0.13 (−0.16, 0.46)], middle [r = −0.03 (−0.33, 0.21)], upper
435
[r = 0.32 (−0.05, 0.62)], and medius+minimus [r = 0.24 (−0.02, 0.48)].
436
437
Across-region correlations. We fit two linear mixed-effects models to assess how differences in
438
sEMG amplitudes across muscles can account for regional growth. Since the response variable
439
was relative muscle size on the log scale, the exponentiated coefficients can be interpreted as the
440
increase in muscle relative to baseline for each additional %MVIC; notably, this effect is
441
multiplicative rather than additive. The first model, which used mean sEMG amplitudes, produced
442
small and variable estimates for both SQ [1.003, PI95% (0.998, 1.008)] and HT [1.002, PI95% (0.997,
443
1.006)] groups. The second model, which used peak sEMG amplitudes, produced even more
444
modest results for both the SQ [1.0003, PI95% (0.9997, 1.0009)] and HT [1.0002, PI95% (0.9996,
445
1.0007)] groups.
446
447
Across-exercise variance. Mean sEMG amplitude’s ability to capture the group effects was
448
inconsistent for lower [indirect effect = −0.55, CI95% (−3.87, 0.58)], middle [0.06, CI95% (−0.82,
449
1.56)], upper [−2.98, CI95% (−8.73, −0.38)], and medius+minimus [−0.73, CI95% (−2.70, 0.14)].
450
Q
ADD
H
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We observed similar results for peak sEMG amplitudes for lower [−0.08, CI95% (−2.27, 0.59)],
451
middle [0.22, CI95% (−1.63, 1.89)], upper [−3.04, CI95% (−8.32, 0.15)], and medius+minimus
452
[−0.86, CI95% (−2.47, 0)]. These estimates can be compared to the group effects (“total effects”)
453
earlier in the Results.
454
455
DISCUSSION
456
To further our understanding of hip extensor exercises and the validity of relying on theory and
457
acute physiological measures for exercise selection, here we acutely (sEMG) and longitudinally
458
(hypertrophy, strength) compared two common hip extension exercises: the back squat and barbell
459
hip thrust. Acutely, HT sEMG amplitudes were generally greater for the HT. However, this did
460
not appear to translate and accurately capture longitudinal adaptations. Across all gluteus muscle
461
hypertrophy outcomes, SQ and HT training yielded modest differences but meaningful growth
462
occurring, except in the gluteus medius and minimus. Thigh hypertrophy outcomes favored SQ in
463
the adductors and quadriceps, with no meaningful growth in either group in the hamstrings.
464
Strength outcomes indicated that hip thrust 3RM changes favored HT, back squat 3RM changes
465
favored SQ, and other strength measures similarly increased in both groups. sEMG amplitudes
466
could not reliably predict hypertrophic outcomes across several analytical approaches. In the
467
following paragraphs, we discuss these results in the context of available evidence and speculate
468
on their potential implications for exercise prescription. Moreover, a summary of findings is
469
provided here in tabular form for convenience to readers (Table 1).
470
471
Table 1. Descriptive scores for each training variable
472
Variable
SQ PRE
SQ POST
SQ Δ
HT PRE
HT POST
HT Δ
SMM (kg)
21.6 (5.0)
22.2 (5.3)
0.7 (0.8)
21.9 (4.8)
22.4 (5.0)
0.5 (0.9)
FM (kg)
20.3 (5.0)
19.5 (4.2)
-0.7 (1.7)
19.7 (6.2)
19.4 (6.0)
-0.4 (1.5)
Squat 3RM (kg)
49.8 (17.6)
71.9 (22.2)
22.1 (8.4)
53.2 (15.7)
61.9 (15.4)
8.68 (5.2)
Hip Thrust 3RM (kg)
79.8 (24.0)
106.7 (31.9)
26.9 (11.7)
81.8 (25.3)
134.4 (27.7)
52.7 (15.4)
Deadlift 3RM (kg)
61.5 (17.5)
70.7 (21.1)
9.2 (5.7)
59.0 (17.0)
68.2 (15.6)
9.2 (5.5)
Wall Push (N)
299.3 (97.2)
322.1 (101.1)
22.8 (39.1)
298.1 (80.9)
327.9 (84.3)
29.8 (36.7)
Gmax Upper CSA (cm²)
52.0 (17.9)
58.5 (16.7)
6.5 (4.9)
50.9 (13.9)
58.0 (15.7)
7.1 (9.8)
Gmax Middle CSA (cm²)
92.2 (22.9)
101.3 (23.1)
9.16 (4.4)
88.71 (16.6)
98.31 (19.2)
9.6 (5.7)
Gmax Lower CSA (cm²)
72.4 (21.0)
86.2 (23.9)
13.8 (4.8)
71.0 (17.2)
86.3 (18.3)
15.3 (7.6)
MED+MIN CSA (cm²)
79.1 (16.4)
79.6 (14.9)
0.5 (4.6)
76.4 (14.1)
79.0 (14.1)
2.6 (4.8)
QUAD CSA (cm²)
61.8 (16.4)
69.8 (17.7)
7.9 (4.8)
63.8 (12.5)
68.1 (12.8)
4.3 (3.4)
ADD CSA (cm²)
41.4 (9.4)
45.6 (9.5)
4.2 (1.7)
40.6 (8.9)
42.2 (9.5)
1.7 (2.3)
HAM CSA (cm²)
12.02(3.83)
12.28(4.47)
0.26 (1.16)
14.64 (3.27)
14.71 (2.83)
0.07 (1.5)
Abbreviations: SMM, skeletal muscle mass; FM, fat mass; RM, repetition maximum; mCSA, muscle cross-sectional
473
area; Gmax, Gluteus Maximus; MED+MIN, Gluteus medius and minimus; QUAD, quadriceps; ADD, adductors;
474
HAM, hamstring. Symbol: Δ, pre-to-post intervention change score. Note: all data are presented as mean (standard
475
deviation).
476
477
Hypertrophy Outcomes
478
The primary finding of interest was that upper, middle, and lower gluteus maximus muscle
479
hypertrophy was similar after nine weeks of training with either the squat or hip thrust. This may
480
seem to run counter to recent evidence suggesting muscle tension in lengthened positions augments
481
growth (14) since the sticking region for the squat occurs in greater hip flexion as compared to the
482
hip thrust. Importantly, much of the previous work on this topic is in muscles being worked in a
483
more isolated fashion (2, 4, 30). Thus, the equivocal findings may suggest that the context in which
484
the muscle is experiencing lengthened loading critically determines subsequent adaptations.
485
Muscle contributions, and not just positions, may need to be jointly considered in determining
486
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16
whether superior hypertrophy outcomes would be achieved. This idea is loosely supported by
487
sEMG and musculoskeletal modeling research, suggesting the gluteus maximus may not be
488
strongly recruited toward the bottom of the squat (9, 17). This notion would suggest the nervous
489
system does not strongly recruit the gluteus maximus while at its longest length in the squat,
490
precluding one from maximizing the benefits of stretch-augmented hypertrophy.
491
In addition to motor control governing how the gluteus maximus contributes to and adapts
492
from the squat, there are study-specific considerations. Both exercises may stimulate similar
493
muscle hypertrophy in untrained populations given that RT in general elicits rapid growth early
494
on, creating a ceiling effect on growth rate and thus observed growth. Alternatively stated, skeletal
495
muscle hypertrophy in novice trainees may be less influenced by nuances in exercise selection.
496
Notwithstanding, our results suggest that a nine-week set-equated training program with either the
497
hip thrust, or squat elicits similar gluteal muscle hypertrophy in novice trainees.
498
Finally, our data show that thigh hypertrophy favored the squat, whereas thigh hypertrophy
499
was minimal in the hip thrust. This is perhaps unsurprising and is consistent with previous
500
literature. The adductors, particularly the adductor magnus, have the largest extension moment
501
contribution at the bottom of a squat (17). Thus, the nervous system may favor its recruitment for
502
this purpose. In line with this finding, adductor magnus mCSA changes favor a greater squat depth
503
(31). Hamstring mCSA changes did not occur in either group, in accordance with previous work
504
(31). Critically, these data imply that the hip thrust exercise primarily targets gluteus muscle
505
hypertrophy while limiting non-gluteal thigh muscle hypertrophy; in other words, the hip thrust
506
appears to be more gluteus maximus-specific.
507
508
Strength Outcomes
509
Both groups effectively increased strength outcomes for all exercises tested. However, HT RT
510
better increased hip thrust strength and SQ RT better increased back squat strength, which is to be
511
expected due to training specificity (32). Back squat 3RM increased by 17% in the HT group and
512
44% in the SQ group, while hip thrust strength increased by 63% in HT group and 34% in SQ
513
group. In contrast, deadlift and wall push outcomes increased similarly in both groups. Deadlift
514
increased by 15% in SQ and 16% in HT, and wall push increased by 7.6% in SQ and 10% in HT.
515
516
Using acute first bout sEMG to Predict Hypertrophy
517
Our secondary aim was to evaluate the ability of sEMG to forecast longitudinal adaptations. In
518
agreement with previous work (9), gluteus muscle sEMG amplitudes during the hip thrust exercise
519
were greater across all measured gluteal sites. However, these sEMG amplitude differences did
520
not reliably translate to greater hypertrophy, no matter what analytical approach we took.
521
Specifically, i) individuals with greater sEMG amplitudes did not consistently experience greater
522
growth; ii) regions with greater sEMG amplitudes did not consistently experience greater growth;
523
iii) differences in sEMG amplitudes between exercises could not consistently explain differences
524
in growth, in large part since the hypertrophy results were equivocal. This finding implies that
525
acute sEMG readings during a workout bout are not predictive of hypertrophic outcomes, and this
526
viewpoint is supported by a recent review by Vigotsky et al. (12). As indicated by the authors,
527
inconsistent relationships between EMG amplitudes and muscle growth have been previously
528
reported, which may be due to one or several reasons, ranging from biases in the sEMG recordings
529
to assumptions about how adaptations occur (12). Evidently, the reliance on acute sEMG
530
measurements may in fact be an over-reliance, but more work is needed in this realm.
531
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17
Finally, we also verbally asked participants which exercise they “felt more” in the gluteal
532
muscles after testing both exercises. All participants indicated they felt the hip thrust more in the
533
gluteal region. However, these data were not quantified and, despite these anecdotal sensations
534
and sEMG differences indicating more gluteus muscle excitation during HT, hip thrust RT and
535
squat RT elicited similar applied outcomes. These findings highlight the importance of
536
longitudinal investigations.
537
538
Limitations
539
Our study has a few limitations to consider. First, our participants were young untrained men and
540
women; thus, results cannot necessarily be generalized to other populations including adolescents,
541
older individuals, or trained populations. Additionally, like most training studies, this study was
542
limited in duration. It should also be noted that gluteal hypertrophy was the main outcome, and the
543
MRI coil was placed over this region as subjects were lying prone. Thus, compression may have
544
affected the thigh musculature, and distal measures were not obtained for the thigh. Finally,
545
training volume was equated, and frequency was set at two training days per week. Therefore,
546
results can only be generalized to this protocol.
547
Although we did not consider female participants’ menstrual cycle phase or contraceptive
548
usage, we do not view this as a limitation. In this regard, several reports indicate that contraceptives
549
have no meaningful impact on muscle hypertrophy in younger female participants during periods
550
of resistance training (33-38). Likewise, well-controlled trials indicate that the menstrual cycle
551
phase does not affect strength characteristics (39), and that variations in female hormones during
552
different phases do not affect muscle hypertrophy and strength gains during 12 weeks of resistance
553
training (40).
554
555
Future Directions
556
Future research should aim to examine a group that performs both exercises on a volume-equated
557
basis to determine if there are synergetic effects. Comparing these exercises with different
558
volumes/frequencies is also warranted as exercises may have differing volume tolerances. From a
559
mechanistic standpoint, future studies should characterize anabolic signaling between different
560
points on the length-tension curve as well as ascertain where a muscle exists on this curve with
561
more clarity.
562
563
Conclusions
564
Squat and hip thrust RT elicited similar gluteal hypertrophy, whereas quadriceps and adductors
565
hypertrophy was superior with squat training. Further, although strength increases were specific
566
to exercise allocation, both forms of RT elicited similar strength transfer to the deadlift and wall
567
push. Importantly, these results could not be reliably predicted from acute data (sEMG). These
568
current data provide trainees with valuable insight concerning two widely popular hip-specific
569
exercise modalities, and this information can be leveraged for exercise selection based on specific
570
structural or functional goals.
571
572
ACKNOWLEDGEMENTS
573
We thank the participants who volunteered and participated in the study. We also thank Bradley
574
Ruple, Josh Godwin, and C. Brooks Mobley for their assistance and insight throughout the project.
575
We also thank Jeremy Ethier for donating whey protein to the study. B.M.C. and M.H disclose
576
that they sell exercise related products and services. However, neither was involved in any aspect
577
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(which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
The copyright holder for this preprintthis version posted June 24, 2023. ; https://doi.org/10.1101/2023.06.21.545949doi: bioRxiv preprint
18
of the study beyond assisting with the study design and providing funds to partially cover
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participant and MRI costs through a gift to the laboratory of M.D.R. All other co-authors have no
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apparent conflicts of interest in relation to these data.
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DATA AVAILABILITY
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Raw data related to the current study outcomes will be provided upon reasonable request by
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emailing the latter corresponding author (M.D.R.) at mdr0024@auburn.edu.
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FUNDING INFORMATION
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Funding for this study was made possible through gift funds (some of which were donated by the
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International Scientific Research Foundation for Fitness and Nutrition and B.M.C.) to the M.D.R.
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laboratory. Other financial sources included indirect cost sharing (generated from various
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unrelated contracts) from the School of Kinesiology, M.C.M. being fully supported through a T32
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NIH grant (T32GM141739), and D.L.P. being fully supported by a Presidential Graduate Research
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Fellowship (fund cost-sharing from Auburn University’s President’s office, the College of
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Education, and the School of Kinesiology).
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.CC-BY-NC-ND 4.0 International licenseavailable under a
(which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made
The copyright holder for this preprintthis version posted June 24, 2023. ; https://doi.org/10.1101/2023.06.21.545949doi: bioRxiv preprint
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