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An Electromyographical Comparison of the Squat and Knee Extension Exercises
Abstract
The seated knee extension is commonly used with the parallel squat to promote balance between the vastus medialis (VM) and vastus lateralis (VL). No controlled studies have examined the relative contributions of each muscle during these exercises, so this study employed EMG analysis to determine their contributions. Ten experienced lifters performed squats and knee extensions at their 10-RM. Sets were separated by 15 min rest and the order of performance was reversed between sessions, which were 1 week apart. EMG was collected on the VL and VM of the dominant leg during the first and last repetition of each exercise. Since EMG activity differed significantly between the two testing days, each was analyzed separately. No significant differences were found between the root mean square of the amplitude of the EMG for the VL and VM during either exercise. The parallel squat elicited more electrical activity than the knee extension in both muscles, and the downward shift in frequency of the EMG signal was greater for both the VM and VL during the parallel squat. The results question the value of the knee extension as a supplemental exercise in this case.
(C) 1994 National Strength and Conditioning Association
... To determine which muscles are being developed during the squat and to what degree, it is helpful to quantify muscle activity through the use of EMG. To date, there are 16 known studies that have quantified muscle activity about the knee during the dynamic squat (6,13,17,18,25,27,34,38,40,54,55,58,65,(68)(69)(70). Eleven of these studies performed the barbell squat with an external load (17,18,34,40,54,55,58,65,(68)(69)(70), whereas the remaining five studies (6,13,25,27,38) performed the BW squat. ...
... To date, there are 16 known studies that have quantified muscle activity about the knee during the dynamic squat (6,13,17,18,25,27,34,38,40,54,55,58,65,(68)(69)(70). Eleven of these studies performed the barbell squat with an external load (17,18,34,40,54,55,58,65,(68)(69)(70), whereas the remaining five studies (6,13,25,27,38) performed the BW squat. The primary knee muscles utilized during the squat are the quadriceps, hamstrings, and gastrocnemius, and co-contractions among these muscles are believed to enhance knee stability (15,16,31,46,47,73,74). ...
... Quadriceps activity progressively increased as the knee flexed and decreased as the knees extended, with peak activity occurring at approximately 80 -90°knee flexion. Similar results were observed in several other studies (18,27,40,55,58,69). Quadriceps activity remained fairly constant beyond 80 -90°knee flexion, which has also been observed in other studies (58,68,69). ...
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.
... Strength training exercises have been assessed to compare the use of single and multijoint exercises and their effects in muscle recruitment. [6][7][8][9][10][11] Information gathered from these studies provided evidence for improving strength training prescription and optimization of training programs. 12,13 The option for multijoint exercises has been suggested for begin- ...
... Major attention has been given to assess activation of lower limb muscles with conflicting findings from these studies. [6][7][8]10 For the upper limb, only two studies had focus on the assessment of shoulder horizontal adductors (i.e. pectoralis major and anterior deltoid) with no differences in activation of these muscles comparing single to multijoint exercises. ...
... To a certain level, our results could not be fully related to most studies because they had focus on lower limb exercises. [6][7][8]10 Others assessed shoulder horizontal adductors during upper body exercises 9,11 which is limited compared to our approach where assessments of the muscle group that acts in the shoulder horizontal abduction were conducted. Therefore, our study expands the existing knowledge in muscle function during strength training exercises. ...
Aim:
Although comparison between multi and single joint exercises has been conducted, there is insufficient evidence that these exercises could lead to different muscle activations. The aim of this study was to compare deltoid muscle activation during multi and single joint exercises.
Methods:
Twelve male participants (23.4±1.6 years) with at least one year of strength training experience were assessed performing inclined lat pull-down, reverse peck deck and seated row exercises. Surface electromyography was used to measure activation of anterior, middle and posterior portions of deltoid muscle during each exercise. Deltoid activation was recorded during maximum voluntary isometric contraction (MVIC) and during dynamic isoinertial exercises of ten maximum repetitions for inclined lateral pull-down, reverse peck deck and seated row.
Results:
There was no difference in activation of the anterior portion of deltoid muscle for any of the three exercises (P=0.08). The middle portion presented greater activation during the reverse peck deck (P=0.03) and during the seated row (P=0.03) compared to the inclined lat pull-down. For the posterior portion of deltoid muscle there was greater activation during the reverse peck deck (P=0.001) compared to the seated row and to the inclined lat pull-down.
Conclusion:
Results indicate that reverse peck deck and seated row should be more appropriate for recruitment of the middle portion of the deltoid muscle than the inclined lat pull-down. Differently, the reverse peck deck should be primarily used rather than the seated row and the lat pull-down for recruitment of the posterior portion of the deltoid muscle.
... muscle activitv during the squat from the quadriceps, hamstrings, giuteus maximus, thigh adductors. abdominals, obliques, and erector spinae (6,8,14,17,20,25,(29)(30)(31)(34)(35)(36). These are the largest and most powerful muscles in the body and generate a high force production and energy expenditure when active. ...
... Ankle moment arms peaked at maximum KF, which is consistent with squat data from Escamilia et al. (8) and Isear et al.(14), which show peak gastrocnemius activity near maximum KF. Several studies have shown moderate to high activity from the quadriceps during the squat (8,20,25,(29)(30)(31)34,35). with peak activity occurring near maximum KF (8,14,25,30.31,35). ...
The purpose of this study was to quantify biomechanical parameters employing two-dimensional (2-D) and three-dimensional (3-D) analyses while performing the squat with varying stance widths.
Two 60-Hz cameras recorded 39 lifters during a national powerlifting championship. Stance width was normalized by shoulder width (SW), and three stance groups were defined: 1) narrow stance squat (NS), 107 +/- 10% SW; 2) medium stance squat (MS), 142 +/- 12% SW; and 3) wide stance squat (WS), 169 +/- 12% SW.
Most biomechanical differences among the three stance groups and between 2-D and 3-D analyses occurred between the NS and WS. Compared with the NS at 45 degrees and 90 degrees knee flexion angle (KF), the hips flexed 6-11 degrees more and the thighs were 7-12 degrees more horizontal during the MS and WS. Compared with the NS at 90 degrees and maximum KF, the shanks were 5-9 degrees more vertical and the feet were turned out 6 degrees more during the WS. No significant differences occurred in trunk positions. Hip and thigh angles were 3-13 degrees less in 2-D compared with 3-D analyses. Ankle plantar flexor (10-51 N.m), knee extensor (359-573 N.m), and hip extensor (275-577 N.m) net muscle moments were generated for the NS, whereas ankle dorsiflexor (34-284 N.m), knee extensor (447-756 N.m), and hip extensor (382-628 N.m) net muscle moments were generated for the MS and WS. Significant differences in ankle and knee moment arms between 2-D and 3-D analyses were 7-9 cm during the NS, 12-14 cm during the MS, and 16-18 cm during the WS.
Ankle plantar flexor net muscle moments were generated during the NS, ankle dorsiflexor net muscle moments were produced during the MS and WS, and knee and hip moments were greater during the WS compared with the NS. A 3-D biomechanical analysis of the squat is more accurate than a 2-D biomechanical analysis, especially during the WS.
... Averaging over the entire exercise, OKCE generated approximately 45% more rectus femoris activity than CKCE, while CKCE generated approximately 20% more vastus medialis activity and approximately 5% more vastus lateralis activity than OKCE. These findings are in agreement with Signorile et al. (52) who found significantly more vasti activity during the squat exercise than during the knee extension exercise. This suggests that OKCE may be more effective in developing the rectus femoris, while CKCE may be more effective in developing the vasti muscles. ...
... Comparing muscle activity in OKCE, the vastus medialis, vastus lateralis, and rectus femoris all generated a similar amount of muscle activity. In a comparison of muscle activity in CKCE, the two vasti muscles produced approximately 50% greater activity than the rectus femoris, which is in accordance with squat data from Wretenberg et al. (66) Furthermore, the vastus medialis and lateralis generated approximately the same amount of muscle activity, which is in agreement with squat data from Signorile et al. (52). These findings have important clinical implications when one is deciding which exercise modality to choose during knee rehabilitation. ...
Although closed (CKCE) and open (OKCE) kinetic chain exercises are used in athletic training and clinical environments, few studies have compared knee joint biomechanics while these exercises are performed dynamically. The purpose of this study was to quantify knee forces and muscle activity in CKCE (squat and leg press) and OKCE (knee extension).
Ten male subjects performed three repetitions of each exercise at their 12-repetition maximum. Kinematic, kinetic, and electromyographic data were calculated using video cameras (60 Hz), force transducers (960 Hz), and EMG (960 Hz). Mathematical muscle modeling and optimization techniques were employed to estimate internal muscle forces.
Overall, the squat generated approximately twice as much hamstring activity as the leg press and knee extensions. Quadriceps muscle activity was greatest in CKCE when the knee was near full flexion and in OKCE when the knee was near full extension. OKCE produced more rectus femoris activity while CKCE produced more vasti muscle activity. Tibiofemoral compressive force was greatest in CKCE near full flexion and in OKCE near full extension. Peak tension in the posterior cruciate ligament was approximately twice as great in CKCE, and increased with knee flexion. Tension in the anterior cruciate ligament was present only in OKCE, and occurred near full extension. Patellofemoral compressive force was greatest in CKCE near full flexion and in the mid-range of the knee extending phase in OKCE.
An understanding of these results can help in choosing appropriate exercises for rehabilitation and training.
... R ecently, many studies have analyzed muscle activity during different strength exercises (14,25,28,29,37). The superficial electromyographic (EMG) technique is often used to identify the participation of a muscle or muscle group in different performance techniques of many exercises (2)(3)(4)6,17,27,33). Exercises commonly used in a strength training program seem to be more interesting to analyze during those analyses (20,23,24,35,36,39). ...
... Although the mechanical changes during strength exercises variations can modify muscle activity pattern, studies have not quantified how mechanical changes affect the hip and knee extensor muscle activity pattern during LP exercises at different submaximum loads lifted (5,11,12). Furthermore, these studies have been done only with men (5,6,12,(35)(36)(37). Thus, the specific purpose of this study was to analyze how mechanical changes and the loads lifted could modify the hip and knee extensor muscle activity in women during different (26), and Woods and Bigland-Ritchie (38), we propose the hypothesis that muscle activity could differ during performance of the 3 LP exercises and that these differences would depend on the load lifted. ...
Many studies have analyzed muscle activity during different strength exercises. Although the leg press (LP) is one of the most common exercises performed, there is little evidence of lower limb muscle activity patterns during this exercise and its variations. Thus, this study aimed to verify how mechanical changes and loads affect lower limb muscle activity during the performance of different LP exercises. Fourteen women performed 3 LP exercises: 45 degrees LP (LP45), LP high (LPH), and LP low (LPL) at 40% and 80% of the 1 repetition maximum. The electromyographic activity of the rectus femoris, vastus lateralis, biceps femoris, gastrocnemius, and gluteus maximus was recorded. Results suggested that mechanical changes affect lower limb muscle activity and that it is related to the load used. At moderate effort levels, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than during the LPH. At a high effort level, the rectus femoris and vastus lateralis (quadriceps) were more active during the LPL than the LPH. Again, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than the LPH. On the other hand, gluteus maximus activity was greater during the LPH than the LPL. This study found that coordination patterns of muscle activity are different when performing LP variations at high or moderate effort levels because of mechanical changes and different loads lifted during the different LP exercises. These results suggest that if the goal is to induce greater rectus femoris and vastus lateralis (quadriceps) activation, the LPL should be performed. On the other hand, if the goal is to induce gluteus maximus activity, the LPH should be performed.
... This brought the suggestion that one can chose between SJ and MJ based on personal preferences and practical aspects, without any negative impact on the results obtained from the intervention. Although less evidence is available for the lower body, studies about muscle activation [25,26], muscle strength [18], and hypertrophy [27] showed the same trends for thighs and hip muscles. However, information for calf muscles is scarce and controversial. ...
... Our main finding is that there was no difference for muscle activation for any muscle analyzed. This agrees with previous findings in upper and lower body muscles [15,16,25,26] and confirms the suggestion that plantar flexors have a great involvement in lower body MJ exercises [28,48]; however, the results were, to some extent, unexpected. ...
The present study aimed to compare soleus, lateral, and medial gastrocnemius muscles activation during leg press and calf raise exercises in trained men. The study involved 22 trained men (27.1 ± 3.6 years, 82.7 ± 6.6 kg, 177.5 ± 5.2 cm, 3.6 ± 1.4 experience years) who performed one set of each exercise using a 10-repetition maximum (10RM) load in a counterbalanced randomized order and separated by 10 min of rest. The electromyographic signal was measured for the three major plantar flexors: soleus, medial, and lateral gastrocnemius. A comparison between exercises showed that the mean adjusted by peak values during the leg press were 49.20% for the gastrocnemius lateralis, 51.31% for the gastrocnemius medialis, and 50.76% for the soleus. Values for calf raise were 50.70%, 52.19%, and 51.34% for the lateral, medial gastrocnemius, and soleus, respectively. There were no significant differences between exercises for any muscle (lateral gastrocnemius (p = 0.230), medial gastrocnemius (p = 0.668), and soleus (p = 0.535)). The present findings suggest that both leg press and calf raises can be used with the purpose to recruit triceps surae muscles. This bring the suggestion that one can chose between exercises based on personal preferences and practical aspects, without any negative impact on muscle activation.
... The magnitudes and patterns of quadriceps activity in the current study have also been observed duririg the barbell squat (4,5,(27)(28)(29). Both the vastus medialis auid vastus lateralis produced approximately the same amouat of activity, which is in agreement with vasti data from several squat studies (4,5,18,24,27). The lower activity observed in the rectus femoris compared to the vasti muscles nay be due to its biarticular function as both a hip flexor and knee extensor. Increased activity from the rectus fem(ris wouild increase hip flexor torque, with a con'nomitant ucrease in the amount of hip extensor torque needed from the hamstrings, gluteu s maximus, and adductor magnus (is hial fibers) to extend the hip. ...
Strength athletes often employ the deadlift in their training or rehabilitation regimens. The purpose of this study was to compare muscle activity between sumo and conventional style deadlifts, and between belt and no-belt conditions.
Six cameras collected 60-Hz video data and 960-Hz electromyographic data from 13 collegiate football players who performed sumo and conventional deadlifts with and without a lifting belt, employing a 12-RM intensity. Variables measured were knee angles and EMG measurements from 16 muscles. Muscle activity were averaged and compared within three 30-degree knee angle intervals from 90 to 0 degrees during the ascent, and three 30-degree knee angle intervals from 0 to 90 degrees during the descent.
Overall EMG activity from the vastus medialis, vastus lateralis, and tibialis anterior were significantly greater in the sumo deadlift, whereas overall EMG activity from the medial gastrocnemius was significantly greater in the conventional deadlift. Compared with the no-belt condition, the belt condition produced significantly greater rectus abdominis activity and significantly less external oblique activity. For most muscles, EMG activity was significantly greater in the knee extending intervals compared with the corresponding knee flexing intervals. Quadriceps, tibialis anterior, hip adductor, gluteus maximus, L3 and T12 paraspinal, and middle trapezius activity were significantly greater in higher knee flexion intervals compared with lower knee flexion intervals, whereas hamstrings, gastrocnemius, and upper trapezius activity were greater in lower knee flexion intervals compared with higher knee flexion intervals.
Athletes may choose to employ either the sumo or conventional deadlift style, depending on which muscles are considered most important according to their training protocols. Moderate to high co-contractions from the quadriceps, hamstrings, and gastrocnemius imply that the deadlift may be an effective closed kinetic chain exercise for strength athletes to employ during knee rehabilitation.
... This implies that squat and LP exercises may be more effective in vasti development compared with rectus femoris development. Within the squat, LPH, and LPL exercises, the VM and VL produced approximately the same amount of activity, which is in agreement with squat and LP data from several studies (11,27,34). ...
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.
... The magnitudes and patterns of quadriceps activity in the current study have also been observed duririg the barbell squat (4,5,(27)(28)(29). Both the vastus medialis auid vastus lateralis produced approximately the same amouat of activity, which is in agreement with vasti data from several squat studies (4,5,18,24,27). The lower activity observed in the rectus femoris compared to the vasti muscles nay be due to its biarticular function as both a hip flexor and knee extensor. Increased activity from the rectus fem(ris wouild increase hip flexor torque, with a con'nomitant ucrease in the amount of hip extensor torque needed from the hamstrings, gluteu s maximus, and adductor magnus (is hial fibers) to extend the hip. ...
Improper lifting techniques may increase injury risks and decrease performance. The aim of this study was to compare and contrast biomechanical parameters between sumo and conventional style deadlifts and between high- and low-skilled lifters who participated in the powerlifting event during the 1999 Special Olympics World Games.
Two synchronized video cameras collected 60 Hz of data from 40 subjects. Parameters were quantified at barbell liftoff (LO), when the barbell passed the knees (KP), and at lift completion.
Compared with the conventional group, the sumo group had a 100% greater stance width, 20% smaller hand width, 10% less vertical bar distance, a more vertical trunk at LO, a more horizontal thigh at LO and KP, a less vertical shank at KP, and greater forefoot abduction. The sumo group generated ankle dorsiflexor, knee extensor, and hip extensor moments, whereas the conventional group produced ankle plantar flexor, knee flexor and extensor, and hip extensor moments. Compared with low-skilled lifters, high-skilled lifters had a 40% greater barbell load, 15% greater stance width (sumo group only), greater knee flexion at LO (conventional group only), greater knee extension at KP, a less vertical shank position at LO (sumo group only), 15% less vertical bar distance, less first peak bar velocity between LO and KP (conventional group only), smaller plantar flexor and hip extensor moment arms at LO and KP, and greater knee extensor moment arms at LO.
The sumo deadlift may be more effective in working ankle dorsiflexors and knee extensors, whereas the conventional deadlift may be more effective in working ankle plantar flexors and knee flexors. High-skilled lifters exhibited better lifting mechanics than low-skilled lifters by keeping the bar closer to the body, which may both enhance performance and minimize injury risk.
... 3,13,14 Additionally, it is believed that the strain that some single-joint exercises place on the maturing graft may adversely affect the long-term stability of the reconstructed knee. 13,15,16 Biomechanical, electromyographic, and strain gauge studies have been used to compare and contrast single-and multiple-joint exercises 3,13,15,[17][18][19] ; in response, some authors 10,12 have recommended the exclusive use of multiple-joint exercise and the exclusion of traditional single-joint exercise. ...
To characterize the bilateral lower-extremity kinematics and kinetics associated with squatting exercise after anterior cruciate ligament (ACL) reconstruction.
We evaluated bilaterally sagittal plane kinematics and kinetics of the ankle, knee, and hip joints during submaximal squatting exercise in rehabilitating patients after ACL reconstruction. Comparisons were performed between involved and noninvolved limbs, and regression models were created to examine the relations between the bilateral kinetic differences and time postsurgery.
A motion analysis laboratory.
Eight adults (27.9+/-6.8y) with unilateral ACL reconstruction (postsurgical time, 30+/-12wk).
Not applicable.
Sagittal plane ankle, knee, and hip peak net moments of force, maximum joint excursion angles, and peak vertical ground reaction forces.
Peak vertical ground reaction forces did not differ between limbs. The peak knee extensor moment generated during the submaximal squatting exercise was 25.5% greater in the noninvolved limb than in the involved limb (P=.003). The peak ankle plantarflexor moment did not differ between limbs (P=.85); however, there was a trend toward a greater hip extensor moment in the involved limb (P=.06). The ratio of the peak hip extensor moment to the peak knee extensor moment was 46.5% greater in the involved limb (P=.02). Only the peak dorsiflexion angle differed between limbs (P=.02). None of the linear models examining the relations between differences in the involved limb and noninvolved limb kinetics, and postsurgical time, were statistically significant.
Patients performing the squat exercise, within 1 year of ACL reconstructive surgery, used 2 strategies for generating the joint torques required to perform the movement: (1) in the noninvolved limb, patients used a strategy that equally distributed the muscular effort between the hip and knee extensors, and (2) in the involved limb, patients used a strategy that increased the muscular effort at the hip and reduced the effort at the knee. These intra- and interlimb motor-programming alterations (ie, substitution strategies) could potentially slow or limit rehabilitation, and induce strength and performance deficits.
... The observed change in SI for the quadriceps muscle was greater during KE than LP. This would infer this (Signorile et al. 1994), suggesting that the multi-joint parallel squat evokes greater vastus medialis and lateralis EMG response than the knee extension. It should however be recalled that activation of the quadriceps during LP and KE differs through the range of motion. ...
Exercise-induced shifts in signal intensity (SI) of magnetic resonance (MR) images were examined to assess indirectly muscle use in closed- and open-chain knee extensor exercises. Eight men performed five sets of 8-12 repetitions in the leg press (LP) and the seated knee extension (KE) exercises at 50, 75 and 100%, respectively of the 5 x 10 repetition maximum (RM) load. Prior to exercise and after each load setting, images of the thigh were obtained. The increase in SI (Delta SI) of the quadriceps at 100% load was greater (P < 0.05) after KE (32.1 +/- 9.0%) than after LP (21.9 +/- 9.2%). Regardless of load, the four individual muscles of the quadriceps showed similar changes in SI after LP. The three vastii muscles showed comparable increases in SI after KE. M. rectus femoris showed greater (P < 0.05) Delta SI than the vastii muscles at 100%. Neither exercise produced increase in SI of mm. semimembranosus, semitendinosus, gracilis or biceps femoris. Mm. adductor magnus and longus showed increased (13.3 +/- 6.5%; P < 0.05) SI after LP, but not after KE, at 100% load. The present data also infer greater involvement of the quadriceps muscle in the open-chain knee extension than in the closed-chain leg press exercise. The results of the current investigation also indicate similar over-all use among the three vastii muscles in LP and KE, but differential m. rectus femoris use between the two exercises. This report extends the merits of the MR imaging technique as an aid to study individual muscle involvement in a particular exercise task.
... Signorile et al. (11) compared the activation of thigh muscles in squats and leg extensions. The EMG data of the vastus lateralis and vastus medialis showed no significant variation of the root-mean-squared EMG activity in the 2 typologies of exercise. ...
Many strength trainers believe that varying the stance width during the back squat can target specific muscles of the thigh. The aim of the present work was to test this theory measuring the activation of 8 thigh muscles while performing back squats at 3 stance widths and with 3 different bar loads. Six experienced lifters performed 3 sets of 10 repetitions of squats, each one with a different stance width, using 3 resistances: no load, 30% of 1-repetition maximum (1RM), and 70% 1RM. Sets were separated by 6 minutes of rest. Electromyographic (EMG) surface electrodes were placed on the vastus medialis, vastus lateralis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus, gluteus medium, and adductor maior. Analysis of variance and Scheffè post hoc tests indicated a significant difference in EMG activity only for the gluteus maximus; in particular, there was a higher electrical activity of this muscle when back squats were performed at the maximum stance widths at 0 and 70% 1RM. There were no significant differences concerning the EMG activity of the other analyzed muscles. These findings suggest that a large width is necessary for a greater activation of the gluteus maximus during back squats.
... It has been used extensively for therapeutic treatment of ligament lesions, patellofemoral dysfunctions, total joint replacement, and ankle instability (14,56). Moreover, the closed-chain stance required for performance reduces anterior cruciate ligament (ACL) strain (64), making it superior to the knee extension for rehabilitation of ACL injury (21,65). ...
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.
... It is common to suggest that when MJ exercises are performed, many muscles or muscle groups are recruited, and the assumption that some muscles are more or less stimulated is often based on motor unit recruitment analysis. Although it is often believed that a muscle is better stimulated during isolation exercises, the evidence for this assumption is weak; previous studies have not shown increased motor unit recruitment during SJ exercises (Signorile et al. 1994;Wilk et al. 1996;Gentil et al. 2007). It is important to remember that even if a muscle shows increased motor unit recruitment during a given exercise, quantitative analysis of motor unit recruitment might not reflect the physiological stimuli or stress imposed on the muscles. ...
The aim of this study was to examine the effect of adding single-joint (SJ) exercises to a multi-joint (MJ) exercise resistance-training program on upper body muscle size and strength. Twenty-nine untrained young men participated in a 10-week training session. They were randomly divided in 2 groups: the MJ group performed only MJ exercises (lat pulldown and bench press); the MJ+SJ group performed the same MJ exercises plus SJ exercises (lat pulldown, bench press, elbow flexion, and elbow extension). Before and after the training period, the muscle thickness (MT) of the elbow flexors was measured with ultrasound, and peak torque (PT) was measured with an isokinetic dynamometer. There was a significant (p < 0.05) increase in MT (6.5% for MJ and 7.04% for MJ+SJ) and PT (10.40% for MJ and 12.85% for MJ+SJ) in both groups, but there were no between-group differences. Therefore, this study showed that the inclusion of SJ exercises in a MJ exercise training program resulted in no additional benefits in terms of muscle size or strength gains in untrained young men.
... Rabita et al. 8 encontraram maior ativação do RF em relação ao VM e VL tanto pré quanto pós-período de treinamento de força. Signorile et al. 25 reportaram que a atividade elétrica do VM e VL é maior no agachamento do que na extensão de joelho para uma carga de mesma intensidade relativa. Por outro lado, no presente estudo, não foram encontradas diferenças significativas na ativação muscular entre os músculos do quadríceps femoral, possivelmente, pela condição isométrica utilizada, a qual reduz a influência do encurtamento muscular e consequente deslocamento das fibras musculares e do ponto motor em relação aos eletrodos. ...
The aim of this study was to compare maximal isometric force (MIF) and the electrical activity of the vastus medialis, vastus lateralis, rectus femoris, gluteus maximus and biceps femoris long head muscles between maximal voluntary contractions (MVC) performed at different joint angles, and to identify the most suitable positions to normalize the electromyography (EMG) signals from each of these muscles when they are activated under dynamic conditions. Ten men ranging in age from 20 to 30 years, who were familiar with strength training exercise, were studied. MVC at different joint angles of the knee extensors and flexors (0°, 60°, 90°) and hip extensors (-30°, 0°, 60°) and flexors (90°, 120°) were tested. The MIF values differed
significantly between the 60° knee flexion and 60° and 90° knee extension positions (p<0.01). The same was not observed for hip flexion or extension (p>0.05). Significantly higher EMG values were only observed for the rectus femoris muscle at 90° knee extension (p<0.01). No differences between muscles were found for knee flexion, hip flexion or hip extension at the joint angles tested (p>0.05). These results suggest that the 60° knee joint flexion position is the most suitable for assessment of knee extension and flexion MIF, and that all positions tested in this study are suitable for the assessment of hip flexion and extension.
... Although electromyography assessment was not adopted in this study, it can be speculated that the higher values of indirect markers of muscle damage observed for the BS vs. KE exercises can be justified by a greater myoelectric activity in the knee extensor muscles during the first exercise as previously reported by Escamilla et al. (9) and Wilk et al. (24). At the same relative load (10RM), Signorile et al. (21) observed that BS induced a higher electrical activity of the quadriceps muscles compared with KE. In addition, an elevated metabolic demand induced by the higher amounts of muscles evocated during the BS, and consequently, a more pronounced level of fatigue (13) may explain the aforementioned outcomes. ...
de Camargo, JBB, Braz, TV, Batista, DR, Germano, MD, Brigatto, FA, and Lopes, CR. Dissociated time course of indirect markers of muscle damage recovery between single-joint and multi-joint exercises in resistance-trained men. J Strength Cond Res XX(X): 000-000, 2020-This study compared the time course of indirect markers of muscle damage after multi-joint and single-joint exercises. Ten resistance-trained men (years: 26.9 ± 3.0; total body mass: 83.2 ± 13.8 kg; height: 176 ± 7.0 cm; resistance training [RT] experience: 5.5 ± 2.4 years; RT frequency: 5.3 ± 0.7 sessions; relative squat 1 repetition maximum: 1.4 ± 0.3) performed, in a random order, 5 sets of 8 repetition maximum of the back squat (BS) and knee extension (KE) exercises. Rectus femoris muscle thickness (MTRF), leg circumference (LC), and muscle soreness (MS) were recorded at baseline (pre), 0, 12, 24, and 36 hours after each exercise protocol. There was a significant increase (p < 0.05) in dependent variables at every time point after both the multi-joint and single-joint exercise sessions. However, MTRF and LC were greater at 0 and 36 hours, and MS was greater at 24 and 36 hours after BS when compared with KE (all p < 0.05). This study shows that resistance-trained individuals can experience significant higher levels of indirect markers of muscle damage when performing a multi-joint lower-limb exercise compared with a single one.
... 3,13,14 Additionally, it is believed that the strain that some single-joint exercises place on the maturing graft may adversely affect the long-term stability of the reconstructed knee. 13,15,16 Biomechanical, electromyographic, and strain gauge studies have been used to compare and contrast single-and multiple-joint exercises 3,13,15,[17][18][19] ; in response, some authors 10,12 have recommended the exclusive use of multiple-joint exercise and the exclusion of traditional single-joint exercise. ...
Corna S, Nardone A, Prestinari A, Galante M, Grasso M, Schieppati M. Comparison of Cawthorne-Cooksey exercises and sinusoidal support surface translations to improve balance in patients with unilateral vestibular deficit. Arch Phys Med Rehabil 2003;84:1173–84.
... Surface electromyography (sEMG) has been used to examine several aspects of muscle activity during various weight training exercises (4,6,8,14,15,18,20,21). Wright et al. (22) studied normalized, integrated EMG activity of the hamstrings (BF and ST) to compare the efficiency of 3 resistance training exercises, including the leg curl, stiff-leg deadlift (similar to the Romanian deadlift [RDL]), and back squat. ...
The dorsal muscles of the lower torso and extremities have often been denoted the 'posterior chain.' These muscles are used to support the thoracic and lumbar spine as well as peripheral joints including the hip, knee, and ankle on the dorsal aspect of the body. This study investigated relative muscle activity of the hamstring group and selected surrounding musculature during the leg curl, good morning, glute-ham raise, and Romanian deadlift (RDL). Twelve healthy, weight trained men performed duplicate trials of single repetitions at 85% 1RM for each lift in random order, during which surface electromyography and joint angle data were obtained. Repeated measures analysis of variance (RMANOVA) across the four exercises was performed to compare activity from the erector spinae (ES), gluteus medius (GMed), semitendinosus (ST), biceps femoris (BF), and medial gastrocnemius (MGas). Significant differences (p<0.05) were noted in eccentric muscle activity between exercise for the MGas (p<0.027), ST (p<0.001), BF (p<0.001), and ES (p=0.032), and in concentric muscle activity for the ES (p<0.001), BF (p=0.010), ST (p=0.009), MGas (p<0.001), and the GMed (p=0.018). Bonferroni post hoc analysis revealed significant pairwise differences during eccentric actions for the BF, ST, and MGas. Post hoc analysis also revealed significant pairwise differences during concentric actions for the ES, BF, ST, MGas, and GMed. Each of these showed effect sizes that are large or greater. The main findings of this investigation are that the ST is substantially more active than the BF among all exercises, and hamstring activity was maximized in the RDL and glute-ham raise. Therefore, athletes and coaches who seek to maximize involvement of the hamstring musculature should consider focusing on the glute-ham raise and RDL.
... Firstly, it is impractical to add whole body vibration to knee extension as it is not practical to place resistance equipment on to the vibration platform. Secondly, it has previously been shown that squats produce both greater amounts of myoelectrical activity and greater reduction in M DF in the vastus medialis and lateralis compared to knee extension [17]. Shift in MDF has long been used as an indicator of fatigue during isometric contractions [18]. ...
The effects of whole body vibration (WBV) on EMG timing, frequency and amplitude have previously been studied, however to best of the authors knowledge there have been no studies on the effect of WBV on the conduction velocity of myoelectrical signals. Muscle fibre conduction velocity, EMG frequency and amplitude of the vastus lateralis were therefore assessed in twelve male participants (1.81 +/- 0.1 m, 82.2 +/- 10.7 kg, 25.4 +/- 4.0 years) at the start and end of partial static squats, both with and without WBV (40 Hz 1.9 mm vertical displacement). Significant differences were found in the median frequencies, but not in the conduction velocity or signal amplitude. The observed changes are indicative of whole body vibration increasing the vastus lateralis muscle activity but not to a level indicative of physiological fatigue. These observations are of use to exercise and rehabilitation practitioners considering the use of vibration in exercise protocols.
... RE sessions consisted of 3 sets on a leg extension machine followed by 3 sets on a leg press machine (Gym80, Gelsenkirchen, Germany) with a resting phase of 120 s between sets and 180 s between exercises. Both exercises have been shown to sufficiently activate the vastus lateralis muscle [66]. RE requires the standardization of several parameters (e.g., loading, movement speed, and exercise mode) that can affect force generation and muscle activities [67]. ...
The acute resistance exercise (RE)-induced phosphorylation of mTOR-related signaling proteins in skeletal muscle can be blunted after repeated RE. The time frame in which the phosphor-ylation (p) of mTOR S2448 , p70S6k T421/S424 , and rpS6 S235/236 will be reduced during an RE training period in humans and whether progressive (PR) loading can counteract such a decline has not been described. Aim: (1) To enclose the time frame in which pmTOR S2448 , prpS6 S235/236 , and pp70S6k T421/S424 are acutely reduced after RE occurs during repeated RE. (2) To test whether PR will prevent that reduction compared to constant loading (CO) and (3) whether 10 days without RE may re-increase blunted signaling. Methods: Fourteen healthy males (24 ± 2.8 yrs.; 1.83 ± 0.1 cm; 79.3 ± 8.5 kg) were subjected to RE with either PR (n = 8) or CO (n = 6) loading. Subjects performed RE thrice per week, conducting three sets with 10-12 repetitions on a leg press and leg extension machine. Muscle biopsies were collected at rest (T0), 45 min after the first (T1), seventh (T7), 13th (T13), and 14th (X-T14) RE session. Results: No differences were found between PR and CO for any parameter. Thus, the groups were combined, and the results show the merged values. prpS6 S235/236 and pp70s6k T421/S424 were increased at T1, but were already reduced at T7 and up to T13 compared to T1. Ten days without RE re-increased prpS6 S235/236 and pp70S6k T421/S424 at X-T14 to a level comparable to that of T1. pmTOR S2448 was increased from T1 to X-T14 and did not decline over the training period. Single-fiber immunohistochemistry revealed a reduction in prpS6 S235/236 in type I fibers from T1 to T13 and a re-increase at X-T14, which was more augmented in type II fibers at T13 (p < 0.05). The entity of myofibers revealed a high heterogeneity in the level of prpS6 S235/236 , possibly reflecting individual contraction-induced stress during RE. The type I and II myofiber diameter increased from T0 and T1 to T13 and X-T14 (p < 0.05) Conclusion: prpS6 S235/236 and pp70s6k T421/S424 reflect RE-induced states of desensitization and re-sensitization in dependency on frequent loading by RE, but also by its cessation.
... Differences (p<0.05) in response for any particular muscle group between KE and LP are denoted by à muscle is more involved during KE than supine LP. At first, this may appear to contrast other observations ( Signorile et al. 1994), suggesting that the multi-joint parallel squat evokes greater vastus medialis and lateralis EMG response than the knee extension. It should however be recalled that activation of the quadriceps during LP and KE differs through the range of motion. ...
... The effect of foot placement angles has primarily been investigated by examining the change in electromyography muscle activity [12][13][14][15][16] but also by kinematic and kinetic analyses. While stance width affects muscle activity in the lower extremities, varying foot placement angles during squats does not seem to play a major role on either muscle activity or knee joint contact forces [17,18]. ...
Background
Squatting is a core exercise for many purposes. The tissue loading during squatting is crucial for positive adaptation and to avoid injury. This study aimed to evaluate the effect of narrow, hip and wide stance widths, foot position angles (0°, 21°, and 42°), strength exercise experience, and barbell load (0 and 50% body weight, experts only) during squatting.
Methods
Novice (N = 21) and experienced (N = 21) squatters performed 9 different variations of squats (3 stance widths, 3 foot placement angles). A 3D motion capture system (100 Hz) and two force plates (2000 Hz) were used to record mediolateral knee displacement (ΔD*), range of motion (RoM) at the hip and knee joints, and joint moments at the hip, knee, and lower back.
Results
Both stance width and foot placement angles affected the moments at the hip and knee joints in the frontal and sagittal planes. ΔD* varied with stance width, foot placement angles and between the subjects’ level of experience with the squat exercise as follows: increasing foot angle led to an increased foot angle led to an increased ΔD*, while an increased stance width resulted in a decreased ΔD*; novice squatters showed a higher ΔD*, while additional weight triggered a decreased ΔD*.
Conclusions
Suitable stance width and foot placement angles should be chosen according to the targeted joint moments. In order to avoid injury, special care should be taken in extreme positions (narrow stand-42° and wide stance-0°) where large knee and hips joint moments were observed.
Electronic supplementary material
The online version of this article (10.1186/s13102-018-0103-7) contains supplementary material, which is available to authorized users.
... Most of these studies have focused on the knee biomechanics with the aim of enhancing the strength performance and minimizing the injury risk [4,37,228,280]. As such, the closed chain nature of the squat has been shown to reduce the anterior cruciate ligament strain thereby proving its rehabilitation superiority compared to the knee extension exercise [241,287]. Even though some of these studies also calculated knee joint reaction forces during deep squatting [74,97,280], none report on the HJRF during deep squatting in young adults. ...
The hip functions as a ball and socket joint, with cartilage layers that cover the joint surfaces on both sides protecting it from impacts and permitting smooth movements. When the cartilage is impaired by mechanical, infectious or inflammatory causes, the joint might eventually wear down - a disabling condition known as osteoarthritis. Recent literature indicates that up to 80\% of all osteoarthritis cases are potentially caused by subtle hip variations: the round shape of the ball (femur head) that is disturbed by a bump or/and the socket (acetabulum) that overcovers the femur head. These abnormal variants can give rise to conflicts and altered load distribution in the hip joint. When the load on the joint is no longer evenly distributed, peak stresses can arise in certain areas of the hip posing a risk of developing focal cartilage damage. Since the apparent prevalence of these morphological hip abnormalities is reported to be much higher than the number of actual patients, the question remains how to differentiate potential patients from incidental findings.The aim of this thesis was to describe and explore the impact of shape variation in the hip joint and by doing so improve the understanding of the mechanical environment of the hip joint. First differences in hip anatomy between white and Chinese subjects were mapped using a cross sectional design. Pelvic computed tomography scans of 201 subjects (99 white Belgians and 102 Chinese; 105 men and 96 women; 18-40 years old) were assessed. Ten radiographic parameters predisposing to femoroacetabular impingement were evaluated. The white subjects had a less spherical femoral head than the Chinese subjects. The Chinese subjects had less lateral acetabular coverage than the white subjects. A shallower acetabular configuration was predominantly present in Chinese women. Static and dynamic variation in hip joint reaction forces was evaluated using an experimental computational modeling design. We therefore calculated the hip joint reaction force and hip flexion angle in a virtual representative male Caucasian population by means of musculoskeletal modeling of three distinct sitting configurations: a simple chair, a car seat and a kneeling chair configuration. The observed median hip joint reaction force in relation to body weight and hip flexion angle, respectively, was 22.3$\%$ body weight and 63° for the simple chair, 22.5$\%$ body weight and 79° for the car seat and 8.7$\%$ body weight and 50° for the kneeling chair. The kneeling chair appears to hold the greatest potential as an ergonomic sitting configuration for the hip joint since it requires the lowest hip flexion angle and hip joint reaction force of these 3 distinct sitting configurations. Dynamic mapping of deep squat hip kinetics was performed in young, athletic adults using a personalized numerical model solution based on inverse dynamics. Thirty-five healthy subjects underwent deep squat motion capture acquisitions and MRI scans of the lower extremities. Musculoskeletal models were personalized using each subject’s lower limb anatomy. The average peak hip joint reaction force was found to be 274$\%$ body weight. Average peak hip and knee flexion angles were 107° and 112° respectively. Deep squatting kinetics in the younger population differ substantially from the previously reported in vivo data in older subjects. In order to map variation in cartilage stress, a numerical discrete element analysis algorithm was developed. A validation study with hip joint contact stress data from 10 healthy subjects calculated by means of subject-specific finite element analysis was performed. Furthermore an efficient cartilage anatomy prediction tool was defined that does not require manual cartilage image segmentation. We showed that this novel population-averaged cartilage anatomy prediction method, integrated with the discrete element analysis algorithm could provide an efficient platform to predict cartilage contact stresses in large populations compared to subject specific finite element analysis. The mechanical effect of arthroscopic cam resection in femoroacetabular impingement was explored with a case-control study design. For this purpose, patient-specific discrete element models from 10 cam type femoroacetabular patients (all male, aged 18-40 years old) were defined based on preoperative CT and postoperative MRI scans. Complete cam resection postoperatively on MRI was confirmed with alpha angles $<$ 55°. The preoperative and postoperative peak contact stress findings during impingement testing were compared against a matched virtual control group. Peak contact stress was significantly elevated in patients with cam type femoroacetabular impingement during impingement testing with increasing amount of internal rotation. This effect was however normalized following arthroscopic cam resection and loading patterns matched those of the control group. Using multidimensional statistics and personalized load and stress predictions, we were able to demonstrate that the important population variation in shape and joint mechanics adds to differences in the onset and progression of cartilage lesions of the hip joint. Further, our work contributes to an improved identification and classification of patients who are truly at risk for developing cartilage damage. The final step of this thesis was to gradually transfer these findings into practice at the operating theater. We demonstrated that an accurate surgical treatment of cam lesions has the potential to effectively restore the normal mechanical environment of the hip.
... EMG activity depends on multiple factors, such as length of the muscle, number of the joints involved in the exercise [27][28][29] , configuration of the training load 6,30 and subject´s training status. Under a high force requirement the neuromuscular system would demand a recruitment of MU close to maximal, however, for the submaximal efforts it is possible that this recruitment occurs in a different manner, depending on the situation and even on the subject, with the purpose of maintaining the efficiency of the task. ...
This study investigate the effect of 10-week strenght training on the amplitude of the electromyographic (EMG) signal of vastus medialis, vastus lateralis and rectus Femoris. Twenty three untrained volunteers performed 3-5 sets (3 sets-weeks 1 and 2; 4 series-weeks 3 and 4; 5 series weeks 5 to 10) with 6 repetitions, intensity of 50% of 1 repetition maximum (1RM), 3 min rest between sets and 6 s repetition duration at the knee extensor exercise. One group (5:1) performed concentric action of 5 s and eccentric of 1 s and the other (3:3) performed concentric of 3 s and eccentric of 3 s. The VM, VL and RF EMG (RMS) activities were recorded in each repetition of the three series at the first training session and the first three series at the last session. The protocol 5:1 led to EMG reduction in all portions, with a greater number of repetitions presenting differences at the VL and RF. VM and RF presented similar results at Group 3:3. It was verified that all the differences occurred in the second half of the series. It was also verified differences in EMG ratios just in group 3:3 and only in VM/ VL and VM/RF. These results suggest that the coordination was not affected when equivalent repetitions of series were compared. It was also suggested that these results were influenced by the reduced degrees of freedom of the exercise and the training load progression adopted. Resumo-Este estudo investigou o efeito de 10 semanas de treinamento de força na resposta eletro-miográfica (EMG) do vasto medial, vasto lateral e reto femoral. 23 voluntárias executaram 3 a 5 séries de 6 repetições, intensidade de 50% de 1 repetição máxima (RM), 3 minutos de pausa entre as séries e duração da repetição de 6 s no exercício extensor de joelhos. Um grupo (5:1) realizou a duração da ação concêntrica em 5 s e excêntrica em 1s e outro grupo (3:3) realizou a concêntrica em 3s e a excêntrica em 3s. A atividades EMG (RMS) destas três porções do quadríceps foram registradas em cada repetição das 3 séries da primeira sessão de treinamento e nas três primeiras séries da última sessão. Os resultados mostraram diferenças na metade final das séries, sendo que no grupo 5:1 houve redução na EMG em todas as porções e o VL e o RF mostraram redução em um número maior de repetições. No grupo 3:3 o VM e o RF apresentaram redução. Para as relações de ativação entre as porções, diferenças foram identificadas apenas no grupo 3:3 nas relações VM/VL e VM/RF em um número reduzido de repetições. Estes resultados apontam que a coordenação entre as porções sofreu poucas alterações quando comparadas as repetições equivalentes de cada série. Sugere-se que os reduzidos graus de liberdade do movimento utilizado e a progressão da carga de treinamento tenham sido os fatores que conduziram a este resultado
... The first known study to compare muscle activity between SJ and MJ exercises was published by Signorile et al. [37], who measured sEMG amplitude of the quadriceps muscles of trained males while performing 10 repetition maximum (RM) MJ (parallel squats) and SJ (knee extensions) exercises. Tests were performed in two sessions, 1 week apart. ...
Resistance exercises can be considered to be multi-joint (MJ) or single-joint (SJ) in nature. Many strength coaches, trainers, and trainees believe that adding SJ exercises to a resistance training (RT) program may be required to optimize muscular size and strength. However, given that lack of time is a frequently cited barrier to exercise adoption, the time commitment resulting from these recommendations may not be convenient for many people. Therefore, it is important to find strategies that reduce the time commitment without negatively affecting results. The aim of this review was to analyze and discuss the present body of literature considering the acute responses to and long-term adaptations resulting from SJ and MJ exercise selection. Studies were deemed eligible for inclusion if they were experimental studies comparing the effects of MJ, SJ, or MJ ? SJ on dependent variables; studies were excluded if they were reviews or abstracts only, if they involved clinical populations or persons with articular or musculoskeletal problems, or if the RT intervention was confounded by other factors. Taking these factors into account, a total of 23 studies were included. For the upper and lower limbs, analysis of surface electromyographic (sEMG) activation suggests that there are no differences between SJ and MJ exercises when comparing the prime movers. However, evidence is contrasting when considering the trunk extensor musculature. Only one study directly compared the effects of MJ and SJ on muscle recovery and the results suggest that SJ exercises resulted in increased muscle fatigue and soreness. Long-term studies comparing increases in muscle size and strength in the upper limbs reported no difference between SJ and MJ exercises and no additional effects when SJ exercises were included in an MJ exercise program. For the lumbar extensors, the studies reviewed tend to support the view that this muscle group may benefit from SJ exercise. People performing RT may not need to include SJ exercises in their program to obtain equivalent results in terms of muscle activation and long-term adaptations such as hypertrophy and strength. SJ exercises may only be necessary to strengthen lumbar extensors and to correct muscular imbalances.
... The effect of foot placement angles has primarily been investigated by examining the change in electromyography muscle activity [12][13][14][15][16] but also by kinematic and kinetic analyses. While stance width affects muscle activity in the lower extremities, varying foot placement angles during squats does not seem to play a major role on either muscle activity or knee joint contact forces [17,18]. ...
Following publication of the original article [1], the authors reported an error in the following sentence on page 8: “In general, knee varus (negative ΔD*) is a much more common deficit than valgus, and a more negative ΔD* value in the novice squatters compared to the experienced ones was therefore expected.”
... Most of these studies have focused on the knee biomechanics with the aim of enhancing the strength performance and minimizing the injury risk (Wilk et al. 1996;Salem et al. 2003;Adouni and Shirazi-Adl 2009;Bersini et al. 2016). As such, the closed chain nature of the squat has been shown to reduce the anterior cruciate ligament strain thereby proving its rehabilitation superiority compared to the knee extension exercise (Yack et al. 1993;Signorile et al. 1994). Even though some of these studies also calculated knee joint reaction forces during deep squatting (Dahlkvist et al. 1982;Wilk et al. 1996;Escamilla et al. 2001b;Han et al. 2013), none report on the hip joint reaction force (HJRF) during deep squatting in young adults. ...
The goal of this study was to report deep squat hip kinetics in young, athletic adults using a personalized numerical model solution based on inverse dynamics. Thirty-five healthy subjects underwent deep squat motion capture acquisitions and MRI scans of the lower extremities. Musculoskeletal models were personalized using each subject’s lower limb anatomy. The average peak hip joint reaction force was 274 percent bodyweight. Average peak hip and knee flexion angles were 107° and 112° respectively. These new findings show that deep squatting kinetics in the younger population differ substantially from the previously reported in vivo data in older subjects.
... Moreover, Yamashita et al. [34] found that rectus femoris myoelectric activity was markedly depressed during combined hip and knee extension compared to the vastus medialis. In addition, there are studies showing that SJ exercise produces greater overall EMG myoelectric activity and MRI contrast shifts compared to MJ [28,32], although other studies contradict these findings [35,36]. Overall, these data suggest that simply performing MJ movements is not sufficient to maximally engage the rectus femoris and perhaps the quadriceps as a whole, which in turn potentially may have implications on long-term muscular development. ...
Resistance training volume, determined by the number of sets performed (set-volume) is considered one of the key variables in promoting muscle hypertrophy. To better guide resistance exercise prescription for weekly per-muscle training volume, the purpose of this paper is to provide evidence-based considerations for set-volume ratios between multi-joint (MJ) and single-joint (SJ) exercises so that practitioners can better manage prescription of training volume in program design. We analyzed this topic from three primary areas of focus: (1) biomechanical and physiological factors; (2) acute research; and (3) longitudinal research. From a biomechanical and physiological standpoint, when considering force production of different muscle groups, the moment arm of a given muscle, “motor abundance”, the link between biomechanics and exercise-induced fatigue, as well as the amount of time in voluntary muscle activation, a logical rationale can be made for SJ exercises producing greater hypertrophy of the limb muscles than MJ exercises (at least from specific exercises and under certain conditions). This would mean that sets for a MJ exercise should be counted fractionally for select muscles compared to an SJ exercise (i.e., less than a 1:1 ratio) when prescribing set-volumes for given muscles. When considering results from acute studies that measured muscle activation during the performance of SJ and MJ exercises, it seems that MJ exercises are not sufficient to maximize muscle activation of specific muscles. For example, during performance of the leg press and squat, muscle activation of the hamstrings is markedly lower than that of the quadriceps. These results suggest that a 1:1 ratio cannot be assumed. Current longitudinal research comparing the effects of training with MJ vs. SJ or MJ + SJ exercises is limited to the elbow flexors and the evidence is somewhat conflicting. Until more research is conducted to derive stronger conclusions on the topic, we propose the best advice would be to view set-volume prescription on a 1:1 basis, and then use logical rationale and personal expertise to make determinations on program design. Future research should focus on investigating longitudinal hypertrophic changes between MJ and SJ in a variety of populations, particularly resistance-trained individuals, while using site-specific measures of muscle growth to more systematically and precisely compute effective individualized set-volumes.
... surface EMG (sEMG) and intramuscular EMG (iEMG Others have then analysed the muscular activity of the HBBS in comparison to common therapeutic exercises (Andersen et al., 2006;Hamlyn, Behm, & Young, 2007;Nuzzo, McCaulley, Cormie, Cavill, & McBride, 2008), open kinetic chain exercises (Escamilla et al., 1998;Maddigan, Button, & Behm, 2014;Signorile et al., 1994;Wilk et al., 1996), the frontsquat (Gullett, Tillman, Gutierrez, & Chow, 2009;Yavuz, Erdağ, Amca, & Aritan, 2015), and single-leg squats (DeForest, Cantrell, & Schilling, 2014;McCurdy et al., 2010). Furthermore, the HBBS has been used to demonstrate differences in muscular activity resulting from training status / experience (Panissa, Azevedo Neto, Julio, Pinto E Silva, & Franchini, 2013;Pick & Becque, 2000), training time-of-day (Sedliak, Finni, Peltonen, & Hakkinen, 2008), and to examine the existence of a 'sticking point' (van den Tillaar, Andersen, & Saeterbakken, 2014). ...
The barbell back-squat is one of the most common exercises in strength and conditioning practice; especially in Olympic weightlifting and powerlifting. There are two main bar placements within the back-squat; the high-bar and low-bar positions. The high-bar position, favoured by Olympic weightlifters, closely resembles the upright body position of the two competition lifts of the sport; the snatch and clean and jerk. The low-bar position, favoured by powerlifters, typically allows greater loads to be lifted by utilising the posterior-chain musculature during the back-squat (one of the three competition lifts in the sport). Unfortunately, little research exists comparing the high-bar back-squat with the low-bar back-squat, and no research has examined either lift above 90% of one repetition maximum. Furthermore, no authors have biomechanically compared the high-bar back-squat to the Olympic lifts (e.g. snatch and clean and jerk). The aims of this thesis were to (1) review the current literature and quantitatively assess the kinetic and kinematic findings among the limited research; (2) compare and contrast the high-bar back-squat and low-bar back-squat up to maximal effort; and (3) assess the differences and/or similarities between the high-bar back-squat and the Olympic lifts. Through an extensive literature review, the high-bar back-squat was found to commonly present a larger hip angle, smaller knee angle and equivalent ankle angle compared to the low-bar back-squat; inferring the high-bar placement creates a more upright truck position for the lifter and requires more quadriceps muscle activation. Experimentally, these findings were confirmed with the high-bar back-squat producing larger hip angles and smaller knee angles compared to the powerlifters (16–21% larger and 10–12% smaller, respectively) and low-bar controls (16–21% larger and 10–12% smaller, respectively). While the Olympic weightlifters and powerlifters lifted similar relative loads, the low-bar controls were able to lift 2.5–5.2% larger relative loads compared to the high-bar controls. As expected, the high-bar back-squat also showed similar kinematics to the snatch and the clean but substantially different kinetics across all loads lifted. Performing a back-squat with a low-bar placement, situates the lifter (advanced and recreational) in a stronger position to lift larger loads compared to the high-bar placement. The establishment of a more advantageous kinematic posture during the low-bar back-squat could potentially maximise the utilisation of the stronger posterior hip musculature thus increasing the stability and moment arm at the hip. The low-bar back-squat therefore appears to provide the best chance of lifting the largest relative load. The kinematic similarities in posture between the high-bar back-squat and the Olympic lifts suggests the potential of similar trunk, hip and thigh muscular activity of key stabilising muscles and repetitive positional alignment in the “catch” position. The differing kinetics however, are more likely due to technical differences between the high-bar back-squat, snatch and clean; wherein the Olympic lifts require additional elements of upper-body strength and stability. The high-bar back-squat does appear to yield an efficient carryover to the Olympic lifts as a suitable supplementary exercise; provided the technical components of the lifts are maintained.
... However, this is improbable, since previous research found that quadriceps muscle activation was similar during leg press and knee extension exercises (Wilk et al., 1996). Moreover, previous studies found that there were no differences in muscle activity (Signorile et al., 1994;Welsch et al., 2005) and muscle strength gains (Gentil et al., 2015b) when multi joint exercises were compared to single joint ones. ...
The purpose of this study was to compare strength gains in the lower limbs, assessed by one maximum repetition (1RM) and isokinetic peak torque (PT), in young men undergoing a resistance training (RT) program. Twenty-seven young men performed resistance training twice a week for 11 weeks. Training involved two exercises for the lower body, two for the upper body and one for the midsection performed with three sets of 8-12 repetitions to momentary muscle failure. Before and after the training period, participants performed the 1RM test in the 45° leg press and knee extension PT in isokinetic dynamometry. The Pearson correlation coefficient was used to assess the relationship between the changes in 1RM and PT, and the Bland-Altman test was performed to check for agreement between the strength changes of both tests. There were significant changes in 1RM and PT of 23.98% and 15.96%, respectively (p < 0.05). The changes in leg press 1RM were significantly higher than the ones in PT. The Bland-Altman analysis revealed that the tests were not equivalent. In conclusion, professionals and researchers involved in strength assessment should be aware that the results obtained by PT and 1RM are not equivalent when evaluating individual responsiveness and/or the efficacy of an intervention on muscle strength, as the results obtained show large variations and can be even conflicting.
... In pivot throwing, greater activation of the gastrocnemius, tibialis anterior, and hamstrings appeared in the pivot foot in wide stance, whereas the stride foot demonstrated greater activation of the gastrocnemius, tibialis anterior, and quadriceps femoris in wide stance, suggesting that adopting the wide stance in pivot throwing maximizes muscle activation in the lower limb. From the lower-limb kinematics perspective, previous studies have revealed the greatest muscle activation in the quadriceps femoris, hamstrings, and gastrocnemius at knee flexion angles of 80° to 90° (Escamilla et al., 2001;Isear et al., 1997;Ninos et al., 1997;Signorile et al., 1994;Stuart et al., 1996), 50° to 70° (Escamilla et al., 1998;Wilk et al., 1996), and 60° to 90° (Escamilla et al., 1998;Isear et al., 1997), respectively. The knee flexion angle in wide stance of weight-shift throwing was found to be similar to the flexion angle for maximum muscle activation; thus the catcher could have greater muscle activation in wide stance. ...
This study investigated the differences in joint motions and muscle activities of the lower extremities involved in various squatting postures. The motion capture system with thirty-one reflective markers attached on participants was used for motion data collection. The electromyography system was applied over the quadriceps, biceps femoris, tibialis anterior, and gastrocnem-ius muscles of the pivot and stride leg. The joint extension and flexion in wide squatting are greater than in general squatting (p = 0.005). Knee joint extension and flexion in general squatting are significantly greater than in wide squatting (p = 0.001). The adduction and abduction of the hip joint in stride passing are significantly greater than in step squatting (p = 0.000). Further-more, the adduction and abduction of the knee joint in stride passing are also significantly greater than in step squatting (p = 0.000). When stride passing is performed, the muscle activation of the hamstring of the pivot foot in general squatting is significantly greater than in wide squatting (p < 0.05), and this differ-ence continues to the stride period. Most catchers use a general or wide squatting width, exclusive of a narrow one. Therefore, the training design for strengthening the lower extremity mus-cles should consider the appropriateness of the common squat width to enhance squat-up performance. For lower limb muscle activation, wide squatting requires more active gastrocnemius and tibialis anterior muscles. Baseball players should extend the knee angle of the pivot foot before catching the ball.
The aim of this study was to analyze electromyography (EMG) responses of vastus lateralis muscle to different whole-body vibration frequencies. For this purpose, 16 professional women volleyball players (age, 23.9 +/- 3.6 years; height, 182.5 +/- 11.1 cm; weight, 78.4 +/- 5.6 kg) voluntarily participated in the study. Vibration treatment was administered while standing on a vibrating platform with knees bent at 100 degrees (Nemes Bosco-system, Rome, Italy). EMG root mean square (rms) and was recorded for 60 seconds while standing on the vibrating plate in the following conditions: no vibrations and 30-, 40-, and 50-Hz vibration frequencies in random order. The position was kept for 60 seconds in each treatment condition. EMGrms was collected from the vastus lateralis muscle of the dominant leg. Statistical analysis showed that, in all vibration conditions, average EMGrms activity of vastus lateralis was higher than in the no-vibration condition. The highest EMGrms was found at 30 Hz, suggesting this frequency as the one eliciting the highest reflex response in vastus lateralis muscle during whole-body vibrations in half-squat position. An extension of these studies to a larger population appears worthwhile to further elucidate the responsiveness of the neuromuscular system to whole-body vibrations administered through vibrating platforms and to be able to develop individual treatment protocols.
Objectives: This case report describes in detail the rehabilitation exercise program, provide postoperative therapeutic objectives/recommendations and to facilitate the return to a possible schedule of ADL and participation in sports after the surgical treatment of quadriceps tendon rupture. Also, the exact surgical technique is described.
Design: A single case report.
Participant: The patient was an active 53-year-old man who sustained this injury as a result of a sudden misstep with his left foot into a hole, while he was trekking across muddy countryside. Clinical examination of the knee revealed skin ecchymosis, swelling and tenderness over the distal thigh. Plain radiographs showed patella baja, and the scheduled magnetic resonance imaging (MRI) showed interrupted continuity of the quadriceps tendon and the patella. A diagnosis of quadriceps tendon rupture was made and the patient was scheduled to undergo surgical intervention the following day.
Rehabilitation exercise program: A well-structured rehabilitation exercise program was followed in order to ensure rapid recovery and good functional outcomes. His postoperative course progressed normally, demonstrating a return to the normal activities of daily living at 6 weeks, full active range of motion at 16 weeks, and return to sports recreational activities at 5 months.
Conclusions: An early surgical treatment and subsequently a well-structured rehabilitation exercise program have contributed to maximize the functional outcomes of the patient and provide a rapid and safe return to the activities of daily living (7th week) with participation in non-contact sports after the 18th week.
To compare different types of rehabilitation for anterior knee pain.
Prospective, randomized, blinded, and controlled study of 64 participants with anterior knee pain.
Outpatient rehabilitation clinic and testing laboratory.
Participants were assigned in randomized fashion to three rehabilitation groups: traditional home rehabilitation (n = 20); physical therapy (n = 21); and home rehabilitation with a modified vastus medialis obliquis (VMO) specific straight leg raise (Muncie method; n = 23).
Clinical data was obtained at 0, 2, 6, and 12 weeks. Cybex testing was performed at 0, 6, and 12 weeks.
Clinical outcome for the Muncie method indicated a statistically significant improvement in subjective pain and functional impairment ratings. Cybex testing in patients using the Muncie method demonstrated a statistically significant improvement in pain-free isometric contractions and maximum voluntary contraction. There were no significant differences between traditional home therapy and physical therapy.
Findings suggest that the Muncie method results in improved clinical outcome at a lower cost than traditional home and physical therapy and possibly improved VMO/quadriceps muscle balance. Patients with anterior knee pain may benefit from applying the Muncie method in a home therapy program.
Muscle activations and knee joint loads were compared during squatting and lunging before and after lower extremity neuromuscular fatigue. Electromyographic activations of the rectus femoris, vastus lateralis and biceps femoris, and the external knee adduction and flexion moments were collected on 25 healthy women (mean age 23.5 years, BMI of 23.7 kg/m2) during squatting and lunging. Participants were fatigued through sets of 50 isotonic knee extensions and flexions, with resistance set at 50% of the peak torque achieved during a maximum voluntary isometric contraction. Fatigue was defined as a decrease in peak isometric knee extension or flexion torque ⩾25% from baseline. Co-activation indices were calculated between rectus femoris and biceps femoris; and between vastus lateralis and biceps femoris. Fatigue decreased peak isometric extension and flexion torques (p<0.05), mean vastus lateralis activation during squatting and lunging (p<0.05), and knee adduction and flexion moments during lunging (p<0.05). Quadriceps activations were greater during lunging than squatting (p<0.05). Thus, fatigue altered the recruitment strategy of the quadriceps during squatting and lunging. Lunging challenges quadriceps activation more than squatting in healthy, young women.
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.
There is a paucity of research into the importance of performing strength training exercises in postures specific to the movements they are attempting to facilitate. In addressing this question, 27 previously trained subjects were randomly allocated into heavy weight training and control groups. The weight training group performed 4-6 sets of 6-10 repetitions of the squat and bench press lifts twice a week for 8 weeks. Prior to and after the training period the following tests were conducted: bench press throw at 30% of maximal load, vertical jump, maximal squat and bench press lifts, push-up test performed over a force platform, 40-m sprint, 6-s cycle, and isokinetic tests assessing upper and lower body musculature in varying actions. The results supported the concept that posture is important in training as those exercises conducted in similar postures to the training recorded the greatest improvement in performance. For example, after completion of the training the weight training subjects significantly increased by approximately 12% the maximal load lifted in the bench press exercise and the peak torque in the isokinetic bench press test. However, performance in the isokinetic horizontal arm adduction test was not significantly changed. We speculate that the phenomenon of posture specificity may, at least in part, be caused by the differing postures altering the neural input to the musculature. The results stress the importance of selecting exercises in which the posture closely resembles that of the movements they are attempting to facilitate.
Traditional models of speed-accuracy relations and limb control are steady-state models that fail to consider the learning history and strategic approach of the performer. Work from this laboratory indicates that a performer adjusts his/her behaviour from trial-to-trial to optimise not only the speed and accuracy of performance, but also energy expenditure. Because some errors have greater temporal and energy costs than others, most performers execute movements that are prepared such that potential errors are of minimal expense. The trajectories and subsequent endpoint distributions of rapid aiming movements depend on advance knowledge about the availability of afferent information for online control, as well as the costs associated with undershooting or overshooting the target position with the initial impulse. With practice, a performer is able to reduce the trial-to-trial variability associated with goal-directed movement through more consistent movement planning processes and more rapid online control. Part of the optimisation process is related to the development of an internal model of performance against which early afferent feedback can be evaluated. This framework for examining speed, accuracy and energy expenditure in goal-directed reaching can be used to help understand the breakdown of efficient limb control due to fatigue, ageing and pathology.
Resistance training increases strength in adults, however, the debate over whether or not adolescents and pre-adolescents can achieve similar gains continues. Safety concerns with respect to children’s strength training is also of major concern for all involved. This paper will briefly review current literature and examine the positions of organisations such as the National Strength and Conditioning Association (NSCA), Sports Medicine Australia (SMA) and the American Orthopaedic Society for Sports Medicine (AOSSM). The research into children’s resistance training involves both pre-adolescents and adolescents, and pre-pubescent and pubescent children with the majority focused on pre-adolescents (classification usually made using Tanner, 1962). Throughout this paper the term ‘children’ will be used to refer to both of these groups.
This paper reviews strength increases in children and explores the physiological factors involved. Motor control, range of motion and other benefits will also be addressed. The information reviewed will be synthesised to address the questions of frequency, intensity, duration, number of sets and compound or isolated exercises. This paper will recommend guidelines for Children’s Resistance Training Programs and thereby enable those people working with children to make better-informed decisions regarding resistance training.
Understanding the 'human operator' is a central concern of both ergonomists and sport and exercise scientists. This cutting-edge collection of international research papers explores the interface between physical, cognitive and occupational ergonomics and sport and exercise science, illuminating our understanding of 'human factors' at work and at play. Drawing on a wide diversity of disciplines, including: applied anatomy biomechanics physiology engineering psychology design The book explores themes of central importance within contemporary ergo-nomics and sport and exercise science, such as performance, health, environment , technology and special populations. Contemporary Sport, Leisure and Ergonomics establishes important methodological connections between the disciplines, advancing the research agenda within each. It is essential reading for all serious ergonomists and human scientists.
Six experienced lifters performed 3 squats in each of 4 foot positions: -10[degrees] inward, 0[degrees], 10[degrees] outward, and 20[degrees] outward. These were performed at 2 weight conditions: 65 and 75% of 1 repetition maximum. Surface electromyographic activity of the vastus medialis, vastus lateralis, and rectus femoris on the right leg was analyzed in terms of the activity duration and peak levels of activity. Results and analysis of variance indicated that the foot rotation position did not influence the mean peak activity or mean duration of activity of vastus medialis, vastus lateralis, or rectus femoris. The practice of adopting foot rotation to selectively strengthen individual muscles of the quadriceps group was not supported by this study, which involved smaller, more readily adopted, and comfortable levels of foot rotation than did those previously investigated.
(C) 2000 National Strength and Conditioning Association
The purpose of the present study was to compare myoelectric activity of selected lower limb muscles during squat, leg press and hack squat exercises performed with different loads. Ten powerlifter males (age: 27 ± 4.85 yrs; height: 177 ± 5098 cm; weight: 80±12.13 kg) were participated in the study. Subjects performed all three exercises namely, squat, leg press and hack squat at 70% and 90% of their one-repetition maximum (1 RM). Surface electromyographic signals from peroneus longus, medial gastrocnemius, tibialis anterior, vastus medialis, vastus laterlis, biceps femoris, semitendinosus, adductor longus and tensor fascia muscles were recorded using ME 6000 system at a sampling frequency of 2000 HZ while performing each exercise. ANOVAs with repeated measures were employed for statistical analysis (p<0.05). The results indicated a greater myoelectric activity for vastus medialis and vastus lateralis muscles during performing hack squat and the squat exercises in comparison to the leg press exercise at different loads. The hack squat machine takes the pressure off the back and hips so can be used as a safe exercise for strengthen the quadriceps muscle group. Therefore, hack squat exercise could be recommended as a suitable exercise for both squat and leg press exercises among individuals with low back pain and sport injuries.
Objective: To investigate the relationship between strength and electromyographic (EMG) signal in different intensities in the bench press exercise. Methods: Eleven healthy resistance trained men (22.8 ± 3.5) participated into the present study. Maximal isometric strength was determined in the bench press exercise using a load cell. Muscle activation was assessed using surface electromyography (EMG) signals from the muscles pectoralis major, anterior deltoid and posterior deltoid at intensities ranging to 60-90% of maximal voluntary contraction (MVC), in the bench press exercise. This procedure allowed the analysis of the strength/EMG relationship. Results: In all muscles assessed, there were significant differences in the normalized muscle activation between the intensities of 60 and 70% of the MVC, as well as between 70 and 80% (P < 0.05), while there were no differences between 80 and 90% of MVC. In addition, there were significant correlations between strength and EMG signals for the muscles pectoralis major (r = 0.43, P = 0.04), anterior deltoid (r = 0.52, P = 0.01), and posterior deltoid (r = 0.32, P = 0.046). Conclusions: These results suggest that levels of muscle activation near to maximal are obtained at the intensity of 80 of MVC and no additional motor unit recruitment are achieved at 90% of MVC.
BACKGROUND: Joint instability may be a key agent contributing to the progress of developmental dysplasia of the hip (DDH). Neurac technique is a new modality focused on activating neuromuscular function and improving joint stability. Neurac technique may be helpful for delayed diagnosed DDH. OBJECTIVE: To observe the therapeutic efficacy of Neurac training on DDH patients. METHODS: A female patient of 23 years old with delayed diagnosed DDH received Neurac training for 14 days was retrospective analyzed. RESULTS AND CONCLUSION: The pain was relieved at 14 day after treatment. The Harris scoring showed that the hip function was improved. At 6 months follow-up, the results indicated that the remission was kept fine. Patient with delayed diagnosed DDH may get fine remission of pain and function through Neurac treatments. The effectiveness can last for a long time.
[Purpose] A leg press generally included in a weight training program to develop the quadriceps. However little is known about the mechanism of the load in lower extremity by the different knee alignment. The purpose of this study is to compare the muscle activity in the different knee alignment during leg press exercise. [Methods] Four normal knee and Five genu varum performed the leg press using three stance of narrow, medium and wide stance with the load of 75%/1 RM. Surface EMG date were collected (1000 Hz) from vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), adductor longus (AL), biceps femoris (BF), tibialis anterior (TA), gastrocnemius (GAS), soleus (SOL). Integrated EMG (iEMG) values were calculated for each muscle during each rep. A video camera recorded the performing form during leg press from the frontal plane. [Results and Discussion] As the leg press was to strengthen of the thigh muscle. VM, VL and RF of both groups worked strongly. However SOL of genu varum worked as strong as the level of activity of the thigh, iEMG of the SOL showed low value significantly by using wide stance. When the genu varum group performed maximal knee flexion using the narrow, their ankle was valgus on the video screen. This result may become cause of SOL higher activity during leg press. From this we can derive the argument that it will be necessary to take that stance into consideration when athletes who are genu varum performs leg press.
The status of the following programs is reported: study of the stereochemistry of halogen atom reactions produced via (n,..gamma..) nuclear reactions with diastereomeric molecules in the condensed phase; decay-induced labelling of compounds of biochemical interest; reactions of energetic tritium species in graphite; and positron lifetime measurements in ..gamma..-irradiated organic solids. (LK)
This study evaluated the biceps femoris (BF), rectus femoris (RF), and vastus lateralis (VL) activation and activation ratios of a variety of resistance training exercises characterized by knee extension, and determined if subject strength or gender affects these variables. The exercises evaluated included the leg extension, squat, deadlift, lunge, and step up. Subjects included 20 athletes and recreationally active college students. Electromyography (EMG) of the muscles expressed as a percentage of maximum voluntary isometric contraction (MVIC), as well as the BF to RF and BF to VL EMG ratio, were determined for each exercise. There was no significant interaction between gender and exercise type for the RMS EMG of the BF (p = 0.67), RF (p = 0.53), or VL (p = 0.06). Main effects were found for the RMS EMG of the BF (p = 0.00), RF (p = 0.00), and VL (p = 0.00), as well as the RMS EMG of the BF to RF activation ratio (p = 0.00) and BF to VL activation ratios (p = 0.003), between exercises. Peak RMS EMG was also assessed. Post hoc analysis identified specific differences in muscle activation and ratios between exercises. Clinicians should consider the magnitude of muscle activation and activation ratios when prescribing hamstring and quadriceps exercises.
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