Core Muscle Activation in Three Lower Extremity Exercises With Different Stability Requirements

Abstract

Saeterbakken, AH, Stien, N, Pedersen, H, and Andersen, V. Core muscle activation in three lower extremity exercises with different stability requirements. J Strength Cond Res 36(2): 304-309, 2022-The aim of the study was to compare core muscle surface electromyography (sEMG) during 3-repetition maximum (3RM) and the sEMG amplitude in the turnover from the descending to ascending phase in leg press, free-weight squats, and squats using the Smith machine. Nineteen women with 4.5 (62.0) years of resistance training were recruited. After one familiarization session, the subjects performed 3RM in randomized order measuring electromyographic activity in the rectus abdominis, external oblique, and erector spinae. The exercises with the lowest stability requirements (leg press) demonstrated 17-59% and 17-42% lower core muscle sEMG amplitude than free weights and the Smith machine, respectively. No statistically significant differences were observed between the Smith machine and free weights. No statistically significant differences in turnover sEMG amplitude in the rectus abdominis between the exercises was observed, but lower sEMG amplitude was observed in external oblique and erector spinae in leg press compared with the other exercises. The 3RM loads in leg press were 54 and 47% greater than squats using the Smith machine and free weights, with 5% greater loads with the Smith machine than with free weights. In conclusion, lower mean and turnover core muscle sEMG amplitude were observed with the leg press but greater 3RM loads compared with squats with the Smith machine and free weights. The authors recommend that resistance-trained individuals use squats to include the core muscles in the kinetic chain, but there is no evidence that greater stability requirements (free weights instead of the Smith machine) will result in greater core muscle sEMG amplitude.

Core Muscle Activity during Physical Fitness Exercises: A Systematic Review

“…One of the novel findings of this systematic review was that free-weight exercises (e.g., deadlift, hip-thrust, or back squat) showed the greatest ES muscle activation [38,46]. In this regard, some researchers [74] recommend adding destabilizing bars to free-weight exercises because when used with heavy weights, these bars have been designed to make the lifting action harder.…”

“…All parts of the feet are in contact with the floor. This exercise may vary depending on specific protocols (e.g., back squat on unstable surfaces, on Smith machine, different loads, or half-squat) [28,30,38,44,48,53,69,74,77,83].…”

Evaluation of the Lower Limb Muscles’ Electromyographic Activity during the Leg Press Exercise and Its Variants: A Systematic Review

“…Five studies were rejected directly because the samples included inexperienced participants. All the study participants reported a minimum of six months resistance training experience; this is because the experience time and exercise familiarization variable may significantly affect the muscle activation elicited during an exercise, hence the importance of having a homogeneous and experienced sample [30][31][32][33][34].…”

“…Therefore, the intensity normalization method should be standardized when comparing several exercises from among the studies in order to achieve conclusive outcomes. For instance, apparently a~70% 1RM intensity normalized as %MVIC might be set as an appropriate intensity for the strength training electromyographic studies [6,12,14,33,34]. Besides the disparities regarding the intensity and the sEMG normalization methods used in the studies included in the review, some other differences were found regarding the methodological process.…”

“…The sample sizes ranged between eight and eighteen subjects. Only three studies had a female sample [14,20,34], and just one evaluated a mixed sample [35]. More studies that include women are needed given the notable anthropometric and biomechanical differences between the sexes; muscle activation differences could also be found [39][40][41].…”