IT IS WELL KNOWN that muscular strength and power

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1 ORIGINAL ARTICLE The Feasibility of Measuring Joint Angular Velocity With a Gyro-Sensor Takeshi Arai, RPT, PhD, Shuichi Obuchi, RPT, PhD, Yoshitaka Shiba, RPT, PhD, Kazuya Omuro, RPT, Chika Nakano, RPT, Takuya Higashi, RPT ABSTRACT. Arai T, Obuchi S, Shiba Y, Omuro K, Nakano C, Higashi T. The feasibility of measuring joint angular velocity with a gyro-sensor. Arch Phys Med Rehabil 2008;89:95-9. Objectives: To determine the reliability of an assessment of joint angular velocity using a gyro-sensor and to examine the relationship between ankle angular velocity and physical functions. Design: Cross-sectional. Setting: Kinesiology laboratory. Participants: Twenty healthy young adults (mean age, 22.5y) and 113 community-dwelling older adults (mean age, 75.1y). Interventions: Not applicable. Main Outcome Measures: Maximal ankle joint velocity was measured using a gyro-sensor during heel-rising and jumping with knee extended. The intraclass correlation coefficient (ICC) was used to determine the intertester and intratester reliability. The Pearson correlation coefficient was used to examine the relationships between maximal ankle joint velocity and isometric muscle strength and isokinetic muscle power in young adults and also to examine the relationships between maximal ankle joint velocity and functional performance measurements such as walking time in older adults. Results: High reliability was found for intertester (ICC.96) and intratester reliability (ICC.96). The data from the gyro-sensor highly correlated with muscle strength (r range,.62.68; P.01) and muscle power (r range,.45.79; P range,.01.05). In older subjects, mobility functions significantly correlated with the angular velocity of ankle plantarflexion. Conclusions: Measurement of ankle angular velocity using a gyro-sensor is both reliable and feasible, with the results representing a significant correlation to muscle power and performance measurements. Key Words: Muscles; Rehabilitation; Reliability and validity by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation From the Department for Prevention of Dependence on Long-term Care, Tokyo Metropolitan Institute of Gerontology, Itabashi-ku, Tokyo Met, Japan (Arai, Obuchi); Department of Allied Health Science (Shiba) and Graduate School of Medical Science (Omuro, Nakano), Kitasato University, Sagamihara-shi, Kanagawa Prefecture, Japan; and Department of Rehabilitation, Kameda General Hospital, Kamogawashi, Chiba Prefecture, Japan (Higashi). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Takeshi Arai, RPT, PhD, Dept for Prevention of Dependence on Long-term Care, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi-ku, Tokyo, , Japan, arait@tmig.or.jp or mm01004arai_ takeshi@hotmail.com /08/ $34.00/0 doi: /j.apmr IT IS WELL KNOWN that muscular strength and power decrease with increasing age. 1 It has also been reported that age-related decreases in maximal power production take place to a greater degree than such reductions in maximal muscle strength in the elderly. 1-4 The results of several studies have suggested that muscle power may be more directly related to impaired physical performance than strength. 5,6 The significance of impairments in muscle power has been shown in studies confirming the positive association between muscle power and functional mobility tasks and identification of peak muscle power as a strong physiologic predictor of functional limitations and disability in older people. 1,3,7-9 A loss of muscle power has been shown to have profound effects on functional activities such as walking up stairs, standing up from a chair, and overall gait. 10 Although it is clear that heavy-resistance training has profound effects on muscle size, 11,12 strength, and power in older people, 13 high-velocity training has recently been recommended Muscle power is defined as the product of force and velocity (power force velocity). To improve muscle power, not only muscle strength but also the velocity of muscle contraction should be increased. Therefore, measurement of joint angular velocity might play an important role in the assessment of muscle function, and an increase in this velocity may be the main outcome of power training. If we want to monitor the joint angular velocity during assessing or training muscle function, an isokinetic machine must be provided and set up. Because of the lack of convenience and the cost of the devices, assessments of muscle power have not been performed routinely in clinical settings as have measures of muscle strength. We now focus our attention on the gyrosensor, which can measure angular velocity and is smaller and less costly than isokinetic equipment. The use of this device to capture the movement of the human body has been well documented in previous studies. 20,21 If the utility of the simpler methodology that we applied in the current study were to be established, the measurement of joint angular velocity using a gyro-sensor would be available in clinical settings to extrapolate the muscle function of physically disabled people. In particular, this angular velocity measurement should be used as an outcome measure of exercise training for frail elderly subjects and for patients with neuromuscular disease whose ability to produce muscle power has declined. Therefore, the first purpose of this study was to determine the reliability of measurement of ankle joint angular velocity using a gyro-sensor. In this study, ankle joint movement (plantarflexion) was selected because previous research has reported a strong relationship between muscle power of the ankle plantarflexor and physical functional performance. 5 The second purpose was to examine whether there is a relationship between maximal ankle joint angular velocity and physical performance measurements such as walking velocity or balance function. 95

2 96 MEASURING JOINT ANGULAR VELOCITY, Arai METHODS Participants To assess the reliability, 20 collegiate healthy volunteers (mean age standard deviation [SD], y) with no neurologic or orthopedic complaints participated in this study. In addition, 113 older volunteers (mean age SD, y) participated in this study. Measurements of ankle joint velocity and other physical performance measurements were performed in these older volunteers. The older volunteers were residents of the 3 cities in Japan (Itabashi, Sagamihara, Yokosuka) and were recruited by advertisements in publications in these communities and through clubs for the elderly in these areas. The inclusion criteria for older adults were as follows: communitydwelling, aged 65 years and older, and did not meet any exclusion criteria. The exclusion criteria for participation were (1) cerebrovascular or cardiovascular accidents reported within the past 6 months; (2) acute liver problems or the active phase of chronic hepatitis; (3) diabetic mellitus with a history of hypoglycemic attack, or with fasting levels of plasma glucose concentrations of 200mg/dL or higher, or with complications such as retinopathy or nephropathy; (4) systolic blood pressure above 180mmHg or diastolic blood pressure above 110mmHg at rest; and (5) diagnosis of heart disease, an orthopedic problem, or dementia made by a medical doctor and recommendation by this doctor that the subject be excluded. The study protocol was examined and approved by the ethics committee of the Society of Physical Therapy Science in Japan. The details of this study were explained to all participants before the start of the study, and informed consent was obtained from all participants by a document. Procedure The main measure of this study was the maximal joint angular velocity of ankle plantarflexion. To capture the angular velocity of the metatarsal, a gyro-sensor a ( mm) was fixed on the left first metatarsal bone at the dorsum of the foot so that the axis of the sensor accorded the sagittal plane (fig 1). Data from the gyro-sensor were captured at 200Hz. Younger subjects performed 2 tasks, which included 2 methods of heel-rising in a standing position with maximal effort. In the first method, they were not permitted to jump off the floor, whereas in the second they could jump off the floor if it was possible. They were instructed not to flex their knees during heel-rising. The starting position of subjects was a standing position with the knees and hips extended, the foot width kept the same as the shoulders, and the arms folded on the chest. They performed each heel-rising tasks 3 times consecutively, Fig 1. (A) Frontal plane. (B) Sagittal plane. and the average maximal angular velocity at each of 3 attempts was calculated. To determine the intertester reliability, 2 research assistants (A, B) measured the angular velocity of each subject on the same day in a random order. And to determine the intratester reliability, research assistant A measured the same subjects after an approximately 1-week interval. Muscle Strength and Power Measurements Younger subjects performed a sequence of muscular functional tests, including muscle strength and power assessments. The muscle strength and power of the ankle plantarflexor were measured on an isokinetic dynamometer (Myoret). b The muscle strength of the ankle plantarflexor was measured as an isometric peak torque at 0 of ankle plantarflexion. The duration of the measuring isometric torque was 5 seconds, and the average peak torque was calculated based on 3 trials. The muscle power of the ankle plantarflexor was measured as a peak power during concentric contraction of the plantarflexor at 60, 120, and 180 per second. Power was tested consecutively in 5 trials at each angular velocity. Each subject was placed in a supine position, and the axis of the left ankle joint was fixed to the dynamometer axis using a footplate attachment. The arms were placed alongside the body, with the hands grasping fixed handles for stabilization. Body motions other than ankle rotation were further restricted by straps over the lower leg and waist. Before testing, subjects were familiarized with the equipment, and they practiced several repetitions for each attempt. Physical Functional Measurements Older subjects performed a sequence of physical functional tests. The physical functions followed were measured. One-leg standing with eyes open and closed was measured as an indicator of static balance. 22,23 Subjects performed the posture twice, and the measurement recorded was the maximum value of these 2. The maximum value was set at 60 seconds. The Functional Reach Test (FRT) was performed to measure dynamic balance. 24,25 Subjects performed the test twice, and the measurement recorded was the maximum value. A Timed Up & Go (TUG) test was performed to measure functional balance. 26 To represent maximal abilities to perform the task of the TUG test, we slightly modified the methodology of this test. The instruction to subjects was modified as follows: Please return to the chair as quickly as you can without falling. Each subject performed the test twice; we used the minimum time needed to carry out the task as the TUG score. Preferred and maximum walking times were measured to represent walking abilities. 27 Subjects were asked to walk a track that had a total length of 16m. The examiner recorded with a stopwatch the time each subject took to walk along the middle 10m of the track. Each subject tried the test twice, and the minimum time was adopted as the record. The sit and reach test (SRT) was measured as an indicator of hamstring flexibility. 28 The equipment c for the SRT was used. Handgrip strength 29 and isometric knee extension strength 30,31 were measured to represent upper and lower dominant-limb strength. Handgrip strength was measured using a hand dynamometer. c Isometric knee extension strength was measured while subjects were sitting on a treatment table with the knees and hips at 90 of flexion. We used a handheld dynamometer d for testing knee extensor strength. The dominant leg was measured twice, and the recorded measurement was the maximum value. These measurements were applied because of their reliability and convenience and because they have frequently been used in

3 MEASURING JOINT ANGULAR VELOCITY, Arai 97 Table 1: Angular Velocity First Evaluation Second Evaluation Task Tester Mean SD Range Mean SD Range Heel-rising A B ND ND Jumping with knee fixed A B ND ND NOTE. Values are in degrees per second. Abbreviation: ND, data not needed. research studies to show physical frailties and the relationship of the balance function to the occurrence of falls. Because we were thinking about how to disseminate the measurement that we were studying, we decided that it was necessary to simplify our methodology and to use low-cost equipment. These assessments were performed by trained physical therapists and research assistants. Statistical Analysis The intraclass correlation coefficient (ICC) was used to evaluate intertester reliability and retest reliability of the assessments of ankle joint angular velocity using a gyro-sensor. The Pearson correlation coefficient was used to evaluate the relationship between angular velocity and the muscle strength and power in younger subjects and the relationship between angular velocity and physical functional performance in older subjects. Because it was assumed that the magnitude of angular velocity investigated by the gyro-sensor was affected by each subject s body weight, we adjusted the unit (angular velocity [in deg/s] body weight [in kg]) before we calculated the Pearson correlation coefficient between gyro-sensor and muscle function and physical performance measures. The level of statistical significance was set P less than.05. We used SPSS statistical software e for Windows. RESULTS All testing procedures were performed safely, and no adverse events occurred. The results of joint angular velocity of ankle plantarflexion are shown in table 1. There was excellent intertester and intratester reliability (ICC range,.95.96) (table 2). The adjusted data calculated from gyro-sensor data significantly correlated with muscle strength and power, except for the data at 120 /s in younger subjects (r range,.45.79; P range,.01.05) (table 3), and the angular velocity data from older people correlated with some physical functions in older subjects (r range,.30.53; P.01). The angular velocity of ankle plantarflexion did not significantly correlate with 1-leg standing with eyes closed and the SRT (P.05) (table 4). DISCUSSION Many studies have indicated that in direct comparisons, muscle power consistently describes more of the variance in mobility function than muscle strength. 5 Power is defined as Task Table 2: Reliability n Intratester Intertester ICC 95% CI ICC 95% CI Heel-rising Jumping with knee fixed Abbreviation: CI, confidence interval. the product of force and velocity. Because assessing and enhancing an ability to directly produce muscle power is more essential than strength measurements, it has been thought that the angular velocity produced during joint movement should be measured. We therefore need a simple and reliable device to measure joint angular velocity. In the present study, the reliability of measurement of joint angular velocity using a gyrosensor was investigated; the results showed excellent intratester and intertester reliability. Angular velocity as measured with a gyro-sensor highly correlated with muscle peak torque and peak power. We therefore believe that our measurement is valid for assessing angular velocity during ankle plantarflexion and that it has the ability to produce the muscle power of the ankle plantarflexor. It is intensely meaningful that angular velocity has a stronger correlation with peak power than peak torque, but it is difficult to understand why the highest correlation coefficient between angular velocity and peak power was observed at lower angular velocity (60 /s). At the beginning of the movement in the heel-rising task, it might be necessary to create large torque with low angular velocity so that subjects can lift their body weight. In addition, we applied a protocol that was similar for both younger subjects and community-dwelling older people to represent the relationship between physical function and the angular velocity of ankle plantarflexion. Considering the repercussion of their knees, we did not apply the jumping task, which was used in younger subjects, for older subjects. The angular velocity of ankle plantarflexion significantly correlated with many physical functions in older subjects, except for 1-legged standing with eyes closed and the SRT. Lower or no relationships were found in balance and flexibility measurements compared with strength and mobility measurements. In addition to muscle function, balance function consisted of some elements including the neuromuscular system. Especially without visual information, more effort was required by the neuromuscular system to achieve postural control, because sensory input was Table 3: Correlation Coefficient (r) With Muscle Function Tester Task n 0 /s Torque 60 /s 120 / s Power 180 /s A Heel-rising Jumping with knee fixed B Heel-rising * Jumping with knee fixed *P.05. P.01.

4 98 MEASURING JOINT ANGULAR VELOCITY, Arai Table 4: Correlation Coefficient (r) With Physical Performance in Older Adults Measurements n r 1-leg standing with eyes open (s) * 1-leg standing with eyes closed (s) FRT (cm) * TUG test (s) * Preferred walking time (s) * Maximum walking time (s) * SRT (cm) Handgrip strength (kg) * Knee extensor strength (kg) * *P.01. limited to only the vestibular and somatosensory (proprioceptive) systems. It was thought to be more challenging for subjects with a lower physical functional level to control the sway of their body mass without visual information. The results of this research did not contradict those from past studies 1,3,5,7-9 that showed the relationship between the muscle power of the lower extremities and mobility. We therefore should consider the joint angular velocity as a meaningful parameter of muscle function. In strength training, not only resistance but also joint angular velocity should be prescribed to subjects by the physician or therapist. However, with the development of this equipment, feedback information on angular velocity could be made available to help patients who are suffering from neuromuscular disorders such as cerebrovascular disease, Parkinson s disease, and ataxia to control their muscle activation. Because the protocol that we applied in this study was very simple and was not burdensome to patients, this measurement should be included as a clinical measurement. This methodology might be used clinically in settings such as clinics, bedside rehabilitation, or community-based rehabilitation. The implications of the use of this device should be examined in further studies. CONCLUSIONS The objectives of the study were to establish the reliability of a new clinical measurement of muscle power of the lower extremity and to examine the relationship between ankle angular velocity and physical functions. The angular velocity of ankle plantarflexion during the heel-raising task was measured using a gyro-sensor. The results of the study showed that our procedure was reliable, and the angular velocities of subjects were related to their muscle functions. In addition, mobility functions that require more muscle power of the lower extremities highly correlated with the angular velocity of ankle plantarflexion in older adults. It is very meaningful to measure the angular velocity for evaluating the muscular function of physically disabled people. Our simplified methodology should be considered in clinical settings. References 1. Metter EJ, Conwit R, Tobin J, Fozard JL. Age-associated loss of power and strength in the upper extremities in women and men. 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