no effect of a single remote voluntary contraction on

NO EFFECT OF A SINGLE REMOTE VOLUNTARY CONTRACTION ON PERFORMANCE IN WOMEN SOCCER PLAYERS BRYNA G. GALLEGOS, LEE E. BROWN, JARED W. COBURN, ANDREW J. GALPIN, AND VANESSA L. CAZAS Department of Kinesiology, Center for Sport Performance, Human Performance Laboratory, California State University, Fullerton, California ABSTRACT

INTRODUCTION

Gallegos, BG, Brown, LE, Coburn, JW, Galpin, AJ, and Cazas, VL. No effect of a single remote voluntary contraction on performance in women soccer players. J Strength Cond Res 27(2): 416–420, 2013—Remote voluntary contractions (RVCs) are defined as muscle contractions remote from, yet concurrent with, the prime mover. Previous studies suggest this phenomenon may produce an ergogenic effect on performance. Currently, little research has examined the effects of a single RVC on complex performance in women athletes. The purpose of this study was to examine the effect of RVC on kick velocity and throw-in velocity in women soccer players. Fourteen women with competitive soccer experience in the past 2 years participated. Subjects performed 3 maximal effort kicks and 3 maximal effort throw-ins with and without RVC. The RVC condition consisted of maximal jaw clenching on a mouth guard during the concentric phase of each kick and each throw-in. During the control condition (CON), subjects were instructed to keep their mouths open, and no mouth guards were used. Analyses demonstrated RVC had no effect on kick velocity (CON: 65.65 6 8.38 km$hr21, RVC: 66.90 6 9.40 km$hr21) or throw-in velocity (CON: 49.55 6 5.65 km$hr21, RVC: 49.31 6 3.81 km$hr21). In conclusion, RVC via jaw clenching does not appear to enhance or negate kick or throw-in velocity in women soccer players. Therefore, athletes and coaches may choose to use mouth guards as they see fit.

KEY WORDS concurrent activation potentiation, velocity, power

Address correspondence to Lee E. Brown, [email protected]. 27(2)/416–420 Journal of Strength and Conditioning Research Ó 2013 National Strength and Conditioning Association

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n the constant quest to optimize muscular strength and performance (1,9,11–14,17,18,25–27), the challenge of finding nonchemical and economically feasible methods of augmenting strength and power remains a primary focus of many sports training programs. Concurrent activation potentiation has been proposed as such a means of enhancing performance through remote voluntary contractions (RVCs) or the simultaneous activation of muscle groups remote to the prime mover (4). Remote voluntary contraction and the neural mechanisms behind it can be classified as a potentiation phenomenon. As potentiation effects are often described based either on their mechanism of action or by the time course in which they occur, the term concurrent activation potentiation can be used to describe the potentiation effects of RVC, as it occurs in conjunction with the activation of the muscles serving as the prime movers (4). This prospective augmentation has the potential to increase peak force production and increase the rate of velocity development among other effects during training or athletic performance. Previous studies have demonstrated differing effects of RVC on a range of muscle actions. Although a number of studies have shown that RVC has no effect on muscle actions (2,15), a variety of other studies present contradictory evidence indicating that RVC does increase force production, rate of force development, work, power, or muscle activation (5–8,20,21). In attempts to explain these contradictory results, some researchers have postulated that RVC may not have an effect on activities involving rapid stretch shortening cycle movements (15). However, this too is debatable as Ebben et al. (5) reported an increase in the rate of force production and a decrease in time to peak force for participants in the RVC condition while performing a countermovement jump. Additionally, it remains unclear as to whether RVC produces the same ergogenic effect in women as in men. Although multiple studies demonstrate no difference in the effect of RVC between genders (5), some have found RVC to be less efficacious in women when compared with men (8).

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Journal of Strength and Conditioning Research There is a need to determine the parameters that govern the underlying mechanisms of RVC, including gender, simple vs. complex movements, and single vs. multijoint activities. To our knowledge, limited research has been conducted on the effect of RVCs on velocity production of complex multijoint movements in women. Therefore, the purpose of this study was to examine the effect of RVC via jaw clenching with a mouth guard on kick and throw-in velocity of women soccer players.

METHODS Experimental Approach to the Problem

This study investigated the effect of RVCs (via maximal jaw clenching) on ball velocity using a 1 group repeated measures design with pre- and posttest measurements. Subjects performed soccer kicks and soccer throw-ins in 2 different conditions. Resulting mean and maximal ball velocity were compared between conditions. We used soccer players so as to be sport specific and have experienced players performing skills in which they were proficient. Subjects

Fourteen women (age: 22.79 6 2.6 years, mass: 63.18 6 7.34 kg, height: 165.1 6 8.98 cm) with competitive soccer experience in the past 2 years volunteered. Competitive soccer experience was defined as participation on a recreational, an intramural, or a collegiate soccer team for at least 1 season in the past 2 years. Subjects were recruited from University women’s soccer teams and Kinesiology classes. Exclusion criteria included any current ankle, knee, and/or hip pathology that would result in functional limitation of maximally striking a soccer ball or any current back, shoulder, elbow, and/or wrist pathology that would result in functional limitation of maximal overhead throwing. Subjects were asked to not participate in resistance training for at least 12 hours before testing and to refrain from static stretching before testing. All subjects were informed of the risks associated with the study and read and signed an informed consent document approved by the University Institutional Review Board. Procedures

Subjects were tested one at a time with one visit to the laboratory. During that visit, they were informed of testing details, then signed the informed consent document, and finally, their height, mass, and age were recorded. Before testing, subjects performed a dynamic upper and lower body warm-up on a grass soccer field. Dynamic exercises included high-knees (jogging with exaggerated hip flexion to approximately parallel to the ground), “buttkickers” (or alternating extreme knee flexion with a neutral hip), skip-and-twist (skip with alternating trunk rotation), skip-and-swing (skip with alternating shoulder horizontal abduction and horizontal adduction), and forward gate swings (a shuffle alternating between left and right hip flexion combined with horizontal adduction). Each exercise was performed for 30 m in a consecutive manner. Testing began

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directly after the warm-up. Thirty seconds of rest was given between trials and 2 minutes between conditions. For the RVC condition, subjects were instructed to maximally contract their jaw muscles by biting down on a mouth guard (Everlast Single Mouthguard) during the concentric phase of their kicks and throw-ins. The mouth guards were submerged in heated water until they became malleable, then subjects were instructed to place the softened mouth guard in their mouths, bite down firmly, and suck the air out of their mouths, thus forming the mouth guard to their teeth and pallet. For the control condition, subjects were instructed to complete their kicks and throw-ins with an open mouth and pursed lips, so as to avoid jaw clenching. Additionally, the proper kick and throw-in techniques were explained and demonstrated to each subject. Once everything was explained, the first subject randomly selected which testing condition order and movement they would do first by drawing slips of paper from a cup. After subject 1, all other subjects performed testing in a counterbalanced fashion. Kick Velocity

Subjects were positioned 1 meter in front of a regulation-size soccer goal on a grass field, so to avoid the need for accuracy and encourage maximal effort for each kick. The ball location was measured and marked for standardization. A 2-step run-up approach was used, and subjects were asked to kick the ball as hard and fast as possible into the goal with their dominant leg. Two sub-maximal practice kicks were given to insure proper spacing from the ball and correct technique, followed by 30 seconds of rest. Maximal kick velocity was measured (in kilometers per hour) with a speed gun (Sports Radar 3600; Sports Radar LTD, Homosassa, Florida, USA) set up 30 cm above the ground directly behind the ball. The speed gun was calibrated immediately before each session according to the instructions provided in the user’s manual. A size-5 soccer ball with standard inflation pressure was used. Subjects completed 3 kicks in each testing condition. Throw-in Velocity

A 3-m distance was delineated with cones directly in front of the same regulation size soccer goal used during

TABLE 1. Mean velocity values for control (CON) and remote voluntary contraction (RVC) conditions in kilometers per hour.* CON

RVC

Throw-in (km$hr21) 46.03 (5.34) 45.17 (4.25) Kick (km$hr21) 60.38 (8.74) 62.38 (10.49) *Values are expressed as mean (SD). There were no interactions, but there was a main effect for movement with kick velocity being significantly greater than throwin velocity.

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TABLE 2. Maximum velocity values for control (CON) and remote voluntary contraction (RVC) conditions in kilometers per hour (km$hr21).*

Throw-in (km$hr21) Kick (km$hr21)

CON

RVC

49.55 (5.65) 65.65 (8.38)

49.31 (3.81) 66.90 (9.40)

*Values are expressed as mean (SD). There were no interactions, but there was a main effect for movement with kick velocity being significantly greater than throwin velocity.

the kick trials. Subjects were instructed to begin at one cone holding the ball in front with both hands, then approach the second cone via whatever approach technique they would typically use during a game, and throw the ball into the goal as hard and fast as possible without crossing the goal line. Torso and hip rotation were prohibited. The throw-in motion began, they brought both hands over their heads, hyperextended their backs and flexed their shoulders. They then threw the ball overhead while both feet remained in contact with the ground during ball release. They performed 2 submaximal throw-ins to ensure proper technique, then 3 maximal attempts. Thirty-seconds rest was given between each trial. Maximal throw-in velocity was measured with the same speed gun as kick velocity located 1 m behind the participants at ball height during each throw. The same size-5 soccer ball with standard inflation was used as that for kicking. Statistical Analyses

All data were analyzed using the Statistical Package for the Social Sciences (version 19.0; SPSS Inc., Chicago, IL, USA). Tests included two 2 3 2 (condition 3 movement) ANOVAs comparing kick and throw-in mean and maximal velocities. Intraclass correlation coefficient reliability values for all measurements ranged from 0.82 to 0.90.

RESULTS There were no interactions or main effects for condition for mean or maximum values. There were main effects for movement for both mean and maximal throw-in and kick values with kick speed being significantly greater than throw-in speed (Tables 1, 2).

DISCUSSION The purpose of this study was to investigate the effect of a single RVC (via maximal jaw clenching) on kick and throw-in velocity of women soccer players. Our results demonstrated that maximal jaw clenching did not augment or negate performance in either movement. This may have been due to the fact that only one muscle RVC was used or due to the multijoint complexity of the task.

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Previous studies have demonstrated various effects of RVC on a range of movements, including isokinetic knee extension and flexion, bench press throws, reaction time, vertical jump, 10-m sprint, and plyo-press power quotient (3PQ), countermovement jump, back squats, jump squats, and postural stabilization (2,3,5–8,15,19). The potentiating phenomenon related to RVC can be attributed to the theory of motor overflow or “functional synergy” (8). Essentially, when one part of the motor cortex is active, connections to other areas of the motor cortex are affected because the divisions responsible for control of muscle force and movement are overlapping and interconnected (5,6,24). Hoy et al. (10) defines motor overflow as a term used to describe involuntary movement accompanying the production of voluntary movement. Additionally, motor overflow can also be attributed to the intercortical communication and the transcallosal facilitation (TCF) process. The TCF hypothesis suggests that when a cortical region is activated as a result of voluntary movement, activation of the same area in the opposite hemisphere may occur. This is possible through interhemispheric connections (10). Earlier research has presented evidence indicating that either one RVC or a combination of RVCs may lead to augmented performance of a muscle (2,3,5–8,15,19,22,23). Ebben et al. (7) investigated the effect of RVC on knee extensor torque, where RVC conditions consisted of jaw clenching, bilateral and contralateral grip, the Valsalva maneuver, or a combination of the three. Their results demonstrated that utilization of a combination of RVCs resulted in greater peak and average torque when compared with utilization of any single RVC alone or none at all. In our study, maximal jaw clenching was the solitary RVC used. Our results may have been enhanced had multiple RVCs been simultaneously performed. In addition to jaw clenching, our subjects could have also performed the Valsalva maneuver or used fist clenching. Although the addition of these RVCs may have enhanced performance, our purpose was to examine a novel and easily applied technique that would not drastically alter sport technique. Although RVCs are often applied in combination, Ebben et al. (5) investigated the effect of jaw clenching on rate of force development, time to peak force, and peak force during the countermovement jump. Results of that study showed that rate of force development and time to peak force during a countermovement jump were significantly greater with jaw clenching compared with no clenching; demonstrating the ergogenic effect of jaw clenching alone on jumping ability. These results are in contrast with ours, which could be because of our use of a more complex multijoint movement. Many previous studies have examined the effect of RVC on single joint movements alone (2,7,8). If multijoint movements were tested, they were performed with very specific criteria for proper execution (5,6) and were relatively simple in nature—for example, countermovement jump (5) and back and jump squats (6). One such study examined the effect of RVC on

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Journal of Strength and Conditioning Research knee extensor torque and found that utilization of RVCs augmented torque production (7). In contrast, a separate study of similar design did not report improvements in knee extensor torque and rate of velocity development (RVD) with double hand gripping RVCs (2). Specifically, their results indicated RVC had no effect on knee extension peak torque and may negatively affect RVD (at 180 d$s21). However, the authors noted the lack of performance enhancement may have been attributed to the fact that only 1 muscle RVC was utilized or that subjects performed each knee extension separately, making the time of RVC use minimal. Other studies have investigated the effect of RVC on more complex movements (3,5,6). The results of these studies indicate that RVCs have a beneficial effect on movements such as countermovement jumps (5); back squat and jump squat (6); and vertical jump, bench throw, and 3PQ (3). However, RVC did not seem to have an ergogenic effect on reaction time or 10-m sprint time (3). It is important to note the difference in movements found to be enhanced by RVC compared with those on which RVC had no effect. The vertical jump, bench throw, 3PQ (3), countermovement jump (5), squat, and jump squat (6) were enhanced through the performance of RVC, whereas 10-m sprint and reaction time where not effected by RVCs. The latter 2 tests require multiple joints and multiple “movements” (such as multiple strides during the 10-m sprint and multiple steps during the reaction time test) for a single “completion” of the movement, whereas the tests mentioned formerly require multiple joints but only one “movement” to complete a single repetition (1 vertical jump, 1 squat, and 1 bench throw). The tests investigated in our study more closely resemble the 10-m sprint and reaction time tests in that multiple joints and multiple movements were involved in the completion of each kick and throwin. Thus, the lack of results in this study may be attributed to this complex vs. simple movement characterization. Another factor that may have contributed to the results attained in this study is gender differences, although some studies have demonstrated no difference in the effect of RVC between gender (2,5). Such was the case in a study conducted by Cherry et al. (2) investigating the effect of RVC (fist clenching) on knee extensor peak torque and velocity development. Cherry et al. found there to be no ergogenic effects of RVC for either men or women. Similarly, in a study conducted by Ebben et al. (5) examining the effect of RVC via jaw clenching on countermovement jump, results demonstrated that RVC increased the rate of force development and decreased the time to peak force for both genders. In both cases, gender appeared to play no role in the outcome. Conversely, Dunn-Lewis et al. (3) demonstrated that RVCs via mouth guard usage improved the performance of upper-body loaded power exercises in both men and women but lower-body power exercises in men only. Likewise, Ebben et al. (8) examined the effect of RVC via jaw clenching, hand gripping, and Valsalva maneuver on knee extensor and flexor performance, and although both men

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and women produced higher peak torque and power during knee extension in the RVC condition, only men saw an increase in rate of torque development and work during extension and peak torque and power during flexion (8). Similarly, Stumbo et al. (19) examined RVC via maximal hand gripping and found an increase in men’s knee extensor torque but no effect in women. Unfortunately, our results were not able to shed any light on this conflicting outcome. It is important to note that although our results seem to indicate there were no obvious beneficial performance effects of mouth guard utilization, there were also no negative effects on performance. This is supported in the study by Rapisura et al. (16), where they demonstrated that mouth guard use in women did not have a positive or negative effect on heart rate, rate of perceived exertion, minute ventilation, oxygen consumption, or respiratory exchange ratio. Therefore, the decision to wear a mouth guard or not is left to the athlete and coach. In summary, RVCs do not always produce enhanced performance outcomes. To our knowledge, this seems to be one of the first studies to look at the effects of jaw clenching as an RVC on sports-specific, multi-joint, complex movements; therefore, more research is necessary to determine the proper RVC methods necessary to elicit positive outcomes in these activities.

PRACTICAL APPLICATIONS Remote voluntary contraction via maximal jaw clenching did not have an effect on soccer kick or throw-in velocity in this study. When training involves complex movement patterns incorporating multiple joints, such as kicking and throwing, coaches may use jaw clenching alone as a solitary RVC becauase it was not detrimental but also did not provide an ergogenic effect. Our data show that in this particular set of circumstances with these 2 specific movements, maximal jaw clenching via a mouth guard seems to have no effect, either positive or negative, on velocity production. Our study did not investigate the countless other movements that one may execute during participation in a soccer game. Thus as a coach, one may either chose to use the mouth guard or not, as there are no observable negative effects, yet there is still the potential for positive effects in other movements. The choice is left completely to the athlete and coach.

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