Conducting Accelerometer-Based Activity Assessments in Field-Based Research

PURPOSE

The purpose of this review is to address important methodological issues related to conducting accelerometer-based assessments of physical activity in free-living individuals.

METHODS

We review the extant scientific literature for empirical information related to the following issues: product selection, number of accelerometers needed, placement of accelerometers, epoch length, and days of monitoring required to estimate habitual physical activity. We also discuss the various options related to distributing and collecting monitors and strategies to enhance compliance with the monitoring protocol.

RESULTS

No definitive evidence exists currently to indicate that one make and model of accelerometer is more valid and reliable than another. Selection of accelerometer therefore remains primarily an issue of practicality, technical support, and comparability with other studies. Studies employing multiple accelerometers to estimate energy expenditure report only marginal improvements in explanatory power. Accelerometers are best placed on hip or the lower back. Although the issue of epoch length has not been studied in adults, the use of count cut points based on 1-min time intervals maybe inappropriate in children and may result in underestimation of physical activity. Among adults, 3-5 d of monitoring is required to reliably estimate habitual physical activity. Among children and adolescents, the number of monitoring days required ranges from 4 to 9 d, making it difficult to draw a definitive conclusion for this population. Face-to-face distribution and collection of accelerometers is probably the best option in field-based research, but delivery and return by express carrier or registered mail is a viable option.

CONCLUSION

Accelerometer-based activity assessments requires careful planning and the use of appropriate strategies to increase compliance.

The Technology of Accelerometry-Based Activity Monitors: Current and Future

PURPOSE

This paper reviews accelerometry-based activity monitors, including single-site first-generation devices, emerging technologies, and analytical approaches to predict energy expenditure, with suggestions for further research and development.

METHODS

The physics and measurement principles of the accelerometer are described, including the sensor properties, data collections, filtering, and integration analyses. The paper also compares these properties in several commonly used single-site accelerometers. The emerging accelerometry technologies introduced include the multisensor arrays and the combination of accelerometers with physiological sensors. The outputs of accelerometers are compared with criterion measures of energy expenditure (indirect calorimeters and double-labeled water) to develop mathematical models (linear, nonlinear, and variability approaches).

RESULTS

The technologies of the sensor and data processing directly influence the results of the outcome measurement (activity counts and energy expenditure predictions). Multisite assessment and combining accelerometers with physiological measures may offer additional advantages. Nonlinear approaches to predict energy expenditure using accelerometer outputs from multiple sites and orientation can enhance accuracy.

CONCLUSIONS

The development of portable accelerometers has made objective assessments of physical activity possible. Future technological improvements will include examining raw acceleration signals and developing advanced models for accurate energy expenditure predictions.

Calibration of accelerometer output for adults

This paper reviews the collective experience of monitor calibration studies in adults and seeks to answer the following questions: What has been done? What have we learned? What could be done to further enhance the comparability of results from future calibration research? Calibration studies in adults have typically used oxygen consumption as a criterion measure, similar types of source activities, and linear regression to obtain prediction equations that calibrate the activity counts to measured activity intensity levels. However, the methodological diversity of these studies has produced a great deal of variation in the resulting prediction equations and cut points, even when using the same monitor. Thus, data obtained from a relatively robust activity monitoring technology that captures many dynamic physical activities reasonably well have been splintered by the calibration process into a wide range of summary measures that are much less comparable than they could otherwise be. This heterogeneity in calibration results reduces our ability to interpret data obtained from accelerometers between different research groups, across the life span, between populations, and probably between the different monitor types. This report reviews and critiques methods typically used for developing calibration equations and determining activity count cut points for identifying specific intensities of PA among adults, and it highlights the need for flexible research methods that can enhance the comparability of results from future calibration studies.

Pedometer measures of free-living physical activity: comparison of 13 models

PURPOSE

The purpose of this study was to compare the step values of multiple brands of pedometers over a 24-h period. The following 13 electronic pedometers were assessed in the study: Accusplit Alliance 1510 (AC), Freestyle Pacer Pro (FR), Colorado on the Move (CO), Kenz Lifecorder (KZ), New-Lifestyles NL-2000 (NL), Omron HJ-105 (OM), Oregon Scientific PE316CA (OR), Sportline 330 (SL330) and 345 (SL345), Walk4Life LS 2525 (WL), Yamax Skeletone EM-180 (SK), Yamax Digi-Walker SW-200 (YX200), and the Yamax Digi-Walker SW-701 (YX701).

METHODS

Ten males (39.5 +/- 16.6 yr, mean +/- SD) and 10 females (43.3 +/- 16.6 yr) ranging in BMI from 19.8 to 35.4 kg.m-2 wore two pedometers for a 24-h period. The criterion pedometer (YX200) was worn on the left side of the body, and a comparison pedometer was worn on the right. Steps counted by each device were recorded at the end of the day for each of the thirteen pedometers.

RESULTS

Subjects took an average of 9244 steps.d-1. The KZ, YX200, NL, YX701, and SL330 yielded mean values that were not significantly different from the criterion. The FR, AC, SK, CO, and SL345 significantly underestimated steps (P < 0.05) and the WL, OM, and OR significantly overestimated steps (P < 0.05) when compared with the criterion. In addition, some pedometers underestimated by 25% whereas others overestimated by 45%.

CONCLUSION

The KZ, YX200, NL, and YX701 appear to be suitable for most research purposes. Given the potential for pedometers in physical activity research, it is necessary that there be consistency across studies in the measurement of "steps per day."

Principles of design and analyses for the calibration of accelerometry-based activity monitors

The term "calibration" in accelerometry research has come to mean the conversion of counts into other established measurement units. In this article, two types of calibration research are described. Unit calibration (or interinstrument variability) is described as a reliability issue, whereas value calibration is described as more of a validity issue. Principles for design of accelerometry-based validation studies are described to provide a guide for future calibration research. The population must be representative of the intended population in terms of demographics and size, monitors must be representative of the population of monitors that would be available, and activities in the protocol must be representative of the types of activities performed by the intended population. It is also important to employ appropriate analytical strategies in this type of research. A case study employing the appropriate design principles is included to demonstrate how results can vary depending on the type of analyses that are used. Direct comparisons are made between a mixed model regression approach and an approach based on receiver operator characteristic curves.

Motion sensor accuracy under controlled and free-living conditions

PURPOSE

Two studies were conducted to examine the concurrent accuracy of the Yamax SW-200 (YAM), Omron HJ-105 (OM), and Sportline 330 (SL) pedometers, as well as a CSA accelerometer.

METHODS

In study 1, motion sensor performance was evaluated against actual (observed) steps taken during 5-min bouts at five different treadmill speeds (54, 67, 80, 94, and 107 m x min) using a two-way repeated measures ANOVA (instrument x speed). Additionally, the direction and magnitude of motion sensor error was examined. In study 2, pedometer performance during 24 h of free-living was evaluated against the steps detected by the CSA criterion. The direction and magnitude of pedometer error was also examined in the free-living condition.

RESULTS

In study 1, the SL showed significant differences from actual steps taken at all treadmill speeds (P < 0.05). Further, the absolute value of percent error was greatest for the SL at all treadmill speeds. At the slowest treadmill speed (54 m x min), the absolute value of percent error increased for the YAM and OM. In study 2, only the SL detected fewer steps than the CSA criterion (P < 0.05). The YAM demonstrated the lowest absolute value of percent error under free-living conditions.

CONCLUSIONS

Different brands of motion sensors detect steps differently; therefore, caution must be used when comparing step counts between studies that have employed different brands of motion sensors. Taking into consideration the results of both studies and the initial walking test used for instrument screening purposes, it appears that, of the three pedometers tested, the YAM pedometer is most consistently accurate under both controlled and free-living conditions. Future research must consider presenting motion sensor accuracy in absolute terms so that the magnitude of error is not underestimated.

Clinimetric review of motion sensors in children and adolescents

BACKGROUND AND OBJECTIVES

To review the clinimetric quality of motion sensors used to assess physical activity in healthy children and adolescents (2-18 years).

METHODS

A systematic literature search was performed in PubMed, Embase, and SpycINFO. The clinimetric quality of two pedometers (Digi-Walker, Pedoboy), four one-dimensional accelerometers (LSI, Caltrac, Actiwatch, CSA/ActiGraph), and three three-dimensional accelerometers (Tritrac-R3D, RT3, Tracmor2) was evaluated and compared using a 20-item checklist.

RESULTS

Overall, the quality of the studies (n = 35), and therefore the level of evidence for the reproducibility, validity, and feasibility of the motion sensors was modest (mean = 6.4 +/- 1.6 out of 14 points). There was strong evidence for a good reproducibility of the Caltrac in adolescents (12-18 years), a poor reproducibility of the Digi-Walker in children (8-12 years), a good validity of the CSA/ActiGraph in children and adolescents (8-18 years), and a good validity of the Tritrac-R3D in children (8-12 years).

CONCLUSIONS

The CSA/ActiGraph and the Caltrac are the only motion sensors in which the reproducibility, validity, and feasibility have been examined in different age groups. Further studies of the reproducibility of motion sensors in preschool children, improvement of the quality of clinimetric studies, and evaluation of the acceptability of motion sensors are warranted.

Force treadmill for measuring vertical and horizontal ground reaction forces

We constructed a force treadmill to measure the vertical, horizontal and lateral components of the ground-reaction forces (Fz, Fy, Fx, respectively) and the ground-reaction force moments (Mz, My, Mx), respectively exerted by walking and running humans. The chassis of a custom-built, lightweight (90 kg), mechanically stiff treadmill was supported along its length by a large commercial force platform. The natural frequencies of vibration were >178 Hz for Fz and >87 Hz for Fy, i.e., well above the signal content of these ground-reaction forces. Mechanical tests and comparisons with data obtained from a force platform runway indicated that the force treadmill recorded Fz, Fy, Mx and My ground-reaction forces and moments accurately. Although the lowest natural frequency of vibration was 88 Hz for Fx, the signal-to-noise ratios for Fx and Mz were unacceptable. This device greatly decreases the time and laboratory space required for locomotion experiments and clinical evaluations. The modular design allows for independent use of both treadmill and force platform.

Pedometer Accuracy in Nursing Home and Community-Dwelling Older Adults

PURPOSE

The accuracy of pedometers has not been thoroughly tested with older adult populations. The purpose of the present study was to examine the effects of walking speed and gait disorders on the accuracy of Yamax pedometers with nursing home residents (NH) relative to older adults living in the community.

METHODS

Pedometer accuracy was evaluated against observed steps taken during a self-paced walking test (slow, normal, and fast speeds) in 26 NH residents and 28 seniors' recreation center members (SC). Devices were attached to clothing at the waist. Walking speed was ascertained from the timed walk and a gait assessment was conducted. Percent error was calculated as ([pedometer steps - observed steps]/observed steps) x 100.

RESULTS

The walking speeds of both samples increased across self-selected paces (P < 0.0001). The community-dwelling older adults walked significantly faster (P < 0.0001) in all trials and had significantly higher (P < 0.0001) gait assessment scores (indicating fewer gait problems). Gait scores were positively associated with walking speed and pedometer percent error. Pedometers significantly underestimated NH residents' observed steps taken by 74% (slow), 55% (normal), and 46% (fast) paces (P < 0.0001). In the SC sample, the instruments failed to detect 25%, 13%, and 7% of actual steps taken, respectively (P < 0.0001). The magnitude of the error was greater for NH versus SC older adults (P < 0.0001) across all trials.

CONCLUSIONS

Slow walking speed and gait disorders hamper the utility of pedometers for physical activity measurement in frail seniors, such as NH residents, when worn at the usual attachment site. Pedometers, however, can be confidently used with ostensibly healthy older adult populations for both assessment and motivation purposes.

Evaluation of methods to assess physical activity in free-living conditions

PURPOSE

The purpose of this study was to compare different methods of measuring physical activity (PA) in women by the doubly labeled water method (DLW).

METHODS

Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Body composition, basal metabolic rate (BMR), and peak oxygen consumption were also measured. Physical activity-related energy expenditure (PAEE) was then calculated by subtracting measured BMR and the estimated thermic effect of food from TDEE. Simultaneously, over the 7 d, PA was assessed via a 7-d Physical Activity Recall questionnaire (PAR), and subjects wore secured at the waist, a Tritrac-R3D (Madison, WI), a Computer Science Application Inc. activity monitor (CSA; Shalimar, FL), and a Yamax Digi Walker-500 (Tokyo, Japan). Pearson-product moment correlations were calculated to determine the relationships among the different methods for estimating PAEE. Paired t-tests with appropriate adjustments were used to compare the different methods with DLW-PAEE.

RESULTS

There was no significant difference between PAEE determined from PAR and DLW. The differences between the two methods ranged from -633 to 280 kcal.d(-1). Compared with DLW, PAEE determined from CSA, Tritrac, and Yamax was significantly underestimated by 59% (-495 kcal.d(-1)), 35% (-320 kcal.d(-1)) and 59% (-497 kcal.d(-1)), respectively. VO2peak explained 43% of the variation in DLW-PAEE.

CONCLUSION

Although the group average for PAR-PAEE agreed with DLW-PAEE, there were differences in the methods among the subjects. PAEE determined by Tritrac, CSA, and Yamax significantly underestimate free-living PAEE in women.

Reliability and validity of two frequently used self-administered physical activity questionnaires in adolescents

BACKGROUND

To create and find accurate and reliable instruments for the measurement of physical activity has been a challenge in epidemiological studies. We investigated the reliability and validity of two different physical activity questionnaires in 71 adolescents aged 13-18 years; the WHO, Health Behaviour in Schoolchildren (HBSC) questionnaire, and the International Physical Activity Questionnaire (IPAQ, short version).

METHODS

The questionnaires were administered twice (8-12 days apart) to measure reliability. Validity was assessed by comparing answers from the questionnaires with a cardiorespiratory fitness test (VO2peak) and seven days activity monitoring with the ActiReg, an instrument measuring physical activity level (PAL) and total energy expenditure (TEE).

RESULTS

Intraclass correlation coefficients for reliability for the WHO HBSC questionnaire were 0.71 for frequency and 0.73 for duration. For the frequency question, there was a significant difference between genders; 0.87 for girls and 0.59 for boys (p < 0.05). The intraclass correlation coefficients the IPAQ varied between 0.10 and 0.62 for the reliability. Spearman correlation coefficients for validity for both the WHO HBSC questionnaire and the IPAQ (recoded into low, moderate and high activity) measured against VO2peak were fair, ranging between 0.29 - 0.39. The WHO HBSC questionnaire measured against VO2peak for girls were acceptable, ranging between 0.30 - 0.55. Both questionnaires, except the walking question in IPAQ, showed a low correlation with PAL and TEE, ranging between 0.01 and 0.29.

CONCLUSION

These data indicate that the WHO HBSC questionnaire had substantial reliability and were acceptable instrument for measuring cardiorespiratory fitness, especially among girls. None of the questionnaires however seemed to be a valid instrument for measuring physical activity compared to TEE and PAL in adolescents.

Sources of variation in back and leg dynamometry

Three investigations were carried out to examine the concurrent validity and the reliability of a portable dynamometer (Takei Kiki Kogyo) for the measurement of back and leg strength. First, leg extension strength of 19 subjects was measured using the Takei dynamometer and compared to the isometric knee extension strength of the dominant (right) leg measured using a computer-controlled dynamometer (Lido Active, Davis, CA). The back extension strength of 18 subjects was also compared between the two dynamometers. Second, back and leg strengths of 36 subjects, aged 19-30 years, were measured twice using the Takei dynamometer. Six days separated the test and retest. Third, back and leg strengths of four subjects, aged 21-30 years, were measured at six different times of the solar day. Significant relations (p < 0.001) were obtained between the Takei and Lido dynamometers for leg strength (r = 0.90) and back strength (r = 0.79). Significant test-retest correlations (p < 0.001) were found for leg strength (r = 0.80) and back strength (r = 0.91). Group mean (+/- SD) leg strength values of test (1450.4 +/- 428.6 N) and retest (1432.8 +/- 449.1 N) did not differ ((p > 0.05). A small (4.5%) but significant difference was found between the test (1057.2 +/- 309.9 N) and retest (1106.2 +/- 334.4 N) mean values for back strength (p < 0.05). A time of day effect was evident for back and leg strength (p < 0.05); on average the peak times occurred at 16:53 h and 18:20 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of three methods to assess muscular strength in individuals with spinal cord injury

The aim of the project was to compare three methods for measuring muscle strength in individuals with SCI: the manual muscle test (MMT), the hand-held myometry and the isokinetic dynamometry (Cybex). Thirty-eight (38) subjects, 31 men and seven women (age range = 14-63; lesion from C5 to L3) were included in this project. Muscle strength assessment of upper limbs was performed at admittance and discharge using MMT and myometry for the left and right side, and using Cybex dynamometer for the stronger side. The testing sessions were at least a day apart and performed by a single evaluator (trained physiotherapist). Significant and non-significant differences of myometry mean strength values were observed between consecutive levels of MMT. However, the range of myometry scores within each MMT grade led to significant overlaps between two adjacent MMT grades of each muscle group. Variables correlations were observed between the strength values measured by MMT and myometry with paraplegia (0.26 < or = r < or = 0.67) and tetraplegia (0.50 < or = r < or = 0.95). Similar results were observed when compared MMT and Cybex with the stronger side. Moderate to strong correlations were observed between the strength values measured by myometry and Cybex with paraplegia (0.70 < or = r < or = 0.90) and tetraplegia (0.57 < or = r < or = 0.96). These results suggest that the MMT method does not seem to be sufficiently sensitive to assess muscle strength, at least for grade 4 and higher and to detect small or moderate increases of strength over the course of rehabilitation. Since outcome measures is an important issue in rehabilitation, objective measurements of strength should be used in clinical settings. Considering cost and assessment time, the myometry technique seems to be highly valuable.

A treadmill ergometer for three-dimensional ground reaction forces measurement during walking

This report describes new treadmill ergometer designed to measure the vertical and horizontal ground reaction forces produced by the left and right legs during walking. It was validated by static and dynamic tests. Non-linearity was from 0.2% (left vertical force) to 1.4% (right antero-posterior force). The resonance frequency was from 219 (right vertical direction) to 58 Hz (left medio-lateral direction). A calibration "leg", an air jack in series with a strain gauge, was developed and used to produce force signals comparable to those obtained during human locomotion. The mean differences between the force measured by the calibration leg and treadmill ergometer at 5 km h(-1) were 3.7 N (0.7%) for the left side and 6.5 N (1.2%) for the right. Measurements obtained during human walking showed that the treadmill ergometer has considerable potential for analysing human gait.

Grip strength and hand position of the dynamometer in 204 Finnish adults

A primary purpose of this study was to establish data on hand strength by Jamar dynamometer for normal Finnish adults aged 30 to 50 years. A second aim was to find out how five various breadths of grip affect the strength value. A sample of 103 male and 101 female adults, aged 19 to 62, from the southern part of Finland were tested using standardized positioning and instructions. Male and female subjects reached the highest grip strength using the third handle breadth of dynamometer, except females over 50 years. Female grip strength was 60% to 70% less than male grip strength. There was no significant difference in strength between dominant and non-dominant hands.

Comparisons of four methods of estimating physical activity in adult women

PURPOSE

To compare four different methods of measuring physical activity (PA) in adult women under free-living conditions.

METHODS

Twelve women participated in a 7-d period during which PA was assessed via self-report, accelerometry and step-counting. Subjects wore at the waist a Tritrac-R3D accelerometer, a Computer Science Application Inc. activity monitor (CSA), both of which measure bodily accelerations in various planes, and a Yamax Digi-Walker-500 that records steps. After the 7-d period subjects responded to a 7-d Physical Activity Recall interview (PAR).

RESULTS

Physical activity-related energy expenditure (PAEE) determined from PAR was significantly higher than PAEE estimated from either the Tritrac, CSA, or the Yamax data. Time spent in light, moderate, and hard physical activity was not significantly different between PAR, CSA, and Tritrac. Log-transformed activity counts from CSA were highly correlated with log-transformed Tritrac results (r > 0.90). Number of steps recorded by the Yamax was significantly correlated with untransformed Tritrac and CSA results.

CONCLUSIONS

Based upon comparisons with PAR, Tritrac, CSA, and Yamax underestimate the amount of PAEE by 25, 46, and 48%, respectively. The correspondence between the Tritrac and CSA results suggests that both devices produce similar estimates of bodily movement in free-living women. The relationships among results for Tritrac, CSA, and Yamax indicate that the number of steps recorded by the Yamax is representative of the amount of physical activity performed during the day as estimated by Tritrac and CSA. These results should be useful when selecting a method to measure PA in individuals under free-living conditions.

Efficacy of a gravity-independent resistance exercise device as a countermeasure to muscle atrophy during 29-day bed rest

AIM

This study determined changes in knee extensor and plantar flexor muscle volume during 29 days of bed rest with or without resistance exercise using a gravity-independent flywheel ergometer.

METHODS

Seventeen men (26-41 years) were subjected to 29 days of bed rest with (n = 8) or without (n = 9) resistance exercise; Supine Squat (SS) and Calf Press (CP) performed every third day. Quadriceps and triceps surae muscle volume was determined before and after bed rest and force and power were measured during training. Prior to these interventions, reproducibility of this device for training and testing was assessed in 23 subjects who performed bilateral maximal concentric, eccentric and isometric (MVC) knee extensions and plantar flexions over repeated sessions with simultaneous measurements of force, power and electromyographic (EMG) activity.

RESULTS

Quadriceps and triceps surae muscle volume decreased (P < 0.05) 10 and 16%, respectively, after 29 days bed rest. Exercise maintained quadriceps volume and mitigated triceps surae atrophy. Thus, either muscle showed different response across subject groups (P < 0.05). Force and power output during training were either maintained (P > 0.05) or increased (P < 0.05). EMG amplitude in the training mode was similar (SS; P > 0.05) or greater (CP; P < 0.05) compared with that elicited during MVC. Peak force and power test-retest coefficient of variation (CV) ranged 5-6% and 7-8% for SS and CP, respectively.

CONCLUSION

The present data suggest that this resistance exercise paradigm counteracts quadriceps and abates the more substantial triceps surae muscle atrophy in bedridden subjects, and therefore should be an important asset to space travellers.

Tests of cycling performance

Performance tests are an integral component of assessment for competitive cyclists in practical and research settings. Cycle ergometry is the basis of most of these tests. Most cycle ergometers are stationary devices that measure power while a cyclist pedals against sliding friction (e.g. Monark), electromagnetic braking (e.g. Lode), or air resistance (e.g. Kingcycle). Mobile ergometers (e.g. SRM cranks) allow measurement of power through the drive train of the cyclist's own bike in real or simulated competitions on the road, in a velodrome or in the laboratory. The manufacturers' calibration of all ergometers is questionable; dynamic recalibration with a special rig is therefore desirable for comparison of cyclists tested on different ergometers. For monitoring changes in performance of a cyclist, an ergometer should introduce negligible random error (variation) in its measurements; in this respect, SRM cranks appear to be the best ergometer, but more comparison studies of ergometers are needed. Random error in the cyclist's performance should also be minimised by choice of an appropriate type of test. Tests based on physiological measures (e.g. maximum oxygen uptake, anaerobic threshold) and tests requiring self-selection of pace (e.g. constant-duration and constant-distance tests) usually produce random error of at least approximately 2 to 3% in the measure of power output. Random error as low as approximately 1% is possible for measures of power in 'all-out' sprints, incremental tests, constant-power tests to exhaustion and probably also time trials in an indoor velodrome. Measures with such low error might be suitable for tracking the small changes in competitive performance that matter to elite cyclists.

Comparison of two waist-mounted and two ankle-mounted electronic pedometers

This study compared two ankle-mounted pedometers [StepWatch 3 (SW-3(Ankle)) and Activity Monitoring Pod 331 (AMP(Ankle))] and two waist-mounted pedometers [New Lifestyles NL-2000 (NL(Waist)) and Digiwalker SW-701 (SW-701(Waist))] under controlled and free-living conditions. In part I, 20 participants walked on a treadmill at speeds of 27-107 m min(-1). Actual steps were counted with a hand counter. In part II, participants performed leg swinging, heel tapping, stationary cycling, and car driving. In part III, 15 participants wore all pedometers for a 24 h period. The SW-3(Ankle) displayed values that were within 1% of actual steps during treadmill walking at all speeds. The other devices underestimated steps at slow speeds but all gave mean values that were within +/-3% of actual steps at 80 m min(-1) and above. The SW-3(Ankle) registered some steps during heel tapping, leg swinging, and cycling, while the AMP(Ankle) was only responsive to leg swinging. During car driving no devices recorded more than eight steps, on average. Over 24 h, the AMP(Ankle) recorded 18% fewer steps than the SW-3(Ankle) (P<0.05), while the SW-701(Waist) and the NL(Waist) recorded 15 and 11% less than the SW-3(Ankle), respectively (NSD). The SW-3(Ankle) has superior accuracy at slow treadmill walking speeds (although it was also more likely to detect "fidgeting" activities). Over 24 h, the SW-3(Ankle) tended to give higher estimates of steps per day than the other ankle- and waist-mounted pedometers.

Trunk strength testing with iso-machines. Part 1: Review of a decade of scientific evidence

This review of the scientific literature on isokinetic and isoinertial testing of dynamic trunk strength related to low back pain using "iso-machines" identified 108 items published in the past decade. There was inadequate scientific evidence to support the use of iso-machines in preemployment screening, routine clinical assessment or medico-legal evaluation.

High reliability of performance of well-trained rowers on a rowing ergometer

High retest reliability is desirable in tests used to monitor athletic performance, but the reliability of many popular tests has not been established. The aim of this study was to determine the reliability of performance of a 2000-m time-trial lasting approximately 7 min performed on a Concept II rowing ergometer. Eight well-trained rowers (peak oxygen uptake 61+/-5 ml x kg(-1) x min(-1); mean +/- standard deviation) performed the time-trials on three occasions at 3-day intervals. Mean power (313+/-38 W in trial 1) improved by 2.3% (95% confidence interval 0.1 to 4.5%) in trial 2 and by a further 0.9% (-1.4 to 3.3%) in trial 3. The variability of performance for individual rowers expressed as a coefficient of variation for mean power was 2.0% (1.3 to 3.1%), and the retest correlation was 0.96 (0.87 to 0.99). Variability and changes in performance expressed as time to complete the test were approximately one-third those of mean power, apparently because simulated velocity is proportional to the cube root of power on this ergometer. Such high reliability makes this combination of ergometer, athlete and test protocol very suitable for monitoring rowing performance and for investigating factors that affect performance in short, high-intensity endurance events.

Muscles in microgravity: from fibres to human motion

In simulated or actual microgravity, human and animal postural muscles undergo substantial atrophy: after about 270 days, the muscle mass attains a constant value of about 70% of the initial one. Most animal studies reported preferential atrophy of slow twitch fibres whose mechanical properties change towards the fast type. However, in humans, at the end of a 42-days bed rest study, a similar atrophy of slow and fast fibres was observed. After microgravity, the maximal force of several muscle groups showed a substantial decrease (6-25% of pre-flight values). The maximal power during very short "explosive" efforts of 0.25-0.30s showed an even greater fall, being reduced to 65% after 1 month and to 45% (of pre-flight values) after 6 months. The maximal power developed during 6-7s "all-out" bouts on an isokinetic cycloergometer was reduced to a lesser extent, attaining about 75% of pre-flight values, regardless of the flight duration. In these same subjects, the muscle mass of the lower limbs declined by only 9-13%. Thus, a substantial fraction of the observed decreases of maximal power is probably due to a deterioration of the motor co-ordination brought about by the absence of gravity. To prevent this substantial decay of maximal absolute power, we propose that explosive exercise be added to the daily in-flight training schedule. We also describe a system aimed at reducing cardiovascular deconditioning wherein gravity is simulated by the centrifugal acceleration generated by the motion of two counter rotating bicycles ridden by the astronauts on the inner wall of a cylindrical space module. Finally, cycling on circular or elliptical tracks may be useful to reduce cardiovascular deconditioning in permanently manned lunar bases. Indeed, on the curved parts of the path, a cyclist generates an outward acceleration vector (ac). To counterbalance ac, the cyclist must lean inwards, so that the vectorial sum of ac plus the lunar gravity tends to the acceleration of gravity prevailing on Earth.

The utility of isokinetic dynamometry in the assessment of human muscle function

Isokinetic dynamometry has become a favoured method for the assessment of dynamic muscle function in both clinical research and sports environments. Several indices, such as peak torque, are used in the literature to characterise individual, group or larger population performance via these sophisticated data acquisition systems. Research suggests that there are several competing demands on the design of the measurement protocol which may affect the measurement of isokinetic strength and subsequent suitability of data for meaningful evaluation and interpretation. There is a need to increase measurement rigour, reliability and sensitivity to a level which is commensurate with the intended application, via more elaborate multiple-trial protocols. However, this may be confounded by logistical and financial constraints or reduced individual compliance. The net effect of the interaction of such demands may be considered to be the utility of the isokinetic dynamometry protocol. Of the factors which impinge on utility, those which relate to reliability afford the most control by the test administrator. Research data suggest that in many measurement applications, the reliability and sensitivity associated with all frequently-used indices of isokinetic leg strength which are estimated via single-trial protocols, are not sufficient to differentiate either performance change within the same individual or between individuals within a homogeneous group. While such limitation may be addressed by the use of protocols based on 3 to 4 inter-day trials for the index of peak torque, other indices which demonstrate reduced reliability, for example the composite index of the ratio of knee flexion to extension peak torque, may require many more replicates to achieve the same level of sensitivity. Here, the measurement utility of the index may not be sufficient to justify its proper deployment.

Relationship between Accumulated Walking and Body Composition in Middle-Aged Women

PURPOSE

The purpose of this study was to examine the relationship between objectively determined physical activity (pedometer counted steps per day) and body composition variables in middle-aged women.

METHODS

Height, weight, body fat percentage (%BF), waist circumference, and hip circumference were measured on eighty women (50.3 +/- 6.8 yr). For 7 d after testing, each subject wore a pedometer throughout the day while following her normal daily routine. Each morning the pedometer was reset to zero, and each evening the subject recorded the steps accumulated during the day. Pearson product moment correlations were used to examine the relationship between average steps per day and body composition variables. Subjects were placed in groups to reflect different levels of physical activity: inactive (<6000 steps x d), somewhat active (6000-9999 steps x d), and regularly active (> or = 10,000 steps x d). ANOVA was utilized to determine whether body composition variables varied across activity groups. Significance was set at P < 0.05 for all tests.

RESULTS

: A significant correlation was found between average steps per day and %BF (-0.713, P < 0.0001); body mass index (BMI) (-0.417, P < 0.0001); waist circumference (-0.616; P < 0.0001); hip circumference (-0.278; P = 0.013); and waist-to-hip ratio (-0.652; P < 0.0001). There was a significant difference in body composition variables among activity groups, with higher values found in the less active groups.

CONCLUSION

This is the first study to specifically examine the relationship between steps per day and body composition in middle-aged women. Although the cross-sectional nature of this study does not allow causal relationships to be determined, women who walked more had lower %BF. Additionally, the average BMI of women who accumulated 10,000+ steps x d was in the normal range.

Percutaneous Achilles tendon repair

Fourteen patients underwent percutaneous Achilles tendon repairs between 1982 and 1989 for ruptures approximately 2 to 8 cm from the calcaneal insertion. They were evaluated subjectively (questionnaires) and objectively (physical examinations, Cybex II dynamometer). The minimum follow-up time was 2 years with an average of 3.8 years. Subjectively, all of the patients were satisfied with their overall results. Objectively, no significant difference was demonstrated by Cybex II evaluation at 60 and 120 deg/sec. A significant difference was seen at 180 deg/sec, but this represented only a 13% loss of power. No infections, delayed wound healing, reruptures, or evidence of thrombophlebitis were noted. There was one sural nerve injury.