One of the main purposes of a warm-up prior to training and competition is to maximize performance and prevent injuries (Chaouachi, et al., 2010; Fradkin, et al., 2010; O' Sullivan et al., 2009; Safran et al., 1989; Shellock and Prentice, 1985). Warm-up is typically composed of a submaximal aerobic activity, stretching of the major muscle groups, as well as general and sport specific exercises performed at or near competition intensities (Taylor et al., 2008). Low to moderate aerobic activity increases body and muscle temperature, muscle compliance and efficiency of physiological responses (Bishop, 2003). Stretching, following submaximal aerobic activity, has been shown to further increase range of motion (Bandy et al., 1998; Magnusson and Renstrom, 2006; Magnusson et al., 1996) and to enhance performance (Young and Behm, 2002) while it may also reduce the incidence of injury (Cross and Worell, 1999; Hartig and Henderson, 1999; McHugh and Cosgrave, 2010). However, there is evidence that pre-exercise stretching may not decrease the risk of injury (Pope et al., 2000; Small et al., 2008; Thacker, et al., 2004) or may even be harmful (Shrier, 1999; Weldon and Hill, 2003). Thus, although pre-exercise stretching is common practice for many athletes, its effects have been questioned (Shrier, 2004; Haff, 2006).
Previous studies, reported that static stretching may temporarily decrease the ability of the stretched muscles to generate power output (Behm et al., 2001, 2004; Fowles et al., 2000; Nelson et al., 2001). This has been attributed to both neuromuscular inhibition and a decrease in muscle stiffness due to alterations of the viscoelastic properties of the musculotendinous unit (Alter, 1996; Knudson et al., 2011). The duration and intensity of the static stretching exercises seem to play a critical role in these impairments, with long lasting, intense stretching exhibiting a greater decrease in subsequent power generating ability (Behm and Chaouachi, 2011).
The final part of a typical warm-up involves general and sport specific explosive movements that may induce a phenomenon called post-activation potentiation (PAP), (Gelen, 2010; Hilficker et al., 2007). PAP is characterized by increased muscle force and power output in the next 4-20 minutes following voluntary conditioning contractions performed at high intensities (Tillin and Bishop, 2009). PAP is greater in individuals with high levels of muscle power, who also have a higher proportion of type II fibers (Hamada et al., 2000; Young et al., 1995) and shorter twitch contraction time (Vandenboom et al., 1995).
The acute effects of stretching and potentiating exercises in warm-up routines are opposing, i.e. stretching exercises decrease and PAP exercises increase muscle power. However, there is limited information on the combined effects of stretching and PAP exercises during warm-up. In a recent study, Tsolakis and Bogdanis (2012) examined the combined effect of static stretching and potentiating exercises in elite fencers. The main finding of their study was that although short (15 s) and long (45 s) durations of stretching resulted in a similar increase in hip flexion ROM by 12.6%, subsequent countermovement jump (CMJ) performance was significantly reduced by 5.5% only after the long duration static stretching protocol. In contrast, Chaouachi et al. (2010) reported that static stretching to the point of discomfort did not affect sprint and jumping performance in elite athletes and attributed it to their high training status. These data suggest that there may be different responses to stretching and PAP protocols, depending on the training status, baseline flexibility and muscular power.
In most studies, static stretching may increase compliance and thus reduce the stiffness of the muscle-tendon unit (Bacuraeu et al., 2009, Winchester et al., 2008), but this effect is transient (Magnusson and Renstrom, 2006) and depends on the duration (Yamaguchi and Ishii, 2005), and intensity of the stretching protocols. This reduction in stiffness of the muscle-tendon unit results in a decreased performance during subsequent explosive muscle actions. On the other hand, according to "sarcomere give' theory stretching of an active muscle causes a rapid increase of force after the onset of stretch, followed by a sudden yielding of the sarcomeres, which may affect subsequent muscle performance (Flitney and Hirst, 1978).
The combined effects of stretching and conditioning exercises during warm-up may be influenced by the flexibility and muscle power of the performer, as well as by the volume of exercise. Gymnastics is a sport that is generally characterized by high levels of strength and power relative to body weight, as well as high flexibility (Arkaev and Sutsilin, 2004). Interestingly, athletes of the different gymnastics disciplines are characterized by varying levels of flexibility and muscle power. Artistic gymnasts are much stronger than rhythmic gymnasts, while rhythmic gymnasts are mainly characterized by their flexible joints and compliant muscles (Smolefski and Gaverdofski, 1999).
This led us to investigate the hypothesis that the different levels of flexibility and muscle power of those groups of athletes influence their responses to warm-up protocols containing different volumes of stretching and conditioning exercises. Therefore, the aim of the present study was to manipulate the volumes of stretching and muscle potentiating exercises and examine their combined effects on counter-movement jump performance (CMJ) and straight leg raise range of motion (ROM). Two different stretching durations (short and long) were used in combination with conditioning tuck jumps, commonly used to induce PAP (Masamoto et al., 2003; Till and Cooke, 2009; Tsolakis and Bogdanis, 2012). One of the advantages of using three subgroups of elite level gymnasts (male and female artistic and female rhythmic gymnasts) is that each group is characterized by different levels of flexibility and CMJ performance. Thus, the effect of differences in baseline level of CMJ performance and flexibility on the responses to the two warm-up programs was examined.
Thirty-four rhythmic and artistic gymnasts (10 male, 14 female artistic gymnasts and 10 female rhythmic gymnasts), all members of the Greek national team took part in this study. The physical characteristics of the participants are shown in Table 1. All gymnasts had long competing experience of official international F.I.G (Federation Internationale de Gymnastique) competitions: Olympic Games, World Championships, European Championships. Nine gymnasts were Olympic Games qualifiers and 15 participated in World Championships. Rhythmic and artistic gymnasts were training for six days a week (two training sessions per day) for approximately 48 and 34 hours per week respectively and participated in competitions according to the national and the international calendar of the F.I.G. The training sessions of artistic gymnastics included specific physical conditioning, as well as general and specific technical preparation on the apparatuses six times per week. The physical conditioning part aimed to improve strength, flexibility, anaerobic fitness, muscular endurance. It contained resistance training, strength exercises using body weight, strength oriented gymnastic skills and combinations of the skills (Jemni et al., 2006). Static and dynamic flexibility exercises were performed in every training session for 20 min as part of the warm-up. In addition, dynamic flexibility training (with light weights and elastic bands) was performed as part of the physical conditioning for 30-35 min in the end of every morning training session and static flexibility exercises for 20-30 min in the end of every afternoon training session focusing especially on the individual needs of every gymnast. Rhythmic gymnastics training incorporated special physical conditioning for static and dynamic flexibility before and after training, strength skills, balance training, speed capacities and technical preparation with and without apparatuses six times a week. Static and dynamic flexibility exercises were performed for 30 min in every training session as part of the warm-up. Dynamic flexibility training (with and without light weights and elastic bands) was performed as part of the physical conditioning for 40-45 min in the end of every morning training session and static flexibility exercises for 30-35 min in the end of every afternoon training session.
The gymnasts were free of injury and testing was performed during the competitive training period. Adult gymnasts, gave consent to participate in the study while written parental consent was provided for non-adult gymnasts. The study was approved by the University's Institutional Review Board and all procedures were in accordance with the Helsinki declaration...