The issue of “grunting” (GR) or vocal disinhibition has plagued tennis players worldwide with some believing that it influences the outcomes of matches. The popular press is replete with negative comments by players about the use of GR, shrieking, or screeching in tennis (1,2,23,24,34). During the 2009 French Open, Aravane Rezaï's complaints to the umpire about Michelle Larcher de Brito's “shrieking,” forced the Grand Slam supervisor to officiate the controversy (14). Although not officially penalized, Larcher de Brito was subsequently booed off the court. Hall of Famer, Navratilova (29) has said, “The GR has reached an unacceptable level. It is cheating, pure, and simple. It is time for something to be done.” To emphasize the point that GR is unnecessary, she cites the success of Roger Federer, a nongrunter (14). Although excessive GR is frowned on, most players still grunt during competitions (35). Currently, the International Tennis Federation does not have a rule on GR (3); however, the Women's Tennis Association is taking active steps in controlling GR during matches (32).
Current studies suggest that tennis players and other athletes may have a physiologically valid reason for GR as it improves muscle recruitment and force production. A recent on-court study by O'Connell et al. (30) demonstrated ∼5.0 mph increase in serves and forehands when collegiate players grunted. This increase was seen regardless of their GR experience, beliefs about GR, or gender. They also found significant increases in isometric serve and forehand pull forces during GR. Ikai and Steinhaus (17) and Welch and Tschampl (37) found significant increases in forearm flexion force and grip force during shouting and during a kiap, respectively. Morales et al. (28) reported small, competitively important increases in the deadlift during GR in both powerlifters and control subjects.
Grunts, shouts, or kiap generated by the performer are not the only methods of increasing force production during a maximal or near-maximal strength task (17,28,30,37). Loud auditory stimuli provided through headphones increases isometric grip force, reaction time, and time-to-reach-peak force (5). Auditory verbal encouragement has been shown to increase isometric biceps force and triceps contraction forces up to 5 and 8%, respectively (19,27). Interestingly, Sinnett and Kingstone (35) have found that GR negatively affects opponents' decision making, resulting in slower responses and increased errors as to ball direction. Thus, the athlete's perception of whether the “noise” is “cheering or jeering,” as well as the timing of various stimuli, may benefit or detract from individual players.
Grunting increases peak serve and forehand velocity and isometric serve and forehand force (30); is considered to be cheating (29); and is forcing tennis ruling bodies to revisit, rewrite, and/or enforce rules (32). Perhaps tennis stroke velocities and forces can also increase with more quiescent breathing forms? Thus, the purpose of this investigation was to examine the effect of 4 forms of breathing, i.e., GR, valsalva maneuver (VM), forced inspiration (FI), and forced expiration (FE) on maximum force production during a simulated forehand stroke in collegiate tennis players and (2) to examine the effects of GR, FI, VM, and FE on muscle recruitment during a simulated forehand stroke in collegiate tennis players. In addition, we measured air volume to determine whether it differed during the 4 breathing conditions.
Experimental Approach to the Problem
A repeated measures experimental design was used to analyze the effects of 4 breathing conditions (independent variable) on isometric force production and air volumes (dependent variables). Repeated measures multivariate experimental design was used to compare the effects of the designated breathing conditions (FE, FI, GR, and VM, independent variable) on peak surface electromyographic (sEMG) activity (dependent variable) in the 7 muscle groups (subject's anterior deltoid, pectoralis major, rectus abdominus, lumbar erector spinae, thoracic erector spinae, and external and internal oblique muscle groups). Each study participant completed 1 practice session and 1 test session at the same time of day within 7 days, separated by 2 days. The experimental design supports the purpose of comparing different breathing conditions on isometric forehand forces. These comparisons will allow expansion on recently published work (30) on static and dynamic forehands during GR and non-GR conditions. The results of this investigation along with previous work (30) will assist tennis players, coaches, officials, and officiating bodies to determine the effects of GR vs. other breathing techniques during match and team play.
A convenience sample of 10 division III varsity collegiate tennis players (5 men, 5 women) was studied during their spring tennis season. Testing commenced in the evening at approximately 5 PM Central Standard Time (CST) on practice days. Subjects' mean age was 19.6 ± 1.5 years; mean ± SD, range = 18–22 years, with a mean height of 167.64 ± 12.7 cm and body weight of 62.73 ± 10.91 kg. Participants were current, healthy, active team members who were nongrunters. They were participating in only functional resistance training (box jumps, medicine ball throws, etc.) once per week. The study had been approved by the University Research Review Committee and after an extensive review of procedures, risks, and benefits, volunteers provided written informed consent.
Subjects attended 2 laboratory sessions between 5:00 and 7:00 PM CST. During session 1, subjects reported to the laboratory completed a Physical Activity Readiness Questionnaire (PAR-Q) and were asked to self-identify physical limitations or recent injuries that would have precluded participation in the study. Subjects were then measured for height and weight using a calibrated scale and stadiometer. Session 1 was a practice session and subjects were outfitted with sEMG electrodes, a facemask for air flow/volume measurements, and were asked to practice maximal isometric tennis forehands while using each of the 4 breathing conditions described below.
Electromyographical Measurement of Muscle Activity
The skin surface over anterior deltoid (∼4 cm below clavicle), pectoralis major (oblique angle to clavicle, ∼2 cm below clavicle, medial to axillary fold), rectus abdominus, lumbar erector spinae (at level of iliac crest, 2 cm lateral to spine), thoracic erector spinae (2-cm lateral to T-12), external (lateral to rectus abdominis, directly cephalic to the anterior superior iliac spine, halfway between the iliac crest and ribs), and internal oblique muscle (caudal to external obliques and anterior iliac spine) groups was shaved and lightly abraded with an antiseptic pad before electrode (9,26). Disposable adhesive sEMG electrodes were placed approximately in parallel with the orientation of the underlying fascicles using a bipolar arrangement with an interelectrode distance of 20 mm (9). Active electrodes were placed over 8 muscles (dominant side of the body), and a reference electrode was used to decrease noise. Wireless EMG signals were received remotely through TeleMyo 2400T G2 hardware and software (Noraxon U.S.A. Inc., Scottsdale, AZ). Raw EMG data were band pass filtered between 20 and 500 Hz and fully rectified by analysis software.
The anterior deltoid, pectoralis major, rectus abdominus, lumbar erector spinae, thoracic erector spinae, and external and internal obliques were individually tested for maximal voluntary isometric contractions (MVIC) through shoulder flexion, shoulder horizontal adduction, standing trunk flexion, lumbar extension, thoracic extension, and standing trunk flexion with left rotation, respectively (26,33). Maximal amplitude of EMG signals noted in the MVICs was used to normalize data during each breathing condition (9,26). Noraxon EMG hardware/software has been shown to have a coefficient of variation of 6% and an intraclass correlation coefficient (ICC) of 0.90 (22).
For the determination of the rate of change in EMG, the root mean square of the bandpass-filtered muscle activity was calculated for a 100 milliseconds time window. So that individuals could be compared, data under each breathing conditions were reported as percentages of peak EMG averaged across the 3 trials of each breathing condition.
To examine the independent variable, subjects were asked to exhale, inhale, grunt, or valsalva for specific contraction sets while performing isometric forehands. Subjects performed 4 sets of 3 repetitions for each breathing condition and sets were selected randomly. Subjects were outfitted with a rubber facemask/headpiece, and air volume was measured with a calibrated pneumotach and spirometry software (Cosmed USA Inc., Chicago, IL). Equipment was calibrated on each test day for air volume using a 2-L syringe. Subjects were instructed to begin breathing maneuvers and force production simultaneously. Volumetric data were recorded and the single best ventilatory maneuver from each breathing set (FI, FE, VM, and GR) was calculated for data analysis using proprietary pulmonary function software. Before all testing, subjects were given a practice day where they were fully outfitted with EMG electrodes and facemask and practiced the 4 breathing conditions and concomitant force production using the J-Tech force transducer.
Measurement of Isometric Forehand Force
Subjects stood in a square stance forehand position on an Isotrak platform (J-Tech Medical, Midvale, UT). In addition to a stable platform, the Isotrak includes a vertical pole and horizontal arm (with force transducer), which can be positioned and repositioned vertically and horizontally. The calibrated force plate traducer (calibrated daily before testing) is located at the distal end of the horizontal arm of the J-Tech was adjusted to the height of each subject's umbilicus. Subject's dominant hands were positioned on the force plate in line with their front foot, and their elbow joints were flexed to represent an isometric forehand ball striking position. Once appropriately positioned, subjects maintained their stance and performed forehand force tests with 4 randomly ordered (FE, FI, VM, and Gr) breathing conditions. Subjects performed 3 repetitions of maximal 2- to 3-second isometric forehands with each breathing condition with 30-second rest between contractions. Sixty seconds of rest was provided between breathing conditions. Peak forces were averaged for the 3 trials of each breathing condition and were used for comparative purposes. Within-day pilot study results revealed single measure and average measures ICC of 0.934 and 0.966, respectively, for isometric forehand force production using the 4 breathing conditions.
A repeated-measures multivariate analysis of variance (RM-MANOVA) was used to compare the effects of the designated breathing conditions on peak EMG activity in the 7 muscle groups. Separate repeated measures ANOVAs were used to analyze the effect of breathing condition on isometric force production and air volume. Pairwise post hoc comparisons were used to identify which breathing conditions differed on all variables. All data were analyzed at the 0.05 alpha level using PASW 18.0 (SPSS Inc., Chicago, IL).
The RM-ANOVA revealed a significant effect of breathing condition (F = 3.608, p = 0.07, power = 0.54) on force production (Table 1, Appendix 1). Forehand forces during FE and GR conditions did not differ (p = 0.36), but forces during GR were greater than during FI (p = 0.014) and VM (p = 0.04) conditions (Figure 1).
The RM-MANOVA examining the effect of breathing condition on muscle activity revealed a significant overall effect (F = 1.866, p = 0.031, power = 0.94). Pairwise comparisons revealed significantly greater anterior deltoid activity in FE (57.5%) vs. VM (48.13%) (p = 0.07). Percent MVIC increases in anterior deltoid activity (Figure 2) for GR (59.11%) and VM were also different (p = 0.29). Grunting and FE were not different for the anterior deltoid. Internal oblique activity was significantly greater in GR (113.39%) than FI (89.8%) (p = 0.01) or VM (p = 0.01), and FE (100.65%) and GR values were not different (Figure 3). Thoracic erector spinae activity was significantly greater during FE (37.38%) (p = 0.017) and VM (39.53%) (p = 0.02) than FI (37.28%), and FE and VM values were not different (Figure 4).
No differences in %MVIC were seen between the 4 breathing conditions for the pectoralis major, external oblique, lumbar extensors, or rectus abdominus. The %MVIC increased for all breathing conditions by 91.98, 5.31, 48.92, and 32.34% for these muscle groups, respectively.
Forced expiration, GR, FI, and VM air volumes were 4.07 L ± 1.7, 2.36 L ± 1.15, 2.05 L ± 0.58, and 1.63 L ± 0.54, respectively. These air volumes were significantly different among the 4 breathing conditions (F = 8.588, p < 0.001). Tukey's post hoc tests revealed that FE volume was significantly greater (p ≤ 0.01) than FI, GR, or VM volumes.
In this study, GR and FE forehand push forces were not significantly different, but GR forces were 14.26 and 14.73% greater than FI or VM forces, respectively. In a previous on-court study, we found that GR allowed for a 19.09% and 4.9 mph greater forehand pull force and forehand ball velocity vs. quiescent conditions (30). Thus, forceful exhalation without a GR sound should generate an important competitive increase in forehand velocity.
These findings are important to players, coaches, and officials as, rather than perform a VM or grunt, strength coaches can encourage players to forcefully exhale during a tennis stroke. The small numerical difference in isometric forehand force with GR and forceful exhalation in the current investigation may result in a small difference in forehand velocity (30) and little if any competitive advantage. Of paramount importance to players who have grunted in the past or those who chose to forcefully exhale in the future, placing a forehand inbounds supersedes velocity.
The current investigation involved close attention to the type of breathing that occurred during each isometric forehand contraction. It is somewhat difficult to compare the results of the current investigation to that of a previous investigation (30). Although a previous field study requiring quiescence (dB <25% of maximal grunt level) during forehands, subjects could have been performing a VM (30). If that were the case, the force difference noted in this study (14.73%) between GR and VM was similar to that of the field study (30). Force differences between this study and previous study (30) may be due to the size and quality of the sample, differences in body positioning, differences in handles, and the differences between whether forces were generated through pushing (this study) or pulling. Push forces have been shown to be less than pull forces (10), and that is, case when comparing pull vs. push forehand forces between current and previous findings.
The results of the current investigation generally support those of Ikeda et al. (18) who examined seated subjects performing isometric contractions of the knee and elbow flexors/extensors and the shoulder ab/adductors during normal breathing, forced inhalation, forced exhalation, or VM. In their investigation, significantly greater forces were seen during FE during 3 maximal isometric tasks, and peak forces during VM and FE for all types of muscle contractions were similar. In the current investigation, we found that GR and FE forces were not different but GR forces greater than FI or VM.
In terms of muscle recruitment, during the generation of maximal isometric forehand forces, the internal oblique, pectoralis major, external oblique, anterior deltoid, lumbar extensors, thoracic extensors, and rectus abdominus muscle contracted at 99.97, 91.98, 82.75, 55.31, 48.92, 33.19, and 32.34% MVIC, respectively, across all breathing conditions. The sEMG activity of the internal oblique, anterior deltoid, and thoracic erector spinae differed across the 4 breathing conditions, partially explaining force differences during GR and FE vs. FI or VM.
Internal oblique activity during FE (100.65%) and GR was not different during the isometric forehand. Internal oblique activity was significantly greater in GR (113.39%) than VM (96.05%) or FI (89.8%). The internal oblique acts as a trunk flexor and ipsilateral lateral flexor, and the subjects in this investigation assumed that torso position during testing. The internal oblique is important for both expiration and trunk motion, and reports of internal oblique strain in tennis players are found in the literature (25).
Interestingly, shoulder torque seems to be greatest in the square stance (6), and anterior deltoid activity (%MVIC) was significantly greater during FE (57.5%) or GR (59.11%) than during VM (48.13%). The anterior deltoid assists the pectoralis major in horizontal adduction, and high activity for the anterior deltoid has been reported during the forehand volley (4,8) However, the anterior deltoid and pectoralis major activity has been reported to be unrelated to ball velocity (33). During the isometric forehand force tests in the current investigation, the pectoralis major was very active during all breathing conditions. The %MVIC increases in pectoralis major activity in this study were similar to those published elsewhere (12). The %MVIC of the pectoralis major, external oblique, and erector spinae muscles in the current isometric investigation were higher than that noted in a dynamic study (8); however, isometric studies generally produce greater effort and subsequent recruitment.
Thoracic erector spinae activity was significantly greater during FE (37.38%) (p = 0.017) and VM (39.53%) than FI (37.28%), and FE and VM values were not different. Thus, the thoracic erector spinae seemed to provide stabilization during VM during maximum unilateral forehand forces and during resting breathing or breathing with lighter loads (36). Erector spinae activation is equivalent during dynamic open or square stance forehands (20).
Wang and McGill (36) found minimal changes in trunk musculature recruitment (%MVIC <5%) during quiet, unloaded breathing but noted increases in spine stability well above this mark under loaded conditions. They suggest that spine stability increases with increasing lung volume and that stability peak occurs close to peak inspiration. This supports the concept of inspiring deeply during the backswing component of a forehand stroke and exhaling as force is generated. In a dynamic lifting study where breathing was not controlled, Lamberg and Hagins (21) noted higher inspired volumes at liftoff of a load. The higher FI values in the current investigation were expected due to the submaximal intensity of the work task. As discussed by Lamberg and Hagins (21), we also noted a tendency of our subjects toward inhalation before deep exhalation and force production.
Morales et al. (28) demonstrated a 2 and 5% increase in the isometric deadlift in power lifters and controls with GR. Other investigators have shown that forearm force and grip forces increased 12.2 and 7% with shouting and kiap, respectively (17,37). Li and Laskin (22) found that maximal isometric finger flexion forces increased significantly (10%) from FI to FE, but that the VM had no effect on force production. Ikeda et al. (18) found that peak forces during FE were 5.1–9.0% greater than during normal breathing for shoulder adduction, elbow extension, and knee extension, and that peak forces during FE and VM were not different. The findings of the current investigation are supportive of these previous findings.
Force production findings with the VM vary (18,22), and there are some potential health challenges if the VM is used repetitively in maximal or near-maximal exertions. Increased intra-abdominal pressure (IAP) seen with maximal contraction of torso musculature has been believed to decrease lumbar spine compressive forces; however, concomitant abdominal muscle contraction likely increases spinal loading, offsetting any benefit (7). Additionally, because the VM increases IAP, it significantly increases systolic pressure, diastolic pressure, mean blood pressure, and rate pressure produce (RPP) (13). This transient increase in blood pressure may occasionally result in intracerebral bleeding (15); however, venous return decreases causing blood pressure to ultimately return to or below baseline levels (13). Middle cerebral artery blood flow velocity also decreases significantly, and this may lead to weightlifter's blackout (31). These responses are mediated by the autonomic nervous system (16). Today, most authoritative sources only recommend a very brief VM during maximal efforts of highly trained athletes (11). Clearly, FE represents a safer alternative during a maximal forceful contraction or forehand stroke.
In summary, FE and GR produce similar isometric tennis forehand forces, and EMG data generally support these findings. Previous work (30) suggests that GR results in increased forehand velocities and forces. Grunting creates an advantage for the grunter (29,35) and is under extreme scrutiny (1,2). Thus, it would seem prudent and safer for strength training professionals to encourage or coach forceful exhalation in an effort to generate more forceful but quiescent tennis forehand strokes.
The authors thank Darrell Hnizdor, MEd, Laboratories Coordinator for his assistance with this project.
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Measures of variance for EMG and force data.*