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Trunk Muscle Activation in the Back and Hack Squat at the Same Relative Loads
Abstract
The hack squat (HS) is likely to produce a greater 1 repetition maximum (1RM) compared to the back squat (BS). This can be attributed to the support of the trunk during the HS compared to no support during BS. This support however, may compromise trunk muscle activation (TMA), therefore producing different training adaptations. Accordingly, the purpose of this study was to compare 1RM in BS and HS and TMA at 4 relative loads, 65, 75, 85 and 95% of maximal system mass. Ten males completed 3 test sessions:1) BS and HS 1RM, 2) HS & BS neuromuscular test familiarization, and, 3) Neuromuscular test for 3 reps at 4 loads for BS and HS. BS TMA was significantly greater (p<0.05) than HS for all muscles and phases except rectus abdominus in concentric phase. TMA increased (p<0.05) with load in all muscles for both exercises and phases apart from lumbar sacral erector spinae in HS eccentric phase. Mean HS 1RM and submaximal loads were significantly (p<0.0001) higher than the equivalent BS loads. Duration of the eccentric phase was higher (p<0.01) in HS than BS but not different in concentric phase. Duration increased significantly (p<0.01) with load in both exercises and both phases. Despite higher absolute tests loads in HS, TMA was higher in BS. TMA is sensitive to load in both exercises. BS is more effective than HS in activating the muscles of the trunk and therefore arguably more effective in developing trunk strength and stability for dynamic athletic performance.
... T he leg press is a typical exercise for lower limb strengthening. 21,45,50 The widespread applicability offered by this exercise is explained by the simplicity of its technique since it is a guided movement, 8 along with its transference to functional movements such as walking, squatting, running, or jumping. 6,8,13,17 This means that the exercise can be included in any training program regardless of the participants' age 10,19,32 or training goal, whether it be for rehabilitation, 2,6,8,43 injury prevention and return to play, 17,26 health, 2,52 or athletic performance. ...
... 21,45,50 The widespread applicability offered by this exercise is explained by the simplicity of its technique since it is a guided movement, 8 along with its transference to functional movements such as walking, squatting, running, or jumping. 6,8,13,17 This means that the exercise can be included in any training program regardless of the participants' age 10,19,32 or training goal, whether it be for rehabilitation, 2,6,8,43 injury prevention and return to play, 17,26 health, 2,52 or athletic performance. 13,17 Given the leg press exercise's versatility, it is essential that trainers and athletes understand the muscle activation elicited during its use, as a key factor in the concomitant development of muscle mass and strength. ...
... 21,45,50 The widespread applicability offered by this exercise is explained by the simplicity of its technique since it is a guided movement, 8 along with its transference to functional movements such as walking, squatting, running, or jumping. 6,8,13,17 This means that the exercise can be included in any training program regardless of the participants' age 10,19,32 or training goal, whether it be for rehabilitation, 2,6,8,43 injury prevention and return to play, 17,26 health, 2,52 or athletic performance. 13,17 Given the leg press exercise's versatility, it is essential that trainers and athletes understand the muscle activation elicited during its use, as a key factor in the concomitant development of muscle mass and strength. ...
Background:
The leg press is one of the most typical exercises for strengthening the lower limbs. The objectives of this study were to compare 5 inclined leg press exercise conditions, varying the feet width stance (100% or 150% hip width), the feet rotation (0° or 45° external rotation) on the footplate and using 2 different movement velocities (MVs; maximum intended, and 2:2 seconds steady-paced velocities) to determine their effect on muscle activation as well as on the kinematic parameters between trained men and trained women.
Hypotheses:
There will be no significant differences in muscle activation with regard to the feet position. The higher the MV, the greater the muscle activation.
Study design:
A cross-sectional cohort study.
Level of evidence:
Level 3.
Methods:
A repeated-measures between-group design was performed to examine muscle activation and kinematic parameters for the different conditions between gender groups. The level of significance was set at alpha = 0.05 for all statistical analyses.
Results:
Muscle activation presented no differences between conditions regarding feet width stance or feet rotation. Furthermore, muscle activation was greater during positive phases than negative phases of the exercise for all conditions and was also greater under maximum intended velocity conditions compared with steady-paced conditions. Otherwise, the muscle activation pattern presented slight differences by gender. In men, the greatest muscle activation was for the vastus medialis, followed by the vastus lateralis (VL), rectus femoris (RF), and gluteus medialis (GMED), while in women, the greatest muscle activation was for the vastus medialis, followed by the RF, VL, and GMED. Finally, greater mean propulsive velocity, maximum velocity, maximum power, and footplate displacement values were reported for men than for women under all the conditions.
Conclusion:
The inclined leg press exercise produces the highest muscle activation in the vastus medialis, regardless of the velocity, feet stance, or gender.
Clinical relevance:
Given that there are no differences in muscle activation regarding the feet stance, a participant's preferred feet stance should be encouraged during the inclined leg press exercise. Furthermore, the MV would preferably depend on the session objective (a training or a rehabilitation program), being aware that there is greater muscle activation at higher speeds. The inclined leg press exercise could be performed as a closed kinetic chain exercise when the main objective is to activate the vastus medialis.
... Porém, vale mencionar que a lordose lombar natural deverá ser preservada durante todo o movimento, ou seja, o executante não precisa apoiar toda a região lombar no encosto, porque haverá uma retificação da coluna lombar. Com relação à ação muscular, o estudo de Clark (82) observou menor ativação do vasto lateral no Hack em comparação ao agachamento com barra. No entanto, se essas diferenças serão suficientes para induzir menor hipertrofia seletiva do vasto lateral no Hack após um período de treinamento, requer confirmação por uma investigação longitudinal. ...
... No entanto, se essas diferenças serão suficientes para induzir menor hipertrofia seletiva do vasto lateral no Hack após um período de treinamento, requer confirmação por uma investigação longitudinal. O agachamento Hack também exigirá menor ativação dos músculos da região inferior do tronco (82) . Além disso, também vale ressaltar que no Hack a sobrecarga absoluta deverá ser superior ao agachamento com barra livre (82) , o que naturalmente aumenta as forças compressivas. ...
... O agachamento Hack também exigirá menor ativação dos músculos da região inferior do tronco (82) . Além disso, também vale ressaltar que no Hack a sobrecarga absoluta deverá ser superior ao agachamento com barra livre (82) , o que naturalmente aumenta as forças compressivas. ...
... in back squat. 1 We and others have shown a load effect for trunk muscle activation in this exercise. [1][2][3][4]11 Activation increased by load in eccentric and concentric phases for all four trunk muscle sites: rectus abdominus (RA), external oblique (EO), lumbar sacral erector spinae (LSES), and upper lumbar erector spinae (ULES). 1,2 Higher trunk muscle activation in concentric phase of loaded back squat compared to the descent has been demonstrated in our laboratory 1,2 and by others. ...
... [1][2][3][4]11 Activation increased by load in eccentric and concentric phases for all four trunk muscle sites: rectus abdominus (RA), external oblique (EO), lumbar sacral erector spinae (LSES), and upper lumbar erector spinae (ULES). 1,2 Higher trunk muscle activation in concentric phase of loaded back squat compared to the descent has been demonstrated in our laboratory 1,2 and by others. 11,12 Understanding how trunk muscle activation responds to the same relative back squat load in strong compared to weaker participants will contribute to establishing this exercise as an effective method of developing dynamic trunk stability. ...
... Back squat training and test loads calculated according to system mass max (SM) assume that 89% of body mass is included in external load. 1,2 The remaining 11%, (ie, shanks and feet) do not move vertically in squat exercise. ...
This study measured how back squat strength (1RM) affected trunk muscle activation in performing squats, squat jump (SJ) and countermovement jump (CMJ). Fifty males, completed two test sessions. Squat 1RM was tested first. Participants were assigned to three groups; (i) strong group (SG), (ii) middle group (MG) or (iii) weak group (WG), based on relative squat 1RM. Test 2, EMG data were collected for 4 trunk muscle sites; rectus abdominus, external oblique, lumbar sacral erector spinae and upper lumbar erector spinae while performing (3 reps) SJ, CMJ and squats at 65, 75 and 95% 1RM. Squat and jump phases were determined from a linear transducer and 30o tertiles for each phase, from a knee goniometer. Normalized root mean square RMS increased significantly with load for each muscle site in both squat phases. Trunk muscle activation was significantly lower in SG vs WG in eccentric and concentric squat phases. Concentric and flight phase RMS in both jumps was lower in SG vs WG. RMS increased significantly for each eccentric tertile and first concentric tertile. Greater squat strength is associated with lower trunk muscle activation in squats and jumps and trunk muscle activation was highest in the two deepest 30o squat segments. In conclusion, back squat strength training to parallel, where top of thighs are horizontal, is an effective method of developing dynamic trunk stability. This article is protected by copyright. All rights reserved.
... Hence, these do not represent training overload in preparation for activities that characterise most sports and athletic events. Researchers have begun to investigate trunk muscle activation in a number of dynamic, loaded free weight exercises to determine their suitability for the development of dynamic trunk strength and stability [29][30][31][32][33][34][35][36][37]. Surface electromyography methodology shows there is good evidence that loaded exercises performed in a standing position are an effective method of overloading the trunk stabilization system in a dynamic manner. ...
... There is growing evidence in the literature that external load in free barbell exercises performed in a standing position is related to muscle activation of trunk stabilisers [29,30,33,34,37,50]. Impact of this stimulus on core stability in dynamic athletic performance is more difficult to demonstrate. ...
Background: Core stability training has grown in popularity over 25 years, initially for back pain prevention or therapy. Subsequently, it developed as a mode of exercise training for health, fitness and sport. The scientific basis for traditional core stability exercise has recently been questioned and challenged, especially in relation to dynamic athletic performance. Reviews have called for clarity on what constitutes anatomy and function of the core, especially in healthy and uninjured people. Clinical research suggests that traditional core stability training is inappropriate for development of fitness for heath and sports performance. However, commonly used methods of measuring core stability in research do not reflect functional nature of core stability in uninjured, healthy and athletic populations. Recent reviews have proposed a more dynamic, whole body approach to training core stabilization, and research has begun to measure and report efficacy of these modes training. The purpose of this study was to assess extent to which these developments have informed people currently working and participating in sport. Methods: An online survey questionnaire was developed around common themes on core stability training as defined in the current scientific literature and circulated to a sample population of people working and participating in sport. Survey results were assessed against key elements of the current scientific debate. Results: Perceptions on anatomy and function of the core were gathered from a representative cohort of athletes, coaches, sports science and sports medicine practitioners (n = 241), along with their views on effectiveness of various current and traditional exercise training modes. Most popular method of testing and measuring core function was subjective assessment through observation (43%), while a quarter (22%) believed there was no effective method of measurement. Perceptions of people in sport reflect the scientific debate, and practitioners have adopted a more functional approach to core stability training. There was strong support for loaded, compound exercises performed upright, compared to moderate support for traditional core stability exercises. Half of the participants (50%) in the survey, however, still support a traditional isolation core stability training. Conclusion: Perceptions in applied practice on core stability training for dynamic athletic performance are aligned to a large extent to the scientific literature. Keywords:
... Hence, these do not represent training overload in preparation for activities that characterise most sports and athletic events. Researchers have begun to investigate trunk muscle activation in a number of dynamic, loaded free weight exercises to determine their suitability for the development of dynamic trunk strength and stability [29][30][31][32][33][34][35][36][37]. Surface electromyography methodology shows there is good evidence that loaded exercises performed in a standing position are an effective method of overloading the trunk stabilization system in a dynamic manner. ...
... There is growing evidence in the literature that external load in free barbell exercises performed in a standing position is related to muscle activation of trunk stabilisers [29,30,33,34,37,50]. Impact of this stimulus on core stability in dynamic athletic performance is more difficult to demonstrate. ...
Background:
Core stability training has grown in popularity over 25 years, initially for back pain prevention or therapy. Subsequently, it developed as a mode of exercise training for health, fitness and sport. The scientific basis for traditional core stability exercise has recently been questioned and challenged, especially in relation to dynamic athletic performance. Reviews have called for clarity on what constitutes anatomy and function of the core, especially in healthy and uninjured people. Clinical research suggests that traditional core stability training is inappropriate for development of fitness for heath and sports performance. However, commonly used methods of measuring core stability in research do not reflect functional nature of core stability in uninjured, healthy and athletic populations. Recent reviews have proposed a more dynamic, whole body approach to training core stabilization, and research has begun to measure and report efficacy of these modes training. The purpose of this study was to assess extent to which these developments have informed people currently working and participating in sport.
Methods:
An online survey questionnaire was developed around common themes on core stability training as defined in the current scientific literature and circulated to a sample population of people working and participating in sport. Survey results were assessed against key elements of the current scientific debate.
Results:
Perceptions on anatomy and function of the core were gathered from a representative cohort of athletes, coaches, sports science and sports medicine practitioners (n = 241), along with their views on effectiveness of various current and traditional exercise training modes. Most popular method of testing and measuring core function was subjective assessment through observation (43%), while a quarter (22%) believed there was no effective method of measurement. Perceptions of people in sport reflect the scientific debate, and practitioners have adopted a more functional approach to core stability training. There was strong support for loaded, compound exercises performed upright, compared to moderate support for traditional core stability exercises. Half of the participants (50%) in the survey, however, still support a traditional isolation core stability training.
Conclusion:
Perceptions in applied practice on core stability training for dynamic athletic performance are aligned to a large extent to the scientific literature.
... Contrary to traditional beliefs (7,8), this research found that free-weight and machinebased modalities were similarly effective to increase strength capacity throughout a wide region of the force-velocity spectrum (∆ differences 1.8%, Figures 2-4). The assumed superiority of free-weight modality conventionally widespread among practitioners has been mostly based on i) longitudinal studies testing only free-weight exercises as a dependent variable (12,13,15) and ii) acute investigations attributing a greater muscle activity to this modality (4)(5)(6). Regarding the modality tested, results of the current study, together with those obtained by a recent metaanalysis on the topic (11), demonstrated that comparing free-weight and machine-based modalities by testing only one of them (mostly free-weight) could lead to inaccurate conclusions due to the specificity principle (Figures 2-4). Indeed, the aforementioned meta-analysis also Copyright © 2023 by the American College of Sports Medicine. ...
Purpose:
To compare the effects of free-weight and machine-based resistance training on strength, hypertrophy, and joint discomfort.
Methods:
Thirty-eight resistance-trained men participated in an 8-week resistance program allocated into free-weight (n = 19) or machine-based (n = 19) groups. Training variables were identical for both modalities, so they only differed in the use of barbells or machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the intensity throughout the program. Strength changes were evaluated using 8 velocity-monitored loading tests (4 exercises x 2 modalities) and included the relative one-repetition maximum (1RMRel), as well as the mean propulsive velocity against low (MPVLow) and high (MPVHigh) loads. Ultrasound-derived cross-sectional area (CSA) of quadriceps (proximal and distal regions), pectoralis major, and rectus abdominis was measured to examine hypertrophy. Complementarily, WOMAC and DASH questionnaires were administrated to assess changes in lower- and upper-limb joint discomfort. Outcomes were compared using ANCOVA and percentage of change (∆) statistics.
Results:
Each group significantly (p < 0.001) increased 1RMRel, MPVLow, and MPVHigh for both modalities tested, but especially in the one they trained. When considering together the 8 exercises tested, strength changes for both modalities were similar (∆ differences ≤1.8%, p ≥ 0.216). Likewise, the CSA of all the muscles evaluated was significantly increased by both modalities, with no significant differences between them (∆ difference ≤ 2.0%, p ≥ 0.208). No between-group differences (p ≥ 0.144) were found for changes in stiffness, pain, and functional disability levels, which were reduced by both modalities.
Conclusions:
Free-weight and machine-based modalities are similarly effective to promote strength and hypertrophy without increasing joint discomfort.
... 1,2 Traditionally, practitioners have promoted the superior efficacy of free-weight over machine-based resistance training for increasing these positive adaptations. This assumption has mainly been supported by the higher acute activation produced by free-weight exercises in agonist/synergist and trunk muscles, [3][4][5] which would theoretically maximize intermuscular coordination and athletic capacities. 6,7 Nevertheless, investigations comparing the long-term effects of these resistance training modalities are scarce and heterogeneous. ...
Background
Although the superior effectiveness of free‐weight over machine‐based training has been a traditionally widespread assumption, longitudinal studies comparing these training modalities were scarce and heterogeneous.
Objective
This research used the velocity‐based method to compare the effects of free‐weight and machine‐based resistance training on athletic performance and muscle architecture.
Methods
Thirty‐four resistance‐trained men participated in an 8‐week resistance training program allocated into free‐weight (n = 17) or machine‐based (n = 17) groups. Training variables (intensity, intraset fatigue, and recovery) were identical for both groups, so they only differed in the use of a barbell or specific machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity‐based method was implemented to accurately adjust the planned intensity. Analysis of covariance and effect size (ES) statistics were used to compare both training modalities on a comprehensive set of athletic and muscle architecture parameters.
Results
No between‐group differences were found for any athletic (p ≥ 0.146) and muscle architecture (p ≥ 0.184) variable. Both training modalities significantly and similarly improved vertical jump (Free‐weight: ES ≥ 0.45, p ≤ 0.001; Machine‐based: ES ≥ 0.41, p ≤ 0.001) and lower limb anaerobic capacity (Free‐weight: ES ≥ 0.39, p ≤ 0.007; Machine‐based: ES ≥ 0.31, p ≤ 0.003). Additionally, the machine‐based group meaningfully enhanced upper limb anaerobic power (ES = 0.41, p = 0.021), whereas the free‐weight group significantly improved the change of direction (ES = ‐0.54, p = 0.003) and 2/6 balance conditions analyzed (p ≤ 0.012). Changes in sprint capacity (ES ≥ ‐0.13, p ≥ 0.274), fascicle length, and pennation angle (ES ≤ 0.19, p ≥ 0.129) were not significant for either training modality.
Conclusion
Adaptations in athletic performance and muscle architecture would not be meaningfully influenced by the resistance modality trained.
... With each increase in load during arm-ergometer exercise, the paraspinal muscle activity also increased (Marks et al., 2012). In other studies, while the exercise loading method varied, paraspinal muscle activity during biceps curl (Oliveira Ade and Gonçalves, 2009) and squat exercises (Clark et al., 2019) Frontiers in Physiology frontiersin.org 02 also increased due to the increased loading. ...
Objectives: Ergometer exercise was considered a new loading method that can be used for participants who are unable to assume the core strengthening exercise posture commonly used to strengthen the erector spinae and multifidus. This study aimed to investigate with healthy participants whether arm and leg ergometers could be used for core strengthening exercises and whether different exercise sites would affect the results.
Methods: The study was conducted with 15 healthy adult male participants aged 20–35 years. The intervention consisted of arm- and leg-ergometer exercises performed by the participants. The exercise protocol consisted of three 1-min sessions (rest, 50W, and 100 W), which were measured consecutively. Surface electromyography (sEMG) was measured during the sessions. Maximal voluntary contraction (MVC) of the erector spinae and multifidus was also measured, during which sEMG was measured. The sEMG during ergometer exercise was calculated as a percentage of the MVC (calculated as % MVC). The root mean square (RMS) was recorded from the sEMG activity. Muscle activity of the erector spinae and multifidus was compared between ergometer exercises and between intensity levels. Heart rate (HR) was recorded by electrocardiogram.
Results: In the arm-ergometer exercise, the % MVC values of the erector spinae were 6.3 ± 3.1, 10.9 ± 5.4, and 16.9 ± 8.3% at rest, 50 W, and 100 W conditions, respectively. The multifidus was 4.6 ± 2.9, 9.2 ± 5.6, and 12.6 ± 7.6% at rest, 50 W, and 100 W conditions, respectively. The respective % MVC values during the leg-ergometer exercise were 3.8 ± 1.7, 7.2 ± 3.8, and 10.4 ± 4.0% at rest, 50 W, and 100 W conditions, respectively. Leg-ergometer exercises were 2.6 ± 2.1, 6.9 ± 5.7, and 10.3 ± 6.8% at rest, 50 W, and 100 W conditions, respectively. The activities of the two muscles increased at comparable levels with increased workload in both types of exercises ( p < 0.01, each). HR increased with the increased workload and the increase was larger during arm-than leg-ergometer exercises.
Conclusion: These results demonstrate that both arm- and leg-ergometer exercises are potentially alternative methods for erector spinae and multifidus training for healthy participants. Further research is needed to target elderly.
... However, the combined approach had the largest increase in vertical displacement, followed by the leg strength only group, with CST having the lowest increase. It should be noted the leg strength program was machines based, so it is unclear if free weights would have had a greater impact on performance due to their ability to elicit higher trunk muscle activity compared to machines at the same relative load (Clark et al., 2019). This study suggests that CST on its own is insufficient to drastically improve performance, but when combined with resistance training it can have a more potent effect. ...
Introduction: Exercises designed to improve the function of the core are a centerpiece of many athletic training programs. Current core stability (CS) ideology, testing protocols, and training methods originated from research into low back pain, yet are commonly applied within the sports performance domain. CS is a controversial concept with significant debate around how effective core stability training (CST) is for athletic populations. The majority of CS exercises and assessments currently emphasize muscular endurance. This exclusive focus may not be appropriate when training or monitoring athletes involved in dynamic sporting activities. To improve our understanding on this topic, the goal of this thesis is to investigate current perspectives and viewpoints, relating to CS and CST, held by practitioners in the sports performance domain.
Methods: An online questionnaire and semi-structured interview were performed to gather subjective data from industry experts and professionals working with athletes. Both studies were designed to understand current thoughts and opinions around three key themes; current understanding of CS, how CS is being monitored in practice, and how practitioners are training CS.
Results: The online questionnaire was completed by 64 respondents, while 10 industry experts were interviewed. There was a lack of a universal language amongst industry professionals when describing CS and many differing opinions related to key CS concepts. An important finding was that very few practitioners are objectively assessing the core, with little consideration given to monitoring maximal core strength. It was found that nearly all participants implement direct CS exercises, however, opinions on how to best train the core varied significantly. The results of this thesis demonstrate wide ranging viewpoints and opinions related to CS and CST amongst industry professionals, despite over 30 years of related research.
Discussion and Practical Implications: The findings from this thesis highlight the extent of divided industry perspectives. Specifically, five key areas were identified to improve our understanding in this area. The alignment of terminology and the development of an evidence-based CST framework are needed to streamline coaching practice. Maximal core strength is an underappreciated area and research exploring its relationship to athletic performance is desperately needed. Moreover, the development of cheap field tests to assess this quality are needed. Finally, longer term intervention studies are also required to substantiate the effectiveness of CS programs.
Key Words: Core Stability, Core Stability Training, Trunk, Lumbopelvic Control
... Exercise with standing upright, squatting, and bending postures is considered as a core exercise for flexing and extending the hip, knee, and ankle joints to activate a wide range of supporting muscles of the lower trunk [8,9]. Some studies suggest squatting posture training for the lumbar region [10,11]; however, the methods shown in these studies cover insufficient references to the lumbar spine flexion and extension [12,13]. Besides, bending exercises have shown a greater trunk flexion on a decline standing position while an incline standing position triggers a greater trunk extension [13]. ...
This study investigates changes in lumbar erector spinae (LES) muscle endurance, perceived low-back pain (LBP), and perceived exercise fatigue in older adults, and analyzes the trends of these changes during a 5-week lumbar exercise. Sixteen older adults with LBP were equally and randomly divided into two groups: the experimental group with incline-standing and the control group with the level-standing positions. They were separately treated with lumbar exercise tasks and 10 seconds of muscle endurance tests using surface electromyography (sEMG). There was a trend of changes in both groups. The exercise tasks led to increase LES muscle endurance in the experimental group (53.7%) and the control group (45.4%) and decrease perceived LBP score significantly with the incline-standing position. There was no significant difference between the two groups in perceived exercise fatigue (p>0.05). Trunk flexion and extension with an incline-standing position can be an effective method to increase LES muscle endurance and reduce LBP in older adults.
... For example, it has been previously observed that during a back squat, LLES was less activated when the exercise was done with partial depth (which requires less pelvic tilt maintenance) vs. full depth (16). In the same way, during hack and Smith machine squats, conditions that require minor stability, lower LLES activation was also observed compared to traditional bar squat (3,7). Greater stability requirement seems to be a main factor that induces higher LLES since even when an exercise is done with a greater external load due to greater muscular action. ...
The present study aimed to compare the activation of the lower lumbar erector spinae, gluteus maximus, biceps femoris, and rectus femoris in two trunk positioning (straight, and inclined) during three lunge exercises (static, step-forwarding, and walking) in trained young women. Twelve women (24 ± 3 years) were selected and then performed, in a randomized crossover design, the lunge exercise (with an overload of 30% of body weight) in each of six conditions to analyze the surface electromyography signals of the mentioned muscles. There was revealed that, for erector spinae, higher activations (%MVIC) were observed (P < 0.05) when trunk was positioned inclined (straight = 20 ± 15, inclined = 40 ± 29) and during walking lunge (static = 24 ± 16, forward = 26 ± 22, walking = 40 ± 33); for gluteus maximus, higher activations were observed during step-forward and walking lunges (static = 31 ± 12, forward = 54 ± 20, walking = 58 ± 30); for biceps femoris and rectus femoris, all conditions conferred similar activations (P > 0.05). Results indicate that positioning the trunk forward-inclined induces greater lower lumbar erector spinae activation; trunk and exercise variations do not influence the activation of tight muscles; and, if the aim is to achieve greater activation of gluteus maximus muscle in young women, lunge exercise has to be performed in step-forwarding or walking ways.
... Real-time velocity feedback was provided to the participants (T-Force System, Ergotech, Murcia, Spain) and examiners delivered verbal encouragement to ascertain the maximal intended velocity [26,31]. Immediately after the 1RM test, the participants proceeded to perform the five different leg press conditions while the examiners recorded the data. ...
Knee joint muscle activation imbalances, especially weakness in the vastus medialis oblique, are related to patellofemoral pain within the female population. The available literature presents the leg press as an exercise which potentially targets vastus medialis oblique activation, thus reducing imbalances in the quadriceps muscles. The main aim of the present study was to compare thigh muscle activation and kinematic parameters under different conditions during the inclined leg press exercise in a young female population. A cross-sectional study was conducted on 10 young, trained females. Muscle activation of the vastus medialis oblique, vastus lateralis, rectus femoris and gluteus medialis was analyzed under five different inclined leg press conditions, modifying the feet rotation (0-45 • external rotation) and the stance width (100-150% hip width) on the footplate. All the conditions were performed at two different movement velocities: controlled velocity (2" eccentric-2" concentric) and maximal intended velocity. Mean propulsive velocity, maximum velocity and maximum power were also assessed. The results show that both controlled velocity conditions and maximal intended velocity conditions elicited a similar muscle activation pattern with greater activation during the concentric phase (p < 0.001, ηp 2 = 0.96). The maximal intended velocity conditions showed greater overall muscle activation (p < 0.001, ηp 2 = 0.91). The vastus medialis oblique presented the greatest muscle activation, followed by the rectus femoris, vastus lateralis and, the gluteus medialis. Furthermore, the inclined leg press condition with 0º feet rotation, 100% hip width distance and the maximal intended velocity generated the greatest kinematic parameter outputs. In conclusion, the inclined leg press exercise might be an optimal exercise to target vastus medialis activation regardless of the feet rotation and stance width conditions.
... In this regard, some authors attributed a preferential activation of vastus medialis to the external feet rotation [15,23], whereas others assessed the influence of knee external or internal resistance on vastus medialis during leg press [20,24]. Finally, various authors have assessed the influence of exercise intensity on muscle activity during the leg press exercises [6,12,25]. ...
The aim of this study was to analyze the literature on muscle activation measured by surface electromyography (sEMG) of the muscles recruited when performing the leg press exercise and its variants. The Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to report this review. The search was carried out using the PubMed, Scopus, and Web of Science electronic databases. The articles selected met the following inclusion criteria: (a) a cross-sectional or longitudinal study design; (b) neuromuscular activation assessed during the leg press exercise, or its variants; (c) muscle activation data collected using sEMG; and (d) study samples comprising healthy and trained participants. The main findings indicate that the leg press exercise elicited the greatest sEMG activity from the quadriceps muscle complex, which was shown to be greater as the knee flexion angle increased. In conclusion, (1) the vastus lateralis and vastus medialis elicited the greatest muscle activation during the leg press exercise, followed closely by the rectus femoris; (2) the biceps femoris and the gastrocnemius medialis showed greater muscular activity as the knee reached full extension, whereas the vastus lateralis and medialis, the rectus femoris, and the tibialis anterior showed a decreasing muscular activity pattern as the knee reached full extension; (3) evidence on the influence of kinematics modifications over sEMG during leg press variants is still not compelling as very few studies match their findings.
Surface electromyographic activities of the erector spinae and multifidus during graded arm- and leg-ergometer exercise were investigated. Fifteen young healthy male participants performed arm- and leg-ergometer exercises at 50W and 100W for 1 min, while monitoring the electrocardiograms of the paraspinal muscles and heart rate, and the root mean squares of the electromyograms were calculated. Time series of contractions of the paraspinal and extremity muscles during both exercises were assessed (n = 7). Both paraspinal muscle activities increased with increased workload in both exercises similarly (P < 0.01, each). Heart rate increased with increased workload, and the increase was greater for arm-ergometer exercise than for leg-ergometer exercise. Each contraction time of trunk and limb muscles suggested that the paraspinal muscles facilitated trunk rotation and prevented excessive lateral bending of the trunk, respectively. The activities of these paraspinal muscles increased with increased workload similarly in both exercises, although heart rate response was different between them.
Purpose
In this study we measured neural activation (EMG) in four trunk stabilizer muscles and vastus lateralis (VL) in trained and novice participants during a set of squat repetitions to volitional fatigue at 85% 1RM.
Methods
Forty males were recruited into two groups, novice (NG: n = 21) and experienced (EG: n = 19), according to relative squat 1RM. Participants were tested twice to: (1) determine squat 1RM, and (2) complete a single set of repetitions to volitional fatigue at 85% 1RM. Relative squat 1RM; NG < 140% body mass, EG > 160% body mass. Neuromuscular activation was measured by EMG for the following: rectus abdominus (RA), external oblique (EO), lumbar sacral erector spinae (LSES), upper lumbar erector spinae (ULES) and VL in eccentric and concentric phase. Completed repetitions, RPE and EMG in repetition 1 and at 20, 40, 60, 80 and 100% of completed repetitions were analysed.
Results
No group differences were found between number repetitions completed and RPE in repetitions to volitional fatigue at 85% 1RM. Neuromuscular activation increased significantly in all muscle groups in eccentric and concentric phase apart from RA in the eccentric phase. Trunk neuromuscular activation was higher in NG compared to EG and this was significant in EO, LSES and ULES in eccentric phase and LSES in the concentric phase. VL activation increased in both phases with no group differences.
Conclusion
Trunk neuromuscular activation increases in a fatiguing set of heavy squats regardless of training status. Increased back squat strength through training results in lower neuromuscular activation despite greater absolute external squat loads.
Movement control and muscle function for pelvic movement in the frontal plane (pelvic elevation) are important for various single-leg sports activities. We aimed to clarify mechanical characteristics of pelvic squat (P-Sq: single-leg squat exercise with emphasis on pelvic elevation, developed by our research group) compared with the double-leg squat (D-Sq) and single-leg squat (S-Sq). Twelve male track and field athletes performed D-Sq, S-Sq, and P-Sq exercises at various loads (90%, 75%, and 60% of 1-repetition maximum [1RM]), using maximum effort. Kinematic and kinetic data were calculated using data recorded with a motion capture system and force platforms. We observed the highest values with P-Sq, followed by S-Sq and D-Sq under all load conditions as follows: peak vertical ground reaction force and rate of force development (RFD), range of pelvic elevation, peak pelvic elevation velocity, peak powers associated with hip abduction torque and trunk lateral flexion torque. In P-Sq, RFD at 90% 1RM was smaller than under the other load conditions, whereas peak vertical ground reaction force at 90% 1RM was larger than under the other load conditions. There were no differences among load conditions with regard to hip abduction and trunk lateral flexion torques and powers. Therefore, characteristics of P-Sq compared to those of D-Sq and S-Sq are 1) larger and faster pelvic elevation, using related muscles (hip abductors and trunk lateral flexors) under all load conditions, 2) larger peak ground reaction force with pelvic elevation under large load conditions, and larger RFD in pelvic elevation under low load conditions.
Over the last two decades, exercise of the core muscles has gained major interest in professional sports. Research has focused on injury prevention and increasing athletic performance. We analyzed the guidelines for so-called functional strength training for back pain prevention and found that programs were similar to those for back pain rehabilitation; even the arguments were identical. Surprisingly, most exercise specifications have neither been tested for their effectiveness nor compared with the load specifications normally used for strength training. Analysis of the scientific literature on core stability exercises shows that adaptations in the central nervous system (voluntary activation of trunk muscles) have been used to justify exercise guidelines. Adaptations of morphological structures, important for the stability of the trunk and therefore the athlete’s health, have not been adequately addressed in experimental studies or in reviews. In this article, we explain why the guidelines created for back pain rehabilitation are insufficient for strength training in professional athletes. We critically analyze common concepts such as ‘selective activation’ and training on unstable surfaces.
Abstract The aim of this study was to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading. Two-dimensional kinematical data were collected and electromyographic activities of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and erector spinae were measured while participants (n = 12, 21.2 ± 1.9 years old) were completing front and back squat exercises with maximum loading. Paired sample t-test was used for comparisons between two techniques. Results showed that the electromyographic activity of vastus medialis was found to be greater in the front squat compared to the back squat during the ascending phase (P < 0.05, d = 0.62; 95% CI, -15.0/-4.17) and the whole manoeuvre (P < 0.05, d = 0.41; 95% CI, -12.8/-0.43), while semitendinosus (P < 0.05, d = -0.79; 95% CI, 0.62/20.59) electromyographic activity was greater in the back squat during the ascending phase. Compared to the front squat version, back squat exhibited significantly greater trunk lean, with no differences occurring in the knee joint kinematics throughout the movement. Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading.
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.
The aim of the study was to evaluate maximal isometric (dynamometer based {MVC-NORM} and isometric squat {MIS-NORM}) and sub-maximal EMG normalisation methods (60%-NORM, 70%-NORM, 80%-NORM) for dynamic back squat exercise (DSQ-EX). The absolute reliability (limits of agreement {LOA}, coefficient of variation {CV%}), relative reliability (intra-class correlation coefficient {ICC}) and sensitivity of each method was assessed. Ten resistance-trained males attended four sessions. Session one assessed maximum back squat strength (three repetition maximum {3RM}). In the remaining three sessions Vastus lateralis (VL) and Bicep femoris (BF) EMG were measured whilst participants completed normalisation tasks and DSQ-EX sets at 65%, 75%, 85% and 95% of 3RM. MIS-NORM produced lower intra-participant CV% compared to MVC-NORM. 80%-NORM produced lower intra-participant CV% than other sub-maximal methods for VL and BF during eccentric and concentric phases. 80%-NORM also produced narrower 95% LOA results than all other normalisation methods. The MIS-NORM method displayed higher ICC values for both muscles during eccentric and concentric phases. The 60%-NORM and 70%-NORM methods were the most sensitive for VL and BF during eccentric and concentric phases. Only normalisation methods for the concentric action of the VL enhanced sensitivity compared to unnormalised EMG. Overall, dynamic normalisation methods demonstrated better absolute reliability and sensitivity for reporting VL and BF EMG within the current study compared to maximal isometric methods.
An analysis system for barbell weightlifting exercises is proposed to record reliable performance and neuromuscular responses. The system consists of surface electromyography (sEMG) synchronized with electrogoniometry and a barbell position transducer. The purpose of this study was to establish the reliability of the three components of the system. Nine males (age 28.9 ± 4.8 years, mass 85.7 ± 15.1 kg) performed squat exercise at three loads on three separate trial days. A data acquisition and software system processed maximal knee angle (flexion), mean power for the concentric phase of squat exercise, and normalized root mean square of the vastus lateralis. Inter-trial coefficients of variation for each variable were calculated as 5.3%, 7.8%, and 7.5% respectively. In addition, knee joint motion and barbell displacement were significantly related to each other (bar displacement (m) = 1.39-0.0057 × knee angle (degress), with goodness-of-fit value, r² = 0.817), suggesting knee goniometry alone can represent the kinematics of a multi-joint squat exercise. The proven reliability of the three components of this system allows for real-time monitoring of resistance exercise using the preferred training methods of athletes, which could be valuable in the understanding of the neuromuscular response of elite strength training methods.
The purpose of this study was to compare rectus abdominis and erector spinae muscle activity during isometric (prone bridge [PB] and superman [SM]) and dynamic strengthening exercises (back squat, front squat [FS], and military press). Participants (n = 10, age 21.8 ± 2.6 years; body mass 82.65 ± 10.80 kg, 174.5± 7.2 cm), performed each exercise in a randomized order, using a repeated-measures design. Electromyographical (EMG) activity (sampling at 2,000 Hz) of the rectus abdominis (RA) and the erector spinae (ES) muscles was recorded throughout the duration of the exercises. Intraclass correlations demonstrated the highest levels of reliability for muscle activity during the isometric exercises; however, all exercises demonstrated high level of reliability (r = 0.764-0.998, p ≤ 0.01). The PB demonstrated significantly greater (p < 0.01) RA activity compared to all other exercises. The ES activity was significantly (p < 0.01) greater during the FS (1.010 ± 0.308 root mean square value [RMS (V)]) and SM (0.951 ± 0.217 RMS[V]) and compared to all other exercises, although there was no significant difference (p > 0.05) between the FS and the SM exercise. The PB may be the most suitable exercise for strengthening the RA, compared to dynamic exercises at a low to moderate load, because of a higher level of muscle activity. The FS may be a useful alternative to isometric exercises when strengthening the ES, because it results in slightly higher muscle activity levels when using only a light to moderate load. Because of the dynamic nature of the FS, this may also be more beneficial in transferring to activities of daily living and sporting environments.
The squat is one of the most frequently used exercises in the field of strength and conditioning. Considering the complexity of the exercise and the many variables related to performance, understanding squat biomechanics is of great importance for both achieving optimal muscular development as well as reducing the prospect of a training-related injury. Therefore, the purpose of this article is 2-fold: first, to examine kinematics and kinetics of the dynamic squat with respect to the ankle, knee, hip and spinal joints and, second, to provide recommendations based on these biomechanical factors for optimizing exercise performance.
Core stability and core strength have been subject to research since the early 1980s. Research has highlighted benefits of training these processes for people with back pain and for carrying out everyday activities. However, less research has been performed on the benefits of core training for elite athletes and how this training should be carried out to optimize sporting performance. Many elite athletes undertake core stability and core strength training as part of their training programme, despite contradictory findings and conclusions as to their efficacy. This is mainly due to the lack of a gold standard method for measuring core stability and strength when performing everyday tasks and sporting movements. A further confounding factor is that because of the differing demands on the core musculature during everyday activities (low load, slow movements) and sporting activities (high load, resisted, dynamic movements), research performed in the rehabilitation sector cannot be applied to the sporting environment and, subsequently, data regarding core training programmes and their effectiveness on sporting performance are lacking.
There are many articles in the literature that promote core training programmes and exercises for performance enhancement without providing a strong scientific rationale of their effectiveness, especially in the sporting sector. In the rehabilitation sector, improvements in lower back injuries have been reported by improving core stability. Few studies have observed any performance enhancement in sporting activities despite observing improvements in core stability and core strength following a core training programme. A clearer understanding of the roles that specific muscles have during core stability and core strength exercises would enable more functional training programmes to be implemented, which may result in a more effective transfer of these skills to actual sporting activities.
The strength and stability of the knee plays an integral role in athletics and activities of daily living. A better understanding of knee joint biomechanics while performing variations of the squat would be useful in rehabilitation and exercise prescription. We quantified and compared tibiofemoral joint kinetics as well as muscle activity while executing front and back squats. Because of the inherent change in the position of the center of mass of the bar between the front and back squat lifts, we hypothesized that the back squat would result in increased loads on the knee joint and that the front squat would result in increased knee extensor and decreased back extensor muscle activity. A crossover study design was used. To assess the net force and torque placed on the knee and muscle activation levels, a combination of video and force data, as well as surface electromyographic data, were collected from 15 healthy trained individuals. The back squat resulted in significantly higher compressive forces and knee extensor moments than the front squat. Shear forces at the knee were small in magnitude, posteriorly directed, and did not vary between the squat variations. Although bar position did not influence muscle activity, muscle activation during the ascending phase was significantly greater than during the descending phase. The front squat was as effective as the back squat in terms of overall muscle recruitment, with significantly less compressive forces and extensor moments. The results suggest that front squats may be advantageous compared with back squats for individuals with knee problems such as meniscus tears, and for long-term joint health.
Electromyographic (EMG) activity of selected hip and trunk muscles was recorded during a squat lift, and the effects of two different lumbar spine postures were examined. Seven muscles were analyzed: rectus abdominis (RA), abdominal obliques (AO), erector spinae (ES), latissimus dorsi (LD), gluteus maximus (GM), biceps femoris (BF), and semitendinosus (ST). The muscles were chosen for their attachments to the thoracolumbar fascia and their potential to act on the trunk, pelvis, and hips. Seventeen healthy male subjects participated in the study. Each subject did three squat lifts with a 157-N crate, with the spine in both a lordotic and kyphotic posture. The lift was divided into four equal periods. EMG activity of each muscle was quantified for each period and normalized to the peak amplitude of a maximal voluntary isometric contraction (MVIC). A two-way analysis of variance (ANOVA) for repeated measures was used to analyze the effects of posture on the amplitude and timing of EMG activity during the lift. Two patterns of EMG activity were seen: a trunk muscle pattern (RA, AO, ES, and LD) and a hip extensor pattern (GM, BF, ST). In the trunk muscle pattern (TP), EMG activity was greatest in the first quarter and decreased as the lift progressed. In the hip extensor pattern (HP), EMG activity was least in the first quarter, increased in the second and third quarters, and decreased in the final phase of the lift. Differences (P < .05) were seen among subjects and in the timing of the muscle activity in all muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
The objective of this study was to determine differences in electromyographic (EMG) activity of the soleus (SOL), vastus lateralis (VL), biceps femoris (BF), abdominal stabilizers (AS), upper lumbar erector spinae (ULES), and lumbo-sacral erector spinae (LSES) muscles while performing squats of varied stability and resistance. Stability was altered by doing the squat movement on a Smith machine, a free squat, and while standing on two balance discs. Fourteen male subjects performed the movements. Activities of the SOL, AS, ULES, and LSES were highest during the unstable squat and lowest with the Smith machine protocol (p < 0.05). Increased EMG activity of these muscles may be attributed to their postural and stabilization role. Furthermore, EMG activity was higher during concentric contractions compared to eccentric contractions. Performing squats on unstable surfaces may permit a training adaptation of the trunk muscles responsible for supporting the spinal column (i.e., erector spinae) as well as the muscles most responsible for maintaining posture (i.e., SOL).
This study examined cycling economy before and after 8 wk of maximal leg-strength training.
Seven previously untrained males (25 +/- 2 yr) performed leg-strength training 3 d.wk(-1) for 8 wk using four sets of five repetitions at 85% of one repetition maximum (1RM). Body mass, lean-leg muscle mass (LLM), percentage of body fat, and leg strength (1RM) were measured at 0, 4, and 8 wk of training. Cycling economy was calculated as the deltaVO2/deltaWR (change in the O2 cost of exercise divided by the change in the power between two different power outputs).
There were significant increases in LLM and 1RM from 0 to 4 wk of training (LLM: 25.8 +/- 0.7 to 27.2 +/- 0.8 kg; 1RM: 138 +/- 9 to 215 +/- 9 kg). From 4 to 8 wk of training, 1RM continued to increase significantly (215 +/- 9 to 266 +/- 8 kg) with no further change observed in LLM. Peak power during incremental cycling increased significantly (305 +/- 14 to 315 +/- 16 W), whereas the power output achieved at the gas-exchange threshold (GET) remained unchanged. Peak O2 uptake and the O2 uptake achieved at the GET also remained unchanged following training. Cycling economy improved significantly when the power output was increased from below the GET to above the GET but not for power outputs below the GET.
Maximal leg-strength training improves cycling economy in previously untrained subjects. Increases in leg strength during the final 4 wk of training with unchanged LLM suggest that neural adaptations were present.
The objective of this study was to investigate the validity of power measurement techniques utilizing various kinematic and kinetic devices during the jump squat (JS), squat (S) and power clean (PC). Ten Division I male athletes were assessed for power output across various intensities: 0, 12, 27, 42, 56, 71, and 85% of one repetition maximum strength (1RM) in the JS and S and 30, 40, 50, 60, 70, 80, and 90% of 1RM in the PC. During the execution of each lift, six different data collection systems were utilized; (1) one linear position transducer (1-LPT); (2) one linear position transducer with the system mass representing the force (1-LPT+MASS); (3) two linear position transducers (2-LPT); (4) the force plate (FP); (5) one linear position transducer and a force plate (1-LPT+FP); (6) two linear position transducers and a force place (2-LPT+FP). Kinetic and kinematic variables calculated using the six methodologies were compared. Vertical power, force, and velocity differed significantly between 2-LPT+FP and 1-LPT, 1-LPT+MASS, 2-LPT, and FP methodologies across various intensities throughout the JS, S, and PC. These differences affected the load-power relationship and resulted in the transfer of the optimal load to a number of different intensities. This examination clearly indicates that data collection and analysis procedures influence the power output calculated as well as the load-power relationship of dynamic lower body movements.
This study examined supramaximal cycling performed to exhaustion at 120% of peak O(2) uptake (120% VO(2)peak) before and after 8 weeks of strength training. Eight previously untrained men completed 8 weeks of leg-strength training 3 days week(-1) on a hack-squat machine; four sets, five repetitions at 85% of one repetition maximum each session. Anaerobic capacity was quantified by determining the maximal accumulated O(2) deficit during supramaximal cycling. After 8 weeks of strength training, one repetition maximum for the hack squat significantly increased by 90 +/- 33% when compared to before training. However, 8 weeks of strength training did not increase the maximal accumulated O(2) deficit. Nevertheless, after 8 weeks of strength training, there was a significant increase in time to exhaustion for cycling at 120% VO(2)peak. The increase in time to exhaustion after 8 weeks of strength training was accompanied by a significant increase in accumulated O(2) uptake. In conclusion, 8 weeks of strength training improves supramaximal cycling performance in previously untrained subjects. However, increases in time to exhaustion for supramaximal cycling following strength training are associated with an increase in the contribution of the aerobic energy system rather than an improvement in anaerobic capacity.
The purpose of this study was to examine the extent of activation in various trunk muscles during dynamic weight-training and isometric instability exercises. Sixteen subjects performed squats and deadlifts with 80% 1 repetition maximum (1RM), as well as with body weight as resistance and 2 unstable calisthenic-type exercises (superman and sidebridge). Electromyographic (EMG) activity was measured from the lower abdominals (LA), external obliques (EO), upper lumbar erector spinae (ULES), and lumbar-sacral erector spinae (LSES) muscle groups. Results indicated that the LSES EMG activity during the 80% 1RM squat significantly exceeded 80% 1RM deadlift LSES EMG activity by 34.5%. The LSES EMG activity of the 80% 1RM squat also exceeded the body weight squat, deadlift, superman, and sidebridge by 56, 56.6, 65.5, and 53.1%, respectively. The 80% 1RM deadlift ULES EMG activity significantly exceeded the 80% 1RM squat exercise by 12.9%. In addition, the 80% 1RM deadlift ULES EMG activity also exceeded the body weight squat, deadlift, superman, and sidebridge exercises by 66.7, 65.5, 69.3, and 68.6%, respectively. There were no significant changes in EO or LA activity. Therefore, the augmented activity of the LSES and ULES during 80% 1RM squat and deadlift resistance exercises exceeded the activation levels achieved with the same exercises performed with body weight and selected instability exercises. Individuals performing upright, resisted, dynamic exercises can achieve high trunk muscle activation and thus may not need to add instability device exercises to augment core stability training.
Trunk muscle activation (TMA) has been reported during back squat exercise, however reliability and sensitivity to different loads alongside kinematic measures has not. Hence the aim was to determine the interday reliability and load sensitivity of TMA and kinematics during back squats. 10 males performed 3 test sessions: 1) back squat 1RM, 2) and 3) 3 reps at 65, 75, 85 and 95% of system mass max (SMmax). Kinematics were measured from an electrogoniometer and linear transducer, and surface electromyography (sEMG) recorded 4 muscles of the trunk: rectus abdominis (RA), external oblique (EO), upper lumbar erector spinae (ULES) and lumbar sacral erector spinae (LSES), and a reference leg muscle, the vastus lateralus (VL). sEMG amplitude was root mean squared (RMS). No differences (p>0.05) found between tests for any kinematic and RMS data. CV demonstrated moderate interday reliability (~16.1%) for EO, LSES and ULES but not RA (29.4%) during the velocity-controlled eccentric phase; whereas it was moderately acceptable for just LSES and ULES (~17.8%) but not RA and EO (27.9%) during the uncontrolled concentric phase. This study demonstrated acceptable interday reliability for kinematic data while sEMG for most trunk muscle sites was moderately acceptable during controlled contraction. sEMG responded significantly to load.
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The purpose of this study was to compare muscle activity and kinetics during the back squat and overhead squat performed at three relative intensities (60, 75 and 90% 3RM). Fourteen subjects (age: 26 ± 7 yrs, height: 182.5 ± 13.5 cm, body mass: 90.5 ± 17.5 kg) performed each exercise using a within-subjects crossover design. In addition, a selection of trunk isolation exercises were included to provide additional comparisons. Squats were performed on a force platform with electromyographic (EMG) activity of the anterior deltoid (AD), rectus abdominis (RA), external oblique (EO), erector spinae (ES), gluteus maximus (GM), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (GA) recorded throughout. The overhead squat demonstrated significantly greater (p<0.05) activity in the anterior trunk muscles (RA and EO) during the eccentric phase. However, the magnitudes of the differences were relatively small (∼ 2 to 7%). In contrast, the back squat displayed significantly greater (p<0.05) activity in the posterior aspect of the trunk (ES) and all lower-body muscles during the concentric phase. Kinetic comparisons revealed that significantly greater peak force (p<0.05) was developed during the back squat. EMG comparisons between the trunk isolation exercises and squat variations demonstrated substantially greater anterior trunk activity during the isolation exercises, whereas the highest activity in the posterior aspect of the trunk was obtained during the squats (p<0.05). The results of the study do not support the hypothesis that the overhead squat provides a substantially greater stimulus for developing the trunk musculature compared with the back squat.
THE SELECTION OF TRAINING LOADS FOR THE DEVELOPMENT OF MUSCULAR FORCE AND POWER FOR ATHLETIC PERFORMANCE IS CURRENTLY AN AREA OF MUCH INTEREST AMONG BOTH STRENGTH AND CONDITIONING PRACTITIONERS AND SPORTS SCIENTISTS. THIS ARTICLE REVIEWS THE RESULTS OF TRAINING STUDIES USING SQUAT AND JUMP SQUAT MOVEMENTS IN AN ATTEMPT TO CLARIFY THE PRACTICAL APPLICATION OF RESEARCH FINDINGS TO LOAD PRESCRIPTION FOR THE DEVELOPMENT OF ATHLETIC PERFORMANCE.
The purpose of this investigation was to determine the effect of stable and unstable conditions on one repetition maximum strength and muscle activity during dynamic squatting using absolute and relative loading.
Ten recreationally weight-trained males participated in this study (age = 24.1 +/- 2.0 y, height = 178.0 +/- 5.6 cm, body mass = 83.7 +/- 13.4 kg, 1RM/body mass = 1.53 +/- 0.31), which involved two laboratory sessions separated by 1 wk. Linear position transducers were used to track bar displacement while subjects stood on a force plate for all trials. Vastus lateralis (VL), biceps femoris (BF) and erector spinae (L1) muscle activity (average integrated EMG [IEMG]) was also recorded during all trials. During the first session subjects complete a one repetition maximum test in a stable dynamic squat (S1RM = 128.0 +/- 31.4 kg) and an unstable dynamic squat (U1RM = 83.8 +/- 17.3 kg) in a randomized order with a 30-min rest period between conditions. The second session consisted of the performance of three trials each for 12 different conditions (unstable and stable squats using three different absolute loads [six conditions] and unstable and stable squats using three different relative loads [six conditions]).
Results revealed a statistically significant difference between S1RM and U1RM values (P < or = .05). The stable trials resulted in the same or a significantly higher value for VL, BF and L1 muscle activity in comparison with the unstable trials for all twelve conditions.
Unstable squatting is of equal or less (depending on the loading condition) benefit to improving or maximizing muscle activity during resistance exercise.
The purpose of this experiment was to determine whether free weight or Smith machine squats were optimal for activating the prime movers of the legs and the stabilizers of the legs and the trunk. Six healthy participants performed 1 set of 8 repetitions (using a weight they could lift 8 times, i.e., 8RM, or 8 repetition maximum) for each of the free weight squat and Smith machine squat in a randomized order with a minimum of 3 days between sessions, while electromyographic (EMG) activity of the tibialis anterior, gastrocnemius, vastus medialis, vastus lateralis, biceps femoris, lumbar erector spinae, and rectus abdominus were simultaneously measured. Electromyographic activity was significantly higher by 34, 26, and 49 in the gastrocnemius, biceps femoris, and vastus medialis, respectively, during the free weight squat compared to the Smith machine squat (p < 0.05). There were no significant differences between free weight and Smith machine squat for any of the other muscles; however, the EMG averaged over all muscles during the free weight squat was 43% higher when compared to the Smith machine squat (p < 0.05). The free weight squat may be more beneficial than the Smith machine squat for individuals who are looking to strengthen plantar flexors, knee flexors, and knee extensors.
The objective of this study is to investigate the potentially opposing influence of qualitative and quantitative muscular adaptations in response to high-intensity resistance training on contractile rate of force development (RFD) in the early (<100 ms) and later phases (>200 ms) of rising muscle force. Fifteen healthy young males participated in a 14-week resistance training intervention for the lower body and 10 matched subjects participated as controls. Maximal muscle strength (MVC) and RFD were measured during maximal voluntary isometric contraction of the quadriceps femoris muscle. Muscle biopsies were obtained from the vastus lateralis. The main findings were that RFD in the late phase of rising muscle force increased in response to resistance training whereas early RFD remained unchanged and early relative RFD (i.e., RFD/MVC) decreased. Quantitatively, muscle fiber cross-sectional area and MVC increased whereas, qualitatively, the relative proportion of type IIX muscle fibers decreased. Multiple regression analysis showed that while increased MVC positively influenced both early and late RFD, decreased-type IIX negatively influenced early RFD only. In conclusion, early and late RFD responded differently to high-intensity resistance training due to differential influences of qualitative and quantitative muscular adaptations on early and later phases of rising muscle force.
The present study assessed the anthropometric profile (International Society for the Advancement of Kinanthropometry protocol), flexibility, muscular strength, and endurance of 20 male golfers. These data were collected in order to determine: a) the relationship between these kinanthropometric measures and clubhead velocity; and b) if these measures could distinguish low-handicap (LHG) and high-handicap (HHG) golfers. Ten LHG (handicap of 0.3 +/- 0.5) and 10 HHG (handicap of 20.3 +/- 2.4) performed 10 swings for maximum velocity and accuracy with their own 5-iron golf club at a wall-mounted target. LHG hit the target significantly more (115%) and had a 12% faster clubhead velocity than HHG (p < 0.01). The LHG also had significantly (28%) greater golf swing-specific cable woodchop (GSCWC) strength (p < 0.01) and tendencies for greater (30%) bench press strength and longer (5%) upper am and total arm (4%) length and less (24%) right hip internal rotation than HHG (0.01 < p < 0.05). GSCWC strength was significantly correlated to clubhead velocity (p < 0.01), with bench press and hack squat strength as well as upper arm and total arm length also approaching significance (0.01 < p < 0.05). Golfers with high GSCWC strength and perhaps greater bench press strength and longer arms may therefore be at a competitive advantage, as these characteristics allow the production of greater clubhead velocity and resulting ball displacement. Such results have implications for golf talent identification programs and for the prescription and monitoring of golf conditioning programs. While golf conditioning programs may have many aims, specific trunk rotation exercises need to be included if increased clubhead velocity is the goal. Muscular hypertrophy development may not need to be emphasized as it could reduce golf performance by limiting range of motion and/or increasing moment of inertia.
The aim of this study was to assess the effect of verbal instruction, surface stability, and load intensity on trunk muscle activity levels during the free weight squat exercise. Twelve trained males performed a free weight squat under four conditions: (1) standing on stable ground lifting 50% of their 1-repetition maximum (RM), (2) standing on a BOSU balance trainer lifting 50% of their 1-RM, (3) standing on stable ground lifting 75% of their 1-RM, and (4) receiving verbal instructions to activate the trunk muscles followed by lifting 50% of their 1-RM. Surface EMG activity from muscles rectus abdominis (RA), external oblique (EO), transversus abdominis/internal oblique (TA/IO), and erector spinae (ES) were recorded for each condition and normalized for comparisons. Muscles RA, EO, and TA/IO displayed greater peak activity (39-167%) during squats with instructions compared to the other squat conditions (P=0.04-0.007). Peak EMG activity of muscle ES was greater for the 75% 1-RM condition than squats with instructions or lifting 50% of 1-RM (P=0.04-0.02). The results indicate that if the goal is to enhance EMG activity of the abdominal muscles during a multi-joint squat exercise then verbal instructions may be more effective than increasing load intensity or lifting on an unstable surface. However, in light of other research, conscious co-activation of the trunk muscles during the squat exercise may lead to spinal instability and hazardous compression forces in the lumbar spine.
Chronobiology is the science concerned with investigations of time-dependent changes in physiological variables. Circadian rhythms refer to variations that recur every 24 hours. Many physiological circadian rhythms at rest are endogenously controlled, and persist when an individual is isolated from environmental fluctuations. Unlike physiological variables, human performance cannot be monitored continuously in order to describe circadian rhythmicity. Experimental studies of the effect of circadian rhythms on performance need to be carefully designed in order to control for serial fatigue effects and to minimise disturbances in sleep. The detection of rhythmicity in performance variables is also highly influenced by the degree of test-retest repeatability of the measuring equipment.
The majority of components of sports performance, e.g. flexibility, muscle strength, short term high power output, vary with time of day in a sinusoidal manner and peak in the early evening close to the daily maximum in body temperature. Psychological tests of short term memory, heart rate-based tests of physical fitness, and prolonged submaximal exercise performance carried out in hot conditions show peak times in the morning. Heart rate-based tests of work capacity appear to peak in the morning because the heart rate responses to exercise are minimal at this time of day. Post-lunch declines are evident with performance variables such as muscle strength, especially if measured frequently enough and sequentially within a 24-hour period to cause fatigue in individuals. More research work is needed to ascertain whether performance in tasks demanding fine motor control varies with time of day.
Metabolic and respiratory rhythms are flattened when exercise becomes strenuous whilst the body temperature rhythm persists during maximal exercise. Higher work-rates are selected spontaneously in the early evening. At present, it is not known whether time of day influences the responses of a set training regimen (one in which the training stimulus does not vary with time of day) for endurance, strength, or the learning of motor skills.
The normal circadian rhythms can be desynchronised following a flight across several time zones or a transfer to nocturnal work shifts. Although athletes show all the symptoms of ‘jet lag’ (increased fatigue, disturbed sleep and circadian rhythms), more research work is needed to identify the effects of transmeridian travel on the actual performances of elite sports competitors. Such investigations would need to be chronobiological, i.e. monitor performance at several dmes on several post-flight days, and take into account direction of travel, time of day of competition and the various performance components involved in a particular sport.
Shiftwork interferes with participation in competitive sport, although there may be greater opportunities for shiftworkers to train in the hours of daylight for individual sports such as cycling and swimming. Studies should be conducted to ascertain whether shiftwork-mediated rhythm disturbances affect sports performance.
Individual differences in performance rhythms are small but significant. Circadian rhythms are larger in amplitude in physically fit individuals than sedentary individuals. Athletes over 50 years of age tend to be higher in ‘momingness’, habitually scheduling relatively more training in the morning and selecting relatively higher work-rates during exercise compared with young athletes. These differences should be recognised by practitioners concerned with organising the habitual regimens of athletes.
We chose to investigate tibiofemoral joint kinetics (compressive force, anteroposterior shear force, and extension torque) and electromyographic activity of the quadriceps, hamstring, and gastrocnemius muscles during open kinetic chain knee extension and closed kinetic chain leg press and squat. Ten uninjured male subjects performed 4 isotonic repetitions with a 12 repetition maximal weight for each exercise. Tibiofemoral forces were calculated using electromyographic, kinematic, and kinetic data. During the squat, the maximal compressive force was 6139 +/- 1708 N, occurring at 91 degrees of knee flexion; whereas the maximal compressive force for the knee extension exercise was 4598 +/- 2546 N (at 90 degrees knee flexion). During the closed kinetic chain exercises, a posterior shear force (posterior cruciate ligament stress) occurred throughout the range of motion, with the peak occurring from 85 degrees to 105 degrees of knee flexion. An anterior shear force (anterior cruciate ligament stress) was noted during open kinetic chain knee extension from 40 degrees to full extension; a peak force of 248 +/- 259 N was noted at 14 degrees of knee flexion. Electromyographic data indicated greater hamstring and quadriceps muscle co-contraction during the squat compared with the other two exercises. During the leg press, the quadriceps muscle electromyographic activity was approximately 39% to 52% of maximal velocity isometric contraction; whereas hamstring muscle activity was minimal (12% maximal velocity isometric contraction). This study demonstrated significant differences in tibiofemoral forces and muscle activity between the two closed kinetic chain exercises, and between the open and closed kinetic chain exercises.
Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise.
Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation.
Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60 degrees knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50 degrees knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100 degrees knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee.
The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.
The specific aim of this project was to quantify knee forces and muscle activity while performing squat and leg press exercises with technique variations.
Ten experienced male lifters performed the squat, a high foot placement leg press (LPH), and a low foot placement leg press (LPL) employing a wide stance (WS), narrow stance (NS), and two foot angle positions (feet straight and feet turned out 30 degrees ).
No differences were found in muscle activity or knee forces between foot angle variations. The squat generated greater quadriceps and hamstrings activity than the LPH and LPL, the WS-LPH generated greater hamstrings activity than the NS-LPH, whereas the NS squat produced greater gastrocnemius activity than the WS squat. No ACL forces were produced for any exercise variation. Tibiofemoral (TF) compressive forces, PCL tensile forces, and patellofemoral (PF) compressive forces were generally greater in the squat than the LPH and LPL, and there were no differences in knee forces between the LPH and LPL. For all exercises, the WS generated greater PCL tensile forces than the NS, the NS produced greater TF and PF compressive forces than the WS during the LPH and LPL, whereas the WS generated greater TF and PF compressive forces than the NS during the squat. For all exercises, muscle activity and knee forces were generally greater in the knee extending phase than the knee flexing phase.
The greater muscle activity and knee forces in the squat compared with the LPL and LPH implies the squat may be more effective in muscle development but should be used cautiously in those with PCL and PF disorders, especially at greater knee flexion angles. Because all forces increased with knee flexion, training within the functional 0-50 degrees range may be efficacious for those whose goal is to minimize knee forces. The lack of ACL forces implies that all exercises may be effective during ACL rehabilitation.
Lumbar spine kinematic response to a 1.0 body weight compressive load was measured in vivo by comparison of relaxed and loaded magnetic resonance image sets in the sagittal plane.
To identify and measure acute response mechanisms of the lumbar spine during compression loading.
The isolated ligamentous spine buckles under small loads (88 N); yet, the spine supports >10 times that load in daily activities. Mechanical function of the lumbar spine in vivo is not well understood, and only a few studies examined the spine during in vivo loading.
Magnetic resonance imaging scans of subjects were taken while subjects were relaxed and while supporting a 1.0 body weight compressive load. Vertebral bodies and disc perimeters were digitized, and relative centroid positions were measured and compared between conditions. Lumbar rotation, bending, compression, and disc translation were determined. Two parameter ensembles were analyzed to describe mechanisms of "spine shrinkage" (decrease of projected spine length) and lumbosacral response.
All subjects underwent spine shrinkage (-3.9 +/- 1.2 mm) dominated by cumulative bending, except in three subjects where the rotation component dominated. Levels L2-L4 extended, while L5 flexed, and dL2 through dL4 translated anterior, while dL5 translated posterior. Significant segmental deformations were as follows: L3 extension (-3.3 +/- 3.1 degrees ), dL5 disc translation (-1.4 +/- 1.4 mm), and posterior sacral rotation (3.2 +/- 4.7 degrees ).
Spine shrinkage occurred mainly from spine bending and rotation, with only small contribution from spine compression (shortening along the spine curvature). Response pattern groupings indicated at least two unique subgroups, but the cause remains to be determined.
A biomechanical model of a squat exercise performed on a device using a bar that is restricted to a linear motion was developed. Hip and knee moments were evaluated at varying foot positions. The range of motion of the exercise was limited by the knee joint angle beginning at an 80 degrees angle (flexed) to a 179 degrees joint angle (extended). Variations in foot placement were evaluated for differences in torque applied about the transverse axes of the user's knee and hip joints. Because the user's feet were positioned farther forward (anterior), the moment about the knee decreased whereas the moment about the hip increased. Positive moments were those that resulted in forces to flex the knee and hip joints. Positive knee moments were determined in all conditions when the knee was flexed and became negative when the knee was at or near full extension. The model always produced positive moments about the hip. Thus, foot position is a critical factor in hip and knee moments, and therefore in the muscle groups stressed, in a linear motion squat type exercise.
The Smith machine (SM) (vertical motion of bar on fixed path; fixed-form exercise) and free weights (FWs) (free-form path) are commonly used strength training modes. Exercisers may need to alternate between types of equipment, depending on testing, training, rehabilitation, and/or the exercisers' goals. The purposes of this study were to compare muscle force production for SM and FWs using a 1 repetition maximum (1RM) for the parallel back squat and supine bench press exercises and to predict the 1RM for one mode from 1RM on the other mode. Men (n = 16) and women (n = 16) alternately completed 1RM testing for squat and bench press using SM and FWs. Analyses of variance (type of equipment x sex) and linear regression models were calculated. A significant difference was found between bench press and squat 1RMs for each mode of equipment for all participants. The squat 1RM was greater for the SM than the FWs; conversely, the bench 1RM was greater for FWs than the SM. When sex was considered, bench 1RM for FWs was greater than SM for men and women. The squat 1RM was greater for SM than FWs for women only. The 1RM on one mode of equipment was the best predictor of 1RM for the other mode. For both sexes, the equation SM bench 1RM (in kilograms) = -6.76 + 0.95 (FW bench 1RM) can be used. For women only, SM squat 1RM (in kilograms) = 28.3 + 0.73 (FW squat 1RM). These findings provide equations for converting between SM and FW equipment for training.
The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.
Muscle activation in the loaded free barbell squat: a brief review
- D R Clark
- M I Lambert
- A M Hunter
Clark DR, Lambert MI, Hunter AM. Muscle activation in the loaded free barbell squat:
a brief review. J Strength Cond Res. 2012;26(4):1169-1178.
Resistance training and spotting techniques
- T R Baechle
- R W Earle
Baechle TR, Earle RW. Resistance training and spotting techniques. In: Baechle TR,
Roger E, eds. Essentials of Strength and Conditioning. 2nd ed. Champaign IL: Human
Kinetics; 2000:343-389.
World Medical Association Declaration of Helsinki Ethical Principles for Medical Research Involving Human Subjects
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2013;JAMA Publi(jama.com):E1-E4.