Performance deterioration by internally focused instructions significantly depends on task relevance and possible movement pattern integration to optimize goal achievement
Authors: Werner Inge 
Published: September 2024

Introduction & Purpose
Specific instructions for motor skill execution are an essential tool to support motor learning and performance. Focussing on the movement effect in the environment (external focus) is suggested to provoke higher performance outcomes and better learning (Chua et al., 2021; Wulf, 2013). Although known for about 20 years, coaches still prefer using internally focused instructions in training complex movement skills (Yamada et al., 2022), which refer to defined movement segments and the correspondent body parts to implement movement pattern changes. A detailed look into the extensive body of literature reveals the lack of information about the different effects of instructions on whole-body movement adaptations (Lohse et al., 2014). This knowledge might represent the missing link to explain this mismatch between the well-established benefits of external focus instructions and the prevalent use of internally focused instructions in training practice.
The Constrained Action Hypothesis (Wulf et al., 2001) argues that disrupted automatized control loops are responsible for the detrimental effects of internally focused instructions. Focus on fast leg extension while jumping affects automatized movement control. On the other hand, this concept would expect that instructions referring to more distant body sites than the main acting ones would lead to less interference (Pelleck & Passmore, 2017). The standing long jump, one of the most studied motor skills within the focus debate, served as a reference movement, including leg propulsion and arm swing elements, contributing to maximum jump performance and appropriately addressed separately by adversely focused instructions. This study aimed to prove whether internally focused instructions differ in their effect according to their location and how movement pattern changes differ with externally focused instructions.
Methods
A convenient sample of 36 students (physically active, free of injuries, familiar with standing long jumping but naïve to the focus debate, 17 female, mean age 24.5 ± 2.6 y) took part in the study. Participants were assigned to a group receiving leg instructions or a group receiving instructions regarding the arm swing. After 10 minutes of normed warming up, both groups performed two standing long jumps accompanied by the instruction: “Jump as far as you can!” defined as control trials. Then, presented in a randomized order, additional leg instructions (rapid knee extension, stable landing on heels) and additional arm swing instructions (rapid arm swing, preferred focus) were given, respectively. “Jump as near as possible to a cone” or an externally focused arm swing towards a sign was instructed for external focus conditions, according to the group.
Ground reaction forces (GRF) were measured by an AMTI force plate (Watertown, MA, USA, 1000 Hz), where maximum forces in vertical and horizontal directions were exploited. Jumps were monitored by a Vicon System with eight Bonita B10 cameras and a frequency of 200 Hz (Vicon Motion Systems Ltd., Oxford, UK). Markers were positioned on the wrist, elbow, shoulder, hip, knee, ankle, and the second metatarsophalangeal joint on the left side. The angle of the connecting line from shoulder to ankle towards the floor was computed to identify forward body lean at take-off. Jumping distance, maximum vertical and horizontal GRF, maximum knee angle velocity, maximum arm-trunk angle velocity, and forward body lean in the moment of take-off were calculated as the mean of two trials according to each instruction.
Shapiro-Wilk tests provided normality checks, repeated measures analyses of variance were conducted, added by a covariate (control condition), and a grouping factor (leg instruction versus arm instruction). In case of violation of the sphericity assumption, Greenhouse- Geisser correction was applied. Levene’s test proved homogeneity. Post hoc Tukey tests were executed to compare focus conditions pairwise in case of significant interactions. Partial eta squared (h2p) was computed, giving the effect size of instructions on the performance variable. The level of significance was set to a = .05.
Results
As expected, jumping distance changed significantly according to different instructions (F(1.5, 45.5) = 3.86, p = .026, h2p = .11). In contrast, jumping distance was widest for externally focused conditions (jumping towards a cone) in the leg-instruction group, the widest jumps could be performed when focusing on the rapid arm swing or using the preferred instruction in the arm-instruction group. However, the interaction of repetition and group did not reach significance (F(1.5, 45.5) = 3.13, p = .066, h2p = .10).
Maximum GRF did not change significantly between the conditions. At the same time, maximum horizontal GRF adapted differently within the groups according to the leg- or arm-specific instructions (F(2, 62) = 21.82, p < .001, h2p = .41). In the case of instructions focusing on rapid knee extension, the horizontal GRF significantly decreased (p = .034) as well as for focusing on a stable landing (p = .005). In contrast, horizontal GRF increased when performing explosive arm swings (p < .001).
Maximum knee angle velocity increased in the sample for the explosive knee extension instruction and was not affected when the arm swing was prioritized. Overall, the interaction of instructions and group did not reach significance (F(2, 62) = 2.69, p = .076, h2p = .08). The body position at take-off was significantly affected by different instructions (F(2, 60) = 19.63, p < .001, h2p = .40), showing the highest upright positions when focusing on rapid knee extension as well as stable landings (Figure 1).
Discussion
Internally and externally focused instructions directly modulate movement sequence. Despite the preponderance of externally focused instructions compared to leg-orientated commands, results show a dependency of movement pattern adaptations on targets (e.g., arm, leg) and task relevance (e.g., body forward lean at take-off). Internally focusing on a rapid knee extension while jumping provokes an optimization of leg stretch against ground resistance in a more upright position, causing a significant decrease in horizontal GRF and negatively affecting jumping distance.
On the other hand, the internally focused instruction concerning an explosive arm swing led to a beneficial reduction in the forward lean of the body at take-off, accompanied by an upregulation of the horizontal part of the GRF, which positively affects jumping distance. Interestingly, in the case of internally focusing on the stable landing on heels, the take-off was manipulated towards an upright position to ensure success in the task-relevant landing position. In this case, the Constrained Action Hypothesis would have assumed a low impact on the jumping phase, which was not the case.
The externally focused instruction regarding the arm swing used a sign on the wall to provoke flat take-off angles. Interpreting our results, this position was selected too high and yielded adverse adaptations of the arm swing movement compared to the internal instruction of focusing rapid arm swings. Again, these results point to changes in the optimization strategies of our motor control system gained by specific instructions rather than disrupting automatized control loops in the case of internally focused attention.
Conclusion
Our findings relate to movement pattern adaptations driven by task relevance and optimization strategies conditioned by instructions. Even internally focused instructions might positively impact the movement outcome if adaptations can be integrated into the optimization process. Further research should overcome single performance variable assessment using whole-body movement pattern identification to consolidate our results.
References
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