Hip Thrust And Back Squat Training Produce Comparable Increases In Gluteal Muscle Size And Exhibit Similar Transfer To The Deadlift In Untrained Individuals
A remarkable group of researchers collaborated to carry out a significant study investigating the impact of set-volume equated resistance training on hypertrophy and different strength outcomes using either the back squat (SQ) or hip thrust (HT).
Methods
Untrained participants in college were randomly assigned to either the HT (n=18) or SQ (n=16) groups. During the initial training session, surface electromyograms (sEMG) were recorded from the right gluteus maximus and medius muscles. Following nine weeks of supervised training (15-17 sessions), researchers evaluated muscle cross-sectional area (mCSA) using magnetic resonance imaging, and assessed strength through three-repetition maximum (3RM) testing and an isometric wall push test before and after the training period.
Summary of the study design
Figure 1. shows an design overview. Participants had two pre-intervention visits: one fasted for body composition and MRI, and one non-fasted for strength assessments. These visits were ~48 hours apart. After the pre-intervention strength visit, participants were randomly assigned to either the SQ or HT groups. Two days later, the first workout recorded gluteal muscle excitation via sEMG. Then, 9 weeks of resistance training followed (2 days/week). After the last training session, two post-intervention visits were conducted, mirroring the pre-testing procedures.
Abbreviations: PRE, pre-intervention testing visit; 140 POST, post-intervention testing visit; HT, barbell hip thrust; SQ, barbell squat; body comp., body composition testing 141 using bioelectrical impedance spectroscopy; MRI, magnetic resonance imaging; sEMG, electromyography.
Evaluation of body composition and MRI measurements
Before testing, participants were instructed to fast for 8 hours, avoid alcohol for 24 hours, refrain from intense exercise for 24 hours, and ensure proper hydration. Upon arrival, participants provided a urine sample for urine-specific gravity assessment, which indicated sufficient hydration (USG levels ≤ 1.020). Heights were measured using a stadiometer, and body mass was determined using a calibrated scale. Body composition was assessed through bioelectrical impedance spectroscopy using a 4-lead SOZO device, providing measurements of fat-free mass, skeletal muscle mass, and fat mass.For MRI assessment, gluteus maximus muscle cross-sectional area (mCSA) was measured. Participants were positioned in a prone position on the patient table of the MRI scanner at the Auburn University MRI Research Center. After a brief delay, a T1-weighted turbo spin echo pulse sequence was utilized to obtain transverse image sets. The scans consisted of 71 slices with a thickness of 4 mm and no gap between slices. All measurements were conducted by the same investigator (R.J.B.), who was blinded to the participants’ training conditions.
Evaluation of strength levels
Participants performed a wall push test to measure isometric muscle strength. Using a tri-axial force plate, horizontal force production in newtons (N) was recorded. The test involved pushing against a wall with the dominant leg while maintaining a standardized posture. Two repetitions of three seconds each were performed, and the highest peak horizontal force was analyzed.
Figure 2. depicts the wall push test with one of the co-authors (M.D.R.)
Electromyographic (EMG) recordings during the initial training session
Subjects were instructed to wear loose athletic clothing for the placement of EMG electrodes. Prior to electrode placement, any excess hair was removed, and the skin was cleaned with an alcohol swab. Wireless sEMG electrodes were attached to the right upper gluteus maximus, mid gluteus maximus, lower gluteus maximus, and gluteus medius. Specific placement locations were determined based on established recommendations. A quality check was conducted to ensure signal validity. Maximum voluntary isometric contractions (MVIC) were performed before 10RM testing. EMG signals were recorded during the 10RM sets of the barbell back squat and barbell hip thrust exercises. Signal processing and analysis were performed using dedicated software. EMG data with artifacts were excluded from the analysis.Procedures for resistance training
The resistance training (RT) protocol involved 3–6 sets per session of either barbell hip thrusts for HT participants or barbell back squats for SQ participants. Except for the first week with one session, the following 9 weeks included two sessions per week on non-consecutive days. The set schemes progressed as follows: week 1, 3 sets; week 2, 4 sets; weeks 3–6, 5 sets; weeks 7–9, 6 sets. Participants aimed for a repetition range of 8–12, adjusting the load accordingly if they fell below or exceeded this range. D.L.P. and 1–2 other co-authors supervised all sessions and motivated participants to reach volitional muscular failure, where they couldn’t perform another concentric repetition while maintaining proper form. The exercise form and tempo matched those described in the strength testing section, with squats allowing the lowest achievable depth. Participants were advised to avoid additional lower-body resistance training outside the supervised sessions, and missing up to 2 sessions was acceptable for analysis.Data analysis and figure creation
The data underwent analysis using Jamovi v2.3 (https://www.jamovi.org) and R (version 4.3.0). Three sets of analyses ere conducted. Initially, researchers compared the average and maximum sEMG amplitudes of HT and SQ during the initial training session using paired t-tests. Secondly, they examined the longitudinal impact of HT and SQ training on mCSA and strength. Lastly, they explored the predictive value of sEMG amplitudes from the first session on subsequent growth.Results
Figure 3 displays the CONSORT diagram. A total of 18 participants in the HT group and 16 participants in the SQ group completed the study and were included in the data analysis, except for cases where technical issues prevented data inclusion (e.g., sEMG clipping). The baseline characteristics of the 18 HT participants who completed the intervention were as follows: age: 22 ± 3 years old, BMI: 24 ± 3 kg/m², consisting of 5 males and 13 females. The baseline characteristics of the 16 SQ participants who completed the intervention were as follows: age: 24 ± 4 years old, BMI: 23 ± 3 kg/m², consisting of 6 males and 10 females. Notably, HT participants missed an average of 0.8 ± 0.4 workouts during the study, while SQ participants missed 0.8 ± 0.5 workouts.
Figure 3. depicts participant numbers through various stages of the intervention. All participants were included in data analysis unless there were technical issues precluding the inclusion of data (e.g., EMG clipping).
Figure 4. presents the sEMG results of the initial workout, specifically the data obtained from the right gluteus muscles during a single set of 10RM hip thrust and a single set of 10RM squat. The mean sEMG values were significantly higher during the hip thrust compared to the squat set (p < 0.01 for all sites; Fig. 4b). The peak sEMG values were significantly greater for the upper and middle gluteus maximus (p < 0.001 and p = 0.015, respectively), with only minor differences observed for the lower gluteus maximus or gluteus medius sites (Fig. 4b). The number of repetitions completed during the 10RM sets used for sEMG recordings did not differ between the two exercises (back squat: 9±1 repetitions, hip thrust: 9±2 repetitions).
