Coaches use verbal instruction to focus an athlete's attention on pertinent aspects of a skill. Depending on the context, this focus of attention can be either internal or external (3). An internal instruction directs focus to body movements, joint angles, or the action itself, whereas an external instruction pertains to the desired outcome, an implement (golf club, ball, etc.) or the environment (3,22). Choosing words carefully is critical as proper instructions can “load the working memory,” priming the mind for processing and attention appropriate for that skill (8).
Numerous studies show that adopting an external focus of attention can improve performance in a multitude of domains (balance, accuracy, power, speed, and endurance). In particular, a study by Talpey et al. (21) analyzed the impact of different instructions on countermovement jump (CMJ) performance. Although their instructions were not explicitly external or internal, they reported a significant improvement in jump height (JH) when individuals adopted the “jump height” or external-like focus.
For comparison purposes, we replicated the Talpey et al. (21) protocol while making some modifications. As such, both studies used an unloaded, no arm-swing CMJ. Many studies use the CMJ because of its universal application to sport, as well as its reliability and factorial validity (14,16,17). It also offers insight into movement tendencies, preparedness, response to a particular stimulus, and lower-body power (14,17).
Our study adapted and expanded the Talpey et al. (21) methods to include more explicitly designed focus of attention instructions and a manipulation check survey. Another difference was the use of an elite population in our study: NCAA Division I baseball players. Recognizing that instructions can significantly affect CMJ performance in an untrained population (21), we adopted this variation in hopes of understanding the effect of attentional focus instructions on trained athletes executing a well-practiced skill.
Baseball players were an ideal population for this study because, similar to the CMJ, their sport requires ballistic, high-velocity movement and efficient transfer of kinetic energy from the ground to the rest of the body (5,7). Also reminiscent of the CMJ, baseball players rely on “maximal rested explosive muscular actions” (13). As such, the CMJ test may be a useful and accurate measurement tool for this population.
The purpose of this study was to measure acute differences in CMJ performance (JH, power, velocity, force, eccentric rate of force development [ECC-RFD], and impulse) given opposing focus of attention instructions (internal vs. external) in Division I student-athletes. The findings of this study may help coaches and practitioners determine how to design instructions to best elicit desired performance results.
Experimental Approach to the Problem
To measure the effect of different instructions on CMJ performance, we used a within-subject repeated-measures design. Before the experimental session, all subjects underwent familiarization trials as part of their strength and conditioning program. In these trials, each subject completed 2 sets of the protocol (minus the instruction) in the weight room. Subjects were instructed to maintain normal diets, hydration practices, and sleep schedules before reporting to the testing session. During the single laboratory testing session, which was held during normal training times, subjects heard 2 sets of instructions in a counterbalanced order. One instruction condition had an internal focus, whereas the other instruction had an external. Using random assignment, half of the subjects completed the internal condition first, and half completed the external condition first.
Forty-three NCAA Division I baseball players (mean ± SD, age = 20.0 ± 1.5 years; height = 186.4 ± 6.6 cm; body mass = 88.9 ± 8.8 kg) were recruited. At the time of the study, all subjects were participating in a 3–4×/week resistance training and conditioning program. All had at least 6 months' experience with resistance training, 5 years' experience playing competitive baseball and were considered “experts” at the CMJ. Athletes were recruited through voluntary participation and signed an informed consent form. The study was approved by the University of Kansas Human Research Protection Program.
Upon arrival at the laboratory, participants were taken through a standardized warm-up. First, participants jogged for 4 minutes at a self-selected pace. Then, they completed a 3-minute general stretching routine targeting the hamstrings, quadriceps, gastrocnemius, and gluteal muscles. Next, they performed four 20-m submaximal running build-ups at 60, 70, 80, and 95% maximal effort. After each run, they were instructed to walk slowly back to the starting line. After the running warm-up, participants were given 2 minutes of rest and then asked to perform 2 sets of 4 warm-up CMJs (in the experimental set-up, see Measurement of Squat Jump Variables), at 50 and 95% effort, respectively. Participants then rested for another 2 minutes. After the warm-up, an experimenter (coach) gave each subject a set of baseline instructions, “On every jump, the goal is to jump as high as possible.” Then, the coach gave the first set of attentional focus instructions. The instructions were as follows: internal focus: “In this condition, just concentrate on extending your knees and hips as explosively as possible.” External focus: “In this condition, just concentrate on pushing away from the ground as explosively as possible.” The instructions were designed to be similar in terms of length, sentence structure, and those used by Talpey et al. (21).
No other instructions were given regarding the technique of the CMJs. The same coach delivered all instructions and made every effort to keep tone, inflection, and eye contact consistent for each participant. The use of a coach to deliver instructions was critical for 2 reasons. First, coaching implies a direct connection between athlete and instructor. If instructions are administered through audio recording, the human-to-human interaction is lost. In addition, when the athlete has to hold eye contact with the coach, the likelihood that they are giving undivided attention to the instruction is greater. Second, we wanted this study to be directly applicable to coaching, so it was vital to make this aspect as realistic as possible.
Immediately after hearing the instructions, subjects performed 4 maximal CMJs. Between any 2 CMJs in the same set, they were instructed to rest and reset on the force plate, so they were directly below the linear position transducer (roughly 3–5 seconds). After the first set of 4 CMJs, participants were given a 3-minute rest. During this break they were asked to complete a manipulation check survey. They then heard the same instruction set and performed the second set of 4 jumps in that condition. A 5-minute rest was enforced between sets, during which they completed another manipulation check. At the conclusion of the 5-minute rest, the protocol was repeated for the alternate instruction condition.
During each rest, participants were asked to fill out a short one-question survey. The survey asked “What were you focusing on during the previous 4 trials? If you did not focus on anything in particular, leave the question blank.” They were instructed to be honest, even if they did not focus on the instructions provided.
Measurement of Jump Squat Variables
Participants performed the CMJs on a force platform (Rough Deck HP; Rice Lake Weighing Systems, Rice Lake, WI, USA), while holding a light stretching stick (132-cm length, 3.8-cm diameter, weighing ∼1 kg) across their shoulders as if performing a back squat. The force plate sampled at 1,000 Hz. A position transducer (Transducer Techniques, Temecula, CA, USA) hanging from the ceiling directly above the force platform was affixed to the middle of the stretching stick (Figure 1). The downward countermovement (dip) was not controlled or standardized.
From the force platform + linear position transducer system, we measured JH, peak power (PP), mean concentric power (MCP), peak velocity (PV), mean concentric velocity (MCV), peak force (PF), and mean concentric force (MCF). In addition, we analyzed mean ECC-RFD, relative mean concentric force (rCON), and relative concentric impulse (rCON impulse). Jump height was calculated as the height of the stretching stick at its highest point (peak of the jump) minus its initial height. Peak power, PV, and PF were taken from the entire force curve before take-off (both eccentric and concentric phases). Mean concentric force, MCP, and MCV were measured from just the concentric phase of the jump. Eccentric rate of force development was calculated as the average of the peak eccentric force and the instantaneous eccentric force when the ground reaction force (GRF) returned to body mass. Relative mean concentric force (rCON) was measured as the average vertical force during the concentric phase of the jump relative to body mass (N·kg−1), and relative concentric impulse (rCON impulse) as the integral of the vertical GRF during the concentric phase, relative to body mass (Ns·kg−1).
For force, power, and velocity, we measured both peak and average values. We included both because of discrepancies in the literature as to which is a better predictor of JH and vertical jump performance. Most of the debate surrounds the measurement of power. For example, Baker et al. (2) used mean power for determination of optimal loading in a jump squat. However, other authors have found that PP is a greater predictor of vertical jump performance (1,9). Nevertheless, both versions of the aforementioned variables are reliable (10), and unpublished data from our laboratory indicate ICC ≥0.929 for the variables measured.
Bofore statistical analysis, we removed one subject's data because of software measurement error. To begin, we averaged each subjects' 8 internal condition trials and, separately, their 8 external condition trials. This eliminated outliers and variation in technique. Using the mean internal and external values for each subject, we then averaged all 42 internal condition values and compared them with the averaged external values using paired-sample t-tests. The Statistical Package for the Social Sciences (version 23; SPSS, Inc., Chicago, IL, USA) was used to perform statistical testing, with a significance of p ≤ 0.05. We also calculated the Cohen's d effect size for each difference of mean values. These effect sizes are described as 0.2 = small, 0.5 = moderate, and 0.8 = large.
Force-Time and Position Variables
Data were analyzed using paired-sample t-tests. According to the results of these tests (Table 1), when subjects were instructed using an external focus, they demonstrated significantly (p < 0.05) greater JH, PV, MCP, MCV, mean ECC-RFD, and relative concentric impulse as compared to jumps performed with the internal focus. There was a moderate to large positive effect size (Cohen's d) for each of the significant variables. Figures 2 and 3 illustrate examples of JH and GRF differences between the external cue and internal cue conditions. Peak force, PP, MCF, and relative mean concentric force were not significantly different but demonstrated positive effect sizes. Figure 4 illustrates individual responses for each of the variables that were significantly greater when using an external focus.
Manipulation check surveys were collected after each set of jumps, a total of 4 per subject. These surveys were coded using a method described by Porter et al. (18). The primary investigator sorted each survey into 1 of 4 categories: internal only, external only, mixed, or other. To be coded as internal or external only, the response had to resemble or consist of phrasing mentioned in the instruction set with no mention of the opposing type. The following are examples of internal and external only responses, respectively: internal—“…extending my knees and hips as explosively as possible;” external—“…pushing off the ground as hard as possible.” To be coded as mixed, the response had to contain both internal and external instructions, e.g., “…I focused on pushing away from the ground explosively. I also thought about getting my hips more extended in the jump.” Finally, responses were coded as other if they consisted of information not classifiable as internal/external or reported no particular focus, e.g., “…this time I focused on absolutely nothing. I was just trying to clear my head and not overthink anything.” When comparing responses in the 2 conditions, more subjects reported the correct (desired) focus in the internal focus condition, than in the external focus condition (Table 2).
As a result, more subjects reported a mixed or other focus in the external instruction condition.
In addition, we also calculated the number of times subjects switched their focus within a particular condition. For example, if they reported an internal only focus after the first set of 4 jumps, but a mixed focus after the second set, they were considered to have switched their focus. Roughly, the same number of subjects switched their focus in the internal and external conditions. Three subjects switched focus in both the internal and external conditions, and 17 subjects were perfect in terms of reporting the correct focus of attention for the specific condition.
The primary finding was that jump trials instructed with an external focus demonstrated significantly (p < 0.05) greater JH, PV, MCP, MCV, ECC-RFD, and rCON impulse as compared to jumps performed with the internal focus. The variables of PF, PP, MCF, and rCON force were not significant but demonstrated positive effect sizes.
Of particular interest is the significant increase in ECC-RFD. Most studies analyze concentric or peak RFD as predictors of vertical jump performance (15). However, Laffaye and Wagner (12) argue that ECC-RFD is a better predictor of vertical jump performance because it can illustrate the elasticity of the muscle-tendon structures during the stretch-shortening cycle. They also propose that an increase in ECC-RFD can indicate faster muscle recruitment and greater force production during the eccentric phase (12). Although these inferences were based on studies with an arm swing, it is worth mentioning that our study found significant increases as well.
In the same study, Laffaye and Wagner (12) classified certain athletes based on values of ECC-RFD, rCON, and rCON impulse. They described baseball players as having an “explosive profile,” characterized by high values of ECC-RFD and rCON. Our population of baseball players matched this profile with regard to high values of ECC-RFD, but not rCON.
It is also interesting to note the significant increase in relative concentric impulse (rCON impulse). Greater concentric impulse suggests an increase in the length of the concentric phase, the force, or both (4). By applying greater force or equal force for a longer period, impulse increases (11). One particular study observed that individuals with larger vertical impulses displayed simultaneous increases in vertical velocity at take-off and greater JHs (6). These results demonstrate that impulse and take-off velocity are related.
Take-off velocity is chiefly important in vertical jump performance because the final height of the body's center of gravity is dependent on both vertical velocity and position at take-off (6). In our study, PV is synonymous with take-off velocity. Therefore, the concurrent increases we noted in PV and rCON impulse are consistent with the literature. Our results also indicate a direct relationship between PV and MCV. An increase in PV, which occurs in the concentric phase, seems to parallel the increase in mean velocity of that phase.
With considerable differences in both peak and MCV, it seems surprising that PP was not significant. This result was especially remarkable considering claims that PP is one of (if not the most) influential variable(s) in predicting JH and vertical jump performance (1,9). Comparing our study with those that made these claims, differences in significance can probably be attributed to our method of measuring PP. Most studies restrict the calculation of PP to the concentric phase, yet we measured PP over the entire contact phase. Depending on jump technique, PP occurred in the concentric phase for some and the eccentric for others. Therefore, the PP measurement captured the data accurately only when the individual happened to exhibit PP in the concentric phase. For comparison purposes, future studies should limit PP measurements to the concentric phase.
Similar to many attentional focus studies, our results showed an increase in performance within the external condition (19,21,24). The prevailing theory for these results, the Constrained Action Hypothesis, suggests that the brain defaults to subconscious self-organization when performing a well-practiced skill (like the CMJ). In other words, it subconsciously coordinates motor patterns in the most efficient way possible. When we redirect focus to specific body parts (e.g., extend the hips and knees) instead of the movement as a whole (e.g., push away from the ground), the individual tries to control or adjust the skill in their conscious mind. Therefore, the internal focus interferes with the normal motor process as the individual tries to incorporate the instruction into their current movement pattern (23).
The Constrained Action Hypothesis may explain our manipulation check results. As seen in Table 2, individuals in the internal focus condition demonstrated better recall of the instruction set. Their enhanced recall may be the result of having to process the internal instruction in their conscious mind. Alternatively, the internal instruction may have sounded different or more complex, causing them to think about it longer and store it in the working memory. Either way, this difference in recall may signify a cause for differential performance in the 2 conditions.
The Constrained Action Hypothesis may also explain the connection between improved performance in the external condition and the skill level of the participants. In our population, all subjects were well practiced or “experts” in the CMJ. Based on the Constrained Action Hypothesis, elite performers should be more successful when not consciously thinking about bodily movements. Singer et al. (20) concur that trained performers tend to be more successful when adopting “nonawareness” strategies. Expertise also relates to the athlete's previous experience with coaching. At the Division I level, most athletes receive frequent coaching and diverse cues. This exposure to varied instructions may explain their ability to pick up on nuances in the instruction and apply it to their performance. Had our study used novice athletes, it is possible that any kind of instruction would have been disruptive because these individuals are not accustomed to manipulating movement based on coaching.
Our study was limited, in that we did not measure downward (dip) displacement during the countermovement. At least one study has shown that certain joint angles can explain differences in technique that lead to variance in CMJ performance (21). Dip displacement may also affect other variables such as impulse. For example, when the downward (dip) displacement is less, the athlete tends to load quicker and spend less time in the contact phase. Another limitation of our study is that subjects experienced both conditions within a single experimental session. It is possible that subjects in the second condition had the advantage or disadvantage of still possessing the opposing instructions in their conscious mind. Finally, this study did not include a neutral focus, so it is not possible to determine whether performance decreased with the internal focus condition, or whether it was just less than the external condition.
Future studies should continue evaluating the effect of attentional focus instructions on movement efficiency. Several studies have used electromyography to measure muscular activity in subjects with an external or internal focus. In one vertical jump study, the external focus condition not only produced greater JHs, but also demonstrated simultaneously reduced muscle activity (25). These results are significant because they indicate that the external focus can improve performance while lowering the neural and muscular cost to the athlete.
Unfortunately, none of the existing studies have analyzed electromyography with an elite population. Seeing as trained performers are already efficient in certain movement patterns, it would be interesting to see whether attentional focus instructions can have the same muscular efficiency effects.
This study demonstrates that attentional focus instructions significantly influence several CMJ jump variables (including JH). The finding that instructions can alter efficiency and performance of a skill indicate that they need to be designed and applied to suit the context. According to the literature and this study, if coaches want to optimize a specific performance metric (JH, velocity, power, and rate of force development), they should use external focus of attention instructions.
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Keywords:Copyright © 2019 by the National Strength & Conditioning Association.
peak velocity; peak force; performance; mean concentric power; peak power