See how muscle activation differs (or doesn’t) between the partial and full back squat.
Da Silva, J.J., Schoenfeld, B.J., Marchetti, P.N., Pecoraro, S.L., Greve, J.M., &Marchetti, P.H. (2017). Muscle activation differs between partial and full back squat exercise with external load equated. Journal of Strength and Conditioning Research, 31(6), 1688-1693.
Purpose of the Study:
The purpose of this study was to evaluate the muscle activation between partial and full back squat exercise when performed with the load equated on a relative basis.
The load made equal (equated) because there is an assumption that changes in the range of motion during the squat can affect the magnitude of the load. This is thought to affect muscle activation. In an attempt to regulate this effect, ratings of perceived exertion were also taken into consideration after each set.
15 young, healthy, resistance trained men participated in the study. Subjects had no previous lower back pain, no surgery on lower extremities, and no history of injury with residual symptoms, such as pain, in the lower limbs within the last year.
Procedure or Methods:
Subjects attended 2 sessions in the laboratory separated by 1 week. During the first session, the participants were instructed on the proper squat technique. Condition 1 was the partial squat (0 to 90° of knee flexion). Condition 2 was the full squat (0 to 140° of knee flexion). All participants performed both conditions.
On the first visit to the lab, participants were to establish baseline data to be used on the second visit. The participants warmed-up for 5-minutes on a stationary cycle then performed 10 repetition maximum test of the squat at a self-selected cadence. If the 10 reps were not achieved, the participant was given a 5-minute break, and then the weight was adjusted by 4-10 kg. Participants were given standard instruction regarding exercise technique along with verbal feedback and encouragement. A 30-minute break was given, and then the procedures were repeated for the alternate condition.
On the second visit, participants returned to the lab for the actual recording of data. Again subjects warmed up with 5-minutes on a stationary bike. They then performed 1 set of 10 RM for condition 1 and condition 2 with a 30-minute rest between each condition.
Surface EMG data were collected on the gluteus maximus, vastus lateralis, vastus medialis, rectus femoris, biceps femoris, semitendinosus, erector spinae, and the soleus. Signals collected during all conditions were normalized to maximum voluntary isometric contraction (MVIC).
The surface EMG activity was significantly greater in the partial compared to the full squat for the gluteus maximus, biceps femoris, erector spinae, and soleus. No significant differences were found in any other of the muscles studied.
The main finding of this study was that both the partial and full squat demonstrated a similar overall level of muscle activation of the rectus femoris, but a higher level of activation in the gluteus maximus, biceps femoris, and erector spinae was found in the partial squat.
The higher activation of the gluteus maximus is likely due to it being a single joint muscle positioned at the hip where there is a longer lever arm during the partial squat. The reduced activity in the full squat may be due to the gluteus maximus not being used as much at greater knee flexion angles. Also, at the greater depth, the gluteus maximus is not needed as much to stabilize the pelvis. In some cases, the gluteus maximus may have to relax to permit greater hip flexion angles to be achieved.
The higher activation of the biceps femoris in the partial squat may be explained by it acting as a joint stabilizer at the knee and a prime mover at the hip for extension.
The increase in rectus femoris activation in the full squat is due to the greater moment across the knee joint since it connects to the tibia via the patella tendon. Therefore, as knee flexion increases, activation of that muscle will also increase. The vastus medialis demonstrated the same activation in both conditions and the vastus lateralis activated only slightly more in the partial squat. However, the increased activation in the vastus lateralis was not significant.
The authors believe that the erector spinae activated more in the partial squat in an attempt to control forward trunk motion to control the center of pressure through the range of motion.
Take away for NASM-CPTs:
This study has several implications for the NASM-CPT. First, this is further evidence that a partial range of motion squat is better than no squat. A full squat requires optimal flexibility and range of motion from the ankle, knee, and hip, as well as, total body coordination and strength. While a full range of motion should be the desired end-goal, clients that don’t have the flexibility or strength to achieve it will benefit from the partial squat. Second, a partial squat should also be considered if a client can’t obtain a full squat due to a structural dysfunction or previous surgical alteration. Squatting to just 90° of hip flexion is enough to generate a significant contraction within the gluteus maximus, biceps femoris, erector spinae, and soleus. Third, this study normalized the load for the conditions. So, if using a partial squat more load should be applied to get similar results. Lastly, it should be noted that this should not be used to completely replace a full squat unless the client has permanent limitations. When the client demonstrates functional dysfunctions (short muscles, lack of strength, lack of neuromuscular control, etc.) use this as a temporary method to improve control and strength as flexibility and coordination are worked on to eventually achieve a full range of motion squat.