Lower Extremity Muscle Strength in 6- to 8-Year-Old Children Using Hand-Held Dynamometry : Pediatric Physical Therapy

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Research Report

Lower Extremity Muscle Strength in 6- to 8-Year-Old Children Using Hand-Held Dynamometry

Macfarlane, Tammy S. MSPT, PT; Larson, Cathy A. PT, PhD; Stiller, Christine PT, PhD

Author Information
Pediatric Physical Therapy 20(2):p 128-136, Summer 2008. | DOI: 10.1097/PEP.0b013e318172432d
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INTRODUCTION

Because decreases in strength can lead to functional limitations in children, strength testing is of primary importance in the examination and evaluation of children with disabilities. Although manual muscle testing (MMT) is frequently used for assessing strength in children,1,2 assigning MMT grades relies largely upon the examiner’s judgment of the amount of force generated by the subject and, therefore, is subjective and prone to examiner bias.3,4 In addition, small yet clinically significant changes in strength may not be detected by MMT.5 Individual examiners vary significantly in the amount of force applied to the limb, particularly when assigning MMT grades 3+ to 5.6 For example, Van der Ploeg et al7 reported that MMT grade 4 strength of the elbow flexor muscles for adult males ranged from 10 to 250 N as measured by hand-held dynamometry (HHD). MMT appears to be most appropriate for assigning grades 0 to 3; however, MMT does not adequately quantify muscle strength, particularly for grades 3+ to 5.3

Standardized, reliable, sensitive yet practical methods to obtain quantitative measurements of muscle strength for children are needed in the clinic. Current methods for quantifying muscle strength in children include isokinetic dynamometry or HHD. Although an isokinetic dynamometer has the advantage of being able to accurately measure muscle torque continuously throughout the range of motion, the length of time needed to perform the testing procedures, and the high cost and decreased portability of the unit usually preclude its use in pediatric settings.8 In contrast, HHD offers an objective, portable, and relatively inexpensive method to quantify muscle strength in children.

A hand-held dynamometer is a battery-operated device consisting of strain gauges that records force in Newtons or pounds. HHD is a reliable and valid method for obtaining muscle force or torque measurements in adults4,9–11 and children.12–16 However, normative or reference isometric muscle strength values obtained using HHD are limited, particularly for children. Force reference values obtained using HHD have been reported for some upper and lower extremity muscle groups in children who are healthy (typically developing), aged 3.5 to 16 years.17,18 These studies were significant in that they reported muscle force values partitioned by age and gender for several muscle groups using a relatively large sample of children. The number of children, however, in each age/gender group was relatively small (9 to 23 children) and force rather than torque values were reported. Both force and torque are measures of muscle strength. Because torque [Newton-meters (Nm)] is equal to force (N) times the perpendicular distance (m) from the axis of rotation to the point of force application, torque is a more appropriate measure when comparing strength between children of different heights or when comparing measurements (test-retest) within individual children, especially during the growing years.19

Significant variability in strength has been reported between individual children due to factors associated with growth. In children, strength increases with age, height, and weight.17,18,20,21 There is a positive correlation between age and isometric16–18,22 and isokinetic16,20,22,23 muscle strength in children. Although some suggest that age and height account for the greatest variance in strength in children17,20,22; others report that age and weight were more appropriate predictors of strength in children.18,21 Gender differences16,18,23–25 emerge at puberty as males gain stature and develop increased lean body mass17 and cross-sectional muscle area.22 Males become significantly stronger than females in the majority of upper extremity muscle groups at approximately 10 to12 years of age.17,18,22 Given the interaction between age, gender, height, and weight, it is unclear which of these factors has the greatest effect on muscle strength in children. Muscle strength reference values, therefore, need to be established that partition force and torque according to these factors.

Physical activity has also been found to have a positive effect upon muscle strength in children.26–28 Following progressive resistive training, strength increases have been reported in children who are healthy26 and in children with cerebral palsy.28 Children who participated in a sport’s program were found to be significantly stronger than those who did not participate in a sport’s program.27 It remains unclear as to what type of physical activity, participation in organized sports or the amount of time spent in active play (defined as performing activities such as biking, running, jumping, climbing, skating, or roller blading) promotes increased strength in children.

For children, adequate strength is required for the performance of gross motor skills such as walking, climbing, jumping, and hopping. Because functional performance deficits in children may be due to underlying muscle weakness, there is a need to accurately measure muscle strength in children. Assessment of muscle strength in children is also important when identifying impairments, tracking the course of a given condition, measuring improvement, and determining the effectiveness of intervention.3 Because a limited number of lower extremity muscle force and torque reference values are available for young children, aged 6 to 8 years, and questions remain as to the influence of gender, age, height, weight, and physical activity upon strength in young children, this study was undertaken. The purposes were to: (1) establish muscle force and torque reference values for 6 to 8 years old, healthy (typically developing) children for 6 lower extremity muscle groups including the hip flexors, extensors, abductors and adductors, and knee extensors and flexors; (2) determine the effects of gender, age, height, weight, and physical activity on strength in this age group; and (3) determine intrarater reliability for a single examiner when obtaining muscle force values, determining the distance from the joint center to the point of HHD application and obtaining muscle torque values.

METHODS

Intrarater Reliability

A pilot study was conducted to establish intrarater reliability for the single pediatric physical therapist examiner who would be collecting the muscle force and torque data using the HHD. Data collection, using the instrumentation and procedures outlined below, was performed 1 to 3 days apart using a convenience sample of 17 children who were healthy. Eight males and 9 females participated in the pilot study; the mean age was 7.5 ± 1.4 years, mean height was 128.8 ± 8.9 cm, and mean weight was 28.6 ± 7.1 kg. Data obtained from these subjects were not included in the full study.

Subjects

Subjects included 154 children who were healthy and developing typically, aged 6 to 8 years, recruited from public and private elementary schools. Nearly equal numbers of children were recruited within each age group: 48 six year olds, 55 seven year olds, and 51 eight year olds (Table 1). Numbers of males and females, mean weight and height, and leg dominance for each age group are also presented in Table 1. Children were excluded if within the past 6 months they had any injuries to the spine, pelvis or lower extremity, or had any known mental, learning, or physical disabilities that may have affected their ability to understand the directions and/or perform the required strength tests.

T1-2
TABLE 1:
Demographic Information for the 154 Children

Instrumentation

A Microfet II HHD (Hoggan Health Industries, Draper, UT) was used to record force in pounds (lbs). The Microfet HHD was chosen because it measures both perpendicular and nonperpendicular forces applied to the plate head, which is important when assessing forces generated at the hip and knee. The sensitivity (0.1 lbs) and range (0.8–150 lbs) of the HHD was within the force ranges produced by young children.19 A metal tape measure was used to measure distance (m) from the joint center to the location where the dynamometer was applied.

Procedures

Approval to conduct this study was obtained from the sponsoring institution’s Institutional Review Board. School administrators and classroom teachers from 2 school districts and 12 elementary schools granted permission to allow students to be recruited for participation in this study. Letters, which included an explanation of the purposes of the study; confidentiality and safety procedures; a detailed description of the study procedures; and a child information form which included date of birth, a brief medical history and physical activity level, were sent home with students in grades 1 to 3. Children who met the inclusion criteria and whose parents returned the signed consent form and the completed child information form were invited to participate in this study. All testing took place in the child’s school during times convenient to the children and their teachers. After an explanation of the procedures, the child signed the assent form. Height and weight were measured with the shoes removed using a metal tape measurer and Taylor Precision Products digital scale, respectively. Leg dominance was determined by placing a ball directly in front of the child and asking him/her to kick the ball; the kicking leg was determined to be the dominant leg.

HHD testing procedures were established by combining information provided by a videotaped protocol developed by Bohannon29 and a procedural guide developed by Knutson et al.19 All muscles were tested in their mid-muscle-length position (Fig. 1). Specific subject position, examiner position and stabilization, HHD placement, joint centers/axes, and distance from the joint axis of rotation to HHD placement location are presented in Table 2 for the 6 muscle groups tested. The order of muscle testing as presented in Figure 1 remained the same for each subject. The subject was positioned on a sturdy, adult size chair or the therapy mat in the appropriate test position for each muscle group (Fig. 1 and Table 2). Colorful tape was placed on the mat at two 45° angles to serve as a visual guide when positioning the subjects’ trunk and lower extremities. A pen mark was placed on the body landmarks needed for distance measurements and served as a consistent marker for HHD placement. “Make tests” (the maximal force exerted by the subject while the examiner holds the dynamometer stationary with verbal instructions “push as hard as you can”),30 as opposed to “break tests”(the maximal force produced when the examiner pushes against the child’s body part while the child attempts to hold the test position in response to the verbal instructions “hold, don’t move”)30 were used in this study because less residual muscle soreness is associated with a make test.31 Following 2 practice trials using the nondominant leg, 3 test trials were performed for each muscle group using the dominant leg. A mean of the 3 test trials was used for data analysis. Five-second muscle contraction durations were used to allow subjects to gradually achieve maximal force.31 Rest times of approximately 1 to 2 minutes were used between trials. Total test duration for each subject was approximately 25 to 30 minutes. Upon completion, the child received a small reward such as a ball, toy car, or play dough.

F1-2
Fig. 1.:
A–F, Strength testing positions for the 6 lower extremity muscle groups using a hand-held dynamometer [(A) knee extension, (B) knee flexion, (C) hip abduction, (D) hip adduction, (E) hip flexion, and (F) hip extension].
T2-2
TABLE 2:
Strength Testing Procedures Using Hand-Held Dynamometer19,30

Data Analysis

Using the pilot data (n = 17), intraclass correlation coefficients (ICC) (3, 3) (2-way mixed, absolute agreement) were used to determine intrarater reliability for muscle force, distance from the joint axis to the center of HHD placement, and torque for the single examiner.

Komogorov-Smirnov and the Shapiro-Wilk tests of normality were performed for each muscle group’s force and torque data (n = 154) (pooled for age) (Appendix). Knee flexion and hip adduction force/torque data were not normally distributed; 1 outlier within the knee flexion data and 2 outliers within the hip adduction data were identified and removed [outliers were outside the ±3 standard deviations (SD) range]. The tests for normality were recalculated and the data for all 6 muscle groups were then normally distributed and homogeneous (Levene’s test) (Appendix).

Using the normal data set (outliers removed), descriptive statistics and strength reference values were determined. In addition, muscle torque and force were examined for each age group to determine cutoff values for “normal” versus “below normal” strength. When using the mean minus 2 SDs to determine the cutoff values, no greater than 2% of the children who were apparently healthy were identified as having below normal muscle strength. Therefore, cutoff values were calculated based upon the mean minus 2 SDs for each muscle group within each age group.

To determine gender and age group differences in torque and force for the 6 muscle groups, 2 (gender) × 3 (age) analysis of variance and Bonferroni post hoc analyses were performed. To determine the effects of height and weight upon torque, multivariate analysis of variance for each muscle group was performed. Step-wise, multiple linear regressions were used to determine the best predictor of torque with regards to height, weight, and age group for each muscle group.

Subjects were partitioned into categories based upon the number of hours per day spent in active play (category 1: 0 to 1 hours/day, category 2: 1 to 2 hours/day, and category 3: 3 or more hours/day). Subjects were also partitioned into categories based upon the number of hours per week in which they participated in an organized sport (category 1: no participation, category 2: 1 to 2 hours/week, and category 3: 3 or more hours/week). Multivariate analysis of variance with Student-Newman-Keuls post hoc analyses were performed to determine the effects of time spent in play and time spent in organized sports upon lower extremity muscle force/torque.

RESULTS

Intrarater reliability ICCs for the single pediatric physical therapist examiner ranged from 0.82 to 0.91 for muscle torque measured using the HHD for the 6 muscle groups in the pilot study (Table 3). ICCs ranged from 0.72 to 0.91 when measuring the distance from the location of force application to the joint center (Table 3). Based on these findings, intrarater reliability for the single pediatric physical therapist was considered good to excellent.32

T3-2
TABLE 3:
Intrarater Reliability Intraclass Correlations Coefficients (ICC) for Muscle Torque and Distance from the Joint Center to Hand-Held Dynamometer Location for the Single Pediatric Physical Therapist Rater (n = 17)

The means and SDs for muscle force (Table 4) and muscle torque (Table 5) were determined for each of the 6 lower extremity muscle groups (n = 154) [knee flexion (n = 153) and hip abduction (n = 152); outliers removed].

T4-2
TABLE 4:
Mean ± SD Muscle Force (lbs) for Children, Aged 6 to 8 Years (1-Way ANOVA and Bonferroni Post Hoc Values)
T5-2
TABLE 5:
Mean ± SD Muscle Torque (Nm) for Children, Aged 6 to 8 Years (1-Way ANOVA and Bonferroni Post Hoc Values)

To identify children who may have “below normal” muscle strength, cutoff values for force and torque were determined for the 6- to 8-year-old children for each muscle group (Table 6). Muscle force and torque increased significantly with age for the 6 muscle groups (Tables 4 and 5, Fig. 2). Post hoc analyses revealed that for all muscle groups except hip adduction, torque produced by the 8-year-old children was significantly greater than torque produced by the 7-year-old children and torque produced by the 7-year-old subjects was greater than torque produced by the 6-year-old children (Table 5). For hip adduction torque, there were no significant differences between 7- and 8-year-old children (p = 0.31), however, 7- and 8-year-old subjects produced significantly greater torque than 6-year-old children (Table 5). These same findings were also true for force (Table 4).

T6-2
TABLE 6:
Cutoff Strength Values for Torque and Force for 6- to 8-Year-Old Children
F2-2
Fig. 2.:
Muscle torque (Nm) for the 6 lower extremity muscle groups for 6-, 7-, and 8-year-old children [n = 154 except for knee flexion (n = 153) and hip adduction (n = 152) (outliers removed)]. All comparisons between group torque means for 6 and 7, 7 and 8, and 6 and 8 year olds within each muscle group are significant (p ≤ 0.05 to p ≤ 0.001) except for hip adduction which was not significantly (NS) different between the 7- and 8-year-old children.

There were no statistically significant differences between male and female children (pooled for age) for hip extension torque (F1,148 = 0.53; p = 0.47), hip abduction torque (F1,148 = 0.14; p = 0.71), hip adduction torque (F1,148 = 1.5; p = 0.2), knee extension torque (F1,148 = 0.20; p = 0.65), or knee flexion torque (F1,148 = 1.0; p = 0.31). For hip flexion torque, male children produced significantly greater (F1,148 = 5.8; p = 0.02) torque when compared with female children.

Muscle torque was significantly greater in taller children (p = 0.001–0.03) for the 6 muscle groups. Also, muscle torque was significantly greater in heavier children for all muscle groups (p = 0.001–0.03) except the knee extensors (p = 0.64). Stepwise multiple regression equations revealed that height accounted for the greatest percentage of the variance (28%–49%) for torque for all muscle groups tested. Adding weight [height + weight (r2 = 0.28–0.53)] and age [height + weight + age (r2 = 0.28–0.56)] did not significantly add to the predictive value for torque for all muscle groups. For example, height alone accounted for 47% of the variance for knee extension torque. When weight then age was added, the r2 increased to 0.50 and 0.54, respectively.

Of the 147 children whose parents reported active play, 29 (19.7%), 53 (36.1%), and 65 (44.2%) children spent 0 to 1, 2, or 3 or more hour(s) per day in active play, respectively. The number of hours children spent in active play did not significantly affect muscle torque for the 6 muscle groups (p = 0.06–0.9). One hundred forty parents completed the questions concerning organized sport participation. Of these 140 children, 75 children (53%) did not participate in any organized sport during the time of this study. Thirty-six (26%) and 29 (21%) children participated in 1 to 2 or 3 or more hours of organized sports per week. Hours per week spent in organized sports did not affect knee flexion (F2,137 = 2.52; p = 0.8) or hip extension (F2,137 = 1.89; p = 0.16) torque. However, when compared with children who participated in 2 hours or less of organized sports per week, children who participated 3 or more hours per week produced greater knee extension torque (F2,137 = 3.31; p = 0.04), hip adduction torque (F2,137 = 4.76; p = 0.01), hip abduction torque (F2,137 = 4.13; p = 0.02), and hip flexion torque (F2,137 = 3.54; p = 0.03).

DISCUSSION

Strength Reference and Cutoff Values

The primary purpose of this study was to provide muscle strength reference values for young children for lower extremity muscle groups. These muscle groups are needed for the execution of frequently performed functional gross motor skills such as walking, climbing, jumping, and hopping. Force and torque values measured using HHD are provided for the hip extensors, flexors, abductors and adductors, and knee extensors and flexors to enable clinicians to judge whether their clients of the same age, height, and weight produce muscle strength values that fall within the reference ranges. Until more research findings are available, the reference and cutoff force and torque values provided by this study can be used to identify possible strength deficits in 6- to 8-year-old children. Because 98% of the children who were healthy (typically developing) and who participated in the study produced force/torque values that fell within 2 SDs of the mean, children may be suspected of having muscle weakness if they produce strength values which fall below the given minimum cutoff values. In the current study, the 3 children that produced muscle torques/forces below the given cutoff values were shorter, under-weight females (1.7–3.4 and 1.3–2.5 SDs below mean weight and height, respectively). Therefore, the cutoff values should be carefully applied considering age, height, and weight of the individual child.

Unfortunately, functional abilities were not assessed for the children who fell below the strength cutoff values. However, if muscle weakness is identified and contributes to observable functional limitations, a referral should be made to the appropriate medical specialist and/or intervention should be initiated.

Variables Related to Strength in Children

Similar to past reports,17,18,20,21 higher values of age, height, and weight (either independently or in combination) in the subjects in this study were associated with greater strength in the 6 muscle groups. Height was the strongest predictor of strength when compared with age or weight in children aged 6 to 8 years. Height has also been found to be the best predictor of muscle strength in children in some past studies,22,23 however, others have reported that age or weight are more appropriate predictors of strength.17,18,21 One reason for this ambiguity may be due to the variability in height and weight within each age group during these growth years. In addition, previous studies have included children as old as 16 years, which would factor into the predictive capabilities of age, height, and weight on strength in children due to the significant changes in these variables that occur during puberty.

No strength differences between the genders were expected because the 6- to 8-year-old children in this study were below the average age (10–12 years) when strength differences generally emerge.17,18,22 As expected, there were no gender differences in 5 of the 6 lower extremity muscles tested, however, the boys generated greater hip flexor muscle force and torque than the girls. Similarly, Backman et al17 found that hip flexor strength was greater in boys when compared with girls, aged 5.5 to 7 years. In contrast, Hosking et al24 found no significant differences in strength between boys and girls in any of the 6 muscle groups tested including the hip flexors. The reason for possible gender difference in hip flexor muscle strength remains unclear. Further research is necessary to investigate hip flexor strength differences between boys and girls.

An additional finding of this study was that the number of hours per week spent participating in organized sports activities influenced strength in children, whereas the number of hours spent in active play did not affect strength. Subjects who participated in 3 or more hours of organized sports per week produced higher strength values in 4 of the 6 lower extremity muscle groups. Previous research has reported a positive relationship between participation in exercise or sports programs and muscle strength in children.26,27,33 Because organized sports generally include strengthening exercises or mandatory drills, children who participate in these types of activities may demonstrate improved strength. In contrast to the positive relationship between the participation in organized sports and strength, the number of hours spent in active play (defined as performing activities such as biking, running, jumping, climbing, skating, or roller blading) did not result in any significant strength differences. Because these activities may not always be consistently supervised by an adult or are not as structured as organized sports programs, children may not have been engaged in physical activity for the entire play duration. Although further exploration of the application of these findings to children with identified muscle weaknesses and/or disabilities is necessary, it suggested that pediatric therapists encourage children to participate in organized sports to help increase and/or maintain muscle strength.

Reliability of HHD

This study supported the use of HHD in determining muscle strength in children who are healthy. Intrarater reliability was good to excellent for a single, pediatric physical therapist examiner using HHD to obtain lower extremity muscle force and torque in young children. Similarly, in other studies, intrarater reliability using HHD has been found to be good to excellent when testing children who are healthy16 and children with disabilities.12,14 Interrater reliability was not measured in the current study, however, interrater reliability using HHD has been reported to be good to excellent when testing strength in children who are healthy and children with muscular dystrophy.13

As with all tests and measurements, there are a number of issues that must be addressed to maximize accuracy, reliability, and validity when using HHD. In regards to instrument selection, the specifications of the HHD must be considered to obtain the most accurate strength measurements possible. The HHD range and sensitivity should match the forces produced by the population under examination.19 For example, in this study, based upon information obtained from the literature17,18 and a clinician with expertise in using HHD with children (Knutson, personal communication, 2005),19 the MicroFet II HHD was chosen because the range (0.8–150 lbs) was compatible with the expected muscle forces generated by 6- to 8-year-old children. None of the children produced force values greater than the upper limits of the HHD. In addition, if one expects to capture small changes in strength over time, a HHD with appropriate sensitivity should be used. In the authors’ experience, small yet clinically significant, changes in the strength of patients with spinal cord injury and cerebral palsy can be captured using the MicroFet II HHD because it is sensitive to as little as 0.1 lb changes. In addition, the HHD was factory-calibrated immediately before initiation of this study; we recommend periodic recalibration of the HHD depending upon frequency of use.

Reliability is also enhanced with standardization of procedures, proper training, and experience using the HHD. Standardized HHD methods have been, or are currently being, developed with regards to subject position, joint position, examiner position, proximal joint stabilization, dynamometer placement, and method of resistance application.19,29,34 A clinician who is not experienced using a HHD should undergo training with an experienced clinician or, at a minimum, review the standardized HHD procedures.19,29 In addition, practice on a number of children who are healthy before testing patients with disabilities is recommended. Reliability, particularly in children, may also be affected by an individual child’s motivation, cooperation, the ability to follow directions and his/her accuracy in performing the test motion.17 Therefore, it is recommended that all children, but especially those who are young, be given clear, simple verbal instructions, demonstrations, and practice trials before the performance of formal HHD strength testing.

Clinical Implications

Although MMT may be the most appropriate method for testing muscle strength when a child cannot generate enough force to hold against manual resistance applied by the examiner (MMT grades 1–3),1,2 MMT is not sensitive enough to detect small, yet clinically important changes, in muscle strength particularly for MMT grades which require maintaining a contraction against resistance. HHD is sensitive to small changes in muscle strength,3 particularly for muscles receiving MMT grades 3+ to 5. The ability to accurately document changes in muscle strength is imperative for creating an accurate problem list, establishing appropriate goals and justifying the duration and frequency of intervention.

Torque, as opposed to force, is more reflective of muscle strength across the population, particularly in children, as it normalizes the force value according to the length of the lever arm. Obtaining torque values allows for strength comparisons to be made within an individual growing child and across children of different heights.14 Therefore, we recommend that if at all possible, the distance from the joint center to the application of the HHD (lever arm) be measured to determine torque for the individual child, which can then be compared with the reference values for that child’s age group. Another option would be to normalize the muscle group’s peak force to weight, height, or body mass index. Despite the fact that torque is the more appropriate measurement, it is recognized that due to time constraints in some clinical settings, it may not be possible to measure the lever arm distances. For this reason, both force and torque reference values have been provided by this study. We believe that force can be used for test-retest muscle strength comparisons if care is taken to consistently apply force at the same HHD placement location and if the child has not grown significantly between tests.

When using HHD with children with disabilities or injuries, the prevention of muscle substitution while the child is trying to achieve an isometric contraction is important for measurement accuracy. Alternate test positions to assess strength may need to be considered if unwanted muscle substitution occurs, the examiner is not strong enough to match the patient’s generated force or if the child cannot assume the standardized test positions due to impairments such as loss of range of motion or posture and balance deficits.5,8,31,35,36 In these instances, it is recommended that clinicians clearly document the alternate position and use the same position for future retest strength measurements.

Limitations

A limitation of this study was the use of a convenience sample of children that lived within a similar geographic location and were from a similar socioeconomic class. Therefore, the strength reference values obtained may or may not be representative of the entire population of children in this age group. The inability to control for environmental factors within each elementary school was also a limitation of this study. For example, the time of day of testing and the room environment varied from school to school. Also, the order of muscle testing was the same for every subject; therefore, practice, learning, or fatigue effects cannot be eliminated. The HHD strength data were generated by 1 pediatric physical therapist, therefore, caution should be exercised when interpreting the generalizability of the strength values and the intrarater reliability of the procedures. Finally, because the data involving both the amount of time spent in organized sports and active play activities were compiled from information reported by parents, the amount of physical activity should be considered a rough estimation that may have been subject to parental error or bias.

Future Research

Muscle force and torque normative values need to be established for children in all age groups for trunk and upper and lower extremity muscle groups using larger sample sizes. In addition, because we recommend that HHD be used to quantify strength for MMT grades 3+ and greater, HHD force and torque values need to be determined for MMT grades 3+, 4−, 4, 4+, and 5. Most importantly, an investigation needs to be completed to examine how isometric muscle strength correlates with or affects functional activities in children. Children with mild functional impairments affecting walking, jumping, hopping, and stair climbing could be identified and then tested to determine whether their strength values fall below the cutoff values provided by this study. Conversely, children who fall below the provided cutoff values could be tested further to determine whether they have coexisting functional limitations.

CONCLUSION

This study provides muscle force and torque reference and cutoff values for 6 lower extremity muscle groups as measured by HHD for children who are healthy and typically developing, aged 6 to 8 years old, to enable clinicians to judge whether clients of the same age, height, and weight produce muscle force/torque values that fall within the provided reference ranges. These values can be used to identify muscle weakness that may contribute to functional limitations in children and to monitor changes in strength in this population. Future research is needed to establish strength values for children in other age groups and document the link between strength and function.

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TU7-2
Appendix:
Normality and Homogeneity of Variances for All Muscle Groups (Pooled for Age) (n = 154 Unless Otherwise Indicated)
Keywords:

child; female; human movement system; isometric contraction/physiology; leg/physiology; male; muscle strength; muscle strength dynamometer; skeletal muscle/physiology; reference standards; reproducibility of results; torque

© 2008 Lippincott Williams & Wilkins, Inc.