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 130-140º, 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 30-60º/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 120-180º/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