How does stance width affect muscle activity in squats?

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Why is squat stance width important?

Many EMG studies have shown how the hamstrings are not particularly active during back squats (e.g. Ebben, 2009, Wright, 1999, McCaw, 1998 and Paoli, 2009). Since EMG activity is regarded as being a good indicator of how hard a muscle is working, this suggests that the back squat is not the best choice of exercise for hamstring development. However, does stance width affect how hard the hamstrings work during squats?  In this article, Chris Beardsley (@SandCResearch) reviews a study that attempted to find out.

The study: Stance width and bar load effects on leg muscle activity during the parallel squat, by McCaw and Melrose, Medicine & Science in Sports & Exercise, 1998

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What is the background?

At the time the researchers were performing their study, the predominant question regarding stance width had been posed by bodybuilders. The main question was not whether there was a difference in hamstring activity but whether there was a difference in the activity levels of the individual quadriceps muscles. In fact, claims were being made in various bodybuilding magazines that stance width could be manipulated to develop different parts of the quadriceps musculature to varying extents. Specifically, it was believed that a wider stance would activate the adductors and vastus medialis to a greater extent, while a narrower stance would activate the vastus lateralis more. However, at the time these claims were being made, no studies had been previously performed to assess whether this was in fact the case.

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What did the researchers do?

The researchers wanted to investigate the EMG activity of the rectus femoris, vastus medialis, vastus lateralis, adductor longus, biceps femoris and gluteus maximus during squats of different stances widths. They therefore recruited 9 trained males who had 7 ± 2 years of resistance training experience. Their 1RM squat ranged from 118 – 250kg. The researchers used surface electrodes to measure the EMG activity in these muscles while the subjects performed squats with 60% and 75% of their 1RM. The subjects performed squats for each load with three different stance widths: narrow (75% of shoulder width), moderate (shoulder width) and wide (140% of shoulder width). The subjects were allowed to choose their own foot position (i.e. degree of hip rotation) according to what was most comfortable.

The researchers did not normalize the EMG of each muscle during the squats to a maximum voluntary isometric contraction (MVIC). Normalizing muscle activity to an MVIC allows researchers to see how hard a muscle is working relative to its maximum capacity. Rather, they simply recorded the value in millivolts (mV). This has a specific disadvantage. Some muscle groups are covered more by fat than others and this can lead to greater impedance when testing those muscles, which leads to lower EMG values. Hence, looking at the voltage (mV) alone doesn’t really give us sufficient information to draw strong conclusions about the relative EMG activity of the various muscles. However, the EMG activity of the same muscles in different conditions (stance widths) can be compared.

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What happened?

With 60% of 1RM load

The researchers found that there was no significant difference between the EMG activity of during wide, medium and narrow stance squats of any of the muscles, as the following chart shows:

Squat stance width

Additionally, the chart shows that at 60% of 1RM, there is not even any kind of trend to indicate that there might have been a significant effect if more subjects had been tested. Moreover, although the EMG activity levels were not normalized, it is instructive to note how much larger the EMG activity levels of the quadriceps muscles are in comparison with the hamstrings and gluteus maximus.

With 75% of 1RM load

The researchers found that there was no significant difference between the EMG activity of during wide, medium and narrow stance squats of any of the muscles except the gluteus maximus, as the following chart shows:

Squat stance width

Specifically, the researchers found that, at 75% of 1RM, the activity of the gluteus maximus was significantly greater in the wide stance condition than in the narrow stance condition. However, there was no significant difference between the wide and moderate stance conditions nor between the moderate and narrow stance conditions. This difference in EMG activity with stance width is likely because the gluteus maximus appears to be more active when at a shorter length than when at a longer length, as a number of studies have shown. A wider stance moves the hip into greater degree of abduction, which shortens the gluteus maximus. It also typically externally rotates the hip somewhat, which also causes the muscle to shorten.

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Exploring the findings of other studies

The findings of this study are supported by a similar study performed by Paoli (2009), in which the researchers tested the EMG activity of the vastus medialis, vastus lateralis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus, gluteus medius and adductor magnus in a group of 6 trained male subjects with 3 years of resistance training experience. The researchers tested three stance widths (100, 150, and 200% of great trochanter distance) and three loads (0, 30 and 70% of 1RM). At 70% of 1RM, the researchers found that only the gluteus maximus displayed a significantly different degree of EMG activity between the stance widths, in that the wider stance again showed a greater degree of EMG activity than the narrower stance. The following chart shows the results:

Squat stance width

Again, although the EMG activity levels were not normalized, it is instructive to note how much larger the EMG activity levels of the quadriceps muscles are in comparison with the hamstrings and gluteus maximus.

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What did the researchers conclude?

The researchers concluded that stance width does not affect the degree of muscular recruitment of the quadriceps or hamstrings during the back squat. However, they noted that a greater stance width does lead to increased gluteus maximus activity.

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What are the limitations?

As noted above, the study was limited in that it did not normalize the EMG of each muscle during the squats to a maximum voluntary isometric contraction (MVIC). Rather, they simply recorded the value in millivolts (mV). This has a specific disadvantage. Some muscle groups are covered more by fat than others and this can lead to greater impedance when testing those muscles, which leads to lower EMG values. Hence, looking at the voltage (mV) alone doesn’t really give us sufficient information to draw strong conclusions about the relative EMG activity of the various muscles.

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What are the practical implications?

Using different stance widths during squats is unlikely to develop different parts of the quadriceps preferentially. Stressing individual quadriceps muscles may therefore require other exercises.

Using a wider stance may help to increase gluteus maximus activity during squats. This may make the squat more useful as a way of strengthening the gluteus maximus.

Using a wider stance may prove useful for powerlifters to make better use of the gluteus maximus during squats.

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