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ASEP Procedures recommendation I: Accurate assessment of muscular strength and power

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The content of this manuscript is intended to assist the reader in collecting valid and reliable data for quantifying muscular strength and power. Various drawbacks and pitfalls of specific tests, as well as recommendations for the practitioner are also provided. The content is divided into sections covering isometric, isotonic, field tests, and isokinetic modes of exercise. Inherent in these modes are both concentric and eccentric muscle actions as well as both open and closed kinetic chain activities. For Isometric testing, contractions should occur over a four to five seconds duration with a one second transition period at the start of the contraction. At least one minute of rest should be provided between contractions. For each muscle tested at each position, at least three contractions should be performed although more may be performed if deemed necessary by the tester. For isotonic testing, the 1-RM test should be performed. After the general warm-up, the subject should perform a specific warm-up set of 8 repetitions at approximately 50% of the estimated 1-RM followed by another set of 3 repetitions at 70% of the estimated 1-RM. Subsequent lifts are single repetitions of progressively heavier weights until failure. Repeat until the 1-RM is determined to the desired level of precision. The rest interval between sets should be not less than one and not more than five minutes. The optimal number of single repetitions ranges from three to five. Data and guidelines of the following field tests are also provided; vertical jump, bench press, Wingate anaerobic cycle test (WAT), and the Margaria stair-run test. For isokinetic testing, details are provided for testing peak torque, work, power, endurance, and estimation of fiber type percentages.
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Accurate Assessment of Muscular Strength and Power 1
JEPonline
Journal of Exercise Physiologyonline
Official Journal of The American
Society of Exercise Physiologists (ASEP)
ISSN 1097-9751
An International Electronic Journal
Volume 4 Number 3 August 2001
ASEP Procedures Recommendation
ASEP PROCEDURES RECOMMENDATION I: ACCURATE ASSESSMENT OF
MUSCULAR STRENGTH AND POWER
LEE E. BROWN1 AND JOSEPH P. WEIR2
1Assistant Professor and Director of the Human Performance Laboratory, Arkansas State University, Arkansas
2Associate Professor, Program in Physical Therapy, Des Moines University-Osteopathic Medical Center
Des Moines, Iowa
ABSTRACT
LEE E. BROWN AND JOSEPH P. WEIR. ASEP Procedures Recommendation I: Accurate Assessment Of
Muscular Strength And Power. JEPonline. 2001;4(3):1-21. The content of this manuscript is intended to
assist the reader in collecting valid and reliable data for quantifying muscular strength and power. Various
drawbacks and pitfalls of specific tests, as well as recommendations for the practitioner are also provided. The
content is divided into sections covering isometric, isotonic, field tests, and isokinetic modes of exercise.
Inherent in these modes are both concentric and eccentric muscle actions as well as both open and closed kinetic
chain activities. For Isometric testing, contractions should occur over a four to five seconds duration with a one
second transition period at the start of the contraction. At least one minute of rest should be provided between
contractions. For each muscle tested at each position, at least three contractions should be performed although
more may be performed if deemed necessary by the tester. For isotonic testing, the 1-RM test should be
performed. After the general warm-up, the subject should perform a specific warm-up set of 8 repetitions at
approximately 50% of the estimated 1-RM followed by another set of 3 repetitions at 70% of the estimated 1-
RM. Subsequent lifts are single repetitions of progressively heavier weights until failure. Repeat until the 1-RM
is determined to the desired level of precision. The rest interval between sets should be not less than one and not
more than five minutes. The optimal number of single repetitions ranges from three to five. Data and guidelines
of the following field tests are also provided; vertical jump, bench press, Wingate anaerobic cycle test (WAT),
and the Margaria stair-run test. For isokinetic testing, details are provided for testing peak torque, work, power,
endurance, and estimation of fiber type percentages.
Key Tems: Resistance, Exercise, Isokinetic, Isotonic, Isometric, Contraction
Accurate Assessment of Muscular Strength and Power 2
INTRODUCTION
The assessment of strength and power is fundamental to athletic and human performance. Accurate knowledge
of an individual’s present level of muscular strength is important for both occupational functional capacity
evaluation and appropriate athletic and rehabilitation exercise prescription. This paper is designed to assist the
reader in collecting valid and reliable data pertaining to muscle strength and power. It is also designed to point
out various drawbacks and pitfalls as well as recommendations for the practitioner. To this end, this paper lays
the framework for the proper techniques of collection and interpretation of strength and power tests. It is
divided into sections covering isometric, isotonic and isokinetic modes of exercise. Inherent in these modes are
both concentric and eccentric muscle actions as well as both open and closed kinetic chain activities. While it is
beyond the scope of this paper to detail specific aspects of each of these, the reader should be aware that the
guidelines stated herein apply across each variation of human strength and power expression discussed.
GENERAL CONSIDERATIONS
Certain aspects of strength and power testing are generic to isometric, isotonic, and isokinetic measures. These
include planning, safety, warm-up, familiarization, and specificity. These issues will be addressed here and
factors that are unique to the specific testing modes will be addressed in the appropriate sections below.
Planning
Before undertaking any strength or power test a thorough plan should be in place regarding the type of data to
be acquired. For example, in isokinetic testing one may choose to record peak torque, peak or average power, or
work performed by the specific muscle group of interest. An examiner must determine a priori why and what
they are testing prior to the evaluation and what specific information is of interest. As noted below, strength and
power testing is specialized and returns information based on precise anatomical configurations, muscle length-
tension relationships and velocities of muscle action. The practitioner must also be aware of data reduction
techniques designed to eliminate extraneous information. If a clear understanding of the limitations of testing is
established prior to interpretation, there will be little chance for erroneous conclusions.
Safety
Suitable safety measures should be in place prior to commencing any testing battery. These include, but are not
limited to, inspection of equipment for broken or frayed components, appropriate lighting and temperature of
the environment as well as removal of all hazards near and around the testing site. Emergency procedures need
to be formalized. All testing personnel need to be familiar with these procedures and be certified in basic life
support. Most importantly, all testing should be conducted under the diligent supervision of individuals
experienced in physiological testing and measurement (i.e. an exercise physiologist with ASEP certification -
EPC). Attention to these simple safety measures will help ensure the protection of both examiner and examinee.
Warm Up
While there is little data directly supporting decreased injury risk associated with warm up activities, it is
physiologically reasonable to presume that increased muscle temperature and associated increased muscle
elasticity decreases injuries associated with testing. Warm up activities should include both a general and
specific warm up. The general warm up should consist of light activities such as low resistance leg or arm
cycling designed to raise muscle temperature. Specific warm up activities should include static stretching of the
muscle that will undergo testing. Additional warm up activities involving performing the actual test motions are
addressed in the specific test mode sections below.
Familiarization
Many of the individuals who will undergo strength and power testing may have little or no experience
performing the strength testing maneuvers. While strength testing has generally been shown to be reliable (2),
novice subjects will likely improve strength scores on subsequent testing simply due to increased familiarity
and comfort with the testing (54,71). This is especially true for strength tests that require relatively higher levels
of motor skill such as isotonic testing with free weights. If possible, novice subjects should be given a
familiarization session prior to actual testing. This should involve having the subject proceed through the entire
Accurate Assessment of Muscular Strength and Power 3
test protocol while giving maximal effort. The subsequent testing session should occur at a time in which
residual muscle soreness is over (e.g., 2 to 3 days).
Specificity
It is well established that various aspects of strength are associated with high levels of specificity. For example,
many testing devices on the market today are designed to test and exercise muscles using the open kinetic chain.
That is, only the isolated muscles of one joint are being examined. The information gathered from this type of
testing will lead the examiner to specific conclusions regarding that single joint. Different results and
conclusions may occur with multi-joint testing. Similarly, strength data derived from one type of contraction
mode may correlate poorly with data from another mode. Throughout, it should be kept in mind that testing
should be as specific as possible to the setting in which the information will be applied.
ISOMETRIC TESTING
Isometric contractions are muscle contractions in which the length of the muscle remains constant. No
movement occurs and therefore no physical work is performed; however in a strict sense, isometric contractions
do result in small changes in muscle fiber length and stretching of the elastic components of the muscle.
Isometric testing is also called static testing. The primary advantage of isometric strength testing is that, with
the proper equipment, it is relatively quick and easy to perform which lends itself to testing of large groups of
subjects. A variety of devices have been used to measure isometric strength. These include cable tensiometers,
strain gauges, and isokinetic dynamometers (with speed set to zero). In addition, with the exception of
isokinetic devices, testing equipment is relatively inexpensive. Further, computer interfacing with isometric
recording devices allows for the calculation of additional variables besides strength, such as the rate of force
development (35). Testing at multiple joint angles allows for determination of strength throughout the range of
motion.
The primary disadvantage of isometric testing is that the strength values recorded are specific to the point(s) in
the range of motion at which the isometric contraction occurred, and strength scores at one position may be
poorly correlated with strength scores at other positions (65,90). In addition, since most physical activities are
dynamic, it has been questioned whether static strength measures provide strength data that are specific to
activities of interest, and there are conflicting results in the literature as to whether isometric testing is predictive
of dynamic performance (88). However, isometric strength testing has been shown to provide information
predictive of occupational injuries associated with dynamic lifting tasks (22,45). Further, conflicting results
regarding static versus dynamic relationships may be a reflection of the joint angle used during isometric testing
(65).
In general, isometric strength testing has been shown to be highly reliable as assessed by reliability coefficients
(correlations between 0.85 and 0.99) (2). However, there may still be systematic error. For example, Kroll (54)
found high reliability (0.93) for repeated testing of the wrist flexors when analyzed with intraclass correlation
coefficients (ICC). However, significant differences in mean values were found across test days. Similarly,
Reinking et al. (71) found a relatively high reliability coefficient (ICC = 0.80, standard error of the mean (SEM)
= 19.4% of mean) for isometric testing of the quadriceps (60° of knee flexion) on separate days. However, the
mean values were significantly different, indicating that there were systematic increases in isometric force
across test days. These results suggest that a separate practice session prior to actual testing may facilitate
maximal performance and avoid introduction of systematic bias due to learning effects.
A variety of factors need to be considered with isometric testing. These include the joint angle at which to
perform the testing, the rest interval between consecutive repetitions, the number of repetitions to perform, the
duration of the contraction, and the time interval over which the force or torque is calculated. To date, there are
no specific guidelines for these factors and little data exists which evaluates different procedures.
Accurate Assessment of Muscular Strength and Power 4
Joint Angle
If isometric data are needed for defining strength at specific positions, then testing at joint angles associated
with these positions is warranted (22). However, if there is no joint angle preference, then other criteria for joint
angle selection may be used. Sale (73) has suggested that testing at the joint angle associated with the maximum
force output may serve to decrease error associated with minor errors in joint positioning. For example, the knee
position associated with maximal knee extensor force is approximately midway between full extension and full
flexion at approximately 65 degrees (55). Force-angle curves have been reported for a variety of joints (55)
which can be used to choose the joint angle to be tested.
Duration of Contractions
Sale (73) suggests that isometric contractions of five seconds duration are long enough to allow for peak force
development. Further, subjects can only maintain force at maximum for 1 second (73). Caldwell et al. (20)
recommended a contraction duration of four seconds with a one second transition period from rest to maximal
force. They also suggested that a four-second exertion ensures that a three-second plateau will occur and that
the mean force over this three-second period be recorded. Similarly, Chaffin (21) recommended contraction
durations of four to six seconds. Collectively, the available literature indicates that a contraction period with a
one-second-transition period and a four to five second plateau should be sufficient to achieve a maximal
isometric contraction. It should be noted however, that these recommendations are derived from experience of
the cited authors as opposed to experimental validation.
Rest Intervals
A variety of rest intervals have been proposed in the literature. Sale (73) has suggested that one minute of rest
be provided between trials. Caldwell et al. (20) recommended a rest interval of two minutes. Chaffin (21)
recommended two minutes of rest between trials if a large number of trials (e.g., 15) are performed but rest
intervals may be as short as 30 seconds if only a few trials are performed. Collectively, the available literature
suggests that a one-minute rest period should be sufficient to allow adequate recovery between trials. It should
be noted however, that these recommendations are derived from testing experience as opposed to experimental
validation.
Number of Repetitions
Edwards et al. (29) used three maximal voluntary contractions in testing the quadriceps since the first
contraction was usually “tentative”, while the second and third maximal contractions were usually similar to
one another (coefficient of variation = 2.8%). Zeh et al. (90) reported that the mean of three trials was highly
correlated with the first score of the three and concluded that one repetition provides “a reasonably good
indicator of the subject’s strength in that position”. They also noted that use of two repetitions increased the
precision of the measurement. The advantages of using few test repetitions is decreased injury risk, especially
for testing that stresses the lumbar spine (90). In addition, fewer repetitions will minimize the confounding
effects of fatigue on the strength data. However, their regression analysis did not address potential systematic
bias in the use of only one or two trials. While there is no consensus in the literature, three test repetitions are
likely to be sufficient to elicit a maximal value.
Averaging Interval
Simple mechanical recording devices (e.g., cable tensiometers) typically record the peak force or torque during
a contraction. However, computer interfacing of the recording devices allows for the recording of the mean
force or torque over a given time period. Chaffin (21) has recommended that forces/torques be averaged over a
three second time interval which “avoids the errors induced by tremor and motion dynamics”, however there is
no data directly supporting the superiority of a three second averaging interval over other time intervals.
Further, Sale (73) notes that subjects can only maintain force for 1 second, which suggests that the three-
second recommendation of Chaffin (21) may be too long.
Standardization of Instructions
Caldwell et al. (20) reported high variability in the force-time curves of subjects tested with different
instructions from the tester. They argued that subjects require “explicit instructions” or else they will “develop
their own strategies reflecting diverse interpretation of the task”. Chaffin (21) further recommends that
instructions should be non-emotional and objective and that factors such as noise, spectators, etc be avoided.
Accurate Assessment of Muscular Strength and Power 5
Positioning and Stabilization
Because muscle force is affected by muscle length, and torque output is affected by muscle force and moment
arm (53), changes in positioning can result in changes in isometric measurements that are independent of actual
differences in muscle strength. This is true not only for the specific joint tested but also in adjacent joints that
are crossed by a common muscle. For example, the hamstrings cross both the hip and knee joints and changes in
hip position will affect flexion force at the knee. Therefore, proper stabilization and consistent positioning are
critical for reliable and valid results.
Isometric Standardized Procedures
Isometric testing should involve contractions of four to five seconds duration with a one second transition
period at the start of the contraction. At least one minute of rest should be provided between contractions. For
each muscle tested at each position, at least three contractions should be performed although more may be
performed if deemed necessary by the tester (e.g., due to improved performance over trials). If possible, the
recorded force/torque should be sampled by a computer and averaged over time within each contraction. The
optimal length of the averaging interval has not been determined.
ISOTONIC TESTING
Isotonic contractions refer to contractions in which an object of a fixed mass is lifted against gravity. Most types
of weight training, either with machines or free weights, are referred to as isotonic. The derivation of the term
isotonic means constant (iso-) tension (73), and is technically inaccurate since the force required to lift a weight
changes throughout the range of motion. Other terms such as isoinertial (2,53,64) and DCER (dynamic constant
external resistance (52) have been used to avoid the inaccuracy of the term isotonic. However, as the term
isotonic is so ingrained in the language of exercise physiology, we argue that its use is acceptable provided that
it is operationally defined as described above and is used consistently in that context.
Isotonic testing is typically performed on machines (e.g., Universal, Nautilus, Cybex) that incorporate
adjustable weight stacks for resistance or with the use of free weights. The maximal amount of weight that can
be lifted in one repetition is called the one-repetition maximum (1-RM), and is the most common measure of
isotonic strength. Other measures such as the 3-RM, 5-RM, 10-RM, and the maximum number of repetitions
that can be performed at a fixed resistance can also be determined. While scores on these tests are correlated
with 1-RM, these measures are also affected by muscle fatigue and are not a measure of muscle strength per se.
The advantages of typical isotonic testing are that the necessary equipment is often readily available and, at
least for free weights, is relatively inexpensive (52). In addition, since most resistance training programs
emphasize isotonic training, isotonic testing is specific to the training that is typically performed. Further,
isotonic testing has generally been reported to be reliable (2).
The primary criticism of isotonic testing is that the 1-RM strength score is limited by the weakest point in the
range of motion (i.e., the so-called “sticking point”) (27,73). Therefore, the muscles used are performing sub-
maximally during the range of motion at positions other than the sticking point. In addition, the 1-RM score
does not provide information regarding the rate of force development or force output through the range of
motion (63). Further, typical 1-RM testing provides a measure of concentric performance and no information
about eccentric capability. Also, 1-RM lifts may not be specific to athletic events in terms of movement
patterns, contraction velocities, and accelerations (2).
Isotonic testing of 1-RM involves a trial and error procedure in which progressively heavier weights are lifted
until the weight exceeds the subject’s ability. Subsequent attempts are performed at a lower weight until the
heaviest successful lift is determined. Because of the multiple trials involved, the testing can be confounded by
fatigue (23) and a variety of factors need to be considered to optimize 1-RM performance. These include choice
of starting weight, rest interval between attempts, increments in weight between attempts, use of feedback
Accurate Assessment of Muscular Strength and Power 6
regarding weight to be lifted, and criteria for an acceptable lift. To date, there are no established standards for
these decisions and little data are available to help discriminate between options. The following
recommendations represent general procedures that have been employed in the literature (76,82,85) and which
are consistent with physiological (e.g., recovery from fatigue) and safety considerations.
Isotonic Standardized Procedures
If the subject has experience with the isotonic lift to be performed, a good starting point is to have the subject
estimate his/her maximum. From this estimate, desired percentages of the estimated 1-RM can be calculated.
Similarly, if the subject knows the maximal number of repetitions that can be performed at a given weight, 1-
RM can be predicted using the equations in the subsequent section entitled “Bench Press Prediction Equations.”
The subject should perform a general warm-up of 3-5 minutes of light activity involving the muscle(s) to be
tested (e.g., upper body ergometry prior to upper body strength testing). Next, the subject should perform static
stretching exercises of the involved musculature. After the general warm-up, the subject should perform a
specific warm-up set of 8 repetitions at approximately 50% of the estimated 1-RM followed by another set of 3
repetitions at 70% of the estimated 1-RM. Subsequent lifts are single repetitions of progressively heavier
weights until failure. The initial increments in weight should be evenly spaced and adjusted such that at least
two single lift sets are performed between the three repetition warm-up set and the estimated 1-RM. At failure, a
weight approximately midway between the last successful and failed lift should be attempted. Repeat until the
1-RM is determined to the desired level of precision. The rest interval between sets should be not less than one
and not more than five minutes (85). The optimal number of single repetitions ranges from three to five (52).
FIELD TESTS
Vertical Jump
The vertical jump (VJ) test is the primary test to assess muscular power in the legs. Unfortunately, there are a
variety of procedures and types of VJ reported in different studies (37). There are two primary forms of the VJ
test: the squat jump (SJ) and the counter-movement jump (CMJ). In the SJ, subjects lower themselves into a
squat position and after a brief pause, jump upwards as quickly and as high as possible. No down motion is
allowed immediately prior to jumping upwards. In contrast, in the CMJ subjects start in a standing position,
drop to a squatting position (counter-movement), and with no pause jump upwards as high as possible from the
bottom of the squat. In addition, both the SJ and CMJ can be performed with or without the use of arm motions.
When arm motions are employed, the subject is instructed to thrust the arms forward and upward during the
jump (75). When arm motions are not allowed, the subjects may be required to place their hands on their hips
(3) or hold their hands behind their back (10).
The CMJ results in jump heights and power values that are higher than the SJ (10,75). For example, Sayer et al.
(75) found CMJ jump heights that were 7% higher than SJ and peak power differences of 2.6%. Similarly, use
of arm thrusts has been shown to significantly increase both SJ (10 cm.) and CMJ (11 cm.) performance (36).
Indeed, the effect of arm motion exceeds that of the counter-movement. Currently, there is no consensus
regarding whether arm thrusting should or should not be used during VJ testing. However, Sayers et al. (75)
have argued that the SJ is preferred to the use of the CMJ for the following reasons. First, CMJ technique is
more variable than SJ technique, as the extent of the counter-movement is not consistent across subjects.
Second, regression equations used to predict peak power based on jump height and body mass are more
accurate when using SJ data. Regardless of whether arm thrusts are allowed, or whether one uses the SJ or CMJ,
the subjects need to be evaluated with the same procedures when tested repeatedly and the techniques used
during the testing need to be considered when evaluating test data against published data.
When using the SJ, knee angle and foot position have been shown to affect performance. Martin and Stull (59)
reported that optimal jump height occurred at knee angles of about 115° (as opposed to 90° and 65°) with the
feet separated by about 5-10 inches laterally and 5 inches in the anterior-posterior direction. However, different
studies have employed different knee joint angle requirements and some studies have let subjects determine
their own knee angle starting position. As with arm thrusts, use of different starting positions can affect VJ
Accurate Assessment of Muscular Strength and Power 7
performance and starting position needs to be consistent with repeated testing and should be considered when
evaluating test data against published data.
The reliability of various VJ tests have been reported to be quite high (3,4,11,31,36). For example, Ashley and
Weiss (4) found an intraclass correlation coefficient for a modified CMJ (no torso lean or arm swing) of 0.87
for repeated testing separated by 48 hours. Further, Arteaga et al., (3) found pooled coefficients of variation of
5.4% and 6.3% for SJ and CMJ scores (no arm thrusting was allowed) recorded during six test sessions over a
12 week period, suggesting that there is little variability or learning over time in these tests.
A great deal of variability exists in the literature regarding the warm-up and practice procedures employed
during vertical jump testing. In untrained female subjects, Goodwin et al. (31) used three submaximal practice
jumps prior to actual testing and found an ICC of 0.96 for repeated vertical jump testing. The change in the
body center of mass was the dependent variable. These results suggest that three practice trials are sufficient to
generate reliable vertical jump scores. In addition, Harman et al. (36) reported that three to five submaximal
practice jumps were sufficient for untrained subjects to achieve peak jumping technique, although no data were
presented to support this statement.
A variety of variables can be derived from the VJ. While direct measurement of power output requires the use
of a force plate, estimates of muscular power can be made using prediction equations that incorporate vertical
jump height and body mass (75). The Lewis formula has commonly been used to estimate power output during
the VJ test, however the validity of this formula has been challenged (37). Recently, Sayers et al., (75) reported
that the following equation, based on the SJ, resulted in an accurate prediction of muscular power:
peak power (watts) = 60.7 (jump height [cm]) + 45.3 (body mass [kg.]) - 2055;
SEE = 355 watts
For field-testing, use of the Sayers equation is straightforward and requires only the ability to record body mass
and VJ height. To record VJ height, two procedures are primarily used. First, subjects may simply place chalk
on their fingers and mark a wall as they reach the top of the jump. The difference between the mark at the
height of the jump and a mark from the fingertips at full extension while standing is recorded as the VJ height
(37). Second, commercial devices have been developed that record jump height (4). These devices have a
vertical pole with a series of horizontally oriented metal rods that are free to rotate about vertical when hit by
the fingers. VJ height is based on the highest pin that is moved at the top of the jump.
With respect to specific testing of the VJ, either the SJ or the CMJ may be employed, however the SJ is
preferred. Use of the equation of Sayers et al. (75) should be used to estimate muscular power from jump
height. At least three practice trials should be employed prior to recording test performance. Jump height can be
determined using either chalk marks on a wall or by using a commercial device. With repeated testing, it is vital
that use or non-use of arm thrusts be held constant and that for the SJ, the knee angle at the start of the motion
be consistent.
Bench Press Prediction Equations
The one-repetition maximum (1-RM) is the standard for determining isotonic strength. However, determining
1-RM values for large groups of individuals is very time consuming. For example, Chapman et al. (24) noted
that when testing 98 football players for the 1-RM bench press, three testers were required over six hours of
testing and five testing stations were employed. In addition, it has been suggested that 1-RM testing may expose
those being tested to increased injury risk (24). Therefore, the use of single set tests in which 1-RM values are
predicted based on the number of repetitions performed with a submaximal weight have been used. These types
of tests can markedly decrease the time involved in mass testing (24). In contrast to the six hours and three
testers required for the testing of the 98 football players described above, only one tester and 2.5 hours were
required to test the same subjects using a test in which the maximal number of repetitions that were capable of
Accurate Assessment of Muscular Strength and Power 8
being performed in a single set was determined. It should be noted however, that there are no data to indicate
that these tests are safer than typical 1-RM testing.
The most common exercise to which submaximal isotonic testing has been applied is the bench press, and will
be the focus of this section. Two types of 1-RM prediction tests have been developed. In the first type, subjects
perform the most repetitions that they can at a load that is some percentage of their estimated 1-RM (relative
load test). Alternatively, all subjects can be tested at the same load (absolute load test). The most common
absolute load test involves performing the maximum number of repetitions possible at a load of 225 pounds.
Because this test is frequently used in the National Football League, it has been called the NFL-225 Test (62),
however it is also used with collegiate and high school athletes.
A variety of papers have been published reporting 1-RM bench press prediction equations based on relative load
tests, and many of these have been evaluated by LeSuer et al. (57). In brief, seven prediction equations were
cross-validated with a sample of 67 college students (27 females). For the bench press, the equations derived
from Mayhew et al., (61) (1-RM = 100 rep mass/(52.2 + 41.9 exp [-0.055 reps]), r2 = 0.98, mean difference
between predicted and actual 1-RM = 0.5±3.6 kg) and Wathen (83) (1-RM = 100 rep mass / (48.8 + 53.8 exp
[-0.075 reps]), r2 = 0.98, mean difference between predicted and actual 1-RM = 0.5±3.5 kg) were reported to
most accurately predict the 1-RM bench press. The submaximal load used during the test of the maximal
number of repetitions was chosen based on subject experience to be a load that would cause fatigue (failure)
within 10 or fewer repetitions. Another study (47) also found that the Wathen equation resulted in predicted 1-
RM values that were closest to the actual 1-RM in a variety of upper body exercises in elderly subjects. Of note
is that these equations require only the recording of the mass lifted and the number of repetitions performed.
Gender appears to have little effect on the accuracy of the prediction equations (61), indicating that a common
regression equation can be used for both males and females. Similarly, adding anthropometric variables to
regression equations seems to add little to the predictive ability of the equations (26).
The absolute load NFL-225 Test has also been shown to accurately predict 1-RM bench press strength (24, 62).
The work of Mayhew et al. (62) resulted in a cross-validated prediction equation as follows:
1-RM (lbs) = 226.7 + 7.1 (# reps); SEE = 14.1 lbs.
To date, this equation represents the best prediction equation available for predicting 1-RM bench press from an
absolute load test. Two caveats are worth noting however. First, this test is only effective in subjects whose 1-
RM bench press is at least 225 pounds, and therefore may have limited utility in testing weaker subjects.
Second, the accuracy of the equation decreases as the number of repetitions increase beyond 10 (24,62), which
limits its effectiveness in very strong subjects.
With respect to specific use of submaximal tests to predict 1-RM bench press performance, both relative load
and absolute tests can be used. If using a relative load test, the equation of Mayhew et al. (61) or Wathen (83)
are recommended. If using the NFL-225 test, the equation of Mayhew et al. (62) is recommended. In addition,
the NFL-225 test can only be used with subjects whose 1-RM bench press is 225 pounds.
Wingate Anaerobic Cycle Test (WAT)
This test is intended to measure anaerobic power of the lower body. It is an exhausting test that should be used
with a population accustomed to strenuous vigorous exercise. The resulting data is an indirect measure the
ability of a subject’s lower body to produce high levels of power. Test results are divided into six equal periods
of 5-s where peak power, in Watts, is the highest average power output during any one 5-s period and mean
power is the mean of all six 5-s periods. Fatigue percentage is the difference between peak power and the
power from the lowest 5-s period. Normative values for this test have been published in the literature (41, 60).
Accurate Assessment of Muscular Strength and Power 9
Reliability and Validity
Test re-test reliability of the WAT has generally been reported to be higher than r=0.94 (38, 42). Validity of the
WAT is difficult to measure since there is no universally accepted “Gold Standard” of anaerobic measurement.
However, laboratory studies have been performed comparing the WAT and field tests of anaerobic power.
Moderate correlations with the WAT have been demonstrated between short explosive field measures such as
the vertical jump (mean power r=0.74) (78), 50 yard run time (relative mean power r=0.69) (78), Margaria-step-
test (peak power r=0.79) (5) and multiple repetition isokinetic testing (mean power r=0.78) (42). In addition, the
relative percentage of fast twitch fiber type of the legs has shown moderate correlations (relative peak power
r=0.60) (9).
Resistance
One of the most difficult questions to answer when administering the WAT is what resistance setting to use.
The classic resistance (in kiloponds; kp) is determined by multiplying the subject's body weight in kilograms
(kg) by the constant 0.075 (8,60). While 0.075 kp/kg of body weight appears to work well for sedentary adults
(5), subsequent research has demonstrated that this may not be the optimal setting for other populations (69,28).
In addition, mean power and peak power require different settings for optimization (28) due to the
force/velocity and power/velocity relationships discussed later. The optimal force/velocity relationship when
pedaling has been reported to be approximately 100 rev/min (28). Therefore, it is recommended that non-
athletes use a force of 0.090 kp/kg and athletes use a force of 0.100 kp/kg (41).
Standardized Procedures
During testing, the subject is asked to pedal against a pre-selected opposing resistance at the maximum pedal
rate possible for 30 s. A Monark cycle ergometer is most commonly used for testing. The ergometer should be
calibrated before each test, using standard calibration weights, throughout the full range of the pendulum. A
computerized Wingate testing system (Sports Medicine Industries, Inc., St. Cloud, MN) is available that counts
ergometer flywheel revolutions. Briefly, in consists of an optical sensor, attached to the ergometer frame, which
notes the passage of reflective markers on the ergometer flywheel at 10 cm intervals. A microprocessor then
converts these signals to rev/s.
The subject's saddle height is adjusted to produce five to ten degrees of knee flexion when the foot is at the
bottom dead center position. Warm-up should include 2-3 minutes of cycling at 1 to 2 kp with several all out
bursts interspersed. Resistance is set at the end of the warm-up period by asking the subject to pedal into the
increasing resistance. When the correct resistance is established the subject is instructed to stop pedaling. The
test procedures are then reviewed with the participant. The test begins with a free wheeling start as the
participant pedals as fast as possible with no resistance. The resistance is then either dropped instantly or
ramped up as quickly as possible. If a ramping protocol is used, the first two seconds of the test (when the
subject overcomes the inertia of the initial resistance) should be excluded from data analysis. This action
coincides with the activation of the microprocessor. Pendular oscillations at the onset of the test, outside the
pre-determined opposing resistance, should be minimized through manual restriction. Feedback concerning
elapsed time is given at 10, 15, 20, 25 and 30-s, with 30-s followed immediately by the command "STOP".
Consistent verbal encouragement is provided during the test but no visual feedback should be used. Following
the "STOP" command, the resistance is decreased and the subject cools down at a self-paced cadence to reduce
venous pooling in the legs.
Margaria Stair-Run Test
This is a short-term explosive power test that requires stair climbing. Since this test requires the participant to
climb the stairs two at a time it may not lend itself to use with a young undersized population. Power on the
Margaria test has displayed a moderate correlation (r=0.74) with mean power of the Wingate cycle test
representing adequate validity of anaerobic power (69).
Standardized Procedures
The test requires a staircase and two electronic switch mats interfaced with a digital time clock capable of
recording to one 100th of a second. The mats are placed on the 8th and 12th steps and step height should be
approximately 6.9 inches.
Accurate Assessment of Muscular Strength and Power 10
The subject begins approximately six feet (two meters) from the first step and is instructed to run at top speed
towards the stairs. Upon reaching the staircase, the subject should negotiate the steps two at a time until passing
the second switch mat. The mats will correspond to the fourth and sixth steps taken. Power (P expressed in
Watts) is then derived from the following formula:
P = (W x 9.8 x D)/T
where W = bodyweight of the subject in kg, 9.8 = acceleration of gravity in meters per second2, D = vertical
height (in meters) traveled between switch mats one and two, and T = elapsed time (in seconds) between switch
mats one and two. Increasing the approach distance (six and ten meters) has been shown to increase power
significantly (40).
ISOKINETIC TESTING
Isokinetic exercise is by definition constant velocity and represents a match between mechanically imposed
velocity and the subject’s movement (e.g., knee extension). The reliability of isokinetic testing has been
measured repeatedly (13,77,80) and found to be high. However, a variety of factors need to be controlled or
accounted for in order to generate reliable and valid data. These include factors such as choice of variable
measured (e.g., peak torque, work, or power), proper positioning and stabilization, and data reduction
procedures (e.g., windowing). The following will delineate confounding elements that may impact velocity
specific tests and focus on standardized testing procedures that should be considered when utilizing an
isokinetic device.
Peak Torque, Work, and Power
A wide range of performance variables are available for isokinetic data analysis. Of these, three are particularly
important for strength and power testing. Peak torque is defined as the product of mass, acceleration and lever
arm length. It is the maximum torque produced anywhere in the ROM and is easily identified as the top of the
torque curve (i.e. graphic display of dynamic torque vs. position). As such, peak torque is analogous to the
isotonic 1RM discussed earlier and exhibits an inverse relationship with velocity. While peak torque provides
the exercise professional with information regarding the greatest torque output of the limb tested, and is an
excellent indicator of the subject's maximum strength level, it does not take into account ROM.
Rotational work is defined as the product of torque and distance traveled and is most easily computed as the
area under the torque curve. Since work accounts for distance traveled it reveals a subject's ability to produce
torque throughout the ROM. Like torque, work is inversely related to velocity. Power may be the most
encompassing variable as it accounts for torque, distance and time. Power is defined as the work/time quotient
and demonstrates a parabolic relationship with velocity.
Strictly speaking, peak torque is a measure of an individual's maximum strength while work assesses their
ability to sustain torque output across a limb’s ROM. Power, since it utilizes time in the equation, may be best
described as one's ability to express explosive strength. Each variable communicates strength in a slightly
different manner and should be used judiciously regarding intended outcomes.
Isolation and Stabilization
Isolation in its simplest form is merely testing one muscle group alone with the exclusion of any other group
adding to the test outcome. This is best achieved through proper positioning and strapping (i.e. stabilization) of
the subject in the dynamometer. Using knee extension as an example, isolation occurs through the utilization of
waist and thigh stabilization. The purpose is to restrict motion to knee extension and flexion without extraneous
joint movement about the hip. This will insure that only the quadriceps and hamstring muscle groups are
producing torque through the dynamometer. For example, Weir and colleagues (84), measuring knee extension
torque at 60, 180 and 300 °/s with stabilized and non-stabilized conditions, have shown that extraneous
movements may reduce torque output and change the angle of peak torque production secondary to changes in
muscle length. This same potential error is present at all joints if care is not taken to control for extraneous
Accurate Assessment of Muscular Strength and Power 11
movement. For example, shoulder internal/external rotation torque may be inflated through the addition of trunk
rotation torque if proper stabilization of the torso is not achieved.
Axis of motion
Each dynamometer on the market consists of a lever arm attached to a dynamometer head. Resultant muscle
torque is recorded at this juncture through rotation of the lever. It is critical that the axis of rotation of the
machine and the joint being tested are aligned. If the lever axis and the joint axis are not in alignment, torque
measurements will be invalid. Rothstein (72) and colleagues make a cogent argument for the use of aligned axis
of rotation by stating that errors associated with misalignment may be amplified in joints where the axis
changes with movement. The knee and shoulder are such joints. They further state that since the axis of the
machine is stable any joint with uncontrolled movement will result in measurement error.
Gravity compensation
Since exercise on an isokinetic device is most often performed in a gravity environment, special consideration
must be taken to account for its effects. Using seated knee extension/flexion as an example, one can see that
performing a knee extension movement requires an individual to lift the weight of their limb and the
dynamometers lever arm against gravity. However, during seated knee flexion, gravity assists the motion by
pulling down on the limb and lever. In this scenario, flexion torque may be artificially inflated due to gravity
while the opposite is true for extension.
Without compensating for the effects of gravity the test results are subject to large errors. Winter (89) and
colleagues documented mechanical work errors ranging from 26% to over 500% during knee extension and
flexion exercise at 60 and 150 d/s.
Range of motion
Both physiologic and total range of motion (ROM) need to be considered when performing exercise on a
dynamometer. These are operationally defined as follows: physiologic ROM is the anatomical beginning and
end of the movement while the total ROM is the arc traveled through the physiologic ROM. For example,
shoulder motion from zero to 90 degrees and from 90 to 180 degrees of flexion both have the same total ROM
(90 degrees) but very different physiologic ROM. Since the physiologic ROM affects muscle length and joint
moment arms, it follows that valid comparisons of torque production must be consistent with respect to
physiologic ROM. Similarly, errors associated with ROM measurements may be magnified when interpreting
work and power variables. Since work is the product of torque and distance (W=TxD) and power is a function
of work and time (P=W/T), distance traveled must be precise for comparative purposes. By setting hard stops at
each end of the ROM, the practitioner can insure that all between and within subject comparisons involve the
same physiologic and total ROM.
Standardization of Instructions
Any instructions given to the subject should be consistent from one test to the next and from one subject to
another. Not all individuals respond to the same form of verbal encouragement. Therefore, instructions should
be concise and parsimonious. Furthermore, since the dynamometer is a unique piece of equipment it may not be
familiar to most subjects. This unfamiliarity may cause anxiety in some subjects and lead to misunderstandings
regarding test procedures. Therefore, verbal commands should be explicit as to every facet of the procedure.
This includes, but is not limited to, where to grasp the attachment, how to breath, what to do with the
contralateral limb, how to push in both directions, how to give a maximal effort, what constitutes one full
repetition (e.g. extension and flexion) and how many repetitions to perform.
Practice
Analogous to verbal commands for proper instruction is sufficient practice repetitions. Since the dynamometer
is novel to most subjects, they may require several practice trials in order to achieve reliable torque tracings. It
is recommended that one perform as many repetitions as needed to completely understand what is required
during the testing or training process. This may be as few as three for experienced resistance trained individuals
or as many as 15 for naive subjects.
Accurate Assessment of Muscular Strength and Power 12
Repetitions
Choosing the number of repetitions to include in a test is determined by what information is desired from the
test or what outcome from the exercise session. For strength testing there is no need to perform greater than five
repetitions but one may choose to perform as many as 50 repetitions when endurance is of interest.
Placing a limb in a pre-activated state (i.e. neural activation prior to movement) has been shown to significantly
affect strength variables. Neural pre-activation of muscle units in the exercising limb place that limb in a ready
state which in turn leads to greater torque production. Kovaleski and colleagues (49), using knee extension at
120 through 210 °/s, have documented the use of pre-load (prior neural activation) as superior to isokinetic
training and may afford individuals full ROM strength development based on a reduced acceleration range.
Additionally, the first repetition (beginning from a dead stop without a prior antagonistic muscle action) has
been shown to result in larger areas of acceleration prior to the constant velocity phase (18). Therefore, the first
repetition (of five) during strength testing may be discarded from data analysis as all subsequent repetitions are
immediately preceded by a pre-activation state.
Velocity order
Many dynamometers on the market today have a velocity range between 0 and 500 degrees per second (°/s).
The practitioner must decide which speed to use for testing or training depending on the desired result. When
testing at multiple speeds it may be beneficial to randomize the sequence in order to control for order effects.
However, there is conflicting evidence regarding whether velocity order significantly affects strength variables
such as peak torque, work and power. Timm and Fyke (80) have shown no significant difference in torque
measurements of knee extension at 60, 180 and 300 °/s when varying test speed sequence. However, Kovaleski
and Heitman (48,50,51) have shown velocity progression order to play a role in torque, work and power
production during knee extension at 30 through 210 °/s. The major difference between these seemingly
opposing views appears to be number of repetitions performed. While Timm (80) performed only five
repetitions, Kovaleski and Heitman (48,50,51) performed 10. Therefore, fatigue may have been a factor in the
latter studies and rest intervals may need to be adjusted accordingly.
Bilateral Deficit
Dynamometers can be modified to test both limbs simultaneously (14,15,16). When testing or training is
performed in this manner, the practitioner should be aware of the bilateral deficit phenomenon. That is, when
two limbs are performing maximal muscle actions simultaneously the resultant torque will be less than the sum
of the individual limbs tested in isolation. Brown and colleagues (14,16) have reported that females may show a
decrease in the bilateral deficit with increasing velocity from 60 through 360 °/s, which may be explained
through decreased activation of primarily slow-twitch muscle fibers (14,16). They have also shown significant
torque improvements unilaterally following bilateral training of the knee extensors and flexors at 60 and 180 °/s
(14) along with a decrease in the bilateral deficit with increasing velocity.
Load Range
It has been demonstrated many times (17,18,19,32,33,56,66,67,68) that isokinetic devices, despite their claims
of isokinetic movement, are not truly isokinetic. Exercise on an isokinetic device involves three main phases of
movement: acceleration, constant velocity and deceleration. Inherent in these phases are unique occurrences
that may confound test data and thereby test interpretation (1,6,12). However, the acceleration phase, which is
spent "catching" or matching the isokinetic velocity, is done without resistance from the dynamometer. In other
words, there is a portion of the available ROM during which there is no quantifiable external load. The ROM
with external load or that ROM when there is a match between isokinetic velocity and limb movement is
referred to as load range. Load range becomes increasingly smaller as velocity is increased
(17,18,19,56,66,67,68). The work of Osternig and colleagues (66,67,68) first showed this inverse relationship.
They detailed load range decreases from 92% to 16% at isokinetic speeds from 50 to 400 °/s.
Practically, this means that as the pre-selected velocity of an isokinetic device is increased an exercising
individual receives external overload through an ever-decreasing portion of the full ROM. Couple this effect
with the fact that torque is inversely related to velocity and the result is short-arc low-resistance exercise at high
Accurate Assessment of Muscular Strength and Power 13
speeds with the remaining ROM as acceleration or deceleration. In other words, exercise on an isokinetic device
at high velocities is primarily attempting to reach the pre-determined speed (accelerate and catch the lever arm)
or slow down prior to contacting the end stop (decelerate). Thus, acceleration and deceleration should not be
considered during test interpretation. However, data from these phases are often included in analysis and may
result in erroneous conclusions.
Specific errors associated with artifacts in the non-load range portions of the repetition have been identified and
will be examined in the sections below. Taylor et al. (77) documented increased errors with increased velocity
from 60 to 450 °/s and cautions against ascribing artifact torque to the exercising limb. Tis and Perrin (81)
caution that using a data reduction technique that eliminates the first and last 10 degrees of ROM may eliminate
acceleration and deceleration areas but may also eliminate the peak torque range.
Velocity Overshoot and Torque Overshoot
Prior to the limb receiving machine resistance it must pass through a free acceleration phase (74). Upon
engagement of the resistance portion (load range) there are artifacts manifested in the torque tracings.
Immediately following the acceleration phase of motion the lever arm and attached limb exhibit speed that is
greater than the pre-selected velocity by as much as 200% (70,74,81). This is followed by the dynamometer's
attempt at slowing the limb via a braking mechanism inside the power-head. Velocity overshoot occurs as a
function of the limb accelerating past the desired speed. The subsequent braking results in an obvious torque
spike as it slows the limb to the pre-selected velocity. The effect of this braking is mild at slow speeds such as
60 °/s but increases in magnitude with increased velocity. Velocity and torque overshoot are coincident at the
beginning of the flat load range.
This resultant torque overshoot is caused by the preceding velocity overshoot. As mentioned earlier this spike
will grow with increasing velocity as the braking mechanism of the dynamometer must account for ever
increasing amounts of velocity overshoot. The torque spike may dwarf actual peak torque produced by the
human muscle. Obviously, it is important to remove this artifact prior to test interpretation. At present no
dynamometer on the market will automatically remove torque overshoot so the practitioner must recognize the
artifact and not consider it during analysis. However, some dynamometer systems (e.g., Biodex) attempt to
control these effects by using a data reduction technique called windowing (87). During windowed analysis the
acceleration and deceleration phases of the repetition are eliminated and only the load range data is preserved.
This technique has been shown to increase the reliability of testing via the control of aberrant torque production
(87).
Lever arm oscillation
Another artifact inherent in the torque tracing is oscillation. This occurs immediately following torque
overshoot (25,74). Just after the acceleration phase there is a period of lever arm oscillation that is a function of
the length of the lever and the braking procedure to counteract velocity overshoot. The exercising limb is
attached to the dynamometer lever arm shaft distally but produces torque proximally and may therefore be
thought of as analogous to a long fishing pole. If one grasps a fishing pole at one end and applies a quick
whipping motion the distal end will oscillate back and forth for a short period of time until stabilized. Greater
oscillation occurs with greater lever arm length and greater velocities as the distal end attempts to "catch up"
and then decelerate to the speed of the proximal end (25,74). The probability of error is increased with the
inclusion of lever arm artifacts such as these as it may be impossible to determine actual torque measurements
apart from extraneous data. As with torque overshoot, windowing the data may remove some of the erroneous
data.
Impact Artifact and Isometric Spikes
At the other end of the repetition from acceleration is deceleration that culminates in the stopping of the lever
arm. Many of the confounding elements already mentioned during the acceleration phase occur in reverse order
during deceleration. The dynamometer begins to slow the lever arm in anticipation of stopping at the turn
around point. This causes the lever arm to oscillate somewhat and ultimately results in a large isometric spike at
Accurate Assessment of Muscular Strength and Power 14
the end of the repetition due to the lever arm impacting the mechanical end stop (89). The spike is greater with
increasing velocity, since the limb and lever are moving much faster upon impact. These spikes can be as much
as twice as great as the torque seen during load range and should not be confused with actual muscle torque
production (12,72,77,87).
Isokinetic Standardized Procedures
First position the dynamometer shaft so that it is aligned with the assumed axis of rotation of the joint being
tested. The subject is in either a seated or lying position with the back incline noted on a permanent
measurement scale. The contralateral limb is secured with straps as is the waist and torso. Arms and legs not in
use are either secured with or grasping the straps. Range of motion mechanical stops are set at the beginning
and end of the desired test ROM. The lever arm pad is positioned to place the inferior aspect immediately
superior to the most distal point on the limb. Warm-up on the isokinetic device consists of three submaximal
reciprocal concentric extension and flexion repetitions with increasing intensity (i.e. first repetition at 25%
perceived effort, second repetition at 50% perceived effort, etc.) at the slowest through the fastest speed (13,80).
In addition each subject completes two maximal intensity repetitions at each speed, then rests for one minute
prior to testing. More practice repetitions may be performed if the subject is not comfortable with the test.
Strength and power testing begin from a dead stop with the subjects' limb at one end of the ROM and consist of
five maximal concentric reciprocal extension and flexion gravity corrected repetitions with 30-s rest between
velocities (80). Each subject is encouraged to contact the mechanical end stops during both extension and
flexion motions. Consistent and identical verbal encouragement is provided during the test but no visual
feedback of torque generation is provided. The first and last repetitions are discarded, using only the three
middle reps for analysis, and all data are windowed to eliminate extraneous information as already discussed.
Repetition data is then reduced to strength variables such as peak torque (maximum value), mean torque
(average across all repetitions), total work (max product of torque and distance) or average work (average
product of torque and distance) and expressed in foot-pounds (ft/lbs) or Newton-meters (Nm). Average power
(torque/time quotient) and instantaneous power (product of torque and velocity) are expressed in Watts.
Force and Power/Velocity Curves
The interaction of velocity and human force production has been known for some time. Ever since Hill (34)
established the inverse relationship between force and velocity for concentric muscle actions, human beings
have tried to alter the curve through training and muscular adaptation. Likewise, the parabolic relationship
between power and velocity (44) has sport specific diagnostic and predictive value. In the case of isokinetic
dynamometry the force is rotational and therefore properly referred to as torque.
Since the overall shape of both the torque/velocity and power/velocity curves are well established, it is a simple
task to gather this information from individual subjects utilizing an isokinetic dynamometer capable of
measuring velocity specific torque and power. The data can then be used for comparison purposes between
athletes or as a baseline for future testing. The procedure is to perform a maximum torque test across a velocity
spectrum beginning at 60 °/s, and increasing the velocity by 60 °/s until the maximum velocity of the machine
(e.g.,400-500 °/s) or the individual has been met. As previously explained, it is very important to ensure that
data are evaluated only during the load range portion, as this will prevent the inclusion of extraneous artifacts.
Previous work (19) has shown that males and females display disparate levels of maximum attainable velocity
on this apparatus. Therefore the curves should be evaluated by gender. Figures 1 and 2 represent gender specific
data from our laboratory that are representative of strength/velocity relationships in college age subjects. Note
that not only do the absolute values of males exceed females but also the shapes of the curves are different. The
torque/velocity curve (Figure 1) of males is steeper than females and peak power (Figure 2) occurs later in the
velocity spectrum for males (240 °/s) when compared to females (180 °/s). While this may be partially
explained as a function of muscle mass there is evidence of underlying neural differences between genders (46)
that may further explain the disparity.
Accurate Assessment of Muscular Strength and Power 15
Multiple Repetition Testing
Any discussion of adaptations associated with training stimuli must include individual differences in limb
musculature and fiber type that predispose some subjects to reach greater gains in strength relative to inherent
force/velocity or power/velocity characteristics.
Torque/Velocity Curve
0
50
100
150
200
250
300
60 120 180 240 300 360 400 450 500
Velocity (degrees/s)
ft/lbs
Males Females
Figure 1. Concentric torque/velocity curve by gender measured on a Biodex System 3 Isokinetic Dynamometer.
Power/Velocity Curve
0
50
100
150
200
250
300
350
400
60 120 180 240 300 360 400 450 500
Velocity (degrees/s)
Watts
Males Females
Figure 2. Concentric power/velocity curve by gender measured on a Biodex System 3 Isokinetic Dynamometer.
Accurate Assessment of Muscular Strength and Power 16
Thorstensson (79) hypothesized that muscle quality plays a major role in strength expression. To test his
hypothesis Thorstensson took muscle biopsy samples from the vastus lateralis of 25 trained male subjects
between the ages of 20 and 30 years and stained them for slow twitch (ST) and fast twitch (FT) fiber type. He
then recorded maximal velocity of knee extension motions in an unloaded state and tested for peak torque
isometrically and isokinetically at 180 °/s. Strength test results were not different between individuals with low
and high percentages of FT muscle fibers when compared isometrically. However, when maximal velocity was
measured, significant differences became apparent. That is, subjects with a higher percentage of FT fibers
exhibited greater maximum velocity and strength with a positive correlation of r=0.75 between peak torque at
180 °/s and percentage FT fibers. It was concluded that a high proportion of FT muscle fibers would be
advantageous for high force output at fast motion velocities requisite for success in sport specific activities.
Wickiewicz and colleagues (86) studied the relationship between muscle architecture and the force-velocity
curve in 12 subjects who performed isokinetic knee extension strength at velocities ranging from 0 to 300 °/s.
Comparisons were then made with muscle samples of cadavers for linear displacement of muscle fibers and
architectural data. The results showed that greatest torque at high velocities was related to fast twitch fibers and
the number of fibers in series. Specifically, individuals with longer sarcomeres displayed less torque reduction
at fast velocities while subjects with a larger muscle cross sectional area exhibited the greatest torque outputs at
slow velocities.
Houston (39) examined the relationship between muscle fiber composition and maximal acceleration and torque
capabilities of the knee extensors in 27 subjects using an unloaded apparatus that did not restrict limb motion.
Muscle fiber composition was attained from the vastus lateralis of each subject using needle biopsy techniques
and compared to electromyographic and performance measures during knee extension movements. Positive
correlations between peak velocity and acceleration (r=0.69) were found, as well as acceleration and fast twitch
fiber percentage (r=0.4) with a trend toward a positive correlation between acceleration and fast twitch area.
Gender comparisons demonstrated that the electromechanical delay (time lag between the onset of electrical
neural activity and the beginning of acceleration) was similar for males and females. However, males produced
significantly greater force output than females evidencing a neural bias towards males.
In an experiment in our laboratory (15), following the protocol of Thorstensson, we compared the Wingate
cycle ergometry test with an bilateral isokinetic test of power and found significant correlations between the two
tests for peak power (r=0.84) and mean power (r=0.54) but not fatigue percentage (r=0.37). Wingate peak
power and mean power were significantly greater (p<0.05) than isokinetic values while fatigue percentage was
not statistically different between tests. Males exhibited significantly greater values across all variables when
compared to females with the exception of Wingate fatigue percentage. It was concluded that the bilateral
isokinetic test of power revealed a significant power profile with the cycle ergometry power test.
Multiple Repetition Procedures
The above information points to the ability to estimate an individual’s fiber type from isokinetic strength and
power tests. Specifically, the procedures for the Thorstensson multiple repetition assessment will yield fatigue
percentage of the quadriceps. This can be used to estimate the relative percentage of fast twitch fibers (%FT) of
the vastus lateralis. Subject physical set-up on the isokinetic dynamometer is identical to that discussed earlier.
The velocity should be pre-set to 180 °/s and the ROM limited from 90 degrees of knee flexion to 0 degrees of
extension (horizontal). The test consists of 50 maximal knee extension repetitions with a passive return to 90
degrees (no hamstring activity).
Determine the average peak torque of repetitions 1-3 and repetitions 48-50. Subtract the average of repetitions
48-50 from repetitions 1-3 then divide by the average of repetitions 1-3 then multiply by 100. The answer
(fatigue percentage, FP) should then be inserted into Thorstensson’s formula which will yield percent fast
twitch. 0.9 x (FP) + 5.2 = %FT (r=0.86, p<0.01)
Accurate Assessment of Muscular Strength and Power 17
SUMMARY
Care must be taken to insure proper use of any strength testing equipment and interpretation of data. The
practitioner should be aware of standardized testing procedures such as proper warm-up, safety (including
emergencies) and rest periods, isolation and stabilization of subjects and muscle groups as well as proper axial
alignment of the individual and the apparatus. Instructions should be clear and identical across subjects and
each participant should be afforded the opportunity to become completely familiarized with the procedure and
the apparatus prior to data collection.
A suitable plan should be in place detailing what information is desired from the test combined with the
knowledge of the specificity of strength and power results secondary to mode, procedure and apparatus. Tables
one and two identify possible choices of tests that are specific to a desired outcome.
Table 1. Recommendations for Specific Strength Tests and Outcomes
Desired Outcome Specific Test
1. Lower body strength 1RM Squat
2. Upper body strength 1RM bench press
3. Angle specific torque Isometric
4. Individual muscle torque Isokinetic five reps
5. Muscle Group torque Isotonic 1RM
Table 2. Recommendations for Specific Power Tests and Outcomes
Desired Outcome Specific Test
1. Lower body Vertical jump/Margaria
2. Upper body endurance Bench press for reps
3. Anaerobic endurance Wingate cycle
4. Muscle fiber type Isokinetic multiple repetition
Address for correspondence: Lee E. Brown, EdD, EPC, CSCS,*D, FACSM, Assistant Professor and Director
of the Human Performance Laboratory, Arkansas State University, State University, Arkansas
or
Joseph P. Weir, PhD, FACSM, Associate Professor, Program in Physical Therapy, Des Moines University-
Osteopathic Medical Center, Des Moines, Iowa
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