Warm-up before physical activity is a procedure believed to reduce injury and enhance performance (33). The benefits of warming up are numerous including increasing the temperature of the muscles and connective tissues, increasing the range of movement, reducing the incidence of injury, decreasing the severity of injury, delaying the onset of muscular fatigue, preventing and alleviating muscle soreness, increasing the level of skill and muscular efficiency, and prolongation of sporting life (1,3,8,21,30). Kurtz (20) states the goals of a warm-up are to increase awareness, improve coordination, improve elasticity and contractibility of muscles, and increase efficiency of the respiratory and cardiovascular system. However, researchers have been questioning and researching the effects that warm-ups including common stretching procedures may have on the metabolic system, strength, power production, and performance (6,7,12,13,16-18,25,28,29,33). Although most researchers have shown the negative effects to last for at least 15 to 30 minutes, some of the negative effects have been found to last up to an hour after the warm-up (11).
Young and Elliot (33) studied the effects of static stretching, proprioceptive neuromuscular facilitation (PNF), and maximum voluntary contraction on explosive force production and jumping performance. The results of the study showed a significant reduction in drop jump performance following static stretching compared to the other warm-up procedures. The other modes of stretching had no significant influence on the concentric performance during the squat jump procedure. Church et al. (7) studied the effects of warm-up and flexibility on vertical jump performance. The warm-ups consisted of 10 body weight exercises performed for 20 seconds, the same warm-up routine followed by a static stretching routine, and the same warm-up followed by PNF. The subjects each attempted three trial jumps on the Just Jump system, which were averaged to determine jump height. Church et al. (7) concluded that PNF was the only group that showed a decrease in vertical jump performance. A study by Marek et al. (22) compared the short-term effects of static and PNF stretching on peak torque, mean power output, active and passive range of motion, electromyographic (EMG) amplitude, and mechanomyography amplitude. The authors concluded that there was no significant difference between the static and PNF stretching protocols; both resulted in a similar slight decrease in strength and power.
The effects of passive and active warm-ups on performance have been studied by several researchers (4,23,27). Sargeant (27) found an increase of approximately 11% in maximal peak force and maximal peak power after having the subjects complete a passive warm-up in which the subject were immersed in warm water. Nelson and Kokkonen (23) examined differences in strength after an active warm-up involving ballistic stretching. They found decreases of 7.5% for a 1 repetition maximum (1RM) knee flexion exercise and 5.6% for a 1RM knee extension exercise after the subjects completed the warm-up. Bergh and Ekblom (4) found that an active warm-up involving a bicycle ergometer resulted in increased performance in maximal knee flexion, vertical jump, and sprint performance on a bicycle ergometer.
A dynamic warm-up involves moving joints through a gradually increasing range of motion while increasing the speed of the movement (20). The goal of dynamic warm-ups is to “lead” or “lift” the limbs in a controlled movement through a full range of motion. Dynamic stretching is similar to ballistic stretching in that it uses movement, but dynamic stretching includes movements that may be specific to a sport or movement pattern (14). Using a dynamic warm-up may increase performance mainly as a result of the increase in muscle temperature (32). Stewart et al. (32) found an increase of 7% in squat jump performance after a cycling warm-up. This enhancement has been attributed to an increase in muscle temperature that enhances the rate of ATPase activity (31), which then increases the cross-bridge cycling rate (4). However, dynamic warm-ups can also lead to fatigue, which could negatively affect performance (9,27). Edwards (9) found significantly shorter endurance times for heated muscles. Although Sargeant (27) found increases in maximal peak force and maximal peak power after warming the muscle, he found a greater rate of fatigue and a quicker rate of a decrease in performance.
Although the majority of the studies have focused on men, Burkett et al. (6) studied the effectiveness of 2 specific and nonspecific warm-ups on vertical jump performance in women athletes. The authors used weighted jumps, submaximal vertical jumps, static stretching, and a no warm-up group. The authors (6) concluded that performing a warm-up was better than no warm-up, and using weighted resistance jumps produced the best vertical jump results. The no warm-up group produced statistically inferior results as compared to the warm-up groups. Church et al. (7) used women in their study comparing PNF and static stretching. PNF was found to result in a significant decrease in vertical jumping in women.
There have been numerous studies examining the effects of different warm-ups on power and vertical jumping. However, many of these studies have used small sample sizes. Therefore, the purpose of this study was to investigate the effects of 3 different warm-ups on vertical jump performance using a large sample size. The warm-ups included a 600-m jog, a 600-m jog followed by a dynamic stretching routine, and a 600-m jog followed by a PNF stretching routine. These warm-ups were selected for treatments in the study because they are the warm-ups that are used by the athletes at North Dakota State University. Static stretching is not used as a warm-up for most of the athletes. A second purpose was to determine whether the effects of the warm-ups on vertical jump performance varied by gender. The results of this study will help determine which of the 3 warm-up methods is the most beneficial to maximizing vertical jump performances in athletes.
Experimental Approach to the Problem
A randomized, within-subject experimental repeated-measures design was used in this study. The 3 types of warm-ups that were used in this study were a 600-m jog, a 600-m jog followed by dynamic stretching, and a 600-m jog followed by proprioceptive neuromuscular facilitation (PNF) stretching. All the athletes participated in all the warm-up conditions in a counterbalanced random order. This design was used to minimize the affects of confounding variables such as learning how to vertical jump better during the study and fatigue.
A total of 68 NCAA Division I athletes from North Dakota State University were involved in the study, which included 36 men and 32 women. The means and SDs for the men's age, height (cm), and weight (kg) were 20.5 ± 1.4, 186.9 ± 7.7, and 100.7 ± 17.7, respectively. The means and SDs for the women's age, height (cm), and weight (kg) were 19.8 ± 1.2, 172.9 ± 8.2, and 67.9 ± 9.1, respectively. The study and informed consent form were approved by the North Dakota State University Institutional Review Board. The subjects read and signed an informed consent document. The subjects were involved in a wide variety of sports. Table 1 shows the sports, the number of subjects in each sport, and the season of each sport. All the athletes in the study were involved in an Olympic lift-based resistance training program.
The study was conducted during spring semester finals week; therefore, none of the subjects were involved in any structured training session, making it an ideal time to conduct the study. To ensure that the subjects were not distracted or tired from taking finals and performed to their potential for the study, averages between vertical jump values tested during the sport season and the average of the jumps during the study were compared. The overall average during the sport season was 60.9 cm and the overall average for the study was 60.2 cm, showing that there was little difference between the values found during the study and the values that were found during normal testing for their sport season.
The vertical jump was measured using the Just Jump system. The Just Jump system consists of a 68.6-cm mobile square mat attached to a handheld computer. Validity of the Just Jump system has been previously demonstrated (2,7,19). Church et al. (7) concluded that the Just Jump system is a viable alternative for testing vertical jump based on the manufacturer's reported accuracy of ±0.5 in. Issacs (15) stated that both the Vertec and Just Jump systems provide acceptable measures for vertical jump height. The Just Jump system is more efficient because there is no need to perform calculations to determine the jump height, thus making it a favorable method of testing large groups. The results from all testing sessions were recorded on a spreadsheet developed in Microsoft Excel (Microsoft Corporation, Redmond, Wash.).
The subjects were placed in 1 of 6 groups for the duration of the study. Six groups were used so that there would not be too many subjects at any one testing session and there would not be too long of a time between jumps. The beginning of each session on day 1 started with an explanation of the procedure as well as an outline of the next 2 upcoming sessions. The informed consent form was also explained and signed by the participants. During the first session, the subjects performed one of the following warm-ups: a 600-m jog, a 600-m jog followed by a dynamic stretching routine, or a 600-m jog followed by a PNF routine. The next day, all the subjects participated in a different warm-up, day 3 involved a third type of warm-up for all the subjects. Each session concluded with vertical jump testing consisting of 3 maximum efforts. The vertical jumps were started approximately 2 minutes after the warm-ups, and all 3 jumps for all the subjects were completed within 5-6 minutes. This procedure allowed for optimal control of the warm-up process as well as recovery between maximal vertical jumps. Testing occurred at the same time during each of the 3 consecutive days. The testing procedure followed is found in Table 2.
The vertical jump height was measured with the countermovement technique that takes advantage of the stretch reflex mechanism. All subjects were familiar with the vertical jump technique, having been previously tested as a measure of progress in their respective sports. The subjects were asked to place both feet in the middle of the Just Jump pad, drop their hips to a depth they thought would maximize their jump height and explosively jump as high as possible, focusing on lower body power output. The subjects in each group rotated through testing during the session. The period between each jump was approximately 45 seconds allowing for recovery and maximum performance. The subjects performed 3 jumps, with all jumps being recorded. The average of these jumps was used for the statistical analysis.
The PNF stretches were led by a certified athletic trainer and observed by the researchers to ensure that the athletes were completing the stretches. The PNF stretching used the contract-relax PNF method (26). The stretches and the order in which they were completed can be found in Table 3. The subjects had a partner and took turns stretching each other. The contract-relax method involved the subject contracting the stretched muscle group for a 2 count followed by their partner passively stretching that muscle for a 5 count. This is the PNF procedure that is used by the athletes and athletic trainers at North Dakota State University. An example of the quadriceps stretch of the right leg starts with the subject lying face down in a relaxed position. The partner bent the right knee to a 90° angle and placed the foot on the partner's right shoulder. The left leg of the subject was held down by the partner's straddled left leg. The stretch began with the partner placing his right hand above the knee and the left hand in the center of the buttock of the subject's right leg. The goal of the stretch was to keep the subject's hip fixed to the floor so the stretching occurs in the quadriceps muscle group. During the 2-count contraction, the subject pushed the knee toward the floor followed by a relaxation period of 5 seconds in which the partner lifted the knee while keeping the hip in contact with the floor, thus stretching the quadriceps muscles of the front part of the thigh. This procedure was repeated 3 times with each muscle group.
The dynamic warm-ups were led by one of the researchers who was an assistant strength and conditioning coach and a certified strength and conditioning specialist to ensure that all the subjects completed all the warm-ups. The dynamic warm-ups consisted of 8 exercises, completing 5 repetitions with each leg. The list of exercises and the order in which they were completed can be found in Table 3. The short-step carioca staying low involves the subjects to start facing 1 direction while in a squatting position. The movement began with the subject taking the right leg and crossing it over the left leg in front of the body. The left leg stepped laterally followed by the right leg, which was taken behind the left leg in short-step fashion. Bobo and Dykes (5) give further explanation on the carioca and various other dynamic exercises. This procedure was repeated for 5 repetitions each leg one direction, followed by 5 repetitions the opposite direction. The butt-kicker run focused on quick, smooth action produced at the knee joint. The subject alternately swung the heel of each foot up to each buttock for 5 repetitions with each leg. Each exercise was repeated 2 times with the exception of skipping for height, walking lunges, high knee running, and butt kickers, which were only done once.
Three vertical jump measurements were taken during each testing session and recorded. Although the Just Jump mat reports the vertical jump results in inches, the results were converted to centimeters. The averages of the jumps were used for statistical analysis. SPSS version 12.0 for Windows (SPSS Inc., Chicago, Ill.) was used to calculate descriptive statistics as well as determine the effect of the treatments on vertical jump performance. A 1-way repeated-measures analysis of variance was computed on the combined data as well as on separate men's and women's data. Statistical significance in this investigation was set at p ≤ 0.05. Intraclass correlations were calculated and found to be 0.932, 0.947, and 0.950 for the 600-m jog, the 600-m jog followed by a dynamic stretching routine, and the 600-m jog followed by a PNF routine, respectively.
The vertical jump means after each warm-up routine were very similar. Table 4 shows the means and SDs of the combined, men's only, and women's only vertical jump data.
The results of the combined data (p = 0.927), men's data (p = 0.798), and women's data (p = 0.978) were all found to be nonsignificant. The results of this study showed that there were no significant differences in vertical jumping as a result of the 3 different warm-ups.
Competitive athletes spend much of their time in the pursuit of performance enhancements such as muscle strength, power, flexibility, speed, and nutrition (24). Pearson (24) states that power production and flexibility are the 2 areas of conditioning that receive the least attention. Stretching procedures have been found to affect both power production and flexibility in many studies. In addition to no statistical significant differences found in this study, examination of the means reveals that there was less than <0.2-cm difference in the vertical jump as a result of the 3 different warm-ups. The effect of a stretched muscle is believed to help reduce muscular injuries, but stretching has been found to have a negative effect on force production, thus decreasing power output (7). Church et al. (7) found that PNF stretching resulted in a significant decrease in vertical jump performance. The results from this study contradict the results from the Church et al. (7) study with regard to the effects of PNF on vertical jump performance.
Young and Elliot (33) studied the effects of static stretching, PNF, and maximum voluntary contraction on explosive force production and jumping performance. Although Young and Elliot (33) found a significant reduction in drop jump performance following static stretching, the other modes of stretching had no significant influence on the subject's performance. Young and Elliot (33) also tested the effect of the 4 warm-up conditions in a squat jump procedure. Static stretching was again found to result in significant differences in performance. Static stretching resulted in the worst squat jump performance. However, the study did not find significant differences in performance with the PNF stretching or maximum voluntary contractions procedures. The results of this study support the findings of Young and Elliot (33) regarding a lack of detrimental effects on performance from PNF stretching..
Marek et al. (22) found that both PNF and static stretching resulted in some slight decreases in strength and power. The results of their study are contradictory to the results of this study; PNF stretching was not found to result in any decreases in performance. Marek et al. (22) used a dynamometer to measure performance, while an actual vertical jump was used in this study. This could be 1 reason for the differences found in the effects of PNF stretching. Another possible explanation is that Marek et al. (22) used a longer PNF stretching protocol. The longer protocol could have resulted in greater decreases in muscle stiffness and greater inhibition of the muscle spindles, which could lead to greater decreases in performance.
The majority of studies (4,23,27,32) have found that increasing a muscle's temperature through passive or active methods results in improved performance in power activities where endurance is not a factor. This study found no such benefits, and in fact there where no significant differences in performance between any of the 3 warm-ups. One possible reason for the contradictory results found in this study could be the nature of the warm-up. This study used dynamic activities such as carioca, while the other previously mentioned studies used methods such as immersion in water and bicycling to increase muscle temperature.
The second purpose of this study was to determine whether gender is a factor in determining the stretching procedure that produces the best performance. Church et al. (7) studied the effects of warm-up and flexibility on vertical jump performance using 40 women participants. The main purpose of the study was to determine to what degree warm-up routines affected performance during vertical jump testing. The results of the Church et al. (7) study show that the PNF stretching routine resulted in the lowest vertical jumps. The results of this study showed no significant differences in the women's vertical jump performance after the 3 different warm-ups. Although the results of this study do not support the Church et al. (7) results, a different PNF stretching method was used. The Church et al. (7) study used the contract-relax agonist-contract method of PNF stretching, while this research focused on the contract-relax method of PNF stretching. The methods differ in both the duration of the muscle contraction and the type of contractions involved. According to Fleck and Kraemer (10), the contract-relax agonist-contract method of PNF stretching produces 89% to 110% greater hamstring EMG activity and 9% to 13% more knee joint range of motion than the contract-relax technique. This could result in greater muscular fatigue during the contract-relax agonist-contract compared to the contract-relax PNF method, thus possibly producing a lower vertical jump height.
Burkett et al. (6) studied the effectiveness of 2 specific and nonspecific warm-ups on vertical jump performance in 15 female athletes. Burkett et al. (6) concluded that performing a warm-up is better than no warm-up, and using a weighted resistance will produce the best vertical jump results. The results found in this study contradict the results found by Burkett et al. (6).
Maximum performance in athletics is 1 key to success. Coaches and athletes are constantly striving for an edge over the competition, and certain warm-ups could affect their performance. The ability to start a contest with maximal performance may affect the outcome of the contest. Athletes have a variety of warm-up routines that they feel comfortable with doing before practice and competitions. There are many positive aspects to doing a warm-up such as reducing the chances of injuries and increasing the range of motion of the joints.
Although this study did not find significant differences, many studies have found that the vertical jump can be affected by the warm-up that is completed before performance. Most studies find PNF and static stretching procedures produce the lowest testing results, while dynamic stretching and jump specific movements produce the highest vertical jumps. The detrimental effects have been found to last anywhere from 15 to 60 minutes. This could be problematic for the coach since in most or all sports, warm-ups are completed within 1 hour of the competition. This study found no significant differences in vertical jump performance after the 3 different warm-ups. This study also showed no significant gender differences in vertical jump performance following the 3 different warm-ups.
The results of this study show that the athletes who use a jogging warm-up only, a dynamic warm-up, or a PNF warm-up can be confident that their warm-up will have little or no impact on their vertical jumping performance during competition. All the subject's vertical jumps in this study were completed within 5-6 minutes of the warm-ups. The lack of any significant differences for the 3 warm-ups tested shows that there will be negligible effects, even if the warm-ups are completed shortly before competing.
We thank the North Dakota State University athletes who agreed to participate in this study.
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