The snatch is 1 of 2 lifts used in competitive Olympic weightlifting and is also commonly used in strength and conditioning settings. When performing a snatch, a loaded barbell is lifted overhead from the floor in a single motion. For technical analysis and coaching, the lift is typically broken into 5 phases: the first pull, transition, second pull, turnover, and catch or recovery (11). Success of the lift is determined by the complex interaction of several variables through each phase of the lift (Tables 1 and 2).
Movement of the lifters' body impacts the path of the barbell, which in turn influence the technique used to rapidly turn under the barbell into the catch position (25,33). For example, Whitehead et al. (33) suggested that a rearward barbell displacement trajectory is caused by the lifter shifting center of pressure back to the heels through the first pull, making it necessary for the lifter to jump back to catch the barbell. Controlling anterior-posterior barbell movement through the catch has been identified as a critical component of an efficient lift (7,11,13,17,27). Specifically, the proximity of the bar and the body of the lifter has been used to provide a more complete look into the movement of the barbell and lifter as a system. One such measure is known as the barbell-cervical-hip (BCH) angle. The BCH angle is an investigative measure that views the barbell and lifter as a single system represented by the angle between a vector from the barbell to seventh cervical vertebra and the greater trochanter to seventh cervical vertebra (4,6). The BCH angle is evaluated at 6 separate events (Figure 1): lifting the barbell off the floor (LO), the barbell clearing the knee (CK), extension of the hip joint to push the barbell away from the body (PB), the barbell reaching maximum forward position (MF), the barbell reaching its maximum height (MH), and the barbell being caught overhead (CB). Smaller BCH angles through these events would indicate that the lifter is keeping the barbell closer to the body, allowing the lifter to drop under and catch the barbell in a more biomechanically effective manner (5). The BCH angle can be used as an evaluative measure to see where a potential technical flaw occurred in the lift. Flaws in technique, like the barbell swinging away from the body, are commonly corrected through use of phase breakdown derivative lifts, such as a snatch pull (9) or jump shrug (28), and by modifying verbal coaching cues. Coaching cues are short verbal instructions used to facilitate learning and performance. In strength and conditioning settings, verbal instructions are used to inform athletes about what needs to be accomplished on an upcoming repetition (18). Ultimately, if the instructions are provided correctly, a coach can aid in the athlete's acquisition of the desired movement pattern and outcome.
Recent research in motor control and learning has demonstrated significant effects of attentional focus, through verbal instructions, on performance and skill acquisition (for a review, see Refs. 35,36). The attentional focus research clearly demonstrates how an individual focus of attention (FOA) significantly impacts movement and outcome performance. Further, evidence demonstrates that the instructions provided during practice influence how athletes develop strategies to orient focus during competition (24). Verbal instructions can lead a performer to focus their attention in 2 separate classifications: internal and external.
If a performer is purposely concentrating on the movement of the body while executing a skill, they are using an internal FOA. Conversely, if a performer is concentrating on the movement effects or outcome, they are using an external FOA. For example, an athlete working on sprint acceleration out of a staggered start could use an internal FOA by concentrating on fully extending their knee and pushing their foot behind them as they drive out of the stance. Conversely, if the athletes were to adopt an external FOA, they would concentrate on exerting force through the ground to push the track away as they drive out of the stance. Additionally, an individual may not purposely focus on anything in particular while moving. This is known as a neutral FOA and is interpreted as conscious mental resources not being directed to the body's movements or movement effects.
Observed differences in verbal instructions influence on performance and learning are very different and significant. Studies within the motor control and learning research consistently show that verbal instructions promoting an external FOA lead to improved performance and learning, relative to an internal or neutral FOA. Such improvements in learning and performance associated with an external FOA have been observed across the following biomotor abilities: endurance (19,26), speed (23), strength (20,21,34,37,38,41), and coordination (31,38).
For example, studies of vertical jump and reach tasks show that an athlete's FOA greatly impacts not only movement coordination but also jump height. After receiving an internal instruction to concentrate on the tips of the finger while reaching as high as possible, jump and reach height and COM displacement were significantly decreased, relative to an external instruction to concentrate on reaching the rungs of the measurement device (41). Additionally, the internal focus resulted in lower impulse values and lower joint moments at the ankle, knee, and hip (37). Interestingly, these lower outcomes and performance production measures are observed with greater electromyographic activity, suggesting a performance impact at the neuromuscular level (38).
Wulf and Dufek (37) contend that an internal FOA effectively “freezes” the body's degrees of freedom, supporting this with the finding that joint moments were highly correlated with one another after receiving internal focus cues. Thus, an internal focus seems to constrain the motor system by linking these semi-independent body segments. These studies of verbal instructions have demonstrated that minor changes to instructional cues significantly impact the performance of motor skills across a wide range of populations and tasks.
Current literature on verbal coaching instructions for Olympic weightlifting arises from coaches' experience and observation (3,8,10,29,30,32). For example, Everett (10) suggests that the athlete needs to be instructed what to do rather than letting the barbell to swing away from the body, “We can instruct the athlete to maintain a more upright posture, actively pull the barbell in toward the body with the lats, or to direct the elbows up and to the sides”(p. 86). Furthermore, Takano (29) suggests “The critical point to be emphasized to the athlete in the arm pull is to concentrate on elevating the elbows high to the side instead of elevating the bar. In all movements, it is essential to emphasize the movement of the body parts, rather than the moving of the bar”(p. 36). These types of internal instructions form the basis of coaching education but are inconsistent with current motor control and learning literature. Refining instructional models for coaching education may have an impact on athletic performance and reduction of injury risk. Therefore, the purpose of this study was to investigate the impact an athlete's FOA has on kinematic performance of the snatch. It was hypothesized that an external FOA would lead to improved kinematic performance.
Experimental Approach to the Problem
This study was carried out using a within-participant experimental design to observe the performance differences in the snatch when instructed to use internal and external FOA strategies. Participants performed snatch lifts in 2 experimental conditions: a block of 3 repetitions with instructions designed to elicit an external FOA (EXT) and a block of 3 repetitions with instructions designed to elicit an internal FOA (INT). All participants performed a block of warm-up repetitions first followed by either the INT or the EXT instructional blocks. The order of INT and EXT instructional blocks were randomized to avoid any order effects. Whole kinematics of both the lifter and the bar were recorded using a 12-camera motion capture system (Qualisys, Inc., Gothenburg, Sweden) sampling at 250 Hz.
Twelve competitively active athletes (8 male and 4 female athletes ages 19–27) participated in this study. Participants were required to be in a supervised Olympic weightlifting program for at least 1 year for inclusion. The average height, mass, age, and years of weightlifting experience of the subjects were 173.6 (±11.9) cm, 84.8 (±21.7) kg, 23.7 (±2.9) years, and 3.13 (±2.4) years, respectively. Participant sample size was based on similar FOA studies showing significance (37,38,41). Participants were screened for health risk factors through a health screening questionnaire before data collection. Signed informed consent was obtained from all participants before enrolling in the study, and study protocols were approved by the Institutional Review Board at California State University-Long Beach. Participants were required to wear athletic clothing and their own weightlifting shoes. Participants were not given information about the hypothesis of the experiment before data collection.
Before completing a standardized warm-up, participants were given the option to complete self-myofascial release (SMFR) exercises using a standard foam roller. After the SMFR, a set of 58 reflective markers was applied to create an 11-segment biomechanical model (2). Reflective markers were also placed on both ends of the barbell and knurlings. Because this was part of a larger ongoing study on lifting kinematics, not all markers were included in the current analysis. Of the 58 reflective markers, the following were used in the current analysis: a single marker placed on the seventh cervical vertebra, markers placed bilaterally on the greater trochanter, and markers placed on the ends of the barbell. No additional movements or exercises were performed to control for fatigue. After marker application, an National Strength and Conditioning Association–certified strength and conditioning specialist led participants through a standardized dynamic mobility and weightlifting warm-up.
The experimental task consisted of 6 individual repetitions of a full snatch from the floor. All repetitions were performed at 80% of the participant's self-reported most current training 1 repetition maximum. Four-minute rest periods were provided between repetitions. Augmented feedback was not provided during rest periods; however, participants were encouraged to move and hydrate during those intervals. After the warm-up, participants received internal (INT) or external (EXT) instructions before each individual repetition. Instructions were delivered in 2 randomized, counterbalanced blocks of 3 individual repetitions. To provide context for each instruction, participants were shown a video of an internationally competitive weightlifter performing a snatch before the experimenter delivered the instructions. During the video, the experimenter instructed the participant to “concentrate on how the lifter is able to move his elbows high and to the side” for INT block, and “concentrate on how the lifter is able to move the barbell back and up” for EXT block. After viewing video and clarifying the instructions, the participant began preparation for the upcoming repetition. Before lift-off, the experimenter instructed the participant to “concentrate on moving your elbows high and to the side rapidly” for the INT block of repetitions and “concentrate on moving the barbell back and up rapidly” for the EXT block of repetitions. Internal instructions were developed around recommended instructions from coaching education literature (29). To ensure instructional blocks were comparable in wording and content, the internal instructions were transformed into external instructions to express the intended outcome of that movement.
Marker trajectories were tracked using QTM Track Manager software (Qualisys, Inc.). Raw trajectories from the sagittal plane were exported as text files and read into a custom LabView (National Instrument, Austin, TX, USA) program where they were low pass filtered using a fourth-order Butterworth low-pass filter with a cutoff frequency of 6 Hz (4–6). Cutoff frequency was based on previous research. Future research may find it necessary to address this on a case-by-case basis.
The following dependent variables were then calculated: the BCH angle at 6 events (Figure 1), peak instantaneous vertical barbell velocity (Peak BarVV), peak instantaneous horizontal barbell velocity (Peak BarHV), and peak instantaneous vertical elbow velocity (Peak ElbowVV). Instantaneous velocity was measured as the peak of the entire lift and calculated using the central limit theorem.
The BCH angle for each frame of the lift was calculated using the law of cosines: a2 = b2 + c2 − 2bc × cos (α); α = cos−1 (a2 + b2 + c2/2bc), in which a = distance from bar to trochanter, b = distance from trochanter to C7, c = distance from C7 to bar, and α = BCH angle. Lift off was defined as the first time point in which the barbell's vertical position began to increase. Clearing the knee was identified as the time point in which the barbell's vertical position passed the knee marker's vertical position. Maximum forward position was measured at the time point in which the barbell reached its peak horizontal position away from the lifter. Maximum height was measured at the time point in which the barbell reached its peak vertical position. Catching bar was identified as the time point in which the barbell was at its lowest vertical position after MH, directly before vertical position began to increase as the lifter initiated recovery. After each time point was identified, the subsequent BCH angle at that time point was recorded.
For all dependent variables, all 3 repetitions per condition set were averaged. Unsuccessful repetitions in which the lifter attempted to catch the barbell were included as all data points were still collectable and are representative of the FOA block of instructions. An unsuccessful lift was defined based on the International Weightlifting Federation's Technical and Competition Rules & Regulations for 2013–2016 (1).
Paired samples t-tests were used to establish whether attentional focus instructions influence BCH angles at LO, CK, PB, MF, MH, and CB. Differences in Peak BarVV, Peak BarHV, and Peak ElbowVV were also examined with paired samples t-tests. An alpha level of p ≤ 0.05 was used for all tests. All statistics were performed using Statistical Package for the Social Sciences (IBM Corp, New York, NY, USA) version 23.
Paired samples t-test revealed a significant attentional focus cue effect in Peak ElbowVV (t11 = −3.144, p = 0.009), Peak BarHV (t11 = 2.836, p = 0.016), and BCH angle at MH (t11 = −2.729, p = 0.020). Significant differences between FOA conditions were not observed in any other dependent variables (Tables 1 and 2). Statistical analysis showed significantly greater Peak ElbowVV under the INT condition compared with EXT and Peak BarHV increased significantly under the EXT condition relative to the INT (Table 2). Furthermore, Cohen's effect size value revealed moderate to high significance for Peak ElbowVV (r = 0.69) and Peak BarHV (r = 0.65). Additionally, the analysis revealed significantly greater BCH angle at MH after being cued to focus internally compared with externally with a moderate to high significance according to Cohen's effect size value (r = 0.64) (Table 1).
The purpose of this study was to investigate the impact an athlete's FOA has on snatch kinematics. The snatch is a widely used lift in both competitive weightlifting and strength training settings. Although a large amount of recommended coaching cues exist, the impact that these verbal instructions have on an athlete's FOA and its influence on performance have not been investigated. Examining how to apply qualitatively derived coaching cues was listed as a growing area of interest for coaching the Olympic lifts in a recent review of snatch literature (14). A key foundational step in aligning this area of interest with recent motor control research is to understand how orienting FOA impacts performance.
It was hypothesized that an EXT FOA would lead to improved kinematic performance, relative to an INT FOA. Based on the results, the hypothesis was supported. The INT instructions significantly increased BCH angle at MH, relative to EXT instructions (Figure 2). Additionally, Peak ElbowVV was greater under the INT condition when compared with EXT, and Peak BarHV was greater under EXT condition relative to INT.
Previous kinematic analyses revealed that athletes lifting larger loads relative to their body mass demonstrated smaller BCH angles at MH (5). It was suggested that a greater BCH angle at MH indicates that the lifter begins turning underneath the barbell and initiates the squat early, leading to increased difficulty during the catch. Early initiation of the overhead squat would likely increase difficulty because the lifter must now absorb the vertical and anterior-posterior momentum of the barbell as it descends to a controlled hold overhead.
The increased BCH angle observed during MH occurs after the second pull, during the turnover phase. At the end of the second pull, the lifter's lower limb joints fully extend, imparting force to the barbell, leading to peak barbell velocity and peak barbell displacement, respectively (12,14–16). The rapid, coordinated effort to turn underneath the barbell brings the lifter back to the floor as they adopt the catch position (10,14,42). Timing through this portion of the lift is critical, as speed and accuracy into the catch position dictate if the lift will be completed efficiently. Differential effects of attentional focus, like the ones observed in this study, are explained by Wulf's constrained action hypothesis (39,40), which states that consciously focusing on the movement itself interrupts the fast, reflexive automatic control processes that normally control the action; this prevents the motor system from naturally organizing motor actions, thus negatively impacting performance through conscious, slow, attention demanding movement. Given the importance of timing actions from triple extension to overhead squat position, it is possible that coordination of motor unit recruitment was less favorable when lifters were focused internally, resulting in increased BCH angles at MH. Based on the findings of the current study and the body of attentional focus literature, using instructions that promote an internal FOA is unlikely to optimize technical performance of the snatch lift.
One possible limitation of this line of research is that we can not know exactly what the participant is actually focusing on when they perform the lift. Porter et al. (22) surveyed participants after performing agility drills in EXT, INT, and neutral (CON) conditions. They found that participants in the INT condition reported focusing internally on 76% of trials, whereas those in the EXT condition reported focusing externally on 67% of trials. Finally, of the participants in the CON condition, 10% focused internally, 13% focused externally, and 77% focused on “other.” These results of qualitative data suggest that prescribed instructions do induce the desired FOA most of the time across all 3 conditions. Although we did not survey participants similarly in the current study, our finding that the participants' Peak ElbowVV increased when cued internally, toward the speed and direction of the elbows, relative to EXT, seems to suggest that they were directing attention toward the prescribed cue. Similarly, the increased Peak BarHV observed when cued externally, toward speed and direction of the barbell, relative to INT would also suggest that the participants were directing attention toward the execution of the prescribed cue.
Increased peak BarHV away from the lifter while focusing externally is an interesting finding, given the direction of the cue was back and up. Results from a kinematic analysis of elite lifters by Isaka et al. (17) give us an idea of how horizontal velocity can be used as a means of controlling the barbell's backward movement later in the lift. Results of the analysis revealed that the participants moved the barbell backward toward their body through the first pull and transition, followed by movement away from the body in the second pull. During this movement away from the body, horizontal velocity of the barbell increased sharply. The authors proposed that when extensor muscles maximally activate, the lifter's body is pulled backward, nearly to full extension, because of larger contribution from the hip extensors. They conclude that during first pull and transition, elite lifters pulled the barbell toward their bodies to produce needed vertical acceleration, and resulting posterior movement of the barbell was controlled by the forward acceleration produced in the second pull.
It is conceivable that the lifter overtly focusing on the backward movement of the bar to this point in the lift set the lifter up to produce a more forceful hip extension at PB, thus increasing initial forward bar velocity away from the lifter. One would assume that the barbell moving away from the lifter at a faster velocity would not be beneficial as it is likely to lead to an increased BCH angle at MF. This did not occur in the current study; further, the mean BCH angle at MF after being cued externally (49.26 ± 15.52°) was less than the INT (50.61 ± 21.21°) condition. Isaka's findings combined with our observation that the physical position of the bar away from the lifter (MF) did not increase along with the horizontal barbell velocity gives an indication that this may not have been a negative outcome of the lift. Rather, it seems that the increased horizontal barbell velocity away from the lifter could be used as a mechanism to control the posterior movement of the barbell during the catch.
Characteristics of successful and unsuccessful lifts (1) have been studied throughout weightlifting biomechanics literature (6,11,27). It is generally agreed upon that a single variable cannot be attributed to the success or failure of the lift but rather a multifactorial interaction of variables (14). Focus of attention may very well play an important role influencing the success of a lift. In the current study, we recorded only 6 unsuccessful attempts. Of those unsuccessful attempts, 2 were under EXT and 4 under INT (Table 3). This small number of unsuccessful attempts relative to the total amount of attempts analyzed is likely because of the low load used for the current study. Unsuccessful attempts at lower loads are of interest to the current study because we can rule out strength as the primary issue. Likely, a technical flaw was responsible for the observed unsuccessful attempt. Given the larger amount of unsuccessful lifts observed under the INT condition, we may be observing constrained, inefficient movement as a result of the FOA strategy being used.
In conclusion, the present study adds to the body of literature, suggesting that coaches should give careful thought into how they develop verbal instructions. Coaches should develop instructions directed toward the outcome of the movement rather than the mechanics of the movement. This will allow the lifter to free attentional resources through the use of fast, reflexive automatic control processes. Similar to previous FOA literature (31), future research should address the impact FOA has on electromyography activation because it may provide greater insight to the potential differences in activation sequences between internal and external FOA. Another interesting avenue would be to examine the performance profiles of a larger number of unsuccessful and successful repetitions individually. This could provide context as to how performance production measures, such as velocity and BCH angle, impact a performance outcome measures, such as successful or unsuccessful repetitions. More typically prescribed cues should be investigated using various body segments as the INT focus point. Through collaboration with the motor control community, the field of strength and conditioning may see substantial growth in the manner in which athletes are instructed.
The motor control and learning literature that studies FOA and its impact on performance can provide a great knowledge base for coaches working in the field of strength and conditioning. Similar to how coaches carefully use exercise physiology and biomechanics to guide programming choices, strength and conditioning coaches can plan attentional focus strategies to ensure they are teaching athletes how to optimally focus their attention to improve performance. Coaches can transform instructions they are already using into instructions that direct an athlete's focus toward the outcome of the movement. Additionally, coaches can use metaphors and analogies as a way to direct attention toward the movement outcome. For example, Camargo (3) suggests that coaches can cue an athlete out of sending the bar out and away from the body by using: “Describe how they should imagine the bar is so close it will pull their shirt off.”
Based on the findings of this study and conclusions drawn from the growing body of attentional focus literature, subtle changes in verbal instructions can influence performance production measures of explosive, whole-body movements. It is recommended that coaching cues be short, concise, and specific to the outcome of the critical component that is being practiced. Coaches should evaluate currently used cues based on what concept is being taught and make the appropriate changes to avoid the negative impact an internal focus can have on weightlifting performance by transforming that cue into an external cue. Strength and conditioning coaches can impart the same lessons in a more effective manner by making these small changes to the delivery of verbal instructions.
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