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.

The athlete moves through their full approach creating horizontal acceleration.  

Jumper Running

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 Approach

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.  

Jumper First Foot Impact

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

Pre-Launch ImpactVertical Jump






  1. The Elite group covered 23% more distance through their penultimate stride.
  2. The Elite group displayed less trunk flexion during contact of peak loading of their lead (plant foot).
  3. The Elite group was 30% faster to produce peak force than the Advanced group.
  4. Loading Rates were 35% faster in the Elite group 
  5. Elite group had an 8% higher concentric force on the plant foot.
  6. 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?


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