Transcript Assessing Strength and Endurance

chapter
chapter
66
Assessing
Muscular Fitness
Author name here for Edited books
Objectives
• Identify methods for assessing muscular strength and
endurance
• Understand how type of muscle contraction affects force
production
• Differentiate between advantages and limitations of free
weights as compared to machine weights for assessment
• Learn sources of error in the assessment of muscular fitness
and how to control them
• Learn procedures for conducting 1-RM tests
• Appreciate challenges of conducting muscular fitness
assessments for the elderly and children
• Identify methods for assessing functional strength of elderly
adults
Muscular Strength
• Definition: The ability of a muscle group to develop
maximal contractile force against a resistance in a
single contraction.
• Force developed during muscular contraction is
determined by velocity of the contraction.
• Maximal force is determined at a velocity of zero.
Muscular Endurance
• Definition: The ability of a muscle group to exert
submaximal force for extended time periods.
• Similar to muscular strength, it can be assessed for
static (isometric) or dynamic contractions.
Types of Contractions
• Static (isometric): no visible change in joint
angle
• Dynamic: visible change in joint angle
• Types of dynamic contractions
– Concentric
– Eccentric
– Isokinetic
Concentric Contraction
• Force exerted by muscle or muscle group exceeds
external resistance or load
• Joint angle decreases
• Muscle shortens
Eccentric Contraction
• Joint angle increases
• Muscle lengthens while contracting
• Serves as a braking mechanism to decelerate body
segment movement
Isokinetic Contraction
• Maximal contraction of muscle or muscle group at a
constant velocity throughout entire range of motion
(ROM)
• Specialized machines control velocity of contraction
and adjust external resistance to match the force
produced at degree in the ROM
• Resistance is variable, velocity is constant
Figure 6.2
Assessing Strength and Endurance
• Isometric muscle testing: strength measured
as the maximum force exerted in a single
contraction against an immovable resistance
• MVIC: maximal voluntary isometric contraction
• Devices used to assess static strength and
endurance:
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Dynamometers
Cable tensiometers
Strain gauges
Load cells
(continued)
Assessing Strength and Endurance
(continued)
• Dynamic Muscle Testing: strength measured
as the maximum force exerted in a single
contraction against a movable resistance
• Devices used to assess dynamic strength
and endurance:
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Free weights
Constant-resistance machines
Variable-resistance machines
Isokinetic machines
(continued)
Assessing Strength and Endurance
(continued)
• Hand grip dynamometry for strength:
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Adjust hand grip to accommodate client’s hand.
Set dial to zero.
Stand upright and grasp dynamometer.
Arm position varies between protocol selected.
Client squeezes hand grip quickly and as tightly as
possible and then releases the pressure.
– Extraneous body motion is kept to a minimum.
– Do 3 trials for each hand; 1-minute rest between
trials.
– Select best trial for each hand.
Back and Leg Dynamometry
• Both use same dynamometer; score in kg
• For leg assessment:
– Start with knees flexed to 130o to 140o.
– Use pronated grip with bar across thighs.
– Extend knees but do not engage back muscles to pull bar
straight up.
• For back assessment:
– Fully extend knees and keep head and back erect.
– Use over-under grip with the bar across the thighs.
– Pull bar straight up by rolling shoulders without bending
backward.
Dynamometry Normative Values
• Can use dynamometric scores to determine
static muscular strength:
– Add best strength score for right hand, left hand,
legs, and back.
– Be sure to convert values to lb.
• Can use total dynamometric score to compute
relative static muscular strength score (divide
total score by body weight and multiply by 100).
Table 6.2
Table 6.3
Isometric Strength Assessment
• Use cable tensiometers or strain gauges.
• Follow standardized procedures closely.
• Select proper tensiometer based on anticipated
strength score (above or below 100 lb).
• Isometric assessments specific for single joint angle.
• Testing of multiple muscle groups is recommended for
overall strength score.
• Digital, handheld dynamometers are now available.
• Detailed procedures for digital dynamometry are in
appendix C of textbook.
Figure 6.4a
Figure 6.4b
Dynamic Strength and Endurance
• Constant-resistance machines or free weights are best.
• However, each only assesses maximal strength of
weakest point in joint ROM.
• Why? Mechanical and physiological advantage
changes throughout ROM, but resistance doesn’t.
• Variable-resistance machines (VRM) were created to
address this.
• Load changes throughout ROM with VRMs, so it is
difficult to assess maximal strength.
• Not recommended for strength assessment, but good
for resistance training programs.
Free weights Versus ConstantResistance Machines
Constant-resistance machines
Free weights
• Increase neuromuscular
• Increase neuromuscular
coordination
coordination
• ROM limited by machine
• Allow full ROM
• No spotter required
• Spotter may be required
• Weight increments may
be limited
• Machines may not
accommodate all body
types
Free-Motion Machines
• Eliminate many challenges of free weights and
constant-resistance machines
• Allow movement in multiple planes
• Can allow both constant- and variable-resistance
exercise
• Have many adjustable compartments
• Must simulate starting and ending body position of
validated muscular tests in order to use those
normative values
• Note settings during baseline assessment testing; use
them for follow-up assessment settings.
Dynamic Strength Testing
• One-repetition maximum (1RM): maximum weight
that can be lifted for one complete repetition of the
movement
• Involves trial and error in setting weights
• Has been applied to all age groups, but use
standardized technique to keep all clients safe.
• Spotting for your client is a must.
• 1RM bench press and leg press are good for assessing
upper body and lower body strength.
• Compute relative strength (maximal lift/body mass) and
use normative values.
Dynamic Endurance Testing
• Perform multiple repetitions with weight that is set
submaximal load (%1RM) or set %body mass.
• Individual should be able to perform 12 to 15 reps of
each exercise with weight that is 70% of 1RM.
(continued)
Dynamic Endurance Testing
(continued)
• Other options
– YMCA bench press test: gender-specific resistance
at set cadence
– Seven-item multiple repetition battery: maximum of
15 reps at set % of client’s body mass; add the
number of reps completed over the seven items; use
sum for overall categorization of dynamic muscular
endurance score
Isokinetic Assessment
• Assesses strength, endurance, and power.
• Machine generates resistance equivalent to client’s
muscular force generation (accommodating
resistance).
• Limb moves at constant, preselected velocity.
• Can evaluate peak torque, total work, and total power
for each muscle group tested.
Omnikinetic Assessment
• Accommodating resistance machine that adjusts to
both force and velocity generated by client (variable
force, variable velocity)
• No preset velocity
• Force and velocity adjust downward as client begins to
fatigue (self-accommodating)
• Assesses isokinetic strength and endurance of both
fast-twitch and slow-twitch motor units in the muscle
group.
Field Test Assessments
• Dynamic strength tests: Add additional
weight to client and have them perform the
desired movement as a 1RM.
• Dynamic endurance tests: maximum number
of reps performed for select calisthenic
exercises
– Pull-ups
– Push-ups
– Trunk curls
Sources of Error
• Possible reasons for measurement errors in
fitness testing:
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Client factors
Equipment
Technician skill
Environment
Additional Concepts
• Can estimate 1RM from submaximal tests
• Look for muscle balance: upper versus lower body;
agonist versus antagonist; left versus right side
• Best to express client strength results in relative terms
Working With Older Clients
• Muscular strength and endurance are important
for maintaining functional independence and
activities of daily living (ADLs).
• You can use 1RM assessments with this age
group.
• You may prefer to estimate 1RM from
submaximal loads:
– Brzycki (1993) equation and Wathen (1994)
equation are recommended
Functional Testing for Older Clients
• Rikli and Jones (2001) battery assesses
physical capacity and functional fitness through
2 tests:
– 30-second chair stand
– 30-second biceps curls
• These tests have functional application for
older clients’ ADLs.
• Be sure to follow standardized technique and
follow known safety precautions.
Working With Children
• Children can safely perform 1RM trials.
– Must be closely supervised
– Best results obtained using child-sized equipment
• No support for contention of premature closure
of epiphyseal plates due to strength training
• Follow standard guidelines when testing 1RM:
– Be sure to allow for familiarization trial(s)
– Focus on proper lifting and breathing techniques