Week 10s: Kinetic Data Interpretation Dr. Andrew Greene

Session Outline Recap, key assessment details Using the data –Stance phase kinetics Using the data –Jump performance

Key Documents / Data Drop jump lab report guidelines Assessment section of Moodle site General guidelines on lab report writing General Module resources section of Moodle site Data for lab report Week 8S section of Moodle site

Experimental Aim To assess the effect that arm swing has on the performance and stance phase mechanics of drop jumping Performance –jump height Stance phase mechanics –Your choice of variables (with some constraints) At least one kinetic (force platform derived) variable must be reported and discussed in your assignment

Force Measurement Force Platform: Kistler Model 9281B Force platform (Kistler Instruments Limited, Winterthur, Switzerland) connected to a Kistler Model 9863A Amplifier (Kistler Instruments Limited, Switzerland) Sample Rate: 1000Hz Software: Bioware Version 5.3.0.7 (Kistler Instruments Limited, Switzerland)

Jump Performance Does arm swing influence jumping performance? Jump height is the key performance measure You need to calculate jump height as explained in Week 9 session (using data in kinetics spreadsheet) Also need to provide worked example in appendix. (See example at the end of the presentation)

Assessed Variables Why have we measured variables other than jump height? Potentially help explain how arm swing influences jump performance. Choose variables that you think will provide most insight in this regard (based on theory and literature of biomechanics of vertical jumping)

Statistical Analysis Use t-test to determine if there is a significant difference between the two conditions (arm swing and without arm swing) in all of the variables of interest Reminder of statistics support resources T-test workbook in Research Methods module Statistics and SPSS books in library (e.g. Andy Field –Discovering Statistics Using SPSS) Academic achievement team

Research Methods Moodle

Drop Jump Drop jumping (DJ) is a plyometric activity that involves stepping from a predetermined height, landing and immediately performing a maximum jump. DJ training allows the athlete to increase the pre-activation and pre-stretch of the muscles and allows the coach to assess landing techniques that are vital to the production of force Ball et al, 2010

Drop Jump The aim of a drop jump exercise is to improve the ability of tendons and muscles to store and release elastic energy when exposed to high stretching forces such as those found within jump landings, and support phases of sprinting. DJ’s mimic the rapid deceleration followed by maximal vertical jump observed in a rebounding task, which happens to be the task most commonly associated with ACL injury in basketball Ball et al, 2010

Arm Swing Theory Arm swing thought to act to improve velocity at take off Transmission of force theory (Payne et al., 1968): as the arms are accelerated upwards, a downward force is exerted through the body increasing the ground reaction force, which in turn leads to a greater impulse increasing the vertical velocity of the COM Joint torque augmentation theory (Feltner et al., 1999): reaction force acting on the trunk due to the upward acceleration of the arms causes the hip, knee and ankle joints to slow their rate of extension enabling them to produce greater muscle forces Lees et al, 2004

Arm Swing Theory Pull theory (Harman et al, 1990): towards the later part of the jump, when the arms begin to decelerate, their high vertical velocity relative to the trunk ‘pulls’ on the trunk, transferring energy from the arms to the body. No one-theory exclusively explains enhanced performance in the arm swing jump, but rather the enhanced performance is based on several mechanisms operating together. Increased velocity stems from a complex series of events that allows the arms to build up energy early in the jump and transfer it to the rest of the body during the later stages of the jump. Lees et al, 2004

Drop Jump Forces Drop Jump VGRF is characterised by an Eccentric Phase followed by a Concentric Phase. Direction and velocity of COM critical Eccentric Concentric Moran and Wallace, 2007

Title Eccentric phase CM moving downwards Stored elastic energy (SSC)

Title Concentric phase CM moving upwards Muscles generating movement

Kinetics and Kinematics Moran and Wallace, 2007

Drop Jump Breakdown ECCENTRIC PHASE CONCENTRIC PHASE Peng et al, 2011

Impulse How does GRF indicate improved performance? The Vertical Force and the Time over which the force is applied is called the Impulse The impulse is calculated by the area under the Force Time Curve IMPULSE

Impulse The area under the Force Time curve gives the Impulse Jump Impulse Total Impulse Impulse BW BW

Peaks in Force Fowler and Lees, 1998

First Peak Force First Peak can be interpreted as representing the initial passive loading of the body upon first ground contact (Peak 1), this peak occurring within the first 80ms of impact. It is unlikely that any active force could be generated within this period Fowler and Lees, 1998

Second Peak Force The second peak represents the positive acceleration peak during which the downward velocity of the body was reduced through the eccentric action of hip, knee, and ankle extensors. Fowler and Lees, 1998

Third Peak Force The final peak, occurring shortly before takeoff, was the result of concentric contraction of the previously stretched muscles to drive the body away from the force platform. Fowler and Lees, 1998

Peaks of Force The second peak is not present in all drop jumps owing to different techniques used to complete the jump. Fowler and Lees, 1998

Drop Jump Technique Two types of DJs have been identified, the bounce-drop jump and the countermovement drop jump: The bounce-drop jump requires the subject to jump maximally as soon as possible after landing, focusing on the ankle plantar flexors and involving minimum knee flexion and minimum ground contact time. The countermovement drop jump is characterized by an increase in knee flexion and ground contact time compared with the bounce-drop jump Ball et al, 2010

Drop Jump Characteristics Counter Movement drop jump: Un-trained jumpers Non-habitual jumpers Reduced force generating capacity Bounce Drop Jump: Trained / High Frequency Jumpers High force generating capacity

Force Characteristics The presence of an impact peak has been reported in previous studies and can be attributed to landing technique because of extension at the metatarsophalangeal joint on impact. The absence / reduced impact peak may indicate a more flat footed landing compared with landing on the balls of the feet to absorb the impact in plantar flexors Drop Jumping experience thought to have an impact upon GRF with those subjects with greater experience in drop jumping displaying reduced GRF peaks Ball et al, 2010

Novice Jumpers Although subjects were familiarized with the task, proper drop jump technique can reduce vertical GRF by as much as 20% due to increased muscle pre-activation before ground contact Ball et al, 2010

Increased Drop Height Increasing drop height sees a significant increase in the rate of loading and the GRF Peak Studies have shown no improvement in performance for drop heights of greater than 40cm Benefit of lower drop height (20cm) are the significant reduction in loads on the joints Bobbert et al, 1987

Impact without arms? Might the absence of arms effect the forces at landing?

Drop Jump Effectiveness Drop jumping is a stretch shortening cycle (SSC) activity (rapid stretch followed by rapid shortening of muscles and tendons) Drop jumps exhibit a large magnitude and rate of eccentric loading This stimulates an effective utilisation of the stretch-shortening cycle, and in turn, greater force production in the concentric phase Bobbert et al, 1987; Moran and Wallace, 2007

Drop Jump SSC Wilson et al, 1991

Drop Jump Eccentric Phase (negative phase) assumes that all soft tissues are working eccentrically Eccentric loading of the muscles enhances the storage of elastic energy Transfer from Eccentric → Concentric phase when COM moves upwards Concentric Phase (positive phase) assumes that all soft tissues are working concentrically Amortization is the release of stored elastic energy from the Eccentric phase which acts to enhance the Concentric Phase

Contact Time Ground contact times for drop jumps can range from 0.17 to 0.3 seconds depending on the condition, ability, strength, and technique of the athlete If ground contact time exceeds 0.25 seconds, then power production can be significantly reduced. This reduction in power is because of a delay in the transition from eccentric to concentric phases (the coupling phase), causing a loss of stored elastic energy that is detrimental to power production Wilson et al, 1991; Ball et al 2010; Bates et al, 2013

Contact Time and SSC A delay in the movement causing a pause or delay between the eccentric and concentric phase can negate or reduce the transfer from the SSC Much shorter contact times (0.17 milliseconds) are found in a trained population Power output declines after 0.25 seconds which indicates that some drop jumps performed may not be eliciting a plyometric response and using the stretch-shortening cycle effectively. Wilson et al, 1991; Ball et al 2010; Bates et al, 2013

Contact Time and SSC Finding based upon experienced jumpers or those with high frequency of jumping (basketballers, netballers, volleyballers etc)

Bilateral Force Production Left and Right foot contact have different force profiles Bates et al, 2013

Bilateral Force Production Could arms swing effect this? More control of body position at landing? Bates et al, 2013

Summary Consider different theories that discuss improvement in jump height with arm swing Discuss the kinetic variables that we have collected and displayed Highlight specific studies in the literature that have discussed drop jumps and some of the findings Consider the effects that some of the methodological factors may have had upon the outcome and results

References Ball, N., Stock, C., & Scurr, J. (2010). Bilateral contact ground reaction forces and contact times during plyometric drop jumping. Journal of Strength and Conditioning Research, 24, 2762–2769. Bartlett, R. (2007). Introduction to sports biomechanics: analysing human movement patterns. New York, NY: Routledge. Bates, N. A., Ford, K. R., Myer, G. D., & Hewett, T. E. (2013). Timing differences in the generation of ground reaction forces between the initial and secondary landing phases of the drop vertical jump. Clinical Biomechanics, 28, 796-799. Bobbert et al (1986). Biomechanical analysis of drop and countermovement jumps. European Journal of Applied Physiology. 54, 566-573 Bobbert et al (1987). Drop Jumping II. The Influence of dropping height on the biomechanics of drop jumping. Medicine and Science in Sports And Exercise, 19 (4), 339-346. Fowler, and Lees, A. (1998). A Comparison of the Kinetic and Kinematic Characteristics of Plyometric Drop-Jump and Pendulum Exercises. Journal of Applied Biomechanics, 14, 2260-276.

References Hackney, J.M., Clay, R.L. and James, M. (2016) Force-displacement differences in the lower extremities of young healthy adults between drop jumps and drop landings. Human Movement Science, 49, 79–86. Lees, A., Vanrenterghem, J. & Clercq, D.D., 2004. Understanding how an arm swing enhances performance in the vertical jump. Journal of Biomechanics, 37(12), pp.1929–1940. Linthorne, N.P. (2001). Analysis of standing vertical jumps using a force platform. American Journal of Physics Teachers. 69 (11), 1198-1204. Moran, K and Wallace, E. (2007). Eccentric loading and range of knee joint motion effects on performance enhancement in vertical jumping. Human Movement Science, 26, 824–840 Peng et al (2011). Quadricep and hamstring activation during drop jumps with changes in drop height. Physical Therapy in Sport, 12, 127-132. Wilson, G.J., Elliott, B.C. and Wood, G.A (1991). The effect on performance of imposing a delay during a stretch shortening cycle movement. Medicine and Science in Sports and Exercise. 23 (3), 364-370.

Vertical Velocity TO vf (vt-o) = ? vi (vt-d ) = -2.18 m·s-1 a = ? s = ? t = 0.56 seconds Mass = 88 kg Total Impulse = 763 N.s BW Impulse = 292.5 N.s Jump Impulse = 470.5 N.s Which Calculation do you select? Calculate the Vt-d (Vf) a = ? Vf = ? Vi = -2.18 m·s-1 Jump Impulse Impulse BW BW 0.56 seconds

Vertical Velocity TO Jump Impulse =  m x v Jump Impulse = m x vt-o – m x vt-d

Maximum Jump Height vi (vt-o) = 3.16 m·s-1 a = -9.806 m·s-2 s = ? vf = 0 m·s-1 vi (vt-o) = 3.16 m·s-1 a = -9.806 m·s-2 s = ? t = ? Which Calculation do you select? Calculate the Vt-d (Vf) Vf = 0 m·s-1 s = ? vi (vt-o) = 3.16 m·s-1

Maximum Jump Height vf2 = vi2 + 2.a.s vf = 0 m·s-1 vi (vt-o) = 3.16 m·s-1 a = -9.806 m·s-2 s = ? a = -9.806 m·s-2 s = ? vi (vt-o) =3.16 m·s-1 Vf = 0 m·s-1

Maximum Jump Height vf2 = vi2 + 2.a.s 02 = 3.162 + (2 x -9.806 x s)