Muscle Activity During the Squat – Part 3

In our last article on the squat, we will look at how different depths, foot position, and bar position affects muscle activity of the lower limb. To determine what muscles are active during the squat or for any exercise for that matter, researchers use a device known as “Electromyography” or EMG. EMG evaluates and records the electrical activity of skeletal muscles. The squat is a highly versatile exercise that can target specific muscles groups for both performance and rehabilitation purposes. Having a knowledge of how squat variants, affect muscle recruitment patterns, can assist FTI instructors to modify the squat, to target specific muscles during both rehabilitation and strengthening programs.

Calf muscle

EMG research which has investigated calf muscle activity and force during a squat has observed a moderate amount of calf muscle activity during the squat. Calf muscle activity (Gastrocnemius) increasing as the knee progressively flexes more on the way down; and decreases during on the way up, as knee extension increases (Escamilla 1998). Calf (Gastrocnemius) activity appears to peak between 60 to 90 degrees of knee flexion; to eccentrically control the rate of ankle dorsiflexion during the descent (Escamilla 1998). Finally, positioning the feet directly under the hips during a wall slide squat has been shown to increase calf muscle activity (Blanpied 1999).

Quadriceps

During a squat, the quadriceps are the prime movers, particularly the vasti muscles, which show significantly higher activity than the rectus femoris. Peak quadriceps activity occurs at 80-90 degrees of a squat, with no further increases with greater knee flexion (Escamilla 2001). This data indicates, half squats (to 90 degrees of knee flexion) will maximize quadriceps activity. Descending beyond 90 degrees of knee flexion, which is near the parallel squat position, may not enhance quadriceps development (Escamilla 2001). Finally, when compared to wall squats with scapular support, appears to increase quadriceps activity (Blanpied 1999).

Vastus medial Obliquus (VMO)

The vastus medial obliquus muscle is the most distal segment of the vastus medial muscle. Its specific training plays a major role in maintaining patella position and limiting injuries to the knee. Weakness, timing, and dysfunction of the VMO causes mal-tracking of the patella and subsequent damage to surrounding structures which leads to increased forces on the knees, often resulting in injuries (Lefebvre 2006). Furthermore, imbalances between vastus lateral and VMO enhances the risk for patellofemoral pain (Karst & Willit, 1995). This data demonstrates the importance of early VMO training following a knee injury. Research on VMO activity during a squat shows the VMO contributes 30.88% to the activity of the thigh during the partial squat; yet, it contributes only 18.85 and 20.23% during the parallel and full squats (Caterisano et al., 2002). Other research (Anderson et al., 1998) has investigated if widening the foot position during the squat; affects VMO activity relative to VL activity (VMO: VL ratio). The researchers found a wider foot position did not increase VMO activity. However VMO was more active throughout a 90° range, and increasing knee flexion angles can increase the activity of the VMO relative to the VL. Taken together, these findings suggest squatting to no greater than 90 degrees of knee flexion; may be the optimal squat depth for VMO.

Hamstrings

The hamstrings due to their biarticular nature (crossing both the hip and knee) act eccentrically during the descent, and concentrically during the ascent. However as the knee flexes during the descent, the hip flexes, the length of the hamstrings is maintained throughout the squat; resulting in minimal change to hamstring length. This may increases the length-tension relationship in favor of force production (Escamilla 2001). Research suggests hamstring activity is greatest during the ascent phase of a squat and is strongly related to weight lifted (Wilk et al., 1996). In contrast, during a bodyweight squat, hamstring activity is minimal, and not significant until loads of 12 RM loads are used, presumably to enhance knee stability. Hamstring activity during a squat; reaches peak activity between 50 – 70 degrees of knee flexion. Finally, researchers (Blanpied 1999) observed a significant increase in hamstring activity when squats are performed in a squat hack machine and when performing a wall squat with scapular support with the feet position forward of center mass. Interestingly, both deep squats and half squats appear to stimulate hamstring activity equally. Taken together, these results indicate that the hack squat, the wall squat with scapula support, and both deep and half squats effectively stimulate hamstring activity.
Glute Activity

Research which has investigated the effects of squat depth on gluteus maximus activity have found that gluteus maximus activity increases with depth (Caterisano et al., 2002). However, these results appear to vary with different loads (% of 1RM). Other researchers have found Gluteus maximus recruitment may increase with increases in squat stance width. Finally, Aspe and Swinton, (2014) analyzed the back squat and the overhead squat and found; the back squat elicited greater gluteus maximus activity than the overhead squat. Interestingly, when compared to the front, full, or parallel squats, squatting at full range, did not elicit greater Gluteus maximus activation, suggesting either front, full, or parallel squats are equally effective exercises for Glut development (Contreras et al., 2016).

In conclusion, the results from these studies suggest the squat is an excellent exercise to strengthen the musculature of lower limbs. Also, muscle activity during a squat can be affected foot position, depth, support, and load. Notwithstanding any limitations from these studies, including differences in prescribed training loads, the following generalizations about muscle activity during the squat can be made:

• To maximize calf muscle activity prescribe squats to the parallel thigh position and position the feet directly under the hips.
• To target the quadriceps during a squat, prescribe squats to the parallel thigh position, for rehabilitation prescribe wall squats with a support pad placed at hip level.
• When targeting the VMO, prescribe squats to the parallel thigh position.
• When targeting the hamstrings, prescribe either deep squats or squats to the parallel thigh position with a minimum of 12 RM loads to equally stimulate the hamstrings. When prescribing a body weight squat, prescribe a wall squat with a support pad placed on the scapula and with the feet forward of center mass.
• When targeting the Gluteal muscle group, it is equally effective to prescribing a squat to the parallel thigh position or full range. For variation, front squats to the full range can also be used to stimulate gluteal muscle activity.
• Dispite differences in muscle activity, full range of motion squats are still an affective variation of the squat for general strengthening and athletic development.

References:

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