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Comparison of Kinetic Variables and Muscle Activity During a Squat vs. a Box Squat
Abstract
The purpose of this investigation was to determine if there was a difference in kinetic variables and muscle activity when comparing a squat to a box squat. A box squat removes the stretch-shortening cycle component from the squat, and thus, the possible influence of the box squat on concentric phase performance is of interest. Eight resistance trained men (Height: 179.61 ± 13.43 cm; Body Mass: 107.65 ± 29.79 kg; Age: 24.77 ± 3.22 years; 1 repetition maximum [1RM]: 200.11 ± 58.91 kg) performed 1 repetition of squats and box squats using 60, 70, and 80% of their 1RM in a randomized fashion. Subjects completed the movement while standing on a force plate and with 2 linear position transducers attached to the bar. Force and velocity were used to calculate power. Peak force and peak power were determined from the force-time and power-time curves during the concentric phase of the lift. Muscle activity (electromyography) was recorded from the vastus lateralis, vastus medialis, biceps femoris, and longissimus. Results indicate that peak force and peak power are similar between the squat and box squat. However, during the 70% of 1RM trials, the squat resulted in a significantly lower peak force in comparison to the box squat (squat = 3,269 ± 573 N, box squat = 3,364 ± 575 N). In addition, during the 80% of 1RM trials, the squat resulted in significantly lower peak power in comparison to the box squat (squat = 2,050 ± 486 W, box squat = 2,197 ± 544 W). Muscle activity was generally higher during the squat in comparison to the box squat. In conclusion, minimal differences were observed in kinetic variables and muscle activity between the squat and box squat. Removing the stretch-shortening cycle during the squat (using a box) appears to have limited negative consequences on performance.
... For the back squat exercise much research has examined squat variations [e.g., front squat, box squat, unilateral variants (3, 8,22,24,[33][34][35]37)], placement of the barbell [e.g., high-bar and low-bar (13,21)], body positioning [e.g., variances in the hip, knees, feet, torso, depth (5,6,8,33)], muscle activation (7,8,33), and even squat visual cues (2,8), to name a few. However, much less is known about the effects of the loading implement itself on back squat outcomes, especially regarding specific barbell variations beyond the traditional OL barbell (16,22). ...
... For each set the raw force time curve was plotted on a computer screen, and the beginning and end of each repetition were manually selected so that the peak force during each repetition could be obtained. The force plate is widely considered the gold standard for ground reaction force measurements during dynamic movements, like back squats (24,25). (Figure 2). ...
... The Tendo TM Weightlifting Analyzer System has been shown to be valid (r > 0.85) and reliable (ICC > 0.90) during the back squat exercise in measuring average concentric velocity (12,14,15), but not valid for measuring peak velocity (14), compared to a motion capture criterion reference. Further, the force plate and linear position transducer were not integrated (i.e., using an interface box with an analog-to-digital card) and thus only peak force (from the force plate) and average concentric velocity (from the linear position transducer) are reported, and not power (9,24). ...
This study examined using a traditional Olympic (OL) or safety squat bar (SSB) barbell on force, velocity, and perceived exertion during an acute session of high-intensity back squats in adults. Twelve recreationally trained men (23.0±2.6 years; 88.3±19.1 kg) randomly completed two sessions of 3 sets of 6 repetitions at the same absolute load using the OL barbell or SSB barbell. Force and velocity were measured on every repetition and rating of perceived exertion (RPE) was assessed for each set. A two-way ANOVA (set x barbell) with repeated measures and Sidak post-hoc test (repetitions set-by-set) or paired t-test (repetitions independent of set) were used (p<0.05). Compared to a traditional OL barbell, using a SSB barbell resulted in no significant differences in peak force (2443.0±46.6 vs 2622.9±65.8 N, respectively; d=0.28) or average set RPE (7.8±0.8 vs 8.0±1.2, respectively; d=0.15) during an acute multi-set high-intensity back squat session. In contrast, compared to a traditional OL barbell, using a SSB barbell resulted in significantly (p<0.05) lower average velocity (0.42±0.04 vs 0.38±0.05 m/s, respectively; d=0.27) during the same parameters. When performing the back squat exercise recreationally resistance-trained adults exhibit similar peak force and perceived effort with OL or SSB barbells, but greater velocities can be achieved with the OL barbell. Practitioners working with adults to develop lower body strength and power with the back squat exercise across multiple sets can interchangeably use the OL or SSB barbells to similarly train force, but training velocity is trivially better with the OL barbell acutely.
... An additional derivative of the free weight back squat that is often performed by powerlifters is the box squat [41,48]. The box squat requires the athlete to perform an eccentric phase (i.e., descent) followed by sitting on a box, typically for a minimum of 1 s, prior to executing the concentric phase (i.e., ascent) of the movement [41,48]. ...
... An additional derivative of the free weight back squat that is often performed by powerlifters is the box squat [41,48]. The box squat requires the athlete to perform an eccentric phase (i.e., descent) followed by sitting on a box, typically for a minimum of 1 s, prior to executing the concentric phase (i.e., ascent) of the movement [41,48]. The box squat can be performed in a full movement, in parallel movements, or in partial movements. ...
... The box squat can be performed in a full movement, in parallel movements, or in partial movements. By sitting on the box, the athlete removes much of the effect of the stretch shortening cycle [48]. Generally, when athletes perform the box squat, a wider foot stance is selected compared to traditional back squats [41,48], resulting in different muscle activation patterns [49]. ...
Abstract: There is substantial evidence indicating that increased maximum strength as a result of training with squats, particularly full and parallel squats, is associated with superior athletic capabilities, such as sprinting, jumping and agility. Although full and parallel squats have been strongly associated with sport performance, there is also some evidence that the use of partial squats may provide angle specific adaptations that are likely advantageous for specific sporting activities. Partial squats may be particularly advantageous when trained in conjunction with full or parallel squats, as this practice results in a greater training effect. There is a paucity of evidence that squatting is associated with excessive injuries to the knees, lower back, or other structures. Evidence does indicate that squatting, including full squats, can be undertaken safely, provided an appropriate training methodology is applied. Indeed, based on scientific data, the cost/benefit ratio indicates that squats should be recommended and should be a central strength training exercise for the preparation of athletes in most sports, particularly those requiring strong and powerful whole body and lower body movements.
... In addition to kinematics and EMG, the ground reaction forces of bilateral squatting movements have been examined (7,9,10,16,19), in both loaded (10,16,19), and unloaded conditions (7,9). Similar variables have also been examined during unilateral squatting motions (9,11,18,22,27), however, these studies focused on unloaded single-leg squats for rehabilitation purposes. ...
... In addition to kinematics and EMG, the ground reaction forces of bilateral squatting movements have been examined (7,9,10,16,19), in both loaded (10,16,19), and unloaded conditions (7,9). Similar variables have also been examined during unilateral squatting motions (9,11,18,22,27), however, these studies focused on unloaded single-leg squats for rehabilitation purposes. ...
... To our knowledge, this was also the only study that compared the kinetics of a unilateral and bilateral squat, but it focused on patellofemoral force differences and did not report any comparisons of ground reaction forces (9). In one investigation that compared different squat techniques, peak force and peak power appeared to be similar (19), however, this study compared the box squat and traditional BS, not unilateral and bilateral squats. ...
Muscular activity, vertical displacement and ground reaction forces of back squats (BS), rear-leg elevated split squats (RLESS) and split squats (SS) were examined. Nine resistance-trained men reported for two sessions. The first session consisted of the consent process, practice, and BS 1-repetition maximum testing. In the second session, participants performed the three exercises while EMG, displacment and ground reaction force data (one leg on plate) were collected. EMG data were collected from the gluteus maximus (GMX), biceps femoris (BF), semitendinosus (ST), rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), tibialis anterior (TA), and medial gastrocnemius (MGas) of the left leg (non-dominant, front leg for unilateral squats). Load for BS was 85% one repetition maximum, and RLESS and SS were performed at 50% of BS load. Repeated measures ANOVA was used to compare all variables for the three exercises, with Bonferroni adjustments for post hoc multiple comparisons, in addition to calculation of standardized mean differences (ES). Muscle activity was similar between exercises except for biceps femoris, which was significantly higher during RLESS than SS during both concentric and eccentric phases (ES = 2.11; p=0.012 and ES= 2.19; p=0.008), and significantly higher during BS than the SS during the concentric phase (ES = 1.78; p=0.029). Vertical displacement was similar between all exercises. Peak vertical force was similar between BS and RLESS and significantly greater during RLESS than SS (ES = 3.03; p=0.001). These findings may be helpful in designing resistance training programs by using RLESS if greater biceps femoris activity is desired.
... A number of biomechanical studies have investigated the effects of manipulating features of the squat exercise to alter muscle activity and kinetic output. These manipulations include changes to foot position (20,25), barbell position (11), stability of the surface on which the exercise is performed (1,9,(16)(17)(18), mode of the resistance (19,25), and depth of movement (5,22). In addition, further biomechanical studies have compared muscle activity and kinetic output of common variations of the squat exercise. ...
... In a recent study conducted by McBride et al. (19), the authors compared EMG and kinetic variables produced during performance of the back squat and box squat by experienced powerlifters. The same absolute loads were used for the performance of both exercises, and the kinetic analyses revealed similar peak force and peak power values across all loads tested. ...
... Comparisons of the EMG data revealed a high correspondence for values produced from the muscles of the thigh and posterior trunk. The authors concluded that both exercises produced a similar stimulus despite the fact that the box squat is not as effective in using the stretch-shortening cycle (19). It is likely that the capacity to use the same absolute load in each exercise was influential in producing a similar kinetic and EMG response. ...
The purpose of this study was to compare muscle activity and kinetics during the back squat and overhead squat performed at three relative intensities (60, 75 and 90% 3RM). Fourteen subjects (age: 26 ± 7 yrs, height: 182.5 ± 13.5 cm, body mass: 90.5 ± 17.5 kg) performed each exercise using a within-subjects crossover design. In addition, a selection of trunk isolation exercises were included to provide additional comparisons. Squats were performed on a force platform with electromyographic (EMG) activity of the anterior deltoid (AD), rectus abdominis (RA), external oblique (EO), erector spinae (ES), gluteus maximus (GM), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (GA) recorded throughout. The overhead squat demonstrated significantly greater (p<0.05) activity in the anterior trunk muscles (RA and EO) during the eccentric phase. However, the magnitudes of the differences were relatively small (∼ 2 to 7%). In contrast, the back squat displayed significantly greater (p<0.05) activity in the posterior aspect of the trunk (ES) and all lower-body muscles during the concentric phase. Kinetic comparisons revealed that significantly greater peak force (p<0.05) was developed during the back squat. EMG comparisons between the trunk isolation exercises and squat variations demonstrated substantially greater anterior trunk activity during the isolation exercises, whereas the highest activity in the posterior aspect of the trunk was obtained during the squats (p<0.05). The results of the study do not support the hypothesis that the overhead squat provides a substantially greater stimulus for developing the trunk musculature compared with the back squat.
... Box squat and seated box squat jump: The box squat, in which athletes sit back onto a box before driving upward, is commonly used to strengthen the squat pattern and develop power (55) and RFD (94). When performed with a brief pause at the bottom position (replicating the zero-velocity point in a countermovement), the exercise minimizes elastic energy contributions, requiring the muscle groups involved in the propulsive phase to generate force independently (55). ...
... Box squat and seated box squat jump: The box squat, in which athletes sit back onto a box before driving upward, is commonly used to strengthen the squat pattern and develop power (55) and RFD (94). When performed with a brief pause at the bottom position (replicating the zero-velocity point in a countermovement), the exercise minimizes elastic energy contributions, requiring the muscle groups involved in the propulsive phase to generate force independently (55). The concentric phase should be executed as explosively as possible, using a load where the athlete's power output is maximized. ...
Volleyball, with its global popularity and rigorous competition schedules, presents unique challenges in athlete conditioning and injury risk reduction. This narrative review synthesizes the current understanding of the physical demands and injury risks associated with elite volleyball play, offering a detailed analysis of match play dynamics and prevalent injury mechanisms. It emphasizes the important role of strength and conditioning (S&C) coaches in developing training programs to enhance performance and mitigate injury risks through strategic exercise selection and periodization. The review provides a thorough needs analysis, highlighting specific conditioning requirements for different player positions and detailing effective physical testing protocols. Recommendations are made for implementing structured S&C programs, which are vital for preparing athletes for the physical challenges of competitive volleyball. Practical guidelines are outlined for S&C coaches to optimize training outcomes, including suggestions for drill sequences and conditioning routines that reflect the sport-specific demands of volleyball. Thus, this review aims to equip coaches, trainers, and athletes with the knowledge and tools necessary to elevate their performance and safeguard against injuries, thereby contributing to the advancement and sustainability of volleyball as a high-intensity competitive sport.
... Acceleration performance is reliant upon an athletes' ability to produce high levels of horizontal ground reaction forces (GRF) (20) while research has revealed a significant relationship (P = 0.024) between horizontal GRF and hamstring activity (21). Box squats have previously been shown to be a predominantly knee joint, or quadriceps dominant exercise (22) and it could be argued that, due to its hip dominance and greater activation of the posterior chain, the deadlift may be a suitable alternative (23). The purpose of this study therefore, is to investigate the efficacy of deadlifts and box squats, with a combination of traditional and accommodating resistance, as a potentiating stimulus of standing broad jumps in a multiple set contrast protocol. ...
... This may have been due to the eccentric portion and possible stretch shortening cycle contribution of the box squat, which was not present in the predominantly concentric deadlift. Although subjects were instructed to pause briefly at the bottom position of the box squat, this has been shown to have little impact on the kinetic variables or muscle activation when compared to a non-paused back squat (22). This differs from the findings of Seitz and colleagues (11) (11,26). ...
This study investigated the efficacy of deadlifts and box squats, with a combination of traditional and accommodating resistance, as a potentiating (PAP) stimulus of standing broad jumps (SBJ) in a multiple set contrast protocol. Twelve professional rugby league players (21.4 ± 2.5yrs; 181.3 ± 8.3cm, 91.9 ± 8.8kg; 1RM back squat/BM 1.59 ± 0.21; 1RM deadlift/BM 2.11 ± 0.25; ≥3 years resistance training experience) performed baseline SBJ before a contrast PAP protocol involving 2 repetitions of 85% 1RM box squat or deadlifts, loaded with a combination of traditional barbell weight (70% 1RM) and elastic band resistance (~15% 1RM), followed by two SBJs. Exercises were separated by 90s, and four contrast pairs were performed in total. Using a repeated measures design, all subjects performed the squat followed by the deadlift and finally the control (SBJ only) condition in the same order across consecutive weeks. Changes from baseline in SBJ distance were moderate for the box squat (Effect Size=0.64-1.03) and deadlift (ES=0.80-0.96) and trivial in the control condition (ES=0.02-0.11). The magnitude of differences in PAP effect were considered moderate (d = 0.61) for set 1, trivial for set 2 (d = 0.10) and set 3 (d = 0.05) in favor of box squats, and moderate for set 4 (d = 0.58) in favor of deadlifts. Accommodating resistance, either box squats or deadlifts are an effective means of potentiating SBJ performance across multiple sets of a contrast protocol with only 90s rest.
... The external stimulus of the box makes the box-squat a very different movement, and difficult to directly compare with the HBBS and wider powerlifting style back-squat. However, in contrast to these results, McBride et al. (50) showed a back-squat to produce a significantly smaller peak F v than a box-squat at 70% back-squat 1RM (p # 0.05). Comparable peak F v results (no significant differences) were observed between the back-squat and boxsquat at 60% and 80% 1RM also in this study. ...
... %MVIC (50) Rectified and filtered by 6-pole Butterworth, notch filter 60 Hz and band pass filter 10-200 Hz. ...
The back-squat is a common exercise in strength and conditioning, for a variety of sports. It is widely regarded as a fundamental movement to increase and measure lower-body and trunk function, as well as an effective injury rehabilitation exercise. There are typically two different bar positions used when performing the back-squat; the traditional 'high-bar' back-squat (HBBS) and the 'low-bar' back-squat (LBBS). Different movement strategies are employed to ensure that the center-of-mass remains in the base-of-support for balance during the execution of these lifts. These movement strategies manifest as differences in 1) joint angles, 2) vertical ground reaction forces and, 3) the activity of key muscles. This review showed that the HBBS is characterized by greater knee flexion, lesser hip flexion, a more upright torso and a deeper squat. The LBBS is characterized by greater hip flexion and therefore a greater forward lean. However, there are limited differences in vertical ground reaction forces between the HBBS and LBBS. The LBBS can also be characterized by greater muscle activity of the erector spinae, adductors and gluteal muscles, whereas the HBBS can be characterized by greater quadriceps muscle activity. Practitioners seeking to develop the posterior-chain hip musculature (i.e. gluteal, hamstring and erector muscle groups) may seek to utilize the LBBS. In comparison, those seeking to replicate movements with a more upright torso, and contribution from the quadriceps may rather seek to employ the HBBS in training.
... ratio between countermovement and concentric-only performance) [265]. The eccentric displacement (depth) of these ballistic movements will influence the validity, reliability and subsequent kinematic and kinetic outputs, and therefore needs to be carefully considered [141,[266][267][268]. The depth of bench throw (e.g. ...
... quarter, half, parallel and full) and knee angle (70°-110°) varies between studies, in turn affecting the resultant 1RM [45, 162,181,197,244,248,326,333,336,[344][345][346][347]. The box squat has also been used as replacement and supplementary testing and training exercise and in turn possibly affecting the resultant kinematics and kinetics, but not necessarily maximum strength when performed correctly [45,65,267,305,347]. Bench press depth was not always identified in the studies, but a bar-to-chest depth is required by the International Powerlifting Federation [348] and a handful of studies [162,174,181,248,326,349,350]. ...
An athletic profile should encompass the physiological, biomechanical, anthropometric and performance measures pertinent to the athlete's sport and discipline. The measurement systems and procedures used to create these profiles are constantly evolving and becoming more precise and practical. This is a review of strength and ballistic assessment methodologies used in sport, a critique of current maximum strength [one-repetition maximum (1RM) and isometric strength] and ballistic performance (bench throw and jump capabilities) assessments for the purpose of informing practitioners and evolving current assessment methodologies. The reliability of the various maximum strength and ballistic assessment methodologies were reported in the form of intra-class correlation coefficients (ICC) and coefficient of variation (%CV). Mean percent differences [Formula: see text] and effect size (ES = [X method2 - X method1] ÷ SDmethod1) calculations were used to assess the magnitude and spread of methodological differences for a given performance measure of the included studies. Studies were grouped and compared according to their respective performance measure and movement pattern. The various measurement systems (e.g. force plates, position transducers, accelerometers, jump mats, optical motion sensors and jump-and-reach apparatuses) and assessment procedures (i.e. warm-up strategies, loading schemes and rest periods) currently used to assess maximum isometric squat and mid-thigh pull strength (ICC > 0.95; CV < 2.0 %), 1RM bench press, back squat and clean strength (ICC > 0.91; CV < 4.3 %), and ballistic (vertical jump and bench throw) capabilities (ICC > 0.82; CV < 6.5 %) were deemed highly reliable. The measurement systems and assessment procedures employed to assess maximum isometric strength [M Diff = 2-71 %; effect size (ES) = 0.13-4.37], 1RM strength (M Diff = 1-58 %; ES = 0.01-5.43), vertical jump capabilities (M Diff = 2-57 %; ES = 0.02-4.67) and bench throw capabilities (M Diff = 7-27 %; ES = 0.49-2.77) varied greatly, producing trivial to very large effects on these respective measures. Recreational to highly trained athletes produced maximum isometric squat and mid-thigh pull forces of 1,000-4,000 N; and 1RM bench press, back squat and power clean values of 80-180 kg, 100-260 kg and 70-140 kg, respectively. Mean and peak power production across the various loads (body mass to 60 % 1RM) were between 300 and 1,500 W during the bench throw and between 1,500 and 9,000 W during the vertical jump. The large variations in maximum strength and power can be attributed to the wide range in physical characteristics between different sports and athletic disciplines, training and chronological age as well as the different measurement systems of the included studies. The reliability and validity outcomes suggest that a number of measurement systems and testing procedures can be implemented to accurately assess maximum strength and ballistic performance in recreational and elite athletes, alike. However, the reader needs to be cognisant of the inherent differences between measurement systems, as selection will inevitably affect the outcome measure. The strength and conditioning practitioner should also carefully consider the benefits and limitations of the different measurement systems, testing apparatuses, attachment sites, movement patterns (e.g. direction of movement, contraction type, depth), loading parameters (e.g. no load, single load, absolute load, relative load, incremental loading), warm-up strategies, inter-trial rest periods, dependent variables of interest (i.e. mean, peak and rate dependent variables) and data collection and processing techniques (i.e. sampling frequency, filtering and smoothing options).
... Peak concentric forces were not significantly different between NSS and SS at all intensities (NSS-80 = 3459. 8 ...
... It is theorized that this is because of the suit's ability to store elastic energy during the eccentric phase of the squat and its release in the concentric phase. One can see the same effect with squats that use the stretch-shortening cycle (8). The SS allows the individual to maintain a higher power output at lower intensities when compared to the squats without the suit (NSS). ...
The purpose of this investigation was to examine various kinetic and kinematic variables associated with squats without and with the use of a squat suit. No previous investigation has examined the effect of a squat suit on squat performance. Participants were 8 elite or professional level male powerlifters (height = 178.59 ± 3.5 cm; body mass = 106.8 ± 30.4 kg; age = 25 ± 2.2 yrs; mean 1RM =197.7±53kg). Subjects participated in three testing sessions, with the first session involving a one repetition maximum squat (1RM) without a squat suit. Session two and three involved a testing session completing two trials in the squat at three intensities (80, 90, and 100% of 1RM) either without (NSS) or with a squat suit (SS). The session and order of the intensities were all randomized. Force-, velocity-, and power-time graphs were calculated from data from a force plate and two linear position transducers attached to the barbell. Peak eccentric force was significantly higher during SS at 100% of 1RM (NSS-100 = 3196.2 ± 470.6, SS-100 = 3369.7 ± 589.9 N). Peak concentric velocity was significantly higher during SS in comparison to NSS at all intensities. Peak concentric power was significantly higher during SS at 80% of 1RM (NSS-80 = 1566.5 ± 388.4 W, SS-80 = 1770.4 ± 483.2 W) and 90% of 1RM (NSS-90 = 1493.1 ± 296.2 W, SS-90 = 1723.8 ± 449.5 W). The current investigation has demonstrated significantly different kinetic and kinematic characteristics between squats without and with a squat suit which could ultimately aid in enhancing squat performance.
... Given the widespread use of the squat among athletes, there are several studies that have analyzed the biomechanics of the gesture with the aim of improving performance and preventing injuries (1,3,(12)(13)(14)(15)(16)(17)(18). In fact, it is recommended to perform the squat, which is a closed kinetic chain exercise, with minimal anterior knee displacement in order to optimize performance and reduce the risk of injury (19)(20)(21)(22). ...
Introduction
This study aimed to evaluate the angular kinematics of the hip, knee, ankle, and the linear kinematics of the barbell during the back squat (BS) at different load intensities in powerlifters and weightlifters.
Methods
Seventeen athletes were recruited (n = 14 powerlifters; n = 3 weightlifters). The 1-RM of the BS of each participant was calculated and, 1-week after, each participant was asked to perform 5 trials of the BS at different load intensities (i.e., 60%, 70%, 80%, 90%, 100%) of the 1-RM. An action camera recorded the execution of each BS trial in the sagittal plane and, afterward, the videos were analyzed by measuring the range of motion (ROM) of hip, knee, and ankle for the angular kinematics, and the timing, distances, speeds, and accelerations of the barbell for the linear kinematics.
Results
Regarding the angular kinematics, no significant differences were found in the parameters in the starting and ending positions among the 5 trials, while a significant decrease was found in the hip relative angle (p = 0.026) in the maximum flexion position as load intensity increased. Regarding the linear kinematics, a significant difference was found in the descent acceleration (p = 0.049) in the descent phase, while a significant difference was found in the ascent speed (p < .001) and vertical speed of ascent (p < .001) in the ascent phase, which decreased as load intensity increased.
Discussion
Our findings show that the angular and linear kinematics of BS change as load intensity increases.
... Each participant was guided to perform two CKC motions ( Fig. 1 a, b)., including a box squat (BS) and a deep lunge, as well as two OKC motions ( Fig. 1 c, d) including non-weight bearing active knee extension (OKC-0) and active knee extension with 10 kg loading around the ankle (OKC-10). For the box squat, participants were asked to maintain their hips posteriorly and hold a near-vertical shin position (McBride et al., 2010;Swinton et al., 2012). Considering that the toe direction would affect the knee kinematics, we asked the participants to place their feet in the neutral toe position (Swinton et al., 2012). ...
Background:
Usage of open-kinetic-chain (OKC) or closed-kinetic-chain (CKC) exercises during rehabilitation planning after anterior cruciate ligament (ACL) reconstruction has been debated for decades. However, the ACL elongation pattern during different rehabilitation exercises at different loadings remains unclear.
Objectives:
This study aimed to determine the effects of OKC and CKC exercises on the length of ACL anteromedial bundle (AMB) and posterolateral bundle (PLB) to provide biomechanical support for making rehabilitation schedules.
Design:
Laboratory Descriptive Study.
Method:
Eighteen healthy volunteers were asked to perform two OKC motions, including non-weight-bearing and 10 kg loaded seated knee extension (OKC-0, OKC-10), as well as two CKC motions, including box squat (BS) and deep single-legged lunge (Lunge). Techniques of 2D-to-3D image registration and 3D ligament simulation were used to quantify length changes of ACL.
Results:
The motion which led to the least and most ACL elongation were OKC-0 and OKC-10, respectively. The AMB and PLB were significantly longer in OKC-10 than those in OKC-0 during 0-60° and 0-55° of knee flexion (p < 0.01). Compared with reference length, the AMB and PLB were stretched during 0-30° and 0-10° respectively during OKC-10. During CKC exercises, the AMB and PLB were also stretched from 0 to 25°and 0-5°, respectively. Additionally, no significant difference was found in the length change of ACL bundles between BS and lunge.
Conclusions:
OKC-0 may be safe for the rehabilitation program after ACL reconstruction, and loaded exercises shall be applied when restricted with >30° in early-stage rehabilitation.
... Studies have sought to understand the effect of movement speed and transition time on acute responses related to strength training, but did not observe greater muscle activation during the concentric phase for 1RM conditions involving less SSC [32,33]. These results corroborate the findings of this study: for the condition of 95% of the 1RM, after the pre-sticking period, all muscles demonstrated decreased RMS values. ...
High-performance training program development has benefitted from studies of the mechanisms involved in performing the bench press. This study aimed to analyze the electromyographic and kinematic parameters affecting high-performance athletes during the phases of the Paralympic bench press movement. The root mean square, mean frequency, and frequency median variables were analyzed for the pectoralis major, triceps brachii, and anterior deltoideus. Four females aged 23 to 48 years (mean 39.8 ± 11.2) and six males aged 18 to 41 years (mean 26.5 ± 8.0) performed three attempts at 95% of their dynamic maximum voluntary contraction load, obeying the rules of the modality. For all movement sub-phases, the pectoralis major and deltoideus root-mean-square values indicated greater activation (level of significance of. ρ ≤ 0.05). The triceps brachii presented high values of the frequency domain variables, especially in the concentric phase of the bench press movement, suggesting a firing rate higher than the other muscles studied. Therefore, the triceps muscle must be trained effectively, especially to assist in the concentric phase and the sticking sub-phase. These results suggest that resistance-training programs should include variations in bench press format to optimize the force output during different sub-phases.
... Squats are the most commonly used endurance training for strength development, conditioning, and rehabilitation [4], [5]. Squat movements are also indirectly correlated in daily life, such as sitting, standing, holding children, lifting objects, going up and down stairs [4], [6]. ...
... For the box squat, participants were asked to move their hips posteriorly and try to hold a near-vertical shin position. [17,18] The height of the plyometric box was adjusted to allow all the knees of participants to be at a 90-degree angle when they sit on the box. Considering that the toe direction would affect the knee kinematics, we asked the participants to place their feet in the neutral toe position [18]. ...
A rehabilitation program after anterior cruciate ligament reconstruction is of great importance to obtain a satisfactory prognosis after surgery. However, there is still an onging debate over whether closed kinetic chain or open kinetic chain exercises should be chosen. Our study was designed to compare the in vivo tibiofemoral kinematics during closed kinetic chain and open kinetic chain exercises.
Eighteen healthy volunteers were asked to perform box squat and unloaded/10 kg-loaded seated knee extension. In vivo 3-dimensional analysis of tibiofemoral kinematics of different motions were determined using a dual fluoroscopic imaging system.
The study found significantly more tibial anterior displacement during loaded seated knee extension than during unloaded seated knee extension from 25°–50° of knee flexion (p ≤ 0.031). The knees exhibited significantly more internal tibial rotation and lateral tibial translation during the box squat than both seated knee extensions during mid-flexion. In addition, the knees showed less internal-external (IE) range of motion (ROM) from 20°– 75° of flexion (p < 0.001) and medial-lateral (ML) ROM from 75° to full extension (p ≤ 0.006) during box squat than both extensions. This knowledge may help optimize rehabilitation plans for patients post ACL reconstruction.
... A short ROM, double knee bend technique was used sporadically by some athletes to initiate a stretch shortening cycle just prior to the beginning of the second pull phase. While the stretch-shortening cycle is commonly used in weightlifting events to ensure maximal force and power can be rapidly applied to the barbell (Enoka, 1979;Gourgoulis et al., 2000;Winwood et al., 2015b), evidence supporting its effectiveness for heavy/ strength-based lifts performed over an extended duration, such as the atlas stone lift, is conflicting (McBride et al., 2010;Swinton et al., 2012). ...
Background
The atlas stone lift is a popular strongman exercise where athletes are required to pick up a large, spherical, concrete stone and pass it over a bar or place it on to a ledge. The aim of this study was to use ecologically realistic training loads and set formats to (1) establish the preliminary biomechanical characteristics of athletes performing the atlas stone lift; (2) identify any biomechanical differences between male and female athletes performing the atlas stone lift; and (3) determine temporal and kinematic differences between repetitions of a set of atlas stones of incremental mass.
Methods
Kinematic measures of hip, knee and ankle joint angle, and temporal measures of phase and repetition duration were collected whilst 20 experienced strongman athletes (female: n = 8, male: n = 12) performed three sets of four stone lifts of incremental mass (up to 85% one repetition maximum) over a fixed-height bar.
Results
The atlas stone lift was categorised in to five phases: the recovery, initial grip, first pull, lap and second pull phase. The atlas stone lift could be biomechanically characterised by maximal hip and moderate knee flexion and ankle dorsiflexion at the beginning of the first pull; moderate hip and knee flexion and moderate ankle plantarflexion at the beginning of the lap phase; moderate hip and maximal knee flexion and ankle dorsiflexion at the beginning of the second pull phase; and maximal hip, knee extension and ankle plantarflexion at lift completion. When compared with male athletes, female athletes most notably exhibited: greater hip flexion at the beginning of the first pull, lap and second pull phase and at lift completion; and a shorter second pull phase duration. Independent of sex, first pull and lap phase hip and ankle range of motion (ROM) were generally smaller in repetition one than the final three repetitions, while phase and total repetition duration increased throughout the set. Two-way interactions between sex and repetition were identified. Male athletes displayed smaller hip ROM during the second pull phase of the first three repetitions when compared with the final repetition and smaller hip extension at lift completion during the first two repetitions when compared with the final two repetitions. Female athletes did not display these between-repetition differences.
Conclusions
Some of the between-sex biomechanical differences observed were suggested to be the result of between-sex anthropometric differences. Between-repetition differences observed may be attributed to the increase in stone mass and acute fatigue. The biomechanical characteristics of the atlas stone lift shared similarities with the previously researched Romanian deadlift and front squat. Strongman athletes, coaches and strength and conditioning coaches are recommended to take advantage of these similarities to achieve greater training adaptations and thus performance in the atlas stone lift and its similar movements.
... In regard to strength training, scientific research in the aspect of biomechanics has been more developed in foreign countries [4], and further in-depth research has also been conducted in China. Squat, bench press and hard pull have become a significant focus of biomechanical research [5]. The purpose of this study was to test the strength factors of squat, bench press and hard pull, in order to provide a scientific basis and theoretical reference for strength training. ...
Deep squat, bench press and hard pull are important ways for people to improve their strength. The use of sensors to measure force is rare. Measuring strength with sensors is extremely valuable for people to master the intensity of exercise to scientifically effective exercise. To this end, in this paper, we used a real-time wireless motion capture and mechanical evaluation system of the wearable sensor to measure the dynamic characteristics of 30 young men performing deep squat, bench press and hard pull maneuvers. The data of tibia were simulated with AnyBody 5.2 and ANSYS 19.2 to verify the authenticity. The result demonstrated that the appropriate force of the deep squat elbow joint, the hip joint and the knee joint is 40% 1RM, the appropriate force of the bench press is 40% 1RM and the appropriate force of the hard pull is 80% 1RM. The external force is the main factor of bone change. The mechanical characteristics of knee joint can be simulated after the Finite Element Analysis and the simulation of AnyBody model are verified.
... 70%1RM. Although our sample was considerably older, numerus studies reported optimal loads between 50%1RM and 60%1RM during back squats performed with either free weights or Smith machines among young male athletes (Alcaraz et al., 2011;Cormie et al., 2007a;Cormie et al., 2007b;Cormie et al., 2007c;McBride et al., 2010;McBride et al., 2011), which is consistent with our results. Both the LP and squat use primarily the quadriceps and gluteus maximus. ...
Background:
Age-related decrements in power affect quality of life in older adults; however, no studies have determined the optimal loads that maximize power outputs using the most commonly employed lifting equipment, plate-loaded machines.
Methods:
Fifteen older men (69.2 ± 6.9 y) and 22 older women (68.9 ± 5.9 y) performed two sessions of strength and power testing. Individuals completed ten plate-loaded exercises to determine their maximum dynamic strengths (1RM) and peak power outputs (PP). Power was tested at 40, 50, 60, 70 and 80% 1RM using a linear position transducer. PP was expressed relative to the highest power produced (PPREL).
Results:
Multi-joint exercises produced optimal load values at 50-60%1RM for leg press, 50%1RM for chest press, and 40-60%1RM for seated row, with no significant differences among loads for shoulder press. Single-joint exercise optimal loads were seen at 50-60% for hip adduction, 50-70%1RM for calf raise, 60-80%1RM for biceps curl, and 50-80%1RM for triceps extension, with no significant differences between loads for hip abduction or leg curl. No significant differences were found between sexes for any exercise.
Conclusions:
Different optimal load ranges are required for individual plate-loaded exercises in older persons. Specifically, multi-joint exercises demonstrated a narrow optimal load range favoring the velocity end of the load-velocity curve, while single-joint exercises produced a wider optimal load range extending into the upper limits of the load end of the curve.
... La sentadilla es uno de los ejercicios comúnmente utilizados en el entrenamiento y la rehabilitación de la extremidad inferior, debido que reproduce una actividad funcional con la carga sobre la extremidad 1,2 . Se han descrito distintas modalidades de sentadilla, dentro de los cuales se encuentra la sentadilla monopodal [2][3][4] . La condición monopodal de esta tarea motora aumenta la dificultad de la ejecución, debido a que modifica las estrategias sensoriales y musculares para mantener el control postural 5,6 . ...
Objective: To compare the performance of the isometric single leg squat exercise on a rigid surface versus a spongy surface in relation to the center of pressure and activation patterns of the muscles of the dominant lower limb and spine in healthy young women.Method: 12 healthy women performed the isometric single leg squat on a rigid surface (control) and a spongy surface. A posturograph recorded the areaand velocity of displacement of the pressure center. A surface electromyograph evaluated the muscular activity of multifidus, gluteus maximus, gluteusmedius, vastus medialis and biceps femoris of the supporting leg. Results: The area and the speed of displacement of the center of pressure increased (p <0.05 and p <0.01 respectively) in spongy surface. Femoral bicepsincrease its muscular activity on the spongy surface (p <0.05). There is a correlation between the greater muscular activity of the biceps femoris and thearea and the velocity of the pressure center (p <0.01). Conclusion: Isometric single leg squat performed on a spongy surface, produces a greater disturbance of postural control and greater activity of the bicepsfemoris in healthy young women. The increased activity of this muscle is directly related to the displacement of the pressure center. Keywords: Postural balance; Electromyography; Exercise; Isometric contraction.
... From a mechanical point of view, ballistic push-off performance is thus directly related to the net mechanical impulse produced onto the ground (Winter, 2005). The capability to develop a high net impulse during one lower limb push-off has been associated with muscular mechanical power output capabilities (Newton and Kraemer, 1994;Yamauchi and Ishii, 2007;Samozino et al., 2008;Frost et al., 2010;McBride et al., 2010). Numerous studies have highlighted neuromuscular power as the primary variable related to ballistic performance, yet this analysis only provides a partial representation of the athlete's true maximal mechanical capabilities (Cronin and Sleivert, 2005). ...
Ballistic performances are determined by both the maximal lower limb power output (Pmax) and their individual force-velocity (F-v) mechanical profile, especially the F-v imbalance (FVimb): difference between the athlete's actual and optimal profile. An optimized training should aim to increase Pmax and/or reduce FVimb. The aim of this study was to test whether an individualized training program based on the individual F-v profile would decrease subjects' individual FVimb and in turn improve vertical jump performance. FVimb was used as the reference to assign participants to different training intervention groups. Eighty four subjects were assigned to three groups: an “optimized” group divided into velocity-deficit, force-deficit, and well-balanced sub-groups based on subjects' FVimb, a “non-optimized” group for which the training program was not specifically based on FVimb and a control group. All subjects underwent a 9-week specific resistance training program. The programs were designed to reduce FVimb for the optimized groups (with specific programs for sub-groups based on individual FVimb values), while the non-optimized group followed a classical program exactly similar for all subjects. All subjects in the three optimized training sub-groups (velocity-deficit, force-deficit, and well-balanced) increased their jumping performance (12.7 ± 5.7% ES = 0.93 ± 0.09, 14.2 ± 7.3% ES = 1.00 ± 0.17, and 7.2 ± 4.5% ES = 0.70 ± 0.36, respectively) with jump height improvement for all subjects, whereas the results were much more variable and unclear in the non-optimized group. This greater change in jump height was associated with a markedly reduced FVimb for both force-deficit (57.9 ± 34.7% decrease in FVimb) and velocity-deficit (20.1 ± 4.3%) subjects, and unclear or small changes in Pmax (−0.40 ± 8.4% and +10.5 ± 5.2%, respectively). An individualized training program specifically based on FVimb (gap between the actual and optimal F-v profiles of each individual) was more efficient at improving jumping performance (i.e., unloaded squat jump height) than a traditional resistance training common to all subjects regardless of their FVimb. Although improving both FVimb and Pmax has to be considered to improve ballistic performance, the present results showed that reducing FVimb without even increasing Pmax lead to clearly beneficial jump performance changes. Thus, FVimb could be considered as a potentially useful variable for prescribing optimal resistance training to improve ballistic performance.
... Conversely, Youdas et al. (27) found increases in hamstring activity in both men and women while performing unweighted single-limb squats on a labile surface (foam pad) compared with a stable surface. Anderson and Behm (1) showed greater trunk activation (upper and lower erector spinae, and lower abdominals) during unstable squatting; however, this was contrary to McBride et al. (17) who found no differences in upper erector spinae (at L 1 ) during stable and unstable squatting using both absolute and relative loads. ...
Squat exercise training using instability devices have become increasingly popular for a multitude of reasons. Many devices generate instability at the feet and provide a bottom-up perturbation; however, the effect of a top-down instability device during a squat remains unclear. In order to induce instability at the upper body, a water-filled cylinder called the Attitube® was used. This study analyzed the effects of instability location (top-down, bottom-up, no instability) during a squat exercise in terms of kinematics and muscle activation. Ten male participants were instrumented with 75 reflective markers to track kinematics of the ankle, knee, hip, trunk, and the Bar/Attitube®; and electromyography was recorded from 12 muscles bilaterally. Squats were performed with an Olympic bar on a stable surface, Olympic bar on a BOSU® ball (BALL, bottom-up), and the Attitube® on solid ground (TUBE, top-down). The TUBE showed up to 1.5 times reduction in erector spinae activation and up to 1.5 times less trunk flexion while being performed at a slower velocity. There was also higher abdominal activation in the TUBE, with up to 2.8 times greater oblique activation compared to the stable condition. The BALL increased ankle eversion and knee flexion with higher muscle activation in gastrocnemius, biceps femoris, and quadriceps. Overall, changing the location of instability during a squat changed the motion and muscle activation patterns of the trunk and lower extremities. This provides information for future research into rehabilitation, learning proper squat technique, and for specific training scenarios.
... The squat exercise-commonly considered more functional than the leg press-is the cornerstone of the strength training regimes of many athletes. Isokinetic squat devices have been developed and described (28,45), but to the best of our knowledge, no previous studies have investigated the effects of isokinetic squat resistance training on strength and power in athletes. Therefore, a goal of the present study was to investigate the effects of isokinetic squat exercise training in comparison to OWL and free weight strength and power training (FSPT). ...
Introduction:
This efficacy study investigated the effects of (1) Olympic-style weightlifting (OWL), (2) motorized strength and power training (MSPT), and (3) free weight strength and power training (FSPT) on muscle power.
Methods:
Thirty-nine young athletes (20±3 yr.; ice hockey, volleyball and badminton) were randomized into the three training groups. All groups participated in 2-3 sessions/week for 8 weeks. The MSPT and FSPT groups trained using squats (two legs and single leg) with high force and high power, while the OWL group trained using clean and snatch exercises. MSPT was conducted as slow-speed isokinetic strength training and isotonic power training with augmented eccentric load, controlled by a computerized robotic engine system. FSPT used free weights. The training volume (sum of repetitions x kg) was similar between all three groups. Vertical jumping capabilities were assessed by countermovement jump (CMJ), squat jump (SJ), drop jump (DJ), and loaded CMJs (10-80 kg). Sprinting capacity was assessed in a 30 m sprint. Secondary variables were squat 1-repetition-maximum, body composition and quadriceps thickness and architecture.
Results:
OWL resulted in trivial improvements, and inferior gains compared to FSPT and MSPT for CMJ, SJ, and DJ. MSPT demonstrated small, but robust effects on SJ, DJ and loaded CMJs (3-12%). MSPT was superior to FSPT in improving 30 m sprint performance. FSPT and MSPT, but not OWL, demonstrated increased thickness in the vastus lateralis and rectus femoris (4-7%).
Conclusion:
MSPT was time-efficient and equally or more effective than FSPT training in improving vertical jumping and sprinting performance. OWL was generally ineffective and inferior to the two other interventions.
... Accurate kinematic measurement of the squat movement facilitates the analysis of the neuromuscular data associated with the technical and mechanical execution of the exercise. Researchers have managed this by controlling the duration of descent and ascent [3], by using a force platform to calculate the position of the centre of mass [17], and by incorporating 2 position transducers in conjunction with a force platform to measure horizontal and vertical displacement [32,33]. A flexible electrogoniometer has also been used along with a position transducer in a number of squat studies [8,11,12,37] to measure angular displacement and detemine the phases for sEMG analysis. ...
Trunk muscle activation (TMA) has been reported during back squat exercise, however reliability and sensitivity to different loads alongside kinematic measures has not. Hence the aim was to determine the interday reliability and load sensitivity of TMA and kinematics during back squats. 10 males performed 3 test sessions: 1) back squat 1RM, 2) and 3) 3 reps at 65, 75, 85 and 95% of system mass max (SMmax). Kinematics were measured from an electrogoniometer and linear transducer, and surface electromyography (sEMG) recorded 4 muscles of the trunk: rectus abdominis (RA), external oblique (EO), upper lumbar erector spinae (ULES) and lumbar sacral erector spinae (LSES), and a reference leg muscle, the vastus lateralus (VL). sEMG amplitude was root mean squared (RMS). No differences (p>0.05) found between tests for any kinematic and RMS data. CV demonstrated moderate interday reliability (~16.1%) for EO, LSES and ULES but not RA (29.4%) during the velocity-controlled eccentric phase; whereas it was moderately acceptable for just LSES and ULES (~17.8%) but not RA and EO (27.9%) during the uncontrolled concentric phase. This study demonstrated acceptable interday reliability for kinematic data while sEMG for most trunk muscle sites was moderately acceptable during controlled contraction. sEMG responded significantly to load.
© Georg Thieme Verlag KG Stuttgart · New York.
... The association of Zone 2 versus Zone 3 during squat exercise was investigated in six studies [7,8,11,12,27,28] and 366 effect sizes. Peak power output during squat exercise was higher in Zone 2 than in Zone 3, with a pooled effect size (Hedges' g) of Squat Subjects set up in a standing position while holding a barbell across their shoulders. ...
The development of muscular power is often a key focus of sports performance enhancement programs.
The purpose of this meta-analysis was to examine the effect of load on peak power during the squat, jump squat, power clean, and hang power clean, thus integrating the findings of various studies to provide the strength and conditioning professional with more reliable evidence upon which to base their program design.
A search of electronic databases [MEDLINE (SPORTDiscus), PubMed, Google Scholar, and Web of Science] was conducted to identify all publications up to 30 June 2014. Hedges' g (95 % confidence interval) was estimated using a weighted random-effect model. A total of 27 studies with 468 subjects and 5766 effect sizes met the inclusion criterion and were included in the statistical analyses. Load in each study was labeled as one of three intensity zones: Zone 1 represented an average intensity ranging from 0 to 30 % of one repetition maximum (1RM); Zone 2 between 30 and 70 % of 1RM; and Zone 3 ≥70 % of 1RM.
These results showed different optimal loads for each exercise examined. Moderate loads (from >30 to <70 % of 1RM) appear to provide the optimal load for power production in the squat exercise. Lighter loads (≤30 % of 1RM) showed the highest peak power production in the jump squat. Heavier loads (≥70 % of 1RM) resulted in greater peak power production in the power clean and hang power clean.
Our meta-analysis of results from the published literature provides evidence for exercise-specific optimal loads for power production.
... Sommige onderzoekers hebben alleen GRF data uit een krachtplatform gebruikt 1,2 , andere onderzoekers gebruikten alleen verplaatsingsdata uit een LPT 3,4 en weer anderen combineerden GRF data met verplaatsingsdata uit één [5][6][7] of twee LPT's. [8][9][10] Iedere combinatie gebruikt een andere methode om de prestatievariabelen te meten en te berekenen. ...
Fysieke trainers, fysiotherapeuten en sportwetenschappers kunnen krachtplatforms en/of linear position transducers gebruiken om kinetische (kracht en vermogen) en kinematische (verplaatsing, acceleratie en snelheid) informatie over een beweging te verkrijgen. Hoe meten deze instrumenten dit alles eigenlijk? En met welke andere aspecten moet rekening worden gehouden bij de data verzameling?
... O exercício é realizado em cadeia cinética fechada (CCF) e as suas implicações nas reabilitações de lesões como ligamento cruzado anterior (LCA) são satisfatórias (1,2,3,4,7,8,9); isso se deve sobretudo a menor translação anterior da tíbia (TAT) quando comparado à cadeia cinética aberta (4,10,11). Além dos aspectos reabilitativos do exercício, o treinamento desportivo também o utiliza para objetivos de hipertrofia e fortalecimento de membros inferiores, como também em competições de levantamento de peso olímpico e powerlifiting (1). ...
The squat exercise is widely used to many rehabilitation and strength programs, due
his functional movement in sports performance such as running and jumping and
daily activities. Therefore several articles measure the load in joints of lower
extremity in many conditions. The aim of this papper was to review a series of
articles published between the year of 1971 to 2013, that analyse joint load in the
squat exercise was measured and discussed. In this manner, several pappers agree
that the squat recommendations, with properly execution will be a safe and well
prescribed exercise in rehabilitation and strength programs; however poor technique,
and excess of load, may cause several problems in soft tissues on individuals such
as osteoarthritis. Understanding the biomechanics of the squat such as joint load will
clarify some of applications for physiotherapists, physical educator and clinicians.
... A number of researchers have reported weak relationships between EMG activities during maximum dynamic versus isometric performances (4,8). These differences may be the result of the type of contraction (3), the load or tension produced (1,15), changing angles throughout each individual's ROM (14), the speed of movement and momentum (29), and incorporation of elastic energy from the stretch-shortening cycle (23,28). Therefore, comparisons between these studies, although both examined the interactive effects of knee and foot positions on quadriceps activities, are tenuous. ...
The leg extension (LE) is commonly used to strengthen the quadriceps muscles during training and rehabilitation. This study examined the effects of limb position (POS) and range of motion (ROM) on quadriceps electromyography (EMG) during 8 repetitions (REP) of LE. Twenty-four participants performed eight LE REP at their 8-repetition maximum with lower limbs medially rotated (TI), laterally rotated (TO), and neutral (NEU). Each REP EMG was averaged over the first, middle, and final 0.524 rad ROM. For vastus medialis oblique (VMO), a REP x ROM interaction was detected (p<0.02). The middle 0.524 rad produced significantly higher EMG than the initial 0.524 rad for REP 6-8 and the final 0.524 rad produced higher EMG than the initial 0.524 rad for REP 1, 2, 3, 4, 6, 8 (p<0.05). For rectus femoris (RF), EMG activity increased across REP with TO generating the greatest activity (p<0.001). For vastus lateralis (VL), EMG increased across REP (p<0.001) with NEU and TO EMG increasing linearly throughout ROM, and TI activity greatest during the middle 0.524 rad. We conclude that to target the VMO the optimal ROM is the final 1.047 rad regardless of POS, while maximum EMG for the RF is generated using TO regardless of ROM. In contrast, the VL is maximally activated using TI over the first 1.047 rad ROM or in NEU over the final 0.524 rad ROM.
... An estimated one repetition maximum (1RM), calculated as 1.5 times the participant's body mass, was utilized for warm-up sets of 10 repetitions (50% of 1RM), eight repetitions (60% of 1RM), four repetitions (80% of 1RM), and one repetition (90% of 1RM), which were completed with 2-min. rest intervals between sets as previously described ( Cormie, Deane, & McBride, 2007 ;McBride, Blow, Kirby, Haines, Dayne, & Triplett, 2009 ;Israetel, McBride, Nuzzo, Skinner, & Dayne, 2010 ;McBride, Skinner, Schafer, Haines, & Kirby, 2010 ;McBride, Haines, & Kirby, 2011 ). In order to normalize depth of each squat, the participant was asked to perform all squats at approximately a 70° knee angle. ...
The purpose of this investigation was to assess the effect of resistance exercise performed to volitional failure on ratings of perceived exertion (RPE) using power as an indication of fatigue. 12 male participants (M age= 21.9 yr., SD = 1.3) performed one set of back squats at three different intensities (50%, 70%, and 90% of one repetition maximum) for both a pre-determined number of repetitions (3) and to volitional failure. RPE was significantly different between sets at 50%, 70%, and 90% when performed to a pre-determined number of repetitions, but not during volitional failure. A decrease in power between the first and the last repetitions in the volitional failure sets suggests that fatigue may confound the relationship between RPE and intensity.
... Kipp et al. [38] showed that torque and rate of torque development at the hip during the pull phase of the clean were highest at greater than 75% of one repetition maximum (RM). Finally, McBride et al. [39] compared the effects on performance between the squat and box squat. Even with replacing the stretch shortening cycle that occurs with the squat, no significant differences were found in performance. ...
Returning to both recreational and competitive sport requires the patient demonstrate the ability to perform their activity without pain, without compensation and without apprehension. The primary focus of this article will be to provide progressive weight bearing phased treatment solutions and both objective and empirical return to play testing suggestions. In addition to satisfactorily completing the test battery with maximum effort, the patient must demonstrate the ability to meet the demands for competing within their respective sport specific environment. Returning to competition will most likely include early phase movement screening and clinical clearance followed by late phase athletic and field testing. Hip structure will and must influence training program design. It is therefore important to recognize that indications for return to play must not focus on a single rehabilitation or exercise variable, but rather a combination of clinical, functional and sport specific demands.
The aims of this study were to assess (i) the load–velocity relationship during the box squat exercise in women survivors of breast cancer, (ii) which velocity variable (mean velocity [MV], mean propulsive velocity [MPV], or peak velocity [PV]) shows stronger relationship with the relative load (%1RM), and (iii) which regression model (linear [LA] or polynomic [PA]) provides a greater fit for predicting the velocities associated with each %1RM. Nineteen women survivors of breast cancer (age: 53.2 ± 6.9 years, weight: 70.9 ± 13.1 kg, and height: 163.5 ± 7.4 cm) completed an incremental load test up to one‐repetition maximum in the box squat exercise. The MV, MPV, and the PV were measured during the concentric phase of each repetition with a linear velocity transducer. These measurements were analyzed by regression models using LA and PA. Strong correlations of MV with %1RM (R² = 0.903/0.904; the standard error of the estimate (SEE) = 0.05 m.s⁻¹ by LA/PA) and MPV (R² = 0.900; SEE = 0.06 m.s⁻¹ by LA and PA) were observed. In contrast, PV showed a weaker association with %1RM (R² = 0.704; SEE = 0.15 m.s⁻¹ by LA and PA). The MV and MPV of 1RM was 0.22 ± 0.04 m·s⁻¹, whereas the PV at 1RM was 0.63 ± 0.18 m.s⁻¹. These findings suggest that the use of MV to prescribe relative loads during resistance training, as well as LA and PA regression models, accurately predicted velocities for each %1RM. Assessing and prescribing resistance exercises during breast cancer rehabilitation can be facilitated through the monitoring of movement velocity.
This study aimed to investigate squat jump and countermovement jump kinetics in the knee dominant and hip dominant postures. Participants included 12 male sports science students. They were instructed to perform a squat jump and a countermovement jump with two squat postures: knee-and hip-dominant postures. The jumping motion and ground reaction force were recorded using a motion capture system and a force plate, respectively. A p-value of 0.05 was considered statistically significant. There was a significant interaction for the maximal knee joint extension torque, with the knee-countermovement jump being more than twice higher than that of other conditions, but not for mechanical work of the knee joint, which was significantly greater in the knee posture than in the hip posture. No significant interactions were found in mechanical work and maximal extension torque of the hip joint, both of which were significantly greater in the hip posture than in the knee posture, and in the countermovement jump than in the squat jump. This study showed that the effects of countermovement and posture were different for joints and that these effects were independent in the hip joint, but interacted in the knee joint. In the knee joint, the posture increased the effect of countermovement on extension torque, but the effect on mechanical work was small. This suggests that countermovement in the knee posture has little effect on the lifting work, but results in a great load on the knee extensors.
Background
Differences in the muscular activity between the high-bar back squat (HBBS) and the low-bar back squat (LBBS) on the same representative group of experienced powerlifters are still scarcely investigated. The main purpose of the study was to compare the normalized bioelectrical activity and maximal angles within single homogeneous group between the HBBS and LBBS for 60% one repetition maximum (1RM), 65% 1RM and 70% 1RM.
Methods
Twelve healthy men (age 24.3 ± 2.8 years, height 178.8 ± 5.6 cm, body mass 88.3 ± 11.5 kg), experienced in powerlifting performed HBBS and LBBS with comparable external loads equal 60% 1RM, 65% 1RM, and 70% 1RM. Electromyography (EMG) signals of muscle groups were synchronously recorded alongside kinematic data (joints angle) by means of a motion capture system.
Results
EMG activity during eccentric phase of squat motion were significantly higher during LBBS than in HBBS for all selected muscles (60% 1RM and 65% 1RM) (p < 0.05). All examined muscles were more activated during concentric phase of the squat cycle (p < 0.05). In the concentric phase, significant differences between the loads were generally not observed between just 5% 1RM change in load level for LBBS.
Conclusions
Our results confirmed significant differences in muscles activation between both squat techniques. Muscle activity during eccentric phase of squat motion were significantly higher during LBBS than HBBS. The differences are crucial for posterior muscle chain during eccentric phase of squat cycle.
Researchers have observed physical improvements following the completion of aquatic-based jump training. However, there is a lack of research on the biomechanical specificity of aquatic-based movement. Therefore, the purpose of this investigation was to evaluate the kinetics and kinematics of loaded countermovement jumps performed in water versus land. Twenty young males and twenty-four NCAA division I women's soccer and gymnastics athletes were asked to perform unloaded and loaded countermovement jumps on land and in chest-deep water immersion. A tri-axial force platform and two dimensional videography produced various kinetic and kinematic measures of jump performance. Peak and mean mechanical power outputs (W) were 88% (8919±3744W vs. 4734±1418W; p<0.001) and 81% (3640±1807W vs. 2011±736W; p<0.001) greater for jumps performed in water versus land. Peak dorsiflexion velocity was 688% faster (44±39°/s vs. 5.6±5.4°/s; p<0.001) for jumps performed in water and tended to model similarly with measures of mechanical power and amortization rate. Bodyweight normalized peak and mean mechanical power outputs decreased by 23.6±2.7% and 23.8±1.9% when load was added in the water. The addition of load on land was associated with an 8.7±2.3% and 10.5±4.4% decrease in bodyweight normalized peak and mean mechanical power. Results suggest that the aquatic environment alters movement primarily at amortization and may provide a unique training stimulus. Also, it can be concluded that fluid resistance and buoyancy combine to influence the mechanics of jumping movements performed in the water.
A machine belt squat is a piece of equipment designed to allow the performance of squats while loading weight on the lifter's hips using a belt. The purpose of this investigation was to determine if belt squats differ from back squats in activation of the primary movers, and to determine the predictive capabilities of back squat load, training status, and anthropometric data on belt squat load. Thirty-one participants (16 males and 15 females) completed anthropometric measurements, a demographic questionnaire, a familiarization visit, and two testing visits, completing a 5 repetition maximum test for back squat and belt squat. Surface electromyography was used to measure muscle activation for the left and right vastus medialis (VMO), vastus lateralis (VLO), rectus femoris (RF), and gluteus maximus (GM). Comparison of muscle activation between the two exercises showed significant differences in the left GM (back squat: 0.84 ± 0.45, belt squat: 0.69 ± 0.22, p=0.015) and right GM (back squat: 0.86 ± 0.45, belt squat: 0.71 ± 0.29, p=0.004). Regression analysis computed significant prediction equations for belt squat load for general population, males, females, and advanced lifters. Overall, results indicate that belt squats may significantly differ in GM activation from back squats. Back squat load, as well as other variables, may be effective in accurately estimating appropriate belt squat load. These findings may help to more appropriately program for training with machine belt squats as a back squat alternative.
The purpose of this study was to determine the effect of load changes on angular accelerations of the ankle, knee and hip joints. Accelerations were measured in the squat (S), power clean (PC) and power hang clean (PHC), and compared to the accelerations in the push-off phase of the sprint start (SS). Methods: Nine female Division I college track athletes performed block sprint-starts, single-leg squat jumps (1S0) with 0% of 1RM, squats (jump) with 0, 25, 40% of 1RM, and PC and PHC with 30, 50, 75, 100% of 1RM. The fastest trial of each exercise was analyzed for minimum and maximum angular accelerations. A one-way, repeated measures ANOVA was used to determine any main effect among the variables between the exercises. Established effects were identified further using Least Square Difference post- hoc analysis. Results: Overall, angular accelerations differed mainly between groups of exercises (S vs. PC vs. PHC), less so within the groups (p < 0.05). Only for minimum angular knee joint acceleration in PHC and for minimum angular hip joint acceleration in S was change in acceleration significantly related to change in load. The ankle, knee and hip joint angular acceleration values in S, particularly the low-load S0, 1S0 and S25, were similar to the values measured in the SS. PC and PHC generally had smaller acceleration peaks, yet maximum angular knee and hip joint accelerations of all PCs and of PHC with 30% of 1RM approached the values of SS and S. Conclusion: Results suggest that light-load squat jumps emulate lower limb angular accelerations of the push-off phase in the sprint start much closer than medium- or heavy-load squats, or power cleans or power hang cleans. The lack of load dependency in PC and PHC should be studied further with athletes skilled in Olympic lifts.
Surfing has recently experienced a significant increase in public and commercial interests, which has resulted in a more professional approach being taken to the sport. Whilst a comprehensive profile of the physical and physiological requirements of surfing is yet to be achieved, significant findings have been reported on; movement characteristics of surfing specific activities, the heart rate (HR), blood lactate concentration ([BLa-]), oxygen consumption (VO2), and peak power output (PPO) responses during laboratory and ocean based tests, as well as time-motion characteristics of surfing activity. It is evident from this review that the physical and physiological requirements of surfboard paddling include; upper body muscular endurance, strength, and power, intermittent endurance, aerobic and anaerobic power, and lactate tolerance and clearance. Conversely, wave riding requires; lower body muscular strength, dynamic balance, single leg strength, and rotational power. It is apparent that surfers require an integration of several highly-developed physiological systems to be successful, and hence, it is imperative for the strength and conditioning (S&C) coach to prescribe training modalities and exercises aimed at developing these capacities to the greatest functional level. Whilst the findings reported on the physical and physiological requirements of surfing thus far can assist the S&C coach with effective training prescription for a surfer, further research is required to develop a more thorough understanding of these requirements.
The purpose of this study was to compare the biomechanics of the traditional squat with 2 popular exercise variations commonly referred to as the powerlifting squat and box squat. Twelve male powerlifters performed the exercises with 30, 50, and 70% of their measured 1 repetition maximum (1RM), with instruction to lift the loads as fast as possible. Inverse dynamics and spatial tracking of the external resistance were used to quantify biomechanical variables. A range of significant kinematic and kinetic differences (p < 0.05) emerged between the exercises. The traditional squat was performed with a narrow stance, whereas the powerlifting squat and box squat were performed with similar wide stances (48.3 ± 3.8, 89.6 ± 4.9, 92.1 ± 5.1 cm, respectively). During the eccentric phase of the traditional squat, the knee traveled past the toes resulting in anterior displacement of the system center of mass (COM). In contrast, during the powerlifting squat and box squat, a more vertical shin position was maintained, resulting in posterior displacements of the system COM. These differences in linear displacements had a significant effect (p < 0.05) on a number of peak joint moments, with the greatest effects measured at the spine and ankle. For both joints, the largest peak moment was produced during the traditional squat, followed by the powerlifting squat, then box squat. Significant differences (p < 0.05) were also noted at the hip joint where the largest moment in all 3 planes were produced during the powerlifting squat. Coaches and athletes should be aware of the biomechanical differences between the squatting variations and select according to the kinematic and kinetic profile that best match the training goals.
An optic fibre method was used to measure in humans in vivo Achilles (ATF) and patellar tendon forces (PTF) during submaximal
squat jumps (SJ) and counter movement jumps (CMJ). Normal two-legged jumps on a force plate and one-legged jumps on a sledge
apparatus were made by four volunteers. Kinetics, kinematics, and muscle activity from seven muscles were recorded. The loading
patterns of the tendomuscular system differed among the jumping conditions, but were similar when the jumping height was varied.
Peak PTF were greater than ATF in each condition. In contrast to earlier simulation studies it was observed that tendomuscular
force could continue to increase during the shortening of muscle-tendon unit in CMJ. The concentric tendomuscular output was
related to the force at the end of the stretching phase while the enhancement of the output in CMJ compared to SJ could not
be explained by increases in muscle activity. The stretching phase in CMJ was characterised by little or no electromyogram
activity. Therefore, the role of active stretch in creating beneficial conditions for the utilisation of elastic energy in
muscle was only minor in these submaximal performances. The modelling, as used in the present study, showed, however, that
tendon underwent a stretch-shortening cycle, thus having potential for elastic energy storage and utilisation. In general,
the interaction between muscle and tendon components may be organised in a manner that takes advantage of the basic properties
of muscle at given submaximal and variable activity levels of normal human locomotion.
The strength and stability of the knee plays an integral role in athletics and activities of daily living. A better understanding of knee joint biomechanics while performing variations of the squat would be useful in rehabilitation and exercise prescription. We quantified and compared tibiofemoral joint kinetics as well as muscle activity while executing front and back squats. Because of the inherent change in the position of the center of mass of the bar between the front and back squat lifts, we hypothesized that the back squat would result in increased loads on the knee joint and that the front squat would result in increased knee extensor and decreased back extensor muscle activity. A crossover study design was used. To assess the net force and torque placed on the knee and muscle activation levels, a combination of video and force data, as well as surface electromyographic data, were collected from 15 healthy trained individuals. The back squat resulted in significantly higher compressive forces and knee extensor moments than the front squat. Shear forces at the knee were small in magnitude, posteriorly directed, and did not vary between the squat variations. Although bar position did not influence muscle activity, muscle activation during the ascending phase was significantly greater than during the descending phase. The front squat was as effective as the back squat in terms of overall muscle recruitment, with significantly less compressive forces and extensor moments. The results suggest that front squats may be advantageous compared with back squats for individuals with knee problems such as meniscus tears, and for long-term joint health.
In order to understand the possible mechanisms contributing to enhanced concentric performance in stretch-shortening cycle exercises in vivo the present study examined knee extension torque, electromyogram (EMG) activity and fascicle length of the vastus lateralis muscle in maximal and submaximal human movements. Maximal concentric knee extensions (120 degrees s(-1)) were done after pre-stretch and pre-isometric conditions by nine volunteers. During shortening at the knee angle of 115 degrees (180 degrees = extended) the knee extension torque was found to be greater in pre-stretch condition (272 vs. 248 N m, P < 0.05) although the torque level prior to shortening was smaller than in pre-isometric condition (268 vs. 314 N m, P < 0.05). At the moment of torque enhancement the EMG activity levels or fascicle lengths did not differ between the conditions. It is proposed that besides specific experimental conditions the present enhancement may be related to longer fascicle length prior to shortening (by 4.1 cm, P < 0.05) in pre-stretch condition and to modified length-tension properties. Fascicle length behaviour was found to play an important role also in unilateral, submaximal sledge-jump conditions where pre-loading was altered but the concentric net impulse and joint angular movements were the same. In repeated drop jumps with greater pre-load the changes in fascicle length were smaller than in the counter movement jump that was characterized by a lower force and activity level in the eccentric phase. Results from the present maximal and submaximal loading conditions suggest that the benefits of stretch-shortening cycle muscle function may come through different interactive mechanisms that may be task specific.
The present study examined the behaviour of the Achilles tendon (AT) - triceps surae (TS) muscle complex during running and long jump take-off. High AT forces were measured in the push-off phase in running even with very low EMG activity. In the long jump, high rate of stiffness development was a characteristic of the braking phase of the jump. The results suggest that high and well-coordinated activation patterns of the leg extensor muscles during the preactivation and eccentric phases together with high stretching velocities of muscle-tendon complex provide basis for appropriate tendomuscular stiffness. This together with high force at the end of the eccentric phase enables an effective push-off (concentric) phase.
This study examined whether the elasticity of the tendinous tissues plays an important role in human locomotion by improving the power output and efficiency of skeletal muscle. Ten subjects performed one-leg drop jumps (DJ) from different dropping heights with a constant rebound height. The fascicle length of the vastus lateralis muscle was measured by using real-time ultrasonography during DJ. In the braking phase of the DJ, fascicle lengthening decreased and the tendinous tissue lengthening increased with increased dropping intensity. In the subsequent push-off phase, the shortening of tendinous tissues increased with higher dropping intensity. The averaged electromyographic activities of the preactivation and braking phases increased and those of the push-off phase decreased as the drop height was increased. With higher dropping height but constant submaximal rebound jump, the stretched tendinous tissue length increased with less stretched fascicle during the braking phase. In the subsequent push-off phase, the recoil of tendinous tissues became greater. These results suggest that the increased prestretch intensity has considerable influence on the process of storage and subsequent recoil of the elastic energy during the stretch-shortening cycle action.
The purpose of this study was to compare mechanical efficiency between repeated static jumps (SJ), countermovement jumps (CMJ), drop jumps from 75% of maximum CMJ jump height (75DJ) and drop jumps from 125% of maximum CMJ height (125DJ). Subjects included eight jump-trained males. All subjects completed 30 continuous repetitions in the SJ, CMJ, 75DJ, and 125DJ. Oxygen consumption, peak force and center of mass displacement for each repetition during the four jumping patterns were measured. ME was calculated from a combination of force-time curves, displacement-time curves and lactate-corrected oxygen consumption values. In addition, muscle activity was recorded from the vastus medialis, vastus lateralis and biceps femoris using surface electromyography (EMG). 125DJ and 75DJ resulted in significantly (P < or = 0.05) greater ME in comparison to CMJ and SJ. CMJ resulted in significantly greater ME in comparison to SJ. In addition, braking phase muscle activity was significantly greater in 125DJ and 75DJ in comparison to CMJ. Negative work was significantly different between 125DJ, 75DJ and CMJ (125DJ > 75DJ > CMJ). There was a significant positive correlation (r = 0.68) between ME and negative work performed across 125DJ, 75DJ and CMJ. These findings suggest that stretch-shortening cycle movements, which include a strenuous braking phase combined with simultaneous high muscle activity, increase ME. This may be due to optimal muscle-tendon unit kinetics and usage of stored elastic energy.
The purpose of this experiment was to determine whether free weight or Smith machine squats were optimal for activating the prime movers of the legs and the stabilizers of the legs and the trunk. Six healthy participants performed 1 set of 8 repetitions (using a weight they could lift 8 times, i.e., 8RM, or 8 repetition maximum) for each of the free weight squat and Smith machine squat in a randomized order with a minimum of 3 days between sessions, while electromyographic (EMG) activity of the tibialis anterior, gastrocnemius, vastus medialis, vastus lateralis, biceps femoris, lumbar erector spinae, and rectus abdominus were simultaneously measured. Electromyographic activity was significantly higher by 34, 26, and 49 in the gastrocnemius, biceps femoris, and vastus medialis, respectively, during the free weight squat compared to the Smith machine squat (p < 0.05). There were no significant differences between free weight and Smith machine squat for any of the other muscles; however, the EMG averaged over all muscles during the free weight squat was 43% higher when compared to the Smith machine squat (p < 0.05). The free weight squat may be more beneficial than the Smith machine squat for individuals who are looking to strengthen plantar flexors, knee flexors, and knee extensors.
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.
Force-velocity and power-velocity curves in a vertical jump involving movements around several joints were derived from vertical ground reaction forces and knee angular velocities. The jumps were performed with weights from 10 to 160 kg added on the shoulders. The obtained curves from a semi-squatting static starting position resembled those reported for isolated muscles or single muscle groups. Vertical jumps were also performed in the conditions where the shortening of the leg extensors was preceded by prestretching of the active muscles either through a preparatory counter-movement or dropping down on the force-platform from the various heights ranging from 20 to 100 cm. Prestretching modified through a range of velocities the force-velocity and power-velocity curves by increasing both the ground reaction forces and the calculated mechanical power. Thus the results are similar to those reported in isolated muscles. In studies with isolated muscle preparation the nervous connections have not been intact and therefore it is suggested that increase in the performance of the skeletal muscles through prestretching, in the conditions of the present study, was attributed to the combined effects of the utilization of stored elastic energy and the reflex potentiation of muscle activation.
The conditions associated prior to and during the transition from prestretch to shortening may have considerable influence on the final performance of muscle. In the present study male subjects of good physical condition performed vertical jumps on the force-platform with and without preliminary counter movement. In the counter movement jump (CMJ) the amplitude of the knee bending, velocity of the prestretch and the force attained at end of prestretch were the primary parameters of interest. In addition the coupling time indicating the transition from the eccentric (prestretch) phase to the concentric phase was recorded from the angular displacement and reaction force curves. In the final calculation the mechanical performance parameters of CMJ were always compared with those of the jumps performed without counter movement. The results indicated in general first that CMJ enhanced the average concentric force and average mechanical power by 423 N (66%) and 1158 W (81%), respectively. This potentiation effect was the higher the higher was the force at end of prestretch (p less than 0.001). Similarly, the prestretch speed (p less than 0.001) and short coupling time (p less than 0.01) were associated with enhanced performance during the concentric phase. The average coupling time was 23 ms. The results are interpreted through changes in the prestretch conditions to modify the acto-myosin cross-bridge formation so that the storage and utilization of elastic energy is associated with high prestretch speed, high eccentric force and short coupling time. The role of the reflex potentiation is also suggested as additional enhancement of the final performance.
To isolate any difference muscular contraction history may have on concentric work output, 40 trained male subjects performed three separate isokinetic concentric squats that involved differing contraction histories, 1) a concentric-only (CO) squat, 2) a concentric squat preceded by an isometric preload (IS), and 3) a stretch-shorten cycle (SSC) squat. Over the first 300 ms of the concentric movement, work output for both the SSC and IS conditions was significantly greater (154.8 +/- 39.8 and 147.9 +/- 34.7 J, respectively; P < 0.001) compared with the CO squat (129.7 +/- 34.4 J). In addition, work output after the SSC test over the first 300 ms was also significantly larger than that for the corresponding period after the IS protocol (P < 0.05). There was no difference in normalized, integrated electromyogram among any of the conditions. It was concluded that concentric performance enhancement derived from a preceding stretch of the muscle-tendon complex was largely due to the attainment of a higher active muscle state before the start of the concentric movement. However, it was also hypothesized that contractile element potentiation was a significant contributor to stretch-induced muscular performance under these conditions.
The purpose of this study was to assess the effect of stable vs. unstable conditions on force output and muscle activity during an isometric squat. Nine men involved in recreational resistance training participated in the investigation by completing a single testing session. Within this session subjects performed isometric squats either while standing directly on the force plate (stable condition, S) or while standing on inflatable balls placed on top of the force plate (unstable condition, U). Electromyography (EMG) was recorded during both conditions from the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and medial gastrocnemius (G) muscles. Results indicated peak force (PF) and rate of force development (RFD) were significantly lower, 45.6% and 40.5% respectively, in the U vs. S condition (p < or = 0.05). Average integrated EMG values for the VL and VM were significantly higher in the S vs. U condition. VL and VM muscle activity was 37.3% and 34.4% less in U in comparison to S. No significant differences were observed in muscle activity of the BF or G between U and S. The primary finding in this investigation is that isometric squatting in an unstable condition significantly reduces peak force, rate of force development, and agonist muscle activity with no change in antagonist or synergist muscle activity. In terms of providing a stimulus for strength gain no discernable benefit of performing a resistance exercise in an unstable condition was observed in the current study.
The influence of various loads on power output in the jump squat (JS), squat (S), and power clean (PC) was examined to determine the load that maximizes power output in each lift.
Twelve Division I male athletes participated in four testing sessions. The first session involved performing one-repetition maximums (1RM) in the S and PC, followed by three randomized testing sessions involving either the JS, S, or PC. Peak force, velocity, and power were calculated across loads of 0, 12, 27, 42, 56, 71, and 85% of each subject's 1RM in the JS and S and at 10% intervals from 30 to 90% of each subject's 1RM in the PC.
The optimal load for the JS was 0% of 1RM; absolute peak power was significantly lower from the optimal load at 42, 56, 71, and 85% of 1RM (P < or = 0.05), whereas peak power relative to body mass was significantly lower at 27% of 1RM in addition to 42, 56, 71, and 85% of 1RM. Peak power in the S was maximized at 56% of 1RM; however, power was not significantly different across the loading spectrum. The optimal load in the PC occurred at 80% of 1RM. Relative peak power at 80% of 1RM was significantly different from the 30 and 40% of 1RM.
This investigation indicates that the optimal load for maximal power output occurs at various percentages of 1RM in the JS, S, and PC.