Sprint and high-intensity intermittent efforts are very common activities in team and racket sports such as handball, basketball, soccer, and tennis. These sports are characterized by multiple short sprints, accelerations, and decelerations with changes of direction, which are collectively called repeated-sprint ability (RSA) (26). Because of this, it is plausible to assume that performance in RSA might be a useful indicator for successful in these sports, and the implementation of strategies that enhance RSA performance needs to be taken into account by coaches and athletes.
Some evidence has shown that an individual's RSA is highly dependent on muscle strength and power (28,30). In fact, Wisloff et al. (28) showed that the strength level in the squat exercise was positively correlated with a 10- and 30-m sprint, and a 10-m shuttle run sprint performance. A way to acutely enhance strength and power production, and possibly speed performance, is through the use of postactivation potentiation (PAP). The PAP constitutes an increase in performance after a high-intensity muscle contraction. Therefore, PAP protocol is traditionally used as a warm-up alternative before exercise to improve the performance in sports events or training sessions (1). Some factors probably involved with the PAP are the regulatory myosin light chain phosphorylation, motoneuron excitability, motor units synchronizations, and acute change of the pennation angle of muscle (15,24,27).
Previous studies have shown that the PAP occurs in different activities such as a jump (17), a swimming start (18), the number of throws in Judo (21), and the performance on rowing ergometer (8) and that this phenomenon can last for 18 minutes after conditioning contraction (6). Furthermore, some authors have demonstrated the positive effects of PAP on a 40- and 100-m single sprint (20,23,29). However, to the best of our knowledge, there is no study that has investigated the effects of PAP on intermittent sprint performance. Some studies have found that the PAP could be observed in other activities performed in an intermittent manner (12,17). For example, Güllich and Schimidtbleicher (12) showed that the 8 countermovement jumps, with 20 seconds of rest between them, were potentiated 3 minutes after maximal voluntary contraction. This result indicates that the PAP is not abolished when the individual performs the activity once (i.e., a jump). Thus, it is logical to assume that PAP could also occur in the RSA test. However, an important variable to PAP occurrence seems to be the individual's muscle strength. Gourgolis et al. (11) have shown that the group with 1-repetition maximum (1RM) load in squat exercise >160 kg has a greater PAP (4%) in comparison with the group with a 1RM <160 kg (0.42%). As a result, we believe that the magnitude of PAP in RSA is related to the 1RM.
Thus, the aim of this study was to verify the change in RSA performance after a conditioning contraction and its association with handball players' maximal strength level. It was hypothesized that the players would show improvement on RSA performance after a high-intensity strength exercise and the magnitude of the change would be moderate to strong correlated with squat 1RM level. These results are important for a coach decision to apply or avoid heavy load exercise before handball training or match situations that involve RSA. The development of knowledge concerning the strategies able to improve RSA will enable greater efficiency in training periodization that will allow for improved sprint intermittent performance.
Experimental Approach to the Problem
Previous findings suggested that sprint and muscle strength and power were positively related (30). Because the muscle strength and power can be improved by PAP, we were interested in analyzing the effects of PAP on RSA. Thus, 12 highly trained handball players attended 3 experimental sessions. The first session was used to determine the participants' half squat 1RM load and to familiarize them with the RSA test. On the following 2 occasions, the athletes executed the RSA test once with and once without a prior high-intensity exercise (i.e., conditioning activity in half squat exercise). The high-intensity exercise was applied in an attempt to induce PAP in RSA performance. These sessions were conducted at the same time of the day (in the afternoon), presented in random order, and separated by at least 48 hours (Figure 1). All the tests were performed in May. The participants were instructed to refrain from exhaustive exercise for 24 hours preceding the test, to sleep for a minimum of 6 hours, and to avoid caffeine and food 2 hours before the tests. Furthermore, they were also instructed to maintain the same diet habits throughout the study.
Twelve male handball players (age = 18.7 ± 1.7 years, body mass = 85.9 ± 9.6 kg, height = 185 ± 7 cm) volunteered for this study. The sample size was determined previously by G*Power software (v.3.0.10) assuming α = 0.05 and β = 0.20 based on a previous study (3). The participants were members of the Brazilian National Champion Team. On a weekly basis, each athlete practiced twice a day (90 minutes per session), 5 d·wk−1. The athletes had at least 3 years of experience with strength training, and during the study, they were in the final preparation training period. All the players were informed about the aims, procedures, and risks involved in the study, and a written consent form was obtained from them before participation. They were allowed to withdraw from the study at any time without penalty. The study was approved by the Institutional Ethics Committee and performed in accordance with the ethical standards of the Declaration of Helsinki.
Maximal Dynamic Strength Test (One-Repetition Maximum Test)
The maximal dynamic strength of the lower limbs was assessed through the 1RM test in the half squat exercise (Cybex International, Medway, MA, USA). The 1RM test was preceded by a 5-minute low-intensity run in which the heart rate did not exceed 140 b·min−1 (Polar RS800CX, Electro Oy, Kempele, Finland) followed by a specific warm-up routine composed of 5 and 3 half squat repetitions at an estimated 50 and 70% 1RM, respectively. Body position and foot placement were registered with measuring tapes fixed on the bar and on the ground, respectively. In addition, a wooden seat with adjustable heights was placed behind the subjects to keep bar displacement and knee angle (∼90° knee angle) constant on each half squat attempt. The adjustment of the wooden seat height was performed individually in each test. The 1RM load was defined as the maximum weight that could be lifted once using the proper exercise technique through a full range of motion. A 3-minute rest interval was adopted between attempts, and the subjects had up to 5 attempts to obtain their 1RM. Strong verbal encouragement was given throughout the test.
Repeated-Sprint Ability Test
The RSA test consisted of six 30-m shuttle sprints with a change of direction at 15 m (i.e., 15 m + 15 m). The participants started a new sprint every 20 seconds. For example, if the subject performed the shuttle sprint in 6 seconds, there was a 14-second recovery interval before the next one (4). They were instructed to perform all the sprints in an all-out manner and to avoid pacing strategies. An electronic photocells system was used to record the time of sprints (MultiSprint System, Hidrofit, Belo Horizonte, MG, Brazil). The participants crossed a pair of photocells at the starting line, ran for 15 m, changed direction, and then returned to the starting line. The best sprint time (RSAbest), the mean sprint time (RSAmean), and the percentage sprint decrement (RSAindex) were recorded for statistical analyses. Glaister et al. (10) showed that the reliability of RSAbest is intraclass coefficient correlation (ICC) = 0.79–0.91, RSAmean is ICC = 0.88–0.94, and RSAindex is ICC = 0.66.
The RSAindex was calculated according to the following equation: 100 − (total time/ideal time × 100), where the total time is the time spent to complete the 6 × 30-m shuttle sprints and ideal time is the product of 6 × RSAbest.
Before the conditioning activity, the subjects performed a general warm-up composed of a 5-minute run in which the heart rate did not exceed 140 b·min−1. The conditioning activity comprised 1 set of 5 half squat repetitions at approximately 50% 1RM, 1 set of 3 repetitions at approximately 70% 1RM, and 5 sets of 1 repetition at 90% of 1RM with a 2-minute rest interval between sets. After the conditioning activity, there was a 5-minute interval before the beginning of the RSA test.
Data are expressed as mean ± SD. The Gaussian distribution was analyzed by the Shapiro-Wilk test. Student t-test for dependent samples was performed to compare the RSAbest, RSAmean, and RSAindex, with and without the conditioning activity. A 2-way analysis of variance with repeated measures (sprint × condition) was applied to compare the 6 sprints in the situations with and without the conditioning activity. Sphericity was analyzed by Mauchly's test followed by Greenhouse-Geisser correction when necessary. The significance level was set at p ≤ 0.05. In addition to the comparison analyses, the smallest worthwhile effects were calculated for RSAbest, RSAmean, and RSAindex to determine the likelihood that the true effect was substantially beneficial, trivial, or detrimental. The smallest worthwhile change was calculated based on Cohen's d effect size principle (0.2 multiplied by the between-subject SD). The quantitative chances of beneficial effects were assessed qualitatively as follows: <1% almost certainly not, 1–5% very unlikely, 5–25% unlikely, 25–75% possible, 75–95% likely, 95–99 very likely, and >99% almost certain. If the chances of having a beneficial and detrimental effect were both >5%, the true difference was assessed as unclear (16). Relative changes (%) in performance are expressed as 90% confidence interval. The magnitude of changes after the conditioning activity was expressed by Cohen's d effect size. The threshold values were <0.20 (trivial), 0.20–0.49 (small), 0.50–0.79 (moderate) and ≥0.8 (large) (5). The magnitude of change in RSA parameters (the results without the conditioning activity less the result with) was correlated with 1RM using a Spearman rank correlation.
The average 1RM value in the half squat exercise was 193 ± 27 kg.
Figure 2 shows the average time of the 6 × 30-m shuttle sprint with and without the conditioning activity for all handball players. The condition (F = 12.47; p < 0.01) and the sprint effect (F = 27.01; p < 0.01) presented a significant difference, but no interaction was found (F = 0.64; p > 0.05).
A significant difference between conditions (with and without conditioning activity) was observed for both RSAbest and RSAmean (p < 0.01) but not for RSAindex (p > 0.05). Cohen's d for all RSA parameters with and without the conditioning activity is presented in Table 1. The percentage chances of a beneficial-trivial-detrimental effect with the conditioning activity for RSAbest was 96/4/0, for RSAmean was 92/8/0, and for RSAindex was 12/42/46, respectively. In addition, the relative changes in RSA parameters for the group are presented in Figure 3.
The individual values for the RSAbest, RSAmean, and RSAindex can be observed in Figure 4. Ten athletes improved RSAbest, 9 RSAmean, and 5 RSAindex after the conditioning activity.
The correlation coefficient between 1RM load and magnitude of change for RSAbest after the conditioning activity was very low (r = 0.03). However, the correlation between 1RM and magnitude of change for RSAmean (r = 0.50) and RSAindex (r = 0.56) was moderate.
The purpose of this study was to verify the RSA test performance after a conditioning activity in elite handball players. The primary findings of the study showed that the RSAbest and RSAmean improved significantly, but the RSAindex did not change after the conditioning activity. Furthermore, the magnitude of change after a conditioning contraction in RSAmean and RSAindex was moderately correlated with 1RM.
The 6 sprints analyzed after the conditioning activity exercise presented a significant enhancement, but an interaction between condition and sprint effect was not observed. Analyzing only the RSAbest and RSAmean comparing the protocols with and without the conditioning activity, we observed a significant difference with a high chance of beneficial effect (96 and 92%, respectively) after the conditioning activity, but the magnitude of changes analyzed by effect size was moderate for RSAbest (Cohen's d = −0.54) and low for RSAmean (Cohen's d = −0.41).
The RSA is an important characteristic that affects performance in several sports. Thus, some studies have investigated different strategies to improve this ability. Buchheit et al. (2) demonstrated that handball game–based training increased players' performance in the RSA test. Furthermore, Buchheit et al. (3) found that the execution of repeated shuttle (2–3 sets of 5–6 × 15–20 m) and explosive strength activities increased the RSA test performance. Therefore, finding alternatives to improve the RSA performance is important.
Previous studies have demonstrated the acute increase of performance in a single sprint after PAP protocol. Rahimi (23) observed that 2 sets of 4 repetitions of the squat exercise at 85% of 1RM improved performance in the 40-m sprint by 2.98%. Analyzing the speed of each 10 m for a total of 40 m, Yetter and Moir (29) observed increases in speed in the distances between 10–20 and 30–40 m. The increase of performance after a conditioning activity can also to be observed in greater distances (100 m), in which the mean sprint time changed by 0.19 seconds (20). To the best of our knowledge, this is the first study that observed the acute increase in performance in repeated sprint. In countermovement jumps, Güllich and Schimidtbleicher (12) showed that performing 8 successive jumps with 20 seconds of rest between them increases the performance of the 8 jumps after maximal voluntary contraction. Kilduff et al. (17) observed similar results in countermovement jumps and bench press throws, with a peak power increase at different time frames analyzed after the conditioning activity. Furthermore, Chiu et al. (6) showed that the PAP phenomenon may last 18 minutes after the conditioning contraction, indicating the usefulness of this protocol for situations within this period.
The magnitude of changes in RSAmean and RSAindex was moderately correlated with 1RM (r = 0.50 and 0.56, respectively), suggesting that the stronger subjects have a tendency to greater increases in performance. In agreement with our results, previous work presented moderate correlation (r = 0.49–0.76) between maximum strength and changes in performance after a conditioning activity (7,19,31). Furthermore, Gourgolis et al. (11) observed that the group with 1RM greater than 160 kg in the squat exercise had a mean increase in the countermovement jump of 4% after a conditioning activity protocol, whereas in the group with 1RM <160 kg, the increase was only of 0.42%. It is possible that stronger individuals have a greater amount of type 2 muscle fibers, which are more sensitive to PAP effect (13,14). It seems that an individual's experience with strength training is also important. Chiu et al. (6) found significant increases in peak power during jump squats after 5 sets of 1 repetition at 90% 1RM in the parallel back squat in athletes with experience in explosive strength training, when compared with a group of recreationally trained subjects. It is believed that athletes with experience in strength training would have a smaller neural inhibition and fatigue after the conditioning activity and consequently would increase the performance (6,11). However, for the PAP to occur, there are other variables involved, such as protocol (type of contraction, number of repetitions, sets, interval between sets, intensity) and time of rest after a conditioning contraction (6,9,23).
Despite the fact that some studies showed that lower limb strength is highly correlated to a single-sprint performance (22,25), for the RSA, the correlation was low (22). Slawinski et al. (25) demonstrated that the rate of force development and impulse force is greater for the group of individuals with a lower 10-m sprint time. Newman et al. (22) also observed the importance of strength in a sprint, showing that the isokinetic peak torque in knee extensor at a 240°·s−1 was strongly correlated with a 10-m sprint (r = 0.71). However, the same authors did not observe a strong correlation between the RSA variables with isokinetic peak of torque in extension and flexion at 60, 150, and 240°·s−1, indicating that other variables in addition to muscular strength may influence the performance in RSA. These results are in agreement with those of our study, in which the correlation of 1RM and RSA parameters was low (r < 0.39). Nevertheless, the importance of lower limb strength on RSA test performance cannot be discarded. Buchheit et al. (3) showed that explosive strength training improves the performance in an RSA test. Thus, the increase in performance in RSA after the PAP protocol in this study can be related to an acute increase in lower limb strength that influences the sprint ability. The low correlation discussed previously can be explained by the Young et al. (30) model, in which beyond the lower limb strength, the technique is also very important for activities that involve a change of direction.
The present findings demonstrated that previous conditioning activity exercise improves RSAbest and RSAmean with a small to moderate magnitude of change but without significantly affecting the RSAindex. These results indicate that high-intensity squat exercise may be used as acute intervention applied by the coach to athletes before activities that involve multiple sprints, change of direction, and short periods of rest, and it can also be used as an alternative method of warm-up. The increase in RSA performance could be interesting for handball match situations, such as intercepting the ball, blocking the opponent, dribbling or in counterattacks. Additionally, the PAP assumptions may be used for intermittent sprints training with similar characteristics to the RSA test to attempt greater long-term adaptations. However, more studies are necessary to verify the effectiveness of this type of intervention. Our results also showed that the lower limb strength is moderately correlated to the magnitude of RSAmean change after conditioning activity, indicating that stronger subjects have a greater tendency for PAP and the importance of the development of this variable. Additionally, it is important to point out that the type of protocol can have an effect on the occurrence of PAP. Thus, the findings of this study seem to be especially important because the PAP protocol is extensively used to optimize training of athletes and as an alternative method to the warm-up protocol, and in some activities and subjects, it cannot be recommended.
The authors are grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for their financial support.
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Keywords:© 2013 National Strength and Conditioning Association
agility; speed testing; high-intensity exercise; strength