Muscular Strength/Endurance and Flexibility

KINS – 152 Exercise Physiology

Introduction

Muscular strength and endurance are measures of muscular fitness. Muscular strength is the maximal force generated by a specific muscle or muscle group at a specified velocity. Muscular endurance is the ability to maintain a submaximal force (i.e pushup tests). Muscular strength tests can be divided into 2 basic types. Dynamic strength the force generated by concentric, eccentric, or isokinetic contraction (i.e. 1 repetition maximum). The speed of movement is often not controlled in these measurements. Static strength measures the force generated by muscles during an isometric contraction. During an isometric contraction there is no shortening of the muscle and no joint movement. Muscular fitness testing is plagued by problems of standardization techniques to quantify muscular fitness due to types of muscle contraction (concentric vs eccentric), changes in force with respect to joint angle, and speed of contraction. The National Strength and Conditioning Association (NSCA) and American College of Sports Medicine (ACSM) have tried to address these problems by standardizing muscular strength tests. However, the present normative and standard data relating to muscular fitness are invalid, unreliable and/or outdated.

A new approach to assess muscular fitness and endurance is isokinetic testing. Isokinetic testing can be used to assess muscular strength through a range of motion at a constant velocity. The equipment measures rotational force, torque, generated. Torque refers to a rotational force that is applied about an axis. It is equal to the force applied to lever and measured in foot-pounds or Newton-meters.

Torque = Force x lever arm distance (units are Ft-Lbs or Nm)

The ability to generate muscular force is dependent on the velocity of the contraction (Figure 1). The greatest force a muscle can produce is at low velocities. Therefore, as velocity increases the amount of force generated is decreased. This relationship is also related to the power (F x D/T) whereas: low power is generated by low force and high velocity: moderate velocity and moderate force generate greatest power: and low velocity and high force generate the low power (Figure 2). At low velocities (30-60° per sec), isokinetic testing ...

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Torque = Force x lever arm distance (units are Ft-Lbs or Nm)

Figure 1: Force versus velocity

Figure 2: Power versus velocity

Athletes with higher percentage of type II fibers are able to generate more force at higher velocities (power) versus those with slower type I fibers. Also the fatigue rate during repetitive contractions at certain velocities can be used to indirectly determine fiber type distribution. Humans with a greater percentage of type II fibers (fatigue prone) will have a greater fatigue rate than type I fibers (fatigue resistant). It also appears that muscle can be trained (specificity of training) to generate more power at higher velocities. In most team sports, power is the most crucial variable in terms of explosive athletic performance but is often ignored by coaches and athletes.

Another important component of physical fitness testing is flexibility. Flexibility is the maximum ability to move a joint through a range of motion. Flexibility is dependent on a number of factors including muscle temperature, muscle blood flow and prior exercise. It is also dependent on physical activity and age. Physical activity appears to be the most important determinant of flexibility. Physical inactivity results in the shortening of connective tissue and results in the loss of ROM about a joint. Age also plays a factor due to loss of elastic properties of the connective tissue and decrease in physical activity. However, flexibility can be improved due to physical inactivity and/ or age with a flexibility exercise program.

Flexibility is specific to the movement of the joint. Therefore, flexibility in one area does not represent whole body flexibility. Flexibility can be measured by a number of means including goniometers, flexometers, and inclinometers which measure the ROM. The most popular flexibility measure in the health and fitness setting is the sit and reach test. The sit and reach test measures the flexibility of the trunk indirectly by measuring how far one can reach while sitting down. It is often used to assess the potential for lower back pain but research indicates it correlates poorly with low back flexibility. The rationale for this is unproven and has not been demonstrated (ACSM, 1995)

The purpose of this laboratory is to become familiar with testing of muscular fitness (muscular endurance, static and isokinetic) testing and become proficient in measuring lower trunk flexibility.

Procedures:

Muscular Fitness

Isokinetic (Lido)

Isokinetic testing will be performed on all subjects at speeds corresponding to 60, 180 and 240 degrees per sec
Each individual will perform 3-5 maximum knee extension contractions at the various speeds
Record your peak torque for each three speeds: slow (60°), moderate (180°) and fast (240°)
Record values on board for each individual

Static Strength (hand dynamometer)

Isometric hand grip strength will be administered
Adjust hand grip width of the hand dynamometer so it fits comfortably.
Have the subject stand erect with arms relaxed and by the sides
Place hand dynamometer in hand with dial facing outward
Have subject squeeze hand dynamometer as hard as possible while keeping the arm immobile
Repeat 3 times record best effort

Dynamic muscular endurance (push up test)

For males, assume standard push up position with back straight, head up, hands placed shoulder width apart
Place your fist on the floor below and count the number of repetitions performed by the number of times the chest touches your fist
For females, modify the standard push up position by having them kneel with their knees bent at 90° with ankles crossed.
There is no criteria for completing a push up do not place hands below chest
Count the number of consecutive repetitions performed without rest

Flexibility - Modified sit and reach

Perform a moderate warm-up
The test should be performed with a smooth movement and during exhalation
Have subject remove shoes and sit with back flat against a wall
Place the end of the sit and reach against their feet
The heel should be placed about 10-12 inches apart and feet should flat against the side of the sit and reach box
Have subject reach as far forward with back flat against wall record the position with a meter ruler as zero
The participant should slowly reach forward with the hands parallel and reach as far forward as possible with minimal discomfort. Be sure to keep hands on yardstick and knees stay extended.
The maximum reach as measured by the ruler is the score. Repeat test 3 times. The best trial is used to assess the individual flexibility
Make sure to instruct the patient to not hold breath or not to stretch to where it is causing undue pain.
Refer to table for normative data.

Data Analysis

Make a table of all your results and compare them to norms.
When appropriate interpret absolute and relative norms
Graph the peak torque versus speed for the isokinetic test

Discussion (Please read Ch 7 & 8 , pages 150, 399-402)

1) Which test measures muscular fitness the best? Are the values for each muscular test

consistent? Why? Can muscular fitness be assessed by one test?

2) Based on your graph, at what velocity do you develop the most force? At this velocity do

you also reach peak power? Why?

3) How would you use this knowledge to train an athlete competing in a team sport? You can

choose any team sport to answer this question.

How much potential does a sprinter have who can run the 100 yd dash in 17.0 secs? Why?

What sport might this individual excel at? Why?

Is the sit and reach test a valid measure of your flexibility? Why is stretching an important component of an exercise program? Are there other ways to improve your flexibility without stretching?