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The Effect of Motor Imagery and Static Stretching on Anaerobic Performance in Trained Cyclists

Kingsley, J. Derek1; Zakrajsek, Rebecca A.2; Nesser, Thomas W.1; Gage, Matthew J.3

Journal of Strength and Conditioning Research: January 2013 - Volume 27 - Issue 1 - p 265–269
doi: 10.1519/JSC.0b013e3182541d1c
Original Research
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Kingsley, JD, Zakrajsek, RA, Nesser, TW, and Gage, MJ. The effect of motor imagery and static stretching on anaerobic performance in trained cyclists. J Strength Cond Res 27(1): 265–269, 2013—Athletes perform many different protocols as part of their warm-up routine before competition. Stretching has been suggested to decrease force and power production, whereas motor imagery (MI), the visualization of simple or complex motor activities in the absence of physical movement, may increase force and power production in young healthy individuals. Few studies have investigated either of these in trained individuals. No studies have compared the effects of static stretching (SS) with MI on anaerobic performance in trained cyclists. The purpose of this study was to examine the effects of SS compared with MI and quiet rest (QR) on anaerobic performance in trained cyclists. Thirteen trained cyclists (9 men: 4 women; aged 21 ± 2 years) were assessed for height (1.76 ± 0.07 m), weight (73.4 ± 13 kg), % body fat (10.8 ± 6.2%), and maximal oxygen consumption (V[Combining Dot Above]O2max of 42.0 ± 5.6 ml·kg−1·min−1) on a cycle ergometer. The participants performed 3 randomized sessions consisting of cycling for 30 minutes at 65% of V[Combining Dot Above]O2max before undergoing 16 minutes of SS, MI, or QR followed by an anaerobic performance test. The SS consisted of 3 sets of 30-second stretches of the hamstrings, quadriceps, hip flexors, and piriformis. Imagery was based on the physical, environmental, task, learning, emotion, and perspective approach and was conducted by a trained technician. Both relative and absolute powers, and peak revolutions per minute, were quantified using the Wingate anaerobic threshold test. No significant interactions existed among SS, MI, and QR for relative peak power, absolute peak power, or peak RPM. In disagreement with current literature, this study suggests that neither SS nor a single session of MI immediately affect anaerobic performance in trained cyclists. If an event is <30 seconds, then SS or MI may not affect performance.

1Department of Kinesiology, Recreation, and Sport, Indiana State University, Terre Haute, Indiana

2Department of Kinesiology, Recreation, and Sport Studies, University of Tennessee, Knoxville, Tennessee

3Department of Applied Medicine and Rehabiliation, Indiana State University, Terre Haute, Indiana

Address correspondence to J. Derek Kingsley, derek.kingsley@indstate.edu.

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Introduction

Athletes use a myriad of different methods to improve their performance as part of their warm-up before participating in an event. Motor imagery (MI), defined as the visualization of simple or complex motor activities in the absence of physical movement, is one methodology that many athletes may use to enhance their performance (10,14,17,19,22). It has been suggested that MI can significantly improve not only overall performance but also strength and power (9,14,17,22). Lebon et al. (14) reported significant improvements in the maximum number of repetitions for the leg press and bench press after the use of MI in college-aged, active men and women. Ranganathan et al. (17) observed significant increases in elbow flexion by using only “mental contractions” in young, sedentary individuals, which were correlated with increases in electroencephalogram activity. These data suggest that MI does indeed increase activation of higher brain centers and in turn may increase muscle strength and thus power. Taken together, the majority of research on MI suggests that it can be used to improve strength and power. Currently, the data regarding MI in trained individuals are lacking.

Many athletes also perform static stretching (SS) as part of their warm-up routine before an event. Static stretching has been suggested to decrease muscle force production capacity by decreasing peak torque (4–7,12,15), and lower-body power (18). Samuel et al. have reported that SS may decrease the vertical jump in young, healthy individuals. Furthermore, Power et al. reported a decrease in peak torque after SS in young, healthy individuals. Taken together, these data demonstrate that SS decreases force production in young healthy individuals. In addition, few studies have examined SS in trained cyclists, and none have examined the effect on cycling anaerobic power.

Because many athletes perform both MI and SS as part of their warm-up routine before a performance event, it is important to understand their effectiveness. Currently, the effects of MI have shown positive benefits, whereas SS has demonstrated negative effects in young healthy individuals. However, these modalities have not been compared with each other in terms of anaerobic performance, specifically power. Therefore, the purpose of this study is to compare the effects of MI and SS on anaerobic performance in trained cyclists. We hypothesized that MI would increase anaerobic performance, whereas SS would cause it to decrease as measured by the Wingate anaerobic power test in young, trained cyclists.

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Methods

Experimental Approach to the Problem

This study used a crossover design in which all the participants underwent initial testing for subsequent visits and then through 3 different experimental conditions that were chosen at random. During each test day, the participants exercised at 65% of peak oxygen uptake for 30 minutes as measured by a breath-by-breath metabolic system. After the exercise bout, the participants underwent 16 minutes of MI, SS, or quiet rest (QR). Quiet rest involved the participants sitting while reading the student newspaper. After the 16-minute interventions, the participants completed a Wingate anaerobic threshold test. All testing was completed at the same time of the day (±1 hour) for each participant.

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Subjects

Thirteen aerobically trained male (n = 9) and female (n = 4) volunteers participated in this study (age: 21 ± 2 years; height: 1.76 ± 0.07 m; weight: 73.4 ± 13 kg; % body fat: 10.8 ± 6.2%; V[Combining Dot Above]O2max: 42.0 ± 5.6 ml·kg−1·min−1). The participants were classified as “high active” based on the Lipid Research Clinics questionnaire (2) and had a daily aerobic exercise routine as part of their off-season training regime. The participants had no history of cardiovascular disease, hypertension, or diabetes. Exclusion criteria included orthopedic injuries that would limit their ability to complete the study. In addition, none of the participants smoked or used any medication or supplements. Before participation in this study, all the participants gave written consent and completed a physical activity readiness questionnaire. The investigation was approved by the Institutional Review Board for the use of human participants.

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Preliminary Measurements

On the first visit to the laboratory, the participants underwent anthropometric testing and aerobic capacity assessment. The peak value obtained from the aerobic exercise capacity test was used to determine the subsequent aerobic exercise bouts. The remaining 3 test days were randomized and separated by a minimum of 72 hours. For all testing sessions, the participants were asked to come to the laboratory having abstained from caffeine or alcohol for the previous 12 hours. In addition, the participants were asked to refrain from strenuous physical activity for at least 48 hours before data collection.

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Anthropometry

Body composition was assessed using air displacement plethysmography (BodPod; Life Measurement Instruments Inc., Concord, CA, USA). Body density values were converted to body composition values using the Siri equation. Height was assessed with a wall-mounted stadiometer. Weight was determined on a digital scale (Model TI—500 E Class III; Transcell Technology Inc. scales, Buffalo Grove, IL, USA) to the nearest 0.05 kg.

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Maximal Aerobic Capacity

A graded exercise test on a cycle ergometer (Velotron Dynafit Pro; Racermate Inc., Seattle, WA, USA) was used to determine peak oxygen consumption. This test has been shown to be reliable and valid (1). The participants began cycling at 50 W for a period of 2 minutes as a warm-up. Once the warm-up was completed, the intensity was increased by 50 W every 2 minutes until volitional fatigue. Heart rate was recorded with a heart rate monitor (Polar Electro Inc., Woodbury, NY, USA). Breath-by-breath oxygen consumption was assessed using a Medgraphics Ultima CPX Metabolic Cart (Medical Graphics Corporation, St. Paul, MN, USA) and expressed in 15-second averages. It was considered maximal effort when 2 of the following 4 criteria were met: (a) a respiratory exchange ratio of ≥1.1, (b) no change in the heart rate with an increase in workload, (c) no change in oxygen consumption with an increase in workload, (d) an ≥18 on Borg's ratings of perceived exertion.

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Dietary and Hydration Control

To control for diet, the participants were asked to record what they ate over the past 36 hours before the first experimental day. For all subsequent sessions, they were asked to repeat what they ate initially. In addition, the participants were given a hydration protocol to follow, which included asking them to ingest 600 ml (20 oz.) of water, sports drink, or flavored water 4 hours before going to bed and then again upon immediately going to bed.

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Motor Imagery Protocol

The MI protocol included 2 components: relaxation and MI. During relaxation, the participants were guided through deep breathing for 5 minutes. The purpose of instructing the participants through relaxation was to facilitate gaining control of breathing and physiological responses (e.g., heart rate); however, the focus was not on obtaining a highly relaxed state but to prepare for MI. This was followed by 10 minutes of sport-specific MI, which aligned with the physical, environmental, task, learning, emotion, and perspective (PETTLEP) model (11). Based on neuroscience research findings, this model considers important practical components of motor-based imagery interventions: Physical, Environmental, Task, Timing, Learning, Emotion, and Perspective. The physical nature of the imagery included wearing the same clothing and positioning themselves on the bike as when they are performing. The environmental component included performing imagery in the physical environment that the task was actually performed. To aid in addressing the rest of the components of the PETTLEP model, an imagery script was created specifically for the Wingate anaerobic test. An imagery script was used in which the participants were instructed to focus on their personal thoughts and feelings related to a performance event. A script was preferred during the imagery intervention, rather than video, because imagery took place in the actual environment (19). Specifically, the script addressed the task (i.e., reinforcing participants to focus on thoughts, feelings, and actions as during the physical performance and focusing on the kinesthetic nature of imagery), timing (i.e., same timing as performance of the Wingate anaerobic), learning (i.e., focusing on the “feel” of the movement), and emotion (i.e., experiencing all emotions and arousal associated with performance). With regard to the learning component, “feel” of the movement was emphasized rather than technique because participants were trained cyclists (11). The participants were not instructed on which perspective (internal or external) they should use during imagery. The participants were guided through imagery using the script a total of 2 times. To further reinforce individualizing imagery, the participants were instructed to use the remaining time (3 minutes) for their own use of imagery of the task in which incorporating all elements of the performance was emphasized.

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Static Stretching Protocol

The stretching protocol that was used in the present was very similar to that of Wilson et al. (21). Five different stretches were performed on each leg while lying on a mat. Each stretch was repeated 3 times and held for 30 seconds. While lying on their side, the participants stretched the knee extensors by flexing the knee and pulling their heel into their buttocks. For the knee flexors, the participants straightened their leg and grasped distal to the knee, slowly pulling toward their body while on their side. For the hip flexors, the participants grasped their ankle and while keeping the leg slightly extended pulled the heel in their buttocks. Hip extensors were stretched while the knee was flexed. The participants grasped on the anterior of their knee and pulled the flexed leg into their chest. The stretch for the piriformis was performed by having the participants cross their legs so that their right heel was on the left knee. Then, the participants grasped behind the left knee and pulled toward their chest.

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Anaerobic Performance

Each participant performed the Wingate anaerobic threshold test after each 16-minute intervention using a cycle ergometer and the Velotron Wingate software (Wingate Software Version 1.0; Racermate Inc.). At the beginning of the protocol, the participants began cycling at a low rpm for 20 seconds. The participants were then asked to slowly increase their speed over the next 10 seconds so that they would be at their maximal speed before 7.5% of their body weight was added as the resistance on the flywheel. The participants were asked to maintain their revolutions per minute for 30 seconds. Verbal encouragement was not given for any condition to remove any bias.

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Statistical Analyses

A 1-way analysis of variance was used to compare the effects of SS, MI, and QR on absolute and relative power and maximal rpm. If a main effect was deemed significant, paired t-tests were used for post hoc comparisons. Significance was set a priori at p ≤ 0.05. Values are presented as mean ± SD. All statistical analyses were performed using SPSS Version 18 (SPSS, Inc., Chicago, IL, USA).

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Results

Subjects

Participant characteristics are presented in Table 1. One participant was unable to complete the SS because of scheduling conflicts. There were no differences in respect to gender for any of the data.

Table 1

Table 1

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Flexibility

There was a significant change in the sit and reach after performing the stretching exercises from 25.2 ± 2.2 to 27.3 ± 1.7 cm (p < 0.05).

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Anaerobic Performance

There were no significant differences among MI, SS, or QR (p > 0.05) for any performance variable (Figure 1). Absolute peak power after MI was 1.08% (p > 0.05) higher than QR. In addition, there was a difference of 1.05% (p > 0.05) after SS compared with QR. Relative peak power was 0.86% (p > 0.05) greater in both MI and SS compared with QR. Furthermore, there was a 3.17% (p > 0.05) higher peak revolutions per minute after MI compared with QR, and a 1.90% (p > 0.05) higher peak revolutions per minute after SS compared with QR.

Figure 1

Figure 1

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Discussion

The purpose of this study was to investigate the effects of MI and SS on anaerobic performance in trained cyclists. The primary finding of this study was that the effects elicited from MI or SS on relative and peak power and maximum revolutions per minute were no different than QR (Figure 1).

Herbert et al. (10) reported no change in isometric force production of the elbow flexors after performing MI similar to that of this study. Herbert et al. used 8 weeks of isometric training for the elbow flexors compared with 8 weeks of “mental” isometric training. The findings of Herbert et al. and this study are in contrast to numerous studies that have shown that strength and power may be improved by MI (14,17,22). Lebon et al. (14) demonstrated a significant increase in the maximum number of repetitions for the leg press after MI in young, healthy athletic individuals. Yue and Cole (22) reported data that suggested MI may significantly increase muscle twitch force. Similar findings have also been reported by Ranganthan et al. (17). They demonstrated a significant increase in elbow flexion strength after MI in young, healthy individuals. Previous reports have used MI over a period of weeks, whereas this study used 1 bout. It has been suggested that MI is a skill that must be practiced to gain maximum benefit. Previous data have also suggested that the more realistic the image is, the greater the benefit. This study used a single bout of MI, which may have been insufficient for the participants to gain a quality image, thus limiting its effect on power output. Another difference between this study and previous studies is we assessed power output in aerobically trained athletes. Based on data from this study and others, the effect of MI, either over time or one session, on power output appears to be mixed.

In this study, there was no effect of SS on power, relative or absolute, which is in contrast to current data. Samuel et al. (18) used 3 repetitions of 30-second stretches for the hamstrings and quadriceps in healthy, college-aged individuals. Immediately after the stretches, there was a significant decrease in lower-body power measured via the vertical jump. A study from Power et al. (16) had young, healthy males stretch 3 muscle groups of the lower body; plantar flexors, hamstrings, quadriceps. Each stretch was held for 45 seconds followed with a 15-second rest period and repeated 3 times. After stretching, there was a significant reduction in the maximal voluntary contractile force of the quadriceps. It has been suggested that decreased power because of SS may stem from neurological and mechanical alterations (3,13). Behm et al. (3) reported a significant reduction in twitch force after SS of the quadriceps, which would suggest increased compliance of the muscle-tendon unit (MTU). Interestingly, they also reported no change in tetanic force that was correlated with a decrease in muscle activation. In turn, this would suggest a neurological deficit more so than a mechanical one. In addition, data from Kokkonen et al. (13) demonstrated that after significant increases in the sit and reach, and thus a compliant MTU, there were significant reductions in leg flexion and leg extension. Their results would then suggest a mechanical limitation. Furthermore, the results from this study may differ from those of Power et al. (16) because of differences in methodology. Unlike this study that used a 30-minute warm-up at 65% V[Combining Dot Above]O2max, Samuel et al. (18) performed stretches after a 5-minute warm-up on the treadmill at self-selected speeds, whereas Power et al. (16) asked the participants to cycle at 70 rpm with a resistance of 1 kp for 5 minutes. In this study, each muscle group was stretched for a total of 90 seconds, very different than the 4.5 minutes of stretching of Power et al. (16). It is possible that the SS protocol in this study was not sufficient to elicit changes in performance. In addition, Samuel et al. (18) and Power et al. (16) also used vertical jump tests to quantify power. Power et al. (16) also used the concentric jump and drop jump from a 30-cm-high platform, and isometric maximal voluntary contraction. Taken together, the data are not fully clear as to whether SS has a profound impact on power exercises lasting <30 seconds.

It is also plausible that the training experience of the participants in this study played a role in the lack of changes after SS. Data from Egan et al. (8) reported no change in peak torque after SS in trained National Collegiate Athletic Association (NCAA) Division I Women's basketball players. Similar to this study, the participants underwent 4 stretches for the lower body that were repeated 4 times and held for 30 seconds. After stretching, there was no change in peak torque. The data from this study and from Egan et al. are also in agreement with those of a study from Unick et al. (20), which demonstrated no change in power after SS in NCAA Division II Women's basketball players. Both of these studies suggested that trained athletes may be less susceptible to alterations in the MTU in response to SS than untrained individuals. However, even though the participants in this study were classified as trained individuals, and not specifically collegiate athletes, it still may assist in explaining the lack of effect of SS. It is clear that future studies need to further examine the responses to SS in aerobically trained and untrained individuals.

Results of this study suggest that one bout of MI and SS have no immediate effect on Wingate anaerobic performance in trained individuals. This is in contrast to multiple reports that have suggested increased performance after MI, and decreased performance after SS. However, it is important to note that the participants in this study were “high active” trained athletes, which may have reduced the impact of stretching.

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Practical Applications

Athletes use both SS and MI as part of the warm-up for competition. Three bouts of 30 seconds stretches may improve flexibility without decreasing power output in endurance athletes. Therefore, 3 bouts of 30-second SS may help prepare the athlete without decreasing their performance if the event is short in duration (≤30 seconds). Thus, it is at the coach's discretion to use SS before activity and further explore the impact of MI on power output.

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Acknowledgments

No funding was received for this study.

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Keywords:

sit and reach; flexibility; power; PETTLEP-based imagery

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