Brawn behind performance. John Milton BIO-39

Size: px

Start display at page:

Download "Brawn behind performance. John Milton BIO-39"

Clarence Morris
5 years ago
Views:

1 Brawn behind performance John Milton BIO-39

2 Brain or brawn?

3 Newton was a sports fan I remember that I had often seen a tennis ball struck with an oblique racket describe such a curved line. For a circular as well as progressive motion being communicated to it by that stroke, its parts on that side where the motion conspire must press and beat the contiguous air more violently, and there execute reluctancy and reaction of the air progressively greater. Sir Isaac Newton (1671)

4 What is a force? If something is able to keep a spring deformed, this something is called a force in the static sense. If something is able to accelerate (or decelerate) a mass, this something is called a force in a dynamic sense.

5 Newton s laws of motion The law of inertia: body at rest stays at rest, body moving stays moving The law of acceleration: F=ma Body weight is a force The law of impact and reaction forces: for every action there is an equal and opposite reaction

6 First and second laws: Overstretch injury Must be able to stop momentum once started Cheat : Initiate lift using momentum from different part of body than are training

7 Over-stretch injury (cont.) Most often occurs in weight lifters who are in lowering stage of lift Symptom: Acute pain Sign: injured limb cannot be maintained against gravity Very serious; long time to recover Emphasis on prevention Technique; spotters, etc

8 Third law: The Darkside of Golf Prevalence of injuries is 50-60% For one golfer playing, two have left the game The two hurts: hurts their feelings, hurts their bodies

9 Ground reaction force: locomotion How much force impacts the ground while walking and running? One body weight (BW)? NO Walking 1-2 BW Running Up to 7 BW Why? Muscular forces contribute

10 Convention: F net = F muscle -F load F muscle -F load > 0 Then the muscle shortens

11 Exercise terminology Concentric (shortening) contraction Muscle > load Eccentric (lengthening) contraction Muscle < Load Isometric contraction Muscle = load

12 Generators of muscle force The myofibril The whole muscle including its associated connective tissues The force generated by muscles acting across a joint

13 Contractile proteins Actin = thin filaments Myosin = thick filaments

14 Muscle contraction

15 MF-1: Muscles can only pull For every flexor there is an extensor, etc Push-ups: Triceps contracts, not because biceps elongates

16 educated elbows Co-activation Both antagonist and agonist tend to contract Controls stiffness of movement Trade-off between speed and accuracy

17 MF-2: Muscle-joint complex functions like a third class lever

18 Mechanical advantage MA = effort arm / moment arm Effort arm = E-F Moment arm = R-F First and second class levers have MA > 1, but for third class MA < 1 Why?

19 Advantages of third class lever Speed Distance

20 MF-3: Force generated by a muscle is proportional to its cross-sectional area

21 Muscle size changes hypertrophy Atrophy

22 Effect of 8-week weight training on muscle size

23 Effect of training of one limb on the strength of the other

24 Effect of imagined exercise

25 Motor force principles MF1: Muscles can only pull MF-2: A muscle joint complex functions like a third-class lever MF-3: The force generated by muscles is proportional to its cross-sectional area

Musculoskeletal System. Terms. Origin (Proximal Attachment) Insertion (Distal Attachment)

Musculoskeletal System. Terms. Origin (Proximal Attachment) Insertion (Distal Attachment) Musculoskeletal System Terms Origin (Proximal Attachment) Insertion (Distal Attachment) Agonist- prime mover Antagonist- provides a braking force Synergist- assists indirectly in the movement Musculoskeletal