**Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment**

Lan Le-Ngoc<sup>1</sup> and Jessica Janssen<sup>2</sup> <sup>1</sup>*Industrial Research Ltd, Christchurch* <sup>2</sup>*Burwood Academy of Independent Living, Christchurch New Zealand*

#### **1. Introduction**

52 Rehabilitation Medicine

Vain, A. (1995). Estimation of the functional state of skeletal muscle. In P. H. Veltink &

van der Lee, J. H., Beckerman, H., Lankhorst, G. J., & Bouter, L. M. (2001). The

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responsiveness of the Action Research Arm test and the Fugl-Meyer Assessment scale in chronic stroke patients. *Journal of Rehabilitation Medicine,* Vol*.*33, No.3, (Mar

tone assessment by a myometric method. *Journal of Mechanics in Medicine and* 

and the SEM. *Journal of Strength and Conditioning Research,* Vol*.*19, No.1, (Feb 2005),

Changes in passive tension of muscle in humans and animals after eccentric exercise. *Journal of Physiology,* Vol*.*533, No.Pt 2, (Jun 2001), pp.593-604, ISSN 0022An important component of physical therapy is to conduct assessment of a patient's mobility including muscle strength and joint range of motion (ROM).

The purposes of this study were to investigate the possibility of measuring dynamic muscle strength using a new hand-held device and to assess its validity and reliability. If proven valid and reliable, this device will provide a practical tool for physical therapists to perform dynamic muscle assessment in a clinical setting.

The current standard clinical evaluation and diagnostic tool for muscle strength assessment is the manual muscle testing (MMT) method, using a 5-point grading scale (Clarkson (2000); Petty (2011)). Although it has been a clinically useful tool for over forty years, its accuracy and reliability remains questionable (Cuthbert & Goodheart (2007); Frese et al. (1987)).

To overcome the limitations of the MMT, isometric hand-held dynamometers (HHD) have been developed to aid therapists in clinics (Andrews (1991)). HHDs are generally small and portable, and measure strength objectively in kilograms, pounds or newtons. The clinician holds the HHD between his or her force-applying hand and the patient's limb segment. The clinician stabilises the limb segment while encouraging the patient to exert as much force against the device as possible and the maximum force is recorded by the HHD. Such devices have been proven to have good to excellent reliability in different populations (Andrews (1991); Bohannon & Andrews (1987); Stark et al. (2011)). In a single test, however, they can assess the strength of a patient at only one joint angle, rather than through the patient's entire ROM. Although this technique provides a crucial tool for clinical quantification of joint strength at a fixed static position (isometric), it cannot measure properties from dynamic muscle performance assessments.

Isokinetic dynamometers, such as the Cybex (USA) or the Biodex (USA), are considered as the gold standard in simultaneous strength and angle measurements for the evaluation of dynamic muscular performance (Kannus (1994); Baltzopoulos & Brodie (1989); Osternig (1986); Lund et al. (2005); Drouin et al. (2004)). Strength profiles showing instantaneous torque versus joint angle are generated and a number of properties such as dynamic peak torque, peak torque angle, angle-specific torque, power, and energy used can be determined. The dynamic strength profiles can also be used to detect weaknesses over small

**2. Validity and reliability of dynamic muscle strength assessment**

**2.1 Instrumentation**

Fig. 3).

**2.2 Protocol**

measures.

**2.2.2 Design**

IRL-HDD:

**2.2.1 Participants**

written consent before testing.

session to prevent fatigue.

curves recorded by both dynamometers.

• Defining the zero position of the joint;

participant reaches the end of joint movement.

commencing the measurement;

This section describes the test protocol and the results of using the IRL-HHD to perform concentric elbow flexion and concentric knee extension assessment on human subjects.

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 55

Two dynamometers, the IRL-HHD and the isokinetic dynamometer (Biodex), were used to measure maximal concentric strength for elbow flexion and knee extension. The Biodex measurements were corrected for the effect of gravity caused by the Biodex lever arm. For the IRL-HHD tests, a seat and an arm rest attached to a plinth were used to position and restrain the participants in a similar manner to the tests carried out using the Biodex (see Fig. 2 and

A registered physiotherapist conducted the tests using the IRL-HHD and another registered physiotherapist performed the Biodex tests. Both therapists were blinded from the outcome

Fifteen able-bodied, healthy adults participated in this study, which was approved by the University of Otago (New Zealand) Ethics Committee. All participants provided informed

There were two test sessions for each participant using the IRL-HHD, and one test session using the Biodex. Each test session comprised one sub-maximal contraction, and three repeated maximal strength contractions to perform right elbow flexion and right knee extension. Each measurement was followed by a one minute rest period. The order of sessions was randomized for each participant, and within each session the order in which joints were tested was randomized. The participants were given five minutes rest between each test

The distances from the centre of the force pad to the rotational axis of elbow and knee were recorded for each participant and used to convert measured forces into joint torques. Peak torque, peak torque angle and total work were obtained from the torque versus joint angle

A three-stage procedure was followed to record strength versus joint angle data using the

• Moving the joint to the start position, positioning the device to resist the limb motion and

• Instructing the participant to exert maximal muscular contraction while providing a resistance to control the movement of the joint, and stopping the measurement when the

For concentric elbow flexion, the participant was seated beside the end of the plinth, and the right arm was strapped to an arm rest at 60° shoulder flexion and 30° shoulder abduction

regions of a specific joint's ROM. Other advantages of the isokinetic dynamometer over the current isometric HHDs are that assessor's strength is not an issue; the subject is stabilized consistently during testing; and the joint angle and strength are measured simultaneously during testing (Lund et al. (2005); Martin et al. (2006); Harlaar et al. (1996)). Disadvantages of these devices are their size and cost, which make them impractical for routine clinical examinations (Li et al. (2006);Mital et al. (1995)).

Recognising the needs for better clinical strength assessment tools, there have been a number of attempts to incorporate angle measurement in the strength assessment (Li et al. (2006); Roebroeck et al. (1998)). However, there have been no published results on the use of a single hand-held device to perform dynamic strength measurements on human subjects. A new device, referred to as the IRL-HHD (Fig. 1), is a single hand-held device that can measure force and angle simultaneously while the joint moves through its ROM1. The ability to measure force and angle simultaneously means that it can measure energy or power in a similar manner to an isokinetic dynamometer. In order for the IRL-HHD to capture dynamic joint strength, the assessor must provide sufficient force to resist the limb movement, but also allow the limb to move at a constant and controllable pace. This is not a trivial task and the assessor may not be able to concentrate on keeping the device in perfect alignment with the limb. The algorithm used in the IRL-HHD can measure the required joint angle accurately without having to maintain the alignment of the longitudinal axis of the device with respect to the limb. In some cases, this feature allows the joint to reach its full ROM (see Fig. 2 for an example of measuring concentric elbow flexion where the longitudinal axis of the IRL-HHD does not have to be aligned with the forearm). The IRL-HHD and the assessment techniques have been shown to be reliable and valid by measuring concentric flexion of a simulated mechanical arm, which was used to eliminate the effects of human variability (Janssen & Le-Ngoc (2009)).

Fig. 1. IRL Hand-held dynamometer.

This article describes the validity and reliability trials of the device to measure concentric elbow flexion and concentric knee extension on human subjects. Other possible uses of the IRL-HHD in clinical and on-field assessments are also discussed.

<sup>1</sup> Patent WO/2011/002315 - Inventor: Industrial Research Ltd (IRL)

#### **2. Validity and reliability of dynamic muscle strength assessment**

This section describes the test protocol and the results of using the IRL-HHD to perform concentric elbow flexion and concentric knee extension assessment on human subjects.

#### **2.1 Instrumentation**

2 Will-be-set-by-IN-TECH

regions of a specific joint's ROM. Other advantages of the isokinetic dynamometer over the current isometric HHDs are that assessor's strength is not an issue; the subject is stabilized consistently during testing; and the joint angle and strength are measured simultaneously during testing (Lund et al. (2005); Martin et al. (2006); Harlaar et al. (1996)). Disadvantages of these devices are their size and cost, which make them impractical for routine clinical

Recognising the needs for better clinical strength assessment tools, there have been a number of attempts to incorporate angle measurement in the strength assessment (Li et al. (2006); Roebroeck et al. (1998)). However, there have been no published results on the use of a single hand-held device to perform dynamic strength measurements on human subjects. A new device, referred to as the IRL-HHD (Fig. 1), is a single hand-held device that can measure force and angle simultaneously while the joint moves through its ROM1. The ability to measure force and angle simultaneously means that it can measure energy or power in a similar manner to an isokinetic dynamometer. In order for the IRL-HHD to capture dynamic joint strength, the assessor must provide sufficient force to resist the limb movement, but also allow the limb to move at a constant and controllable pace. This is not a trivial task and the assessor may not be able to concentrate on keeping the device in perfect alignment with the limb. The algorithm used in the IRL-HHD can measure the required joint angle accurately without having to maintain the alignment of the longitudinal axis of the device with respect to the limb. In some cases, this feature allows the joint to reach its full ROM (see Fig. 2 for an example of measuring concentric elbow flexion where the longitudinal axis of the IRL-HHD does not have to be aligned with the forearm). The IRL-HHD and the assessment techniques have been shown to be reliable and valid by measuring concentric flexion of a simulated mechanical arm, which was used to eliminate the effects of human variability (Janssen & Le-Ngoc (2009)).

This article describes the validity and reliability trials of the device to measure concentric elbow flexion and concentric knee extension on human subjects. Other possible uses of the

IRL-HHD in clinical and on-field assessments are also discussed.

<sup>1</sup> Patent WO/2011/002315 - Inventor: Industrial Research Ltd (IRL)

examinations (Li et al. (2006);Mital et al. (1995)).

Fig. 1. IRL Hand-held dynamometer.

Two dynamometers, the IRL-HHD and the isokinetic dynamometer (Biodex), were used to measure maximal concentric strength for elbow flexion and knee extension. The Biodex measurements were corrected for the effect of gravity caused by the Biodex lever arm. For the IRL-HHD tests, a seat and an arm rest attached to a plinth were used to position and restrain the participants in a similar manner to the tests carried out using the Biodex (see Fig. 2 and Fig. 3).

#### **2.2 Protocol**

A registered physiotherapist conducted the tests using the IRL-HHD and another registered physiotherapist performed the Biodex tests. Both therapists were blinded from the outcome measures.

#### **2.2.1 Participants**

Fifteen able-bodied, healthy adults participated in this study, which was approved by the University of Otago (New Zealand) Ethics Committee. All participants provided informed written consent before testing.

#### **2.2.2 Design**

There were two test sessions for each participant using the IRL-HHD, and one test session using the Biodex. Each test session comprised one sub-maximal contraction, and three repeated maximal strength contractions to perform right elbow flexion and right knee extension. Each measurement was followed by a one minute rest period. The order of sessions was randomized for each participant, and within each session the order in which joints were tested was randomized. The participants were given five minutes rest between each test session to prevent fatigue.

The distances from the centre of the force pad to the rotational axis of elbow and knee were recorded for each participant and used to convert measured forces into joint torques. Peak torque, peak torque angle and total work were obtained from the torque versus joint angle curves recorded by both dynamometers.

A three-stage procedure was followed to record strength versus joint angle data using the IRL-HDD:


For concentric elbow flexion, the participant was seated beside the end of the plinth, and the right arm was strapped to an arm rest at 60° shoulder flexion and 30° shoulder abduction

ROM measurements between the IRL-HHD and the Biodex. For knee extension, the Biodex chair and the fixture beneath the chair prevented participants from reaching full knee flexion. In order to provide a meaningful comparison of the peak torque angle, the starting position of the knee extension was set at the maximum possible knee flexion angle but not greater than 110°. Because of this preset starting position, it was not meaningful to report knee ROM

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 57

During testing, the physiotherapist manually recorded any unusual events, such as loss of control, or excessive movement of the IRL-HHD. These tests were discarded from the data set, which was justified on the basis that it would be standard clinical practice to ignore erroneous

The ability of the therapist to maintain the control of the dynamic measurement is discussed

(a) Start and end position of the IRL-HHD measurement

(b) Start and end position of the Biodex measurement

Fig. 3. Concentric knee extension measurements with the IRL-HHD and the Biodex.

measurements using the Biodex.

tests at the time of testing.

in Section 4.1.

(Fig. 2). The zero position of the elbow was identified by placing the device lengthwise on a reference line between the acromion and the lateral epicondyle of the humerus. The device was placed with the force pad 2 cm proximal of the wrist while the arm was fully extended. It is possible to have a negative start angle, which is a measure of elbow hyperextension.

(a) Start and end position of the IRL-HHD measurement

(b) Start and end position of the Biodex measurement

Fig. 2. Concentric elbow flexion measurements with the IRL-HHD and the Biodex.

For concentric knee extension, the participant was seated using the same arrangement as on the Biodex (Fig. 3). The zero position was set against a horizontal surface. The device was placed with the force pad 10 cm proximal of the medial malleolus and the leg was moved to the starting position (110° knee flexion) before commencing the measurement.

The isokinetic mode of the Biodex was used for testing with a maximum speed of 60°/s. In this mode, the start and end ROM had to be set before starting the test. For elbow flexion, the zero elbow position was set so that the participant's arm was supported at 60° shoulder flexion and 30° shoulder abduction (Fig. 2). Unfortunately, the Biodex strap restricted some participants from reaching end ROM, so it was not possible to provide a comparison of elbow 4 Will-be-set-by-IN-TECH

(Fig. 2). The zero position of the elbow was identified by placing the device lengthwise on a reference line between the acromion and the lateral epicondyle of the humerus. The device was placed with the force pad 2 cm proximal of the wrist while the arm was fully extended. It is possible to have a negative start angle, which is a measure of elbow hyperextension.

(a) Start and end position of the IRL-HHD measurement

(b) Start and end position of the Biodex measurement

For concentric knee extension, the participant was seated using the same arrangement as on the Biodex (Fig. 3). The zero position was set against a horizontal surface. The device was placed with the force pad 10 cm proximal of the medial malleolus and the leg was moved to

The isokinetic mode of the Biodex was used for testing with a maximum speed of 60°/s. In this mode, the start and end ROM had to be set before starting the test. For elbow flexion, the zero elbow position was set so that the participant's arm was supported at 60° shoulder flexion and 30° shoulder abduction (Fig. 2). Unfortunately, the Biodex strap restricted some participants from reaching end ROM, so it was not possible to provide a comparison of elbow

Fig. 2. Concentric elbow flexion measurements with the IRL-HHD and the Biodex.

the starting position (110° knee flexion) before commencing the measurement.

ROM measurements between the IRL-HHD and the Biodex. For knee extension, the Biodex chair and the fixture beneath the chair prevented participants from reaching full knee flexion. In order to provide a meaningful comparison of the peak torque angle, the starting position of the knee extension was set at the maximum possible knee flexion angle but not greater than 110°. Because of this preset starting position, it was not meaningful to report knee ROM measurements using the Biodex.

During testing, the physiotherapist manually recorded any unusual events, such as loss of control, or excessive movement of the IRL-HHD. These tests were discarded from the data set, which was justified on the basis that it would be standard clinical practice to ignore erroneous tests at the time of testing.

The ability of the therapist to maintain the control of the dynamic measurement is discussed in Section 4.1.

(a) Start and end position of the IRL-HHD measurement

(b) Start and end position of the Biodex measurement

Fig. 3. Concentric knee extension measurements with the IRL-HHD and the Biodex.

(a) Elbow Flexion (b) Elbow Flexion

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 59

(c) Knee Extension (d) Knee Extension

Fig. 6 shows scatter graphs of the mean peak torque and mean work between the Biodex (x-axis) and the IRL-HHD (y-axis) for elbow flexion, and Fig. 7 shows the corresponding data for knee extension. The error bars show the individual SDs for the Biodex and the IRL-HHD. It is interesting to note that the error bars for the Biodex are generally larger than those for the IRL-HHD, indicating that variability of the tested participants is a significant factor in strength measurements. For elbow flexion, fourteen out of fifteen participants generated peak torques less than 50 Nm. For knee extension, the physiotherapist was unable to resist any torque greater than 100 Nm, whereas five participants generated more than 100 Nm on the

Six repeated measurements with the IRL-HHD and three with the Biodex were used to calculate the ICCs and their 95% confidence intervals. The results are shown in Table 1. The ICC1,1 values of both devices indicates excellent intratester reliability in the peak torque and work for both elbow flexion and knee extension. Repeatability of the peak torque angle of both tests by both devices is rated fair to good. However the confidence intervals indicates that only the knee peak torque angle obtained from the Biodex can be considered as fair to good, while all other peak torque angle measurements are poor. To determine if the mean of three measurements is a more reliable measure of the peak torque angle, the ICCs1,3 of

Fig. 4. Strength profiles of one participant for concentric elbow flexion and knee extension

obtained from the IRL-HHD (a, c) and the Biodex (b, d).

Biodex.

**3.2 Intratester reliability**

#### **2.3 Statistical analysis**

#### **2.3.1 Descriptive statistics**

Descriptive statistics of muscle torques, joint angles and muscular work are presented in Nm, degrees (°) and J respectively. Torque is calculated from the measured peak force times the length from the centre of the force pad to the rotational axis of the elbow or knee. Work is defined as output of mechanical energy, that is, externally applied force multiplied by the distance through which it is applied. In the concentric measurements, work can be found by calculating the area under the torque versus angular displacement curve. Mean and standard deviations (SDs) are reported. All analyses were performed using the Matlab software package (USA).

#### **2.3.2 Intratester reliability**

The degree of correlation between six repetitions of all the maximal strength tests using the IRL-HHD is calculated with the intraclass correlation co-efficient (ICC1,1) defined by Schrout and Fleiss (1979). The same test was performed on the three repetitions of the Biodex. The most critical reliability assessment is the ICC1,1, which assumes that every individual measurement is independent and the error of measurement is assumed to be normally distributed. Other authors have used ICC2,1 for their reliability measurement, which tends to give more optimistic values than ICC1,1. In this article all ICC1,1 results are almost equal to the ICC2,1 values. According to Fleiss (1986), the reliability of an ICC over 0.75 is considered to be excellent, and between 0.4-0.75 as fair to good.

#### **2.3.3 Validity**

The agreement between the two devices can be quantified using the Bland-Altman 95% limits of agreement (LOA) method (Bland & Altman (1986)). The LOA method is based on the mean and SD of the differences between the measurements by the two devices. For repeated measurements, a one-way ANOVA is performed for each device separately. Outcomes of the one-way ANOVA are then used to calculate the lower and upper LOA (mean ± 1.96 times SD)(Bland & Altman (2007)).

#### **3. Results**

#### **3.1 Descriptive Statistics**

Five men and ten women participated in this research. The participants' ages ranged from 23 to 45 years (mean±SD, 32.6±7.2y). Fig. 4 shows typical strength profile plots between the IRL-HHD and the Biodex for one participant. Although the shape of torque versus angle graphs were not the same for the IRL-HHD and the Biodex, both methods show consistency in repeated measurements.

Fig. 5 shows the speed of all measurements obtained with the IRL-HHD. It shows that the physiotherapist was able to control the speed of each measurement very well for the elbow flexion. Only two participants generated speeds more than 100°/s while nine generated speeds less than 80°/s. It was more difficult for the physiotherapist to control the speed for the knee extension and five participants generated speed greater than 100°/s. The range of speeds for those participants was also greater, suggesting that the physiotherapist was not in control of all the tests. Since the speed is controlled entirely from the perception of the assessor, an error of ±20°/s is considered to be reasonable in this study.

Fig. 4. Strength profiles of one participant for concentric elbow flexion and knee extension obtained from the IRL-HHD (a, c) and the Biodex (b, d).

Fig. 6 shows scatter graphs of the mean peak torque and mean work between the Biodex (x-axis) and the IRL-HHD (y-axis) for elbow flexion, and Fig. 7 shows the corresponding data for knee extension. The error bars show the individual SDs for the Biodex and the IRL-HHD. It is interesting to note that the error bars for the Biodex are generally larger than those for the IRL-HHD, indicating that variability of the tested participants is a significant factor in strength measurements. For elbow flexion, fourteen out of fifteen participants generated peak torques less than 50 Nm. For knee extension, the physiotherapist was unable to resist any torque greater than 100 Nm, whereas five participants generated more than 100 Nm on the Biodex.

#### **3.2 Intratester reliability**

6 Will-be-set-by-IN-TECH

Descriptive statistics of muscle torques, joint angles and muscular work are presented in Nm, degrees (°) and J respectively. Torque is calculated from the measured peak force times the length from the centre of the force pad to the rotational axis of the elbow or knee. Work is defined as output of mechanical energy, that is, externally applied force multiplied by the distance through which it is applied. In the concentric measurements, work can be found by calculating the area under the torque versus angular displacement curve. Mean and standard deviations (SDs) are reported. All analyses were performed using the Matlab

The degree of correlation between six repetitions of all the maximal strength tests using the IRL-HHD is calculated with the intraclass correlation co-efficient (ICC1,1) defined by Schrout and Fleiss (1979). The same test was performed on the three repetitions of the Biodex. The most critical reliability assessment is the ICC1,1, which assumes that every individual measurement is independent and the error of measurement is assumed to be normally distributed. Other authors have used ICC2,1 for their reliability measurement, which tends to give more optimistic values than ICC1,1. In this article all ICC1,1 results are almost equal to the ICC2,1 values. According to Fleiss (1986), the reliability of an ICC over 0.75 is considered

The agreement between the two devices can be quantified using the Bland-Altman 95% limits of agreement (LOA) method (Bland & Altman (1986)). The LOA method is based on the mean and SD of the differences between the measurements by the two devices. For repeated measurements, a one-way ANOVA is performed for each device separately. Outcomes of the one-way ANOVA are then used to calculate the lower and upper LOA (mean ± 1.96 times

Five men and ten women participated in this research. The participants' ages ranged from 23 to 45 years (mean±SD, 32.6±7.2y). Fig. 4 shows typical strength profile plots between the IRL-HHD and the Biodex for one participant. Although the shape of torque versus angle graphs were not the same for the IRL-HHD and the Biodex, both methods show consistency

Fig. 5 shows the speed of all measurements obtained with the IRL-HHD. It shows that the physiotherapist was able to control the speed of each measurement very well for the elbow flexion. Only two participants generated speeds more than 100°/s while nine generated speeds less than 80°/s. It was more difficult for the physiotherapist to control the speed for the knee extension and five participants generated speed greater than 100°/s. The range of speeds for those participants was also greater, suggesting that the physiotherapist was not in control of all the tests. Since the speed is controlled entirely from the perception of the assessor, an

**2.3 Statistical analysis 2.3.1 Descriptive statistics**

software package (USA).

**2.3.2 Intratester reliability**

SD)(Bland & Altman (2007)).

**3.1 Descriptive Statistics**

in repeated measurements.

**2.3.3 Validity**

**3. Results**

to be excellent, and between 0.4-0.75 as fair to good.

error of ±20°/s is considered to be reasonable in this study.

Six repeated measurements with the IRL-HHD and three with the Biodex were used to calculate the ICCs and their 95% confidence intervals. The results are shown in Table 1. The ICC1,1 values of both devices indicates excellent intratester reliability in the peak torque and work for both elbow flexion and knee extension. Repeatability of the peak torque angle of both tests by both devices is rated fair to good. However the confidence intervals indicates that only the knee peak torque angle obtained from the Biodex can be considered as fair to good, while all other peak torque angle measurements are poor. To determine if the mean of three measurements is a more reliable measure of the peak torque angle, the ICCs1,3 of

(a) Mean peak torque (b) Mean work

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 61

(a) Mean peak torque (b) Mean work

The graphs of torque versus angle in Fig. 4 suggest that the standardized methods of measurement using the IRL-HHD provided reliable concentric measurement. Speed variation during a single test using the IRL-HHD may be a factor in producing different shapes of the

Fig. 7. Scatter plots of (a) mean peak torque and (b) mean work for knee extension as

measured by Biodex and IRL-HHD. The solid lines are the equality lines.

torque-angle curves between the IRL-HHD and the Biodex.

**4. Discussion**

**4.1 Descriptive statistics**

Fig. 6. Scatter plots of (a) mean peak torque and (b) mean work for elbow flexion as

measured by Biodex and IRL-HHD. The solid lines are the equality lines.

(b) Knee Extension

Fig. 5. Average speeds obtained with the IRL-HHD.

the peak torque angles in the first session of the IRL-HHD tests were found to be 0.80 (0.50, 0.93) for elbow flexion and 0.75 (0.38, 0.91) for knee extension which are within the range of excellent.

#### **3.3 Validity**

The overall mean differences and their SDs between the two devices, and all lower and upper LOA values are shown in Table 2. The differences were calculated by subtracting the Biodex values from the corresponding IRL-HHD values, hence a negative value indicates that the IRL-HHD measurement is smaller than the Biodex measurement. The table also shows the LOA for screened data as will be discussed in Section 4.3.

Fig. 6. Scatter plots of (a) mean peak torque and (b) mean work for elbow flexion as measured by Biodex and IRL-HHD. The solid lines are the equality lines.

Fig. 7. Scatter plots of (a) mean peak torque and (b) mean work for knee extension as measured by Biodex and IRL-HHD. The solid lines are the equality lines.

#### **4. Discussion**

8 Will-be-set-by-IN-TECH

(a) Elbow Flexion

(b) Knee Extension

the peak torque angles in the first session of the IRL-HHD tests were found to be 0.80 (0.50, 0.93) for elbow flexion and 0.75 (0.38, 0.91) for knee extension which are within the range of

The overall mean differences and their SDs between the two devices, and all lower and upper LOA values are shown in Table 2. The differences were calculated by subtracting the Biodex values from the corresponding IRL-HHD values, hence a negative value indicates that the IRL-HHD measurement is smaller than the Biodex measurement. The table also shows the

Fig. 5. Average speeds obtained with the IRL-HHD.

LOA for screened data as will be discussed in Section 4.3.

excellent.

**3.3 Validity**

#### **4.1 Descriptive statistics**

The graphs of torque versus angle in Fig. 4 suggest that the standardized methods of measurement using the IRL-HHD provided reliable concentric measurement. Speed variation during a single test using the IRL-HHD may be a factor in producing different shapes of the torque-angle curves between the IRL-HHD and the Biodex.

adults. Most participants generated peak elbow fexion torques less than 50 Nm, suggesting that the IRL-HHD can be used to measure concentric strength of upper extremities or minor muscle groups in general healthy population. It may also be possible to use the IRL-HHD to assess children's concentric strength and subjects with strength deficiency resulting from

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 63

Intratester reliabilities of peak torque and work are excellent in both elbow and knee measurements with the IRL-HHD and with the Biodex, while the intratester reliabilities of peak torque angle are poor for the IRL-HHD. The intratester reliabilities of the peak torque angle using the Biodex are slightly better than those obtained with the IRL-HHD. The ICCs1,3 of the first sessions using the IRL-HHD indicates a significant improvement in the reliability of measuring the peak torque angle. These values suggest that peak torque angle should be measured by taking the mean of three repeated tests. The ICCs1,3 for peak torque angle are

The conventional method of assessing and grading muscle strength is the manual muscle test. In this study, all of the participants would be rated with a score of 5 as they were all healthy. Quantitative assessments of concentric strength are mostly associated with research or specialized assessments of top athletes, and have not been used in clinical settings. As far we are aware this is the first study using an HHD to perform concentric measurement, so it is not possible to define clinical agreement values to assess the LOA calculated in this paper. Instead, the LOA have been calculated to provide useful benchmarks for future research and

For elbow flexion, the LOA for peak torque are -11.6 and 13.5 Nm and for work are -24.1 and 26.0 J. The LOA of the peak torque angle are -21 and 69° which is unacceptable as a valid

Eliminating participants who generate torque greater than 50 Nm, any tests with speed greater than 100°/s, and the first run of all the Biodex results improves the LOA of all the parameters. They are: -7.0 and 9.9Nm for peak torques, -15 and 53° for peak torque angle, and -12.4 and

Considering that the maximum peak torque is approximately 50 Nm, the LOA are approximately ±20% of the range of measurement, therefore we suggest that the use of IRL-HHD in muscle strength assessment provides the clinician with at least 5 additional scales above the MRC score of 5, assuming that the Biodex measurements are the accepted peak

For knee extension, the LOA in all measurements show unacceptably large ranges. There is an obvious trend between mean strength and difference between the two devices, showing that the stronger the participant, the bigger the difference between the IRL-HHD and the Biodex measurements in peak torque. The LOA calculation with the proposed reduced dataset as discussed for elbow flexion are -23.1 and 28.7 Nm for peak torques, -16 and 41° for peak torque angle, and -13.1 and 41.0 J for total work. This means that for the knee extension test, the LOA of peak torque are approximately ±50% of the range of measurement, which is not a

within the range of excellent for both elbow flexion and knee extension.

conditions such as stroke or spinal cord injury.

a subjective analysis of the LOA is provided.

significant improvement over the conventional method.

measurement of peak torque angle.

16.2 J for work in elbow flexion.

torques of the participants.

**4.2 Intratester reliability**

**4.3 Validity**


NOTE. 95% confidence intervals shown in parenthesis

Abbreviation: PT, peak torque.

Table 1. ICC1,1 for six repetitions with the IRL-HHD and three repetitions with the Biodex, and ICC1,3 for the first session with the IRL-HHD.


Table 2. Agreement between the IRL-HHD and the Biodex for assessing elbow flexion and knee extension.

An angular speed measurement greater than 100°/s indicates that the physiotherapist is overpowered by the participant and that the result is likely to be invalid. Fig. 5 shows that it is possible for a trained assessor to control the concentric assessment speed to within ±20°/s from a target speed of 60°/s, provided that the force generated by the subject is less than the strength limit of the assessor.

Further examination shows that most of the variability in the Biodex arises from the first test in a series of three repeats being sub-maximal. It is recommended for future study that the warm-up phase should consist of more than one sub-maximal concentric movement.

For knee extension, the physiotherapist was unable to resist any torque greater than 100 Nm, whereas five participants generated more than 100 Nm on the Biodex. From the elbow tests, the assessor was overpowered by one participant, who generated 52 Nm peak torque, but was able to perform tests satisfactorily at 43 Nm peak torque, suggesting that the strength limit of this assessor is between 43 Nm and 52 Nm for elbow flexion (approximately 200 N to 250 N in force). Several authors have specified minimum upper limits of assessor's strength necessary for performing isometric measurements using an HHD (Wikholm & Bohannon (1991)). A conservative value is 12 kg of resistive force (Edwards & McDonnell (1974)) while others have suggested a value of 30 kg force (Hyde et al. (1983)). van der Ploeg et al. (1984) stated that an HHD range beyond 220 N is not useful due to stabilization and strength issues. The upper limit of the assessor's strength in this study is in agreement with the published results for isometric measurements. The torque limit of this assessor is expected to be between 52 Nm and 65 Nm for knee extension. Only four of the fifteen participants (27%) generated less than 52 Nm for knee extension, hence it may be concluded that the IRL-HHD and the test protocol described in this article is not feasible for general use in measuring knee extension of healthy adults. Most participants generated peak elbow fexion torques less than 50 Nm, suggesting that the IRL-HHD can be used to measure concentric strength of upper extremities or minor muscle groups in general healthy population. It may also be possible to use the IRL-HHD to assess children's concentric strength and subjects with strength deficiency resulting from conditions such as stroke or spinal cord injury.

#### **4.2 Intratester reliability**

Intratester reliabilities of peak torque and work are excellent in both elbow and knee measurements with the IRL-HHD and with the Biodex, while the intratester reliabilities of peak torque angle are poor for the IRL-HHD. The intratester reliabilities of the peak torque angle using the Biodex are slightly better than those obtained with the IRL-HHD. The ICCs1,3 of the first sessions using the IRL-HHD indicates a significant improvement in the reliability of measuring the peak torque angle. These values suggest that peak torque angle should be measured by taking the mean of three repeated tests. The ICCs1,3 for peak torque angle are within the range of excellent for both elbow flexion and knee extension.

#### **4.3 Validity**

10 Will-be-set-by-IN-TECH

Joint Movement Measurements IRL-HHD Biodex IRL-HHD Session 1

Work 0.97(0.93 to 0.99) 0.95(0.88 to 0.98)

Work 0.86(0.73 to 0.94) 0.98(0.96 to 0.99)

Table 1. ICC1,1 for six repetitions with the IRL-HHD and three repetitions with the Biodex,

Table 2. Agreement between the IRL-HHD and the Biodex for assessing elbow flexion and

An angular speed measurement greater than 100°/s indicates that the physiotherapist is overpowered by the participant and that the result is likely to be invalid. Fig. 5 shows that it is possible for a trained assessor to control the concentric assessment speed to within ±20°/s from a target speed of 60°/s, provided that the force generated by the subject is less than the

Further examination shows that most of the variability in the Biodex arises from the first test in a series of three repeats being sub-maximal. It is recommended for future study that the

For knee extension, the physiotherapist was unable to resist any torque greater than 100 Nm, whereas five participants generated more than 100 Nm on the Biodex. From the elbow tests, the assessor was overpowered by one participant, who generated 52 Nm peak torque, but was able to perform tests satisfactorily at 43 Nm peak torque, suggesting that the strength limit of this assessor is between 43 Nm and 52 Nm for elbow flexion (approximately 200 N to 250 N in force). Several authors have specified minimum upper limits of assessor's strength necessary for performing isometric measurements using an HHD (Wikholm & Bohannon (1991)). A conservative value is 12 kg of resistive force (Edwards & McDonnell (1974)) while others have suggested a value of 30 kg force (Hyde et al. (1983)). van der Ploeg et al. (1984) stated that an HHD range beyond 220 N is not useful due to stabilization and strength issues. The upper limit of the assessor's strength in this study is in agreement with the published results for isometric measurements. The torque limit of this assessor is expected to be between 52 Nm and 65 Nm for knee extension. Only four of the fifteen participants (27%) generated less than 52 Nm for knee extension, hence it may be concluded that the IRL-HHD and the test protocol described in this article is not feasible for general use in measuring knee extension of healthy

warm-up phase should consist of more than one sub-maximal concentric movement.

PT Angle 0.41(0.20 to 0.68) 0.56(0.25 to 0.81) 0.80(0.50 to 0.93)

PT Angle 0.46(0.24 to 0.71) 0.67(0.41 to 0.86) 0.75(0.38 to 0.91)

Elbow flexion Knee extension PT PT angle Work PT PT angle Work

1.0(6.4) 24(23) 1.0(12.8) -39.1(40.3) 2(14) -38.9(52.7)



Elbow flexion PT 0.95(0.91 to 0.98) 0.96(0.90 to 0.98)

Knee extension PT 0.99(0.94 to 0.99) 0.97(0.93 to 0.99)

NOTE. 95% confidence intervals shown in parenthesis

and ICC1,3 for the first session with the IRL-HHD.

Abbreviation: PT, peak torque.

Mean difference (SD)

knee extension.

95% LOA for all data

95% LOA for screened data

strength limit of the assessor.

The conventional method of assessing and grading muscle strength is the manual muscle test. In this study, all of the participants would be rated with a score of 5 as they were all healthy. Quantitative assessments of concentric strength are mostly associated with research or specialized assessments of top athletes, and have not been used in clinical settings. As far we are aware this is the first study using an HHD to perform concentric measurement, so it is not possible to define clinical agreement values to assess the LOA calculated in this paper. Instead, the LOA have been calculated to provide useful benchmarks for future research and a subjective analysis of the LOA is provided.

For elbow flexion, the LOA for peak torque are -11.6 and 13.5 Nm and for work are -24.1 and 26.0 J. The LOA of the peak torque angle are -21 and 69° which is unacceptable as a valid measurement of peak torque angle.

Eliminating participants who generate torque greater than 50 Nm, any tests with speed greater than 100°/s, and the first run of all the Biodex results improves the LOA of all the parameters. They are: -7.0 and 9.9Nm for peak torques, -15 and 53° for peak torque angle, and -12.4 and 16.2 J for work in elbow flexion.

Considering that the maximum peak torque is approximately 50 Nm, the LOA are approximately ±20% of the range of measurement, therefore we suggest that the use of IRL-HHD in muscle strength assessment provides the clinician with at least 5 additional scales above the MRC score of 5, assuming that the Biodex measurements are the accepted peak torques of the participants.

For knee extension, the LOA in all measurements show unacceptably large ranges. There is an obvious trend between mean strength and difference between the two devices, showing that the stronger the participant, the bigger the difference between the IRL-HHD and the Biodex measurements in peak torque. The LOA calculation with the proposed reduced dataset as discussed for elbow flexion are -23.1 and 28.7 Nm for peak torques, -16 and 41° for peak torque angle, and -13.1 and 41.0 J for total work. This means that for the knee extension test, the LOA of peak torque are approximately ±50% of the range of measurement, which is not a significant improvement over the conventional method.

• Measurement of children's dynamic strengths, as children are generally weaker than clinicians. Children are often too small to fit the isokinetic machines, and it would be difficult to strap a young child to the Biodex machine. Children may not be as patient as adults and so a rapid assessment using the IRL-HHD could offer some advantages. • In people with disability, where transferring patients in and out of the isokinetic

Validity and Reliability of a Hand-Held Dynamometer for Dynamic Muscle Strength Assessment 65

• In cases when it is impossible to restrain the patient to the machine e.g. in patients with

Future work should concentrate on developing and carrying out clinical trials for measuring the dynamic strength of people with injury or disability, small muscle groups in adult population or all muscle groups in children. For large muscle group assessments, additional fixtures to provide mechanical advantages for the assessors may be a solution for low-cost

This work was supported by the Foundation for Research Science and Technology, New Zealand (C08X0816). We thank Burwood Academy of Independent Living and the School

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**8. References**

**7. Acknowledgements**

Other factors that may affect the IRL-HHD assessments include: discomfort over the anterior tibial region because of the hard padding of the IRL-HHD force plate; the participants might be trying to control the speed; or they might think that the physiotherapist would not be able to control a maximal effort were they to exert it.
