Muscle damage alters the metabolic response to dynamic exercise in humans: a 31P-MRS study.

We used ³¹P-magnetic resonance spectroscopy to test the hypothesis that exercise-induced muscle damage (EIMD) alters the muscle metabolic response to dynamic exercise, and that this contributes to the observed reduction in exercise tolerance following EIMD in humans. Ten healthy, physically active men performed incremental knee extensor exercise inside the bore of a whole body 1.5-T superconducting magnet before (pre) and 48 h after (post) performing 100 squats with a load corresponding to 70% of body mass. There were significant changes in all markers of muscle damage [perceived muscle soreness, creatine kinase activity (434% increase at 24 h), and isokinetic peak torque (16% decrease at 24 h)] following eccentric exercise. Muscle phosphocreatine concentration ([PCr]) and pH values during incremental exercise were not different pre- and post-EIMD (P > 0.05). However, resting inorganic phosphate concentration ([P(i)]; pre: 4.7 ± 0.8; post: 6.7 ± 1.7 mM; P < 0.01) and, consequently, [P(i)]/[PCr] values (pre: 0.12 ± 0.02; post: 0.18 ± 0.05; P < 0.01) were significantly elevated following EIMD. These mean differences were maintained during incremental exercise (P < 0.05). Time to exhaustion was significantly reduced following EIMD (519 ± 56 and 459 ± 63 s, pre- and post-EIMD, respectively, P < 0.001). End-exercise pH (pre: 6.75 ± 0.04; post: 6.83 ± 0.04; P < 0.05) and [PCr] (pre: 7.2 ± 1.7; post: 14.5 ± 2.1 mM; P < 0.01) were higher, but end-exercise [P(i)] was not significantly different (pre: 19.7 ± 1.9; post: 21.1 ± 2.6 mM, P > 0.05) following EIMD. The results indicate that alterations in phosphate metabolism, specifically the elevated [P(i)] at rest and throughout exercise, may contribute to the reduced exercise tolerance observed following EIMD.

The perceptual response to treadmill exercise using the Eston-Parfitt scale and marble dropping task, in children age 7 to 8 years.

This study assessed the nature of the perceived exertion response to treadmill running in 14 healthy 7-8 year-old children, using the Eston-Parfitt (E-P) Ratings of Perceived Exertion (RPE) scale and a marble dropping task. For the E-P scale and the marble dropping task, the relationships between the RPE and work rate were best described as linear (R2 = .96) and curvilinear (R2 = .94), respectively. This study further suggests that individual respiratory-metabolic cues (oxygen uptake: O2, heart rate: HR, ventilation: VE) may significantly influence the overall RPE to varying degrees in young children. The E-P scale provides an intuitively meaningful and valid means of quantifying the overall perception of exertion in young, healthy children during treadmill running. The marble dropping task is a useful secondary measure of perceived exertion, which provides further insight into the nature of the perceived exertion response to exercise in young children.

Eccentric exercise-induced muscle damage dissociates the lactate and gas exchange thresholds.

We tested the hypothesis that exercise-induced muscle damage would increase the ventilatory (V(E)) response to incremental/ramp cycle exercise (lower the gas exchange threshold) without altering the blood lactate profile, thereby dissociating the gas exchange and lactate thresholds. Ten physically active men completed maximal incremental cycle tests before (pre) and 48 h after (post) performing eccentric exercise comprising 100 squats. Pulmonary gas exchange was measured breath-by-breath and fingertip blood sampled at 1-min intervals for determination of blood lactate concentration. The gas exchange threshold occurred at a lower work rate (pre: 136 ± 27 W; post: 105 ± 19 W; P < 0.05) and oxygen uptake (VO(2)) (pre: 1.58 ± 0.26 litres · min(-1); post: 1.41 ± 0.14 litres · min(-1); P < 0.05) after eccentric exercise. However, the lactate threshold occurred at a similar work rate (pre: 161 ± 19 W; post: 158 ± 22 W; P > 0.05) and VO(2) (pre: 1.90 ± 0.20 litres · min(-1); post: 1.88 ± 0.15 litres · min(-1); P > 0.05) after eccentric exercise. These findings demonstrate that exercise-induced muscle damage dissociates the V(E) response to incremental/ramp exercise from the blood lactate response, indicating that V(E) may be controlled by additional or altered neurogenic stimuli following eccentric exercise. Thus, due consideration of prior eccentric exercise should be made when using the gas exchange threshold to provide a non-invasive estimation of the lactate threshold.

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.

Prolonged unilateral disuse osteopenia 14 years post external fixator removal: a case history and critical review.

Disuse osteopenia is a complication of immobilisation, with reversal generally noted upon remobilisation. This case report focuses on a patient who was seen 18 years following a road traffic collision when multiple fractures were sustained. The patient had an external fixator fitted for a tibia and fibula fracture, which remained in situ for a period of 4 years. Following removal, the patient was mobilised but, still required a single crutch to aid walking. Fourteen years post removal of the fixator, the patient had a DXA scan which, demonstrated a T-score 2.5 SD lower on the affected hip. This places the patient at an increased risk of hip fracture on this side, which requires monitoring. There appear to be no current studies investigating prolonged disuse-osteopenia in patients following removal of long-term external fixators. Further research is required to quantify unilateral long-term effects to bone health and fracture risk in this population.

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 children's 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 children's activity pattern.

Methodological approaches for investigating the biological basis for physical activity in children.

In this insightful article, Eisenmann and Wickel bring together diverse areas of animal and human research to address the issue of the existence of an "activity stat," or biological basis for activity, outlining the evidence accumulated in this area since Rowland's excellent commentary in 1998. As the authors state, there has been progress in this area over the last 10 years, however there are still a limited number of studies that specifically address the possible existence of an activity stat in children, whether the strength of this varies by age, sex or culture, the degree of influence of environmental and social factors on this set-point and therefore the crucial question-if activity level is under central control are activity interventions doomed to failure?

Characteristics of the activity pattern in normal weight and overweight boys.

OBJECTIVE: To assess whether the activity pattern differs between normal weight and overweight boys across weekdays and weekend days. METHODS: Physical activity was recorded every 2 s by accelerometry in 32 normal weight and 15 overweight boys aged 8-10 years for four weekdays and two weekend days (South-West England 2007). 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 =moderate, > or =vigorous, and > or =hard activity) were recorded. RESULTS: Normal weight boys accumulated more > or =hard activity (p<0.05) but other summary measures did not differ by weight status. However, the activity pattern differed in overweight relative to normal weight boys. The most frequent short bouts were shorter and less intense (p<0.05). All long bouts were less intense and > or =moderate long bouts were shorter and less frequent (p<0.05). Overall, less activity was accumulated on weekends (frequency of more intense short bouts, intensity of most frequent long bouts and duration of > or =light, > or =moderate (and for overweight boys > or =vigorous) short bouts dropped-off) (p<0.05). CONCLUSION: Despite equivalent summary activity measures overweight boys exhibited fewer and shorter bouts, particularly sustained > or =moderate bouts, relative to normal weight boys suggesting that the activity pattern may be important for weight control.

Effect of exercise-induced muscle damage on ventilatory and perceived exertion responses to moderate and severe intensity cycle exercise.

This study examined the effect of exercise-induced muscle damage (EIMD) on ventilatory and perceived exertion responses to cycle exercise. Ten healthy, physically active men cycled for 6 min at moderate intensity and to exhaustion at severe intensity before and 48 h after eccentric exercise (100 squats with a load corresponding to 70% of body mass). Changes in ventilation and ratings of perceived exertion (RPE) were calculated for each individual and expressed against time (moderate and severe exercise) and as a percentage of time to exhaustion (severe exercise). Ventilation increased during moderate exercise at 48 h V(E); 34.5 +/- 5.0 to 36.3 +/- 3.8 l min(-1), P < 0.05) but increases in RPE were not significant. During severe exercise at 48 h, time to exhaustion (TTE) was reduced and V(E) (87.1 +/- 14.1 to 93.8 +/- 11.7 l min(-1)) and RPE (15.5 +/- 1.3 to 16.1 +/- 1.4) were elevated (P < 0.05). When expressed as a percentage of TTE, the differences in ventilation and RPE values disappeared. Findings indicate that the augmented ventilatory response to cycle exercise following EIMD may be an important cue in informing effort perception during high-intensity exercise but not during moderate-intensity exercise.

Prediction of maximal oxygen uptake from submaximal ratings of perceived exertion and heart rate during a continuous exercise test: the efficacy of RPE 13.

This study assessed the utility of a single, continuous exercise protocol in facilitating accurate estimates of maximal oxygen uptake V(O)(2max) from submaximal heart rate (HR) and the ratings of perceived exertion (RPE) in healthy, low-fit women, during cycle ergometry. Eleven women estimated their RPE during a continuous test (1 W 4 s(-1)) to volitional exhaustion (measured V(O)(2max)). Individual gaseous exchange thresholds (GETs) were determined retrospectively. The RPE and HR values prior to and including an RPE 13 and GET were extrapolated against corresponding oxygen uptake to a theoretical maximal RPE (20) and peak RPE (19), and age-predicted HRmax, respectively, to predict V(O)(2max)). There were no significant differences (P > 0.05) between measured (30.9 +/- 6.5 ml kg(-1) min(-1)) and predicted V(O)(2max) from all six methods. Limits of agreement were narrowest and intraclass correlations were highest for predictions of V(O)(2max) from an RPE 13 to peak RPE (19). Prediction of V(O)(2max) from a regression equation using submaximal HR and work rate at an RPE 13 was also not significantly different to actual V(O)(2max) (R( 2 ) = 0.78, SEE = 3.42 ml kg(-1) min(-1), P > 0.05). Accurate predictions of V(O)(2max) may be obtained from a single, continuous, estimation exercise test to a moderate intensity (RPE 13) in low-fit women, particularly when extrapolated to peak terminal RPE (RPE(19)). The RPE is a valuable tool that can be easily employed as an adjunct to HR, and provides supplementary clinical information that is superior to using HR alone.

The perceptual response to exercise of progressively increasing intensity in children aged 7-8 years: validation of a pictorial curvilinear ratings of perceived exertion scale.

This study assessed the validity of the Eston-Parfitt (E-P) curvilinear Ratings of Perceived Exertion (RPE) Scale and a novel marble quantity task to provide estimates of perceived exertion during cycle ergometry. Fifteen children aged 7-8 years performed a discontinuous incremental graded-exercise test, and reported exertional ratings at the end of each minute. Significant increases in physiological and perceptual data were observed with increasing work rate. The relationship between work rate and marbles was curvilinear (mean R(2)=.94), supporting the theoretical justification for the E-P Scale. Strong linear (R(2)=.93) and curvilinear (R(2)=.94) relationships between RPE from the E-P Scale and work rate confirmed the robustness of the E-P Scale. Valid exertional ratings may be obtained using the E-P Scale with young children. The novel marble quantity task offers an alternative method of deriving perceived exertion responses in children.

Seasonal changes in children's physical activity: an examination of group changes, intra-individual variability and consistency in activity pattern across season.

BACKGROUND: Components of activity that are more variable over time may be more susceptible to manipulation in activity interventions. AIM: The present study examined variability and consistency of components of children's activity across season. SUBJECTS AND METHODS: Sixty-four 9-11-year-old children wore an accelerometer for 6 days during winter and summer. Activity bouts (>or=4 s) greater than light (>or=LIGHT), moderate (>or=MOD) and vigorous (>or=VIG) intensity were recorded. RESULTS: Intra-individual variability of the activity components across season was greater for bout frequency (CV: >or=LIGHT = 6.6-9.9%, >or=MOD = 10.7-16.1%, >or=VIG = 17.0-26.8%) than bout intensity or duration (CV: >or=LIGHT = 3.4-7.4%, >or=MOD = 3.6-7.8%, >or=VIG = 4.2-10.0%, p<0.05) and for the frequency of >or=VIG bouts compared to the frequency of >or=LIGHT and >or=MOD bouts (p<0.05). All components of the activity pattern tended to track consistently when assessing >or=LIGHT and >or=MOD bouts (intra-class correlations (ICC) = 0.47-83, p<0.05), >or=VIG bouts in boys (ICC = 0.69-0.77, p<0.01) and frequency of >or=VIG bouts in girls (ICC = 0.82, p<0.01). CONCLUSIONS: Bout frequency was the most variable component of activity across season. However, children tended to maintain their rank for bout frequency. It would be of interest to investigate whether bout frequency can be manipulated in an activity intervention.

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. METHODS: Activity was assessed by accelerometry in 57 boys (n = 23) and girls (n = 34). Total activity and time spent in very light (< or =1.9 METs) through to vigorous activity (> or =6 METs) were recorded. Psychological health inventories to assess anxiety, depression and aspects of self-worth were completed. RESULTS: Time accumulated in very light activity had positive correlations with anxiety and depression (r > 0.30, p < 0.05) and negative correlations with aspects of physical self-worth (r > -0.29, p < 0.05). Time accumulated in vigorous activity had negative correlations with anxiety and behavioural conduct (r > -0.30, p < 0.05) and positive correlation with aspects of physical self-worth (r > 0.28, p < 0.05). Children spending over 4 h in very light intensity activity had more negative psychological profiles than children spending under 4 h at this intensity. CONCLUSION: Aspects of psychological health were negatively correlated with very light intensity activity and positively correlated with vigorous intensity activity. Further research should investigate whether reducing time spent in very light intensity activity and increasing time spent in vigorous intensity activity improves psychological health in children.

Relationships between accelerometer-assessed physical activity and health in children: impact of the activity-intensity classification method.

It is unknown whether relationships detected between physical activity intensity and health differ according to accelerometer thresholds used [sample-specific thresholds (SSTs), published thresholds (PTs) or the individualized activity-related time equivalent (ArteACC)]. SSTs were developed through ActiGraph calibration in 52 boys, aged 8-10 years. The boys subsequently wore an ActiGraph for seven days. SSTs, PTs and ArteACC for moderate (MPA) and vigorous (VPA) activity were applied. Waist circumference (WC), peak oxygen consumption (VO2peak) and blood pressure were assessed. After applying SSTs, 48.9% of boys achieved 60+ minutes of daily MVPA, compared with 8.5% with PTs and 100% with ArteACC. MPA and VPA were correlated with WC and VO2peak, regardless of whether PTs or SSTs were used (WC: MPA r = -0.37 to -0.43; VO2peak: r = 0.34 to 0.39, p < 0.05). With ArteACC, only VPA was correlated with WC (r = -0.39, p < 0.01) and VO2peak (r = 0.35, p < 0.05). Relationships with blood pressure were statistically non-significant. Although estimates of the quantity of activity differed according to thresholds used, relationships detected with health were consistent regardless of whether SSTs or PTs were employed. There was no advantage of using SSTs or individualized thresholds. Researchers are encouraged to use PTs to ensure greater comparability between studies. Key pointsStandardized accelerometer intensity thresholds for evaluating children's physical activity do not exist, therefore determining whether relationships between activity and health differ when using different thresholds is of interest.Although prevalence estimates differ according to the choice of accelerometer intensity threshold, relationships detected between activity and various health outcomes in boys are similar, providing the moderate threshold is at least equivalent to an average brisk walk (i.e., ≥ 4 METs).Standardization of thresholds between samples should not impact on relationships determined with health and would allow comparability of prevalence estimates.

Effect of eccentric exercise-induced muscle damage on the dynamics of muscle oxygenation and pulmonary oxygen uptake.

Unaccustomed eccentric exercise has a profound impact on muscle structure and function. However, it is not known whether associated microvascular dysfunction disrupts the matching of O2 delivery (Qo2) to O2 utilization (Vo2). Near-infrared spectroscopy (NIRS) was used to test the hypothesis that eccentric exercise-induced muscle damage would elevate the muscle Qo2:Vo2 ratio during severe-intensity exercise while preserving the speed of the Vo2 kinetics at exercise onset. Nine physically active men completed "step" tests to severe-intensity exercise from an unloaded baseline on a cycle ergometer before (Pre) and 48 h after (Post) eccentric exercise (100 squats with a load corresponding to 70% of body mass). NIRS and breath-by-breath pulmonary Vo2 were measured continuously during the exercise tests and subsequently modeled using standard nonlinear regression techniques. There were no changes in phase II pulmonary Vo2 kinetics following the onset of exercise (time constant: Pre, 25 +/- 4 s; Post, 24 +/- 2 s; amplitude: Pre, 2.36 +/- 0.23 l/min; Post, 2.37 +/- 0.23 l/min; all P > 0.05). However, the primary (Pre, 14 +/- 3 s; Post, 19 +/- 3 s) and overall (Pre, 16 +/- 4 s; Post, 21 +/- 4 s) mean response time of the [HHb] response was significantly slower following eccentric exercise (P < 0.05). The slower [HHb] kinetics observed following eccentric exercise is consistent with an increased Qo2:Vo2 ratio during transitions to severe-intensity exercise. We propose that unchanged primary phase Vo2 kinetics are associated with an elevated Qo2:Vo2 ratio that preserves blood-myocyte O2 flux.

Patterns of habitual activity across weekdays and weekend days in 9-11-year-old children.

OBJECTIVE: To characterize the pattern of activity in boys and girls across weekdays and weekend days. METHODS: Physical activity was recorded every 2 s by uniaxial accelerometry in 84 children, aged 9-11 years, for up to four weekdays and two weekend days. Activity bouts (>or= 4 s and >or= 5 min) greater than light (>or= LIGHT), moderate (>or= MOD) and vigorous (>or= VIG) intensity were recorded. The study took place in the South-West of England in 2007. RESULTS: The mean duration of activity bouts decreased as intensity increased from 11.0+/-1.3 s for >or= LIGHT activity to 6.1+/-1.0 s for >or= VIG activity. The frequency, duration and intensity of bouts were greater in boys than girls, and the frequency and duration of bouts were greater on weekdays than weekend days. Girls accumulated more activity sporadically than boys, whereas boys accumulated more activity in >or= 5-min bouts. CONCLUSION: Sex differences and weekday/weekend differences in activity were largely due to the intensity of the most frequent bouts of activity and frequency of the most intense bouts. Information regarding the pattern of children's habitual activity can be used to inform activity interventions and assess the aspects of the activity pattern that are related to health.

Accelerometer assessment of physical activity in children: an update.

Accelerometry is frequently used to assess physical activity in children. The number of articles in this area has increased dramatically in the last 10 years. The aim of this article is to provide a contemporary overview of accelerometry research in children. Specifically, the review addresses the choice of monitor, choice of epoch, when and for how long activity should be measured, the lack of consensus over how to define a complete day of activity data, issues of compliance, methods for the calibration of activity output, and the richness of data available from accelerometry.

Influence of speed and step frequency during walking and running on motion sensor output.

PURPOSE: Studies have reported strong linear relationships between accelerometer output and walking/running speeds up to 10 km x h(-1). However, ActiGraph uniaxial accelerometer counts plateau at higher speeds. The aim of this study was to determine the relationships of triaxial accelerometry, uniaxial accelerometry, and pedometry with speed and step frequency (SF) across a range of walking and running speeds. METHODS: Nine male runners wore two ActiGraph uniaxial accelerometers, two RT3 triaxial accelerometers (all set at a 1-s epoch), and two Yamax pedometers. Each participant walked for 60 s at 4 and 6 km x h(-1), ran for 60 s at 10, 12, 14, 16, and 18 km x h(-1), and ran for 30 s at 20, 22, 24, and 26 km x h(-1). Step frequency was recorded by a visual count. RESULTS: ActiGraph counts peaked at 10 km x h(-10 (2.5-3.0 Hz SF) and declined thereafter (r=0.02, P>0.05). After correction for frequency-dependent filtering, output plateaued at 10 km x h(-1) but did not decline (r=0.77, P<0.05). Similarly, RT3 vertical counts plateaued at speeds > 10 km x h(-1) (r=0.86, P<0.01). RT3 vector magnitude and anteroposterior and mediolateral counts maintained a linear relationship with speed (r>0.96, P<0.001). Step frequency assessed by pedometry compared well with actual step frequency up to 20 km x h(-1) (approximately 3.5 Hz) but then underestimated actual steps (Yamax r=0.97; ActiGraph pedometer r=0.88, both P<0.001). CONCLUSION: Increasing underestimation of activity by the ActiGraph as speed increases is related to frequency-dependent filtering and assessment of acceleration in the vertical plane only. RT3 vector magnitude was strongly related to speed, reflecting the predominance of horizontal acceleration at higher speeds. These results indicate that high-intensity activity is underestimated by the ActiGraph, even after correction for frequency-dependent filtering, but not by the RT3. Pedometer output is highly correlated with step frequency.

The Measurement and Interpretation of Children's Physical Activity.

The accurate and reliable assessment of physical activity is necessary for any research study where physical activity is either an outcome measure or an intervention. The aim of this review is to examine the use of objective measurement techniques for the assessment and interpretation of children's physical activity. Accurate measurement of children's activity is challenging, as the activity is characteristically sporadic and intermittent, consisting of frequent, short bouts. Objective measures of physical activity include heart rate telemetry, pedometry and accelerometry, and each of these methods has strengths and limitations. Heart rate is suited to the measurement of sustained periods of moderate and vigorous activity, pedometry provides a valid measure of total activity, and accelerometry provides a valid measure of total activity as well as the pattern and intensity of activity. As the weaknesses of heart rate and accelerometry for the assessment of activity are not inter-correlated, a combination of the two methods may be more accurate than either method alone. Recent evidence suggests that the Actiheart, an integrated accelerometer and heart rate unit, provides a more accurate prediction of children's energy expenditure than either heart rate or accelerometry alone. However, the cost of the Actiheart is prohibitive for large-scale studies. The pedometer is recommended when only the total amount of physical activity is of interest. When the intensity or the pattern of activity is of interest, accelerometry is the recommended measurement tool. Key pointsThe use of objective measures to assess physical activity in children is recommended.Pedometers provide an inexpensive objective measure of total activity that is highly correlated with more sophisticated techniques, e.g. accelerometry, and has been used to identify relationships between health and activity in children.Accelerometry allows examination of the temporal pattern and intensity of children's activity, including sporadic physical activity and bouts of physical activity.