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chapter

66

Assessing Muscular Fitness

chapter

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:– 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:– Free weights– Constant-resistance machines– Variable-resistance machines– Isokinetic machines

(continued)

Assessing Strength and Endurance (continued)

• Hand grip dynamometry for strength:– 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 Constant-Resistance Machines

Free weights• Increase neuromuscular

coordination• Allow full ROM• Spotter may be required

Constant-resistance machines• Increase neuromuscular

coordination• ROM limited by machine• No spotter 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:– 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