MAXIMISING BALL RELEASE SPEED IN OVERHEAD THROWING THROUGH OPTIMISING ARM SEGMENT MASSES A thesis submitted for the degree of Doctor of Philosophy by Patrick Fasbender Department of Life Sciences, Brunel University London 28 September 2017 Abstract The tapering distribution of segment masses in the human arm helps in the generation of high ball release speeds in overarm throwing. However, the masses of the individual arm segments might not be optimal; arm segment masses could be optimised in order to improve throwing performance. The aim of this project was to identify and understand the optimal upper arm mass that results in the highest ball release speed in overarm throwing. The first study was a theoretical study, using a simple two-segment model of the arm to determine the optimal combination of arm segment masses that maximises ball release speed. This simplified throw was chosen to identify the basic mechanism causing changes in ball release speed with a heavier upper arm mass. The study identified that there is an optimal upper arm mass, but this optimum depends on the forearm mass and the shoulder torque. Furthermore, the study showed that a heavier forearm mass produces a lower ball release speed. An experimental approach was used in the second study to analyse the effect of additional upper arm mass on ball release speed and throwing mechanics in an overarm throw similar to that used by baseball pitchers. However, group analysis of the ball release speed did not reveal an optimal upper arm mass, and most of the kinematic, kinetic, and temporal variables were not affected by additional upper arm mass. However, analysing the ball release speed of each participant individually revealed that most participants increased their ball release speed, although there was considerable variation in the optimal upper arm mass. As the optimal upper arm masses in this study did not agree with those predicted in the first theoretical study, a 2 more realistic three-dimensional model is needed to simulate the effect of upper arm mass on ball release speed. The third study was a combination of a theoretical and experimental approach. A three-dimensional model of the throwing arm was used to predict the participant’s optimal upper arm mass and to determine the kinematic and kinetic variables that determine the optimal upper arm mass in overarm throwing. Even though the simulations did not accurately predict an athlete’s optimal upper arm mass, the results highlighted that throwing athletes can benefit from a heavier upper arm mass as long as their ability to produce a high internal shoulder rotation angular velocity is not restricted. In summary, the findings of this project highlight that some athletes can benefit from a heavier upper arm mass to maximise their ball release speed without increasing the risk of injuries. However, as the optimal upper arm varies between athletes it is important to analyse each athlete individually. 3 Table of contents Abstract ...................................................................................................................... 2 Table of contents ........................................................................................................ 4 List of figures ............................................................................................................ 13 List of tables ............................................................................................................. 16 Acknowledgments .................................................................................................... 18 General introduction ....................................................................... 19 Literature review .............................................................................. 26 2.1. Throwing a projectile ...................................................................................... 27 2.2. Human evolution and projectile throwing ....................................................... 27 2.3. Classifications of throws ................................................................................ 28 2.4. Determinants of throwing performance .......................................................... 29 2.4.1. Release angle ....................................................................................... 30 2.4.2. Release height ...................................................................................... 31 2.4.3. Release speed ...................................................................................... 32 2.5. Phases of throwing ........................................................................................ 33 2.5.1. Windup ................................................................................................. 34 2.5.2. Stride .................................................................................................... 35 2.5.3. Arm cocking .......................................................................................... 35 2.5.4. Arm acceleration ................................................................................... 36 4 2.5.5. Arm deceleration .................................................................................. 36 2.5.6. Follow-through ...................................................................................... 37 2.6. Kinetic chain .................................................................................................. 37 2.6.1. Conservation of angular momentum ..................................................... 38 2.6.2. Kinetic chain of throwing ....................................................................... 38 Inertial parameters of the kinetic chain ............................................. 39 Temporal variables ........................................................................... 40 Legs .................................................................................................. 41 Trunk ................................................................................................ 43 Shoulder ........................................................................................... 44 Elbow ................................................................................................ 47 Wrist ................................................................................................. 48 2.7. Injuries in overarm throwing ........................................................................... 49 2.7.1. Kinetic variables associated with injuries .............................................. 49 2.7.2. Kinematic variables associated with injuries ......................................... 50 2.7.3. Temporal characteristics associated with injuries ................................. 51 2.8. Experimental vs. simulation design ................................................................ 52 2.8.1. Pros and cons of different study designs .............................................. 52 2.8.2. Force-velocity relationship .................................................................... 53 2.8.3. Computer models of the upper body .................................................... 53 Shoulder models used in throwing studies ....................................... 54 5 Joint rotation sequence in throwing studies ...................................... 54 2.9. Changes of inertial parameters in overarm throwing ..................................... 55 2.9.1. Upper arm mass ................................................................................... 55 2.9.2. Forearm mass ...................................................................................... 57 2.9.3. Risk of injury ......................................................................................... 57 2.10. Summary ..................................................................................................... 58 Optimal mass of the arm segments in overarm throwing: A 2D simulation study. ............................................................................. 60 3.1. Introduction .................................................................................................... 61 3.1.1. Inertial parameters in throwing ............................................................. 62 3.1.2. Importance of upper limbs in throwing .................................................. 64 3.1.3. Temporal lag of joint rotations in throwing ............................................ 64 3.1.4. 2D throwing models .............................................................................. 66 3.1.5. Aims of the study .................................................................................. 67 3.1.6. Hypothesis ............................................................................................ 68 3.2. Methods ......................................................................................................... 69 3.2.1. Participant ............................................................................................. 69 3.2.2. Experimental Setup .............................................................................. 70 3.2.3. Determination of subject-specific simulation characteristics ................. 73 3.2.4. Model description ................................................................................. 74 3.2.5. Dependent variables ............................................................................. 77 6 3.3. Results ..........................................................................................................