Effects of different endurance exercise modalities on migraine days and cerebrovascular health in episodic migraineurs: A randomized controlled trial.

Aerobic exercise training is a promising complementary treatment option in migraine and can reduce migraine days and improve retinal microvascular function. Our aim was to elucidate whether different aerobic exercise programs at high vs moderate intensities distinctly affect migraine days as primary outcome and retinal vessel parameters as a secondary. In this randomized controlled trial, migraine days were recorded by a validated migraine diary in 45 migraineurs of which 36 (female: 28; age: 36 (SD:10)/BMI: 23.1 (5.3) completed the training period (dropout: 20%). Participants were assigned (Strata: age, gender, fitness and migraine symptomatology) to either high intensity interval training (HIT), moderate continuous training (MCT), or a control group (CON). Intervention groups trained twice a week over a 12-week intervention period. Static retinal vessel analysis, central retinal arteriolar (CRAE) and venular (CRVE) diameters, as well as the arteriolar-to-venular diameter ratio (AVR) were obtained for cerebrovascular health assessment. Incremental treadmill testing yielded maximal and submaximal fitness parameters. Overall, moderate migraine day reductions were observed (ηP2 = .12): HIT revealed 89% likely beneficial effects (SMD = 1.05) compared to MCT (SMD = 0.50) and CON (SMD = 0.59). Very large intervention effects on AVR improvement (ηP2 = 0.27), slightly favoring HIT (SMD=-0.43) over CON (SMD=0), were observed. HIT seems more effective for migraine day reduction and improvement of cerebrovascular health compared to MCT. Intermittent exercise programs of higher intensities may need to be considered as an additional treatment option in migraine patients.

Pilates vs. Balance Training in Health Community-Dwelling Seniors: a 3-arm, Randomized Controlled Trial.

The study examined effects of traditional balance vs. mat-based Pilates training on balance and trunk strength in healthy community dwellers. Forty-eight seniors were either stratified to a balance training group (BAL, n=16, 69.1 (SD 5.8) y), Pilates training group (PIL, n=17, 70.8 (6.5) y) or control group (CON, n=15, 69.2 (6.1) y). BAL performed traditional balance training, while PIL conducted mat-based Pilates-exercises (8 weeks, 2 sessions/week 66 min each). Balance performance (single limb stance and perturbed kneeling, Y-Balance test), dynamic and isometric trunk flexion and extension were assessed during pre- and post-testing. According to the magnitude-based inference approach, substantial positive effects in favor of BAL compared to CON were found for the Y-balance score (right leg, effect size (d)=0.68; left leg, d=0.56), trunk extension (d=0.68) and single leg stance (right leg, d=0.61; left leg, d=0.38). Dynamic (d=0.32) and isometric (d=0.15) trunk flexion revealed unclear effects. For the Y-balance score (right leg, d=0.48, left leg, d=0.75) and single leg stance (right leg, +d=0.61%; left leg, d=0.67), interestingly, BAL substantially exceeded PIL. PIL vs. CON revealed unclear effects for most parameters (0.05

Slackline training and neuromuscular performance in seniors: A randomized controlled trial.

Slackline training (balancing on nylon ribbons) has been shown to improve neuromuscular performance in children and adults. Comparable studies in seniors are lacking. Thus, 32 seniors were randomly assigned [strata: age, gender, physical activity (PA)] to an intervention [INT; n = 16, age: 65 ± 4 years, PA: 9 ± 5 h/week] or control [CON, n = 16, age: 63 ± 4 years, PA: 8 ± 4 h/week] group. Slackline training was given for 6 weeks (3 times per week, attendance 97%). Static and slackline standing balance performance, force development, and maximal strength of the ankle muscles were assessed before and after slackline training. Muscle activity (lower limb and trunk) was recorded during balance testing. Moderate to large group × time interactions (0.02 < P < 0.04, 0.11 < ηp (2) < 0.17) in favor of INT were found for slackline standing times (INT: left, +278%, P = 0.02; right, +328%, P = 0.03; tandem, +94%, P = 0.007) and muscle activity during single-limb slackline standing [INT: right: rectus abdominis (RA), P = 0.003, -15%; multifidus (MF), P = 0.01, -15%; left: tibialis anterior (TIB), P = 0.03, -12%; soleus (SOL), P = 0.006, -18%; RA, P = 0.04, -11%; MF, P = 0.01, -16%; gastrocnemius medialis (GM), P = 0.02, -19%]. Static balance performance, ankle strength, and power were not affected. Slackline training induced large task-specific improvements of slackline standing performance accompanied with reductions of lower limb and trunk muscle activity. Transfer effects to static balance and strength measures seem limited.

Influence of physical fitness and activity behavior on retinal vessel diameters in primary schoolchildren.

Retinal vessel alterations have been shown to be associated with cardiovascular risk factors and physical inactivity as early as childhood. In this context, the analysis of physical activity in children has solely been based on questionnaire assessments. The study aimed to examine the association of physical fitness performance and self-reported physical activity with retinal vessel diameters in young children. Three hundred ninety-one primary schoolchildren [7.3 years (SD 0.4)] were examined in this cross-sectional study. The primary outcome was endurance performance measured with the 20-m shuttle run. The additional tests consisted of a 20-m sprint, jumping sidewards and balancing backwards. Retinal microcirculation was assessed using a static retinal vessel analyzer. Parents completed questionnaires about physical and sedentary activities. Endurance performance was associated with narrower retinal venular diameters [-0.9 (95%CI: -1.8; -0.1) measuring units (mu)/ unit shuttle run, P = 0.04] and a higher arteriolar to venular ratio [0.003 (-0.001; 0.006)/unit shuttle run, P = 0.06]. The sprint performance was associated with narrower retinal arterioles [4.7 (0.8; 8.6) mu/unit sprint, P = 0.02]. Indoor playing activity correlated with narrower retinal venules [-0.04 (-0.07; -0.01) mu/per unit, P = 0.02]. Our data suggest that objectively measured endurance performance relates with better retinal vessel health in early childhood.

Fundamental movement skills in preschoolers: a randomized controlled trial targeting object control proficiency.

BACKGROUND: Adequately developed fundamental movement skills, particularly object control dimensions, are considered essential to learn more complex movement patterns and to increase the likelihood to successfully participate in organized and non-organized sports during later years. Thus, the present randomized controlled trial aimed at improving object control dimensions at an early state in a kindergarten setting. METHODS: Catching, throwing, kicking, rolling and stationary dribbling were assessed via gross motor development 2 (TGMD-2) testing in 41 normally developed preschoolers. On a cluster-randomized basis [strata: age, sex and body mass index (BMI)], three kindergartens were randomly assigned to an intervention group (n = 22, INT, age: 4.6 ± 1.0 years; BMI: 16.2 ± 1.1 kg/m(2) ) and three to a control group (n = 19, CON: age: 4.5 ± 1.2 years; BMI: 16.8 ± 1.2 kg/m(2) ). Twelve structured training sessions were given within 6 weeks (12 sessions). The total training volume was 330 min. RESULTS: Moderate time × group interaction were observed for the total sum score (Δ+22%, P = 0.05) and dribbling (Δ+41%, P = 0.002). Adjusting for baseline differences analyses of covariance did not affect these results. Interestingly, likely to most likely practically worthwhile effects were detected for the total sum score, catching and dribbling. CONCLUSION: Object control dimensions such as dribbling and catching that apparently rely on rhythmical movement patterns and anticipatory eye-hand coordination seem to benefit from short-term object control training. These skills are considered important for successful team-sport participation and appropriate sportive motor development.

Jeopardizing Christmas: Why spoiled kids and a tight schedule could make Santa Claus fall?

Santa Claus' spatio-temporal gait characteristics, ground reaction forces during treadmill walking as well as postural sway during loaded, unloaded and cognitive interference tasks were examined in order to estimate his fall risk. Seventeen healthy males, disguised as researchers and students (age: 30±10 years; height: 179±6 years; weight: 76±7kg; BMI: 24±2kg/m(2); physical activity: 12±4h/week) and who still believe in Santa Claus randomly underwent balance and gait analyses with and without cognitive interference. The conditions were to be dressed as "Santa Claus" (wearing costume consisting of a beard, cap, robe, heavy sack with a load of 20kg) or dressed in "normal clothing" (no costume). Spatiotemporal gait parameters (walking velocity, gait variability and stride time, length and width), ground reaction forces (GRF) (left- and right-sided heel strike and push off) and postural sway (30s tandem stance on a force plate) were measured. "Santa-effects" (0.001

Effects of acute bouts of endurance exercise on retinal vessel diameters are age and intensity dependent.

Alterations of retinal vessel diameters are associated with increased cardiovascular risk. We aimed to investigate changes in retinal vessel diameters in response to acute dynamic exercise of different intensities and whether these changes are age dependent. Seventeen healthy seniors (median (IQR) age 68 (65, 69) years) and 15 healthy young adults (median (IQR) age 26 (25, 28) years) first performed a maximal treadmill test (MTT) followed by a submaximal treadmill test (SMTT) and a resting control condition in randomised order. Central retinal arteriolar (CRAE) and central retinal venular (CRVE) diameter equivalents were measured before as well as 5 (t5) and 40 (t40) minutes after exercise cessation using a static retinal vessel analyser. Both exercise intensities induced a significant dilatation in CRAE and CRVE at t5 compared to the control condition (P < 0.001). At t40, the mean increase in CRAE and CRVE was greater for MTT compared to that for SMTT (CRAE 1.7 µm (95 % confidence interval (CI) -0.1, 3.6; P = 0.061); CRVE 2.2 µm (95 % CI 0.4, 4.1; P = 0.019)). However, the estimated difference at t5 between seniors and young adults in their response to MTT compared to SMTT was 5.3 µm (95 % CI 2.0, 8.5; P = 0.002) for CRAE and 4.1 µm (95 % CI -0.4, 8.6; P = 0.076) for CRVE. Wider arteries and veins after maximal versus submaximal exercise for seniors compared to young adults suggest that myogenic vasoconstriction in response to exhaustive exercise may be reduced in seniors. Age-related loss of vascular reactivity has clinical implications since the arteriolar vasoconstriction protects the retinal capillary bed from intraluminal pressure peaks.

Effects of stair-climbing on balance, gait, strength, resting heart rate, and submaximal endurance in healthy seniors.

Stair-climbing serves as a feasible opportunity to remain physically active within everyday-life. Data on neuromuscular and cardiorespiratory performance after regular stair-climbing in seniors are scarce. Forty-eight seniors were stratified to a one- (taking every step, INT1) or two-step strategy (every second step, INT2) or a control group (CON). Thirty-nine seniors [females: n = 22, males: n = 17; age: 70.5 (SD 5.1) years; BMI: 25.8 (3.1) kg/m(2)] completed the 8-week intervention (three weekly sessions). Before and after the intervention, balance, gait, strength, and submaximal endurance (at different intensities) were assessed. Maximal strength and explosive power did not improve significantly (0.10 < P < 0.78). Resting heart rate was significantly reduced in INT2 (-8/min) compared with INT1 (0/min, P = 0.02) and CON (0/min, P = 0.03). Compared with CON, perceived exertion for all intensities (0.007 < P < 0.03) and submaximal exercise heart rate during moderate uphill walking significantly decreased (-11/min; P < 0.05) in INT2. Step counts for forward beam balancing (4.5 cm width) increased in INT2 (P = 0.007) compared with CON. With more pronounced effects in INT2, stair-climbing significantly improved resting and exercise heart rates, perceived exertion, and dynamic balance performance in healthy seniors and may contribute to better overall fitness, reduced fall risk, and less perceived strain during daily life activities.

Effects of slackline training on balance, jump performance & muscle activity in young children.

The study investigated the effects of slackline training (rope balancing) on balance, jump performance and muscle activity in children. Two primary-school classes (intervention, n=21, INT: age: 10.1 (SD 0.4) y, weight: 33.1 (4.5) kg; control, n=13, CON: age: 10.0 (SD 0.4) y, weight: 34.7 (7.4) kg) participated. Training was performed within 6 weeks, 5 times per week for 10 min each day. Balance (static and dynamic stance), countermovement jumps, reverse balancing on beams (3, 4.5 and 6 cm width), slackline standing (single- and double-limb) and electromyographic activity (soleus, gastrocnemius, tibialis anterior) were examined. INT significantly improved single- and double-limb slackline standing (double limb: 5.1 (3.4) s-17.2 (14.4) s; right leg: 8.2 (5.8) s-38.3 (36.0) s; left leg: 10.6 (5.8) s-49.0 (56.3) s; p<0.001; 0.17<ηp²<0.22). Reduced left-leg dynamic sway (-20.8%, p=0.06, ηp²=0.10), improved 4.5 cm balancing (+18.5%, p=0.08, ηp²=0.10) and decreased muscle activity during slackline standing for the mm. soleus (-23%, p=0.10, ηp²=0.18) and tibialis anterior (-26%, p=0.15, ηp²=0.14) was observed for INT. Jump performance remained unchanged (p=0.28, ηp²=0.04). In conclusion, daily slackline training results in large slackline-specific balance improvements. Transfer effects to static and dynamic stance, reverse balancing or jumping performance seemed to be restricted.

A pilot study to measure upper extremity H-reflexes following neuromuscular electrical stimulation therapy after stroke.

Upper extremity (UE) hemiparesis persists after stroke, limiting hand function. Neuromuscular electrical stimulation (NMES) is an effective intervention to improve UE recovery, although the underlying mechanisms are not fully understood. Our objective was to establish a reliable protocol to measure UE agonist-antagonist forearm monosynaptic reflexes in a pilot study to determine if NMES improves wrist function after stroke. We established the between-day reliability of the H-reflex in the extensor carpi radialis longus (ECRL) and flexor carpi radialis (FCR) musculature for individuals with prior stroke (n=18). The same-day generation of ECRL/FCR H-reflex recruitment curves was well tolerated, regardless of age or UE spasticity. The between-day reliability of the ECRL H-reflex was enhanced above FCR, similar to healthy subjects [20], with the Hmax the most reliable parameter quantified in both muscles. H-reflex and functional measures following NMES show the potential for NMES-induced increases in ECRL Hmax, but confirmation requires a larger clinical study. Our initial results support the safe, easy, and efficacious use of in-home NMES, and establish a potential method to measure UE monosynaptic reflexes after stroke.

Contribution of physical education to overall physical activity.

For many children, physical activity (PA) during physical education (PE) lessons provides an important opportunity for being physically active. Although PA during PE has been shown to be low, little is known about the contribution of PA during PE to overall PA. The aim was therefore to assess children's PA during PE and to determine the contribution of PE to overall PA with special focus on overweight children. Accelerometer measurements were done in 676 children (9.3 ± 2.1 years) over 4-7 days in 59 randomly selected classes. Moderate-and-vigorous PA (MVPA; ≥ 2000 counts/min) during PE (MVPAPE), overall MVPA per day (MVPADAY), and a comparison of days with and without PE were calculated by a regression model with gender, grade, and weight status (normal vs overweight) as fixed factors and class as a random factor. Children spent 32.8 ± 15.1% of PE time in MVPA. Weight status was not associated to MVPAPE . MVPAPE accounted for 16.8 ± 8.5% of MVPADAY, and 17.5 ± 8.2% in overweight children. All children were more active on days with PE than on days without PE (differences: 16.1 ± 29.0 min of MVPADAY; P ≤ 0.001; 13.7 ± 28.0 min for overweight children). Although MVPAPE was low, PE played a considerable role in providing PA and was not compensated by reducing extracurricular MVPA.

Effect of multidimensional lifestyle intervention on fitness and adiposity in predominantly migrant preschool children (Ballabeina): cluster randomised controlled trial.

OBJECTIVE: To test the effect of a multidimensional lifestyle intervention on aerobic fitness and adiposity in predominantly migrant preschool children. DESIGN: Cluster randomised controlled single blinded trial (Ballabeina study) over one school year; randomisation was performed after stratification for linguistic region. SETTING: 40 preschool classes in areas with a high migrant population in the German and French speaking regions of Switzerland. PARTICIPANTS: 652 of the 727 preschool children had informed consent and were present for baseline measures (mean age 5.1 years (SD 0.7), 72% migrants of multicultural origins). No children withdrew, but 26 moved away. INTERVENTION: The multidimensional culturally tailored lifestyle intervention included a physical activity programme, lessons on nutrition, media use (use of television and computers), and sleep and adaptation of the built environment of the preschool class. It lasted from August 2008 to June 2009. MAIN OUTCOME MEASURES: Primary outcomes were aerobic fitness (20 m shuttle run test) and body mass index (BMI). Secondary outcomes included motor agility, balance, percentage body fat, waist circumference, physical activity, eating habits, media use, sleep, psychological health, and cognitive abilities. RESULTS: Compared with controls, children in the intervention group had an increase in aerobic fitness at the end of the intervention (adjusted mean difference: 0.32 stages (95% confidence interval 0.07 to 0.57; P=0.01) but no difference in BMI (-0.07 kg/m(2), -0.19 to 0.06; P=0.31). Relative to controls, children in the intervention group had beneficial effects in motor agility (-0.54 s, -0.90 to -0.17; P=0.004), percentage body fat (-1.1%, -2.0 to -0.2; P=0.02), and waist circumference (-1.0 cm, -1.6 to -0.4; P=0.001). There were also significant benefits in the intervention group in reported physical activity, media use, and eating habits, but not in the remaining secondary outcomes. CONCLUSIONS: A multidimensional intervention increased aerobic fitness and reduced body fat but not BMI in predominantly migrant preschool children. Trial registration Clinical Trials NCT00674544.

Stimulatory type A CpG-DNA induces a Th2-like response in human endothelial cells.

Unmethylated CpG-DNA motifs from pathogens are detected by the pattern recognition receptor toll-like receptor 9 (TLR9), eliciting an inflammatory immune response. These DNA sequences have been identified as potent immune modifiers and are used as adjuvants in vaccine research. Since we previously found TLR9 expression and function in human endothelial cells, we have here investigated whether endothelial cells play a role in the recognition of respective ligands and whether their response might contribute to vaccination success. We determined the effect of CpG-DNA on the inflammatory response of human endothelial cells of aortic or skin microvascular origin (HAoEC, HDMEC and HMEC-1) and compared the effects to those of two identically treated human macrophage cell lines. Using the same CpG-DNA D19(chimera) sequence in both cell types, we find the known up-regulation of pro-inflammatory cytokines in macrophages but consistent and significant inhibition of the pro-inflammatory response (IL-6, IL-8, and IFN-beta1) in endothelial cells. This inhibition is accompanied by enhanced proliferation and an increase in IL-10 gene expression. This anti-inflammatory response persists even in the presence of pro-inflammatory cytokines and low LPS concentrations, and is overruled only in the presence of relatively high concentrations of LPS. By testing different sequences, we find the strongest response with phosphorothioate bonds. Our results demonstrate an important regulatory function of endothelial cells in inflammatory responses, and the apparent Th2-like endothelial response in the human system may contribute significantly to the adjuvant activity of CpG-DNA.

Promoting balance and strength in the middle-aged workforce.

The prevalence of sustaining fall-related injuries is high in the middle-aged workforce. Deficits in postural control/muscle strength represent important fall-risk factors. The objective of this study was to examine the impact of balance and strength training followed by detraining on postural control and muscle strength in the workforce. Thirty-two adults with sedentary office work participated in this study and were assigned to an intervention (age 56.0 ± 3.7 yrs) or a control group (age 55.5 ± 3.4 yrs). The intervention group participated in 8 weeks of balance and strength training conducted at the worksite, followed by 8 weeks of detraining. Tests included the measurement of (a) total centre of pressure (COP) displacements during one-legged standing, (b) gait velocity and stride-to-stride variability, (c) peak isometric/isokinetic torque and rate of torque development (RTD) of the plantar flexors, and (d) jumping height. After training, significant improvements in COP displacements, gait velocity, peak isometric/isokinetic torque, RTD, and jumping height were observed. During detraining, muscle strength deteriorated, whereas postural control improved. This fall-preventive training program conducted at the worksite proved to be feasible and effective. It is suggested that this training program should be permanently conducted to maintain/improve muscle strength.

Physical activity, bodyweight, health and fear of negative evaluation in primary school children.

Fear of negative evaluation (FNE) is regarded as being the core feature of social anxiety. The present study examined how FNE is associated with physical activity (PA), body mass index (BMI) and perceived physical health (PPH) in children. Data were collected in a sample of 502 primary school children in first and fifth grades taking part in a randomized-controlled trial ("Kinder-Sportstudie KISS") aimed at increasing PA and health. PA was assessed by accelerometry over 7 days, PPH by the Child Health Questionnaire and FNE by the Social Anxiety Scale for Children--Revised. BMI z-scores were calculated based on Swiss norms. Cross-sectional analyses indicated that children high in FNE exercised less, reported lower levels of PPH and had higher BMI z-scores (P<0.01). Using mixed linear models, the school-based PA intervention did not manage to reduce FNE scores. Overweight children demonstrated a greater increase in FNE (P<0.05) indicating that enhanced weight may be a risk factor for FNE. In conclusion, the associations among high FNE, low PA and increased BMI should be considered when promoting an active lifestyle in children.

Cross-validation of bioelectrical impedance analysis for the assessment of body composition in a representative sample of 6- to 13-year-old children.

BACKGROUND/OBJECTIVES: (1) To cross-validate tetra- (4-BIA) and octopolar (8-BIA) bioelectrical impedance analysis vs dual-energy X-ray absorptiometry (DXA) for the assessment of total and appendicular body composition and (2) to evaluate the accuracy of external 4-BIA algorithms for the prediction of total body composition, in a representative sample of Swiss children. SUBJECTS/METHODS: A representative sample of 333 Swiss children aged 6-13 years from the Kinder-Sportstudie (KISS) (ISRCTN15360785). Whole-body fat-free mass (FFM) and appendicular lean tissue mass were measured with DXA. Body resistance (R) was measured at 50 kHz with 4-BIA and segmental body resistance at 5, 50, 250 and 500 kHz with 8-BIA. The resistance index (RI) was calculated as height(2)/R. Selection of predictors (gender, age, weight, RI4 and RI8) for BIA algorithms was performed using bootstrapped stepwise linear regression on 1000 samples. We calculated 95% confidence intervals (CI) of regression coefficients and measures of model fit using bootstrap analysis. Limits of agreement were used as measures of interchangeability of BIA with DXA. RESULTS: 8-BIA was more accurate than 4-BIA for the assessment of FFM (root mean square error (RMSE)=0.90 (95% CI 0.82-0.98) vs 1.12 kg (1.01-1.24); limits of agreement 1.80 to -1.80 kg vs 2.24 to -2.24 kg). 8-BIA also gave accurate estimates of appendicular body composition, with RMSE < or = 0.10 kg for arms and < or = 0.24 kg for legs. All external 4-BIA algorithms performed poorly with substantial negative proportional bias (r> or = 0.48, P<0.001). CONCLUSIONS: In a representative sample of young Swiss children (1) 8-BIA was superior to 4-BIA for the prediction of FFM, (2) external 4-BIA algorithms gave biased predictions of FFM and (3) 8-BIA was an accurate predictor of segmental body composition.

Reduced cardiorespiratory fitness, low physical activity and an urban environment are independently associated with increased cardiovascular risk in children.

AIMS/HYPOTHESIS: To assist in the development of preventive strategies, we studied whether the neighbourhood environment or modifiable behavioural parameters, including cardiorespiratory fitness (CRF) and physical activity (PA), are independently associated with obesity and metabolic risk markers in children. METHODS: We carried out a cross-sectional analysis of 502 randomly selected first and fifth grade urban and rural Swiss schoolchildren with regard to CRF, PA and the neighbourhood (rural vs urban) environment. Outcome measures included BMI, sum of four skinfold thicknesses, homeostasis model assessment of insulin resistance (HOMA-IR) and a standardised clustered metabolic risk score. RESULTS: CRF and PA (especially total PA, but also the time spent engaged in light and in moderate and vigorous intensity PA) were inversely associated with measures of obesity, HOMA-IR and the metabolic risk score, independently of each other, and of sociodemographic and nutritional parameters, media use, sleep duration, BMI and the neighbourhood environment (all p < 0.05). Children living in a rural environment were more physically active and had higher CRF values and reduced HOMA-IR and metabolic risk scores compared with children living in an urban environment (all p < 0.05). These differences in cardiovascular risk factors persisted after adjustment for CRF, total PA and BMI. CONCLUSIONS/INTERPRETATION: Reduced CRF, low PA and an urban environment are independently associated with an increase in metabolic risk markers in children.

Weight-bearing bones are more sensitive to physical exercise in boys than in girls during pre- and early puberty: a cross-sectional study.

UNLABELLED: We carried out a cross-section study of the sex-specific relationship between bone mineral content and physical activity at sites with different loading in pre- and early pubertal girls and boys. There was significant sensitivity of bone mineral content of the hip to physical exercise in boys, but not in girls. BACKGROUND: Since little is known whether there are sex differences in sensitivity of bone to loading, we investigated sex differences in the cross-sectional association between measures of physical activity (PA) and bone mass and size in pre- and early pubertal children of both sexes. METHODS: We measured bone mineral content/density (BMC/BMD) and fat-free mass (FFM) in 269 6- to 13-year-old children from randomly selected schools by dual-energy X-ray absorptiometry. Physical activity (PA) was measured by accelerometers and lower extremity strength by a jump-and-reach test. RESULTS: Boys (n = 128) had higher hip and total body BMC and BMD, higher FFM, higher muscle strength and were more physically active than girls (n = 141). Total hip BMC was positively associated with time spent in total and vigorous PA in boys (r = 0.20-0.33, p < 0.01), but not in girls (r = 0.02-0.04, p = ns), even after adjusting for FFM and strength. While boys and girls in the lowest tertile of vigorous PA (22 min/day) did not differ in hip BMC (15.62 vs 15.52 g), boys in the highest tertile (72 min/day) had significantly higher values than the corresponding girls (16.84 vs 15.71 g, p < 0.05). CONCLUSIONS: Sex differences in BMC during pre- and early puberty may be related to a different sensitivity of bone to physical loading, irrespective of muscle mass.