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).
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.
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.
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.
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.
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.
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.
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%.
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.
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.
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:
- 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.
- 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.
- 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.
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:Copyright © 2014 by the National Strength & Conditioning Association.
observational learning; resistance training; modeling; technique; performance