Description of Phases and Discrete Events of the Lacrosse Shot

Submitted by John A. Mercer and Jason H. Nielson

Abstract

The lacrosse shot is a vital skill of the offensive player. Despite the growth of the sport of lacrosse, there is a paucity of research on describing the biomechanics of lacrosse specific skills. The purpose of this commentary is to describe the phases and discrete events during a lacrosse shot. Phases are logical groups of movements used to accomplish a common goal whereas discrete events are specific actions that occur during a movement. For the purpose of this commentary, the lacrosse shot described is one that is taken with the intent of shooting as fast as possible. Through inspection of practice, game, and publically available video (30-1000 Hz) for a variety of ability and ages, this lacrosse shot can be described using the following phases: Approach, crank-back, stick acceleration, stick deceleration, follow through, and recovery. Each phase is defined by specific discrete events that indicate the beginning/ending of the phase. This paper forms a frame work for research on the lacrosse shot as well as coaching tips for enhancement of the shot. The end-goal of this work is to assist coaches and players in identifying the critical features of the lacrosse shot that are important for achieving a high-velocity and accurate shot.

Introduction 

Although the sport of lacrosse has a long and rich history, there is a paucity of research on the movements and skills that are part of the game. Participation in lacrosse has grown 10% per year on average from 2001 to 2010 (18). The total increase in number of players (male and female) has grown from 253,931 players in 2001 to 624,593 players in 2010 with the greatest growth in youth and high school levels (18). Overall, youth lacrosse growth has outpaced the growth of any other sport.

Along with this growth has come a need for coaching expertise to teach players critical skills and game play strategy. Interestingly, the sport is lacking in even basic kinematic description of certain key movements. For example, even though some research on lacrosse is emerging on injuries (4, 7, 8, 9, 12), conditioning/testing techniques (11, 15), accuracy (14), passing (13) and shooting (6) kinematics, ball (5), and player (16, 17) characteristics and some early work on teaching lacrosse skills (2, 3), there is no kinematic description of the phases and discrete events of the shot.

It makes sense to develop a description of certain key movements that are part of the shot in order to identify critical features that increase performance and/or skill acquisition. For example, baseball pitching has a strong body of research that includes description of phases and discrete events of the baseball pitch. Kinematic and Kinetic data are often analyzed within a phase in order to compare and contrast different types of pitches, for example (e.g., 10). Presently, there is no such description of the phases and discrete events of the lacrosse shot.

Part of the challenge in forming a model of the lacrosse shot is that there are many different techniques for shooting a lacrosse ball. For example, some players shoot overhand, some underhand, or side arm. Likewise, there are many game situations where the shot technique is unique due to the position of the player shooting as well as the interaction with the defender and/or goalie. For example, players may be positioned just outside the goal crease and will receive a pass and shoot in one continuous motion (i.e., “quick stick”). Likewise, during a game, players are often dodging defenders and shooting on the run while being checked, jumping, and/or having movements hindered in some manner by the defender. For that reason, it is difficult to fit all lacrosse shots into a single descriptive model. Nevertheless, it is important to form a model of the lacrosse shot as a framework for research to identify the critical aspects necessary for an accurate and high speed shot. Therefore, the purpose of this paper is to provide a description of the phases and discrete events of the lacrosse shot.

The Lacrosse Shot

For the purpose of this paper, we will describe the phases and discrete events of a situation where a player is shooting at the goal with maximal velocity. In this scenario, the player is allowed to take approach steps. This would be analogous to a player shooting from the perimeter of the box with no defender hindering or restricting movement in any way. This type of shot is common in a game, especially off a fast break when a face off is won or during a man-up situation (i.e., the opposing team is playing with one less defender due to a penalty situation).

To gain an understanding of the kinematics, we reviewed game, practice, and publically available (YouTube) video taken from a wide range of ability and ages of players that used a variety of recording speeds (30-1000 Hz). In these videos, the camera placement was often unique which allowed for viewing the shot from different perspectives. Overall, the movements could be grouped into logical phases consisting of approach, crank-back (wind-up), stick acceleration, deceleration, follow-through, and recovery. We also felt it was important to further break down the crank-back phase into two smaller phases (i.e., A and B) since we think the preparatory movements in each of these sub-phases are important to shot performance.

In order to describe the phases and discrete events of the shot, it is necessary to first define some lacrosse specific terminology. Figure 1 is an illustration of a player in the act of shooting. We will use the term ‘stick’ when referring to the combination of two main equipment components: The shaft and the head. The head is firmly connected to the shaft (however, the head can be removed and placed on a different shaft). In this illustration, a short stick is used. There are times when a player is shooting using a long-pole or goalie stick; in these situations, the phases and discrete events are the same as presented here, but the movements in each phase may be unique due to the characteristics of the stick (e.g., length, mass, moment of inertia).

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: Illustration of a player in the act of shooting.  Top arm, Bottom arm, Drive leg, and Lead leg are all illustrated.

For player specific terminology, we will use the phrase ‘bottom arm’ to refer to the entire limb distal to the shoulder (i.e., upper arm, forearm, hand) in which the hand is gripping the shaft near the end the shaft. We will use the phrase ‘bottom hand’ when referring specifically to the hand of the bottom arm. We will use ‘top arm’ and ‘top hand’ to refer to the arm/hand that grips the shaft between the bottom hand and stick head. A right handed shot is one in which the right arm is the top arm; a left handed shot is one where the left arm is the top arm.

For the lower extremity, we will use the term ‘drive leg’ to refer to the leg that is planted on the ground pushing the player forward. Likewise, we will use the term ‘lead leg’ to refer to the leg that is planted in front of the player while shooting. Analogous terms for ‘lead leg’ are ‘plant leg’ or ‘blocking leg.’ When shooting right handed, the drive leg is the right leg and the lead leg is the left leg (vice versa for shooting left handed).

The phases of the shot and the discrete events separating each phase are described in Table 1 and described in more detail below.

1. Approach. The approach begins with the player initiating movement and ends when the foot of the drive leg contacts the ground. During this phase, the player is taking several steps advancing towards the goal with the intent to shoot. The number of steps, the style of the approach (e.g., stepping forward, sideways, backwards, cross-over, hopping, etc.), and the velocity of the approach varies between players. However, what is common among all the approach styles is that it ends when the drive leg contacts the ground.
2. Crank back. The crank back is analogous to the wind-up or cocking phase of throwing a ball. This phase consists of the preparatory movements that proceed accelerating the stick (i.e., angular motion) with the intent of releasing the ball towards the goal. The crank back begins with the foot of the drive leg contacting the ground and ends when the top arm reaches maximum elbow flexion. If a 3D motion capture analysis is completed, an alternative ending discrete event would be the moment when stick angular acceleration velocity is continuously in the same direction as during the Stick Acceleration phase (next). We have further sub-divided the crank back phase into two sub-phases (A and B).

o   Crank back – A. The Crank back – A phase begins when the foot of the drive leg contacts the ground and ends when the foot of the lead leg contacts the ground. This phase could also be described as a ‘drive step’ when focusing on the lower extremity.

o   Crank back – B. The Crank back – B phase begins with lead foot contact and ends when the elbow of the top arm reaches maximum flexion. The movements in this phase are still preparatory movements to accelerating the stick towards the goal and would still be considered ‘wind-up’ movements.

3. Stick acceleration. Stick acceleration begins when the elbow of the top arm has reached maximum flexion and then starts extending. This phase ends with ball release. The duration of this phase is very short and dynamic.
4. Stick deceleration. Stick deceleration begins once the ball release has occurred and ends when the elbow of the top arm has reached maximum extension.
5. Follow-through. The follow-through phase begins when the top arm has reached maximum extension and ends when trunk rotation has been terminated.
6. Recovery. The recovery phase begins with the end of trunk rotation and represents the movements the player needs to make to prepare for the next task.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1: The phases and discrete events that describe the lacrosse shot.

Figure 2 is an illustration of the discrete events for the lacrosse shot in a time lapse sequence. Although this gives a good visual of the separation of phases, the figure is limited in that it does not give a sense of the duration of each phase. It would be helpful through future research to document the timing of the phases for different skill levels as well as when comparing left and right handed shots of an individual player.

Figure 2: Phases (bottom) and Discrete Events (top) of the lacrosse shot.

Discussion

The intent of creating a model of the phases and discrete events for the lacrosse shot is to create a framework for research as well as constructing coaching tips for the enhancement of shot speed and accuracy. For example, recently we investigated muscle activity of the top and bottom arms during shooting (1). In that study, we examined the muscle activity ½ second before and after ball release. Although it was insightful to identify the different roles of muscles when considering the top and bottom arms and that the wrist flexors/extensors were more active than suspected, the meaningfulness of that work would be more significant if muscle activity were described for each phase. This type of research would provide insight into the importance of timing of muscle contractions that led to a faster shot velocity. Likewise, that research would lead to developing training programs and drills to develop a faster shot that is also accurate.

The advantage of using the phases as a framework for research is that movements that share a common goal are grouped together. For example, it makes sense to understand muscle activity magnitudes and patterns during the crank-back phase of the shot independent of the magnitudes and patterns during the time when the stick is being accelerated to release the ball. In our previous work (1), the ½ second analysis before ball release likely represented muscle activity during both crank back and stick acceleration phases. We now believe that analyzing muscle activity within each phase is important in identifying the critical features of a shot that allow for high ball velocity at release and/or accuracy of the shot. For example, the initial inspection of elbow flexion/extension patterns has lead to the hypothesis that peak elbow flexion velocity during the crank back-B phase is important to shot velocity (1). It may be that elbow flexion preceding elbow extension during the stick acceleration phase elicits a stretch-shortening reflex that increases elbow extension velocity during the acceleration phase. The analogy is that elbow flexion during crank back-B would serve to function similar in the same manner as the downward (i.e., counter-movement) movement during a vertical jump. The implications of this observation, if it is substantiated by research, is that training programs should be focused on strengthening exercises that incorporate elbow flexion preceding rapid extension vs. simply strengthening elbow extension.

By creating terminology for phases and discrete events, not only will research be given a context of which to formulate description of kinematics and kinetics of the shot, coaching tips may be more directed and purposeful. For example, some players might be able to increase shot speed if unnecessary crank-back movements are eliminated and/or the stick is positioned properly prior to the acceleration phase (i.e., during crank back-B phase). Research is needed to compare and contrast the kinematics during each phase between players with different level of skill as well as between shooting left and right handed. This type of research would likely be helpful to coaches and trainers in order that there is a better understanding of which movements to reinforce and which movements should be eliminated during a shot to maximize speed.

It is important to recognize that the phases and discrete event model presented is limited and there may be times when the model needs to be modified. For example, there may be some benefit to studying shot kinematics when there is no approach phase. This would be analogous to shooting while both feet are planted. Although shot speed is not maximized in this scenario, there are game scenarios when players have to shoot quickly vs. trying to shoot as fast as possible. In this case, the discrete events of drive leg and lead leg contact would need to be modified since both feet are in contact with the ground in this scenario. It is hoped that this commentary will stimulate further research on the lacrosse shot and other models of different styles of shooting are created.

There may also be a need to modify the discrete events used to define each phase. For example, depending on the instruments available to analyze the shot kinematics, the start of stick acceleration may be best defined based upon when the angular velocity of the stick is continuously in the direction of the shot (vs. maximum top arm elbow flexion). In order to capture that, either a 2D top-view or 3D kinematic analysis would need to be carried out. In the present model, we based the discrete event identification from a 2D camera placed either to the side or slightly behind/in front of the player.

It is important to also recognize that the discrete events themselves may not be critical movement characteristics. The importance of the specific discrete events, for this paper, is that they define the start and end of a phase. Biomechanical analyses can then be focused on maximum and/or minimum kinematic and kinetic parameters during each phase. We also believe that it makes sense to compare kinematics and kinetics of the upper and lower body at the occurrence of the discrete events. For example, the horizontal stick position at the moments of drive and lead leg contact may be important characteristics of the shot.

Summary

We have presented a model of the phases and discrete events of the lacrosse shot along with basic terminology (e.g., top arm, top hand, bottom arm, bottom hand, drive leg, lead leg) that can be used when describing movement characteristics during the lacrosse shot. The phases represent groups of movements that share a common goal that contributes to shot speed. Each phase is separated by a discrete event, which is a specific event that occurs in a brief moment in time. In the context of shooting the ball for to achieve maximum velocity, we described the shot using the approach, crank-back (A and B sub-phases), stick acceleration, stick deceleration, follow through, and recovery phases. This model will provide a frame work for lacrosse directed research as well as providing a context for coaching tips to improve shot speed.

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