It is a common practice among athletes competing in track and field throwing events to use specific muscular actions/exercises just before competition to enhance their performance. However, there are no scientific data regarding the effectiveness of such interventions. In the laboratory setting, a single maximum isometric voluntary contraction of 10 seconds duration can increase the twitch response for the following couple of minutes (8). This phenomenon, termed postactivation potentiation, has been documented in both human and animal muscles (9,12).
Field studies have revealed that performance of a single heavy-resistance lower-body exercise either enhances (7,21) or has no effect (11) on explosive performance immediately after. Moreover, it has been shown that a single set of 5 repetition maximum (RM) in bench press has no immediate effect on explosive push-ups (10), whereas explosive exercise, such as the snatch, enhances subsequent jumping performance (13). Thus, it seems that although there is no consensus regarding the acute enhancement of explosive performance with heavy-resistance exercise, high power-demanding tasks (e.g., the snatch) might induce an acute increase in lower-body explosive performance. However, this phenomenon has not been investigated in throwing events such as the shot put.
Postactivation potentiation is a short-lived phenomenon (approximately 3 minutes, ). Thus, resistance exercise (e.g., squat, snatch) cannot be used to enhance throwing performance just before a throwing event. On this basis, we hypothesized that explosive muscular actions such as jumping, which can be performed immediately before a competitive throw, would enhance shot put throwing performance. In the present study, we aimed to evaluate the effect of drop jumping on a simple throwing action in moderately skilled subjects as a preliminary study before its evaluation in throwers during competition. Furthermore, laboratory studies have shown that postactivation potentiation is closely related to muscle fiber-type composition (8,20) and muscular strength (7). Specifically, it has been shown that it is enhanced in stronger subjects and those with a high percentage of type II muscle fibers. However, this phenomenon has not been investigated in throwing.
The purpose of the present study was to investigate the acute effect of drop jumping on throwing performance. Furthermore, we aimed to investigate the influence of muscle fiber-type composition and muscular strength on performance enhancement during a simple throwing action to provide possible insights into the nature of the findings.
Experimental Approach to the Problem
This study addressed the question of whether moderate-trained subjects would acutely increase their throwing performance after the implementation of a small number of intense muscular actions. This research question is based theoretically on the phenomenon of postactivation potentiation (8), and the results of this study might be applied to moderate-level shot put throwers. Moreover, this serves as a preliminary study to further investigate this phenomenon in well-trained throwers. Sixteen subjects (men and women) with basic shot put skills performed a simple (from a kinesiological point of view) throwing action: the squat underhand front shot throw (Figure 1). Subjects performed 3 squat underhand front shot throws after a short warm-up. Subsequently, they performed 5 drop jumps and immediately after they performed another set of squat underhand front shot throws. The underhand shot throw (Figure 1) was chosen as a throwing performance test because it is a commonly used exercise and it is performed very often by shot putters. It is a task that is highly correlated with shot put performance in well-trained shot putters (unpublished data from our national throwers team, 14) and in moderate-trained individuals (19). Moreover, this test was used because it is an easy-to-learn-task by moderate-trained individuals. Our subjects had been using this task for almost 3 months during their university courses; thus, any learning effect during the day of the experiment was minimized. Further, it has been found in a previous study that moderate-trained subjects, as those participated in the present investigation, can use their lower extremities more efficiently during a more simple task, such as the squat underhand shot throw, than during the real shot put performance (18). To further investigate possible mechanisms responsible for the current results, leg press 6RM was used as a muscular strength index and muscle fiber-type composition was determined in vastus lateralis because studies have reported that postactivation potentiation is influenced by muscular strength and the percentage of type II muscle fibers (7,21). Both men and women were recruited because there is limited information regarding gender differences in postactivation potentiation in field studies.
Sixteen volunteers, physical education students (8 men and 8 women), gave their written consent to participate in the study after being informed about the experimental procedures and the possible hazards of the muscle biopsy (men: 22 ± 1 years, height 177 ± 5 cm, weight 77 ± 6 kg; women: 23 ± 3 years, height 170 ± 6 cm, weight 66 ± 7 kg). All subjects had right-hand dominance and followed a shot put skill course of 5 weeks duration (4 hours/week) before their participation in the study. All procedures were approved by the Ethics Committee of the S.P.E.S.S. of the U.O.A.
Squat Underhand Front Shot Throw
The squat underhand front shot throw testing was performed outdoors in the morning hours in a standard shot put circle at an ambient temperature of 20 to 22°C. After a 10-minute warm-up (5 minutes running and then stretching), subjects rested for 3 minutes at a sitting position and subsequently performed 3 underhand front shot throws from a squat position (14, Figure 1). One minute of rest was allowed between each trial. Men used a 6-kg implement, whereas women used a 4-kg implement. This relatively simple throwing action was selected because the subjects participating in the study had only basic shot put skills (18). The same throwing test was repeated immediately after the performance of the drop jumps (e.g., 3 trials with 1-minute rest between). The time between the last drop jump and the first squat underhand shot throw was 20 seconds. The best underhand throwing performance before and the best underhand throwing performance after the drop jumps were used for further analysis. Subjects were vocally encouraged to perform their best during the shot throws. Also, distance targets were used to further stimulate subjects' performance.
Three minutes rest was allowed after the initial 3 underhand throws and before the performance of the drop jumps. Subjects were moved 10 m away from the shot put circle and performed 5 consecutive drop jumps from a concrete level of 40 cm height to a landing area made of concrete. All subjects were familiar with drop jumping through their participation in university courses. They were instructed to land stiff, with the least possible knee bending, and jump as high as possible after their landing. No rest was allowed after each drop jump. After the fifth drop jump, subjects walked quickly to the shot put circle and performed 3 underhand throws as described earlier. The time between the last drop jump and the first squat underhand shot throw was 20 seconds. Subjects were vocally encouraged to jump as high as possible during the drop jumps.
Leg Press 6RM
All subjects were familiar with the leg press exercise through their participation in university courses. Assessment of 6RM muscular strength in leg press was performed according to previous reports (1,19). Briefly, after a short warm-up on a stationary bicycle and stretching exercises, subjects performed incremental submaximal efforts with 6 to 8 repetitions until they were unable to lift a heavier weight for 6 repetitions. Three minutes of rest was allowed between sets. In all cases, 2 of the authors were present and vocally encouraged each trial of each subject.
Muscle Biopsies and Histochemistry
Muscle samples were obtained from the middle portion of vastus lateralis (2), 20 cm from mid patella of the right leg, 1 week after the throwing performance tests. Samples were aligned; placed in embedding compound; and frozen in isopentane, which was precooled to its freezing point. All samples were kept in liquid nitrogen until the day of analysis. Serial cross-sections, 10-μm thick, were cut at −20°C and stained for myofibrillar ATPase after preincubation at pH 4.3 (4,5,15). Biopsy slices from all subjects were stained at the same time in the same jar. A mean of 798 ± 86 muscle fibers were classified as type I or II from each sample. The cross-sectional area of all the classified fibers from each sample was measured with an image analysis system (ImagePro, Media Cybernetics Inc, Silver Spring, Maryland, U.S.A.) at a known and calibrated magnification.
Means ± SD were used to describe variables. Pearson's (r) product moment correlation coefficient was used to explore the relationships among different variables. Independent student t-test was used to investigate differences between males and females and between the groups of subjects distinguished by high or low percentages of type II muscle fibers and 6RM leg press strength. p ≤ 0.05 was used as a 2-tail level of significance. A subgroup of subjects (n = 6) repeated the throw-drop jumping -throw sequence testing, on a different day, for reliability determination. Intraclass coefficients for the throwing performance before and after the drop jumps were R > 0.91.
The percentage of type II muscle fibers in vastus lateralis for the whole group of subjects was 54.8 ± 15%. However, men had a significantly higher fiber cross-sectional area and percentage of type II fiber area as compared to women (Table 1). Squat underhand shot throw performance was significantly increased after drop jumping in all subjects as a group (before: 8.25 ± 1.1 m, after: 8.63 ± 1.3 m, p < 0.01, Figure 2). However, shot put performance was significantly increased in men (before: 8.94 ± 1 m, after: 9.60 ± 0.9 m, p < 0.01) but not in women (before: 7.56 ± 1 m, after: 7.67 ± 0.9 m, ns) immediately after drop jumping.
A close and significant relationship was found between the percentage of type II muscle fiber area and the percentage change in performance before and after drop jumping (r = 0.76, p < 0.01, Figure 3). Moreover, when subjects were divided in 2 equally numbered groups according to their percentage of type II muscle fiber area (> or <55 % type II fiber area), regardless of their gender, the percentage change in performance before and after drop jumping was higher in the group with the higher type II muscle fiber area (% change in shot put performance 0.6 ± 5% vs. 8.7 ± 4%, p < 0.01, Figure 4).
A moderate relationship was found between 6RM leg press strength and the percentage change in squat underhand shot throw performance before and after drop jumping (r = 0.50, p < 0.05). When subjects were divided in 2 equally numbered groups according to their 6RM leg press strength (> or <170 kg), regardless of their gender, the percentage change in performance before and after drop jumping did not differ significantly. Finally, the percentage change in squat underhand shot throw performance before and after drop jumping was not correlated significantly with the squat underhand shot throw performance, either before or after the drop jumps in men or in women, respectively.
The main finding of the present study was that a simple throwing action, such as the squat underhand front shot throw, was enhanced after the performance of 5 consecutive drop jumps from 40 cm in moderately trained subjects. This result might be attributed to the phenomenon of postactivation potentiation, which has been described before in humans and in animals (8,9,12). According to this phenomenon, the force of a twitch contraction is enhanced after the implementation of a maximal voluntary contraction (8). Previous studies have shown that maximum voluntary contraction can induce an increase in explosive lower-body power performance (7) and that heavy squat exercise can cause an acute increase in power output of the lower extremities (21). Moreover, a powerful muscular action, such as the snatch, can lead to an acute increase in jumping performance (13). Similarly, the present results suggest that powerful muscular actions, such as the drop jumps, can cause an acute increase in another powerful muscular action such as throwing the shot, at least in moderately trained subjects.
The increase in squat underhand front shot throw performance after the drop jumps was closely related to the percentage of type II muscle fiber area in vastus lateralis. Similar results have been reported previously in laboratory studies investigating the acute effect of maximum voluntary contractions on subsequent twitch contractions (8,20). However, 1 previous study concluded that fiber-type composition in vastus lateralis is not related to postactivation potentiation caused by a maximum voluntary contraction (16). The discrepancy between the results of the carefully designed laboratory study of Stuart et al. (16) and the present study could be attributed to the much broader range of fiber-type composition among the subjects of our study, as also suggested by Hamada et al. (8). Specifically, Stuart et al. (16) reported a range of type II fiber type percentage between 37 and 65%, whereas Hamada et al. (8) described a wider range of 30 to 84%. The latest was almost identical with the corresponding range documented in the present study (28-80%). Of note, the present data revealed that drop jumps did not enhance shot put performance in females. However, this result might be explained by the significantly lower percentage of type II muscle fiber area in female subjects, as found in our sample (Table 1).
The phenomenon of postactivation potentiation has been attributed to an increase in the phosphorylation of myosin light chains during the preceding intense muscular action, which is thought to increase the sensitivity of actin-myosin to Ca2+ during the following muscular action (6,9,17). Such mechanisms would increase the postactivation potentiation in shot put performance in subjects possessing a higher percentage of type II muscle fibers because these fibers might contribute more to such powerful muscular action. The present results revealed that the relationship between the increase in squat underhand front shot throw after drop jumping correlated more with the percentage of the type II fiber area rather than with the percentage number of type II fibers (r = 0.76, p < 0.01 vs. r = 0.69, p < 0.01). This might suggest that the number of type II myosin molecules is more important than the number of type II cells for this relationship. This is in concert with the hypothesis of the increased phosphorylation of the myosin light chain phosphorylation after the initial intense muscular action. Furthermore, it is plausible that a fast and powerful muscular movement, such as the drop jump, might activate strongly the type II muscle fibers, thus enhancing the phosphorylation of myosin light chains in these fibers and subsequently increase the shot put performance in subjects possessing higher percentages of type II muscle fibers. Similar suggestions have been proposed before (6,17). However, this hypothesis requires further investigation.
Muscular strength (6RM) was moderately related to the increase in squat underhand shot put performance after drop jumping. It has been previously suggested that muscular strength might influence positively the postactivation potentiation (7,20). In a recent study, a tendency toward an increase in jumping performance immediately after 1 repetition at 90% 1RM of the half or quarter squat was reported (11). In the same study, muscular strength was not related to the change in performance after performing the squat. These results, together with the present results, suggest that fiber-type composition has a stronger influence on postactivation potentiation than muscular strength. Alternatively, it might be possible that the use of 6RM as an index of muscular strength could have underestimated the relationship between strength and increase in underhand shot throw performance. It might be argued that there was a learning effect (e.g., better performance in the last throws) that might explain the increase in performance after drop jumping. However, the subjects were already well familiarized with squat underhand shot throwing. Moreover, most of the subjects (11 out of 16) achieved their maximum performance in the second or third trial before drop jumping and in the first or second trial after drop jumping (12 out of 16).
In conclusion, the results of the present study indicate that drop jumping just before a simple shot throwing action induces an increase in performance in moderately trained subjects. This increase in performance was closely related to the percentage of type II muscle fiber area of vastus lateralis and moderately related to the muscular strength of the lower extremities. Gender differences found in this study can be explained by the fiber-type composition of vastus lateralis.
The present data suggest that a powerful movement such as the drop jump from 40 cm can be used effectively to acutely enhance the performance in a simple throwing action in moderately trained males and females. Thus, shot put throwers of a moderate level might be benefited by such an approach. Moreover, throwers with a high percentage of type II muscle fibers in their protagonist lower limb muscles would gain more from such intervention. Drop jumping should be performed immediately before (<30 seconds) the throwing action to be effective. It remains to be investigated whether such a maneuver can enhance performance in well-trained throwers, considering the fact that such athletes possess a relatively high percentage of type II muscle fiber area in the their thigh muscles (3).
We express our gratitude to the subjects who participated in the study. We also wish to thank D. Vontzalidis, MD, and E. Mastoroglou for excellent technical assistance. This work was partly supported by grants from S.A.R.G. of the U.O.A. to G. Georgiadis and G. Terzis. All experimental procedures used comply with Greek governmental laws for human subjects. This work has never been published anywhere else before, either completely or in part.
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Keywords:© 2009 National Strength and Conditioning Association
fiber-type composition; postactivation potentiation; warm-up; shot put