Changing the stability conditions in a back squat: the effect on maximum load lifted and erector spinae muscle activity

Abstract

The aim of this study was to identify how changes in the stability conditions of a back squat affect maximal loads lifted and erector spinae muscle activity. Fourteen male participants performed a Smith Machine (SM) squat, the most stable condition, a barbell back (BB) squat, and Tendo-destabilizing bar (TBB) squat, the least stable condition. A one repetition max (1-RM) was established in each squat condition, before electromyography (EMG) activity of the erector spinae was measured at 85% of 1-RM. Results indicated that the SM squat 1-RM load was significantly (p = 0.006) greater (10.9%) than the BB squat, but not greater than the TBB squat. EMG results indicated significantly greater (p < 0.05) muscle activation in the TBB condition compared to other conditions. The BB squat produced significantly greater (p = 0.036) EMG activity compared to the SM squat. A greater stability challenge applied to the torso seems to increase muscle activation. The maximum loads lifted in the most stable and unstable squats were similar. However, the lift with greater stability challenge required greatest muscle activation. The implications of this study may be important for training programmes; if coaches wish to challenge trunk stability, while their athletes lift maximal loads designed to increase strength.

Trunk Muscle Activation in the Back and Hack Squat at the Same Relative Loads

“…Mean 1RM for HS was 29 kg (18%) greater than BS, significantly more than the 11% difference between Smith Machine and BS 1RM previously reported 14 . As such, we demonstrated that absolute test loads at 65, 75, 85 and 95% SM were higher in HS than BS.…”

“…Research investigating the BS [11][12][13][14][15] , front squat 12,13,16 , and overhead squat 15 have confirmed that the loaded, free barbell squat is an effective method of activating the stabilizing muscles of the trunk. There is also evidence that in BS magnitude of activation across the majority of muscle sites is sensitive to the external load 1,11,17,18 .…”

“…Hamlyn and coworkers 11 (2007) using the mean RMS calculated from a 1 second sample from each phase, eccentric and concentric, showed that LSES and ULES activation was more than twofold higher in back squat at 80% 1RM compared the bodyweight squats. The purpose of erector spinae muscle complex is to extend the trunk, or in the case of BS prevent trunk flexion 14,15,17 . In the free bar exercise this challenge is greater where back and trunk are unsupported.…”

“…There are variations of the squat exercise performed in a machine supported set-up. These include leg press 6,20 , HS 4 and Smith machine squats 14,[21][22][23] and are generally performed at higher absolute loads than BS 14,21 . It is believed that these more stable versions of the squat compromise and reduce TMA due to biomechanical set-up and support 22,23 .…”

“…It is believed that these more stable versions of the squat compromise and reduce TMA due to biomechanical set-up and support 22,23 . Fletcher and Bagley (2014) 14 reported an 11% greater Smith machine one repetition maximum (1RM) compared to BS. Despite this, erector spinae electromyography (EMG) activity was significantly greater in BS compared to the Smith machine squat 1RM test.…”