By Mike Edgar
The development of the posterior chain and specifically the glute musculature has become a major focus of many fitness enthusiasts. There tends to be a fixation on developing this muscle group, whether it be due to cultural norms or simply pressures related to physique-based sports. Some individuals tend to believe that building this muscle group is purely genetic: “you either have it or you don’t.” Other individuals get hyper-fixated on glute-specific isolation exercises, solely doing exercises which ‘target’ and ‘activate’ the glutes to hopefully elicit a greater hypertrophic response. One such exercise which has gained popularity for this reason is the ‘hip thrust.’ It typically involves forming a bridge with your hips in the air while holding some form of resistance over your pelvis. The key to this exercise is generally to not make eye contact with unsuspecting individuals walking by.
Due to its recent popularity, several researchers have studied the exercise to determine if it really is ‘king of the booty builders.’ An initial study by Contreras et al. in 2015 (1) performed a cross-sectional study which investigated the activation levels of the gluteus maximus, bicep femoris and vastus lateralis between the ‘tried-and-true’ back squat and the ‘new-and-sexy’ hip thruster. One aspect of this paper which I really do appreciate is their use of trained females as opposed to non-trained individuals. The importance of this comes from the fact that these motor patterns may vary to a larger degree in an untrained population. Due to the focus of this article, we obviously want to know, which was it? Which exercise better targets the butt? Their results showed that the barbell hip thrust elicited a significantly greater mean (69.5% vs 29.4%) and peak (172% vs 84.9%) activation of the upper gluteus maximus, and mean (86.8% vs 45.4%) and peak (216% vs 130%) activation of the lower gluteus maximus on the EMG compared to the traditional back squat. (1)
There you have it! It seems the hip thruster is the superior exercise to develop one’s glutes… but hold on a second! Can we definitively state that greater muscular activity means greater hypertrophy? Not exactly. A second study by Barbalho et al. in 2020 (2) performed a longitudinal study in well-trained female athletes over 12 weeks, comparing the hip thrust with the back squat. They looked at the strength and hypertrophy changes associated with both. Their findings found that the back squat elicited greater hypertrophy (12.2% vs 2%) for the gluteus maximus. Even more surprisingly, despite the back squat groups greater improvement in back squat strength by the end of the study, they also improved equally in strength with the hip thrust group in regards to the hip thrust exercise (2). From here, it may seem like we are at a bit of a crossroads. If one study showed greater activation, shouldn’t that mean we have a greater strength and muscular response at that same region? Well, no. The systemic adaptations which occur for each exercise are not always directly linked to how much activity shows up on an EMG. A measurement tool which has its inherent limitations, but this may be saved for another article.
Bodybuilding Muscle vs. Functional Muscle
So, where do we go from here? Maybe instead of specific exercises for the glute muscles, we can focus on emphasizing hypertrophy in general. There is a tendency to believe that hypertrophy can be elicited through two means, sarcoplasmic or myofibrillar hypertrophy. The belief was that there were two forms of hypertrophy as stated. The first, sarcoplasmic hypertrophy, was believed to be growth associated to the non-contractile components of the muscle cells. This was purported to be due to ‘muscle size specific training.’ This was theorized to account for the disproportionate size compared to strength in individuals like bodybuilders. The second form of hypertrophy was believed to be myofibrillar hypertrophy, growth specifically related to the contractile elements of the muscle cells which lead to force generation. This was reinforced from the observation of individuals like Olympic weightlifters who could lift three to four times their own body weight despite having a small stature. Do not mistake me for saying that neither of these forms of hypertrophy occur. The argument that was made was purely that specific forms of training could specifically target one form of hypertrophy over the other.
The issue with this belief comes down to basic biochemistry, physiology and cell function. If a cell were to have a disproportionate increase in non-contractile elements, signal conduction and other various cellular processes would be disrupted and therefore lead to many issues such as contractile dysfunction on the macro-level. This has led to research investigating whether such adaptation could occur in humans. A cross-sectional study by Always et al. (3) looked at the functional and structural adaptations of skeletal muscle in trained athletes. They compared muscle biopsies (ouch!) in strength-trained, endurance, active, and sedentary individuals. They found that in each group compared to the sedentary group, there was up to 2.5x greater muscle cross-sectional area in the gastrocnemius. Despite these large differences in fiber areas, the proportional volume of non-contractile components did not differ to any major degree. This was similar despite the group or the fiber type investigated. The authors words were, “This implies that with exercise-induced hypertrophy, the sarcoplasmic reticulum, cytoplasm, and lipid components increase proportionately with contractile protein.” One interesting caveat of this study was that they found a 30% discrepancy for increased mitochondrial volume in the strength training groups showing that this cellular element may have a different response to training or adapt through different pathways. (3)
A second study by Hikida et al. (4) further emphasized this in a 16-week longitudinal study looking at the effects of high-intensity resistance training on the muscle physiology of untrained older men. In this study, they tested all major fibre types (I, IIa, IIb) and had the subjects perform three lower limb exercises: knee extension, double leg press, and half squat, twice weekly. After the 16 weeks, all three major fiber types were significantly larger after strength training, with types I, IIA, and IIB increasing by 46, 34, and 52% while there was no change in cytoplasm-to-myonucleus ratio reported. The interesting aspect of this study is the fact it had the two-fold benefit of showing that these adaptations still occur to the same degree in elderly individuals as well (4). From the findings of both of these studies, we can say with some degree of confidence that hypertrophy on a cellular level is tightly regulated.
Reps or Sets?
So, what can we take from this? Well, it seems like when it comes to hypertrophy, the body adapts one way on the cellular level with no specific difference based on training parameters. This is reinforced further by a study by Morton et al. 2016 and Schoenfeld et al. 2014. Morton et al. 2016 (5) conducted a 12-week resistance training program in well-trained, young males. They had two groups, one which performed 20-25 repetitions per exercise to failure compared to a second group which did 10-12 repetitions to failure. The interesting aspect of this study was the fact they controlled for total volume while using different repetition ranges. The results of this study found no difference in either strength or hypertrophy between groups at the end of the study, in addition to no difference in acute post-exercise anabolic hormones. The only significant difference between both groups was that the lower repetition group had a larger increase in bench press strength at the end of the 12 weeks, which may relate to the idea of specificity of training. (5)
Schoenfeld et al. 2014 (6) performed a similar study looking at the difference between a bodybuilding and powerlifting style routine, but controlled for total training volume. The ‘bodybuilding group’ consisted of 3 sets of 10 repetition maximum (RM) with 90 seconds rest while the ‘powerlifting group’ consisted of 7 sets of 3RM with a 3-minute rest interval. Upon measurement, they found no difference in muscle thickness between groups although both had a significant increase in hypertrophy compared to the beginning of the study. Similar to the study by Morton et al., the powerlifting group had a significant increase in bench press strength compared to the bodybuilding group. Although it may seem based on these results that repetitions and sets do not matter as long as volume is controlled for, there were some interesting points noted from Schoenfeld et al. Firstly, at the end of the 8 weeks, the powerlifting group had accumulated significantly more fatigue with a higher risk of injury from the heavier loads. In addition, from an economics standpoint, the training time required for the powerlifting group was significantly longer than the bodybuilding group (6). As a result, if time demands are in place and your goal is solely to build muscle tissue, it may be more feasible to focus on higher repetition sets with lower rest times.
It’s All About The Angles
In the gym, you may hear about the idea of partial reps to target the muscles differently, but does this really have any backing in science? A study by Noorkõiv al. 2014 (7) aimed to investigate this very idea by looking at the neuromuscular adaptations in response to isometric knee extension training at short versus long muscle lengths. This was done over an 8-week period in nontrained males to determine differences in hypertrophic response related to both. Interestingly, what they found was that only the long length training group saw hypertrophic responses in the quadricep following the experimental intervention (7). One major thing I would like to point out is the idea that these are not mutually exclusive training principles. In a real-world setting, you would generally apply both of these parameters without the need to pick and choose. Therefore, as much as I appreciate the idea behind this study, it may just be an interesting piece of knowledge to throw at your friends.
Where Do We Go From Here?
What I would first like to say is that as much as these principles and findings may guide some parameters of our training or allow us to fixate less on others, the real determinant of progress is adherence. I have always been a large proponent of the phrase, “even a half-assed effort is better than no effort.” So, on that train of thought, if squats are your thing and you enjoy them, then so be it. Keep up with the good work. If you find hip thrusters to be an intrinsically rewarding and fun exercise, then keep at it.
At the end of the day, both of these exercises have shown to elicit anabolic responses and as long as you are capable of approaching your training with the mindset of enjoyment, then you will make progress, nonetheless. In regard to sets and repetitions, this same idea is also highlighted by the research. Find what works best for you, your demands, and your goals. As long as you keep some consistent volume in your program, it may not be worth the stress to fixate on much else. At the end of the day, I tend to believe that true long-term results may be less about focusing on fine-tuning the minute details and more about being consistent with the big things day-in-and-day-out.
1. Contreras B, Vigotsky AD, Schoenfeld BJ, Beardsley C, Cronin J. A comparison of gluteus maximus, biceps femoris, and vastus lateralis electromyographic activity in the back squat and barbell hip thrust exercises. Journal of applied biomechanics. 2015 Dec 1;31(6):452-8.
2. Barbalho M, Coswig V, Souza D, Serrão JC, Campos MH, Gentil P. Back Squat vs. Hip Thrust Resistance-training Programs in Well-trained Women. International Journal of Sports Medicine. 2020 Jan 23.
3. Functional and structural adaptations in skeletal muscle of trained athletes. S. E. Alway, J. D. MacDougall, D. G. Sale, J. R. Sutton, A. J. McComas. Journal of Applied PhysiologyMar 1988,64(3)1114-1120
4. Effects of high-intensity resistance training on untrained older men. II. Muscle fiber characteristics and nucleo-cytoplasmic relationships. Hikida, RS, Staron, RS, Hagerman, FC, Walsh, S, Kaiser, E, Shell, S and Hervey, S. J Gerontol A Biol Sci Med Sci 55:7, B347-54 (2000)
5. Morton RW, Oikawa SY, Wavell CG, Mazara N, McGlory C, Quadrilatero J, Baechler BL, Baker SK, Phillips SM. Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. J Appl Physiol (1985). 2016 May 12:jap.00154.2016. doi: 10.1152/japplphysiol.00154.2016. [Epub ahead of print]
6. Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Sonmez GT, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014 Oct;28(10):2909-18
7. Noorkõiv M, Nosaka K, Blazevich AJ. Neuromuscular adaptations associated with knee joint angle-specific force change. Med Sci Sports Exerc. 2014 Aug;46(8):1525-37