Prospective ten-month exercise intervention in premenarcheal girls: positive effects on bone and lean mass

Lifestyle risk factors for osteoporosis in Asian and Caucasian girls

PURPOSE

We investigated ethnic differences in areal bone mineral density (aBMD; g x cm(-2)) and its determinants at two levels of maturity in Asian- and Caucasian-Canadian girls.

METHODS

Participants were 131 Asian (26 Tanner breast stage I (aTI) and 30 Tanner II (aTII)), and Caucasian (30 Tanner I (cTI) and 45 Tanner II (cTII)) girls. We measured calcium intake by a food frequency questionnaire, general physical activity, and extracurricular sports with a modified Physical Activity Questionnaire for Children and loaded physical activity by 7-d recall. Fat mass, lean mass, and aBMD for the total body (TB), and aBMD at the lumbar spine (LS), proximal femur (PF), femoral neck (FN), and trochanter (TR) were measured by DXA (Hologic QDR 4500). We used ANCOVA (controlling for size and lean and fat mass) to compare bone mineral content (BMC) and aBMD between ethnicities within Tanner stages.

RESULTS

Calcium intake was significantly lower for Asian girls in both TI and TII (P < 0.001) as compared with Caucasians. For physical activity measures, only the general score was greater in cTI than aTI (P < 0.05). Participation in loaded physical activities and extracurricular sports was significantly less for aTII than cTII (both, P < 0.01), whereas general physical activity did not differ. aBMD measures were similar between aTI and cTI. However, TB, PF, FN, and aBMD were significantly lower (approximately 9-14%) in aTII as compared with cTII.

CONCLUSION

Thus, there was greater ethnic disparity in lifestyle factors related to bone health and absolute measures of bone mineral with advanced maturity.

Gain in bone mineral mass in prepubertal girls 3.5 years after discontinuation of calcium supplementation: a follow-up study

BACKGROUND

Calcium supplementation during childhood and adolescence increases bone-mass accrual. Whether or not this benefit persists after discontinuation of supplementation is not known. We previously showed a favourable effect of milk-extracted calcium phosphate incorporated in various foods on accumulation of bone mineral mass in 8-year-old girls. We now report the results of a follow-up study undertaken more than 3 years after the end of calcium supplementation.

METHODS

Anthropometric and bone variables were measured in 116 of the 144 girls whose data had been studied at the end of the supplementation period. The mean time elapsed between the end of the intervention period and this follow-up measurement was 3.5 years. Areal bone mineral density was measured by dual-energy X-ray absorptiometry at the same six skeletal sites as those studied during the intervention phase.

FINDINGS

We were able to remeasure 62 and 54 girls of the calcium-supplemented and placebo groups, respectively. The increase from baseline in the overall mean bone mineral density of the six skeletal sites was still highly significant (calcium-supplemented group 179 mg/cm(2) [SE 8] vs placebo group 151 mg/cm(2) [7], p=0.012). A significant difference in favour of the supplemented group was also seen with respect to mean bone mineral content (p=0.031) and mean bone area (p=0.04). Difference in pubertal maturation did not seem to account for the recorded differences.

INTERPRETATION

Our results suggest that this form of milk-extracted calcium phosphate taken during the prepubertal period can modify the trajectory of bone mass growth and cause a long-standing increase in bone mass accrual, which lasts beyond the end of supplementation.

A school-based exercise intervention augments bone mineral accrual in early pubertal girls

OBJECTIVE

To evaluate the effects of an elementary school-based physical education exercise intervention program on bone mineral accrual in prepubertal and early pubertal girls.

STUDY DESIGN

A total of 14 schools were randomly assigned to control (C) and intervention (I) groups. Girls in the I group completed a 10-minute, 3 times per week circuit of varied jumping activities over 7 months. We measured total body, lumbar spine, proximal femur, femoral neck, and trochanteric bone mineral content and areal bone mineral density and estimated femoral neck volumetric bone mineral density at baseline and final measurement in 87 girls in the I group and 90 girls in the C group. Girls were between 8.7 and 11.7 years at baseline. Tanner stage 1 girls were considered prepubertal; Tanner stages 2 and 3 girls were considered early pubertal. We used analysis of covariance (adjusting for baseline bone values, change in size, age, and maturity) to compare 7-month change in bone mineral content, areal bone mineral density, and volumetric bone mineral density between C and I groups within prepubertal and early pubertal girls.

RESULTS

There was no difference in 7-month change in bone parameters between prepubertal I and C groups. Early pubertal girls in the I group gained 1.5% to 3.1% more bone at the femoral neck and lumbar spine than early pubertal girls in the C group (P <.05); gain at other sites did not differ.

CONCLUSIONS

In girls, early puberty may be a particularly opportune time during growth for simple exercise interventions to have a positive effect on bone health.

Bone mineral density and body composition in boys with distal forearm fractures: a dual-energy x-ray absorptiometry study

OBJECTIVE

To determine whether boys with distal forearm fractures differ from fracture-free control subjects in bone mineral density (BMD) or body composition.

STUDY DESIGN

A case-control study of 100 patients with fractures (aged 3 to 19 years) and l00 age-matched fracture-free control subjects was conducted. Weight, height, and body mass index were measured anthropometrically. BMD values and body composition were determined by dual-energy x-ray absorptiometry.

RESULTS

More patients than control subjects (36 vs l4) were overweight (body mass index >85th percentile for age, P <.001). Patients had lower areal (aBMD) and volumetric (BMAD) bone mineral density values and lower bone mineral content but more fat and less lean tissue than fracture-free control subjects. The ratios (95% CIs) for all case patients/control subjects in age and weight-adjusted data were ultradistal radius aBMD 0.94 (0.91-0.97); 33% radius aBMD 0.96 (0.93-0.98) and BMAD 0.95 (0.91-0.99); spinal L2-4 BMD 0.92 (0.89-0.95) and BMAD 0.92 (0.89-0.94); femoral neck aBMD 0.95 (0.92-0.98) and BMAD 0.95 (0.91-0.98); total body aBMD 0.97 (0.96-0.99), fat mass 1.14 (1.04-1.24), lean mass 0.96 (0.93-0.99), and total body bone mineral content 0.94 (0.91-0.97).

CONCLUSIONS

Our results support the view that low BMC, aBMD, and BMAD values and high adiposity are associated with increased risk of distal forearm fracture in boys. This is a concern, given the increasing levels of obesity in children today.

Muscle cross-sectional area is associated with specific site of bone in prepubertal girls: a quantitative magnetic resonance imaging study

It is well established that forces applied to bone are the result of muscle contraction. However, data regarding the contribution of muscle cross-sectional area (because muscle area is proportional to muscle strength) to cortical bone area before puberty are controversial. We tested the hypothesis that muscle cross-sectional area is associated with total cortical bone area, and whether there is a region-specific relationship between these parameters in prepubertal and early pubertal girls. Seventeen healthy (9-11 years, Tanner stages I-II) white girls participated in the study. We measured bone loading characteristics (maximal ground reaction forces; GRFs) for a drop jump (50 cm) and side-to-side jump (over a 20-cm-high fence) on a multicomponent force platform. Muscle cross-sectional area and bone cortical area (square centimeters) of the proximal third of the left and right lower leg was measured with a 1.5 T magnetic resonance system using a quadrature head coil. The sequence was T(1) weighted, with spin-echo in transverse (tibial) planes and 3 mm sections with no gap (ten slices). The tibial cross-sectional areas were subdivided into three anatomical sectors (SI-SIII), with the tibial centroid as origin. SI extended from the medial tibial border to the most anterior edge, SII extended from the anterior edge laterally to the interosseous border, and SIII extended posteromedially from the interosseous border to the medial tibial border. The nonparametric bone and muscle volume correlations demonstrated that the total muscle cross-sectional area correlated significantly with the total cortical area in both legs (left leg: r(s) = 0.59, p = 0.020; right leg: r(s) = 0.57, p = 0.016). Significant correlations were also found between left and right muscle area and cortical area in SII (r(s) = 0.68, p = 0.003, 0.67, and 0.003, respectively). There was no significant association between the muscle area and cortical area in SI or SIII. In addition, there was a significant correlation between GRFs of the side-to-side jump and total cortical area (left leg: r = 0.75, p < 0.01; right leg: r = 0.78, p < 0.01). Thus, we found that muscle area was most highly associated with bone cortical area in SII, the anterolateral sector of the tibia, which emphasizes the specific interplay of muscles and bone in the lower limb. This relationship was present in a regional, site-specific fashion.

Resistance training and bone mineral density in adolescent females

OBJECTIVE

To examine the effects of 15 months of resistance training on bone mineral density (BMD) in female adolescents (aged 14 to 17 years).

STUDY DESIGN

Participants were randomly assigned to either a training (n = 46) or control group (n = 21). BMD and body composition were measured by using dual-energy x-ray absorptiometry. Strength was assessed by means of one-repetition maximums for the leg press and bench press. The exercise group trained 30 to 45 minutes a day, 3 days per week, using 15 different resistance exercises. Control participants remained sedentary (<2 hours of exercise per week).

RESULTS

Leg strength increased significantly (40%) in the exercise group, but there were no changes in the control group. Femoral neck BMD increased significantly in the training group (1.035 to 1.073 g/cm(2), P <.01) but not in the control group (1.034 to 1.048 g/cm(2)). No significant changes were seen in either group in lumbar spine BMD (1.113 to 1.142 g/cm(2) and 1.158 to 1.190 g/cm(2), respectively) or total body BMD (1.103 to 1.134 g/cm(2) and 1.111 to 1.129 g/cm(2), respectively).

CONCLUSION

Resistance training is a potential method for increasing bone density in adolescents, although such a program would be best done as part of the school curriculum.

The evidence that exercise during growth or adulthood reduces the risk of fragility fractures is weak

There has never been, and will never be, a randomized double-blind placebo-controlled trial demonstrating that exercise in youth, adulthood or old age reduces fragility or osteoporosis-related fractures in old age. The next level of evidence, a randomized, controlled but unblinded study with fractures as an end-point is feasible but has never been done. The basis for the belief that exercise reduces fractures is derived from lower levels of 'evidence', namely, retrospective and prospective observation cohort studies and case-control studies. These studies are at best hypothesis generating, never hypothesis testing. They are all subject to many systematic biases and should be interpreted with extreme scepticism. Surrogate measures of anti-fracture efficacy are the next level of evidence, such as the demonstration of a reduction in risk factors for falls, a reduction in falls, a reduction in fractures due to falls, an increase in peak bone size and mass, prevention of bone loss in midlife and restoration of bone mass and structure in old age.

Dose-response of physical activity and low back pain, osteoarthritis, and osteoporosis

PURPOSE

The purpose of this study was to examine the evidence for causal relationships between physical activity (PA) and low back pain (LBP), osteoarthritis (OA), and osteoporosis (OP), and for dose-response relations involved.

METHODS

Computer database searches and personal retrieval systems were used to locate relevant literature.

RESULTS

PA can be effective in preventing LBP (Category A) but prolonged, heavy loading can lead to LBP (Category C). Specific exercises have not been found effective in treatment of acute LBP (Category A), but PA can be effective in chronic LBP (Category B), especially for diminishing the effects of deconditioning. No evidence indicates that PA directly prevents OA. Large amounts of intensive PA involving high impacts or torsional loadings or causing injuries increases risk of OA (Category C). Light or moderate PA does not increase the risk of OA (Category C). PA can be effective in the treatment and rehabilitation of OA (Category B). High-intensity loading is osteogenic and possibly useful in prevention of OP (Category A) at the loaded site, but low to moderate loading is not osteogenic (Category D). Static efforts and slow movements are ineffective or less effective than fast application of force (Category B). The types of PA to attain the effects mentioned above are known except in the case of prevention of LBP, but dose-response relationships are poorly known; at best, semiquantitatively on the basis of just a few studies.

CONCLUSION

Given the shown primary and/or secondary preventative effectiveness of PA regarding LBP, OA, and OP, research to elucidate the inadequately known dose-response relations should be given high priority.

Quantifying Force Magnitude and Loading Rate from Drop Landings That Induce Osteogenesis

Drop landings increase hip bone mass in children. However, force characteristics from these landings have not been studied. We evaluated ground and hip joint reaction forces, average loading rates, and changes across multiple trials from drop landings associated with osteogenesis in children. Thirteen prepubescent children who had previously participated in a bone loading program volunteered for testing. They performed 100 drop landings onto a force plate. Ground reaction forces (GRF) and two-dimensional kinematic data were recorded. Hip joint reaction forces were calculated using inverse dynamics. Maximum GRF were 8.5 ± 2.2 body weight (BW). At initial contact, GRF were 5.6 ± 1.4 BW while hip joint reactions were 4.7 ± 1.4 BW. Average loading rates for GRF were 472 ± 168 BW/s. Ground reaction forces did not change significantly across trials for the group. However, 5 individuals showed changes in max GRF across trials. Our data indicate that GRF are attenuated 19% to the hip at the first impact peak and 49% at the second impact peak. Given the skeletal response from the drop landing protocol and our analysis of the associated force magnitudes and average loading rates, we now have a data point on the response surface for future study of various combinations of force, rate, and number of load repetitions for increasing bone in children.

Good maintenance of exercise-induced bone gain with decreased training of female tennis and squash players: a prospective 5-year follow-up study of young and old starters and controls

This prospective 5-year follow-up study of 64 adult female racquet sports players and 27 controls assessed the changes in the playing-to-nonplaying arm bone mineral content (BMC) differences to answer three questions: (1) Are training-induced bone gains lost with decreased training? (2) Is the bone response to decreased training different if the playing career has been started before or at puberty rather than after it? (3) Are the possible bone changes related to the changes in training? The players were divided into two groups according to the starting age of their tennis or squash playing. The mean starting age was 10.5 years (SD, 2.2) among the players who had started training before or at menarche (young starters; n = 36) while 26.4 years (SD, 8.0) among those players who had begun training a minimum of 1 year after menarche (old starters; n = 28). At baseline of the 5-year follow-up, the mean age of the young starters was 21.6 years (SD, 7.6) and that of old starters was 39.4 years (SD, 10.5). During the follow-up, the young starters had reduced the average training frequency from 4.7 times a week (2.7) to 1.4 times a week (1.3) and the old starters from 4.0 times a week (1.4) to 2.0 times a week (1.4), respectively. The 5-year follow-up revealed that despite reduced training the exercise-induced bone gain was well maintained in both groups of players regardless of their clearly different starting age of activity and different amount of exercise-induced bone gain. The gain was still 1.3-2.2 times greater in favor of the young starters (at the follow-up, the dominant-to-nondominant arm BMC difference was 22% [8.4] in the humeral shaft of the young starters versus 10% [3.8] in the old starters, and 3.5% [2.4] in controls). In the players, changes in training were only weakly related to changes in the side-to-side BMC difference (r(s) = 0.05-0.34, all NS), and this was true even among the players who had stopped training completely a minimum 1 year before the follow-up. In conclusion, if controlled interventions will confirm our findings that an exercise-induced bone gain can be well maintained with decreased activity and that the maintenance of the bone gain is independent of the starting age of activity, exercise can be recommended for preventing osteoporosis and related fractures.

Role of exercise in preventing and treating osteoporosis

Bone mass at any time of life reflects the totality of events that have impinged on the skeleton to that point. For adults, these events include those that have influenced the acquisition of bone during years of growth, resulting in the achievement of skeletal maturity, or "peak bone mass," as well as those that have subsequently influenced bone losses. For each limb of this trajectory, physical activity has been implicated as a powerful and independent factor. This article reviews current evidence regarding the relation of habitual physical activity to bone acquisition and maintenance, the skeletal consequences of exercise training, and the clinical value of exercise for patients with skeletal frailty.

Effect of physical activity during teenage years, based on type of sport and duration of exercise, on bone mineral density of young, premenopausal Japanese women

In this cross-sectional study, 91 healthy premenopausal women aged 20-39 years were investigated to determine the effect of physical activities during their teenage years on their current bone mineral densities (BMD). We measured whole-body BMD (WBMD), lumbar BMD (LBMD), and radial BMD (RBMD) with dual energy X-ray absorptiometry (DXA). Using a questionnaire, we asked the women about their physical activities during junior and senior high school and at present. We also asked about their current nutritional status and past and current milk intake. After adjusting for age, body mass index (BMI), current total calorie and calcium (Ca) intake, and milk intake when they were teenagers and at present, we determined that subjects who exercised during extracurricular activities at each of the three periods (during junior and senior high school and at present) had significantly higher WBMD and LBMD (P <0.01, respectively) than did those who did not exercise at those times. Subjects who played high-impact sports at each period had significantly higher WBMD and LBMD than did subjects who played low-impact sports (P <0.05, respectively). Subjects who had exercised regularly from their teenage years to the present had significantly higher BMD at all sites than BMD in other subjects after adjusting for the potential confounders described above (P <0.05, respectively). Our data suggest that continuous exercise beginning in junior high school, especially high-impact sports, may be associated with greater current bone mass. It is important to incorporate adequate exercise beginning in the teenage years to lower one's future risk for osteoporosis.

Jumping improves hip and lumbar spine bone mass in prepubescent children: a randomized controlled trial

Physical activity during childhood is advocated as one strategy for enhancing peak bone mass (bone mineral content [BMC]) as a means to reduce osteoporosis-related fractures. Thus, we investigated the effects of high-intensity jumping on hip and lumbar spine bone mass in children. Eighty-nine prepubescent children between the ages of 5.9 and 9.8 years were randomized into a jumping (n = 25 boys and n = 20 girls) or control group (n = 26 boys and n = 18 girls). Both groups participated in the 7-month exercise intervention during the school day three times per week. The jumping group performed 100, two-footed jumps off 61-cm boxes each session, while the control group performed nonimpact stretching exercises. BMC (g), bone area (BA; cm2), and bone mineral density (BMD; g/cm2) of the left proximal femoral neck and lumbar spine (L1-L4) were assessed by dual-energy X-ray absorptiometry (DXA; Hologic QDR/4500-A). Peak ground reaction forces were calculated across 100, two-footed jumps from a 61-cm box. In addition, anthropometric characteristics (height, weight, and body fat), physical activity, and dietary calcium intake were assessed. At baseline there were no differences between groups for anthropometric characteristics, dietary calcium intake, or bone variables. After 7 months, jumpers and controls had similar increases in height, weight, and body fat. Using repeated measures analysis of covariance (ANCOVA; covariates, initial age and bone values, and changes in height and weight) for BMC, the primary outcome variable, jumpers had significantly greater 7-month changes at the femoral neck and lumbar spine than controls (4.5% and 3.1%, respectively). In repeated measures ANCOVA of secondary outcomes (BMD and BA), BMD at the lumbar spine was significantly greater in jumpers than in controls (2.0%) and approached statistical significance at the femoral neck (1.4%; p = 0.085). For BA, jumpers had significantly greater increases at the femoral neck area than controls (2.9%) but were not different at the spine. Our data indicate that jumping at ground reaction forces of eight times body weight is a safe, effective, and simple method of improving bone mass at the hip and spine in children. This program could be easily incorporated into physical education classes.

Acquisition of optimal bone mass in childhood and adolescence

Peak bone mass (PBM), which is achieved by early adulthood, is a key determinant of the lifetime risk of osteoporosis. Because the foundation for skeletal health is established so early in life, osteoporosis prevention begins by optimizing gains in bone mineral throughout childhood and adolescence. Heritable factors account for an estimated 60-80% of the variability in PBM, with diet, physical activity and hormonal status serving as important modifiers of bone accrual. Recent pediatric studies have clarified the tempo and magnitude of gains in bone mineral and the modulating effects of diet, activity and sex steroids. The challenge lies in designing effective means to reverse trends of decreased calcium consumption, increased sodium intake and diminished physical activity among children and adolescents. Equally important is raising the awareness of health care providers to recognize children at risk for suboptimal acquisition of PBM.

The duration of exercise as a regulator of bone mass

Exercise is associated with increased peak bone mineral density (BMD). To determine the relationship between the duration of exercise and BMD, we measured BMD of the axial and appendicular skeleton by dual-energy X-ray absorptiometry (DXA), and speed of sound (SOS), broadband attenuation (BUA), and stiffness index by quantitative ultrasound (QUS) of the calcaneus, in 67 active male national soccer players (mean age 23 years, range 17-35), which included 23 premier-league players exercising 12 h/week (range 8-18), 23 third-league players exercising 8 h/week (range 3-18), and 21 sixth-league players exercising 6 h/week (range 2-10). Results were compared with 24 sedentary age- and gender-matched controls and presented as mean +/- SEM. BMD was higher in all weight-bearing regions for the whole group relative to controls (BMD: total body 6.8 +/- 0.7%, leg 9.6 +/- 0.8%, lumbar spine 13.2 +/- 1.2%, femoral neck 12.7 +/- 1.2% [all p < 0.001]; calcaneus SOS 4.2 +/- 0.3%, BUA 8.7 +/- 1.5%, and stiffness index 24.2 +/- 2.0% [all p < 0.01]). No differences were found in head or arm BMD. There were no differences in BMD or QUS measurements when comparing soccer players exercising for different activity durations. Duration of activity correlated with BMD weight-loaded regions and with QUS, provided it was less <6 h/week (p < 0.01 respectively), but not when exercising more frequently. Femoral neck BMD increased by 3.3% across every hour increase in activity in those with 0-6 h of exercise/week and by 0.7% in those exercising more than this (p < 0.01). We conclude that, in national-league soccer, the BMD needed to attain a bone strength commensurate with that of duration of activity is achieved by 6 h of exercise per week. Beyond this, additional exercise confers no higher BMD. The skeleton adapts to the prevalent level of exercise intensity required and no further.

Increasing weight-bearing physical activity and calcium intake for bone mass growth in children and adolescents: a review of intervention trials

OBJECTIVE

The purpose of this review is to evaluate the current state-of-the-science for interventions to increase bone mass gains in children and adolescents using weight-bearing physical activity or calcium supplementation.

METHODS

Studies were located using computerized and manual searches of the empirical literature. Inclusion criteria were: (a) intervention study targeting weight-bearing physical activity or calcium intake; (b) inclusion of a control group; (c) subject age range under 18 years; and (d) outcome measured bone mineral density or bone mineral content.

RESULTS

Weight-bearing physical activity and calcium supplement intervention studies both consistently show positive effects on bone mass gains in children and adolescents. The most consistent findings for both weight-bearing physical activity and calcium were for lumbar spine and total body bone sites. Only weight-bearing physical activity interventions had significant effects on the femoral neck sites. Low power may have contributed to the lack of statistically significant findings in several studies and also prevented proper evaluation of potential interactions between pubertal status and interventions on bone mass gains.

CONCLUSIONS

Increases in weight-bearing physical activity or calcium intake have positive effects on bone mass gains in children and adolescents. Further research is needed to evaluate: (a) the long-term durability of these effects; (b) specific dose-response associations; (c) interactions between weight-bearing physical activity and calcium intake; and (d) interactions between pubertal development and weight-bearing physical activity or calcium intake on bone mass outcomes.

Exercise and oral contraceptive use suppress the normal age-related increase in bone mass and strength of the femoral neck in women 18-31 years of age

Women who exercise during their second and third decades may increase their peak bone mass and lower their eventual risk for postmenopausal fracture. However, the effects of exercise in younger women can be modulated by the use of oral contraceptives, which may prevent the normal accretion of bone mass that would otherwise occur. We hypothesized that exercise intervention in young adult women would significantly increase both bone mass and the bending rigidity of the femoral neck. We further hypothesized that exercise intervention in the presence of oral contraceptive use would have a negative effect on bone mass and bending rigidity. Women 18-31 years of age (n = 123) were classified by oral contraceptive use (OC, NOC) and age (18-23, 24-31 years), and then randomized into exercise or nonexercise groups. The exercise protocol consisted of three sessions/week of aerobic and nonaerobic exercises, and continued for 2 years. Each 6 months, the femoral neck of each subject was scanned using a Lunar dual-energy X-ray absorptiometry (DEXA) scanner, and bone mineral content, density and geometric information were used to calculate estimated stresses and bending rigidity at the hip. Percent changes from baseline were analyzed using two-way analysis of variance (ANOVA) at 6, 12, 18, and 24 months. Women who neither exercised nor took oral contraceptives (NE/NOC) had the greatest percentage increases in cross-sectional area (4.98 +/- 2.29%), cross-sectional moment of inertia (9.45 +/- 2.37%), total bone mineral density (2.07 +/- 2.09%), fracture index (8.03 +/- 2.03%), and safety factor (20.03 +/- 5.79%) over the 24 month exercise program. Women who exercised and did not take oral contraceptives (E/NOC) declined on most variables related to femoral strength and bone mass, whereas those women who took oral contraceptives were usually intermediate between NE/NOC and E/NOC, whether they exercised or not. These data show that either exercise or OC use is associated with a suppression of the normal increase in bone mass and mechanical strength in the femoral neck in women 18-31 years old, but the combination of exercise and OC use appears to have a less suppressive effect.

The role of physiotherapy in the prevention and treatment of osteoporosis

Osteoporosis is an increasing public health problem that causes loss of life and reduced quality of life in sufferers. Strategies to improve bone density and reduce the likelihood of falls are important in the prevention of osteoporosis. Physiotherapists have a role to play in this condition through exercise prescription, therapeutic modalities, specific techniques and education. Appropriate treatment goals can be established following a thorough assessment of signs and symptoms, risk factors for osteoporosis and functional status. Levels of bone density measured from dual energy X-ray absorptiometry can help guide patient management. Since the aim is to maximize peak bone mass in children and adolescents, participation in a variety of high-impact activities should be encouraged. In the middle adult years, small increases in bone mass may be achieved by structured weight-training and weight-bearing exercise. In the older adult years, particularly if osteopenia or osteoporosis is present, the aim is to conserve bone mass, reduce the risk of falls, promote extended posture, reduce pain, and improve mobility and function.

More broken bones: a 4-year double cohort study of young girls with and without distal forearm fractures

Predictors of childhood fractures have not been investigated previously. This study was undertaken to determine whether a previous history of forearm fracture, low bone mineral density (BMD; both areal bone mineral density [aBMD, g/cm2] and volumetric bone mineral apparent density [BMAD, g/cm3]), or anthropometry, influence fracture risk in young girls. At baseline, two cohorts of girls, aged 3-15 years, were evaluated: 100 had recently broken a forearm (group 1) and 100 were fracture free (group 2). Four years later we restudied 170 of these girls (82 from group 1 and 88 from group 2). We now report the relationships of previous fracture history, baseline BMD (measured by dual-energy X-ray absorptiometry), baseline weight, and height to risk of new fracture. More new fractures occurred in group 1 (37 fractures in 24 girls) than in group 2 (8 fractures in 7 girls; p = 0.0007). The independent predictors for occurrence of a new fracture at any skeletal site in a multivariate model adjusting for age, weight, total body aBMD, and fracture history were previous fracture (hazard ratio [HR], 3.28; 95% CI, 1.41-7.64); age (HR per 1-year increase, 0.91; 95% CI, 0.84-0.99); total body aBMD (HR per 1 SD decrease, 1.92; 95% CI, 1.31-2.81); and body weight (HR per 1 SD increase, 1.49; 95% CI, 1.06-2.08). Girls with two risk factors together had substantially greater fracture risk: previous fracture and low spinal BMAD (HR, 9.4; 95% CI, 2.8-32.0), previous fracture and high body weight (HR, 10.2; 95% CI, 2.8-37.6), or previous fracture and low total body aBMD (HR, 13.0; 95% CI, 3.9-43.1). We conclude that previous forearm fracture, low total body aBMD, low spinal BMAD, and high body weight each increase risk of new fractures within 4 years in young girls. Interventions to reduce the risk of fractures, particularly forearm fractures, in girls warrant further study.

Strength training for children and adolescents

The potential benefits of youth strength training extend beyond an increase in muscular strength and may include favorable changes in selected health- and fitness-related measures. If appropriate training guidelines are followed, regular participation in a youth strength-training program has the potential to increase bone mineral density, improve motor performance skills, enhance sports performance, and better prepare our young athletes for the demands of practice and competition. Despite earlier concerns regarding the safety and efficacy of youth strength training, current public health objectives now aim to increase the number of boys and girls age 6 and older who regularly participate in physical activities that enhance and maintain muscular fitness. Parents, teachers, coaches, and healthcare providers should realize that youth strength training is a specialized method of conditioning that can offer enormous benefit but at the same time can result in serious injury if established guidelines are not followed. With qualified instruction, competent supervision, and an appropriate progression of the volume and intensity of training, children and adolescents cannot only learn advanced strength training exercises but can feel good about their performances, and have fun. Additional clinical trails involving children and adolescents are needed to further explore the acute and chronic effects of strength training on a variety of anatomical, physiological, and psychological parameters.

Quantitative ultrasound (QUS) of the tibia: a sensitive tool for the detection of bone changes in growing boys

The purpose of this study was to determine whether growth-related changes in bone properties can be detected in prepubertal boys using quantitative ultrasound (QUS) and to determine whether resistance training stimulates bone changes. Two groups, each of thirty 9-10 year-old boys, participated in regular physical education classes or in resistance training. Tibial speed of sound (SOS) (SoundScan 2000, Myriad) was assessed at the beginning of the school year and after 8 months. At baseline, there were no differences between groups in tibial SOS, anthropometric measures or pubertal development. At the end of the year, the tibial SOS increased (p<0.001) in both groups to a similar extent. In addition, there were no differences in the increases in height between the two groups. This indicates that resistance training during the physical education program did not induce changes in bone beyond what would be expected by the mere effect of growing. We conclude that changes in tibial SOS, as obtained with QUS, can be detected in groups of prepubertal boys over a period of 8 months.

Calcium requirements of physically active people

Dietary calcium and physical activity have been independently, but inconsistently, associated with the development of increased peak bone mass and reduced bone loss later in life. An examination of the literature points to important effects of dietary calcium on bone health. During the development of peak bone mass, calcium intakes of <1 g/d are associated with lower bone mineral density. At intakes approaching calcium requirements, physical activity is a more important predictor of bone mineral density than is calcium intake. In studies of postmenopausal women, calcium intakes of 1 g (25 mmol/d) appear to be necessary to effect a positive impact of exercise on bone mineral density in the spine. Calcium intakes recommended for protecting bone health appear to be adequate to protect against other disorders with an etiology that includes inadequate dietary calcium. Calcium requirements as modified by physical activity need to be determined for each population subgroup according to sex, age, race, and cultural environment.

The prepubertal years: a uniquely opportune stage of growth when the skeleton is most responsive to exercise?

The growing years may be the most opportune time in life for exercise to result in large increases in bone density, enough to reduce the risk of fracture late in life. However, it is not known if there is an 'optimal' time during growth when the skeleton is most responsive to exercise. Comparing the osteotrophic response to exercise between pre- and peripubertal children is complex because: (i) the development of the skeleton within each stage of puberty is characterised by differing temporal patterns of growth in bone size and mass; (ii) the hormonal regulation of the skeleton is unique to each stage of puberty; and (iii) it is difficult to equate the relative mechanical load placed on the prepubertal compared with the pubertal skeleton. There are sound biological bases for the hypotheses being proposed for both the pre- and peripubertal years being the time when the skeleton is most responsive to exercise; that is, exercise may enhance bone formation in a synergistic fashion in the presence of growth hormone (prepubertal years) or sex steroids (peripubertal years). The paucity of data and the complex methodology make it difficult to draw conclusions as to the most opportune time during growth when exercise may lead to the greatest osteotrophic response. The limited data available support the notion that the prepubertal years may be the most opportune time, due to increases in bone density and periosteal expansion of cortical bone.

Adult female hip bone density reflects teenage sports-exercise patterns but not teenage calcium intake

OBJECTIVE

To examine how cumulative teenage sports histories and time-averaged teenage calcium intake are related to total body bone mineral gain between ages 12 and 18 years and to proximal femur bone mineral density (BMD) at age 18 years. Design. Longitudinal. Setting. University Hospital and local suburban community in Central Pennsylvania.

STUDY PARTICIPANTS

Eighty-one white females in the ongoing Penn State Young Women's Health Study.

OUTCOME MEASURES

Total body and proximal femur (hip) bone measurements by dual energy radiograph absorptiometry; nutrient intakes, including calcium, from 33 days of prospective food records collected at regular intervals between ages 12 and 18 years; and self-reported sports-exercise scores between ages 12 and 18 years.

RESULTS

Cumulative sports-exercise scores between ages 12 and 18 years were associated with hip BMD at age 18 years (r = .42) but were not related to total body bone mineral gain. Time-averaged daily calcium intake, which ranged from 500 to 1500 mg/day in this cohort was not associated with hip BMD at age 18 years, or with total body bone mineral gain at age 12 through 18 years.

CONCLUSIONS

The amount of physical activity that distinguishes a primarily sedentary teenager from one who engages in some form of exercise on a nearly daily basis is related to a significant increase in peak hip BMD.

Non-pharmacological interventions

The aim of non-pharmacological intervention for osteoporosis is to prevent, treat or alleviate the consequences of osteoporosis, the main one of which is fracture. Non-pharmacological interventions consist of a wide spectrum of treatment modalities to decrease pain, correct postural change, improve mobility, enable the patient to follow a normal social life and prevent (further) fracture. An exercise programme can increase bone mass in adolescents and adults, but in the elderly its main emphasis should be on improving muscle strength and balance in order to decrease the risk of falls. Physiotherapy is commonly prescribed to mobilize the patient after a fracture, to decrease muscle spasm and pain, and to improve balance and co-ordination. An orthesis or back support may be used to correct kyphosis and decrease pain. Medication for pain is often needed and should cover both acute severe pain following fracture and chronic pain caused by postural change. A hip fracture is the most severe consequence of osteoporosis. The risk of hip fracture can be decreased by pharmacological treatment to increase bone mass and bone strength. However, in the very elderly the occurrence of falling may be more important than the failure of bone strength. Hip protectors have recently become available and have been shown to decrease the risk of hip fracture after a fall. These shunt the energy from the trochanter away to the sides. Non-pharmacological approaches to treatment are often neglected in daily practice, the emphasis being instead on treatment with drugs that decrease bone resorption and thereby increase bone strength.

Does childhood and adolescence provide a unique opportunity for exercise to strengthen the skeleton?

Osteoporosis is a major, and increasing, public health problem. In this review we examine the evidence that childhood physical activity is an important determinant of bone mineral in adult years, and as such, may help to prevent osteoporosis. Animal studies provide incontrovertible evidence that growing bone has a greater capacity to add new bone to the skeleton than does adult bone. Observational studies in children undertaking routine physical activity and cross-sectional athlete studies in young sportspeople both reveal that activity is positively associated with bone mineral density (BMD). Longitudinal studies in pre- and peripubertal gymnasts reveal BMD gains far in excess of those that can be achieved in adulthood. However, such studies permit only limited conclusions as they contain the potential for selection bias and can be confounded by other determinants of bone mineral (e.g. dietary and lifestyle factors). Thus, research comparing inter-individual playing-to-nonplaying arm differences in bone mineral (e.g., in racquet sports) have proven to be extremely useful. These studies suggest that the BMD differences are clearly greater when bone is subjected to mechanical loading prior to the end of puberty and longitudinal growth of the body (in women, before menarche) rather than after it. Tanner stage II and III appears to be the maturational stage when the association between exercise and BMD becomes manifest in most adolescents. Do conclusions drawn from athlete studies apply to the general population? Randomised intervention studies of physical activity and bone mineral accrual in normal children confirm that childhood activity is strongly associated with bone mineral accrual. Furthermore, some retired athlete studies and a detraining study suggest that adolescent bone gain may, at least partly, persist despite reduced adult physical activity. Mechanisms that may underlie the association between childhood physical activity and bone mineral accrual are outlined. Thus, it appears that physical activity during the most active period of maturity (with respect to longitudinal growth of the body) plays a vital role in optimising peak bone mass and that benefits may extend into adulthood.

Effects of plyometric jump training on bone mass in adolescent girls

PURPOSE

The purpose of this study was to investigate the effects of 9 months of plyometric jump training on bone mineral content (BMC), lower extremity performance, and static balance in adolescent girls (aged 14.6 +/- 0.5 yr; 22.7 +/- 14.0 months past menarche).

METHODS

Exercisers (N = 25) trained 30-45 min, three times per week, performing various exercises using weighted vests (squats, lunges, calf raises) and plyometrics (hopping, jumping, bounding, and box depth jumps). The program was designed to load the lower extremities. Controls (N = 28), matched to exercisers for age and months past menarche, maintained their usual activities. The following were assessed at baseline and 9 months: BMC, strength by isokinetic dynamometry, power (Wingate), and static balance.

RESULTS

Repeated measures ANOVA revealed no significant differences between groups for BMC, nor were the changes in anthropometric or performance variables, analyzed by MANOVA, significant. In follow-up analyses, t-tests for independent samples revealed that both groups experienced a significant (P < 0.01) increase in percent change in bone mass compared to zero, for the whole body (mean: 3.7% exercisers, 3.6% controls), femoral neck (4.5% vs 2.4%), lumbar spine (L2-4) (6.6% vs 5.3%), and femoral shaft (3.4% vs 2.3%), but only the exercisers improved BMC of the greater trochanter (3.1% vs 1.9%). Furthermore, the exercise group significantly improved knee extensor strength (14.7% vs 7.3%) and medial/lateral balance (38.1% vs 9.5%), whereas the control group demonstrated no changes. The variety of lateral movement activities performed by the exercise group may have contributed to the differences observed between groups for greater trochanter bone mineral density (BMD), leg strength, and medial/lateral balance.

CONCLUSION

The trends observed in bone mass between groups suggest that plyometric jump training continued over a longer period of time during adolescent growth may increase peak bone mass.

Overweight and obese children have low bone mass and area for their weight

OBJECTIVES

To determine whether girls and boys categorized from body mass index (BMI) values as overweight or obese for their age have lower bone mineral content (BMC) or lower bone area in relation to total body weight than children of normal adiposity.

DESIGN

Cross-sectional study in a university bone research unit.

SUBJECTS

Two hundred girls and 136 boys aged 3-19 y recruited from the general population by advertisement.

MEASUREMENTS

Total body BMC (g) and bone area (cm2) measured by dual energy X-ray absorptiometry (DXA) in relation to body weight (kg), lean tissue mass (kg) and fat mass (kg) in boys and girls of three different BMI percentile groupings: normal weight (BMI<85th percentile); overweight (85 to 94th BMI percentile); obese (> or =95th BMI percentile).

RESULTS

Obese children had higher BMC, bone area, and fat mass for chronological age than those of normal body weight (P<0.001). In spite of this the observed values for age-adjusted total body BMC and bone area relative to body weight were each lower than predicted values, in both overweight and obese children (2.5-10.1% less, P<0.05) than in children of lower adiposity.

CONCLUSION

In overweight and obese boys and girls there is a mismatch between body weight and bone development during growth: their bone mass and bone area are low for their body weight.

Stress fractures and the female athlete

Stress injury to bone is the result of a temporary disturbance in the equilibrium between bone resorption and bone regeneration. Knowledge of the pathophysiology of bone in health and disease currently encompasses an interactive mode that includes biomechanical, hormonal, nutritional, and genetic factors. The current study will review possible etiologic theories for stress injuries to bone with a special emphasis on gender-related factors. Females may be more at risk for a stress injury to bone because of their unique hormonal environment, and other anatomic and gender factors.

Augmented trochanteric bone mineral density after modified physical education classes: a randomized school-based exercise intervention study in prepubescent and early pubescent children

BACKGROUND

Of the few exercise intervention studies focusing on pediatric populations, none have confined the intervention to the scheduled physical education curriculum.

OBJECTIVE

To examine the effect of an 8-month school-based jumping program on the change in areal bone mineral density (aBMD), in grams per square centimeter, of healthy third- and fourth-grade children.

STUDY DESIGN

Ten elementary schools were randomized to exercise (n = 63) and control groups (n = 81). Exercise groups did 10 tuck jumps 3 times weekly and incorporated jumping, hopping, and skipping into twice weekly physical education classes. Control groups did regular physical education classes. At baseline and after 8 months of intervention, we measured aBMD and lean and fat mass by dual-energy x-ray absorptiometry (Hologic QDR-4500). Calcium intake, physical activity, and maturity were estimated by questionnaire.

RESULTS

The exercise group showed significantly greater change in femoral trochanteric aBMD (4.4% vs 3.2%; P <.05). There were no group differences at other sites. Results were similar after controlling for covariates (baseline aBMD change in height, change in lean, calcium, physical activity, sex, and ethnicity) in hierarchical regression.

CONCLUSIONS

An easily implemented school-based jumping intervention augments aBMD at the trochanteric region in the prepubertal and early pubertal skeleton.

Nutrition interventions in childhood for the prevention of chronic diseases in adulthood

As it becomes increasingly evident that the seeds of many adult disorders are planted in childhood, it is important that pediatric care providers 1) recognize risk factors for adult disease in children and 2) institute effective interventions. Many adult medical conditions are significantly related to or influenced by nutritional factors. This review evaluates three areas in preventive and therapeutic pediatric nutrition: obesity, lipid disorders, and osteoporosis.

A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: the university of Saskatchewan bone mineral accrual study

To investigate the influence of physical activity on bone mineral accrual during the adolescent years, we analyzed 6 years of data from 53 girls and 60 boys. Physical activity, dietary intakes, and anthropometry were measured every 6 months and dual-energy X-ray absorptiometry scans of the total body (TB), lumbar spine (LS), and proximal femur (Hologic 2000, array mode) were collected annually. Distance and velocity curves for height and bone mineral content (BMC) were fitted for each child at several skeletal sites using a cubic spline procedure, from which ages at peak height velocity (PHV) and peak BMC velocity (PBMCV) were identified. A mean age- and gender-specific standardized activity (Z) score was calculated for each subject based on multiple yearly activity assessments collected up until age of PHV. This score was used to identify active (top quartile), average (middle 2 quartiles), or inactive (bottom quartile) groups. Two-way analysis of covariance, with height and weight at PHV controlled for, demonstrated significant physical activity and gender main effects (but no interaction) for PBMCV, for BMC accrued for 2 years around peak velocity, and for BMC at 1 year post-PBMCV for the TB and femoral neck and for physical activity but not gender at the LS (all p < 0.05). Controlling for maturational and size differences between groups, we noted a 9% and 17% greater TB BMC for active boys and girls, respectively, over their inactive peers 1 year after the age of PBMCV. We also estimated that, on average, 26% of adult TB bone mineral was accrued during the 2 years around PBMCV.

Systemic lupus erythematosus and related disorders of childhood

Systemic lupus erythematosus (SLE) remains a challenging autoimmune disease in term of its etiology, pathogenesis, and management. Much progress has been made in the past year in searching for the SLE susceptibility genes, particularly by several genome-wide screening groups. Cumulative evidence about the association of infections and hormones with SLE has been gathered. Researchers believe that childhood SLE involves more severe organ involvement than adult SLE. Central nervous system complicated lupus continues to be problematic because functional imaging can be abnormal in otherwise asymptomatic lupus individuals. Whether these abnormalities result from subclinical central nervous system involvement or from false positives remains to be determined. With the wide use of corticosteroids as a cornerstone therapy for major organ involvement in childhood SLE, potential complications, especially those involving the growing bone or osteoporosis, are a cause of concern. Evidence suggests that regular exercise, as well as calcium and vitamin D supplementation, may help alleviate bone complications. Researchers have also updated information about pediatric antiphospholipid antibody syndrome. Follow-up studies on neonatal lupus and its pathogenesis have progressed, leading to a better understanding of its natural history and, in turn, to proper counseling of mothers of infants with neonatal lupus and of women with positive anti-Ro or anti-La antibodies. Drug-induced lupus in children is not uncommon. Minocycline and zafirlukast have been increasingly used, and were reported to induce lupus in children.

Risk factors for stress fractures

Preventing stress fractures requires knowledge of the risk factors that predispose to this injury. The aetiology of stress fractures is multifactorial, but methodological limitations and expediency often lead to research study designs that evaluate individual risk factors. Intrinsic risk factors include mechanical factors such as bone density, skeletal alignment and body size and composition, physiological factors such as bone turnover rate, flexibility, and muscular strength and endurance, as well as hormonal and nutritional factors. Extrinsic risk factors include mechanical factors such as surface, footwear and external loading as well as physical training parameters. Psychological traits may also play a role in increasing stress fracture risk. Equally important to these types of analyses of individual risk factors is the integration of information to produce a composite picture of risk. The purpose of this paper is to critically appraise the existing literature by evaluating study design and quality, in order to provide a current synopsis of the known scientific information related to stress fracture risk factors. The literature is not fully complete with well conducted studies on this topic, but a great deal of information has accumulated over the past 20 years. Although stress fractures result from repeated loading, the exact contribution of training factors (volume, intensity, surface) has not been clearly established. From what we do know, menstrual disturbances, caloric restriction, lower bone density, muscle weakness and leg length differences are risk factors for stress fracture. Other time-honoured risk factors such as lower extremity alignment have not been shown to be causative even though anecdotal evidence indicates they are likely to play an important role in stress fracture pathogenesis.

The effects of different resistance training protocols on muscular strength and endurance development in children

BACKGROUND

Previous research has shown that children can increase their muscular strength and muscular endurance as a result of regular participation in a progressive resistance training program. However, the most effective exercise prescription regarding the number of repetitions remains questionable.

OBJECTIVE

To compare the effects of a low repetition-heavy load resistance training program and a high repetition-moderate load resistance training program on the development of muscular strength and muscular endurance in children. Design. Prospective, controlled trial.

SETTING

Community-based youth fitness center.

SUBJECTS

Eleven girls and 32 boys between the ages of 5.2 and 11.8 years.

INTERVENTION

In twice-weekly sessions of resistance training for 8 weeks, children performed 1 set of 6 to 8 repetitions with a heavy load (n = 15) or 1 set of 13 to 15 repetitions with a moderate load (n = 16) on child-size exercise machines. Children in the control group (n = 12) did not resistance train. One repetition maximum (RM) strength and muscular endurance (repetitions performed posttraining with the pretraining 1-RM load) were determined on the leg extension and chest press exercises.

RESULTS

One RM leg extension strength significantly increased in both exercise groups compared with that in the control subjects. Increases of 31.0% and 40.9%, respectively, for the low repetition-heavy load and high repetition-moderate load groups were observed. Leg extension muscular endurance significantly increased in both exercise groups compared with that in the control subjects, although gains resulting from high repetition-moderate load training (13.1 +/- 6.2 repetitions) were significantly greater than those resulting from low repetition-heavy load training (8.7 +/- 2.9 repetitions). On the chest press exercise, only the high repetition-moderate load exercise group made gains in 1-RM strength (16.3%) and muscular endurance (5.2 +/- 3.6 repetitions) that were significantly greater than gains in the control subjects.

CONCLUSION

These findings support the concept that muscular strength and muscular endurance can be improved during the childhood years and favor the prescription of higher repetition-moderate load resistance training programs during the initial adaptation period.

Effects of high-impact exercise on ultrasonic and biochemical indices of skeletal status: A prospective study in young male gymnasts

Physical activity has been proposed as one strategy to enhance bone mineral acquisition during growth. The aim of this study was to determine whether frequent impact loading associated with gymnastics training confers a skeletal benefit on pre- and peripubertal male gymnasts. We measured broadband ultrasonic attenuation (BUA, dB/MHz) at the calcaneus (CBUA); ultrasound velocity (m/s) at the calcaneus (CVOS), distal radius (RVOS) and phalanx (PVOS); serum osteocalcin (OC); total alkaline phosphatase (ALP) and insulin-like growth factor-I (IGF-I) every 3-4 months over an 18-month period in elite male gymnasts and matched normoactive controls (pubertal stage </=2). Ground reaction forces of common gymnastics maneuvers were determined using a force platform and loading histories of the upper and lower extremities approximated from video recordings. Ultrasound results were expressed as a standardized score (Z score) adjusted for age, height, and weight. At baseline, no differences were detected between the gymnasts (n = 31) and controls (n = 50) for CBUA, although ultrasound velocity at each site was higher in the gymnasts (0.6-1.5 SD) than the predicted mean in controls (p </= 0. 001). Over 18 months, CBUA Z scores increased significantly in the gymnasts from baseline (0.3 vs. 1.0, p < 0.05, n = 18). In contrast, ultrasound velocity did not increase in either group, although CVOS and RVOS remained significantly higher in gymnasts compared with controls (range p < 0.01 and < 0.001). No differences between groups were found for OC, ALP, or IGF-I at any time. Gymnastics training was associated with on average 102 and 217 impacts per session on the upper and lower extremities, respectively, with peak magnitudes of 3.6 and 10.4 times body weight. These results suggest that frequent high-impact, weight-bearing exercise during the pre and peripubertal period may enhance the mechanical competence of the skeleton, perhaps offering an important strategy for osteoporosis prevention if the benefits are maintained.

The effect of a weight-bearing physical activity program on bone mineral content and estimated volumetric density in children with spastic cerebral palsy

After an 8-month physical activity intervention in children with cerebral palsy, increases in femoral neck bone mineral content (BMC) (9.6%), volumetric bone mineral density (v BMD) (5.6%), and total proximal femur BMC (11.5%) were observed in the intervention group (n = 9) compared with control subjects (n = 9; femoral neck BMC, -5. 8%; v BMD, -6.3%; total proximal femur BMC, 3.5%).

Longitudinal bone mineral density changes in female child artistic gymnasts

Changes in bone mineral density (BMD), and related factors, in female child artistic gymnasts (n = 9) and their age- (+/-0.3 years), height- (+/-2.8 cm), and weight- (+/-1.7 kg) matched controls (n = 9) were prospectively examined. It was hypothesized that gymnasts would possess higher BMD at baseline, 6, and 12 months later and have greater gains in BMD over 1 year compared with controls. BMD (g/cm2) of the total proximal femur (TPF), Ward's triangle (WT), trochanter (Troch), femoral neck (FN), lumbar spine (LS, L1-L4), and total body (TB) were measured by dual-energy X-ray absorptiometry. Physical activity was measured by a 7-day recall; daily dietary intakes of energy and nutrients were estimated from 3-day records. Serum osteocalcin and urinary pyridinium cross-links were measured by radioimmunoassay and high performance liquid chromatography, respectively. Gymnasts versus controls possessed significantly higher BMD at all sites measured. Although not significantly different (p > 0.05), gymnasts compared with controls had moderately larger percentage changes in Troch (% Delta = 8.6 +/- 3.0 vs. 3.8 +/- 5.1%, d = 0.41), FN (% Delta = 6.1 +/- 1.2 vs. 3.9 +/- 1.6%, d = 0.55), LS (% Delta = 7.8 +/- 1.1 vs. 6.8 +/- 1.6%, d = 0.26), and TB BMD (% Delta = 5.6 +/- 0.8 vs. 3.4 +/- 0.7%, d = 0.98) as evidenced by the magnitude of the effect sizes (d). Gymnasts versus controls possessed a lower percentage body fat (p < 0.01) and engaged in more hours of very hard activity (p < 0.0001). Calcium, as a percentage of adequate intake, decreased over 12 months (p < 0.01), and urinary cross-links significantly decreased over 6 months in both groups. Female child gymnasts possess higher BMD at the TPF and related sites, LS, and TB compared with nongymnast controls, and 1 year of gymnastics training moderately increases Troch, FN, LS, and TB BMD for gymnasts compared with controls. These findings lend support to the idea that gymnastics training in childhood helps maximize peak BMD.

Pregnancy-associated osteoporosis with elevated levels of circulating parathyroid hormone-related protein: a report of two cases

Two lactating women who had complained of back pain developed spontaneous vertebral fractures with low bone mineral density (BMD) several months postpartum. The back pain and biochemical abnormalities presented as hypercalcemia and elevated plasma levels of the parathyroid hormone-related protein (PTH-rP) that returned to normal indices with increasing BMD after weaning. The increased circulating PTH-rP might contribute to the pregnancy-associated osteoporosis in women who probably are already osteopenic.

Moderate exercise during growth in prepubertal boys: changes in bone mass, size, volumetric density, and bone strength: a controlled prospective study

Cross-sectional studies of elite athletes suggest that growth is an opportune time for exercise to increase areal bone mineral density (BMD). However, as the exercise undertaken by athletes is beyond the reach of most individuals, these studies provide little basis for making recommendations regarding the role of exercise in musculoskeletal health in the community. To determine whether moderate exercise increases bone mass, size, areal, and volumetric BMD, two socioeconomically equivalent schools were randomly allocated to be the source of an exercise group or controls. Twenty boys (mean age 10.4 years, range 8.4-11.8) allocated to 8 months of 30-minute sessions of weight-bearing physical education lessons three times weekly were compared with 20 controls matched for age, standing and sitting height, weight, and baseline areal BMD. Areal BMD, measured using dual-energy X-ray absorptiometry, increased in both groups at all sites, except at the head and arms. The increase in areal BMD in the exercise group was twice that in controls; lumbar spine (0.61 +/- 0.11 vs. 0.26 +/- 0.09%/month), legs (0.76 +/- 0.07 vs. 0.34 +/- 0.08%/month), and total body (0.32 +/- 0.04 vs. 0.17 +/- 0.06%/month) (all p < 0.05). In the exercise group, femoral midshaft cortical thickness increased by 0.97 +/- 0. 32%/month due to a 0.93 +/- 0.33%/month decrease in endocortical (medullary) diameter (both p < 0.05). There was no periosteal expansion so that volumetric BMD increased by 1.14 +/- 0.33%/month, (p < 0.05). Cortical thickness and volumetric BMD did not change in controls. Femoral midshaft section modulus increased by 2.34 +/- 2. 35 cm3 in the exercise group, and 3.04 +/- 1.14 cm3 in controls (p < 0.05). The growing skeleton is sensitive to exercise. Moderate and readily accessible weight-bearing exercise undertaken before puberty may increase femoral volumetric BMD by increasing cortical thickness. Although endocortical apposition may be a less effective means of increasing bone strength than periosteal apposition, both mechanisms will result in higher cortical thickness that is likely to offset bone fragility conferred by menopause-related and age-related endocortical bone resorption.

The roles of exercise and fall risk reduction in the prevention of osteoporosis

In summary, the optimal model for the prevention of osteoporotic fractures includes maximization and maintenance of bone strength and minimization of trauma. Numerous determinants of each have been identified, but further work to develop preventative strategies based on these determinants remains to be undertaken. Physical activity is a determinant of peak BMD. There also is evidence that activity during growth modulates the external geometry and trabecular architecture, potentially enhancing skeletal strength, while during the adult years activity may reduce age-related bone loss. The magnitude of the effect of a 7% to 8% increase in peak BMD, if maintained through the adult years, could translate to a 1.5-fold reduction in fracture risk. Moreover, in the older population, appropriate forms of exercise could reduce the risk of falling and, thus, further reduce fracture risk. These data must be considered as preliminary in view of the paucity of long-term fracture outcome data from randomized clinical trials. However, current information suggests that the optimal form of exercise to achieve these objectives may vary through life. Vigorous physical activity (including weight-bearing, resistance, and impact components) during childhood may maximize peak BMD. This type of activity seems optimal through the young adult years, but as inevitable age-related degeneration occurs, activity modification to limit the impact component of exercise may become necessary. In the elderly, progressive strength training has been demonstrated to be a safe and effective form of exercise that reduces risk factors for falling and may also enhance BMD. In the frail elderly, activity to improve balance and confidence also may be valuable. Group activities such as Tai Chi may be cost-effective. Precise prescriptions must await the outcome of well-designed, controlled longitudinal studies that include fracture as an outcome. However, increased physical activity seems to be a sensible component of strategies to reduce osteoporotic fracture.

Self-reported ballet classes undertaken at age 10-12 years and hip bone mineral density in later life

The major effect of weightbearing exercise on adult bone mass may be exerted during childhood. We examined the relationship between reported hours of ballet classes per week undertaken as a child and adult bone mineral density (BMD) at the hip, spine, and forearm. We performed a retrospective cohort study in 99 female retired dancers (mean age 51 years, SD 14 years) and 99 normal controls, derived from a twin study, matched hierarchically for age, height, weight and menopausal status. Starting age of ballet was recalled and weekly hours of ballet as a child was self-reported on two occasions. BMD was measured using dualenergy X-ray absorptiometry and reported as a Z-score. Self-reported hours of ballet class undertaken per week at each age between 10 and 12 years was positively associated with a difference in BMD between dancers and controls at both the femoral neck site (beta = 0.73, p = 0.001) and the total hip site (beta = 0.55, p < 0.01). These associations were unaffected by adjustment for covariates including measures of adult activity (current physical activity, years of fulltime ballet), measures of menstrual disturbance (age of menarche, history of irregular menses), dietary history (calcium intake as a child, adolescent or adult) or lifestyle factors (lifetime smoking, lifetime alcohol). Although starting age of ballet was negatively associated with weight-adjusted within-pair hip BMD difference, it was no longer associated after adjustment for weekly hours of ballet. There was no relationship between hours of ballet undertaken as a child and differences in BMD at the lumbar spine or upper limb, at any age. Our data suggest that classical ballet classes undertaken between the ages of 10 and 12 years are independently and positively associated with a difference in hip BMD between dancers and controls. The findings are consistent with the hypothesis that this age range identifies a stage of development when the proximal femur is particularly responsive to weightbearing exercise.