Ann V. Rowlands

Validation of the Genea Accelerometer

PURPOSE The study aims were: 1) to assess the technical reliability and validity of the GENEA using a mechanical shaker; 2) to perform a GENEA value calibration to develop thresholds for sedentary and light-, moderate-, and vigorous-intensity physical activity; and 3) to compare the intensity classification of the GENEA with two widely used accelerometers. METHODS A total of 47 GENEA accelerometers were attached to a shaker and vertically accelerated, generating 15 conditions of varying acceleration and/or frequency. Reliability was calculated using SD and intrainstrument and interinstrument coefficients of variation, whereas validity was assessed using Pearson correlation with the shaker acceleration as the criterion. Next, 60 adults wore a GENEA on each wrist and on the waist (alongside an ActiGraph and RT3 accelerometer) while completing 10-12 activity tasks. A portable metabolic gas analyzer provided the criterion measure of physical activity. Analyses involved the use of Pearson correlations to establish criterion and concurrent validity and receiver operating characteristic curves to establish intensity cut points. RESULTS The GENEA demonstrated excellent technical reliability (CVintra = 1.4%, CVinter = 2.1%) and validity (r = 0.98, P < 0.001) using the mechanical shaker. The GENEA demonstrated excellent criterion validity using VO2 as the criterion (left wrist, r = 0.86; right wrist, r = 0.83; waist, r = 0.87), on par with the waist-worn ActiGraph and RT3. The GENEA demonstrated excellent concurrent validity compared with the ActiGraph (r = 0.92) and the RT3 (r = 0.97). The waist-worn GENEA had the greatest classification accuracy (area under the receiver operating characteristic curve (AUC) = 0.95), followed by the left (AUC = 0.93) and then the right wrist (AUC = 0.90). The accuracy of the waist-worn GENEA was virtually identical with that of the ActiGraph (AUC = 0.94) and RT3 (AUC = 0.95). CONCLUSION The GENEA is a reliable and valid measurement tool capable of classifying the intensity of physical activity in adults.

Measurement of physical activity in children with particular reference to the use of heart rate and pedometry.

SummaryUnderstanding the progression of physical activity behaviour from childhood to adulthood requires a valid, reliable and practical method of assessing activity levels which is appropriate for use in large groups. The measurement of physical activity in large scale research projects requires a method which is low in cost, agreeable to the study volunteer and accurate. Self-report can be used to determine adult activity patterns, but children lack the cognitive ability to recall details about their activity patterns. Heart rate telemetry has been used to estimate daily activity in children as a sole criterion and to validate commercial accelerometers. However, heart rate is an indirect estimate of physical activity which makes assumptions based on the linear relationship between heart rate and oxygen uptake. It is sensitive to emotional stress and body position, and takes longer to reach resting levels after physical exertion compared with oxygen uptake. It also lags behind movement, particularly as children’s physical activity is spasmodic or intermittent in nature. One alternative is the pedometer. Many early studies reported that the pedometer is inaccurate and unreliable in measuring distance or counting steps. While reasonably accurate at mid range speeds, the accuracy of the pedometer decreases in very slow walking or very fast walking or running. However, more recent studies have examined the efficacy of using pedometers to assess daily or weekly activity patterns as a whole, and these have produced more promising results. In this regard, the pedometer has a number of advantages. It is very cheap, objective and does not interfere with daily activities and is therefore appropriate for use in population studies. Commercial accelerometers with a time-sampling mechanism offer further potential and could be used to provide a picture of the pattern of children’s activity. As it has been observed that prolonged activity periods are not typically associated with childhood behaviour patterns, the use of a threshold value for ‘aerobic’ training stimulus is not appropriate as a cut-off value for physical activity. Instead, there is evidence to suggest that the total activity data measured by pedometers over limited periods of time may be more appropriate to assess how active children are.

The effect of type of physical activity measure on the relationship between body fatness and habitual physical activity in children: a meta-analysis

Background: The relationship between activity levels and body fat in children is unclear, despite a large number of studies. The issue is clouded by the wide variety of methods used to assess childrens activity levels. It is important to assess whether the type of activity measure influences the fatness-activity relationship. This is a first step to uncovering the role of modifying variables such as gender, age, maturity, etc. Primary objective: This study uses meta-analytic procedures to synthesize the results of such studies and to assess whether the type of activity measure used has an effect on the strength of the relationship observed. Methods and procedures: Fifty studies were located that satisfied the inclusion criteria. Seventy-eight per cent of the studies showed a negative relationship, 18% no relationship and 4% a positive relationship between physical activity and body fatness. Data were analysed using the meta-analytic procedures described by Rosenthal (Meta-analytic Procedures for Social Research, Sage, 1991). Main outcomes and results: The mean effect size indicated a small to moderate, inverse relationship (r =-0.16). Mean effect sizes differed significantly (F(3,5,2) 8.04, p < 0.001) according to the activity measure used: questionnaire, r =-0.14; motion counters, r =-0.18; observation, r =-0.39; heart rate (HR), r = 0.00. Observation measures elicited a significantly stronger relationship with body fat than did questionnaire or heart rate measures (p < 0.05). However, there was no significant difference between the effect sizes elicited by observation and motion counters. Correlational analyses revealed no effect of age group or gender on the strength of the relationship between fatness and activity. Conclusions: This meta-analysis suggests there is a small to moderate relationship between body fat and activity in children. It is important to note, however, that the size of the relationship depends on the activity measure used. It is therefore recommended that direct measures of movement, such as observation or motion counter methods, are used to assess the relationship of activity levels with health.BACKGROUND The relationship between activity levels and body fat in children is unclear, despite a large number of studies. The issue is clouded by the wide variety of methods used to assess childrens activity levels. It is important to assess whether the type of activity measure influences the fatness-activity relationship. This is a first step to uncovering the role of modifying variables such as gender, age, maturity, etc. PRIMARY OBJECTIVE This study uses meta-analytic procedures to synthesize the results of such studies and to assess whether the type of activity measure used has an effect on the strength of the relationship observed. METHODS AND PROCEDURES Fifty studies were located that satisfied the inclusion criteria. Seventy-eight per cent of the studies showed a negative relationship, 18% no relationship and 4% a positive relationship between physical activity and body fatness. Data were analysed using the meta-analytic procedures described by Rosenthal (Meta-analytic Procedures for Social Research, Sage, 1991). MAIN OUTCOMES AND RESULTS The mean effect size indicated a small to moderate, inverse relationship (r = -0.16). Mean effect sizes differed significantly (F(3,52) = 8.04, p < 0.001) according to the activity measure used: questionnaire, r = -0.14; motion counters, r = -0.18; observation, r = -0.39; heart rate (HR), r = 0.00. Observation measures elicited a significantly stronger relationship with body fat than did questionnaire or heart rate measures (p < 0.05). However, there was no significant difference between the effect sizes elicited by observation and motion counters. Correlational analyses revealed no effect of age group or gender on the strength of the relationship between fatness and activity. CONCLUSIONS This meta-analysis suggests there is a small to moderate relationship between body fat and activity in children. It is important to note, however, that the size of the relationship depends on the activity measure used. It is therefore recommended that direct measures of movement, such as observation or motion counter methods, are used to assess the relationship of activity levels with health.

Technical variability of the RT3 accelerometer.

PURPOSE To evaluate the technical performance of the RT3 triaxial accelerometer. METHODS Twenty-three RT3 accelerometers were subjected to a specific vibration along each sensitive axis in isolation, using a motorized vibration table that produced frequencies of 2.1, 5.1, and 10.2 Hz, respectively. Data were analyzed for frequency and axis effects and inter- and intra-instrument variability. RESULTS ANOVA showed a frequency by axis interaction (F2.1,36.8 = 19.9, P < 0.001). Post hoc tests revealed the Y axis count to be significantly higher than the X and Z axes counts at 5.1 and 10.2 Hz. There was no difference in counts between axes at 2.1 Hz. Interinstrument coefficients of variation (CV) decreased as frequency increased (21.9 to 26.7% at 2.1 Hz, 6.3 to 9.0% at 5.1 Hz, and 4.2 to 7.2% at 10.2 Hz). The intraclass correlation (ICC) between RT3s was 0.99, regardless of the axis. Intra-instrument CV also decreased as frequency increased (2.1 to 56.2%, 0.3 to 2.5%, and 0.2 to 2.9% at 2.1, 5.1, and 10.2 Hz, respectively. CONCLUSION There were no differences in counts recorded on the X, Y, and Z axes at 2.1 Hz; however, the counts recorded along the Y axis were significantly higher than the counts at the X and Z axes at 5.1 and 10.2 Hz. Due to large coefficients of variation for both inter- and intra-instrument variability at 2.1 Hz, testing the inter- and intra-instrument variability of the accelerometers before use is recommended.

Intermonitor variability of the RT3 accelerometer during typical physical activities.

PURPOSE To evaluate the reliability and variability of eight RT3 accelerometers. METHODS The RT3 were subjected to two repeated trials of six activities: rest, walking (4 and 6 km.h-1), running (8 and 10 km.h-1), and sit-stand position (20 min). One person performed all trials (female: age 24 yr, height 158.0 cm, mass 48.2 kg). Each activity lasted 12 min. The middle 10 min were taken from each 12-min trial and used as the output measure (cts.min-1). Data were analyzed for activity ( 6), monitor ( 8), and trial ( 2) effects using four three-way ANOVA: vector magnitude, X (vertical), Y (anterioposterior), and Z (mediolateral) axes. RESULTS Intermonitor coefficient of variation was <6% during locomotive activities, however, increased to 8-25% during sit-stand. A three-way interaction was found for vector magnitude (F35,315=88945.7, P < 0.001) and Y (F35,315=978435.6, P < 0.001) and Z axes (F35,315=103802.8, P < 0.001). A two-way activity x monitor interaction was found for the X axis (F35,315=1037787.0, P < 0.001). Follow-up tests revealed no differences between trials 1 and 2 for vector magnitude, X and Z axes. One monitor recorded significantly lower activity counts in trial 1 compared with trial 2 along the Y axis. Intermonitor differences were evident at 4, 6, 8, and 10 km.h-1 for the Y and Z axes, and at 6, 8, and 10 km.h-1 for the vector magnitude and X axis. Variability between monitors at each activity increased as intensity increased. CONCLUSION Reliability of the RT3 is good; however, intermonitor variability exists. The vertical axis of the RT3 accelerometer showed the least variability and was the most reliable. It is recommended that intermonitor variability and reliability of RT3 on each axis be assessed before use.

Comparison of Accelerometer and Pedometer Measures of Physical Activity in Boys and Girls, Ages 8–10 Years

Abstract Accelerometers record total physical activity and time spent at different intensities. Pedometers indicate total activity only. The aim of this study was to assess the relationship between pedometer counts and attainment of > 60 min of moderate activity. Thirty-four children, ages 8 –10 years, wore a Tritrac accelerometer and Yamax pedometer. Published recommendations of steps per day were compared to attainment of > 60 min moderate activity. Boys who accumulated 13,000 steps.d-1 and girls who accumulated 12,000 steps.d-1 engaged in > 60 min moderate activity. However, 23% of boys and 15% of girls did not reach the pedometer thresholds but did engage in > 60 min moderate activity. In conclusion, these pedometer thresholds provide a reasonable estimation when assessment of physical activity intensity is not possible

Children's physical activity and psychological health: the relevance of intensity.

Aim: To examine the relevance of physical activity intensity when assessing the relationship between activity and psychological health in 9–10‐year‐old children.

The pattern of physical activity in relation to health outcomes in boys.

OBJECTIVE Spontaneous and transitory movement patterns are characteristic of children. The aim of this study was to explore the relationship between short, frequent activity bouts and childrens health. METHODS Physical activity was recorded every 2 s by accelerometry (ActiGraph GT1M) for seven days in 47 boys (age 8-10 years). Summary activity measures and activity pattern characteristics (frequency, intensity and duration of > or = 4 s [short] and > or = 5 min [long] bouts of > or= light [> or = LIGHT], > or = moderate [> or = MOD], > or = vigorous [> or = VIG], and > or = hard [> or = HARD] intensity activity) were recorded. Microvascular function was assessed using laser Doppler perfusion imaging as the forearm skin blood flow response to the iontophoretic application of acetylcholine (endothelial dependent vasodilator) and sodium nitroprusside (endothelial independent vasodilator) at rest and following maximal exercise. Waist circumference, resting blood pressure and aerobic fitness (VO(2peak)) were measured. RESULTS The intensity of short and long > or = LIGHT bouts and the frequency of short and long > or =MOD bouts were correlated with waist circumference (r = - 0.42 to -0.52, p < 0.01) and VO(2peak) (r = 0.42 to 0.47, p < 0.01), but not when scaled for lean body mass. The frequency of short and long > or =LIGHT bouts were associated with change in endothelial function from rest to post-exercise (r = 0.34 to 0.55, p < 0.05). No relationships were evident between blood pressure and activity. CONCLUSION The relationship between the frequency of short bouts (> or =4 s) of activity and health was as strong as relationships identified between longer bouts (> or =5 min) and health. This is encouraging as sporadic intermittent activity is characteristic of childrens activity pattern.

Prediction of DXA-determined whole body fat from skinfolds: importance of including skinfolds from the thigh and calf in young, healthy men and women.

Objective:To investigate the relationship of percent body fat (%fat), assessed by dual energy-X-ray absorptiometry (DXA) or a four-compartment model, with upper body and lower limb skinfolds.Design:Cross-sectional design involving forward stepwise and hierarchical multiple regression analyses to assess the relationship of %fat with skinfolds and a combination of four commonly used upper body skinfolds (biceps, triceps, subscapular and iliac crest) with the calf and thigh skinfolds.Setting:University research laboratory.Subjects:In all, 31 females, mean age 20.9 (±2.0) y, and 21 males, mean age 22.3 (±5.5) y volunteered for this study, which was approved by the Ethics Committee of the School of Sport, Health and Exercise Sciences, University of Wales, Bangor.Measurements:%fat from DXA in both groups, and %fat from a four-compartment (water, bone mineral mass, fat and residual) model (%fat4C) in females only. Skinfolds were measured at the abdomen, iliac crest, biceps, triceps, subscapular, calf and thigh.Results:All skinfolds were positively associated with DXA estimates of %fat (P<0.01). In males and females, the thigh skinfold had the highest correlation with %fat. This was also observed when %fat4C was used as the criterion in females. Stepwise multiple regression analysis using %fatDXA as the criterion selected the thigh (R2=0.82), calf (R2 change 0.04) and iliac crest (R2 change=0.03) for females, and the thigh (R2=0.79), iliac crest (R2 change=0.11) and abdomen (R2 change=0.03) for males (all P<0.01). When %fat4C was used as the criterion in the females, only the thigh was selected as a significant predictor (R2=0.76). Independent prediction factors were created from the sum of biceps, triceps, subscapular and iliac crest (∑4skf) and from the sum of the thigh and calf (∑thigh+calf). These factors were then entered into a hierarchical multiple linear regression analysis to predict percent fat. Order of entry was varied to allow the assessment of unique variance accounted for by each predictor. The sum of the thigh and calf explained more variance in %fatDXA than that explained by the ∑4skf alone, irrespective of the order of entry in both males and females. This was also observed when %fat4C was used as the criterion in the females.Conclusions:The results of this study confirm that lower body skinfolds are highly related to percent body fat in fit and healthy young men and women, and uphold current recommendations by the British Olympic Association to include the thigh skinfold with ∑4skf. Conventional use of the ∑4skf to estimate percent body fat is significantly enhanced by the inclusion of the thigh and calf skinfolds, either independently or in combination. In this group of males and females, the sum of the thigh and calf skinfolds accounted for the most variance in percent fat.

Chronic flexibility gains: effect of isometric contraction duration during proprioceptive neuromuscular facilitation stretching techniques.

Abstract The aim of this study was to assess the effect of two isometric contraction durations during proprioceptive neuromuscular facilitation stretching on gains inflexion at the hip. Forty-three women (M age = 20.0 years, SD =1.3) were assigned to one of three groups: 5-s isometric contraction (5-IC), 10-IC, and control. Flexibility was assessed at baseline and Weeks 3 and 6. Analysis of covariance, controlling for pretest differences, showed a significant interaction, F(2, 33) = 44.1, p <. 001. Flexibility was significantly lower in the control group relative to the 5-IC and 10-IC groups and in the 5-IC group relative to the 10-IC group at 3 and 6 weeks (3 weeks = 101.2 ± 1.4°, 114.3 ± 1.5°, 120.5 ± 1.3°; 6 weeks = 103.0 ± 1.4°, 126.1 ± 1.6°, 133.3 ± 1.4° for control, 5-IC and 10-IC groups, respectively). A longer contraction time led to greater increases inflexibility.