Christian Lindén

Exercise during growth and bone mineral density and fractures in old age

If exercise is to be recommended during growth, benefits in bone mineral density (BMD) must be maintained in old age and shown to prevent fractures. Our cross-sectional study of soccer players suggests that a high BMD is no longer recorded after retirement and fracture frequency is no less than predicted in old age.

A School Curriculum–Based Exercise Program Increases Bone Mineral Accrual and Bone Size in Prepubertal Girls: Two-Year Data From the Pediatric Osteoporosis Prevention (POP) Study†

This 2‐year prospective controlled exercise intervention trial in 99 girls at Tanner stage 1, evaluating a school curriculum–based training program on a population‐based level, showed that the annual gain in BMC, aBMD, and bone size was greater in the intervention group than in the controls.

Daily Physical Education in the School Curriculum in Prepubertal Girls during 1 Year is Followed by an Increase in Bone Mineral Accrual and Bone Width—Data from the Prospective Controlled Malmö Pediatric Osteoporosis Prevention Study

The aim of this study was to evaluate a general school-based 1-year exercise intervention program in a population-based cohort of girls at Tanner stage I. Fifty-three girls aged 7–9 years were included. The school curriculum-based exercise intervention program included 40 minutes/school day. Fifty healthy age-matched girls assigned to the general school curriculum of 60 minutes physical activity/week served as controls. Bone mineral content (BMC, g) and areal bone mineral density (aBMD, g/cm2) were measured with dual X-ray absorptiometry (DXA) of the total body (TB), lumbar spine (L2–L4 vertebrae), third lumbar vertebra (L3), femoral neck (FN), and leg. Volumetric bone mineral density (g/cm3) and bone width were calculated at L3 and FN. Total lean body mass and total fat mass were estimated from the TB scan. No differences at baseline were found in age, anthropometrics, or bone parameters when the groups were compared. The annual gain in BMC was 4.7 percentage points higher in the lumbar spine and 9.5 percentage points higher in L3 in cases than in controls (both P < 0.001). The annual gain in aBMD was 2.8 percentage points higher in the lumbar spine and 3.1 percentage points higher in L3 in cases than in controls (both P < 0.001). The annual gain in bone width was 2.9 percentage points higher in L3 in cases than in controls (P < 0.001). A general school-based exercise program in girls aged 7–9 years enhances the accrual of BMC and aBMD and increases bone width.

Daily physical activity in Swedish children aged 8–11 years

Introduction: Physical inactivity is hypothesized to be a contributing factor in the development of a variety of diseases. Recommendations for an adequate level of physical activity have been proposed. There are few studies in which the physical activity in children has been objectively assessed. The purpose of this study was to estimate objectively the level of physical activity in Swedish children.

Daily physical activity related to aerobic fitness and body fat in an urban sample of children.

This study evaluates associations between objectively measured daily physical activity vs aerobic fitness and body fat in children aged 8–11 years. A cross‐sectional study of 225 children aged 7.9–11.1 years was performed. Abdominal fat mass (AFM) and total body fat (TBF) were quantified by dual‐energy x‐ray absorptiometry. TBF was calculated as percentage of total body mass (BF%). Body fat distribution was calculated as AFM/TBF. Aerobic fitness was measured by indirect calorimetry during a maximal cycle ergometer exercise test. Daily physical activity was assessed by accelerometers for 4 days and daily accumulation of moderate‐to‐vigorous and vigorous activity was calculated. Significant relationships (P<0.05) existed for vigorous activity vs ln BF% (r=−0.40), ln AFM (r=−0.35), TBF/AFM (r=−0.22) and aerobic fitness (r=0.38), whereas moderate‐to‐vigorous activity displayed weaker relationships (−0.22, −0.18, −0.12 NS, and 0.25). Multiple regression analyses with inclusion of possible confounders concluded that vigorous activity was independently related to aerobic fitness and ln BF% or ln AFM. Moderate‐to‐vigorous activity was only independently related to aerobic fitness. In this population, low daily accumulation of vigorous activity was, already in children aged 8–11 years, associated with more body fat and lower aerobic fitness. A similar relation was not found for daily accumulation of moderate‐to‐vigorous activity.

Exercise, bone mass and bone size in prepubertal boys: one-year data from the pediatric osteoporosis prevention study.

This non‐randomized prospective controlled study evaluates a daily school‐based exercise intervention program of 40 min/school day for 1 year in a population‐based cohort of 81 boys aged 7–9 years. Controls were 57 age‐matched boys assigned to the general school curriculum of 60 min/week. Bone mineral content (BMC; g) and areal bone mineral density (aBMD; g/cm2) were measured with dual X‐ray absorptiometry (DXA) of the total body, the third lumbar vertebra (L3) and the femoral neck (FN). Bone width for L3 and FN was calculated from the lumbar spine and hip scan. No differences between the groups were found at baseline in age, anthropometrics or bone parameters. The mean annual gain in L3 BMC was 5.9 percentage points higher (P<0.001), L3 aBMD a mean 2.1 percentage points higher (P=0.01) and L3 width a mean 2.3 percentage points higher (P=0.001) in the cases than in the controls. When all individuals were included in one cohort, the total duration of exercise including both school‐based and spare‐time training correlated with L3 BMC (r=0.26, P=0.003), L3 aBMD (r=0.18, P=0.04) and L3 width (r=0.24, P=0.006). The study suggests that exercise in pre‐pubertal boys influences the accrual of bone mineral and bone width and that a 1‐year school‐based exercise program confers skeletal benefits, at least in the lumbar spine.

BMI and objectively measured body fat and body fat distribution in prepubertal children

Background  Body Mass Index (BMI) is often used as a surrogate estimate of body fat in epidemiological studies. This study explores the association between BMI, body fat and body fat distribution assessed by Dual‐Energy X‐Ray Absorptiometry (DXA) in younger children.

Prediction of fat-free body mass from bioelectrical impedance among 9-to 11-year-old Swedish children

Aim:  Predictive equations for estimating body composition from bioelectrical impedance analysis (BIA) among Scandinavian children are lacking. In the present study, equations for estimation of fat‐free body mass (FFM) and lean tissue mass (LTM) were developed and cross‐validated from BIA using dual‐energy X‐ray absorptiometry (DXA) as the reference measurement of body composition.

Muscle determinants of bone mass, geometry and strength in prepubertal girls

PURPOSE The aim of this study was to compare the relative contribution of peak muscle force (isokinetic peak torque) with surrogate estimates of muscle force, including leg lean tissue mass (LTM) and vertical jump height (VJH), on bone mass, geometry and strength in healthy prepubertal girls (n = 103). METHODS Total leg and FN BMC and leg LTM were measured by DXA; the hip strength analysis program was used to assess FN diameter, cross-sectional area (CSA) and section modulus (Z). Isokinetic peak torque of the knee extensors and flexors (60 degrees .s) were used as direct measures of peak muscle force. VJH was measured as an estimate of neuromuscular function. Total leg length or femoral length was used as a surrogate measure of moment arm length. RESULTS All estimates of muscle function, except VJH, were positively associated with leg BMC (r = 0.72 - 0.90) and FN BMC, geometry and strength (r = 0.35-0.65) (all, P < 0.001). Multiple linear regression analyses revealed that leg LTM and isokinetic peak torque were independently and equally predictive of leg BMC and FN BMC, bone geometry and strength, explaining 8 to 28% of the variance in each of the bone traits after accounting for moment arm length. When isokinetic peak torque was corrected for both leg LTM and moment arm length, it remained an independent predictor of BMC, CSA and Z, but only accounted for an additional 2 to 5% of the variance. CONCLUSION These data suggest that DXA-derived leg LTM can be used as a reasonable surrogate for isokinetic peak muscle forces when assessing bone strength in relation to muscular function in healthy pre-pubertal girls.

A 2-year school-based exercise programme in pre-pubertal boys induces skeletal benefits in lumbar spine.

Aim: The aim of this study was to evaluate if a general school‐based exercise intervention programme in pre‐pubertal boys would render site‐specific benefits in bone mineral accrual and gain in femoral neck structure.