Case Studies

Case Studies


2-Foot Approach Mechanics on Full Approach Vertical (FAV)

Tyler Ray (Vertical Jump Expert) Project Pure Athlete Inc
Ricky Norton (Performance Coach) Norton Performance Training Systems
Tyler Standifird (Asst. Biomechanics Professor)


For this particular study a few areas of interest between two distinct groups of jumpers were examined.   A 6 person study using 3 athletes from an “elite” category (tested 48” or higher on their full approach vertical pre-test 2 days prior) and 3 athletes from an “advanced” category (tested between 40-45” on their full approach vertical).  The athlete approaches the take-off by accelerating through a 3 or 4 step run up. The athlete then takes a large step (penultimate) into their final two contacts (plant foot and block foot). This varies depending on the athletes’ limb dominance (ie. right to left or left to right).  The management of the athletes’ center of mass is an important aspect of jump height. It is hypothesized that athletes in the more elite category will have better control of their COM in relationship to their step sequence as evidenced by a more upright posture at the contact of the plant foot and a longer penultimate stride.  


Elite: 3 athletes who tested 2 days prior with a 48” or higher FAV

Advanced: 3 athletes who tested 2 days prior with a 40”-45” FAV

*SIMI software (Atkyis) was used in conjunction with one high speed camera (120 hz) and two force plates (Bertect) to collect data during 3 jumps on the force plates.

Jumper Running

The athlete moves through their full approach creating horizontal acceleration 


Jumper Approach

Prior to the final two contacts (plant and block foot) the athlete takes a large penultimate stride.  This stride is measured using SIMI software (Atkyis) use in conjunction with the high speed camera set up perpendicular (side angle) to the athletes’ approach.  


Jumper First Foot Impact

At the point of peak force of the plant foot (first contact on the force plates) the angle of the trunk was taken as well as the eccentric and concentric forces, including loading rates and time to peak force. 

Pre-Launch Impact

The same is examined in the second contact (block foot), followed by the take-off angle at toe-off.  

Vertical Jump


The Elite group covered 23% more distance through their penultimate stride.


  1. The Elite group displayed less trunk flexion during contact of peak loading of their lead (plant foot).
  2. The Elite group was 30% faster to produce peak force than the Advanced group.
  3. Loading Rates were 35% faster in the Elite group 
  4. Elite group had an 8% higher concentric force on the plant foot.
  5. Elite group had a 15% higher force on their block foot.


As hypothesized, a longer penultimate stride into a more extended contact position during the plant was observed in the Elite group of jumpers.  This taller contact position may lends itself to managing the athlete’s centre of mass more efficiently in relation to the points of contact. These variables also show a carry-over into the amount of force being applied through the duration of the plant sequence.  There are more factors to consider moving forward, but this initial study helps to outline two very crucial elements of jumping high off of a 2-foot full approach. The most elite jumpers execute their jump with a longer penultimate stride and a more upright posture.  

Keiser Rotational Peak Power Correlated With Exit Velocity From Baseball Bat


Investigating the effect of measured rotational peak power to the exit velocity of a baseball being hit off a tee. High school athletes (n=20) performed a maximal rotational force in both directions(right and left) was determined by measuring the peak force achieved during 6 distinct rotational twist movements on a Keiser Performance Trainer machine set at constant load of 50 pounds per square inch (PSI). Following the rotational test each athlete performed 10 baseball swings hitting a baseball off of a tee and recording the MPH or the ball off of the tee using a Stalker Pro 2 radar gun.


The Keiser Rotational test was determined to be a statistically significant method for predicting average exit velocity when the maximum power output was analyzed against throwing velocity (p<.005). The linear regression model based on peak power output (see figure 1) produced a slope of 0.01, indicating that a 100 watt increase in the Keiser Skate test would result in a 1 mph increase in exit velocity. The model explained 76 percent of the variation in differences in exit velocity.


The data collected for this study indicate that increases in maximal rotational force correlate with an athlete’s ability to hit a baseball at a higher velocity. This can further suggest that coaching an athlete to focus their training on increasing rotational force (Force and Power in the transverse plane) presents the potential to see increased gains in exit velocity when hitting baseballs.

What Field Test Has More Carry Over To Throwing Velocity, Keiser Rotational Peak Power Or Maximum Vertical Jump?



The purpose of this study was to determine if either maximal rotational force of the trunk (as measured by a pneumatic Keiser machine) or maximal vertical leg power (determined by a vertical jump test) have an effect on the maximum throwing velocity of high school baseball athletes. We hypothesize that there will be a much higher carryover with the transverse plane power than the frontal plane power. 

Experimental Design:

High school baseball athletes (n=21) were recruited for the study. Prior to testing, all subjects completed a warm-up protocol that consisted of a thorough dynamic warm up, Jaeger band exercises, plyocare ball drills, and then playing catch with a baseball until the subject’s throwing arm felt capable of throwing at maximum velocity. Subjects then performed 10 maximal-effort throws of a baseball while a Stalker Pro 2 radar gun was used to determine maximum throwing velocity. The single highest observed velocity was recorded for each subject as their maximum throwing velocity value. After the throwing test, maximal rotational force of the non-throwing arm was determined by measuring the peak force achieved during 6 distinct rotational twist movements on a Keiser Performance Trainer machine set at constant load of 50 pounds per square inch (PSI). Following the rotational force test, a maximum vertical jump test was performed using the Vertec device to measure maximal leg power. Linear regression models were used to determine 1) the relationship between rotational force and throwing velocity and 2) the relationship between maximal leg power and throwing velocity. 


Rotational Power:

The linear regression model revealed the relationship between rotational trunk force and throwing velocity to be significant (p<.001). For every 100 unit increase in rotational trunk force, maximum throwing velocity was observed to increase by 1 mph (adjusted R squared = .43). 

See figure 1 

Vertical Jump:

While a general trend did appear to exist, the linear regression model determined that no statistically significant relationship existed between maximal vertical leg power and maximal throwing velocity (p>.05).

See figure 2


The data collected for this study indicate that increases in maximal rotational trunk force correlate with an athlete’s ability to throw a baseball at a higher velocity. Whereas an increase in vertical jump does not have a significant effect on maximal throwing velocity. This can further suggest that coaching an athlete to focus their training on increasing rotational trunk force (transverse plane) presents the potential to see increased gains in throwing velocity. The Keiser Performance Trainer machine is a reliable tool to accomplish this, along with a variety of medicine ball throws, and anti-rotation exercises. Furthermore, this study should be repeated with college and professional baseball players to see if the same outcome holds true at higher levels of play.


Keiser Rotational Power and Pitch Velocity

Ricky Norton (Sports Performance Expert)
Tyler Standifird PhD (Assistant Professor in Biomechanics)


It is well understood that rotational athletes need power and strength in order to perform at a high level. Unfortunately most of the measurements of power and strength in rotational athletes are measured in linear or sagittal movements such as squats, deadlifts, bench presses and other similar type exercises. It would make sense that rotational power measurements would be more closely related to the performance of rotational athletes, but more studies are needed to investigate if this relationship does exist. Keiser machines allow for the measurement of peak rotational power and provide great information to trainers and coaches about movements that may be more closely tied to their rotational athletes. The purpose of this study was to investigate the relationship between rotational power as measured by a keiser machine to throwing velocity in High School and College Pitchers. It was thought that rotational power would be related and important to the maximum velocity in these baseball pitchers. 


Fifteen high school level baseball players participated in the study. First, the athletes went through our standard dynamic warm-up. Then they performed 1 set of 10 reps of each exercise of the Jaeger Band Series. Following that, they each performed 2 sets of 10 reps of a Reverse Throw and a Pivot Pick-Off throw using a 32 Oz Plyocare ball. The pitchers were then given as many throws with a 5 Oz baseball as needed until they felt their arms were warm and ready for testing. Once warm, testing consisted of 10 Pull- Down throws (Crow Hops) for max velocity into a net. Of these ten throws, the last three throws were used for analysis. These last few throws led to the most consistent throwing velocities for analysis. 

Peak power was then assessed using a Keiser Performance Trainer (rotational machine) and was completed on a task that was familiar to many of the players due to training experience (Rotational Chop at chest height). Peak power was assessed after a warm up that consisted of 5 reps at 30 PSI, followed by 5 reps at 35 PSI, followed by 5 reps at 40 PSI. They then tested with 5 reps at 50 PSI. The Peak Power of the 5 reps at 50 PSI was recorded.


A simple linear regression analysis was completed in order to understand the relationship between keiser peak rotational power and pitch velocity. The peak power measured on the keiser appears to be highly related to pitch velocities for the athletes in this study. The R^2 value of 0.467, which suggests that the rotational power of these athletes accounted for nearly 50% of the variability in throwing velocity. This value suggests a moderate to large relationship for these two variables. The data suggests that for every increase of 40 watts of power on the keiser rotation test, the athletes would have a one mph increase in throwing velocity. 


As hypothesized, the findings of this study suggest that rotational power and maximum throwing velocity in baseball players, are related. For the athletes tested in this study, the R^2 value of nearly 0.50 shows a moderate to strong relationship for the two variables under consideration. The findings of this study show evidence to support the importance of training for the improvement of rotational power. Strength and conditioning coaches of baseball players should focus heavily on rotational movements and specifically how they can improve power as measured on a keiser rotational test. Rotational range of motion in the core (Hips & Thoracic Spine), strength of the hips and trunk in rotational movements and improvement on technique, are just some of the areas that can lead to increased performance on the keiser rotational test. Also, improving core stability seems to help increase rotational power, anecdotally. Coaches and trainers should understand these important relationships and should ensure that athletes spend a bulk of their time on movements in the transverse plane, and training exercises that will lead to improvements in rotational power, and not just linear (Sagittal plane) strength. Future studies should continue to investigate these relationships and if more groups of baseball players would have similar results. Also, adding a mound for the pitcher population to see if there is more or less of a relationship to the keiser test. If these relationships continue to be strengthened, it will be important to learn and understand what specific training can improve rotational power and also throwing/pitch velocity.

Towel Drill vs Plyocare 7 oz ball


Pitchers from little league to the majors are always looking for ways to add velocity to their fastball. The towel drill and throwing of weighted Plyocare balls are two common approaches to improving fastball speed and mechanical efficiency. The common belief is that the Plyocare ball drills can create stress on the throwing arm, potentially leading to injury. While the Towel Drill is minimizing arm stress while also being able to work on throwing mechanics. Pitching experts are mixed in their opinions of the efficacy and safety each approach.

Research Question:

This study presents a first look at the effectiveness and safety of both approaches. We aim to gain insight into three important questions:

  1. Are pitchers able to generate more arm speed throwing a Plyocare ball or while completing the towel drill?
  2. Does throwing Plyocare balls or completing the towel drill create more stress on a pitcher’s arm?
  3. Is greater arm speed associated with higher levels of arm stress?

Research Method:

Nine pitchers were recruited to participate in the study. The players are all high school-aged players. Each of the nine is actively working to improve their fastball velocity.

Each pitcher was asked to complete five repetitions of the towel drill and five throws with a weighted Plyocare ball. This lead to a sample of 45 repetitions of the towel drill and 45 plyocare ball throws. During each towel drill repetition and Plyocare ball throw, the participants wore a Motus Arm Sleeve. The Motus device measured both the arm speed and the stress placed on the ulnar collateral ligament for each repetition and throw.  Each throw was “tagged” with the weight of throwing implements (ie. Towel = 3.68 oz and Plyocare ball = 7oz).  Of the 90 data points gathered in the study, one towel drill repetition and one Plyocare ball throw resulted in no score on the Motus device and the data for both was not used in our analysis.

We analyzed the data using paired t-tests with the assumption of non-equal variance. We adjusted our alpha levels using the Bonferroni method. All conclusions of significance are based on a 95% confidence level. We also calculated correlation coefficients to determine if there is a relationship between arm speed and stress.


First, we examined whether the average observed arm speed was higher during the towel drill repetitions or when throwing the weighted Plyocare balls. The average arm speed generated during the towel drill repetitions was 553.25 and the average arm speed when throwing Plyocare balls was 890.52. This was a statistically significant difference.

With respect to arm stress, we find that the towel drill generates significantly less stress than throwing plyocare balls. The average stress measured during the towel drill was 15.66. The average stress observed when throwing the weighted Plyocare balls was 24.14.

Finally, we examined whether greater observed arm speed was associated with higher levels of arm stress. Interestingly, we find no significant relationship between arm speed and arm stress for either the towel drill repetitions or throwing weighted plyo balls. The correlation between arm speed and stress for the towel drill was .0396 and -.0236 for plyo balls.


While certainly not a definitive study, we do present some interesting findings. First, it is not surprising that throwing Plyocare balls generates higher arm speed than the towel drill. We hypothesize that the towel drill creates wind resistance in the towel which would reduce arm speed. This does present a real positive for plyocare ball training in regards to training arm speed.

Our second significant finding is that the Plyocare ball training creates more arm stress than the towel drill. This is a very important finding. While throwing plyocare balls may help a pitcher to train with higher arm speed levels and possibly increase overall arm speed, it may also generate significantly more arm stress.

Taken together, these findings create a quandary for coaches and pitchers. Throwing weighted plyocare balls may well help a pitcher to generate greater arm speed than the towel drill, but does the increased arm stress lead to a higher likelihood of injury? Also, would training with the towel have a negative transfer once a 5oz (normal) baseball is introduced to the athlete. More research is clearly needed to settle this issue.

Finally, we find that there is not a significant relationship between higher levels of arm speed and arm stress for either the towel drill or throwing plyocare balls. This suggests that individual differences among pitchers, such as pitching mechanics, are more likely to predict arm stress than the level of arm speed that the pitcher generates. This is good news. Pitchers may be able to increase arm speed (and by extension velocity) and limit increases in stress on their arms. We recommend tracking all throws with the Motus Sensor to monitor safety of all throwing drills as it relates to each individual athlete. More research is needed to identify how gains in arm speed can be achieved without increasing arm stress.

Kbox Eccentric Power Vs Cmj/Approach Vertical Jump

KBox Eccentric Power Influence on Jump Height

Ricky Norton (Sports Performance Expert)

Tyler Standifird PhD (Assistant Professor in Biomechanics)


The purpose of this study was to understand the relationship between peak eccentric power and jump height in collegiate women’s volleyball players. Power is the rate at which work is done in the body, or the speed at which force can be developed. Force and the rate of the application of force can be a very important part of sports performance including jump height. For this study the idea was to compare the peak eccentric power produced by a group of athletes to their jump height. 


Fifteen collegiate level women’s volleyball players participated in the study. Each athlete performed a series of power output tests and also two jumping tasks. All of the tests were done on campus. The two jumping tasks included a standard counter movement jump (CMJ) and an approach jump (athlete takes as many steps as desired). Prior to jumping, subjects went through a general dynamic warm up and 10 air squat jumps. They each then performed a CMJ jump (first) followed by an Approach Jump (second) reaching for pins on the vertec. They were allowed to take as many attempts until they missed the lowest pin. Their total height on both jumps were then subtracted from their standing reach. Following both types of jumps, the athlete then performed 10 repetitions on the Eccentric KBox. The Average Eccentric Power of the 10 reps was then recorded. An analysis was completed on the data to compare the relationship between eccentric power and jump height.


A simple linear regression analysis was completed in order to understand the relationship between eccentric power and jump height. For both CMJ and Approach Jump, there appeared to be little relationship between KBox average peak power and jump height. The R^2 values for both of these jumps were low (0.16 and 0.17 respectively). Though this number does suggest that the KBox eccentric power did explain 16 and 17% of the variability in the jump performance. The data shows that an increase of around 40 watts of eccentric power would result in a one inch increase in jump height. 


The results of this case study suggest that peak eccentric power as measured by a KBox do not appear to be related to jump height in women’s collegiate volleyball players. The findings of this case study were contrary to what we had originally hypothesized. While power plays an important role in many sport specific activities, it may be that for jump height the speed of the force development may not be as important for performance. None of these athletes had ever used a KBox before and as a result there may be some learning aspect of the device. Athletes who are more comfortable with the apparatus might perform differently. These athletes did a set of ten squats and the average peak power of the 10 reps was taken, compared to the max rep for each type of vertical jump for height. Future studies may try and compare the one rep that showed the highest peak power on the KBox compared with maximal jump height or the maximum power produced in one repetition.  Also, eccentric power may be more closely related with how quickly an athlete can land and jump again, a skill necessary in volleyball and basketball, or the speed of changing directions in a cutting action as displayed in many sports. Future studies could look at how eccentric power is related to change of direction, in particular the speed of repeated jumping and landing tasks such as an RSI (Reactive Strength Index). This study was a good first step in starting to understand the relationship between eccentric power and jumping performance. As this understanding is further developed, trainers could know specifically how eccentric fly-wheel training on a KBox might influence performance and health. Future studies need to consider to explore this relationship.