Recently, a number of studies have illustrated the significant acute effect that resistance training has on jumping performance, arguably caused by postactivation potentiation (2,3,5,20). Postactivation potentiation is defined as an increase in the contractile ability of muscle fibers after a bout of contractions and constitutes an effective method to increase explosive force (7,11,14). The principles of potentiation have been applied by athletes to enhance performance and optimize training or competition (14). A common method of assessing the level of potentiation that has occurred is to measure the vertical jump performance (11). Indeed, several studies have shown that maximal isometric contractions of the knee and hip extensors correlate well with explosive leg power for increasing vertical jump (4,7,12). Historically, vertical jump tests have been widely used to assess isoinertial qualities in the lower-limb musculature (10). Several training modalities have been developed to improve explosive force, such as resistance training using light, moderate, or heavy loads, plyometrics, or ballistic training (15). Power training is commonly conducted using light resistance (40-60% of 1-repetition maximum [RM]) and performed explosively (1). Training with very heavy loads (close to 1RM, usually 80-100% 1RM), performed a few times (1-3 repetitions), is usually followed by relatively long rest periods and induces increases in muscle power. The results from the study by Young et al. (20) suggest that inclusion of a set of squats with 5RM load in a warm-up (4 minutes before performing countermovement jumps [CMJs]) might result in improved performance in activities dominated by the power output of leg extensors. González-Ravé and Garcia-Coll (6) have shown similar results in short-term training using heavy resistance training (85-90% 1RM) 2 days per week. Duthie et al. (5) examined power performance in squat jumps (SJs) and have concluded that contrast training is advantageous for increasing power output but only for relatively high strength levels. The study by Smilios et al. (15) on short-term training has shown that CMJ performance is enhanced when vertical jump sets are alternated with loaded ballistic training, with the use of SJ or half-squat tests performed with low to moderate loads from within the power training zone (30-60% 1RM). These exercises could be implemented in a contrast training program, with all of them being performed in a workout for the same muscle groups.
Acute effects on power using stretching exercises have also been studied. Both coaches and athletes must be warned about the potential adverse effects of performing static stretching on jump height, because it may be affected negatively (8,17,19). The results of Young and Elliot (19) in the acute effects of static stretching on explosive force production indicate that static stretching may have a detrimental effect on performance for activities involving the stretch-shortening cycle. According to Knudson et al. (8), the acute effect of stretching in the warm-up for dynamic physical activities may be counterproductive to CMJ performance for the majority of physically active young people. Similar results have been found by Nelson et al. (13), who report a decrease in vertical jump height for both CMJ and SJ after stretching the hip extensor and knee flexors. Wallmann et al. (17) studied the effects of static stretching of the gastrocnemius muscle on maximal vertical jump using surface electromyographic assessment. Their results show that static stretching had a negative effect on maximal jumping performance (−5.6%) despite increased gastrocnemius muscle activity (+17.9%).
Yamaguchi and Ishii (18) have shown that static stretching from 100 seconds to 30 minutes reduces muscular performance. If recent studies have pointed out the negative acute effect of static stretching on force production, Yamaguchi and Ishii (18) have suggested that leg extension power after static stretching of several muscle groups of the lower limbs, for 30 seconds, was not different from that observed after no stretching, although the subjects of this study were only recreationally active men and not competitive athletes. Yamaguchi and Ishii (18) and Kokkonen et al. (9) have suggested that the mechanisms causing the decrement in muscular performance after static stretching involve both neurological changes (associated with a reduction in neuromuscular activity level during static stretching) and mechanical changes (associated with a decrease in the viscoelastic properties of muscle-tendon structures).
On the other hand, Unick et al. (16) have suggested that the acute effects of static and ballistic stretching may not adversely affect power performance in trained women (women basketball players).
The objective of this study was to examine the acute effects of heavy-load resistance training, static stretching, and heavy loads with static stretching by untrained subjects and to determine whether any of these procedures have an effect on SJs and CMJs. Pre- and postset measurements with a force platform will be used to evaluate the effectiveness of each training program and, perhaps, identify which program provides an advantage in terms of improving power and force production in these subjects.
The hypothesis was that heavy loads and/or stretching would alter SJ and CMJ performance.
Experimental Approach to the Problem
This study looks at the acute effects of exercise in 3 different configurations of performance. This research entailed using a 3-group design involving 3 types of different exercises (treatments: heavy load, heavy load plus static stretching, and static stretching exercises) and their effects on SJ and CMJ. Subjects' SJs and CMJs were measured after every set of heavy-load exercise or static stretching.
Twenty-four men volunteered to participate in this study and were randomly assigned to 1 of 3 groups:
- Group 1: Heavy-load exercises (n = 8; age 21.6 ± 1.1 years; height 169.8 ± 6.8 cm; mass 65.5 ± 14.4 kg).
- Group 2: Heavy resistance exercises and stretching (n = 8; age 22.3 ± 1.6 years; height 173.1 ± 8.5 cm; mass 72.4 ± 12.7 kg).
- Group 3: Stretching (n = 8; age 21.8 ± 1.4 years; height 172.4 ± 5.7 cm; mass 67.3 ± 8.9 kg).
The study was approved by the University of Porto, the potential risks were explained, and all subjects gave written informed consent to participate in the study. All subjects were sport science and physical education students, and none were actively engaged in any type of systematic physical training. None of the subjects had previously performed specific strength training or stretching when this study started, and all of them were free of musculoskeletal disease. All subjects were instructed not to perform excessive physical activity before the testing sessions but to continue with their normal routines.
Before the testing session, the participants in groups 1 and 2 undertook a familiarization session that allowed subjects to practice the testing procedures and strength exercises and established a 3RM load for the half-squat exercise in the Smith machine, setting the knee angle at 90°. The subjects in groups 1 and 2 warmed up with 10 repetitions with a load of approximately 60% of their individual 1RM. To establish the 3RM load, the subjects attempted 3 repetitions of a load, and, when successful, the weight was increased by 5 or 6 kg, before the testing began for the half-squat exercise (5). Group 3 subjects performed 3 stretching exercises, holding each stretch for 15 seconds. The stretches included a seated bilateral hamstring stretch, a standing unilateral quadriceps stretch, and a standing unilateral calf stretch, and the subjects in this group also performed SJs and CMJs. The purpose of this session was to familiarize the subjects with the procedures, to allow time to learn SJ and CMJ procedures, and to determine the 3RM value in groups 1 and 2.
Subjects performed the standardized warm-up at the start of the session. The standardized warm-up consisted of 5 minutes of cycling (light aerobic) followed by 3 minutes of rest for all groups. The participants were instructed to “cycle at a comfortable speed” that was observed to be a consistent pace. This low-intensity cycling was intended to produce an increase of core body temperature, although this was not measured (19). All groups then performed a pretest, which consisted of 2 vertical jump tests. Two vertical jump types were performed, an SJ and a CMJ. Each subject's SJ and CMJ performance was evaluated using a force platform (Bertec 4060-15), which recorded flight time (seconds), time of force production (seconds), and force production (N); jump height (cm) was computed afterwards.
The SJ was performed from a starting position, with a 90° knee angle. Each subject kept his hands on his hips during the jumps. Three maximal jumps were recorded, and the best maximum in terms of height was taken for further analysis. The rest period between jumps was always 30 seconds. Each subject was given external encouragement throughout all the tests.
In the CMJ, each subject stood in an upright position, flexed the knees and hips into a squat position, and then immediately extended the knees and hips into an upward jump.
We chose to use vertical jumps because they provide further insight into the force capabilities of the leg extensor muscles (12). Moir et al. (12) suggest that vertical jump assessment in athletes and recreationally active men can be achieved with a high degree of reliability.
Group 1 performed 3 sets of 4 repetitions of half-squats against an 85% 1RM load. Each set was followed by SJ and CMJ measures. This results in 3 posttest measures of SJ and CMJ. Three minutes of rest were allowed between sets.
For the static stretching intervention, group 3 performed 3 sets of 3 stretches. The stretches included a seated bilateral hamstring stretch, a standing unilateral quadriceps stretch, and a standing unilateral calf stretch. The SJ and CMJ posttests were measured after the performance of every set of 3 stretches. Three minutes of rest were allowed between sets. For the static stretching treatment in group 3, subjects stretched the target muscle in both legs slowly and carefully until reaching a position at which the subject stopped the stretching. This position was held for 15 seconds. The stretch procedures are shown in Table 1.
Finally, group 2 performed 3 sets of 4 repetitions of half-squats against 85% 1RM and 3 stretch exercises (seated bilateral hamstring stretch, standing unilateral quadriceps stretch, and standing unilateral calf stretch) for 15 seconds. The subjects completed SJ and CMJ measures after each set. Three minutes of rest were allowed between sets.
The protocol for all groups is shown in Table 2.
The participants in the study (both at the familiarization session and at the training session) were under close supervision by 2 qualified exercise leaders to ensure proper technique and to minimize the risk of injury.
The statistic program SPSS 13.0 for Windows (SPSS Inc., Chicago, Ill) was used to compute mean ± SD and other statistic parameters. The test-retest reliability was estimated using Cronbach alpha. A general linear model with repeated measures was used to determine whether there were significant vertical jump differences between the treatment groups in jump height (cm), time of force production (seconds), and force production (N). A Bonferroni post hoc test was used to compare pretest, postest 1, postest 2, and postest 3.The criterion for statistical significance was set at an alpha level of 0.05 for all comparisons.
Vertical Jump Responses
The test-retest reliability results for each variable tested are presented in Table 1. The results from the Cronbach alpha test showed a large correlation of data from within a group. The mean vertical jump scores for SJ and CMJ are displayed in Tables 3 and 4. Data in Figures 1 and 2 depict absolute SJ and CMJ values. Figure 1 shows that SJ increased in set 1 and remained unchanged in sets 2 and 3 for heavy-load exercises while remaining unchanged in heavy-load plus stretching exercises. In addition, SJ increased after stretching training in set 1, remained unaltered in set 2, and increased in set 3.
Figure 2 illustrates that CMJ had a decrease in set 1 in heavy-load exercises, but it had an increase in sets 2 and 3. The stretching exercises showed an increase in set 1 and remained unchanged in sets 2 and 3. The heavy-load plus stretching exercise group decreased jump height in set 2, whereas set 3 remained unaltered with respect to set 1.
A general linear model between groups was then conducted to examine the interaction between treatments and changes in jump height in sets. Jump height in CMJ remained unchanged along the 3 groups, and therefore the effects of exercise chosen and sets were not significant. In addition, the results for SJ were not significant, but they displayed a tendency to have significant differences between sets (p < 0.06), considering the treatment type. In the SJ, mean jump height showed significant differences between sets (p < 0.00) without taking treatment type into consideration. Therefore, when comparing the changes in jump height in SJ and CMJ within a single session, there were no significant differences in mean jump height between sets within the training session when considering treatment type.
Vertical Ground-Reaction Force
The vertical ground-reaction forces for SJ and CMJ are displayed in Tables 5 and 6. Vertical ground-reaction force was 2.31 and 2.05% lower when sets 1, 2, and 3 were compared with the pretest in heavy-load exercises in CMJ. In heavy-load plus stretching exercises, there was a decrease in set 1 and increases in sets 2 and 3; consequently, vertical ground-reaction force showed an increase of 3.5% when set 3 was compared with the pretest. In the stretching exercises group, vertical force showed an increase in set 1, a decrease in set 2, and an increment in set 3. Finally, the vertical ground-reaction force showed an increase of 3.29% when set 3 was compared with the pretest (Figure 3).
A general linear model was used to analyze the vertical ground-reaction force in CMJ and showed significant differences (p < 0.001) between sets in each group.
In SJ (Figure 4), the force continued to be lower in set 3 with respect to the pretest in heavy-load, heavy-load plus stretching, and stretching exercises. The force was 4.23% lower when set 3 was compared with the pretest in heavy-load exercises, and it showed a 9.16% decrease in heavy-load plus stretching exercises. In stretching exercises, the force continued to be lower in set 3 with respect to the pretest (1.94%). The vertical ground-reaction force results in SJ were significant (p < 0.000) between sets and training in each group.
The purpose of this study was to clarify the acute effects of heavy resistance exercises and stretching on vertical jump performance. To the best of our knowledge, no other study has examined the acute effects of mixed heavy-load stretching exercises in a session compared with heavy-load plus stretching exercises on SJ and CMJ performance.
This study also examined the subjects' ability to use the effects of heavy preload exercise on subsequent explosive power activities. No initial effects of the heavy-load exercises or heavy-load plus stretching exercises on SJ and CMJ were found. The study's main finding was that strength exercises using heavy loads or heavy-load plus stretching exercises did not have a significant effect on maximal jump height in untrained subjects. The stretching exercise group and the heavy-load exercise group showed increases in SJ, but these were not significantly different from all the other scores. In addition, our results show that the heavy-load plus stretching exercise group and the stretching group showed an increase in CMJ, although these values were not statistically significant.
Several studies (13,15-19) have shown that muscular performance was not different after static stretching. In this study, changes in force production improved performance after heavy-load plus stretching exercises and stretching exercises (p < 0.00), but these exercises revealed no significant differences in vertical jump scores because of limitations in applying these changes to the treatment of untrained subjects. In addition, there were significant differences in the mean jump height between sets within the training session without considering the treatment type.
These results differ from those of several previous studies, which found a decrease in vertical jump as a result of stretching (13,17). In a study performed by Young and Elliot (19), a significant reduction in drop-jump performance after a static stretching routine was found. Nelson et al. (13) also found a significant decrease in SJ and CMJ as a result of static stretching.
Our hypotheses were that heavy loads or stretching would alter SJ and CMJ performance and induce increases in muscle power and that the different protocols would make it easier for the subjects to benefit from repeated exposure to the protocol. Therefore, these results do not support our hypotheses. The lack of acute enhancements found in this study is similar to the findings of McBride et al. (11) but is in contrast to the results of Baker (1), Young et al. (20), Gullich and Schmidtbleicher (7) and González-Ravé and García-Coll (6). This may suggest that stronger athletes experience greater potentiation than fatigue, whereas the opposite occurred in the sample of sport science students. The exact mechanism responsible for the decrease in postactivation potentiation is unclear. No tests on the level of neuromuscular activation were performed. Therefore, the mechanism responsible could not be assessed. Familiarization seemed to play an initial role in performing SJ and CMJ in sport science students (14), because none of the subjects had previously performed strength training with heavy loads during their workouts. On the other hand, postexercise fatigue in strength training using heavy loads could be another reason for these results. The results of this research are, therefore, specific to the population and cannot be generalized for different populations (e.g., athletes, sedentary people). This would be an explanation for the significant differences in mean jump height between sets within training sessions without taking treatment type into consideration.
Training with very heavy loads (close to or at 1RM, usually 80-100% 1RM) and performed with few (1-3) repetitions is usually followed by relatively long rest periods (23) and induces increases in muscle power. Gullich and Schmidtbleicher (7) measured the H-reflex response for highly trained athletes vs. sport science students and found that highly trained athletes had a higher degree of positive change in the H-reflex response and that its effect lasted longer, which seems to be in accordance with our study. Young et al. (20) have reported that an increase in CMJ height correlated significantly with 5RM strength. However, we did not find any significant differences.
Scott and Docherty (14) have shown how the principles of postactivation potentiation have been applied to enhance athletic performance and optimize training protocols in which heavy resistive exercise (5RM) is performed before CMJs and horizontal performance.
In SJ, we found a decrease in force production for the 3 groups. In addition, we found a lower percentage change in SJ when comparing the pretest results with set 3 (2.23% in heavy-load exercises, 9.16% in heavy-load plus stretching exercises, and 1.94% in stretching exercises) for the sport science students, although these values were not statistically significant. Therefore, the use of a heavy load is required to activate all motor units and probably to achieve the greatest neuromuscular activation in elite athletes before competing (7). Our study found increases in vertical force for CMJ in heavy-load plus stretching exercises and only stretching exercises, and a decrease in the heavy-load exercise program. In CMJ, force production was 2.05% lower when set 3 was compared with the pretest in heavy-load exercises. There was a clear trend for the force values to decrease during the session in all groups for SJ and the heavy-load exercises group for CMJ, which may indicate a fatigue effect during each set of the training sessions for the 3 groups that is attributable to some limitations in applying the protocol to the training of untrained subjects. Besides, the use of heavy-load exercises increased SJ, but not significantly. It is possible that very heavy resistances (85-90% 1RM), with slower lifting speeds, may not provide an optimal stimulus for enhanced jump height in SJ and CMJ and force production in heavy-load treatments. It may temporarily attune neural output to a slower speed than is optimal for maximum power production (7). Perhaps the use of moderate load (i.e., 60% 1RM) could increase the performance of untrained subjects and be adequate enough to alter neuromuscular function and, consequently, increase SJ and CMJ (6,7). The study by Smilios et al. (15) has reported the effects of heavy resistance training on SJ, where there is no prestretching of the muscles and performance mainly resides on neural activation of the muscles without reflex and elastic energy contribution. The results of Smilios et al. (15) show an increase in CMJ performance, but the applied loads did not seem to present different short-term effects in SJ using contrast training (3 sets of 5 repetitions with loads of 30 and 60% 1RM, with 3 minutes of rest in 4 sessions: 2 sessions with 30% 1RM and 2 sessions with 60% 1RM).
In addition, Smilios et al. (15) have shown that performing light exercises (30% 1RM) and moderate exercises (60% 1RM) could cause a short-term increase in CMJ performance. Perhaps the level of activation using light or moderate loads in sport science students would be adequate enough to alter neuromuscular function and, consequently, increase CMJ and SJ.
On the other hand, static stretching significantly reduces leg strength, as well as jump height, in SJ and CMJ (13). Conversely, in our study the use of static stretching in quadriceps and half-stretches in both legs for 15 seconds increased SJ and increased CMJ, but not significantly. Therefore, the results in this study show that CMJ after static stretching in the lower limbs for 15 seconds (1 set of 15-second stretching each) did not differ from CMJ after no stretching. This suggests that static stretching neither improves nor reduces muscular performance. These results differ from those of several previous studies that have found decreases in vertical jumps as a result of stretching. Previous studies have suggested that mechanisms causing decrements in muscular performance after static stretching involved both neurological (reduction in neuromuscular activity level) and mechanical changes (viscoelasticity of muscle tendon structures), although the reason for the discrepancy between the results of previous studies (13,16,18,20) and those of this study could not be clarified from this study's results.
The static stretching method (15 seconds) may lead to improvements in SJ in physically active young persons. The results of this study will add to the growing volume of conflicting research regarding stretching on specific performance variables. Unick et al. (16) have indicated that the acute effects of static and ballistic stretching may not adversely affect power performance in trained women (basketball players), which agrees with our results in SJ.
These findings suggest that for activities involving muscle function related to SJ or CMJ (e.g., basketball, volleyball), acute exercises using stretching, heavy loads, or heavy loads plus stretching do not have a significant effect on maximal jump height in untrained subjects. On the basis of this study and others, there is limited support for the use of heavy resistance training before a power movement to enhance performance. It might be a good idea for untrained or physically active subjects to use moderate loads (i.e., 60% 1RM) or even light loads. Familiarization seemed to play an initial role in performing SJs and CMJs, and postexercise fatigue in stretching, heavy-loads and heavy-load plus stretching exercise could be another reason for these results in this kind of population. Although we found an increase in force production for CMJ in heavy-load plus stretching exercise and stretching exercise, we also found a decrease for CMJ after heavy-load exercise and a decrease in SJ performance as a consequence of the 3 preexercise exertions.
1. Baker, D. Acute and long-term power responses to power training: observations on the training of an elite power athlete. Strength Cond J
23(1): 47-56, 2001.
2. Baker, D. Acute effect of alternating heavy and light resistances on power output during upper-body complex training. J Strength Cond Res
17: 493-497, 2003.
3. Baker, D and Newton, RU. Acute effect on power output of alternating an agonist and antagonist muscle exercise during complex training. J Strength Cond Res
19: 202-205, 2005.
4. Burkett, LN, Philips, WT, and Ziuraitis, J. The best warm-up for the vertical jump
in college-age athletic men. J Strength Cond Res
19: 673-676, 2005.
5. Duthie, GM, Young, WB, and Aitken, DA. The acute affects of heavy loads on jump squat performance: an evaluation of the complex and contrast methods of power development. J Strength Cond Res
16: 530-538, 2002.
6. González-Ravé, JM and Garcia-Coll, V. Respuestas agudas al entrenamiento de fuerza máxima en deportistas femeninas (in Spanish). Arch Med Dep
114: 283-290, 2006.
7. Gullich, A and Schmidtbleicher, D. MVC-induced short term potentiation
of explosive force. New Stud Athl
11: 67-81, 1996
8. Knudson, D, Bennett, K, Corn, R, Leick, D, and Smith, C. Acute effects of stretching are not evident in the kinematics of the vertical jump
. J Strength Cond Res
15: 98-101, 2001.
9. Kokkonen, J, Nelson, AG, and Cornwell, A. Acute muscle stretching inhibits maximal strength performance. Res Q Exerc Sport
69: 411-415, 1998.
10. Logan, P, Formasiero, D, Abernethy, P, and Lynch, K. Protocols for the assessment of isoinertial strength. In: Physiological Tests for Elite Athletes
. C.J. Gore and Australian Institute of Sport, eds. Champaign: Human Kinetics, 2000. pp 200-222.
11. McBride, JM, Nimphius, S, and Erickson, TM. The acute effects of heavy load squats and loaded countermovement jumps on sprint performance. J Strength Cond Res
19: 893-897, 2005.
12. Moir, G, Button, C, Glaister, M, and Stone, MH. Influence of familiarization of the reliability of vertical jump
and acceleration sprinting performance in physically active men. J Strength Cond Res
18: 276-280, 2004.
13. Nelson, AG, Cornwell, A, and Heise, G. Acute stretching exercises and vertical jump
stored elastic energy. Med Sci Sports Exerc
28(Suppl.): 101, 1996.
14. Scott, SL and Docherty, D. Acute effects of heavy preloading on vertical and horizontal jump performance. J Strength Cond Res
18: 201-205, 2004.
15. Smilios, I, Pilianidis, T, Sotiropoulos, K, Antonakis, M, and Tokmakidis, S. Short term effects of selected exercise and load in contrast training on vertical jump
performance. J Strength Cond Res
19: 135-139, 2005.
16. Unick, J, Kieffer, HS, Cheesman, W, and Feeney, A. The acute effects of static and ballistic stretching on vertical jump
performance in trained women. J Strength Cond Res
19: 206-212, 2005.
17. Wallmann, HW, Mercer, JA, and McWhorter, JW. Surface electromyographic assessment of the effect of static stretching
of the gastrocnemius on vertical jump
performance. J Strength Cond Res
19: 684-688, 2005.
18. Yamaguchi, T and Ishii, K. Effects of static stretching
for 30 seconds and dynamic stretching on leg extension power. J Strength Cond Res
19: 677-683, 2005.
19. Young, W and Elliot, S. Acute effects of static stretching
, propioceptive neuromuscular facilitation stretching, and maximum voluntary contractions on explosive force production and jumping performance. Res Q Exerc Sport
72: 273-279, 2001.
20. Young, WB, Jenner, A, and Griffiths, K. Acute enhancement of power performance from heavy load squats. J Strength Cond Res
12: 82-84, 1998.
Keywords:© 2009 National Strength and Conditioning Association
potentiation; vertical jump; muscle activation; muscular performance; static stretching