Muscle fiber type distribution and fiber size of triceps brachialis in elite tennis players.

Resumen muscle fiber type distribution and fiber size of triceps brachialis

Tennis is an excellent exercise model to study muscle plasticity in response to chronic exercise. Tennis players submit their dominant-arm to a huge amount of physical activity compared to their contralateral arm (Jacobson et al. 1984; Pirnay et al. 1987; Tsuji et al. 1995). In consequence, the muscle mass of the dominant arm is about 20% higher compared to that of the non-dominant arm in elite tennis players (Calbet et al. 1998; Sanchis Moysi et al. 1998). Although it is reasonable to assume variations in the relative contribution of the muscle groups to the overall muscle hypertrophy of the dominant arm, to our knowledge, the relative contribution of the size of individual muscles has not been investigated in tennis. Studies using electromyography have shown that triceps brachialis plays an important role on power generation in the different tennis strokes (Chow et al. 1999; Miyashita et al. 1980; Van Gheluwe and Hebbelinck 1986). The knowledge of the morphologic adaptations of triceps brachialis in elite tennis players could be very useful for designing more specific and efficient strength training programs for tennis players.

Introduction

Tennis is an excellent exercise model to study muscle plasticity in response to chronic exercise. Tennis players submit their dominant-arm to a huge amount of physical activity compared to their contralateral arm (Jacobson et al. 1984; Pirnay et al. 1987; Tsuji et al. 1995). In consequence, the muscle mass of the dominant arm is about 20% higher compared to that of the non-dominant arm in elite tennis players (Calbet et al. 1998; Sanchis Moysi et al. 1998). Although it is reasonable to assume variations in the relative contribution of the muscle groups to the overall muscle hypertrophy of the dominant arm, to our knowledge, the relative contribution of the size of individual muscles has not been investigated in tennis. Studies using electromyography have shown that triceps brachialis plays an important role on power generation in the different tennis strokes (Chow et al. 1999; Miyashita et al. 1980; Van Gheluwe and Hebbelinck 1986). The knowledge of the morphologic adaptations of triceps brachialis in elite tennis players could be very useful for designing more specific and efficient strength training programs for tennis players. The aim of this study was to assess the effect of tennis participation on the fiber size of triceps brachialis muscle of the dominant compared to that of the non-dominant arm and its relationship with the overall muscle mass of the dominant arm.

Methods

Participants Four elite tennis players (23.0 ± 1.0 yr, mean ± SEM) from the Canary Islands accepted to participate in this study that was approved by the ethical committee of the University of Las Palmas the Gran Canaria. The exact nature and purpose of the project was explained to all volunteers who then gave their informed consent. All the tennis players have been participating in professional or first level amateur tennis competitions during, at least, the previous four years. The mean time they have been spending on tennis training or competitions has been 24 ± 9 hours per week. Three players were right handed and one left handed. One of the right handed players played a two hands backhand while the other three players played the one hand backhand stroke. Table 1 summarizes the general characteristics of these tennis players.

Table 1. General subject’s characteristics (mean ± SD).

Materials Muscle biopsies were taken from lateral aspect of the triceps brachialis (short head) of both arms. A section of the muscle samples was cut off, mounted in embedding medium, and frozen in isopentane cooled to its freezing point in liquid nitrogen and stored ?80°C until further analysis. In serial transverse muscle sections, fiber types were stained for myofibrillar ATPase as described previously (Brooke and Kaiser 1970). In addition, the muscle mass of the dominant and non-dominant arm was also determined using dual-energy x-ray absorptiometry (DXA) (QDR-1500, Hologic Corp., Waltham, MA), as previously described (Sanchis-Moysi et al. 2004). From the whole body scans the percentage of body fat (%) was also determined (Sanchis Moysi 1998). Table 1 summarizes the main characteristics of the subjects. Statistical analysis Data were analysed using the SPSS mainframe statistical program. Side-to-side comparisons were carried out using a one-tailed Student’s t-test. Statistical significance was set at P<0.05 level. Results are presented as means ± standard error of the mean.

Results and discussion

Marked differences existed between the dominant and the contralateral arm for muscle mass (3606 ± 76 versus 3154 ± 268 g , P < 0.001). This result is in concordance with previous studies carried out in our laboratory that showed a 10-20% more muscle mass in the dominant compared with the contralateral arm in elite tennis players (Calbet et al. 1998; Sanchis Moysi et al. 1998). The increased muscle mass of the dominant arm and particularly the relative higher hypertrophy of the triceps brachialis can only be explained as a consequence of the mechanical demand sustained by this muscle, since any other genetic, nutritional or hormonal mechanism is also acting on the contralateral arm which has smaller fibers. Compared to the non-dominant the type 1, 2a and 2x muscle fiber were hypertrophied in the dominant arm by 36% (4018 ± 457 and 5472 ± 556 ?m2), 31% (6185 ± 1015 and 8109 ± 1542 ?m2) and 39% (5333 ± 1389 and 7430 ± 1370 ?m2), respectively (Figure 1). The mean area of all muscle fibers was 33% higher in the dominant than in the non-dominant arm (P<0.05). Although we can not compare our results with other studies, since there are no published data on muscle fiber type and cross-sectional areas of lateral aspect of the triceps brachialis in either tennis players or other athletes, the values obtained in this study for cross-sectional areas are similar to that reported, for example, in the long head of the triceps brachialis in cross country skiers (Calbet et al. 2005).

Figure 1. Cross sectional cut from tennis player triceps brachialis lateral aspect muscle biopsies. Non dominant arm (left); Dominant arm (right).

The inter-arm difference in muscle mass (14%) was smaller than the difference in cross sectional area of the triceps brachialis (33%), emphasizing the relative importance of this muscle in tennis players. In the last three decades, studies using cinematography and electromyography have shown that a elbow extension movement, with participation of triceps brachialis occurs in most tennis strokes (Van Gheluwe and Hebbelinck 1986). For example, during the service stroke triceps brachialis muscle contributes to the active acceleration of the racket previous to the ball impact (Van Gheluwe and Hebbelink 1986). In the forehand stroke, the triceps display strong activity during ball impact in order to counteract the maximal contraction of biceps brachialis and brachioradialis (Slater-Hammel 1948; Van Gheluwe and Hebbelinck 1986). The backhand stroke demands the extension of the elbow joint approximately 40º from the backswing position to impact as a means of generating racket speed (Elliott et al. 1989), this movement implies the participation of triceps brachialis, in both, the one hand and the two hands backhand stroke (Roetert and Ellenbecker 1998). Triceps muscle also shows a high electrical activity during the forward swing phase of the forehand and the backhand volleys, being greater during the backhand volley (Chow et al. 1999). In this study we provided direct morphological evidence showing the importance that this muscle has for racket actions in tennis players. The fact that the magnitude of hypertrophy of the muscle fibers of the lateral aspect of the triceps brachialis is more than twice the mean increase in muscle mass also suggests that this muscle is submitted to an overload likely higher than that supported by other muscles of the arm. This adaptative change allows to increase the power production specially during the serve stroke but also during other tennis strokes. The muscle cross-sectional area and the fiber type determines the power production of a muscle (Aagaard and Andersen 1998). It seems reasonable to assume a relationship between the triceps brachialis hypertrophy and morphology of the dominant arm and the increased maximal strength of elbow extension movement found on the dominant arm of the tennis players (Bencke et al. 2002; Cohen et al. 1994; Kibler and Chandler 1989). As a consequence, this muscle hypertrophy could also contribute to impel higher ball velocities during the tennis serve (Bencke et al. 2002; Pugh et al. 2003). However, the influence of muscle strength on ball speed in tennis has generated some controversy, since it may depend on more factors than just the strength of the musculature recruited in each specific action (Ellenbecker 1991; Elliott et al. 1990).

In fact, it has been reported that tennis practice is not associated with a significant increment in total lean mass in professional tennis players compared to non active population of the same age (Calbet et al. 1998; Sanchis Moysi et al. 1998). Nevertheless, tennis players have more chances to accomplish appropriately with tennis requirements if they increase their maximal dynamic strength (MDS) as a way to enhance the peak force developed during ball strokes (Konig et al. 2001; Sanchis Moysi 2004). Supporting this idea several studies show that strength training can improve racket speed (Kleinöder 1990) and ball velocity (Kraemer et al. 2003; Kraemer et al. 2000). In agreement, a recent study has analyzed the influence of triceps brachialis morphology on shot put performance (Terzis et al. 2003). Terzis et al. (2003) showed that despite the fact that is commonly accepted that shot put performance is mainly determined by the ability of the lower body to produce power, elbow extensors’ isokinetic torque, type II fiber area of triceps brachialis and estimated arm cross-sectional area of the arm significantly correlated with shot put performance (Terzis et al. 2003). Tennis actions may generate several stimuli known to elicit muscle hypertrophy. For example to maintain the position of the racket a strong grip is needed in many instances. This strong grip is likely supported by a isometric contraction of elbow and flexor and extensor muscles. It is well established that isometric contractions are able to elicit muscle hypertrophy (Kanehisa et al. 2002). Tennis practice increases the maximum grip strength (Kibler et al. 1988) and the maximal strength during the elbow extension movement in the dominant arm (Bencke et al. 2002; Cohen et al. 1994; Kibler and Chandler 1989). A maximum grip strength of 600 N has been reported in the dominant arm in elite tennis players (Kibler and Chandler 1989). The inter-arm difference in grip strength is around 30% in female and 40% in male competitive adult tennis players (Kibler et al. 1988; Kraemer et al. 2003). Moreover, upper limb side differences in elite tennis players has been found during an isometric maximal voluntary contraction in the elbow extension movement (Bencke et al. 2002). In addition to this strength gains, moderately but significant correlations have been observed between ball speed in the tennis serve and both, the grip strength (Cohen et al. 1994; Elliott 1982; Pugh et al. 2003) and the isokinetic extension torque measured at the elbow in elite tennis players (Pugh et al. 2003).

It seems reasonable to defend that forceful muscle contractions during service and forehand strokes may also elicit forceful eccentric and concentric muscle actions which are also known to stimulate muscle hypertrophy (Seger et al. 1998). Overall, these studies support that swinging a tennis racket many times during training sessions and competitions can be considered as a powerful stimulus for muscle hypertrophy in the dominant arm (Bencke et al. 2002). Our findings suggest that a moderate muscle hypertrophy of the dominant arm could also contribute to the strength gains of the dominant arm and the increase in ball velocity. Future studies will be needed to verify this hypothesis. In addition, other mechanisms could also contribute to the greater strength of the dominant arm of tennis players. It has been suggested that higher co-ordination of the neuromuscular system and increased muscle activation of specific muscles of the dominant arm involved in tennis strokes could also contribute to the impressive asymmetry in arm muscle strength in tennis players (Sanchis Moysi 2004). The impact forces sustained by the dominant arm of the tennis players combined with the elevated tensions generated by the muscles that attach in the bones of the upper extremity also stimulate osteogenesis as a protective mechanism for the osseous structure. It is well documented that tennis practice increase the bone mineral content (BMC) and density (BMD) of the dominant arm (Sanchis Moysi 1998; Sanchis-Moysi et al. 2004). The high BMC and BMD in the dominant arm of the tennis player is related to the arm muscle mass (Calbet et al. 1998) and several studies have reported that regional lean mass correlates with both regional BMC and regional BMD (Baumgartner et al. 1996; Nichols et al. 1995). Moreover , it has been shown recently that the myostatin-deficient mice, which show increased muscle mass, has also a more pronounced osteotrophic response to exercise (Hamrick et al. 2006). All together these studies support the concept that both impact loading and muscle hypertrophy contribute to the enhancement of BMC and BMD in tennis players.

Conclusions

We are reporting for the first time the effect of long lasting tennis participation on the structure of the lateral aspect of the muscle triceps brachialis in elite tennis players. Long term tennis participation is associated with marked muscle hypertrophy of all fiber types in the lateral portion of the muscle triceps brachialis. The inter-arm difference in muscle mass was smaller than the difference in cross sectional area of the triceps brachialis, emphasizing the relative importance of this muscle in tennis players.

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