Attentional Focusing Strategies Influence Muscle
Activity During Isokinetic Biceps Curls
Edge Hill University, Department of Sport and Physical Activity, Ormskirk, United Kingdom
The Football Association, Lilleshall, Shropshire, United Kingdom,
Department of Sport, Health and Exercise Science, University of Hull, Hull, United Kingdom
The present study assessed the influence of different attentional focusing instructions upon muscular activity during biceps curl movements. Twenty-nine participants carried out 10 biceps curl repetitions on an isokinetic dynamometer at 60oás-1 using control, internal (focusing upon arm movements) and external (focusing upon movement of the bar) attentional focusing strategies whilst Electromyography (EMG) activity of the biceps brachii was recorded. Significantly higher levels of EMG activity were observed in the internal and control conditions when compared to when an external strategy was used. When data was normalised against the control condition, the internal strategy resulted in significantly higher levels of EMG activity when compared to the external strategy. Attentional focusing strategies and instructions influence the observed muscular activity, which has direct implications for both skill execution and physical training settings. Coaches, trainers, and physiotherapists should be aware of the effects that different instructional emphases can have at a muscular level.
Research has demonstrated that an external focus of attention is more beneficial to performers than an internal strategy during motor skill performance and learning (see Wulf, 2007 and Wulf & Prinz, 2001 for reviews). Operationalised along the dimension of direction, an external focus of attention has been defined as when a performerÕs attention is directed towards an outcome of, or the effects of, the movement being produced (e.g., a goal, target, intended effect). An internal focus is induced when a performerÕs attention is directed towards the actual bodily movements being produced during a movement (Wulf & Prinz). The benefits of utilising an external focus have been demonstrated in a number of tasks, such as standing balance (McNevin, Shea, & Wulf, 2003), golf (Wulf, Lauterbach, & Toole, 1999), volleyball and soccer kicks (Wulf, McConnel, Gartner, & Schwarz, 2002). The observed detriment of an internal focus has been explained with reference to the constrained action hypothesis (McNevin et al., 2003; Wulf, McNevin, & Shea, 2001). Specifically, individuals asked to adopt an internal focus try to consciously control their movements. This constrains the motor system, inadvertently disrupting automatic control processes. In contrast, focusing on the movement effect by adopting an external focus allows unconscious or automatic processes to control the movement (Vance, Wulf, Tšllner, McNevin, & Mercer, 2004).
Using a more dynamic skill, Zachry, Wulf, Mercer and Bezodis (2005) considered the effects of attentional focusing instructions on muscular activity during basketball free throws. Participants were instructed to focus on the "snapping" movement of their wrist (internal focus) during the follow through or focus upon the centre of the rear of the basketball hoop (external focus). As well as performing more accurately, EMG activity of the biceps brachii and triceps brachii muscles was lower when external focus instructions were used. The observed decreased EMG activity when external focus instructions were utilised is suggested to represent an increase in movement economy (Vance et al., 2004; Zachry et al., 2005). Whereas the increased EMG activity, and impaired movement quality, associated with internal focus instructions was attributed to increased noise in the motor system (Zachry et al.).
An external focus of attention has therefore been shown to have beneficial implications for specific sporting performance. However, applications such as strength training and physical rehabilitation might prioritise maximal muscular output over movement efficiency. In their discussion of functional strength and power training, Ives and Shelley (2003) highlighted that to gain specific muscular adaptations requires controlling the nature of physiological effort through the use of appropriate cognitive and attentional states. Therefore, instructions which increase muscular activity might have practical relevance in rehabilitation and strength training settings.
Although it offers a valuable approach to investigating the effects of different attentional focusing strategies upon movement quality and the mechanisms involved, outside those studies discussed, little research has addressed muscular activity. To develop this line of research, the present study aimed to expand upon the findings of Vance et al. (2004) assessing whether attentional focusing instructions can influence muscular activity during biceps curls. An area of concern in the methodology used by Vance et al. was that movement time was not controlled in Experiment 1, and in Experiment 2 only average speed throughout the range of movement was controlled. Furthermore, the metronome may have placed additional attentional demands upon participants (listening for the click), and caused interference between internal and external sources of information, reducing confidence in the observed results. The present study replicated the biceps curl task, but used an isokinetic dynamometer to maximise control over both the range and speed of movement. This apparatus also localises muscular effort to the biceps, thereby minimising contributions from other muscle groups. It is acknowledged that there are issues with manipulating a true control condition in studies manipulating attentional focus, since without specific instructions participants focus will be directed wherever they wish throughout the trials. However, the present study will compare attentional focusing instruction manipulations against a no-attentional instruction condition, which utilised instructions typically used in such tasks (but with no specific attentional direction).
Twenty-nine participants (Male 16 Female 13) with mean age of 19.6 (± 1.3) yrs. All participants were experienced in the exercise task, but were na•ve to the purpose of the study. The methodology was approved by university departmental research and ethics committee.
To avoid the problems with inter-individual variations, this study utilised a within-subjects design. All participants performed the exercise task using a strategy with no attentional emphasis, an external and an internal attentional focus strategy. As highlighted by McNevin and Wulf (2002), any effects of attentional focus would increase our confidence that this variable has an immediate influence on performance.
Apparatus and Task
Participants completed unilateral isokinetic contractions of the elbow flexor of their dominant (throwing) limb on a Biodex (System 3, Biodex Medical Systems, New York) isokinetic dynamometer, under three instructional conditions; no-attentional direction, internal focus and external focus. The primary task was to exert maximal effort throughout the entire range of movement during ten repetitions of isokinetic concentric elbow flexions at 60o¥s-1 (1.05 rad¥s-1). No trial repetitions were performed during testing. A passive concentric elbow extension returned the test limb to the start position for each repetition. The range of movement was standardised to the participant-specific full range of elbow flexion. Chair orientation standardisation was such that the dynamometer lever arm crank axis aligned with the elbow joint axis of rotation, and the length of the lever arm was adjusted for comfortable grip. To minimise contribution of additional musculature to elbow flexion, restraints were applied across the test arm, proximal to the elbow joint so as not to restrict movement, and across the chest.
Telemetric electromyographical (EMG) activity (Noraxon, Arizona, USA) was obtained for the biceps brachii of the test arm by a trained technician. A pair of disposable bi-polar silver-silver chloride passive surface electrodes (Medicotest, Denmark) were placed on the muscle belly of the biceps. Electrode location was sited and marked as the visual midpoint of the contracted muscle belly obtained during an isometric maximal voluntary contraction. The orientation of the electrode pair was made parallel to the direction of the muscle fibre alignment, with a separation of 8mm between the electrodes. Electrode skin site was prepared by shaving, cleansing and scored with a sterile lancet in the direction of alignment of the electrode pairs. A third, reference electrode was placed on the (inactive and bony) lateral epicondyle of the elbow. The pre-amplified electrode leads were connected to an 8-channel transmitter unit (Noraxon Telemyo 2400T) adjacent, but not connected to the participant. The active EMG leads had a pre-amplifier (gain 500) and 10-1000 Hz band-pass. A sampling frequency of 1500 Hz was used to collect the EMG signal. Data collection was manually initiated prior to the first repetition and terminated following the final repetition. The stationary period immediately preceding the exercise period over which EMG was to be analysed was used to determine a threshold value to quantify muscle inactivity. This off-set value was accounted for in all subsequent analysis of the EMG data. Normalisation of the data (for example to maximal voluntary contraction) was not performed due to the additional error introduced by this process and the experimental design used. The repeated measures design negated the influence factors such as electrode positioning and inter-electrode separation on the signal value.
Prior to participation, participants were shown round the laboratory and equipment whilst given an introduction to the study. Informed consent form making clear the method and procedures to be undertaken were completed and any questions were answered. After the introduction to the study, participants completed three familiarisation sessions prior to testing, during which no consideration was given to varying experimental conditions. After which, and on a single test day, participants used different attentional focusing strategies: the first trial was No Instruction, the subsequent trials were counter-balanced internal, and external strategies. The no-instruction condition was completed before the counter-balanced attentional focus conditions to avoid subjects using previous test strategies perceived to be successful. Prior to the task beginning, participants were given their allocated attentional focusing instructions for that trial verbally and in writing by the researcher. No additional verbal encouragement was given during the exercise task and visual feedback from the dynamometer or the EMG capture was not provided.
Internal and external instructions were similar to those used in Vance et al. (2004), with participants instructed to "focus upon the movement of the arm during the lift" (internal focus) and "focus upon the movement of the crank handle during the lift" (external focus) respectively. In the no-instruction condition, participants were given no additional instructions other than to produce maximal force throughout the full range of elbow flexion. Participants were told that they should not look at the crank/arm itself, rather they should look straight ahead and concentrate on using the instructions they had been given. The passive elbow extension was also performed in isokinetic mode such that the recovery time between repetitions was standardised. Upon completion of all trials, participants were debriefed as to the purpose of the study and any questions were addressed.
Data processing of the EMG signal was conducted using Noraxon software (MyoResearch XP Master). Raw data were low-pass (300Hz) and high-pass (10 Hz) filtered. The processed EMG signal was further analysed to determine the peak (EMGpk) obtained over the ten repetitions. The total integrated EMG (iEMG) activity over the ten repetitions was also determined as a measure of total muscular activity over the exercise set. This process was repeated for each experimental condition. Data was further processed such that EMGpk and iEMG were normalised relative to the values obtained in the no-instruction condition for each subject, thereby accounting for variation between subjects. Dependent measures were analysed using one-way within-subjects ANOVAs.
Peak Muscular Activity
The type of attentional focusing strategy used significantly effected EMGpk (F(2,56)=6.50, p=0.002, partial eta squared = 0.20). LSD post hoc analysis revealed that peak activity was significantly lower in the external (566.75 + 309.89 μV) condition when compared to the internal (637.01 + 329.19 μV) and no-instruction conditions (654.47 + 350.18 μV), which were themselves not significantly different (see Figure 1).
With data normalised relative to the value obtained in the no-instruction condition, the type of attentional focusing strategy used again significantly effected EMGpk (F(1,28)=6.50, p=0.017, partial eta squared = 0.19). Peak activity was significantly larger in the internal (102% + 25%) condition when compared to the external condition (93% + 16%) (see Figure 2).
Total Muscular Activity
The attentional focusing strategy used also significantly effected iEMG (F(1.55,43.54) = 9.43, p=0.001, partial eta squared = 0.25), with Greenhouse-Geisser Corrections. LSD post hoc analysis revealed that iEMG was significantly lower in the external (5586.42 + 3122.64 μV•s) condition when compared to the internal (6056.24 + 2549.22 μV•s) and no-instruction conditions (6575.48 + 3769.77 μV•s), which were themselves also significantly different (see Figure 3).
Normalised to the no-instruction condition, the type of attentional focusing strategy used significantly effected iEMG (F(1,28)= 5.26, p=0.03, partial eta squared = 0.16). Total iEMG in the internal condition (93% + 16%) was significantly greater when compared to the external condition (88% + 18%) (see Figure 4).
The aim of the present study was to quantify the influence of attentional focusing instructions on muscular activity during a single arm isokinetic biceps curl. Specifically, this study replicated the study of Vance et al. (2004) with the addition of more stringent movement speed control. Such control for movement speed reduced the potential attentional demand and fluctuations in movement speed that may have been present during Vance et al.Õs use of a metronome to time movements. Lower levels of muscular activity were observed in the biceps brachii when externally focused instructions were employed, when compared to both internal and no-instruction conditions. When compared to the internal strategy, significantly lower levels of biceps activity were observed for the external strategy when EMG activity was normalised relative to the no-instruction condition. These results support the findings of Vance et al. and Zachry et al. (2005), whilst advancing the findings of Vance et al. by replicating the findings during a more controlled movement execution. In previous research addressing movement quality, when no attentional instruction conditions have been included (e.g., Wulf, Hš§, & Prinz, 1998; Wulf & McNevin, 2003; Wulf, WŠchter, Wortman, 2003) participantsÕ performance is typically similar to that seen under internal focus conditions, in that they are poorer than compared to the external condition. Similarly, the increased muscle activity in the no-instruction and internal conditions here also suggests that participants were adopting similar strategies. However, such assumptions would have to be tested more directly.
The reduction in muscle activity when utilising an external focus goes some way to highlighting the mechanisms associated with improved movement efficiency demonstrated in numerous studies promoting external instructions (see Wulf & Prinz, 2001). As demonstrated by Zachry et al. (2005), reduced muscular activity induced through an external focus of attention was associated with increased accuracy on a basketball free-throw task. The reduced muscular activity when an external focus is adopted supports the notion that external instructions promote more efficient control mechanisms during movement execution (e.g., Vance et al., 2004). Whereas the detrimental effects of an internal focus are due to ÔnoiseÕ in the motor system, as suggested by the constrained action hypothesis, which has now been observed at a muscular level.
Suggesting application within sporting settings yet to receive attentional focus interest, Vance et al. (2004) indicate that if the aim of a movement is to produce a skill based weight lifting movement such as power-lifting, then focusing externally upon the movement outcome (e.g., the weight being lifted) should be more effective. Therefore expanding the potential beneficial application of external focus instructions from more finer skill execution (e.g., tennis, balance) to power production skills. Instructors within these settings should be aware of the implications of such suggestions, and research should identify effective external focus points that could be utilised for attentional direction instructions (e.g., movement of the weight or bar). However, in some situations, the aim of a movement is to maximise the activity of a specific muscle group, using simple movements such as the biceps curl in the present study. Weight-training or rehabilitative exercises often isolate the contribution of a single muscle group, for example to promote muscle growth or strength gains. As such, the increased muscular activity observed in the internal and no-instruction conditions, although detrimental to skill execution, may well be beneficial in such specific circumstances if increased muscular activity is the aim.
The present study has controlled for speed of movement, using a speed representative of that used in standard weight training. However, in sporting contexts, and some weight training techniques, movements are performed over a range of speeds dependant upon the training goal. Further research should assess whether the influence of attention focus is speed or movement type (e.g., isotonic) dependent. Vance et al. (2004) observed that movements were generally performed quicker when an external focus was utilised. Furthermore, although Vance et al. suggest that an external focus would be beneficial for power-lifting skills, research has yet to address directly the influence attentional focusing instructions on such strength and force production skills. One final limitation of the present study is that no data was collected from the triceps for comparison, therefore not fully presenting the muscular activity present throughout bicep curl movements.
In conclusion, the findings presented provide further support to research demonstrating increases in muscular activity when an internal, compared to an external, focus of attention is induced through instruction (e.g., Vance et al., 2004; Zachry et al., 2005). Such findings provide valuable insight into the mechanisms associated with the often detrimental effects of an internal focus and the benefits of an external focus. The present discussion has also considered the potential benefits of internal focus where the goal is to increase muscular activity (e.g., sports rehabilitation, strength and conditioning) rather than skill execution, but research has yet to address this. In movement performance and learning settings, instructions emphasising an external focus of attention are most effective (see Wulf & Prinz, 2001). The weight trainer, personal trainer and physical therapist, equipped with the knowledge that specific instructions/focuses induce specific muscle activation patterns and movement quality, can direct attention appropriately depending upon the aims of the training session or movement to be executed. In particular, practitioners should be aware of the potential sources of information that can be utilised within their instructions to direct attention externally. Movement effects within the environment, the movement of implements (e.g., rackets, golf clubs, skies, weights), and intended outcomes (e.g., targets) are useful reference points for focusing attention externally through instructions, and should be incorporated whilst avoiding reference to (internal) bodily movement information. In addition, Wulf (2007) suggests that the use of analogies and metaphor could also be potentially useful methods for manipulating an external attentional focus in situations where no obvious reference point or implement is available. By tailoring instructions in these ways, practitioners will be able to influence individualsÕ movement effectiveness and efficiency.
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Correspondence concerning this article should be sent to David Marchant, Edge Hill Univeristy, Department of Sport and Physical Activity, Wilson Centre, Ormskirk, L39 4QP, United Kingdom, Phone: +44-(0)1695-5848710, Email: David.Marchant@edgehill.ac.uk