BIOMECHANICS IN A NUTSHELL Helping Your Students Understand Movement MN AAHPERD FALL CONFERENCE Wayzata High School, Wayzata, MN October 12 & 13, 2012 Bridget A. Duoos, Ph.D. Sherry L. Folsom-Meek, Ph.D. Health and Human Performance Department of Human Performance Department Minnesota State University, Mankato University of St. Thomas St. Paul, Minnesota

Today we will discuss the following movement concepts: Center of gravity Balance Applying force Receiving force Starting Stopping

Two Ways To Teach Movement Concepts Stand alone Tied into the unit

CENTER OF GRAVITY C of G or CG, Center of Mass Point around which the body’s mass is equally distributed Body’s weight is equally balanced in all directions

CENTER OF GRAVITY Sum of torques produced by weights of the body’s segments equals zero Balance point Used for analysis purposes Line of gravity drops straight down from C of G

CENTER OF GRAVITY

CENTER OF GRAVITY We will locate it in an…. Odd shaped piece of tag board Sports equipment On your body

CENTER OF GRAVITY Odd Shaped Piece of Tag Board Cut odd shapes from tag board Punch a hole anywhere in tag board Insert a dowel through hole, should move freely Tie a small loop in the end of a 10-12” piece of string Tie a washer at the other end of string Place loop over dowel, let hang freely

CENTER OF GRAVITY Odd Shaped Piece of Tag Board Once movement has stopped, partner traps string to paper and draws a line along the string Punch a second hole anywhere in paper Repeat process…put dowel through new hole, hand string, trap and draw line The spot where the two lines cross is the center of gravity of the odd shaped paper

CENTER OF GRAVITY Sports Equipment Activity Find the center of gravity of the sports objects Consider material made out of C of G is pulled to heavier end Put an “X” over the spot you identified on the picture

CENTER OF GRAVITY Sports Equipment Activity Check yourself by trying to balance the objects with your finger. Move your extended finger along the object until you get it to balance.

CENTER OF GRAVITY In Your Body Activity Calculate your CG by: -your height x.57 (boys) = ____ -your height x.55 (girls) = ____ Measure from floor up to determine where your CG is located

STABILITY Resistance to disruption of equilibrium Balance is the ability to control equilibrium

STABILITY Resistance to disruption of equilibrium Balance is the ability to control equilibrium

STABILITY How easy is it to tip over?

BALANCE FACTORS Mass/weight of body or part Height of C of G of body or part Size of base of support of body or part Magnitude of friction that determines “sticking” to form axis of rotation

EQUILIBRIUM S tatic Dynamic not moving moving no change velocity no change in direction

STABILITY In sports there are times when we maximize stability and times when we minimize stability

STABILITY The vertical jump is easier for young children to perform than the horizontal jump. If there is a target to reach for with the vertical jump, students tend to jump higher. The horizontal jump is difficult for some children, as they have to put their center of gravity outside the base of support to take off.

CONTROLLING BALANCE DURING MOVEMENT Changing Speed or Direction Starting Put C of G as close to base edge as possible Stopping Put C of G as far back from leading edge as possible

STABILITY Pick Up the Money Stand with your heels against the wall. Try to pick up the money on the floor in front of you without tipping over. Can you do it? Next, try standing with your heels about 12” from the wall. Try to pick up the money on the floor in front of you without tipping over. Can you do it?

STABILITY Pick Up the Money Explain why you were successful one time and not the other. Use the following terms in your explanation: C of G, base of support, rotary equilibrium

STABILITY Push-Ups! Assume a push-up position. Your partner should draw a picture of you in this position. Outline your base of support on the diagram.

STABILITY Push-Ups! Assume the push-up position. Remove one hand from the floor. Your partner should draw a picture of you in this position. Outline your base of support on the diagram.

STABILITY Push-Ups! What adjustments do you have to make to maintain your balance when you lift your hand off the floor?

Who assesses balance? – DAPE teachers and GPE teachers – OTs – PTs – Neurologists – Biomechanists Assessing Balance

Protocols: – Romberg (feet together, arms at sides) – Mann (heel-to-toe) – One-foot protocols: Stork stand with arms at sides; note what examinee does with arms 90 degree bent leg with hands on hips (BOT-II) Generally people balance better on one foot than the other; note foot used Assessing Static Balance

– Eyes open and eyes closed Generally can balance at least 2 times longer with eyes open than eyes closed; balance on each leg should be assessed Examinee should get into balanced position before closing eyes How measure: – Time in balance (10 s is most common) – Forceplate used by biomechanists—measure pattern of sway around the line of gravity Assessing Static Balance

Common measures: – Walking heel-to-toe on a line or very low balance beam – Walking backwards – Always eyes open – Notes on performance—What should you look for? Assessing Dynamic Balance

STARTING and STOPPING STARTING STOPPING C of G low C of G forward C of G backward Only a small torque will upset equilibrium

STARTING and STOPPING Run as Fast as You Can! Sprint the width of a volleyball court. Stop ON the line marked by the cone with BOTH feet. Partner stands by end line and observes.

STARTING and STOPPING Run as Fast as You Can! Were you able to stop exactly on the line? Why or why not? What changes occurred in body lean as the runner approached the line? Provide examples of where this movement occurs in sport.

APPLYING & RECEIVING FORCES Increase base of support in direction of giving or receiving force

APPLYING & RECEIVING FORCE I Can Tip You Over! Stand facing your partner one stride away. One partner assumes a lateral stride. One partner assumes a front to back stride. Place your palms against your partner’s. Attempt to push each other off balance.

APPLYING & RECEIVING FORCE I Can Tip You Over! Which partner loses their balance first and most easily? Identify the partner by the stride they assumed. Explain why this happened. Use base of support, C of G, line of gravity and stability in your explanation.

QUESTIONS?

END!!!