Until relatively recently, the conventional back squat was the tool of choice for lower body strength development. However, the split squat is now gaining ground and is used by many strength and conditioning coaches.
But what do we actually know about the split squat and how does it compare to the conventional back squat? Well, there aren’t actually that many studies out there, so this post is a quick round-up of all of them I could track down.
(Too much detail? Skip to the practical implications)
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What’s the background?
The split squat can be performed with the back foot planted on the ground, or with the back foot elevated onto a bench or box. The split squat includes variations known as the Bulgarian (split) squat, the rear foot elevated split squat, and pitcher squat or modified unilateral squat. It is often used by strength and conditioning coaches as a replacement for the conventional back squat.
However, while the conventional back squat has been extensively researched (for references see Schoenfeld, 2010), the split squat has not been subject to the same degree of scrutiny.
The split squat is performed with the legs straddling the body’s center of mass in the sagittal plane. It can be performed with a barbell in the back squat position on the upper trapezius (e.g. McCurdy, 2010),with dumbbells held at arms’ length at the sides or with resistance bands looped under the front foot and over the shoulder (e.g. as lunges performed in Jakobsen, 2012).
As previously mentioned, while it is commonly performed with the rear foot elevated upon a box or bar (e.g. McCurdy, 2010), it can also be performed with the rear foot placed on the ground. With the rear foot placed on a box, McCurdy (2010) found that around 85% of the load was supported by the front foot.
A small number of studies have investigated acute biomechanical variables during split squats, while one study has investigated the chronic effects of a training program involving split squats.
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What have acute studies found?
Reliability of exercise performance
Reliability is an important feature of resistance training exercises if they are to be used to measure progress in any key strength measure. McCurdy (2004) tested the reliability of split squats with elevated rear foot and conventional back squats using the same relative loading (1RM and 3RM loads) in untrained male and female subjects. They found that the average 1RM and 3RM split squat loads were (first attempt/second attempt) 114.6 ± 17.9/121.6 ± 17.7kg and 98.6 ± 21.5/103.0 ± 21.5kg for males respectively and 44.0 ± 9.9/45.76 ± 10.7kg and 35.9 ± 10.4/39.77 ± 10.4kg respectively. The results are shown in the chart below:
The researchers reported that the test-retest measures were highly reliable and the split squat can therefore be used with confidence to assess unilateral lower body strength.
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Differences in split squat strength between dominant and non-dominant legs
A common assumption about unilateral exercise is that the dominant limb will prove stronger than the non-dominant limb. Indeed, some studies have reported differences between dominant and non-dominant limbs in lower body tasks (e.g. Hunter, 2000).
However, McCurdy (2005) investigated the difference in 1RM split squat strength on the dominant and non-dominant legs in untrained males and females. They did not find any significant difference in split squat strength between legs although the dominant leg was non-significantly stronger by a very small margin for both males and females. Male split squat strength was (dominant/non-dominant) 107.0 ± 5.2 and 106.0 ± 5.2kg while female split squat strength was 45.3 ± 2.5/45.0 ± 2.5kg. The results are shown in the chart below:
The chart shows that there was great similarity between the strength of the dominant and non-dominant legs in untrained subjects. Whether this implies that the net joint torques in the active leg are similar when performed by either the dominant or non-dominant legs is uncertain however, as Flanagan (2007) found that net joint torques are not equal on the right and left sides during the conventional back squat exercise.
Further research is therefore required both to confirm the finding of similar strength in the dominant and non-dominant limbs of the split squat in trained subjects and also to ascertain whether the net joint torques are different between sides despite similar loading. However, it is important to note that just because strength is equal between sides, it doesn’t mean that the exact same form is used or that the exact percentage of quadriceps and posterior chain contribution is used.
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Correlations between split squat performance and balance
Some researchers have proposed that lower body strength and balance are closely linked. Fukagawa (1995) reported an independent effect of strength on performance in a balance test performed by nursing home residents. However, performance in the split squat does not appear to correlate with specific balance tasks.
McCurdy (2006) investigated the relationship between 1RM split squat strength and balance ability on the stork stand and computerized wobble board in untrained males and females. They did not find any significant correlations between balance on the computerized wobble board and 1RM split squat strength nor between balance scores on the stork stand and 1RM split squat strength for either the males or females.
Therefore, where balance improvements are required, improving split squat strength may not be beneficial.
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Joint moments
The joint moments of split squats appear to differ from those of conventional back squats. Meyer (2005, unpublished masters thesis) investigated the joint moments in split squats with an elevated rear foot and compared them with the joint moments in conventional back squats in male athletes.
The athletes performed conventional squats with light, moderate and heavy loads (60, 70, and 80% of 1RM) and split squats with light, moderate and heavy loads (20, 25, and 30% of conventional back squat 1RM). Meyer reported that the split squat displayed greater hip extension moments than the conventional back squat with similar relative loading (323 ± 89Nm vs. 288 ± 97Nm).
Additionally, they found that the split squat displayed smaller knee extension moments than the conventional back squat with similar relative loading (118 ± 26Nm vs. 186 ± 30Nm). The results are shown in the chart below:
From these numbers, we can calculate that the hip-to-knee extension moment ratio was higher in split squats than in conventional back squats (1.57 ± 0.53 vs. 2.80 ± 0.71). The split squat is therefore 1.8 times as hip-dominant as the conventional back squat. While the study was unpublished and therefore not peer reviewed, we can gain some comfort regarding the data, as the ratios for the conventional back squat are very similar to those reported by Bryanton (2012), which ranged from 1.2 – 1.5 with similar relative loads.
Consequently, the split squat may be useful to substitute for the conventional back squat where a program requires a greater emphasis on hip-dominant exercises.
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Joint angles
The torso angle during split squats appears to be less than that during conventional back squats. McCurdy (2010) investigated the joint angle movements in female athletes performing a split squat with elevated rear foot and a conventional back squat using the same relative loading (85% of 3RM). They found that peak torso angle during split squats was less than that during conventional back squats (33.68 ± 7.6 degrees vs. 40.65 ± 7.0 degrees).
Meyer (2005, unpublished masters thesis) also investigated joint angles during split squats with an elevated rear foot and conventional back squats and observed that the forward lean of the trunk in the split squat was less than that in the conventional back squat (25 ± 12 degrees vs. 35 ± 6 degrees). The results are shown in the chart below:
Meyer suggested that this difference in torso angle might imply a reduced level of spinal loading. Whether this is the case is uncertain, although when Swinton (2012) investigated the differences between conventional, powerlifting and box squats, they found that the box squat displayed a significantly lower torso angle than the conventional squat (26.9 ± 3.8 degrees vs. 33.5 ± 4.6 degrees) and a concurrently significantly lower L5/S1 moment.
So reduced torso angle may indeed imply reduced lumbar spinal loading. Therefore, the split squat may be useful to substitute for the conventional back squat where reduced lumbar spinal loading is necessary or desirable.
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Force, power and rate of force development
Certain force-related variables are different between jump squats using split squat and conventional back squat techniques. Sleivert (2004) tested jump squat power output in male athletes with both conventional back squat and split-squat techniques. The optimal load for power output between 30 – 70% of 1RM was compared in each case. They found that peak power output and average power output were not significantly different between the conventional back squat and split squat techniques.
However, they did report that peak force was significantly greater during the split squat (19.10 ± 3.25N/kg vs. 14.88 ± 2.22N/kg), peak rate of force development was significantly greater during the split squat (41.10 ± 12.59N/s/kg vs. 33.04 ± 8.74N/s/kg) but peak velocity was significantly lower during the split squat (1.64 ± 0.17m/s vs. 1.97 ± 0.13m/s). They noted that the larger force but smaller velocity during the split squat resulted in similar power outputs for both squat techniques at the optimal load for power (albeit measurements were only taken between 30 – 70% of 1RM).
Whether such differences exist similarly between the split squat and conventional back squat as well as between jump squats performed with split squat and conventional back squat techniques is unclear, however.
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EMG activity
The research is conflicting whether there are any significant differences in respect of EMG activity during split squats and conventional back squats. McCurdy (2010) investigated the EMG activity of gluteus medius, hamstrings, and quadriceps in female athletes performing a split squat with elevated rear foot and a conventional back squat using the same relative loading (85% of 3RM). They found that gluteus medius and hamstring EMG activity were significantly higher during the split squat than during the conventional back squat while quadriceps EMG activity was significantly higher during the conventional back squat than during the split squat.
However, Jones (2012) measured the EMG activity of the biceps femoris, erector spinae, gluteus medius and vastus lateralis in male resistance-trained athletes performing a split squat with elevated rear foot and a conventional back squat using the same relative loading (10RM). They did not discern any differences in EMG activity between the two exercises.
McCurdy (2010b) also investigated the EMG activity of the external obliques in female athletes performing a split squat with elevated rear foot and a conventional back squat using the same relative loading (85% of 3RM). They found that the EMG activity of the external obliques was non-significantly higher for the split squat.
These findings suggest that the split squat can likely be substituted for the conventional back squat for developing lower body strength similarly across the various leg muscles with the proviso that the hamstrings may be stressed more effectively and the quadriceps less effectively during split squats. However, future research is required to confirm this finding.
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Hormonal response to exercise
Resistance training can alter the levels of endocrine hormones post-exercise, especially after workouts designed for hypertrophy. This observation led to what has become known as the hormone hypothesis. The hormone hypothesis proposes that acute post-exercise hormonal secretions assist in the process of muscular hypertrophy. However, while this hypothesis received strong support for a number of years, it was recently been called into question (see further Schoenfeld, 2013).
Migiano (2010) found that neither unilateral nor bilateral upper body resistance training was able to produce a post-exercise increase in anabolic hormones, while it was known from Linnamo (2005) that incorporating lower body bilateral exercise into a workout produced a post-exercise increase in anabolic hormones. Therefore, it has been suggested that unilateral lower body resistance training might fail to produce a post-exercise rise in hormones in the same way as upper body exercise.
However, Jones (2012) measured testosterone concentrations in male resistance-trained athletes after workouts in which they performed either split squats with elevated rear foot or conventional back squats using the same relative loading and set/rep scheme (4 sets of 10RM with 90 seconds rest between sets). They found that testosterone concentrations rose post-exercise similarly following both split squat and conventional back squat workouts.
To the extent that the hormone hypothesis is supported, split squats and conventional back squats are therefore likely to have similar beneficial effects on post-exercise hormonal milieu.
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What do chronic studies tell us?
McCurdy (2005) compared two 8-week resistance training programs in which untrained subjects performed either bilateral or unilateral squat training 2 days per week. The bilateral group performed conventional back squats and front squats and the unilateral group performed split squats with rear foot elevated, lunges and step-ups.
Both groups performed similar loading and volume protocols. There was no significant difference in either the improvement in the conventional back squat or the improvement in the split squat between groups, suggesting that both exercises are suitable for improving both bilateral and unilateral lower body strength.
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What are the practical implications?
For strength and conditioning coaches:
Since the test-retest measures of the split squat have been reported to be highly reliable, the split squat can be used with confidence to assess lower body strength.
For everyone resistance training:
Since the results of EMG studies indicate that there is little difference between the split squat and conventional back squat, the split squat can be substituted for the conventional back squat for developing lower body strength.
The split squat may involve a greater ratio of hip-to-knee moments, greater hamstring EMG activity and less quadriceps EMG activity. It may therefore be useful to substitute for the conventional back squat where a program requires a greater emphasis on hip-dominant exercises.
The split squat involves a lower torso angle. Lower torso angles during squats are associated with reduced lumbar spinal moments. Therefore, the split squat may be useful to substitute for the conventional back squat where reduced lumbar spinal loading is desirable.
Since testosterone concentrations rise post-exercise similarly following both split squat and conventional back squat workouts, both types of squats are therefore likely to have similar beneficial effects on post-exercise hormonal milieu and consequent hypertrophy.
For powerlifters:
For powerlifters, it is critical to note that the back squat is both a training tool and the event itself. Specificity and event practice are therefore important here. So while split squats may be useful as assistance work for some powerlifters, it is highly unlikely that the split squat would be able to replace conventional back squats in a powerlifting program.
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