Assessment of Muscle Strength, Endurance and Flexibility

EXS 490

 

Why Assess Musculoskeletal Fitness?

•      The “fitness” of our musculoskeletal system is related to:

•      Function: our ability to perform tasks requiring muscle strength and power

•      Health: risk of chronic diseases and/or injury

•      Function:

–    Ambulation

–    Recreation / leisure

–    ADL’s

•      Health:

•     Falls

•     Chronic low back pain

•     Glucose Intolerance

•     Decreased metabolic rate and obesity

 

Purpose of Physical Assessment

•      Document disabilities and impairments

•      Detect previously unrecognized conditions

•      Provide therapy for reversible issues

•      Establish a baseline for future planning

•      Identify need for specific exercise prescription

•      Assess efficacy of intervention

 

Purpose of Measurement

•      Describe:    to define the population

•      Screen:       identify individuals at risk

•      Assess:       determine the degree of decrement and determine appropriate                                       intervention

•      Monitor:     review progress of individual and efficacy of treatment

•      Predict:       identify expected outcomes/set goals

 

Choosing an Assessment Tool

•      Factors that must be considered prior to administering a physical assessment:

–    Age of the participant

–    Physical limitations of the participant

–    Goals of the assessment

–    Testing environment

–    Availability of equipment

 

Assessment Considerations: Pre-testing

•      Physician clearance and/or referral, if necessary

–    ACSM guidelines

•      Medical history

•      Activity history & PAR-Q

•      Lifestyle history

•      Resting HR and BP

•      Familiarization (practice) (4-9 RT sessions recommended by Kraemer et al., 2005)

 

Other Testing Considerations

•      In active/semi-active individuals:

     Use standard tests, modified as appropriate

•      Delivery of test instructions

•      Precede performance testing with appropriate warm-ups

•      End performance testing with appropriate cool-downs

–    Mostly stretching for strength

•      Make pre- & post-testing conditions the same

–    Time of day, fatigue, motivation, all matter

•      Appropriateness of instrument

–   specific to your population

–   validity

–   reliability

–   sensitivity

–   acceptability

–   practicality

 

Sources of Error during Performance-based Tests

•      Client

–   Motivation, fatigue

•      Technician

–   Experience with technique, bias, standardization, encouragement

•      Equipment

–   Calibration, appropriate fit to client

•      Environment

–   Room temperature, time of day, distractions

 

Musculoskeletal Assessment

•     Muscle Fitness

–   Strength vs endurance vs. power

–   Total body fitness vs. specific muscle fitness

–   Performance or functionally oriented?

•     Skeletal Fitness

–   Bone densitometry vs. ultrasound

 

Testing Modalities

•      Muscle Strength/Endurance:

–    Dynamic or static strength (free-weights/machine, isometric or isokinetic dynamometry)

–    Strength (1-RM) and endurance not well correlated

•      Muscle Power:

–    Wingate Anaerobic Power test, isokinetic dynamometry, vertical jump, stair climb

•      Flexibility Assessments:

–    Goniometers

–    Inclinometers

 

Assessment of Muscle Strength: 1-Repetition Maximum

•      Regions tested:

–    Common: bench press & leg press (ACSM)

–    Additional: arm curl, lat pull-down, leg extension & flexion

•      Considerations:

–    Risk of injury (reduce by including warm-up; spotting and monitoring client)

–    Physical limitations of client

–    Mode of testing (free weights vs. machine)

 

Assessment of Muscle Strength: 1-Repetition Maximum (how to)

•      Instructions:  (Kraemer et al. Ch 3 in Skinner, 2005)

–    Warm up: 5-10 reps at 40-60% of estimated 1-RM

–    1 min rest with light stretching specific muscle group

–    3-5 reps @ 60-80% of estimated 1-RM

–    Increase weight conservatively and have client attempt 1-RM; allow 3-5 min. rest between successive attempts; continue until client fails to complete the lift

–    1-RM should be achieved in 3-5 attempts

•      Evaluation:

–    Normative data available for most ages

–    Expressed as relative strength (1-RM/body weight) in kg

 

Example of 1-RM Values

1RM bench press (kg) for collegiate athletes:

Div 1 Linebacker          163

Div 1 QB                     126

College BsktB male      102

College BsktB female   51

College track female     47

From Baechle and Earle, NSCA Text, 2000

 

Modifications of RM testing

•      While the estimated injury rate during 1-RM testing is relatively low, modifications of this technique may be suitable for certain populations

E.G.:  6-RM strength test

    - 5-10 reps at 50% estimated 6-RM

    - 1 min rest with light stretching

    - 6 reps at 70% estimated 6-RM

    - 2 min rest

    - 6 reps at 100 to 105% of estimated 6-RM

    - 2-3 min rest

    - Adjust weight up or down by 2.5-5% and try 6-RM again

    - Not more than 2 attempts

 

Estimating 1-RM from Higher RM

Prediction of 1-RM from endurance testing is valid only if reps in endurance test are <10:

•   Men: 1-RM= weight lifted (lb)/(1.0278-reps to fatigue x 0.0278)

•   Women (40-50yrs): 1-RM= (0.92 x weight lifted in kg) + 0.58 x repetitions) – 3.41

•   Older women (60-70 yrs): 1-RM=(0.92 x weight lifted in kg) + 0.79 x repetitions) – 3.73

 

Assessment of Muscle Strength: Isometric Dynamometry

•      Devices used:

–    Handgrip dynamometer: grip strength

–    Leg & back dynamometer: lower extremity strength

•      Considerations:

–    Appropriateness of testing device for population (i.e., size, height, etc.)

–    Physical limitations of client

–    Not ideal if RT was dynamic (specificity issue)

Assessment of Muscle Strength: Isometric Dynamometry

•      Instructions:

–    Handgrip: upright posture, arm at side, maximal effort, best of 3 maximal efforts

–    Leg: trunk erect, knees flexed to 130-140Ί, hold bar across thighs and extend legs, best of 3

–    Back: erect posture, knees extended, alternated grip on bar and maximal upward lift, best of 2

•      Evaluation:

–    Data standardized to average adult; for >50 years, reduce normative scores by 10%

–    Expressed as absolute or relative strength in kg

 

Assessment of Muscle Strength: Isokinetic Dynamometry

•       Assesses strength development at constant speed

•       Can assess site-specific strength as allowable by testing device

•       Protocol:

–     Speed set at 30-60Ί/sec

–     2-3 submaximal trials, followed by 3-5 maximal trials (till drop in performance noted), best of max. trials

–     Measured as peak strength (lb or kg) or peak torque (ft-lb, Nm)

•       Norms provided by manufacturer (may vary by instrument, speed, etc.)

 

Assessment of Muscle Endurance: Free-weight or machine-based

•      Three suggested techniques:

–    Maximal # of lifts at 70% of 1-RM weight

•    No norms, but most individuals should be able to lift this weight 12-15 reps

•    Must standardize lifting velocity

–    Bench press at fixed weight (YMCA)

•    Maximal repetitions at a cadence of 30 reps/min

–   Test ends when cadence cannot be maintained

•    Men: 80-lb bar; Women: 35-lb bar

•    Norms for 18-65 yrs of age

–    Seven item battery (arm curl, bench press, lat pull-down, tricep ext., leg ext., leg curl, bent-knee sit-up)

•    Weight set as % of body weight (use table)

•    Measure # of reps, up to 15 per item, add total and compare to norms; college-aged referents only

 

Norms for 1 min sit-up test, 20-29 yr

# sit-ups in 1 min for % rank

%ile      men                  women

  90             52                49

  70             45                41

  50             40                35

  30             35                30

  10             30                23

From Baechle & Earle, NSCA Text, 2000

 

Assessment of Muscle Endurance: Isometric Dynamometry

•      Protocols:

–    Same testing devices as muscle strength. Choice of two protocols, each based on results of strength test

1) Begin test at maximal strength and measure the % decline in strength over a 1 minute period

2) Measure time client can maintain 50% of his/her maximal voluntary strength

•      Evaluation:

–    Data standardized to average adult; for >50 years, reduce normative scores by 10%

 

Assessment of Muscle Endurance: Isokinetic Dynamometry

•      Assesses endurance at fixed speed

•      Can assess site-specific endurance as allowable by testing device

•      Protocol:

–    Speed set at 120-180Ί/sec

–    1 maximal trial: measure # of reps until torque reaches 50% of initial value

–    Measured as # of reps

•      Norms provided by manufacturer (may vary by instrument, speed, etc.)

 

Assessment of Endurance: Push-Up Test

•      Easily administered field test to assess upper body endurance

•      Measures # of push-ups completed without rest

–    Men: standard push-up position, must lower to tester’s fist placed on the floor directly underneath client’s chest

–    Women: modified bent-knee push-up, no criterion for degree of lowering

•      Norms for adults: 20-60+ yrs.

•      Other tests include sit-ups, pull-ups

 

Assessment of Power: Wingate Anaerobic Power test (WAPt)

•      Measures “power” of anaerobic energy systems by measuring pedaling or arm cranking for 30 sec at maximal speed against a constant force

•      Measurement in Watts and age and gender specific norms are available (Inbar et al., 1996)

 

WAPt Protocol

•      Warm-up:

–    5-10 minute warm-up against light resistance to HR of 150-160 bpm

•      Test:

–    Start test by having subject pedal maximally against a low resistance to optimum cadence (~90 rpm)

–    Full load applied and 30-sec. test officially starts

•    Load applied dependent on individual (see chart)

–    Count maximal revolutions in 30-sec period, usually done by computer and translated to Watts

•      Cool-down:

–    3-5 minute cool-down of light cycling required!

–    HR return to ~120 bpm

 

Assessment of Power: Vertical Jump Test

•      Assessment of leg power

•      After warm-up, client should perform multiple trials until a plateau or decrease in scores are observed

•      Scored as difference between person’s standing height and maximum jump and touch height

•      Age-based norms available

 

Assessment of Power:  Stair Sprint Test

•      Measures leg power

•      Maximal speed to ascend six stairs (may be influence by body weight)

•      After warm-up, individual ascends stairs as fast as possible, taking 3 stairs at a time

–    Average distance traveled is usually 1.05m

•      Measured in kgm/min using following formula:

–    Force = clients body weight in kg

–    Distance = vertical distance of six stairs

–    Time = time from contact with first step, to contact with last step

 

Assessment of Muscle Function in Older Adults

•      Strength/Endurance:

–    Sit-to-stand (# reps in 30-sec.)

–     or Timed chair-stand

–    Arm curl (# reps in 30-sec.)

•      Balance

–    static vs. dynamic

–    one-leg stand (eyes open/closed)

•      Gait

–    Tandem gait, S-curve walk

–    Get-Up-and-Go test

 

Flexibility Assessments

•      Range of Motion (ROM) – generally what is estimated in flexibility assessments

•      Can be affected by joint structure and by ligaments, muscle and tendon surrounding

 

•      Devices

–    Goniometer – Most common, used to measure joint angles, good if techniques are standardized

–    Inclinometer – Similar principle to carpenter’s level, used to track arc of motion, acceptable for complex movements.

•     Many tests available, for almost any joint.

•     Relationship between flexibility and fitness still studied

–   More evidence apparent in older subjects

•     Relationship between flexibility and injury?

–   Some evidence of increased hip and knee injuries in inflexible ballet dancers

–   Differing results with low back pain

–   Differing flexibility needs seem to be correlated with sport specificity

–   Evidence of more economical running in inflexible runners

 

Measurement of Bone Strength

•      The ability of bone to resist fracture is related to its strength as a material

•      Bone mineral density provides an easily obtained, and accurate measure of bone strength (Bouxsein, 1993)

 

Dual Energy X-ray Absorptiometry (DXA)

•      DXA  measures BMD non-invasively and accurately

•      DXA uses low dose radiation to determine bone mineral density

•      The amount of x-ray that transmits through the skeleton is proportional to the density of mineral deposition within a specific region of interest

 

Bone Strength: Ultrasound

•      Quantitative Ultrasound is a relatively new tool for estimating bone strength, and hence risk of osteoporosis

•      Uses sound waves to estimate density at the heel, shin bone and kneecap by measuring the amount of attenuation of the waves as it is applied across the skeletal site

–    Attenuation affected by both the material and geometric properties of bone

Ultrasound: Screening Tool

•      Diagnostic capacity is still in question

–   Used as screening tool:

•   Low incidence of false negative tests, but large incidence of false positives

–   Poor at measuring efficacy of treatment and/or rates of loss due to poor precision error (5-10%)

•      Advantage over DXA with respect to radiation, ease of administration, cost

 

Summary

•      Choose proper assessment based on individual

•      Screen prior to testing

•      Use proper testing techniques to maximize accuracy of results

•      Interpret results to client

•      Re-test at later time, if appropriate, and ensure similar testing conditions