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Power training with the Bravo

Case study by Cory Hofmann

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Lower extremity power is valuable in a variety of sports and athletic endeavors.  Many existing protocols focus on plyometrics or strength training to increase vertical jump height, a measure of power.  This study sought to quantify the effects of a 10 week training progression involving strength, endurance, and power developing exercises.  A variety of exercises were developed utilizing the Cybex Bravo, Arc Trainer, and Eagle Leg Press, in addition to other equipment such as medicine balls and elastic bands.  As a result of this protocol, 5 physically active individuals saw an average vertical jump increase of 3.9 inches in addition to significant increases in several other measures of lower extremity force production and absorption.  These data suggest that a novel protocol involving progressing focuses and a variety of different exercises was effective at increasing lower extremity power in a physically active population.  Future studies should compare a similar protocol to ones focused on plyometrics.

A 10-week protocol consisting of strength, endurance, and power training was effective in increasing vertical jump height

Authors

Steve Arnold SPT1; Keisuke Kanno DPT, CSCS2; Chip Gosewisch CSCS, CPT2

1 Duke University School of Medicine Doctor of Physical Therapy Division Durham, NC

2 Fischer Physical Therapy and Conditioning Phoenix, AZ

Abstract

Lower extremity power is valuable in a variety of sports and athletic endeavors. Many existing protocols focus on plyometrics or strength training to increase vertical jump height, a measure of power. This study sought to quantify the effects of a 10 week training progression involving strength, endurance, and power developing exercises. A variety of exercises were developed utilizing the Cybex Bravo, Arc Trainer, and Eagle Leg Press, in addition to other equipment such as medicine balls and elastic bands. As a result of this protocol, 5 physically active individuals saw an average vertical jump increase of 3.9 inches in addition to significant increases in several other measures of lower extremity force production and absorption. These data suggest that a novel protocol involving progressing focuses and a variety of different exercises was effective at increasing lower extremity power in a physically active population. Future studies should compare a similar protocol to ones focused on plyometrics.

Introduction

The athletic world is full of young athletes, weekend warriors, and those with aspirations to become professional athletes. It is also full of coaches, agents, and managers who are continuously pushing athletes to improve physical ability. Often in sports such as basketball,volleyball, and football, power in the lower extremities is viewed as a significant indicator of an athlete's potential and worth. Many successful protocols to increase jump height focus on plyometric jumping or strength training with volleyball (Ziv & Lidor 2010) and basketball players(Ziv & Lidor 2010, Ziv and Lidor 2010b). However, there is little information about the potential effects of a modified vertical jump height protocol progression focusing on strength, endurance,and power training. Therefore, the goal of this research study is to determine the effectiveness of a novel 10-week exercise protocol progression focusing on strength, endurance, and finally power training.

Background

Five healthy, physically active subjects participated in this study (Table 1).

Table 1. Subject information and athletic backgrounds

  Subject 1 Subject 2 Subject 3 Subject 4 Subject 5
Age (Sex)  24 (M) 40 (M) 34 (M) 30 (M) 22 (F) 
Height  6'1" 5'8.5" 5'8" 6'2" 4'11.5"
Athletic Background  Works out 3-4x/wk, recent R MCL strain that is fully healed, recreational basketball Works out 3-4x/wk, club baseball pitcher, recreational mountain biking Works out 5-7x/wk, Personal trainer, ultra-marathon runner, former D1 baseball Works out 3-4x/wk Works out 3-4x/wk, recreational hiking, running, former D1 gymnast

Procedures

Outcome variables

Measurements were taken at baseline, 4 weeks, 7 weeks, and 10 weeks. Each measurement coincided with an exercise phase change which will be discussed later. Measurements included the following:

Body Weight (BW): BW was measured to the nearest five-tenths of a pound. Subjects removed only their shoes and were weighed with other workout clothing on.

Vertical Jump (VL): VL was measured to the nearest five-tenths of an inch using PowerJump vertical jump testing equipment. Subjects stood flat footed and reached as high as possible for starting reach position. Subjects were instructed to swing arms down during the loading process and jump as high as possible. No approach steps were allowed in this VL test, and subjects were not allowed to flex their knees while in the air. Subjects continued with test trials until they missed the next 0.5 inch level two times in a row.

Single Leg Hop and Stop: Performed as described in Juris et al. 1997. One practice trial was performed, and then two more trials were performed. The average distance was recorded.

Functional Single Leg Hop and Stop: This test was identical to single leg hop and stop except the constraints of contralateral 90 deg hip flexion and hands on hips were removed. The subjects were allowed to perform the test with the instruction to “jump as far as possible.” One practice trial was performed and then two more trials were performed and the distance average recorded.

Broad Jump (BJ): Broad Jump was measured with the subjects’ heels beginning on the 0.0 m.Subjects were instructed to jump as far as possible without the requirement of sticking the landing. One practice trial was performed and then two more trials were performed and the distance average recorded.

Cybex Eagle Leg Press single leg 6 repetition maximum: Participants “warmed up” with a set of double leg, leg press with whatever each subject considered a warm up weight. Participants then attempted to reach a single leg, 6 repetition maximum and the weight recorded was the highest value at which the subject could perform 6 repetitions. The Cybex Eagle was set up at the “2” seatback position, and the plate was set so that the subjects’ knees would be flexed to about 90 degrees during each repetition at the greatest point of knee flexion.

Single Leg Stance Excursion Test: On a Total Gym Functional Testing Grid with a 90 cm radius and with smaller circles at each 10 cm mark, each subject performed 3 single leg stance excursions with each extremity (1 practice excursion, 2 scored) in the following movements:Anterior reach, Medial reach, Rotational Medial reach, and Posterior Reach. For anterior reach,subjects began with stance heel on 0 cm and reached contralateral leg/foot along the sagittalline of the mat. The measurement was made at the heel of the contralateral heel. For medial reach, the subject began with the stance foot bisected by the frontal plane line and with the inside of the foot along 0 cm mark on the sagittal plane line. The subject then reached the contralateral leg along the frontal plane line while keeping the toes pointed forward, and the measurement was made at the medial border of the foot. For rotational medial reach, starting position was same as medial reach, except the subjects turned contralateral foot to point along the frontal plane line, and the measurement was made at the subjects’ heel during the reach.For posterior reach, the subject began with the stance heel on the 50 cm mark on the sagittal plane line. They reached posteriorly along the sagittal plane line while pointing the contralateral toes forward and the measurement was made at the heel of the contralateral limb. For all movements, each subject removed shoes and was instructed to reach the contralateral leg in the desired direction without lifting stance heel off the mat or kicking the contralateral foot into the air. A trial was disqualified if the subject demonstrated any of the above deviations, in addition to touching the mat with the contralateral foot.

Maximum Single Leg Squat Knee Flexion Angle: With the subject maintaining both hands on hips and contralateral hip flexion of 90 degrees, the subject performed a single leg squat as deep as they could as long as they could return to starting position. Knee flexion angle was measured with a goniometer with the axis on the knee joint line, distal arm towards the center of the lateral malleolus, and the proximal arm up the femur towards the center of the greater trochanter. Two trials were performed and the average measurement was taken.

Exercise Progression

For all exercises, weight was self-selected as the subjects felt they were able to progress comfortably. However, subjects were advised to choose a weight that would leave them fatigued upon completion of each set’s designed repetition number. Many of the exercises were performed on the Cybex Bravo, Arc Trainer, and Eagle Leg Press (Cybex International, Medway, MA), in addition to other equipment such as medicine balls and elastic bands. The protocol can be broken down into three distinct phases, outlined below (Tables 2-4).

Table 2. Phase 1 – Strength; 4 weeks, 2 workouts/week, 3 sets x 8 repetitions for each exercise

Power Jump Performed on the Cybex Bravo, with a non-weighted belt that clipped into each side of the machine. Each arm of the machine was positioned at its lowest height setting and at the “11” setting for its frontal plane position. Subjects performed the jumps as high as they could jump with a quick, plyometric loading pattern.
Unilateral Leg Press This exercise was performed on the Eagle Leg Press. Each subject prepositioned themselves as indicated in the setup for the 6 repetition maximum described above. Subjects performed repetitions with one leg and then switched to the other without a break. Subjects were monitored to avoid pushing with uninvolved leg.
Single Leg Pistol Squat Performed on the Bravo with a Cable bar. The bar was clipped into the Bravo at the same setting described in the Bravo Power Jump. Subjects placed the bar upon their shoulders and performed a single leg squat with the contralateral leg in front of them.
Split Bar Cable Extension This exercise was performed on the Bravo with a cable bar. The bar was clipped into one side of the Bravo as described in the Power Jump. The subject began in staggered stance, both knees slightly bent and the bar was held on the shoulders, behind the head. The side with the cable attached was held on the opposite shoulder of whichever leg was ahead in stance. The subject would lunge into the lead stance leg with opposite shoulder and bar approximating to the lead stance knee. Then the subject would return to the upright, starting position.
Unilateral Donkey Calf Raise This exercise was performed on the Cybex Donkey Calf Raise Machine. A single leg calf raise was performed with each subject advised to use a weight where great toe extension could be achieved with all repetitions.

For Phase 2A (Endurance), exercises from the Strength Phase were performed with a repetition change to 3 sets of 15 repetitions. This phase lasted for 2 weeks, with two workouts each week. This included a change in weight based on completing 15 repetitions to the point of fatigue. Also, there was a change made to the Single Leg Pistol Squat. For this exercise during the Endurance phase, only the side of the bar contralateral to the single leg performing the squat was clipped into the Bravo. This imposed a frontal plane moment during the squat in addition to the sagittal plane component.

Table 3. Phase 2B - Transition; 1 week, 2 workouts/week, refer to exercise descriptions for sets/reps

Advanced Power Training Performed on the Arc Trainer 750A in adaptive power mode. The resistance level chosen was the highest resistance level at which the subject could achieve “Max Speed” (180 strides per minute) during the 15 second “on” period described below. Ten repetitions were performed of 15 seconds of maximal exertion followed by 45 seconds of active rest, maintaining a range of 60-80 strides per minute.
Slideboard with Theraband Frontal Plane slideboard training was performed on a Goaler One Performance Training slideboard that measured 53” across. An appropriate resistance Theraband, chosen by each subject, was worn around the subject’s distal tibia, just above the ankles. Three sets of 15 second repetitions were performed with the subject continuously sliding to the right and to the left on the slideboard.
Posterior Transverse Lunge with Green Superband This lunge was performed with a thick green SuperBand. One end of the band was looped around a fixed structure while the other was looped just above the subject’s waist. For the starting position, the subject faced the direction of the fixed structure and then performed a posterior, transverse lunge in a direction 45 degrees posterior to the frontal plane and then returned to the starting position. The starting position also was set at the maximum distance the subject could control the band’s resistance throughout the entire lunge movement. Three sets of 8 repetitions were performed.

Table 4. Phase 3 - Power; 2 weeks, 2 workouts/week, 3 sets of 6 repetitions; 1 week, 2 workouts/week, 4sets of 4 repetitions

Power Jump Performed on the Cybex Bravo, with a non-weighted belt that clipped into each side of the machine. Each arm of the machine was positioned at its lowest height setting and at the “11” setting for its frontal plane position. Subjects performed the jumps as high as they could jump with a quick, plyometric loading pattern.
Unilateral Leg Press This exercise was performed on the Cybex Eagle Leg Press. Each subject pre-positioned themselves as indicated in the setup for the 6 repetition maximum described above. Subjects performed repetitions with one leg and then switched to the other without a break. Subjects were monitored to avoid pushing with uninvolved LE. As described in Phase 1. In addition, subjects were advised to perform these repetitions with more explosiveness to replicate the jumping motion.
Medicine Ball Triple Extensions This exercise was performed on a turf field with the subject starting about 15-20 yards away from a concrete wall. This exercise was included to train an explosive jumping movement. The subject stood, back to the wall, and held the 12-pound medicine ball with two hands. The subject then loaded the lower and upper extremities (LE, UE) as if to jump and launched the medicine ball (MB) overhead towards the wall.
Overhead Medicine Ball Slam For this exercise, each set was performed with a different starting LE position. For the first set, LEs were shoulder width apart and the 12-pound MB was brought overhead and rapidly slammed into the ground. For the second set, the left LE was the lead leg. The subject shifted weight from the left LE to the right LE, raised the MB overhead, and then slammed the ball into the ground in one fluid motion. This was then repeated with the right LE as the lead leg for the third set. During the last week during 4 sets x 4 reps, the front slam with LE shoulder width apart was repeated for the fourth set.
Unilateral Donkey Calf Raise This exercise was performed on the Cybex Donkey Calf Raise Machine. A single leg calf raise was performed with each subject advised to use a weight where great toe extension could be achieved with all repetitions.

Data analysis

Hop Symmetry, stop to hop ratio, and stop symmetry values were calculated based on Juris etal. (1997). All values were normalized to the height of each subject (%Ht). A Wilcoxon signed-rank test was performed to compare the differences between pre-test and post-test performance across all variables. Effect sizes were calculated based on Cohen (1988). In studies of low sample size, it is important to take into account both effect size and statistical significance when drawing conclusions.

Results

As a result of the present protocol, vertical jump increased by an average of 3.9 inches (P =0.042, d = 1.00; Table 2). Right hop, and both leaps exhibited a statistically significant increase, while left hop exhibited a high effect size without being statistically significant (d = 1.77). There were no significant changes in hop symmetry, stop to hop ratio, or stop symmetry.

Table 5. Lower body force production and absorption variables before and after the ten week training protocol. * indicates statistically significant change compared to pre-test (P<0.05)

   Pre-test  Post-test  Effect size
Vertical Jump (in)  22.60 26.50* 1.00 
Standing broad jump (m) 2.42 2.60 0.73 
R Hop (%Ht) 76.45 90.45*  2.21 
L Hop (%Ht) 75.58 89.86 1.77 
L to R Leap (%Ht) 81.83 92.79* 1.40 
R to L Leap (%Ht) 80.80 91.73* 1.13 
       
Hop Symmetry 0.96 0.96   
R Stop to hop ratio 1.09 1.04   
L Stop to hop ratio 1.06 1.02   
Stop Symmetry 0.93 0.93   

SLS Excursion test results indicate that on average, the subjects improved on seven of the eight possible values (Table 3). Knee angle during the SLS did not change significantly, and SL 6RMleg press testing was not able to be completed for all subjects.

Table 6. SLS Excursion test results, and single squat performance measure before and after the ten week protocol. * indicates statistically significant change compared to pre-test (P<0.05).

  Right Left
SLS Excursion (cm) Pre Post Effect Size Pre Post Effect Size
Anterior 64.7 72.4* 1.10 66.2 71.6* 0.78
Medial 66.3 77.9* 1.89 67.4 78.4* 1.63
Rotational Medial 58.1 70.2* 1.45 58.1 67.7* 1.91
Posterior 82.1 93.3* 1.06 85.8 91.4 0.60
 
SLS Knee angle (deg) 102.4 111.1   102.7 107.6  

Discussion

Several measures of lower body power exhibited a statistically significant increase following the ten-week protocol. In addition, gains in lower body strength were also evident. The increases in hop and leap distance, coupled with the lack of change in hop and stop symmetry, indicate that there were meaningful bilateral increases in force production as well as force absorption.Wojtys and Huston (2000) discussed the importance of the muscles crossing the knee in absorbing forces during impact and loading. They also discovered that, even at 12 to 18 months post ACL reconstruction, neuromuscular control and muscle strength was deficient compared to the uninjured leg. This sheds light on the importance of paying strict attention to force absorption symmetry in the lower extremities, and that therapeutic exercise aimed at restoring force absorption symmetry should be part of the rehabilitation regimen.

The results from the present study suggest that this ten week program was effective in increasing lower body strength and power, as well as yielding symmetrical gains in force production and absorption. It is important to note that all of the significant findings in Table 1 and Table 2 demonstrated effect sizes which signify that a “large difference” exists.

It should also be noted that at the beginning of the study and throughout, subjects were participating in varying levels of activity. It is interesting to note that all subjects had strong athletic backgrounds, and still demonstrated significant increases in strength and power as   of this protocol. Subject 1 had recently strained his R MCL and had not been taking part in his normal routine for about 4-6 weeks prior to starting the protocol. This could have impacted his increase of six inches in the vertical jump performance measure, the greatest increase of all the subjects, as he potentially had the most room for improvement. The smallest increase in vertical jump was two inches by Subject 5, a 4’11.5” female. Even though the subjects did have different normal activity levels which were sustained throughout the study, all subjects increased vertical jump, broad jump, and single leg hop and leap distances, again suggesting that this 10week protocol was effective in improving lower body strength and power. Future studies should compare this protocol to ones focused solely on plyometrics, to compare their effectiveness.

References

Juris P, Phillips E, Dalpe C, Edwards C, Gotlin R, and Kane D. A Dynamic Test of Lower Extremity Function Following Anterior Cruciate Ligament Reconstruction and Rehabilitation. J Orthop Sports Phys Ther. 1997;26(4): 184-191.

Wojtys EM and Huston LJ. Longitudinal Effects of Anterior Cruciate Ligament Injury and Patellar Tendon Autograft Reconstruction on Neuromuscular Performance. Amer J Sports Med. 2000;28(3): 336-344.

Ziv G and Lidor R. Vertical Jump in female and male volleyball players: a review of observational and experimental studies. Scand J Med Sci Sports. 2010;20(4): 556-67.

Ziv G and Lidor R. Vertical jump in female and male basketball players: a review of observational and experimental studies. J Sci Med Sport. 2010b;13(3):332-9.

Cohen, J. (1988). Statistical power analysis for the behavioral sciences. (2nd ed.) Hillsdale, NJ: Earlbaum.

 

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