Strength coaches and experienced weight trainers have often urged younger, less experienced athletes to take weight off the bar and to squat deeper, with varying degrees of success. They suggest that deeper squats produce better strength and size gains, even though the weight used is lighter.
But how sound is the science behind this claim? Fortunately, a recent study performed a direct comparison using two training groups, one using parallel squats and the other using partial squats. Let’s take a look at the study and see what it has to say.
The study: Effect of range of motion in heavy load squatting on muscle and tendon adaptations, by Bloomquist, Langberg, Karlsen, Madsgaard, Boesen and Raastad, in European Journal of Applied Physiology, 2013
What is the background?
Resistance training is well-known for producing various muscular adaptations, including increased strength, larger cross-sectional area, greater neural control, altered muscle architecture, changed fiber-type and alterations in the length-tension relationship.
What’s more, the exact extent and nature of each of these types of adaptation depends upon various factors, including loading, volume, range of motion and speed of movement.
However, in respect of range of motion, research is limited, although prior studies have reported differences in the effect of parallel and partial squats on countermovement jump performance, with parallel squats producing a superior training effect.
Additionally we know from a small number of studies that resistance training also affects connective tissue, although research in this area has been less extensive than research into muscular adaptations. However, recently, studies in humans as well as animals have reported that tendon strength is increased following resistance training.
What did the researchers do?
The researchers wanted to investigate whether parallel and partial squats with the same relative loads produced different muscular and tendon adaptations and improvements in vertical jump performance.
On the basis of prior studies, the researchers hypothesized that vertical jump performance would be increased further by the parallel squat training. However, on the basis of the greater absolute loads used, the researchers hypothesized that tendon cross-sectional area would be increased to a greater extent by the partial squat training.
Therefore, the researchers recruited 24 male subjects who had been resistance training for at least 6 months, including performance of the squat exercise. The subjects were divided into two groups, a parallel squat group and a partial squat group. The subjects performed a periodized program comprising 3 squat workouts per week for 12 weeks. The partial squats were performed to 60 degrees of knee flexion while the parallel squats were performed to 120 degrees of knee flexion.
Before and after the 12-week training program, the researchers performed performance tests including a 1RM squat test, isometric knee extension torque tests at 40, 75 and 105 degrees of knee angle and both squat and countermovement jump tests.
The researchers also measured the cross-sectional area of the thigh muscles and of the patellar tendon using magnetic resonance imaging (MRI) at 9 distances in a proximal-to-distal order. They measured total lean body mass using dual energy X-ray absorption (DEXA). Using ultrasound, they also calculated muscle architecture parameters (pennation angle and muscle thickness) of the right vastus lateralis. Finally, they used microdialysis to measure collagen synthesis in the patellar tendon.
1RM squat improvements
The researchers reported that both groups increased 1RM for both parallel and partial squats. However, the parallel squat group improved at both parallel and partial squat performance similarly, while the partial squat group improved partial squat performance by a greater amount and parallel squat performance by a lesser amount, as shown in the chart below:
Isometric knee extension torque improvements
The researchers reported that maximal isometric knee extension torque increased at different knee angles to different extents, as shown in the chart below. At 105 degrees, the increase in maximal isometric knee extension torque was significantly greater in the parallel group than in the partial group.
Countermovement and squat jump performance improvements
The researchers reported that both groups increased countermovement and squat jump performance. However, the parallel squat group improved countermovement jump performance by a non-significantly greater amount and squat jump performance by a significantly greater amount than the partial group. These results are shown in the chart below:
The researchers reported that muscular cross-sectional area of the front thigh was increased at all measured sites in the parallel squat group but increases were only found at the two most proximal sites in the partial squat group. Additionally, they noted that muscular cross-sectional area was increased by more at all sites in the parallel squat group. The charts below shows the increases in muscular cross-sectional area in different sites in the front and rear thigh:
The researchers reported that both groups significantly increased pennation angle as a result of the training programs. However, there was no significant difference between groups.
Tendon cross-sectional area
The researchers did not detect any changes in either tendon cross-sectional area of the patellar tendon or in collagen synthesis for either group.
What did the researchers conclude?
The researchers concluded that a 12-week periodized program of both parallel and partial squat training produced increases in 1RM parallel and partial squat, countermovement jumping performance and muscle pennation angle.
The researchers also concluded that only parallel squat training produced significant improvements in jumping performance, isometric knee extension strength and front thigh muscle cross-sectional area at 9 different measured points. They concluded that partial squat training only produced increases in front thigh muscle cross-sectional area at the two most proximal sites.
What were the limitations?
The study was limited by the small sample size, which may have led to differences being disregarded as non-significant which a larger sample size might have detected. Additionally, the study was limited in that it did not test a group that performed both parallel and partial squats to see whether the adaptations were additive or conflicting.
What are the practical implications?
Parallel squats are superior for improving jumping performance and should therefore be preferred over partial squats for athletes participating in sports that involve jumping or leaping movements.
Parallel squats are superior for improving thigh muscle cross-sectional area and should therefore be preferred over partial squats for bodybuilders and physique athletes looking to increase the size of the leg muscles.
Partial squats increase thigh muscle cross-sectional area in the proximal regions only. Therefore, where an increase in muscle size of only this particular area of the leg musculature is required, partial squats may be useful.
Partial squats do not necessarily lead to greater increases in tendon strength in comparison to parallel squats. Therefore, it may not be valuable for bodybuilders to perform partial squats in order to increase tendon strength with a view to reducing their risk of tendon damage.
Parallel squats are superior for improving parallel squat 1RM performance and should therefore be preferred over partial squats for powerlifters who compete in federations that require parallel squat depth to be performed in competition.
Partial squats can still lead to an improvement in parallel squat 1RM performance. Therefore, where an advanced athlete has stalled at increasing parallel squat 1RM through parallel squat training, partial squats can be used as a viable alternative or accessory lift.
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