Assessing Explosive Power Production Using the Backward Overhead Shot Throw and the Effects of Morning Resistance Exercise on Afternoon Performance

Abstract

Ekstrand, LG, Battaglini, CL, McMurray, RG, and Shields, EW. Assessing explosive power production using the backward overhead shot throw and the effects of morning resistance exercise on afternoon performance. J Strength Cond Res 27(1): 101–106, 2013—The purpose of this study was to determine if performing a morning total-body resistance exercise workout affects explosive power in an afternoon session. The secondary goal was to assess the usefulness of the backward overhead shot throw (BOST) as a measure of explosive power in experienced thrower in the sport of athletics. Throwers (N = 14) performed 1 control and 1 experimental trial on separate days. The control consisted of BOST and a vertical jump (VJ) testing performed in the afternoon. For the experimental trial, the participants reported for a short resistance training session in the morning then repeating the BOST and VJ testing 4–6 hours later. The BOST distance (meters) and VJ peak power (watts) were correlated in both trials (r ∼ 0.64, p < 0.05). The BOST distance improved in experimental trial over control (p < 0.05), but VJ power failed to improve. The results indicate that a morning resistance exercise bout can improve competitive throwing performance later on the same day. The results also suggest that BOST may be a useful performance testing tool for throwers in the sports of athletics.

Introduction

Optimal performance in the throws events of the sport of athletics requires both technique and explosive lower and upper body power. Although assessing technique is subjective, explosive power can be objectively measured. The vertical jump (VJ) is one of the most commonly used test (^{3,9,15,19,24,29,30,33}) to assess explosive power. However, the movement of the VJ focuses primarily on hip and leg function and includes little trunk or arm contribution to total power production (^24,29,30), which is important for throwing events in athletics. In addition, the VJ focuses on accelerating body mass only and ignores the element of momentum production and transfer to an implement (^29,30). Therefore, the VJ may not be the optimal way to assess power for throwers. The backward overhead shot throw (BOST) test is commonly used in physical testing batteries for the throws events because it is related to actual competitive throwing (²¹). The BOST movement requires leg, core, and upper body power, and the use of an implement (e.g., weighted ball) and is believed to be a better indicator of throwing performance than the VJ (³⁰). However, little research is available on the usefulness of the BOST as a test of explosive power production.

Several studies have shown that a single bout of resistance exercise performed 3–20 minutes before competition enhances explosive power (^{1,15,16,23,27,28,33}). In addition, anecdotal evidence also exists for the ergogenic effects of resistance exercise warm-up on competitive power performance (²³). However, during competition in throwing events, there is the potential for an extended period between the warm-up bout and the competitive performance. Some evidence suggests that there are several neural mechanisms for performance enhancement that may extend beyond the 3- to 20-minute window examined in most studies, including central nervous system activation (³³), decreased reflex inhibition (²⁶), reduced anxiety (¹⁴), and improved psychological preparedness (^4,5). Thus, a systematic study on how resistance exercise several hours before competition impacts competitive performance should be explored.

Given the dependence of the throwing events on physical conditioning and preparedness, the potential for an acute bout of resistance exercise to enhance competitive throws performance merits future investigation. Therefore, the purpose of this study was to determine if performing a morning total-body resistance exercise workout affects backwards overhead shot throw (BOST) and vertical jump (VJ) performance in an afternoon session. The secondary purpose was to explore the usefulness of the BOST compared with the more commonly used VJ as a measure of explosive power production for throwers in the sport of athletics. We theorized that because the BOST requires both upper and lower body power in its execution, the BOST may be more applicable than the VJ as a measurement of power in throwers.

Methods

Experimental Approach to the Problem

The study used a repeated measure, counterbalanced design, with all the subjects completing both the experimental (resistance training session in the morning of the afternoon testing of explosive power using the JV and BOST) and control (no resistance training in the morning) trials. All the subjects completed 3 sessions, each on separate days within 1 week. The first session was a familiarization session that included securing informed consent form, a prescreening for participation, recording of demographics, measurement of the physical characteristics, introduction to study warm-up protocol, familiarization to the VJ and BOST tests, and the estimation of maximal power for the power clean and back squat exercises. Then explosive power was assessed in the subsequent trials (experimental and control) in 2 different days. Finally, a counterbalance design was also employed within the trials with half of the subjects performing the VJ before the BOST and the other half performing the BOST followed by the VJ.

Subjects

The subjects consisted of 14 throwers aged 20.7 ± 2.5 years, with a body mass of 95.1 ± 26.9 kg and a height of 178.8 ± 11.0 cm. The subjects included several national caliber throwers, and all had a minimum of 4 years of throwing experience and were currently training. Each counterbalancing group consisted of 4 men and 3 women. Before participating in the study, all signed an informed consent previously approved by the Biomedical Institutional Review Board for Human Subjects Research at the University of North Carolina at Chapel Hill. All the subjects were healthy and free of any injury that would have precluded successful completion of study. The subjects were required to have had at least 4 years of recent experience in ≥1 of the following events in athletics: shot put, discus, hammer, javelin, or weight-throw. In addition, all must have had at least 1 year of weight training experience that includes the power clean and back squat lifts. All the subjects were also currently training for their respective events.

Procedures

Instrumentation

Physical preparedness for study participation was assessed using the Participation Questionnaire. The subject height was measured using a Perspective Enterprises Portable Infant/Adult stadiometer (Portage, Michigan, USA). Body mass was measured using a medical scale (Model No. BP15-400T, Type 15; Chatillon, Largo, FL, USA). Standing vertical reach was determined using a 5-m closed-reel fiberglass tape measure (Economy model, M-F Athletic, Cranston, RI, USA) secured to the wall. Vertical jump was then measured using a Vertec jump measuring device (Gill Athletics, Champaign, IL, USA). For the BOST test, women used a 4-kg shot, and men used a 7.26-kg shot polyvinyl soft-shelled shot (Hadar Athletic, Humboldt, IA, USA). These weights are consistent with regulation implement weight assignments (IAAF Competition Rules, 2009) and have been previously used physical performance testing practices (^21,24), The distance of the throws were measured using a 50-m open-reel steel measuring tape (M-F Athletic). The back squat and power clean exercises for the experimental trials were performed on a wooden platform using a 20-kg Olympic lifting bar with steel and rubberized Olympic lifting plates (Eleiko Sport AB, Halmstad, Sweden). Finally, to ensure that hydration status would not compromise performance during testing, urine specific gravity was assessed before each testing session using a refractometer (TS Meter, American Optical Corp., Keene, NH, USA).

Familiarization Session

Before participating in the study, all the subjects signed an informed consent form and physical characteristics measurements were recorded at the Applied Physiology Laboratory. The subjects next moved to an indoor athletic facility, where they completed a warm-up protocol typically used by experienced throwers (⁴). This warm-up consisted of 20 different movements, each over a straight 20-yd distance. The first 10 yd consisted of stretching poses or movements interspersed with jogging steps. The second 10 yd was a run at an approximate 80–90% of the subject's fastest sprint, as perceived by the subject. At the end of 20 yd, the subject was instructed jog back to the starting point.

Familiarization to the VJ test was performed next. The subjects began by standing under the Vertec with feet at a self-selected width. They then squatted down without moving their feet and moved immediately to execute a countermovement VJ for maximal height. The subjects were encouraged to use an arm swing and a countermovement dip with the legs before the jump to maximize jump height.

The subjects were then instructed on the BOST test (^21,29,30) (Figure 1). The subjects began by standing with their heels on a line holding the shot with two hands at arms' length. They then squatted down with the shot held between the knees and explosively extended the hips, knees, and ankles with maximum effort, releasing the shot upward and backward overhead with arms straight. The goal of the exercise was to throw the shot as far as possible.

Figure 1: Backward overhead shot throw (BOST) technique.

The familiarization session concluded in the weight room facility where 4 repetition maximum (4RM) testing for the power clean and back squat were performed (¹³). Submaximal 4RM testing was used instead of maximal testing to reduce the risk of injury associated with lifting maximal loads (⁷). The results of this testing were used to predict the 1RM using the equation of Brzycki (⁷). From the 1RM, 35, 50, and 85% resistance was estimated, which was used for the workout session for the experimental trial.

Control Trial

The control trial was completed between 13:00 and 15:00 hours to minimize the effects of diurnal changes on the testing performances (^4,6). For this trial, the subjects did not perform resistance exercises in the morning but were tested for VJ and BOST performances in the afternoon. Before any activity, the subjects were questioned regarding timing of last meal, sleeping patterns, and qualitative level of fatigue and muscle soreness. To ensure proper hydration status, the subjects then provided a small urine sample that was analyzed by refractometry for specific gravity. Dehydration (as indicated by a urine specific gravity >1.025 g·cm⁻¹) or excessive muscle soreness were causes for rescheduling the session to the following day. As a secondary measure, body mass was also taken and compared with the familiarization session measurement.

All the subjects then performed the warm-up protocol practiced during the familiarization session. This was followed by the power testing. For the BOST, the subjects were given 3 practice and 3 measured throws (¹²). The measured throws were recorded to the nearest centimeter. A rest interval of 5 minutes was given between attempts. To ensure proper BOST technique, a research team member, a US Athletics Level 1 certified instructor, rated the technique for the 3 measured throws using a 5-point scale, with “1” representing “poor” technique and a “5” an excellent technique. All throws rated at a “3” or better, or the best attempt should no throw meet the requirements for a rating of “average,” were recorded.

The protocol for the VJ was similar to that used by Stockbrugger and Haennel (²⁹). The subjects completed all the attempts consecutively, with a 1-minute rest interval between attempts. Each continued to jump for height until no additional plastic crossbar markers were touched or moved on 2 consecutive attempts on the Vertec. Vertical jump was measured as the subject's reach subtracted from the height of the plastic crossbar they were able to touch. Peak power (Ppeak) was then calculated in watts using the regression equation previously validated by Johnson and Bahamonde (¹⁹): Ppeak = 78.5VJ + 60.6 m − 15.3 hours − 1308. Vertical jump VJ is the maximum vertical jump height attained (centimers), m is body mass (kilograms), and h is the subject's height (centimeters).

Experimental Trial

This trial consisted of a morning resistance training session and an afternoon testing session. For the morning session, the participants reported between the hours of 8:00 am and 10:00 am. After confirming proper hydration and fatigue status, all the subjects performed the standard warm-up from the familiarization trial and also a brief moderate resistance exercise warm-up program. The resistance warm-up included 4 sets of 6 repetitions of the power clean at 35% of 1RM then switching to the back squat exercise and completing 1 set of 6 repetitions at 50% of 1RM, and 1 set at 85% of 1RM (^15,22,31). The main resistance exercise session consisted of the back squat exercise performed to fatigue (failure to complete the lift on any single repetition or 2 successive repetitions with improper form) and 4 repetitions per set in the more technically challenging power clean exercise, to ensure maximal effort and speed of movement (^15,22,31). The subjects were encouraged verbally to move the barbell at the fastest possible speed in both exercises (^2,31). At least 3 but not >5 minutes of rest was given between each set, and 5 minutes of rest was given between exercises (^{15,17,25,31,33}). The subjects then refrained from exercising or sleeping until the afternoon testing session.

The subjects reported 4–6 hours after the completion of the morning resistance exercise session for the afternoon session. This period of time was selected because it is a feasible amount of time between a resistance training session and the first competitive throw (should a resistance exercise warm-up actually be used on the day of a competition) and because the time closely resembled time periods used in previous research (^11,32). After the subjects answered the sleep-fatigue-food consumption questionnaire, underwent the urine specific gravity test, body mass measurements, and standard warm-up, the BOST and VJ tests were performed in the same order as in Control trial.

Statistical Analyses

All data were analyzed using SPSS Version 16.0 for Microsoft Windows (SPSS, Inc., Chicago, IL, USA). Paired-samples t-tests were used to compare BOST performance between the control and experimental conditions. In addition, a paired t-test was also used to compare group mean VJ peak power (watts) between the control and experimental conditions. To determine the reliability of the BOST, an ICC was computed for the 3 attempts within the experimental and control trials. Pearson correlations between BOST performance and the VJ were performed to assess the association between the 2 measures of power. The highest recorded BOST distances (meters) and VJ peak power (watts) and height (centimeters) were used for the correlation analyses. Significance in all cases was determined with a probability value of p ≤ 0.05. Because of the small sample size, the effect size was computed. Cohen (10) defined effect sizes as “small, d = 0.2,” “medium, d = 0.5,” and “large, d = 0.8.”

Results

The BOST performance was significantly greater for the experimental trial compared with the control trial (11.76 ± 1.37 vs. 11.46 ± 1.28 m; p < 0.05). No statistically significant difference (p = 0.488) was found for VJ peak power between control and experimental trials: 6,901 ± 1,531 vs. 6,943 ± 1,490 W, respectively. All correlations between BOST performance and vertical jump are presented in Table 1. The BOST performance (centimeters) and VJ peak power (watts) within the control and experimental trial were significantly correlated (r = 0.68–0.65, p ≤ 0.012). Correlations between VJ height (centimeters) and BOST (centimeters) correlations were low and not significant (r = 0.14–0.14; p > 0.62). The ICC between the BOST trials was high r = 0.84 and the standard error of measurement (SEM) was quite low, 0.55 m. In addition, Cohen's d for effect size was large d = 1.77; effect size 0.664.

Table 1: Correlations between backward overhead shot throw (BOST) performance and vertical Jump.*

Discussion

The results of this study showed significant improvement in BOST performance when the throwers performed resistance exercise 4–6 before throwing. Although studies have shown an effect of a resistance training performed before VJ performance (^{11,15,16,22,27}), to our knowledge, there is no research on the effects of resistance exercise on subsequent BOST performance. However, our finding support several studies using VJ that have shown that a bout of resistance exercise performed 3–20 minutes before competition enhances explosive power (^{1,15,16,23,27,28,33}). Our novel finding was that any effect of the resistance training can be sustained up to 6 hours. This 6-hour window has greater application to performance than the short 3- to 20-minute window, because the longer interval would mean greater access to resistance equipment and fit into an athlete's precompetition schedule. Although the mean difference between trials was approximately 30 cm, which may not be considered large, at high levels of competition events are often won by a couple of centimeters.

Although resistance training in the morning improved BOST performance it did not improve vertical jump performance. One other study has suggested that resistance training does not improve VJ (¹⁵), but that study used only 5 minutes between the resistance exercise and the VJ test. A possible explanation is the potential kinematic differences between the VJ and BOST movements. No research exists for the biomechanical comparison of the VJ and the BOST, there is arm-involvement in both the VJ and the BOST; however, the movements are not similar (⁸). Compared with the VJ, the arm movements in the BOST are more closely approximated by the power clean Olympic-style lift. Therefore, the use of a power clean exercise may have produced neurological effects (muscle recruitment patterns) beneficial for the specific kinematics of the BOST but not to the VJ, perhaps by better preparing the upper body musculature for throwing.

The BOST appears to be a highly reliable measure with high ICC and very little standard error of measure. In addition, the significant correlation of BOST distance with VJ peak power output lends support to the BOST as a valid test of explosive power performance. However, the VJ peak power production explained only 42–43% of the variation in BOST scores, which means that approximately 58% of the variability in BOST scores is still unaccounted and explained by other factors. The BOST may rely more on technique, upper body and core strength than the VJ, which focuses more on leg power. In agreement, Stockbrugger and Haennel (²⁹) suggested that individual physical characteristics and physiological adaptation to specific training regiments contributes to different strategies used by athletes when executing the backward overhead medicine ball throw, a maneuver similar to the BOST (²⁹). Also, there is considerable difference among throws events athletes with respect to training practices, which results in each athlete having a unique set of physical and technical characteristics. Within the sample used in this study, the athletes were also in various stages of their training cycles ranging from detraining and rest to peak competitive shape, which could have an effect on their physical and mental approach to testing. These results suggest that future research on the BOST should seek to lend both content and criterion validity to the construct evidence provided here.

Previous studies on BOST have only correlated VJ height (centimeters) to BOST distance (meters) and not VJ power output (watts). These studies also found moderate or weak relationships between VJ height and BOST distance (^18,24), suggesting that the VJ height and the BOST are not capturing the same constructs. Because these studies only examined VJ height, we theorized that VJ power (watts) might translate more realistically to the mechanics of BOST. Because the correlations between VJ height and BOST were lower than for VJ power (watts), our results would support this theory. Thus, we recommend using VJ power rather than height when relating power output to performance in throwers.

One possible limitation was familiarity with the VJ techniques was initially greater that for the BOST. Attempts were made to minimize the influences of learning on performance by requiring subject to practice both the VJ and BOST techniques during the familiarization session (¹²). Also, to confirm that a training effect did not appear to have skewed the results of performance on the BOST test, the median BOST technique ratings were 4.5 for both trials, with a range of 3.0–5.0. Therefore, improvements in BOST technique between trials would not have accounted for the large improvement in BOST scores. Obtaining a significant sample of highly qualified thrower was difficult. However, Cohen's d suggests that the effect size is very large at over the 95th percentile. Thus, we are confident that the resistance exercise did have a significant effect on the BOST performance. The reader should keep in mind that the intent of our study was not to validate the BOST as an indicator of throwing performance for field athletes. Further, our results should not be interpreted as such. We simply wanted to compare it with vertical jump power as an alternative to VJ for estimating power in throwers. Further studies should validate the BOST against throwing performance in a larger, more diverse sample of athletes.

Practical Applications

The findings of this study indicate that a morning resistance exercise bout consisting of both light and heavy resistances performed at maximal velocity may help afternoon competitive throwing performance on the same day. Thus, when possible, thrower should consider a short resistance session the morning of an afternoon competition. The results also suggest that for the thrower in the sport of athletics, the BOST may be a better assessment of overall explosive power that the VJ measured in height. The involvement of the entire body and the transfer of force to an implement, distinguish the BOST from the VJ and make it more suited to throws events (^24,29,30).

Acknowledgments

The research team would like to thank the subjects, athletic departments, and coaching staffs from the University of North Carolina at Chapel Hill, Appalachian State University, Duke University, and North Carolina Central University for their participation, support and cooperation which made this study possible.