The king of strength exercises: can it be made loads better?

Perhaps more so than in any other free weight exercise, the quality of the movement and maintaining strict form during the movement are absolutely essential to success when performing squats. Novices or athletes who are unsure exactly what this entails are strongly recommended to read this article, which provides an in-depth, step-by-step breakdown of how to perform squats with excellent form!

Once the basic movement has been perfected however, there are nuances in technique (most notably the depth of the squat) that can affect how the muscles of the lower limbs are targeted during the exercise. In addition, the loading (weight) used may also impact the activation of the muscles due to increased demands placed on the hips, knees and ankles during the exercise. In reality, squat loading and depth interact to play a combined role in determining how muscles are activated during exercise. This is perhaps unsurprising because we know that the intensity of a squat exercise is determined by the combination of squat depth and weight load⁽⁹⁾.

Loading impacts

To date, much has been written about squat depth (also feet and heel position) on muscle activation. But there’s relatively little data on how loading affects activation, so that is what we will focus on from here on. Let’s start with a brand new study on experienced resistance trained men by Korean scientists, which has explored the impact of how weight loading affects the movement patterns during the squat at the hip, knee and ankle joints⁽¹⁰⁾. In this study, the researchers sought to investigate movement pattern changes in the lower extremities as a result of load increases during the back squat exercise, and determine whether there was an association between performing squats and lower extremity injuries.

Eight individuals with experience of squat training were recruited for the study. The subjects performed back squats with loads of 25%, 50%, 100%, and 125% of their bodyweight while being monitored using high definition video and motion detector cameras. Images were taken from several angles and included ground cameras to detect any changes in movement patterns at the ankles. The results showed that as the barbell load increased, posture, form and performance were maintained (which goes to show that strict form can be maintained, even at relatively high weight loadings). However, the rotational moments (forces) experienced by the joints differed according to loading, particularly in the saggital plane (the vertical plane through the middle of the body that divides it into left and right sides - see figure 2).

Figure 2: Changes in joint forces with increasing weight loading

Black, blue, red and green plots = 25%, 50%, 100% and 125% of bodyweight loading respectively. 0.0 = start point of squat; dotted line = bottom position of movement; 100.0 = finish of exercise. At loadings over 100% of bodyweight, the ankle, knee and hip joints all increased large increases in forces, especially in the saggital plane (left hand column).

The researchers concluded that their findings showed increased ankle and hip moments (twisting forces) occur to maintain a stable and consistent posture while withstanding increased weight load. This suggests that additional resistance training for the muscles that control the internal and external rotation of the ankle and hip joints should be performed in a training program alongside squats in order to ensure stable squats while maintaining good form. In addition, by using an extrapolation method, the estimated moments for additional weight loads at 150% and 175% of bodyweight were predicted and found to increase dramatically. The researchers therefore cautioned against using loadings in excess of 1.5 times bodyweight in order to avoid injury.

Load and squat depth interactions

The effects on the joints of loading during squatting may not just be down to the weight load used, but a function of the combination of loading and squat depth. A 2020 study looked at peak knee extensor forces at squat depths of above-parallel, parallel, and full depths, and with differing loads of 0 (unloaded), 50, and 85% of 1 repetition maximum (1RM) loading in recreationally active women⁽¹¹⁾. It found that depth and load had a combined on peak knee forces, and that lower loads at deep squat positions generated equivalent forces at the knee compared to higher loadings at less deep positions.

These findings were replicated by a 2021 study on squats, which found the peak knee extensor forces displayed a depth-by-load interaction such that within each depth, as load increased so did peak force⁽¹²⁾; however, within each loading band, the effects of increasing depth were different. In short, it concluded that if knee joint loading is a concern, clinicians or coaches should carefully monitor the depth and load combinations being used.

Heavier loads for glutes and calves

Yet another study on how the combination of loading and squat depth interact with each other looked at the muscular effort in the knee extensors (quadriceps of the frontal thigh) and how it changed as load and squat depth were varied⁽¹³⁾. This study found that knee extensor effort increased with greater squat depth but not barbell load, whereas the opposite was found for the calf muscles. Meanwhile for the glutes (buttocks), both greater squat depth and barbell load increased muscle effort levels. Overall, these findings suggested that training for the knee extensors can be performed with relatively low loadings but using a deeper squat position. Meanwhile, heavier barbell loadings are recommended to train the gluteal and calf muscles.

Movement velocity and weight loading

Before we summarize and provide practical recommendations, let’s look at some quite recent research on how loading affects velocity and acceleration patterns when lifting the bar in the upwards phase of squats, especially under heavier loadings. In a study by Norwegian scientists, researchers compared muscle activation and kinematics in free-weight back squats with different loadings⁽¹⁴⁾.

Thirteen resistance-trained males with at least three years experience conducted squats at a range of loadings from 30%-100% of their 1-rep max (1-RM). Importantly, these loads were lifted at high-maximum velocities. While they conducted these trials, the barbell kinematics (movement patterns) and muscle activity of the vastus lateralis, vastus medialis, rectus femoris (key muscles of the quadriceps), semitendinosus, biceps femoris (key muscles of the hamstrings), and gluteus maximus (buttocks) were measured in the upward phase of each load.

With increasing loads, the barbell velocity decreased, the upward phase duration increased, and the peak velocity occurred later. This was to be expected as it’s harder to accelerate heavier loads so velocities will decrease. What was interesting however was while muscle activation increased with increasing loadings, this increase was not linear. In general and with the exception of the heaviest load (1-RM), a similar level of muscle activation in these prime muscle movers was observed for loads between 40% and 60% of 1-RM and between 70% and 90% of 1-RM (see figure 3).

Figure 3: Quadriceps muscle activation during maximal velocity squats at different loadings

The take home message from these findings is that in most of the muscles activated during squats, maximal lifting velocity may help compensate for decreased loads, which could allow resistance-trained athletes and individuals in rehabilitation to avoid heavy loads but still get the same muscle activation. Therefore resistance-trained athletes can decrease the loading but have similar muscle activity when lifting with maximal velocity.

By decreasing the loading, mechanical stress decreases and recovery time is reduced, which means that using lower loads with maximal lifting velocity may allow athletes to increase the total volume without increasing the risk of injury – particularly relevant for athletes undergoing post-injury rehab. These findings on maximal velocity squat lifts also means that athletes’ preferences (faster, lighter, more or heavier, slower, fewer reps) can be accommodated without significantly affecting the expected benefits.

Putting these findings into practice

There quite a lot to digest here so let’s finish with a bulleted summary of the recent main findings on squat loading and what they mean for athletes engaging in lower-limb strength training:

·       Provided you remain focused and your form is strict, increasing your squat loadings does NOT mean that your posture will be negatively affected, even at loadings in excess of 100% of your bodyweight.

·       If you use heavier loads (approaching or in excess of 100% of bodyweight) combine your squat training with some ankle and calf training (eg calf raises and the use of a wobble board) and some inner/outer thigh (adductor/abductor) training to improve internal and external ankle and hip rotation strength.

·       Athletes should refrain from using squat loadings above 150% of bodyweight due to increased injury risk.

·       Consider total loading as a combined effect of squat weight and depth. Where it’s inconvenient or tricky to add a small amount of weight, dropping a couple of inches lower in the squat exercise can generate a small increase in loading.

·       Avoid deep squats (below 90 degrees) completely where knee health is a concern.

·       If loadings are light, the quadriceps of the frontal thigh can still be activated and effectively targeted by using deeper squats; however, to maximally activate the glutes of the buttock region and the calf muscles, heavier loadings will be required.

·       Faster upward squat velocities (with strict form!) at low loadings (50-80% of 1RM) can produce similar muscle activations as using higher loadings. This means, athletes can use higher-velocity training using relatively low loads instead of heavy loading to make good gains. This not only may leave you feeling more refreshed, but is also a preferred strategy when performing strengthening following an injury!

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