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Kinematic and Kinetic Improvements Associated With Action Observation Facilitated Learning of the Power Clean in Australian Footballers

Sakadjian, Alex1,2; Panchuk, Derek1,3; Pearce, Alan J.4

Journal of Strength and Conditioning Research: June 2014 - Volume 28 - Issue 6 - p 1613–1625
doi: 10.1519/JSC.0000000000000290
Original Research

Sakadjian, A, Panchuk, D, and Pearce, AJ. Kinematic and kinetic improvements associated with action observation facilitated learning of the power clean in Australian footballers. J Strength Cond Res 28(6): 1613–1625, 2014—This study investigated the effectiveness of action observation (AO) on facilitating learning of the power clean technique (kinematics) compared with traditional strength coaching methods and whether improvements in performance (kinetics) were associated with an improvement in lifting technique. Fifteen subjects (age, 20.9 ± 2.3 years) with no experience in performing the power clean exercise attended 12 training and testing sessions over a 4-week period. Subjects were assigned to 2 matched groups, based on preintervention power clean performance and performed 3 sets of 5 repetitions of the power clean exercise at each training session. Subjects in the traditional coaching group (TC; n = 7) received the standard coaching feedback (verbal cues and physical practice), whereas subjects in the AO group (n = 8) received similar verbal coaching cues and physical practice but also observed a video of a skilled model before performing each set. Kinematic data were collected from video recordings of subjects who were fitted with joint center markings during testing, whereas kinetic data were collected from a weightlifting analyzer attached to the barbell. Subjects were tested before intervention, at the end of weeks 2 and 3, and at after intervention at the end of week 4. Faster improvements (3%) were observed in power clean technique with AO-facilitated learning in the first week and performance improvements (mean peak power of the subject's 15 repetitions) over time were significant (p < 0.001). In addition, performance improvement was significantly associated (R 2 = 0.215) with technique improvements. In conclusion, AO combined with verbal coaching and physical practice of the power clean exercise resulted in significantly faster technique improvements and improvement in performance compared with traditional coaching methods.

1College of Sport and Exercise Science, Victoria University, Melbourne, Australia;

2Melbourne Football Club, Melbourne, Australia;

3Institute of Sport, Exercise, and Active Living, Victoria University, Melbourne, Australia; and

4Cognitive and Exercise Neuroscience Unit, Center for Mental Health and Wellbeing, School of Psychology, Deakin University, Melbourne, Australia

Address correspondence to Alex Sakadjian, alex.sakadjian@live.vu.edu.au.

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Introduction

Commonly referred to as demonstration, observational learning, or modeling (16), action observation (AO) can be defined as the interaction between a model and an observer. The actions of a model are viewed, causing adaptations of the observer's behaviors to match the outcomes and processes of the events demonstrated by the model (16,17,21,37). Horn and Williams (17) propose that for effective skill acquisition to be achieved, the transfer of information from instructor to learner is critical. In skill acquisition, the most common mode of information transfer is demonstration, from which the general movement patterns of the skill are observed by the learner (21,38). Action observation has been used as an effective method of communicating this information from instructor to learner, especially to novice learners (21).

Most AO-related studies have focused on fine, simple, or sport-specific skills and investigations have provided support to using AO for improving motor skills in both elite (5) and novice (2) level athletes. Buccino et al. (7) who investigated musically naive subjects observing an expert model playing guitar chords, demonstrated that through the use of AO, novel motor patterns can be developed. Similarly, Porro et al. (27) demonstrated that force production was increased after an AO intervention despite no physical training of the muscle tested. The investigation by Porro et al. (27) was one of the few studies found in the literature that investigated and reported changes to kinetic variables as a result of an AO intervention. The study was well controlled, and the improved muscle force results can be strongly attributed to the AO intervention; however, the muscle and motor skill that was investigated lacked specificity to athletic- or sport-related motor skills and muscles. The benefits of AO have also been used to investigate sport-specific skill acquisition. Weeks and Anderson (36) reported that improvements in the acquisition and retention of an overhead volleyball serve after exposure to video footage of a model performing the same skill with ideal form. The subjects in the study had either never performed the skill before or had not practiced the skill in the previous 3 years, which provides evidence of the benefits of AO in learning a skill and then retaining the learned skill for novice or detrained individuals. Baudry et al. (5) also investigated AO-facilitated learning of a sports skill, reporting greater improvements in gymnastic pommel horse technique for the group that received video modeling and feedback than the control group who did not.

The evidence discussed above demonstrates the beneficial impact that AO can have on learning a new motor skill and the subsequent improvements in performance of that motor skill. However, it is apparent that the benefits of using the AO concept have received limited research in a resistance training (RT) environment that is specific to sport performance, despite the obvious requirements for athletes to learn proper lifting techniques to improve strength and power qualities. Strength and conditioning (S&C) is a vital aspect of athletic preparation, especially at the elite levels of competition. The professional standards and guidelines of the National Strength and Conditioning Association (26) has made recommendations on athlete:S&C coach ratios and presented data across various sports athlete:S&C coach ratios; which vary between 3 and 14.8 athletes to 1 coach. The recommendations and guidelines do, however, suggest increased supervision for novice athletes, or athletes who have no experience in technical lifts, such as the power clean. Anecdotal evidence has suggested that in club-based sports systems, where the opportunities to fund S&C coaches is limited, working with large athlete:S&C coach ratios (i.e., 1:25) is not uncommon, making teaching and appropriate supervision of the technical aspects of RT exercises challenging. Taking the time to provide athletes proper technique coaching has, at times, been considered inefficient use of time for S&C staff (who need to supervise a number of athletes concurrently) and has provided a rationale for S&C coaches to question the prescription of exercises such as the power clean from the athletic conditioning program altogether, replacing them with simpler (e.g., squat jump) exercises. With the positive effects of AO-facilitated learning reported in skill acquisition literature, the application of AO theory to S&C practices of athletes could potentially assist S&C coaches in facilitating the learning of athletes in novel and technical exercises.

In terms of AO effects related to RT, Ram et al. (28) found that technique was improved for novice learners in groups that were exposed to observing a model with ideal form for both a barbell squat exercise and a balancing skill while also reporting an improvement in movement outcome for the barbell squat task. McCullagh and Meyer (25) also used a barbell squat exercise with a cohort that had never performed free weight squats previously; they reported that the observation of either skilled or novice models resulted in improved learning of the squat exercise with marginally greater improvement in form for the group that observed skilled models. Rucci and Tomporowski (30) investigated the effect of 3 different types of augmented feedback (video-only, verbal-only, and video-verbal) on hang power clean technique. The video-only and video-verbal feedback groups watched a video of themselves after performing each set of the exercise, therefore a self-model design AO intervention. Results demonstrated an improvement in hang power clean technique for both verbal-only feedback and video-verbal feedback groups, whereas the video-only group failed to show improvement in technique. Perhaps the RT study most similar to this study was performed by Winchester et al. (39) who investigated changes in bar-path kinematics specific to power clean technique while also investigating whether changes were also seen in kinetic variables after 4 weeks of power clean training. Winchester et al. (39) reported that both kinematics of the bar and kinetic variables specific to the power clean improve with training and feedback.

This study investigated the application of AO on facilitating the learning (kinematics) and performance (kinetics) of athletes in a novel and technical exercise (power clean) by using portable and readily available video playback technology to facilitate the AO process. The aim of this research was to determine (a) whether the use of AO would better/faster facilitate the learning of a complex novel RT exercise and (b) whether improvements in performance were associated with an improvement in lifting technique. It was hypothesized that the group who received AO to facilitate learning would improve power clean technique (kinematics) faster than the traditional coaching (TC) group. It was also hypothesized that improvement in power clean technique will be associated with improvements in power clean performance (kinetics).

With limited literature reporting the use of AO in the RT environment, this is the first study to investigate the influence of AO on learning the correct lifting technique of the power clean exercise. The aim for this study was to provide evidence for S&C coaches to apply more efficient practices (e.g., AO) when teaching the power clean exercise to their athletes. To the best of our knowledge, this is also the first study to investigate whether performance of the power clean is enhanced as a result of improved lifting technique in the power clean exercise. This will allow S&C coaches to appreciate the performance benefits, not only the safety benefits of lifting with good technique.

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Methods

Experimental Approach to the Problem

A randomized between groups with repeated measures study design was used to test the hypothesis that the group who received AO to facilitate learning would improve power clean technique (kinematics) faster than the TC group. Kinematic (process measures) and kinetic (mean peak power output [PPO]) data were collected before intervention, at the end of weeks 2 and 3, and after intervention at the completion of week 4. Subjects were randomly assigned to 2 groups (TC and AO) and underwent the training intervention during the general preparation phase of the annual periodized program to limit the effects of “other training” being performed by subjects.

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Subjects

Subjects (n = 15, mean ± SD; age: 20.9 ± 2.3 years, height: 183.4 ± 8.4 cm, body mass: 83.1 ± 6.4 kg) and 1 skilled model (age: 24 years, height: 179 cm, body mass: 82 kg) were recruited from 1 elite, state-level Australian football club. The football club provided written support to use their athletes in the study. All subjects were briefed on the potential risks associated with their involvement in the study and provided written informed consent before participation. All methods were approved by the Victoria University Human Research Ethics Committee and were conducted according to the standards established by the Declaration of Helsinki. Selection criteria for subjects to be included in this study were trained men aged between 18–30 years, but with no experience (novice) performing or receiving formal coaching of the power clean exercise. Subjects were excluded from the study if they were untrained (to reduce the potential of muscle damage) and had a musculoskeletal injury within the previous 6 months before participating in this study. After pretesting, subjects were allocated, through alternate assignment, into 2 groups: the AO group (n = 8) and the TC group (n = 7).

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Equipment

Barbell and Resistance

Subjects performed the power clean exercise with a standard Olympic barbell weighing 20 kg. Pilot testing indicated that an additional 10 kg added to the barbell would provide a moderately challenging resistance while also being safe for novice subjects during learning. The additional 10-kg load was made up from a 2.5-kg weight plate added to each side of the barbell. Also added to each side of the barbell were two 2.5-kg custom-made translucent training discs (made of clear Perspex), which were designed to the same dimensions as a standard 20-kg Olympic-sized weight plate. This allowed for an unobstructed view of body segment positions during performance and later analysis of the power clean, and a starting height of the barbell at the same level as if there were 20-kg Olympic-sized weight plates on each side of the barbell. The 30-kg total load of the barbell was unchanged throughout the training and testing phase.

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Video Cameras

All test trials performed by the subjects and the skilled model were video recorded at 25 frames per second. Two video cameras were set up on tripods; one 90° lateral to the right side of the subject/model (Panasonic, Osaka, Japan) and the other one directly in front to the subject/model (JVC, Yokohama, Japan). The skilled model was video recorded on 1 occasion, during the preparatory phase of the study. Subjects were recorded performing the power clean exercise during a pretest, at the end of weeks 2 and 3, and a post-test taken at the end of week 4.

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Tendo Unit

A weightlifting analyzer (Tendo Sports Machines, Trenčín, Slovak Republic) was used to provide power clean performance data. The Tendo unit attaches to the barbell and provides instantaneous data on PPO (Watts) that were taken during pretest, at the end of weeks 2 and 3, and during the post-test at the end of week 4. The Tendo unit's microcomputer settings were set up to the manufacturer's recommendations for Olympic lifting exercises.

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Procedures

Subjects attended 12 training sessions over a 4-week period (3 sessions per week, including a pretesting, post-testing, and familiarization session). All the power clean training sessions were conducted in the early evening, before the subjects commencing their formal football training sessions. All subjects performed the power clean exercise for 3 sets of 5 repetitions with 2 minutes rest between sets. Baechle and Earle's (3) power clean technique coaching cues were used as the reference to formulate the coaching cues provided to the subjects.

Subjects were introduced to the power clean exercise during the familiarization session that was the first of the 12 sessions and included a demonstration and the basic coaching cues of the exercise. The selected number of repetitions (5) was at the higher end of the 3 to 5 repetitions recommended by Baechle and Earle (3) for power training, and also relates to Carrol and Bandura's (9) findings that higher repetitions result in more accurate reproductions of the movement and better facilitates the learning process. The AO group watched the skilled model (AO intervention) 5 times before performing each set, which was the same number of repetitions subjects were required to physically perform.

Video, from the sagittal and frontal planes, of a skilled performer (model), performing 3 sets of 5 repetitions of power clean trials was collected and used as the vision shown to the subjects from the AO group during the study. Video editing software, Final Cut Pro (Apple, Inc., Cupertino, CA, USA) was used to synchronize the sagittal plane footage with the frontal plane footage, and the 2 video angles were put side by side in a split screen video. The video footage of the skilled model performing 5 repetitions of the power clean was shown to the experimental group on a tablet computer (iPad 2; Apple, Inc., USA).

Before training and testing sessions, subjects undertook a general and standardized warm-up of 1 set of 10 deadlifts with the same barbell and load that was used to perform the power clean, followed by 1 set of 10 body weight squats and 1 set of 5 body weight jump squats, all with 1 minute rest between each exercise. The TC group received verbal coaching cues that would be considered standard practice when coaching in the field, whereas the AO group also received verbal coaching cues, but observed video of the skilled model presented on a tablet computer. The AO group was exposed to 5 repetitions on each occasion of watching the skilled model vision (AO intervention), which was the same number of repetitions subjects were required to physically perform (total of 15 in 3 sets of 5 repetitions). The AO intervention was administered before commencing the first, second, and third set.

Only the testing sessions of the subjects were recorded for analyses. During these sessions, subjects wore plain black compression tights and a plain black long sleeved compression top (Slazenger, Shirebrook, England) on which key joint center landmarks were placed for kinematic analysis. The compression garments provided freedom of movement but minimized joint center marker movement while performing the power clean exercise.

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Statistical Analyses

Kinematic (process measures, which are the steps involved in completing a task or skill such as a power clean, e.g., hip angle) and kinetic (mean peak power output) data were analyzed off-line. Power clean technique data were measured using the criteria listed in Table 1. Differences in process measures and performance for each repetition were averaged for the 15 repetitions for each time point (before intervention, at the end of weeks 2 and 3, and after intervention). Video recordings of testing sessions were analyzed using a biomechanical video analysis software (Kinovea version 0.8.15, www.kinovea.org). This software enabled the analysis of technique process measures of the power clean exercise such as joint angles and distances.

Table 1

Table 1

To determine whether technique changed over time, each dependent variable was analyzed separately using linear mixed modeling with group (TC and AO) as a fixed factor and week, set, and repetition as repeated measures (12). The fit of the model was adjusted by inclusion of random intercepts and slopes, changing the variance structure, and removing nonsignificant effects and goodness-of-fit between models was compared using Akaike information criterion. This analysis allowed us to determine the relative change within each group over time and differences between instruction methods. Effect sizes were calculated using Cohen's d. Post hoc tests for significant effects were followed up using a Bonferroni correction with significance set at p ≤ 0.05.

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Results

All subjects involved in the study completed the training intervention of the 12 sessions, including testing, with no reports of injuries being sustained.

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Kinetic Changes

Table 2 shows group-by-time interaction results for mean peak power output (Watts), which was used as a measure of power clean performance. Mean peak power output significantly changed over time, F (3,141.51) = 22.80, p < 0.001. Changes across time showed that mean peak power increased significantly from pretest to the end of week 2 (MΔ = 34.501, SE = 8.43, p < 0.001), the end of week 3 (MΔ = 66.09, SE = 10.49, p < 0.001), and the post-test (MΔ = 86.10, SE = 10.94, p < 0.001). There was a significant increase in peak power from the end of week 2 to the end of week 3 (MΔ = 31.59, SE = 9.87, p = 0.010) and from the end of week 2 to the post-test (MΔ = 51.60, SE = 10.76, p < 0.001). The interaction of group and time was not statistically significant, F (3,141.51) = 1.65, p = 0.180.

Table 2

Table 2

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Kinematic Changes

Changes in kinematic variables across the intervention are summarized in Figures 1–5.

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4

Figure 4

Figure 5

Figure 5

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Torso Angle (O) Relative to Horizontal

In the start phase (Figure 1), there was significant interaction of group and time, F (3,189.40) = 7.07, p < 0.001, d = 0.67; the AO group increased torso angle across all testing times relative to the pretest while there was no change for the TC group. During the first pull phase (Figure 2), there was significant interaction of group and time, F (3,220.21) = 11.29, p < 0.001, d = 0.78; the TC group had a significant decrease in torso angle across all testing times relative to the pretest whereas there was no change in the AO group. There was no significant interaction during the second pull phase (Figure 3; p = 0.164).

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Hip Angle (O)

In the start phase (Figure 1), there was significant main effect of time, F (3,191.84) = 4.49, p = 0.005, d = 0.53; both groups demonstrated a similar increase in hip angle from the pretest across testing times. There was also a significant main effect of time in the first pull phase (Figure 2), F (3,206.35) = 23.31, p < 0.001, d = 1.17, indicating both groups demonstrated similar increases in hip angle across testing times. There was a significant interaction of group and time during the second pull phase (Figure 3), F (3,196.03) = 2.70, p = 0.047, d = 0.41; the TC group increased hip angle at the end of week 2 and at the post-test relative to the pretest, whereas the AO group had no changes. There was a significant interaction of group and time for the catch phase (Figure 4), F (3,216.55) = 5.16, p = 0.002, d = 0.54; both groups decreased hip angle across testing times relative to the pretest; however, no further changes occurred after the end of week 3. In the absorption phase, Figure 5, there was a significant interaction of group and time, F (3,313.30) = 3.40, p = 0.018, d = 0.36; both groups decreased hip angle across all testing times relative to the pretest.

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Knee Angle (O)

In the start phase, there was significant interaction of group and time, F (3,196.94) = 4.28, p = 0.006, d = 0.52; the AO group had a significant decrease in knee angle at all testing times relative to the pretest, whereas the TC group did not change. During the first pull phase, there was a significant interaction of group and time, F (3,193.51) = 31.38, p < 0.001, d = 1.40; both groups had a significant increase in knee angle across all testing times relative to the pretest. During the second pull phase, there was a significant interaction of group and time, F (3,198.09) = 7.81, p < 0.001, d = 0.69; the TC group increased their knee angle across all testing phases relative to the pretest, whereas there was no change in the AO group. At the catch phase, there was a significant interaction of group and time, F (3,211.39) = 7.54, p < 0.001, d = 0.65; the AO group decreased their knee angle across all testing times relative to the pretest, whereas the TC group only decreased knee angle in week 3 and the post-test. In the absorption phase, there was a significant interaction of group and time, F (3,279.59) = 6.50, p < 0.001, d = 0.53; both groups had a significant decrease in knee angle across all testing times relative to the pretest, whereas the TC group also had a significant decrease from week 2 to the post-test.

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Ankle Angle (O)

A significant main effect of time was observed in the start phase (Figure 1), F (3,216.27) = 16.49, p < 0.001; relative to the pretest; ankle angle decreased across all testing times, and there was a decrease from week 3 to the post-test also observed. A significant main effect of time in the first pull phase was seen (Figure 2), F (3,193.51) = 31.38, p < 0.001, d = 1.40; ankle angle increased across all testing times relative to the pretest; however, there were no changes after the end of week 2. A significant interaction of group and time was observed in the second pull phase (Figure 3), F (3,210.86) = 2.67, p = 0.049, d = 0.39. Although both groups increased ankle angle relative to the pretest, the AO group did not change after the end of week 2, whereas the TC group increased from the end of week 2 to the post-test. There was a significant main effect of time in the catch phase (Figure 4), F (3,188.14) = 9.15, p < 0.001, d = 0.76; ankle angle decreased from the pretest to the end of week 2 and the post-test. There was also a significant interaction of group and time during the absorption phase (Figure 5), F (3,194.01) = 2.74, p = 0.045, d = 0.41; the TC group had a significant decrease in ankle angle across all testing times relative to the pretest, whereas the AO group only decreased significantly from the pretest to the end of week 2.

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Shoulder Angle (O)

There was a significant main effect of time for shoulder angle during the catch phase (Figure 4), F (3,239.88) = 56.40, p < 0.001, d = 1.68; shoulder angle increased across all testing time relative to the pretest but did not show any additional increases after the end of week 2.

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Distance (m) Between Shoulders and Barbell

There were no significant differences between groups or across time during the start phase (Figure 1; p = 0.159). There was, however, a significant interaction of group and time during the first pull phase (Figure 2), F (3,191.72) = 6.52, p < 0.001, d = 0.64. Both groups showed a significant increase in distance from the pretest to the end of week 2; and only the TC group changed beyond that time. In the catch phase (Figure 4), there was a significant main effect of time in the distance between the final catch position to most forward position of the barbell, F (3,199.61) = 27.24, p < 0.001, d = 1.28; relative to the pretest, the distance between the barbell and the final catch position decreased.

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Group Comparison of Power Clean Technique Change Over Time

A comparison of the mean percentage change of lifting technique relative to each time point between the TC and AO groups are shown in Figure 6. Data from the kinematic interaction comparisons were normalized relative to the post-test and the % change at each time point was calculated to show the rate of improvement.

Figure 6

Figure 6

From pretest to the end of week 2, the TC group had achieved 6.3% improvement in technique, whereas during the same time, the AO group improved technique by 9.3%, demonstrating a quicker rate of improvement in the AO group compared with the TC group. Testing at the end of week 3 showed a 9.0% improvement in technique for the TC group, whereas the AO group had an improvement of 9.3%. Post-test testing revealed a 10.4% improvement in technique for the TC group, whereas at the same time point the AO group improved by 10.3%.

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Association Between Change in Technique and Change in Performance

A linear regression analysis was conducted between change in technique and change in performance (mean peak power output). Results of the linear regression analysis showed a 21.5% association between a change in technique and a change in performance.

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Discussion

The aim of this study was to investigate whether the use of AO resulted in faster learning of a novel and complex RT exercise. A secondary aim was to determine whether improvements in performance were associated with an improvement in lifting technique. To the best of our knowledge, this is the first study to investigate whether performance of the power clean was improved as a result of improving lifting technique though added AO coaching in the power clean exercise. Because investigations on the learning effects of AO in RT is currently limited, discussion will also draw on the motor learning and skill acquisition literature, where most AO research has been conducted.

Results showed significant kinematic changes occurred for both TC and AO groups over time (Figures 1–6). Both groups improved power clean lifting technique, as seen from the kinematic changes of the power clean technique process measures, during a 4-week training intervention consisting of physical practice and coaching. However, as hypothesized, the AO group that received the AO intervention of watching a video of a skilled model improved power clean technique faster than the TC group who did not receive AO. A 3% difference in improvement between groups from pretest to the end of week 2, which was the largest differential seen (Figure 6) when compared with any other time point, providing evidence that AO had its greatest influence during the initial stages of the acquisition process. From the end of week 2 onward, there was a plateau in technique change seen for the AO group, which resulted in a similar overall change in learning to the TC group at post-test. This plateau may have been as a result of the barbell load remaining constant throughout the duration of the training intervention.

Another key finding of this study and supporting the second hypothesis was that there was a 21.5% association between change in power clean technique and change in kinetic performance. With many considerations and guidelines to be adhered to when undertaking RT for reasons such as injury prevention (3,18,23), lifting with proper technique is stressed as one of, if not, the single most crucial factor when undertaking RT. The importance of correct technique within RT is well documented for reasons such as maintaining safety and reducing the likelihood of injury (3,18). The association presented in this study suggests that correct technique should also be considered beneficial for improving the performance of the power clean exercise. The results should be interpreted with an element of caution because of the barbell load remaining constant especially because the load/resistance is a significant factor in determining power output (performance). Other factors that may have led to improved initial kinetic measures include increases in motor unit recruitment, firing rate, and synchronization (3,11,13,31,32).

These results concur with previous AO investigations demonstrating: (a) AO-facilitated learning is more beneficial for learning than when AO is not present during the acquisition phase of a motor skill (2,5,14); (b) AO in conjunction with verbal instruction and physical practice results in more efficient learning of motor skills when compared with learning with verbal coaching and physical practice alone (2,9,19,22); (c) the use of a skilled model during learning of a skill facilitated by AO (1,6,15,29,40), because of a skilled model providing a correct example of the skill and may also provide information to the observer relating to the strategy used to perform the skill (21); and (d) improved learning of a novel, complex RT exercise, which is more specific to common athletic movements (7,36). Specific to RT, this study, like that by Ram et al. (28), demonstrated improvement in technique using novice learners observing a skilled model but using a more complex RT exercise, the power clean, appropriate for well-trained athletes. The study by Winchester et al. (39) did not have a control group, instead drawing comparisons of bar-path kinematics results from their cohort to the results reported by Stone et al. (35). The visual feedback (AO) provided to subjects of the Winchester et al. (39) investigation, who were experienced performers of the power clean, was in the form of 2-dimensional video of watching their own bar-path trajectory. Also, the kinematic variables investigated were specific to bar-path trajectory, whereas this study used kinematic variables of the subjects' body movements. Furthermore, in a similar finding to the association between change in power clean technique and change in kinetic performance reported in this study, Winchester et al. (39) reported that as improvements in bar-path kinematics specific to power clean technique were achieved, there were also improvements in kinetic variables such as peak power and peak force.

The benefits seen in this study of AO-facilitated learning can be explained by both behavioral and neurophysiological concepts, which have been previously reported in the literature. The results reported in this study may be explained by the visual perception theory; movements of the AO group were potentially constrained toward more accurate performances of the skill after being exposed to the AO intervention where the relative motions of the model were demonstrated. The other behavioral concept explaining the AO process is Bandura's (4) social learning theory. This study used a skilled model for the AO intervention that, based on the social learning theory, provided a reference of correctness for the subjects in the AO group. The use of highly skilled models provides multiple benefits to the quality of demonstration provided, such as a correct example of the skill shown to the observer and also the strategy used by the model to perform the skill.

Although this study did not conduct neurophysiological measures, results may also be explained through neurological links between AO and action execution reported in earlier investigations (7,8,10,33) and attributed to the mirror neuron system (20). Buccino et al. (7), and, more recently, Sartori et al. (33) reported that neuromuscular activation patterns during observed skills were the same as neuromuscular activation patterns during the execution of the observed skill. These findings suggest that the AO intervention in this study could have resulted in greater motor control than the group who did not receive the AO intervention and potentially be a contributing factor to the faster learning demonstrated by the AO group.

A potential limitation of this study was the constant weight of the barbell throughout the training intervention, which may have been a contributing factor for the plateau seen in technique improvement for the AO group. This may have also contributed to nonsignificant group-by-time interaction results obtained for power clean performance because the load of the barbell is critical in the calculation of power. However, maintaining a constant weight of the barbell was necessary to allow for analysis of AO effects on learning because this was the primary aim of the study.

Future research should explore whether a greater volume of AO results in greater/faster learning; or whether there is a specific threshold, which, if exceeded, makes AO redundant (i.e., ceiling effect). Future studies should also aim to explore whether kinetic (performance) measures can be modeled during AO as opposed to kinematic measures. McCullagh and Little (24) have explored the effectiveness of modeling performance measures as opposed to process measures; however, updated investigations should be conducted. Determining whether there is an association between the complexity of the skill being learned and the effectiveness of AO would be beneficial. Future investigations should also aim to extend on this study by having the joint center markers visible on the model during observation by subjects. This may further facilitate the AO learning process by emphasizing the critical components of the skill referred as relative motion in Scully and Newell's (34) visual perception theory.

In conclusion, this study produced significant and novel data by combining the successful use of AO reported in motor learning literature with current issues faced by S&C coaches relating to teaching complex RT exercise techniques. Results showed faster learning of power clean technique and improved performance when conventional training techniques were facilitated by AO than when learning the same skill without AO. This study extends on investigations of AO effects in RT and sports skills by not only investigating pre and post-test performance but also tracking the time course of changes throughout the training intervention. The approach used here provides a greater depth of analysis and highlights changes in process measures that would otherwise be ignored in traditional pretest and post-test designs. The demonstration of AO effects in men also increases the generalizability of findings of AO in RT where most investigations have been conducted with female subjects. The benefits of AO-facilitated learning can be applied to S&C practices with athletes at the elite level to coach correct technique, working with junior and developing athletes to coach basic fundamental skills, personal trainers introducing new or refining learned exercises for clients and by exercise physiologists retraining and teaching motor skills during rehabilitation from neuromuscular conditions.

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Practical Applications

From an applied perspective, the results of this study have demonstrated how benefits associated with implementing AO-facilitated learning into RT training sessions can be achieved in a timely manner. It also addresses a number of other practical considerations, including:

  1. Strength and conditioning coaches can assist athlete development by using video playback technology (e.g., tablet computers) to demonstrate appropriate technique. Although video feedback is not an innovative practice per se, its practical use has been limited because of cost and portable access. Inexpensive, portable, and flexible playback technologies can be positioned throughout the gym by S&C coaches to assist coaching and refining of RT exercise technique.
  2. The application of AO in team environments can be an effective way of managing large athlete:coach ratios. Providing athletes with an elite model demonstrating correct technique can provide athletes with a reference for correctness that can be viewed as often as an athlete chooses when the coach is unavailable and can be a more efficient use of time.
  3. Complex RT exercises, like the power clean, can benefit from the use of AO. Using the approach demonstrated in this study, coaches can include complex lifts in training programs that they may have previously excluded.
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Acknowledgments

The authors thank the subjects who took part in the study. The authors disclose no conflicts of interest. Also, results of this study do not constitute endorsement of any product by the authors or the NSCA. This study was funded by a Research Student Grant from Victoria University (Melbourne, Australia) awarded to A. Sakadjian.

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Keywords:

observational learning; resistance training; modeling; technique; performance

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