The standing heel-rise test for ankle plantar flexion: criterion for normal.

Background and Purpose. Manual muscle testing with the examiner providing the resistance has long been a standard test of muscle strength. Through the use of extremities acting as levers, clinicians have been able to effectively apply resistance to all muscle groups except the the ankle plantar flexors. As a result, a standing heel-rise test that uses body weight as the resistance has been substituted. The number of heel-rises that represent normal plantar-flexor "strength" and the ability of subjects to repeatedly use that "strength" remain unresolved. Because walking is an endurance task, the hypothesis tested by this study was that individuals without known weakness would be able to perform more than the standard recommended one to five standing heel-rises. The purpose of this study was to measure the number of standing heel-rises that individuals without known weakness could accomplish. Subjects. Two hundred three subjects were studied for their ability to do standing heel-rises, as is done when testing plantar-flexion strength using the upright test. There were 122 male subjects and 81 female subjects, ranging in age from 20 to 59 years. Methods. Each subject was asked to do as many standing heel-rises as he or she could, with careful monitoring of body and limb alignment and of ankle motion, with specific criteria for stopping. Results. The average number of heel-rises was 27.9 (SD= 11.1, minimum= 6, maximum= 70) for all groups and both genders, with no differences between male and female subjects. The lower 99% confidence interval was 25. Conclusion and Discussion. A recommendation is made to change the standard of testing plantar-flexion function, when using the standing heel-rise test, to require 25 repetitions for a grade of Normal.

Manual muscle testing (MMT) has been a standard clinical measure used to assess muscle forces since its introduction by Lovett[1] in the early 1900s. All grading is based on the ability of a subject to move voluntarily against gravity and to resist a force applied by an examiner.[2-5] A muscle is judged to have Normal strength when the patient can hold rigidly against the examiner's maximum effort.[2,5] We contend the purpose of the MMT is to identify areas of weakness that may prevent individuals from meeting the normal demands of daily life. This measure is different from quantifying the force generated by the muscles of athletes.

Measurements of muscle force are thought to be needed to enable clinicians to judge a patient's potential for function. In the case of walking, tests for hip, knee, and ankle muscles are required. In designing a manual testing system for the lower extremity, the basic challenge was to find techniques that enable examiners to exert a force (using mainly their triceps and pectoral muscles) to counter the force of muscles capable of supporting body weight. Leverage was the answer. When testing the hip muscles, resistance is applied proximal to the knee to give the examiner the leverage advantage of the full length of the femur. Similarly, muscles crossing the knee joint are challenged by applying the resisted force proximal to the ankle. The foot, however, lacks the length necessary for challenging the ankle plantar-flexor muscles. Static calculations indicate that normal plantar flexors are capable of producing a force that approximates 2.7 times the subject's body weight to counter the torque demand caused by the floor reaction acting on the forefoot at terminal stance.[6] Although most examiners, by taking advantage of a long lever, can produce torques that exceed those produced by muscle groups such as the hip abductors and extensors, this is not possible when testing the triceps surae muscles. During a manual test of the plantar flexors, for example, the examiner's force would have to equal the subject's body weight, a force that far exceeds the average arm strength of many examiners.[7-10] During normal walking, the demand on the triceps surae muscles increases as the body mass advances from loading response through terminal stance, with active contraction during approximately 90% of this period and with a peak torque demand during 52% of each stance period.[11-16]

During the peak poliomyelitis era (1940-1955), practitioners recognized the inadequacy of a non-weight-bearing test of plantar-flexor force.[5] They substituted a standing heel-rise test, which relied on weight bearing challenge the plantar flexors.[2,3,5] The standing heel-rise test consists of lifting the contralateral foot so that the plantar flexors being tested simulate singlelimb support, the ipsilateral knee is fully extended, and the heel is lifted off the floor through maximum plantar-flexion range. During this test, the subject is allowed light finger touch only for balance support.[2] Unresolved, however, was the number of heel-rises that represented normal capacity. Kendall and McCreary[3] and Beasley[5] required only a single heel-rise to evaluate "normal" capacity. Because persons without weakness are capable of performing more than a single heel-rise, this test represents a vigorous test not influenced by a subject's ability to repeatedly generate force. The standing heel-rise test was modified by Daniels and Worthinghamm,[2] who suggested that patients performing four to five repetitions be assigned a Normal grade, regardless of age or gender, with instruction to go through "a full range-of-motion." The actual number of heel-rise repetitions required for "normal" muscle function has never been documented. There is no evidence that defines the maximum number of heel-rises that can be expected of subjects with normal plantar-flexor muscle function.

Clinical experience with patients with post-polio syndrome has shown that such limited heel-rise capability (1-5 repetitions) does not allow the patient a normal gait.[17] For example, in our opinion, a patient who can maximally complete 5 repetitions will demonstrate weakness in the calf musculature by excessive dorsiflexion in midstance to terminal stance and will lack heel-off at terminal stance. Our recent clinical experience with patients who have spinal cord injuries has shown that patients who can achieve 10 standing heel-rise repetitions and therefore were relieved of their anklefoot orthoses have returned to the clinic demonstrating a loss of force production with repeated efforts that led to impairment in their gait. Their loss of force-generating capacity was identified by gait deviations (excessive dorsiflexion during stance) and retesting using the standing heel-rise test. Beasley[5] reported a systematic overgrading when MMT was used and implied that patients who had been defined as having "good to normal" muscle function actually had as much as a 60% strength deficit and therefore that the reliability of such assessments is generally in doubt. Studies of patients with post-polio syndrome have shown a loss of muscle function secondary to chronic fatigue believed to be related to overuse.[18-21]

Although the standing heel-rise test continues to be used by clinicians, some published research has described only instrumented, non-weight-bearing methods, utilizing both isometric and isokinetic techniques.[7-9,22] The purpose of this study, therefore, was to further refine the standing heel-rise test by assessing the number of heel-rises that can be accomplished by both male and female subjects without known weakness. A documented standard that reflects the normal number of heel-rises could provide an improved clinical guideline for testing plantar-flexion function.

Method

Subjects

We tested 203 subjects (122 men and 81 women) (Tab. 1). The mean age of the male subjects was 34.7 years (SD=8.5), and the mean age of the female subjects was 29.3 years (SD=5.0). The mean height and weight of the male subjects were 178.9 cm (SD=7.9) and 79.7 kg (SD=11.5), and the mean height and weight of the female subjects were 164.8 cm (SD=6.0) and 60.0 kg (SD=8.6). The right lower extremity was the dominant limb tested for both gender groups (940% and 95% for the male and female subjects, respectively) (Tab. 1). Each subject was screened for, and excluded if he or she had, any history of musculoskeletal or joint pathology involving the hip, knee, or ankle. All subjects gave informed consent before participating in the study.

Table 1. Subject Description

Variable               X            SD

Men (n=122)
   Age (y)             34.7          8.5
   Height (cm)        178.9          7.9
   Weight (kg)         79.7         11.5
   Dominant limb
     Right            115
     Left               7
Women (n=81)
   Age (y)             29.3          5.0
   Height (cm)        164.8          6.0
   Weight (kg)         60.0          8.6
   Dominant limb
     Right             77
     Left               4

Instrumentation

A parallelogram electrogoniometer (Antonelli D, Rehabilitation Engineering Center, Rancho Los Amigos Hospital, Downey, Calif; unpublished report; 1975) fitted with a digital readout was used for measuring range of motion at the ankle during the heel-rises. This goniometer was designed to measure angular motion only in the sagittal plane and to adapt to a variable axis of motion. A metronome was used to aid in maintaining a consistent rhythm of heel-rises for each subject. This goniometer has been shown to have an error of 100% when used at the knee,[23] and less than that when used at the ankle.[11] We did not examine the reliability of these measures in the context of our study.

Procedure

Each subject's height and weight were measured at the outset of the session. Testing was conducted on the dominant limb. Previous studies[8,9] have shown the nondominant limb to be stronger than the dominant limb. Testing was done on the dominant limb because we believed that a standard based on the weaker of two normal limbs would have a broader application. This functional preference was determined by having the subjects kick a ball that was rolled to them.[24] With the subject in a standing position, the ankle goniometer, strapped to the leg and midfoot, was calibrated so that a tibia-foot angle of 90 degrees was read as zero on the digital meter (Figure). Subjects were instructed to stand straight and to rise and lower on the balls of their feet in rhythm with the metronome, which was set at a rate of one heel-rise every 2 seconds. Each subject was allowed to touch the examiner with a single finger for balance. The test was terminated if the subject leaned or pushed down on the examiner, the subject's knee flexed, the plantar-flexion range of motion decreased by more than 50% of the starting range of motion, or the subject quit or asked to stop. There were three testers for each subject. One tester provided the finger-touch support, one tester observed the subject laterally for any extraneous trunk lean or knee flexion, and one tester managed the electrogoniometer output.

Data Analysis

The data were screened, and descriptive statistics were calculated and summarized. These data included the means of the subjects' age, height, and weight and identification of the dominant limbs (Tab. 1). Means and standard deviations for the standing heel-rise repetitions and degrees of plantar flexion achieved were calculated, as were the upper and lower 99% confidence intervals of the mean. The formula for calculating the confidence interval, as specified by the manufacturer of the Crunch Software(*) used in this study, was

[Mathematical Expression Omitted]

A two-sample t test was used to compare the differences between the male and female groups for both repetitions and plantar-flexion angle.

Significance testing was set at an alpha level of .05. Only data that reached this level of significance will be discussed as being different in the "Results" and "Discussion" sections. All data were analyzed using Crunch Software.

Results

Repetitions

The mean number of standing heel-rise repetitions was 27.9 (SD = 11.1, minimum=6, maximum=70). The upper and lower 99% confidence intervals for the whole group were 29.8 and 25.8, respectively. There were no differences in the mean number of standing heel-rise repetitions accomplished between male and female subjects (Tab. 2). The mean number of heel-rise repetitions for the male subjects was 27.8 (SD=11.5), with upper and lower confidence intervals of 30.5 and 24.9, respectively (Tab. 2). The mean number of heel-rise repetitions for the female subjects was 28.4 (SD=9.8), with 99% confidence intervals of 30.8 and 25.2, respectively (Tab. 2).

[TABULAR DATA OMITTED]

Angle (Degrees of Plantar

Flexion)

The female subjects achieved a greater plantar-flexion angle during the standing heel-rise test than did the male subjects. The mean plantar-flexion angle achieved at 28 repetitions was 24.9 degrees (SD=9.5) for the male subjects and 34.6 degrees (SD=10.1) for the female subjects (Tab. 2).

Discussion

The subjects of this study compared closely with those of other studies[7,8,22] in age, height, and weight. Although the muscle testing literature[2,3,5] recommends 1 to 5 repetitions as a test for normal muscle function, this study provides a new standard for repetitions. The average number of standing heel-rise repetitions completed in this study was 28, almost six times the maximum number currently recommended.[2]

Walking demands that the plantar flexors restrain forward momentum when the body mass passes over the stance limb.[11-13,15,25-28] During each stride, the soleus muscle is active approximately 45% of the gait cycle, and throughout the muscle's period of activity the intensity continually increases, reaching 80% of the maximum heel-rise demand.[11] A similar demand is placed on the gastrocnemius muscle. Consequently, both endurance and high force are required. This level of effort contrasts sharply with the average level of quadriceps femoris muscle activity (ie, peak effort of 35% and duration of activity of 20% of the gait cycle).[11]

Although studies using instrumented techniques consistently show that male subjects produce greater torque than do female subjects,[7,8,22] our study showed no differences between male and female subjects in number of standing heel-rise repetitions achieved. The differences in body mass would explain this result. We contend that a test that challenges the individual against his or her own body mass produces a more relevant, functional result. The male subjects were 32% heavier than the female subjects. This body mass difference could be the equalizer. If male subjects can generate more force, but are heavier, this could explain their equality with female subjects, in number of repetitions, when doing the standing heel-rise test.

When the torque data from previous studies[7,8] were converted to force values, the following was revealed. Up to the age of 60 years, the force capability of the calf muscles exceeds that of body weight, by 10% to 75%.[7,8] Even though the body mass accounts for less than the force capability of the plantar flexors, it still provides a major challenge of 58% to 90% of muscle capability in subjects less than 60 years of age. For subjects over 60 years of age, the body mass is 10% to 15% greater than the plantar-flexion muscles' force-producing capability.[7]

Ineffectiveness in the response of the plantar flexors causes instability during walking and therefore increases energy cost and decreases safety.[11,25,29] Whipple et al[29] measured the power and peak torque in a group of nursing home residents with a history of falling (mean age=82 years) compared with a control group (mean age=85 years).[28] Compared with the control group, the "fallers" showed a marked loss of power and peak torque (77% and 79%, respectively) in the ankle musculature. An accurate determination of force-generating capacity, therefore, is especially important to avoid overestimating functional capability, especially in older subjects.

Conclusions and

Recommendations

We believe that a non-weight-bearing manual test of ankle plantar-flexion strength is inadequate because of the inability of the examiner to counter the torque produced by the plantar flexors with normal arm strength. Given that the role of the plantar flexors is to counter high degrees of torque produced by the forward momentum of the body mass, and that the MMT is inadequate, the following recommendations are set forth. We recommend that the standing heel-rise test be the clinical method of choice for evaluating ankle plantar-flexor function. We also recommend that clinicians require 25 standing heel-rise repetitions as the standard for a grade of Normal.

Beasley[5] calculated the force to body weight ratios (F/BW), and accordingly we make the following recommendations: Poor (2)=maximum manual resistance, but unable to achieve a single heel-rise (F/BW=.312), and Fair (3)=able to hold body weight once in a heel-up position, but unable to raise body weight from neutral (F/BW=.823).

BR Lunsford, PT, was Assistant Director, Clinical Services, Physical Theraphy Department, Rancho Los Amigos Medical Center, Downey, CA 90242, when this study was conducted. She is currently Visiting Assistant Professor, School of Physical Therapy, Texas Woman's University, and Contract Physical Therapist, The Institute for Rehabilitation and Research, Houston, TX. Address all correspondence to Mrs Lunsford c/o School of Physical Therapy, Texas Woman's University, 1130 MD Anderson Blvd, Houston, TX 77030 (USA).

J Perry, MD, is Chief, Pathokinesiology Service, Rancho Los Amigos Medical Center, and Professor of Orthopedics, University of Southern California, Los Angeles, CA 90007.

References

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