Lab Q/A

EXS 31600 Exercise Physiology Laboratory

Lab 3

Objectives

• Understanding the force-velocity relationship

• Determine fiber type composition

• Examine the load/velocity profile utilizing a linear position transducer

• Calculate the H:Q ratio

• Examine different muscular fitness measurements

• Examine Muscle swelling

Definitions

• 1-repetition maximum (1RM): maximum amount of weight or load that can be lifted one time

• Muscular endurance: ability to exert submaximal forces repetitively

• Muscular fitness: combination of muscular endurance and maximal strength

• Muscular strength: highest amount of force that can be generated by a muscle or group of muscles during a single contraction

• Repetition maximum (RM): maximum amount of weight the can be lifted for a prescribed repetition range (i.e.,10RM is the heaviest weight that can be lifted 10 times)

Definitions

• Muscular power: ability to exert force per unit of time, or the rate of performing work

• Force: mass multiplied by acceleration, expressed as a newton (N)

• Velocity: vector quantity calculated by dividing displacement by time (m/s)

• Torque: a measure of the force that can cause an object to rotate about an axis [Newton/meter (N·m)]

• Fatigue: decline in muscle power output

Background

• Musculoskeletal or muscular fitness is associated with numerous health benefits

• Reduced risk of heart disease, osteoporosis, glucose intolerance, and musculoskeletal injuries

• A healthy musculoskeletal system is associated with an improved ability of activities of daily living and quality of life

• High levels of musculoskeletal fitness = positive health status

• It is suggested that muscular fitness is related to a reduced all- cause mortality risk

Background

• It is important to evaluate and should be considered during the health and wellness screening process

• No single assessment evaluates total-body muscular strength or endurance

• Musculoskeletal fitness testing is specific to the muscle groups tested, the velocity of the movement, type of contraction and ROM used, and the type of equipment

Connective Tissue Covering

• Connective tissue transfers force to tendon which transfers force to bone

• Movement

• Epimysium • Surrounds the entire muscle

• Perimysium • Surrounds bundles of muscle

fibers (Fascicles)

• Endomysium • Surrounds individual muscle fibers

Muscle Fiber Type • Three muscle fiber types:

• 1. Slow-oxidative fibers (Type I) combine low myosin-ATPase activity with high oxidative capacity

• Slower contraction speed

• High mitochondria and myoglobin content

• Red muscle fibers

• 2. Fast-oxidative-glycolytic fibers (Type IIa) combine high myosin- ATPase activity with high oxidative capacity and intermediate glycolytic capacity

• Intermediate

• Fast twitch

IIa

I

IIx

Muscle Fiber Type

• 3. Fast-glycolytic fibers (Type IIx) combine high myosin-ATPase activity with high glycolytic capacity

• Faster contraction speed

• Fewer mitochondria and myoglobin

• Large storage of glycogen

• White muscle fibers IIa

I

IIx

Comparison of Maximal Shortening Velocities Between Fiber Types

Typical muscle fiber composition of athletes and nonathletes

Sport % Slow Fibers

(Type One)

% Fast Fibers (Types Two

X and Two A)

Distance runners 70 to 80 20 to 30

Track sprinters 25 to 30 70 to 75

Nonathletes 47 to 53 47 to 53

Force regulation in muscle

Number and types of motor units recruited.

• More motor units = greater force.

• Fast motor units = greater force.

Muscle length. • “Ideal” length for force generation.

• Increased cross-bridge formation.

Force-Velocity Relationship

• At any absolute force the speed of movement is greater in muscle with higher percent of fast-twitch fibers.

• Higher peak power

• The maximum velocity of shortening (contraction) is greatest at the lowest force.

• True for both slow and fast fibers

• Example of trying to lift 100 lbs vs 1 lb • Need less force production to overcome the

resistance at 1 lb compared to 100 lbs

Muscle Force-Velocity Relationships

Skeletal Muscle and Aging

• Sarcopenia – age related loss of muscle mass and function

• The rate of loss of muscle power (3-4%/year) is however about 2 fold greater than that of isometric force (1- 2%/year)

• Power needed for activities of daily living

• Size and number of muscle fibers ↓ with age • Type I and Type II

• Strength ↓ offset by resistance exercise

1RM Testing

• Gold standard when evaluating dynamic muscular strength

• Requires the client to exert maximal force dynamically through a ROM in a controlled manner while maintaining proper technique

• It is often difficult to obtain an accurate and reliable 1RM for a first timer

• May be under the number of attempts or because the client may have unstable technique

• If experienced; 1RM is more reliable

H:Q Ratio

• Hamstring strength (N*m) / quadriceps strength (N*m) x 100

• Why is this important: • Lower H:Q ratios are associated with quadriceps-

dominant patterns. • H:Q ratios in healthy subjects range from 0.5 to 0.8

• “Athletes with lower H:Q ratios are thought to preferentially use their quadriceps muscles to stabilize the knee during dynamic activities (Hewett 2000)”

• This suggests that inadequate quadriceps or hamstring strength (H:Q) can result in compensatory mechanisms that may place an individual at risk for ACL injury.

Biodex Dynamometer

https://www.tien-i.com/blog_detail/17-why-torque-is-so-important-to-hand-tools

What can the Biodex do?

• Control speed or rates of a movement (degrees per second)

• Velocity

• Test both isometric and isokinetic movements

• Used to test a wide range of muscle actions

• Used by physical therapists and rehab clinics for rehabilitation

What about Force and Velocity?

• We can measure the force applied to the attachment of the biodex for the specific movement either during a static contraction (isometric) or during a dynamic (isokinetic) contraction.

• Additionally, we can control the velocity at which the movement is performed and measure the amount of force at different velocities.

Linear Position Transducer

• Measures barbell velocity in resistance training

• May help design resistance training programs

• Velocity assessment is becoming more popular as an alternative to using percentages based on an individual’s 1RM

• Concept is based on the load- velocity relationship

Push-Up Test

• Tests of upper-body muscular endurance • Pectoralis major

• Anterior deltoid

• Triceps

• No time limit and requires only minimal equipment

• Performed in a continuous fashion and requires the subject to maintain a straight back at all times

• The test is stopped when proper technique cannot be maintained for two consecutive repetitions

Push-Up Classification

Exercise and muscle fatigue

Muscle fatigue

• Fatigue defined as a decline in muscle power output

• Decline in muscle power output occurs due to: 1. Decrease in muscle force production at cross-bridge level

2. Decrease in muscle shortening velocity

Cause of muscle fatigue dependent upon exercise intensity that produced fatigue

Muscle Fatigue

Mechanisms Responsible for Muscle Fatigue

Mechanisms of fatigue during heavy, very heavy, and severe exercise (1-10 min).

• Causes of fatigue are multifactorial-range from decreased Ca+2 release from SR to accumulation of metabolites that inhibit myofilament sensitivity to Ca+2

• Key metabolites that contribute to fatigue include increases in Pi , H +, and free

radicals.

• H+ ions bind to Ca+2 binding sites on troponin-preventing Ca+2 binding and contraction.

• Both Pi and radicals modify cross-bridge head and reduces number of cross- bridges bound to actin.

• Collectively, these factors act to promote fatigue.

Mechanisms Responsible for Muscle Fatigue

• Mechanisms of fatigue during moderate intensity exercise (>60 min).

• Causes of fatigue during prolonged endurance exercise include increased radical production and glycogen depletion.

• Accumulation of Pi and H + in muscle do not contribute fatigue during moderate

intensity exercise.

• Radical accumulation in muscle fibers modifies cross-bridge head and reduces number of cross-bridges bound to actin (force production reduced).

• Depletion of muscle glycogen reduces TCA cycle intermediates and decreases ATP production via oxidative phosphorylation.

Muscle Cell Swelling

• Training induces skeletal muscle growth • It’s a slow process

• Muscle growth can occur in as little as 2 weeks • However, it may be due to edema (swelling)

• Acute swelling may be viewed as a positive response following RT

• Indication of future growth?

• Long term swelling is an indirect marker of muscle damage

Pre Post 5 min 10 min 30 min Bost bout 2

5 min bout 2

10 min bout 2

30 min bout 2

3

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

Pre Post 5 min 10 min 30 min Bost bout 2

5 min bout 2

10 min bout 2

30 min bout 2

M u

s c le

T h

ic k n

e s s (

c m

)

Time Course of Muscle Swelling

Muscle Thickness at 70% Site (cm)

Experimental

Control

A*

b* b*

c*

Procedures for Lab 3

H:Q Protocol

• We will utilize the system and make the necessary adjustments based on the subject

• Subject will perform 10 concentric repetitions for the knee extensor muscles and knee flexor muscles

• Subject will perform the movement as hard and as fast as possible against the pad

• Velocity is set 120° • Dominant leg will be utilized for lab

• Which leg you kick a ball with

Fiber Type Composition Protocol

• Based on an individual’s muscle fiber type composition, we can be predicted how quickly an individual will fatigue.

• For this protocol, the subject will perform knee flexion and extensions for 50 consecutive reps at a velocity of 180°/sec.

Fiber Type Composition Protocol

• The torque of first 5 extensions and the torque of the last 3 extensions will be used to determine the fatigue index and fiber type of the individual.

• For the max torque, take the average of the three highest values from the first 5 extensions. This allows for a familiarization period if it occurs.

• The final torque will be the average of the final 3 extensions.

• Calculate: • Fatigue Index % • % Fast Twitch Muscle Fiber

Composition • % Slow Twitch Muscle Fiber

Composition

1RM Procedure

• Have your client warm up by completing 5 to 10 repetitions of the exercise at

40% to 60% of the estimated 1-RM.

• Have the client rest for 1 min. This is followed by 3 to 5 repetitions of the exercise

at 60% to 80% of the estimated 1-RM.

• Have the client rest for 2 min and attempt the 1-RM lift. If successful, increase the

weight conservatively. • 5% to 10% for upper body exercise and

• 10% to 20% for lower body exercise.

• The client should rest 2 to 4 min before attempting the next weight increment.

• Follow this procedure until the client fails to complete the lift. The 1-RM typically

is achieved within three to five trials.

• Record the 1-RM value as the maximum weight lifted for the last successful trial.

Bicep Curl Procedure

• Stand against the wall with your heels and shoulders.

• From a full extension of the elbow, lift the dumbbell all the way towards your shoulder

• Bring the dumbbell back to its starting position (elbow fully extended)

• Complete as many repetitions as possible until you are no longer able to maintain a neutral spine position or complete any more deadlifts

• Record the total number of deadlifts completed

Push-Up Test Procedures

• Step 1: Lead the subject through a 10 min warm-up that includes both a general warm-up and dynamic stretching routine targeting the musculature of the upper body

• Step 2: Instruct the subject to assume the proper starting position

• Men: standard position

• Women: modified position

Men

Women

Push-Up Test Procedures

• Step 3: Have the subject lower the body while maintaining a straight back until the chin touches the mat. The stomach should not touch the mat at any time during the assessment

• Step 4: Once the chin touches the mat, the subject should push by extending the arms until achieving a straight-arm position. Record each successful push-up as it is performed

• Step 5: Without resting, the subject should repeat steps 3 and 4 until no longer able to maintain a straight-back position or complete any more push-ups

• Step 6: Record the total number of push-ups completed. Compare the subjects results with the data presented in table 12.9 and record the appropriate classification

In-Person Lab

• Please wear appropriate clothing and shoes for testing • Athletic wear

• No jeans

• No sandals

• For the lab assignment, you will input your data and your partner’s data for comparison

• We will begin testing once the class starts