Abstract
Background Repeated heel raises have been proposed as a method of ankle plantar-flexor strength testing that circumvents the limitations of manual muscle testing (MMT).
Objective The study objective was to examine the relationships among ankle plantar-flexion isometric maximum voluntary contraction (MVC), repeated single-limb heel raises (SLHRs), and MMT in people with myositis.
Design This was a cross-sectional study with a between-group design. The ability to complete 1 SLHR determined group assignment (SLHR group, n=24; no-SLHR group, n=19).
Methods Forty-three participants with myositis (13 women; median age=64.9 years) participated. Outcome measures included MVC, predicted MVC, Kendall MMT, and Daniels-Worthingham MMT.
Results The Kendall MMT was unable to detect significant ankle plantar-flexor weakness established by quantitative methods and was unable to discriminate between participants who could and those who could not perform the SLHR task. Ankle plantar-flexion MVC was not associated with the number of heel-raise repetitions in the SLHR group (pseudo R2=.13). No significant relationship was observed between MVC values and MMT grades in the SLHR and no-SLHR groups. However, a moderate relationship between MVC values and MMT grades was evident in a combined-group analysis (ρ=.50–.67).
Limitations The lower half of both MMT grading scales was not represented in the study despite the profound weakness of the participants.
Conclusions Both Kendall MMT and Daniels-Worthingham MMT had limited utility in the assessment of ankle plantar-flexor strength. Repeated SLHRs should not be used as a proxy measure of ankle plantar-flexion MVC in people with myositis.
The performance of many fundamental upright activities of daily living, such as walking, running, and rising from a chair, depends on adequate concentric and eccentric functioning of the ankle plantar-flexor muscles.1–3 Therefore, physical therapists must adequately measure ankle plantar-flexor muscle force to assess lower extremity impairments. Clinical measurement of ankle plantar-flexor muscle force is especially important in people with health conditions that result in calf weakness, including people with idiopathic inflammatory myopathies. Although many types of idiopathic inflammatory myopathies are chiefly characterized by proximal muscle involvement, inclusion body myositis affects distal muscle groups.4 The importance of ankle plantar-flexor muscle force in upright activities and the preferential involvement of distal muscle groups in people with inclusion body myositis place a premium on valid and reliable tests of ankle plantar-flexor muscle function.
The measurement of plantar-flexor strength poses unique challenges. Manual muscle testing (MMT), a method of measuring muscle force, is frequently used by health care professionals5–7; however, many investigators have cited the limitations of MMT for measuring the forces generated by large lower extremity muscle groups, such as the ankle plantar-flexor muscles.8–11 For example, MMT may exhibit a ceiling effect,10,12 in part because its interpretation varies according to an examiner's inability to “break” the force generated by a patient.8 A ceiling effect occurs when many people attain the maximum score on a given test, and a floor effect is observed when many people attain the lowest possible score.13 The ankle plantar-flexor muscles pose unique challenges that confound an examiner's ability to detect weakness in this muscle group using MMT. The short lever arm and triplanar motion of the foot and ankle minimize the mechanical advantage of an examiner during the administration of MMT.14,15 Examiner strength is usually insufficient to overcome ankle plantar-flexor force, even when significant strength deficits have been confirmed by objective methods of assessment.16 The force capacity of the ankle plantar-flexor muscles is augmented by the bipenniform orientation of muscle fibers of the gastrocnemius muscle and the lever system of the ankle.17 For these reasons, the maximum MMT grade for the ankle plantar-flexor muscles may not be equated with an absence of muscle impairment.
A weight-bearing test of ankle plantar-flexion performance has been proposed to circumvent the shortcomings associated with MMT. This test requires that a patient complete multiple repetitions of single-limb heel raises (SLHRs) while standing only on the tested limb (Fig. 1).5 However, the SLHR test demonstrates a floor effect in some patient populations because it cannot discriminate levels of weakness in people who are unable to complete 1 SLHR. A clinical algorithm combining standard MMT and repetitions of the SLHR test ostensibly avoids the ceiling and floor effects demonstrated by these methods, respectively (Tab. 1).5 The assessment properties of the SLHR test are becoming better known; the test has been shown to have acceptable interrater reliability,18,19 normative performance values have been suggested,14,20,21 and age- and sex-adjusted scoring criteria have been proposed.22 However, the construct validity of the SLHR test has yet to be established.
Performance of the single-limb heel raise during manual muscle testing of the ankle plantar-flexor muscles.
Manual Muscle Testing (MMT) Grading Criteriaa
The 3 aims of this cross-sectional study were: (1) to characterize ankle plantar-flexion performance by group assignment (based on the ability to independently complete 1 or more SLHRs) in people with intrinsic muscle disease, (2) to ascertain the validity of 2 popular MMT approaches for quantifying ankle plantar-flexor strength by examining the relationship between peak isometric ankle plantar-flexor force and the Daniels-Worthingham method5 or the Kendall method,6 and (3) to determine whether SLHR repetitions were associated with peak isometric ankle plantar-flexor force. We hypothesized that traditional MMT with the “break test” would consistently overestimate ankle plantar-flexor strength relative to a quantitative peak force measurement. Given the metabolic demands and submaximal force requirements of SLHR repetitions, we also hypothesized that peak isometric ankle plantar-flexor force would not be associated with SLHR repetitions.
Method
Participants
Adults who had inclusion body myositis and participated in a prospective natural history project (National Institute of Neurological Disorders and Stroke protocol 02-N-0121) were recruited to participate in the present study. Inclusion criteria required the participants to be over the age of 40 years and to have a diagnosis of sporadic inclusion body myositis confirmed by established clinical and histological criteria based on neurological findings and muscle biopsy.23 Exclusion criteria included severe cardiovascular disease, renal disease, joint instability that affected a tested muscle group, and advanced muscle disease that precluded regular travel to the hospital. We estimated that a total enrollment of 40 participants would be needed to attain adequate study power (β=.80; noncentrality parameter, δ=2.94; critical t=2.02; α=.05, 2-tailed) to detect a 25% between-group difference in ankle plantar-flexion isometric maximum voluntary contraction (MVC).24 Data for the sample size calculation were derived from a pilot study concerning the reliability of quantitative MVC methods and featured 10 people who were not included in the data set for the present study.
A total of 49 potential participants were screened for the present study. One person was excluded because of a diagnosis of hereditary inclusion body myositis. One person was excluded because of severe cardiovascular disease. Four people were excluded because of advanced muscle disease that limited regular visits to the hospital. As a result, 43 people were enrolled and participated in the present study.
Procedure
After informed consent was obtained, all participants received quantitative muscle strength testing, MMT of the ankle plantar-flexor muscle group, and SLHR testing.
Quantitative muscle strength testing.
The peak force of the dominant ankle plantar-flexor muscles was obtained with isometric MVC tests. All MVC tests were performed on a fixed-frame dynamometer (Aeverl Medical LLC, Gainesville, Georgia) with SM 250-12 load cells (Interface, Scottsdale, Arizona), computer-assisted data acquisition, and a sampling rate of 16 Hz (no filtering was deemed necessary). The test position was supine with the knees fully extended and the ankle positioned at 90 degrees via an inclinometer measurement (eFigure). A towel was placed under the Achilles tendon to provide adequate clearance between the shoe heel and the examination table. Participants wore Oxford-style lace-up shoes.
The first and fifth metatarsal heads were palpated through the shoe upper, and a cuff was placed around the metatarsophalangeal joints and connected to a nonelastic vinyl strap attached to the load cell. The tester provided manual stabilization at the ipsilateral shoulder and proximal tibia. The strap was adjusted to avoid contact with the participant and to maintain a parallel orientation to the floor to minimize any deviation of the force vector. The tibia was positioned in neutral rotation so that the foot was vertical, and the strap was anchored proximally so that it was aligned as closely as possible with the center of the ankle and knee joints. This positioning was used to ensure that the force vector was in line with the tibia and to avoid unwanted foot eversion or inversion during MVC testing. The load cell was calibrated in accordance with manufacturer guidelines and reset to 0 before each MVC attempt to account for the passive plantar-flexor force of the foot exerted against the cuff.
One or 2 submaximal isometric contractions were performed to prepare the ankle plantar-flexor muscles for testing and to provide familiarization with the task. Participants were instructed to exert maximal plantar flexion against the load cell cuff at the verbal command of the tester. Three MVC attempts lasting 5 seconds each were completed, and knowledge of the results was provided after each trial. Each MVC attempt was followed by a 30-second rest period. The mean value of the 2 best attempts was used for the data analysis. Consistent-time-of-day testing was used for all participants.
Our method of ankle plantar-flexion MVC testing by fixed dynamometry appeared to be reliable on the basis of our pilot tests and participant results. High interrater reliability (intraclass correlation coefficient [2,3]=.85, P<.001, standard error of the measurement=3.3 kg) was observed in our assessment of 10 adults who were healthy (mean age=51.1 years, SD=6.3) and had no sensorimotor impairment (J.A.S., unpublished data, 2007). In addition, the intrasession test-retest reliability of fixed dynamometry involving our participants with inclusion body myositis was excellent (intraclass correlation coefficient [3,1]=.98, P<.001, standard error of the measurement=3.6 kg).
Observed peak force values obtained from the study participants were compared with predicted values derived from normative data for people who were healthy.25 These normative data were obtained with methods similar to those used in the present study. The peak force data were obtained with a load cell and expressed as a regression formula with age, body side, muscle group, and sex as factors.25 The ratios of the study participants' observed peak forces to the predicted peak forces were calculated and converted to percentages of the predicted values (Tab. 2). The peak force data also were scaled to body weight (kilograms of MVC force/kilograms of body weight, resulting in a unitless value) to allow for comparisons among participants, independent of stature.
Descriptive Statisticsa
MMT.
The method used for MMT of the dominant ankle plantar-flexor muscles was adapted from the methods described by Hislop and Montgomery5 and Kendall et al.6 The form of ankle plantar-flexion MMT described by Hislop and Montgomery (in the textbook Daniels and Worthingham's Muscle Testing: Techniques of Manual Examination)5 allows for a weight-bearing SLHR test and a break test for people unable to perform the SLHR task. The participant's prone position with terminal knee extension and the examiner's application of force in the caudal direction on the plantar surface near the metatarsal heads in the present study were similar to the break test described by Hislop and Montgomery5 and Kendall et al.6 The break test and the SLHR test were used for all participants.
SLHR testing.
After removing their footwear, participants stood with their fingertips at shoulder level against a wall for tactile feedback and nominal external support. A gait belt was placed around the waist for safety. Participants established balance on the dominant lower extremity, maintained an upright posture perpendicular to the floor, and were instructed to rise as high as possible on their toes. Participants were allowed to use a consistent self-selected rate of movement during the task, and a clinician stood nearby to provide guarding for safety. All participants were informed of the criteria for ending the test. These criteria included leaning forward or using the momentum from trunk or hip flexion to complete a repetition, knee flexion of the ipsilateral limb during the performance of the SLHR, task activity exceeding 2 minutes, an inability to complete a repetition, 2 consecutive incomplete repetitions, and requesting to stop the test. An incomplete repetition was operationally defined as one in which the base of the fifth metatarsal tubercle and midfoot did not fully rise from the floor. No incomplete SLHR was included in the SLHR count used to determine the MMT grade. Knowledge of performance was provided only to inform participants of incomplete repetitions and the attainment of test-ending criteria.
Our examiners demonstrated acceptable interrater reliability for grading the SLHR portion of the Daniels-Worthingham MMT5 (kappa=.73) during pilot testing involving 10 single-session observations of tasks performed by adults with intrinsic muscle disease (mean age=53.7 years, SD=11.2) (M.O.H., unpublished data, 2007). One examiner (M.O.H.) completed all MVC and MMT tests, which were conducted 24 to 48 hours apart to avoid participant fatigue. A standardized testing order was used to ensure that the examiner was unaware of the SLHR group assignment. The order of testing was MVC testing followed, on the next day, by Kendall MMT,6 Daniels-Worthingham MMT,5 and the SLHR as the final MMT component.
Data Analysis
Characterizing ankle plantar-flexion performance and participant characteristics.
Descriptive statistics were used to depict participant attributes and characterize the assessment of ankle plantar-flexion performance with MMT. Nonparametric statistics were used throughout the present study because of departures from normality of the data and the ordinal data associated with the MMT grades. Therefore, all data were expressed as median values and interquartile ranges (IQRs). The Mann-Whitney U test was used to evaluate differences in demographics and outcome variables on the basis of group membership. A significant Mann-Whitney U test result regarding ankle plantar-flexion MVC and MMT scores indicated the ability of these characteristics to distinguish between participants who could and those who could not complete at least 1 SLHR.
Determining the relationship between MMT and MVC.
Spearman correlation coefficients (ρ) were used to determine the relationship between MMT grades and MVC values. Unilateral, dominant-side MVC and SLHR values were used for all analyses. A significant Spearman correlation coefficient indicated that the ankle plantar-flexion MVC might be related to the MMT scores attained by the participants. The magnitude of the association among the variables was based on Munro's criteria for significant findings.26
The Daniels-Worthingham5 MMT grading scale includes 8 intervals, with “+” or “−” designations associated with grade 2. This grading scale was converted into whole numbers to facilitate data analysis because MMT grade 2+ was attained by at least 1 participant during data collection. The Daniels-Worthingham5 MMT grading scale conversion is summarized in Table 1. If a participant was unable to perform 1 SLHR, then Daniels-Worthingham5 MMT grades 3 through 5 were not attainable and testing reverted to the manual break test for the attainment of grade 2+ or lower. In addition, MMT grades were evaluated for floor or ceiling effects. The criterion for an unacceptable floor or ceiling effect was attainment of the minimum or maximum score by more than 50% of the participants.13
Examining the association between SLHR repetitions and MVC.
Logistic regression was used to determine whether SLHR task performance was associated with peak isometric ankle-plantar flexor force. The variance in the ankle plantar-flexor force values explained by SLHR repetitions was expressed as Cox-Snell pseudo R2 with an ordinal data model. The −2 log likelihood was used for the goodness-of-fit statistic to examine residual values, and the chi-square test was used to determine whether the independent variable enhanced the logistic regression model.26 A significant logistic regression equation suggested that SLHR repetitions were associated with ankle plantar-flexion MVC in our participants.
Unless stated otherwise, the alpha level was set at .05, and P values of less than or equal to .05 were considered significant for all inferential statistics. SPSS statistical software, version 10.0 for Windows, was used for all analyses (SPSS Inc, Chicago, Illinois).
Role of the Funding Source
This study was funded by the National Institute of Neurological Disorders and Stroke (protocol 02-N-0121) Intramural Research Program and was supported by the Rehabilitation Medicine Department, National Institutes of Health.
Results
Characterizing Ankle Plantar-Flexion Performance
Significant group differences were evident for ankle plantar-flexion MVC, with higher forces being attained in the SLHR group (P<.001). Normative data equations indicated that the participants had considerable ankle plantar-flexor weakness; 23% and 37% of normal peak ankle plantar-flexor forces were generated in the no-SLHR and SLHR groups, respectively.
Despite this weakness, the break test was negative for approximately 80% of the participants. Kendall MMT6 was unable to discriminate between participants who were able and those who were unable to perform the SLHR task. A ceiling effect was observed with Kendall MMT6 for both groups, as 100% of the SLHR group and 58% of the no-SLHR group attained the maximum grade of 10. Not surprisingly, median Daniels-Worthingham MMT5 grades were significantly different in the 2 groups (P<.001) because grades 3 to 5 require the ability to perform 1 or more SLHRs. Technically, no ceiling or floor effect was observed with Daniels-Worthingham MMT.5 However, 53% of the participants in the no-SLHR group attained MMT grade 2+ (negative break test). Participants with Daniels-Worthingham MMT5 grade 2+ exhibited 14% to 38% of the predicted ankle plantar-flexion MVC. Group differences were not significant for sex, age, body mass index, or age at disease onset. The complete descriptive statistics for the 43 participants are shown in Table 2.
Relationship Between MMT and MVC
No significant relationship was observed between ankle plantar-flexion MVC values and MMT grades in the SLHR and no-SLHR groups. A moderate strength of association between MVC values and MMT scores was evident in a combined-group analysis (ρ=.50–.67, P≤.001) (Tab. 3). The addition of repeated heel raises to Daniels-Worthingham MMT5 yielded a stronger association with ankle plantar-flexion MVC than the Kendall MMT6 break test.
Correlation Between Maximum Voluntary Contraction and Manual Muscle Testing (MMT) Grade for the Ankle Plantar-Flexor Musclesa
Association Between SLHR Repetitions and Ankle Plantar-Flexion MVC
The logistic regression equation for the relationship between SLHR repetitions and MVC in the SLHR group did not yield a viable model (pseudo R2=.13, P=.24) (Fig. 2). The median number of heel raise repetitions completed by participants in the SLHR group was 13 (IQR=8–22, range=1–30). A large amount of overlap in MVC values across Daniels-Worthingham MMT5 grades was observed despite the mutually exclusive scoring criteria used in the present study. An annotated scatter plot depicting the relationship between MVC values and Daniels-Worthingham MMT5 grades in all participants is shown in Figure 3. Despite the sharing of MVC ranges between MMT grades, we believed that there was not adequate representation to treat each MMT grade as an independent category or variable level in a credible Kruskal-Wallis analysis. Therefore, we opted for a visual depiction of the differences among MMT grades on the basis of corresponding MVC values in Figure 3.
Scatter plot of single-limb heel raise repetitions and ankle plantar-flexion maximum voluntary contraction. For participants who were able to perform the single-limb heel raise test, pseudo R2=.13 (P=.24), −2 log likelihood=63.1, chi-square test=2.8, and goodness-of-fit=.34. Data were derived from unilateral values for the dominant lower extremity, and force values were scaled to body weight. The straight dashed line represents the line of best fit, and the curved dashed lines indicate the 95% confidence intervals.
Annotated scatter plot of Daniels-Worthingham manual muscle testing (MMT) grades and ankle plantar-flexion maximum voluntary contraction values for all participants. The Daniels-Worthingham MMT grades attained by the participants were converted to whole numbers as follows: original grade 5=8, grade 4=7, grade 3=6, grade 2+=5, and grade 2=4.
Discussion
Repeated heel raises have been proposed as a method of ankle plantar-flexor strength testing that circumvents the limitations of MMT. Our study aims were to characterize the ankle plantar-flexion performance of the SLHR and no-SLHR groups, ascertain the validity of MMT for the ankle plantar-flexor muscles by examining the relationship between MVC and the Kendall method6 or the Daniels-Worthingham method,5 and determine the association between SLHR repetitions and ankle plantar-flexion MVC.
Poor Association Between MMT and Ankle Plantar-Flexion MVC in Participants With Significant Muscle Weakness
The participants had profound muscle weakness. Comparisons with normative data revealed that the participants in the SLHR group produced less than 40% of the predicted ankle plantar-flexion MVC and that those in the no-SLHR group produced less than 25%. These data suggested considerable strength deficits in both groups. Although the participants appeared to be ideal candidates for the manual assessment of muscle strength on the basis of the magnitude of their weakness, they exhibited a narrow range of MMT scores. Participants in both groups attained MMT grades 8 to 10 with Kendall MMT,6 and participants in the no-SLHR group attained MMT grades 2 and 2+ with Daniels-Worthingham MMT.5 These narrow ranges of scores illustrate the difficulty of using MMT to capture weakness of the ankle plantar-flexor muscles.
The observation of people with frank muscle weakness exhibiting high plantar-flexion MMT scores is consistent with previous work involving people with myositis. A study of the reliability of MMT for children with juvenile idiopathic inflammatory myopathies by Jain et al27 showed that raters consistently issued the highest score (ie, Kendall MMT6 grade 10 of 10) when assessing ankle plantar-flexor muscles. In addition, a study involving 172 participants with myositis revealed that plantar-flexion MMT scores did not reflect generalized weakness indicated by the participants' total (summed) MMT scores.2 Although the total MMT scores in these participants were 75.2% to 84.2% of the maximum score (Kendall MMT,6 10-point scale, highest attainable total score=240), the median scores for the ankle plantar-flexor muscles were 9.0 (IQR=8–10) for participants with polymyositis and 10.0 (IQR=9–10) for those with dermatomyositis and juvenile idiopathic inflammatory myopathies. The prevailing clinical notion is that the expression of weakness in myositis minimally involves the distal extremities.2,7 However, despite the pathological differences between inclusion body myositis and other forms of myositis, the findings in the present study raised the possibility that the apparent preservation of ankle plantar-flexor strength in idiopathic myopathies is attributable to MMT method limitations rather than phenotypic patterns of muscle impairment.
Limitations in the Ability of the SLHR Test to Serve as a Proxy Measure of Ankle Plantar-Flexor Strength
In the present study, SLHR repetitions were not significantly related to ankle plantar-flexion MVC. Our results indicated that the number of SLHR repetitions was not associated with more than 13% of MVC variance in our sample. Investigators previously cited the limitations of MMT with the break test for assessing the strength of the ankle plantar-flexor muscles,14,16 and the use of SLHR repetitions has been proposed as an alternative assessment method.5,14 The research literature is incongruent regarding the ability of SLHR repetitions to serve as a proxy measure of muscle strength. Several investigators21,28–30 referred to SLHR repetitions as a test of muscular endurance. This view of the test is supported by observed changes in the median power frequency of electromyographic spectral density that occur during SLHR repetitions.29,31 Shifts in the median power frequency during fatiguing activities are consistent with changes in the recruitment level and synchronization of motor units.21 Although we did not measure fatigue associated with ankle plantar-flexion MVC, our findings supported the idea that SLHR repetitions represent an aspect of muscle performance beyond peak force.
Although MVC is not equivalent to muscle endurance, a threshold level of strength is required to engage in repeated functional activities.32 For example, no participant in our sample with a scaled ankle plantar-flexion MVC value of less than or equal to 0.13 (13% of body weight) completed 1 SLHR repetition. However, participants who completed 25 to 30 SLHR repetitions exhibited scaled ankle plantar-flexion MVC values ranging from 0.22 to 0.65, representing a wide range of strength. Therefore, the ability to perform 1 SLHR repetition does appear to be influenced by strength, as group assignment was associated with significant differences in peak MVC values.
Despite the difference in strength between the SLHR and no-SLHR groups, Kendall MMT6 displayed a ceiling effect across all participants. In contrast, the inclusion of both the break test and the SLHR test eliminated ceiling and floor effects for Daniels-Worthingham MMT5 across all participants. Nevertheless, the lack of association between ankle plantar-flexion MVC and SLHR repetitions raised doubts about the valid use of Daniels-Worthingham MMT5 grades 3 to 5 to estimate muscle strength. Our visual depiction of the relationship between Daniels-Worthingham MMT5 and ankle plantar-flexion MVC suggested that many of the MMT grades attained by our participants did not represent mutually exclusive categories of muscle strength (Fig. 3). Furthermore, our findings indicated that the adoption of SLHR repetitions as an isolated field test21 to measure ankle plantar-flexor strength should be used with caution in people with considerable weakness.
Our results indicated that the attainment of the maximum MMT grade on both scales did not imply an absence of muscle impairment in our participants. Given the difficulty that we observed in using MMT to detect ankle plantar-flexor weakness in people with muscle disease, our findings suggest that even greater challenges may be encountered when testing patients who do not have as much profound weakness.
Study Limitations
There were several limitations of the present study. Our participants with inclusion body myositis did not have isolated ankle plantar-flexor weakness. Therefore, weakness in other proximal lower extremity muscle groups may have affected the ability to stabilize the ipsilateral limb during the SLHR task. However, multiple muscle impairments are not listed as potential confounding factors in the literature,5,21 and MMT methods were traditionally designed to assess people with lower motor neuron disease.6,16 Also, fully characterizing the relationship between MMT and MVC was difficult without a representation of each MMT grade in the analysis. For example, no participant in our sample had “trace” or “absent” ankle plantar-flexion contractions. Nevertheless, given the high representation of maximum MMT grades in our data as well as the profound weakness of our participants, the lack of variation in MMT grades may have been related more to the limited measurement qualities of MMT grading criteria than to the clinical presentation of our sample. Finally, MMT for all participants was conducted by a single investigator. Consequently, the magnitude of agreement between that examiner and other examiners is unknown.
Conclusion
Our data suggest questionable validity of both Kendall MMT6 and Daniels-Worthingham MMT5 for the assessment of ankle plantar-flexor strength in people with considerable strength deficits. The maximum grade of 10 for Kendall MMT6 was attained by 81% of the participants despite wide variations in ankle plantar-flexion MVC values. In contrast, a wider range of scores was obtained with Daniels-Worthingham MMT5 when SLHR repetitions were incorporated into the assessment of the ankle plantar-flexor muscles. However, our findings indicated that SLHR repetitions were not significantly associated with ankle plantar-flexion MVC values in people with inclusion body myositis. Therefore, the integration of SLHR repetitions into Daniels-Worthingham MMT5 for the ankle plantar-flexor muscles may not represent a valid approach to strength assessment for this muscle group.
It is important that we did observe significant differences in ankle plantar-flexion MVC between the SLHR and no-SLHR groups. Consequently, the ability to perform 1 SLHR may have important implications for the clinical assessment of strength and should be the subject of further investigation. Additional research is needed to develop a reliable and valid assessment of ankle plantar-flexor strength that is suitable for clinical use.
Footnotes
Dr Harris-Love, Dr Davenport, Dr Joe, and Dr Dalakas provided concept/idea/research design. Dr Harris-Love, Mr Shrader, Dr Davenport, Ms McElroy, and Dr Dalakas provided writing. Dr Harris-Love provided data analysis. Dr Harris-Love, Mr Shrader, Dr Joe, Dr Rakocevic, Ms McElroy, and Dr Dalakas provided project management and clerical support. Dr Dalakas provided fund procurement. All authors provided data collection and consultation (including review of manuscript before submission). The authors thank Dr Jerome V. Danoff for critical reading of the article.
This study was approved by the National Institute of Neurological Disorders and Stroke Institutional Review Board of the National Institutes of Health.
Portions of this work were presented at the World Confederation for Physical Therapy Congress; June 6, 2007; Vancouver, British Columbia, Canada.
This study was funded by the National Institute of Neurological Disorders and Stroke (protocol 02-N-0121) Intramural Research Program and was supported by the Rehabilitation Medicine Department, National Institutes of Health.
- Received March 24, 2013.
- Accepted November 26, 2013.
- © 2014 American Physical Therapy Association
References
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