Stride width discriminates gait of side-fallers compared to other-directed fallers during overground walking.

PURPOSE: The purpose was to identify differences in gait characteristics between older fallers with a tendency to fall sideways compared to those who do not fall to the side. METHOD: The authors conducted a prospective, case control study of ambulatory adults older than 70 residing in retirement communities. Measurements included spatial and temporal gait parameters and prospective fall surveillance. RESULTS: In all, 29 participants fell to the side, and 64 fell in other directions (forward, backward, straight down); 46 participants experienced no falls. Side-fallers exhibited narrower stride widths compared to other-directed fallers, and stepwise and discriminant analysis correctly classified 67% of side-fallers and other-directed fallers using only stride width. DISCUSSION: This study suggests that side-fallers, who have narrower stride widths compared to those who fall in other directions, may not be adapting their gait to compensate for lateral instability. More research is needed to determine whether narrow gait contributes to unstable walking patterns.

MRI-derived body segment parameters of children differ from age-based estimates derived using photogrammetry.

Body segment parameters are required when researching joint kinetics using inverse dynamics models. However, the only regression equations for estimating pediatric body segment parameters across a wide age range were developed, using photogrammetry, based on 12 boys and have not been validated to date (Jensen, R.K., 1986. Body segment mass, radius and radius of gyration proportions of children. Journal of Biomechanics 19, 359-368). To assess whether these equations could validly be applied to girls, we asked whether body segment parameters estimated by the equations differ from parameters measured using a validated magnetic resonance imaging (MRI) method. If so, do the differences cause significant differences in joint kinetics during normal gait? Body segment parameters were estimated from axial MRIs of the left thigh and shank of 10 healthy girls (9.6 +/- 0.9 years) and compared to those from Jensen's equations. Kinematics and kinetics were collected for 10 walking trials. Extrema in hip and knee moments and powers were compared between the two sets of body segment parameters. With the exception of the shank mass center and radius of gyration, body segment parameters measured using MRI were significantly different from those estimated using regression equations. These systematic differences in body segment parameters resulted in significant differences in sagittal-plane joint moments and powers during gait. Nevertheless, it is doubtful that even the greatest differences in kinetics are practically meaningful (0.3% BW x HT and 0.7% BW x HT/s for moments and power at the hip, respectively). Therefore, body segment parameters estimated using Jensen's regression equations are a suitable substitute for more detailed anatomical imaging of 8-10-year-old girls when quantifying joint kinetics during gait.

The effects of hormone replacement therapy and resistance training on spine bone mineral density in early postmenopausal women.

This study evaluated the additive effects of hormone replacement therapy (HRT) and a 1-year site-specific resistance-training (RT) program involving two free weight exercises (i.e., squat and deadlift) 2 days/week as a strategy to reverse or attenuate bone loss at the lumbar spine in early postmenopausal women. Participants from a group of self-selected HRT or non-HRT (N=141) users were randomly assigned to RT (exercise) or no training, creating four groups: 1) non-HRT plus RT [NHRT plus exercise (n=35)]; 2) HRT plus RT [HRT plus exercise (n=37)]; 3) HRT no resistance training [HRT no exercise (n=35)]; or 4) control [non-HRT no resistance training group (n=34)]. Mean age and months past menopause did not differ between groups (52.1+/-3.0 years and 52.8+/-9.9 months, respectively). Post-menopausal status was confirmed by follicle-stimulating hormone levels > or =40 mIU/mL. Bone mineral density (BMD) of the spine was assessed by Dual Energy X-ray Absorptiometry (Hologic), at baseline and month 12. Data were analyzed using a 4 (experimental condition) x 2 (time) repeated measures multivariate analysis of variance to determine the effects of RT on HRT and non-HRT in early postmenopausal women. The main effects for group (P<0.007), time (P<0.001), and the group by time interaction (P<0.001) were each significant. Control participants experienced an average of -3.6% reduction of BMD at the spine. HRT treatment with no exercise showed bone loss of -0.66%. One year of RT produced increases in spine BMD of +0.43% and +0.70%, respectively for the NHRT plus exercise, and HRT plus exercise groups with no differences between the NHRT and HRT exercise groups. In conclusion, RT alone was as effective as HRT in preventing bone loss at the spine and was more effective than HRT alone in attenuating bone loss at the spine. Moreover, there was no additional benefit in combining HRT with RT for preventing bone loss at the spine in this group of early postmenopausal women.

Site-specific response of bone to exercise in premenopausal women.

We studied the response of bone at specific skeletal sites to either lower body exercise alone or complemented with upper body exercise in premenopausal women. Thirty-five exercisers and 24 age-matched controls completed the 12-month study. Exercising women (N = 35) were randomly assigned to either lower body resistance plus jump exercise (LOWER) (N = 19) or to lower and upper body resistance plus jump exercise (UPPER + LOWER) (N = 16). Exercisers trained three times per week completing 100 jumps and 100 repetitions of lower body resistance with or without 100 repetitions of upper body resistance exercise at each session. Intensity for lower body exercise was increased using weighted vests for jump and resistance exercises, respectively. Intensity for upper body exercise was increased using greater levels of tautness in elastic bands. Bone mineral density (BMD) at the total hip, greater trochanter, femoral neck, lumbar spine and whole body were measured by dual energy X-ray absorptiometry (Hologic QDR-1000/W) at baseline, 6 and 12 months. Data were analyzed first including all enrolled participants who completed follow-up testing and secondly including only those women whose average attendance was > or =60% of prescribed sessions. Group differences in 12-month %change scores for BMD variables were analyzed by univariate ANCOVA adjusted for baseline differences in age. Post hoc tests were performed to determine which groups differed from one another. Initial analysis showed significant differences in greater trochanter BMD between each exercise group and controls, but not between exercise groups (2.7%+/-2.5% and 2.2%+/-2.8% vs. 0.7%+/-1.7%, for LOWER and UPPER + LOWER vs. controls, respectively; p < 0.02) and near significant group differences at the spine (p = 0.06). Excluding exercisers with low compliance, group differences at the greater trochanter remained, while spine BMD in UPPER + LOWER was significantly different from LOWER and controls, who were not significantly different from one another (1.4%+/-3.9% vs. -0.9%+/-1.7% and -0.6%+/-1.8%, for UPPER + LOWER vs. LOWER and controls, respectively; p < 0.05). No significant differences among groups were found for femoral neck, total hip or whole body BMD. Our data support the site-specific response of spine and hip bone density to upper and lower body exercise training, respectively. These data could contribute to a site-specific exercise prescription for bone health.

Oral contraceptive use in young women is associated with lower bone mineral density than that of controls.

Osteoporosis is a skeletal disease affecting 44 million Americans. A primary strategy to prevent osteoporosis is to develop a high peak bone mass in youth. Oral contraceptives (OCs) alter hormones in women and could affect bone mass development. Fifty percent of American women between the ages of 20 and 24 years use OCs. However, the interaction between OCs and skeletal mineralization is poorly understood. Our aim was to compare bone mass [bone mineral density (BMD)] of young women who had a history of OC use, with regularly menstruating controls. We recruited 98 women who were 18 to 25 years of age and had a history of OC use (n=44, 3.4+/-1.9 years of OC use) and controls (n=58). BMD at the hip, whole-body, and spine [anterior-posterior (AP) and lateral grams per square centimeter] was measured by dual-energy X-ray absorptiometry (DXA). Physical activity [in metabolic equivalents (METs)] was measured via questionnaire, and grip strength was evaluated with an isometric dynamometer. Groups were similar in body mass index (BMI), fat mass, grip strength, calcium intake and physical activity, but OC users were slightly older than controls (21.3+/-1.9 years vs 20.3+/-1.6 years, P<0.05). In analysis of covariance, controlled for age and BMI, controls had significantly greater BMD than OC users at the AP and lateral spine, femoral neck, greater trochanter, total hip, and whole body (P<0.05). We conclude that, in this cross-sectional analysis, oral contraceptive use by young women may compromise bone health during a time when mineral is still accruing.

The association between hormone therapy use and changes in strength and body composition in early postmenopausal women.

OBJECTIVE: To prospectively examine potential differences in upper- and lower-body muscle strength, lower-body power, lean muscle mass, total body fat, intra-abdominal fat, and energy expenditure (METS) variables in early postmenopausal women. Measurements were taken at baseline and 12 months. DESIGN: Prospective, 1-year non-randomized [self-selected hormone therapy (HT) and non-HT-replaced], longitudinal study with participation from 136 normally active, early [14.2 +/- 9.8 mo past menopause (51.1 +/- 3.0 y) mean age +/- SD] postmenopausal women. Total body fat mass, lean mass, and bone mass were assessed by dual-energy x-ray absorptiometry (Hologic), METS (6-mo activity recall questionnaire) upper- and lower-body peak force by isokinetic dynamometry (KinCom 500H, Chattex Corp.), and leg power by the Bassey Power Rig (Nottingham, UK). RESULTS: We observed no significant differences in central adipose tissue, total fat mass, lean muscle mass, strength, or lower limb power. However, estrogen did promote a maintenance affect in bone mineral density at the spine and total hip and an increase in greater trochanter bone mineral density (P < 0.01) in the estrogen-replaced group. CONCLUSION: Our findings suggest that HT does not play a role in either increasing or maintaining strength, lean muscle mass, lower limb power, or the attenuation of increases in total body or abdominal fat, at least in this group of postmenopausal women during the initial years of menopause

One year of oral calcium supplementation maintains cortical bone density in young adult female distance runners.

We conducted a double-blind, placebo-controlled, randomized trial to determine whether 1 year of supplemental calcium intake would augment hip [greater trochanter, GT, femoral neck (FN), total hip (TH)], spine (LS), and femoral mid-shaft (Fmr) BMD in female distance runners. Twenty-three women (age: 23.7 +/- 4.7 yrs, height: 165.6 +/- 6.3 cm, weight: 55.7 +/- 6.1 kg) were randomly assigned to receive either 1000 mg/d of supplemental calcium (N = 13) or placebo tablets (N = 10) for 1 year. BMD was determined by DXA (Hologic 1000-W) and tablet compliance by self-report logs. Compliance averaged 79% and 71% for supplement and placebo groups, respectively. Calcium supplementation did not affect hip or spine BMD, but did prevent loss at the femoral mid-shaft (GT: -0.5% vs. 0.2%, FN: 0.9% vs. 1.1%, TH: -0.3% vs. 0.2%, LS: 0.3% vs. 1.2%, Fmr: 0.1% vs. -1.8%, for calcium vs. placebo, respectively). We conclude that the addition of 800 mg/d of supplemental calcium to the diet of young adult female distance runners with habitual calcium intakes of approximately 1000 mg/d, prevents cortical but not trabecular bone loss.

Musculoskeletal response to exercise is greatest in women with low initial values.

INTRODUCTION: The "initial values" principle of exercise training states those with the lowest initial values of a physiologic system have the greatest capacity for improvement in response to training. We sought to determine whether initial values predicted the musculoskeletal response to training in premenopausal women (N = 31) who participated in a 1-yr program of resistance and jump training designed to improve physical indices of fracture risk. Significant improvements in trochanteric bone mineral density (BMD), hip abductor strength, power, and postural stability occurred in response to training. METHODS: To determine the predictive power of initial values, we performed separate stepwise regression analyses for each variable including the following dependent variables: age, initial value, highest weight lifted during training, and total number of exercise sessions attended. RESULTS: In each case, the initial value was the most significant predictor of percent change in response to training. Initial values explained 15-29% of the variance in the magnitude of the training response. For each unit lower BMD of the greater trochanter (0.01 g.cm-2), the training response was 12% greater. For each unit decrease in initial strength (1 N.m), power (1 W), and stability (1 SI unit), the training response was 1.0%, 0.2%, and 8.0% greater, respectively. When categorized by quartile of initial values, women in the lowest quartile had two- to fivefold greater improvements in musculoskeletal measures than those in the upper quartile. CONCLUSION: Women who began training with the lowest initial values had the greatest improvements in hip BMD, hip abductor strength, leg power, and postural stability. These results support the training principle of initial values and suggest that this training program may be most successful in premenopausal women with lower values of musculoskeletal indices of fracture risk.

Spine bone mineral density increases in experienced but not novice collegiate female rowers.

PURPOSE: There is evidence that rowing exercise targets the spine, but the dose of exercise required to build bone is poorly understood. To further explore this topic, we studied the bone response at the spine in novice and experienced female collegiate rowers over their 6-month competitive season. We hypothesized that, with rowing strokes similar between groups during training, experienced rowers would produce greater force at the spine than novices and thus, gain more bone mineral density (BMD). METHODS: Subjects included 16 experienced rowers (21.2 +/- 1.2 yr) who had been rowing 26 +/- 10 months and 19 novice rowers (19.5 +/- 0.8 yr) who had been rowing three months and 14 controls (19.2 +/- 1.6 yr). BMD was assessed by DXA at baseline and after the 6-month competitive season. During the season, all rowers participated in the same training program and took approximately the same number of strokes per training session (1000-1200 repetitions). On the 2000- and 6000-m rowing ergometer tests experienced rowers had faster times, indicating that their power output, and thus force production, was greater than novices. RESULTS: In ANCOVA, adjusting for body mass index, age, and initial BMD, the experienced rowers demonstrated a 2.5% increase at the spine that was significantly different than that of the novice rowers, but BMD change scores in the rowing groups were not different than controls. CONCLUSION: Because the number of strokes (repetitions) was similar between rowing groups during training, the higher power output in experienced rowers produced higher forces at the spine over the 6-month period that resulted in gains in spine BMD. These results support the theory that force magnitude is a key variable in osteogenesis.

Bone health across the lifespan--exercising our options.

Exercise is frequently extolled as an osteoporosis treatment. In reality, the use of exercise as an osteoporosis intervention lies more in its ability to: 1) maximize peak bone mass attained in youth; 2) maintain bone mass or reduce age-related bone loss; and 3) preserve muscle strength and postural stability to reduce the risk of falling and fracturing in the later years.

Morphological and functional characteristics of skeletal muscle fibers from hormone-replaced and nonreplaced postmenopausal women.

We tested the hypothesis that cross-bridge mechanisms of contraction differed in early postmenopausal women who did or did not receive hormone replacement therapy (HRT). Vastus lateralis biopsies were obtained from 17 postmenopausal women (49-57 years old), 8 of whom were on HRT for the previous 24 +/- 5 months and 9 of whom were never on HRT. Electrophoresis and enzyme histochemistry revealed that fiber myosin heavy chain (MHC) isoform distribution, the cross-sectional area (CSA) of slow and fast fibers, and the relative CSA occupied by each, were similar for HRT and non-HRT groups. Single permeabilized fibers containing type IIa MHC had greater Ca(2+)-activated peak specific force, unloaded shortening velocity, and peak power than fibers containing type I MHC, but in all cases the values for HRT and non-HRT groups were similar. In this cross-sectional study, we found no evidence that Ca(2+)-activated fiber function, MHC isoform distribution, or relative CSA occupied by slow and fast fibers differed between HRT and non-HRT groups.

Physical activity, body fat, and serum C-reactive protein in postmenopausal women with and without hormone replacement.

The objective was to determine whether higher physical activity is associated with lower serum C-reactive protein (CRP), independent of oral hormone replacement therapy (HRT) status and body fatness, in 133 postmenopausal women using a cross-sectional exploratory design at a university research laboratory. The subjects were 133 postmenopausal women, age 50-73 years, with no evidence of coronary artery disease or diabetes. The main outcome measures were: serum CRP, physical activity as measured by Stanford 7-day activity recall, body fat (both total and regional) as measured by dual energy X-ray absorptiometry (DXA), and anthropometry (waist and hip circumference). Secondary outcome measures included fasting plasma glucose and insulin as well as fasting serum triglycerides, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol. Higher physical activity energy expenditures were significantly associated with lower serum CRP levels (r = -0.18, P = 0.041), independent of oral HRT use, age, smoking behavior, alcohol consumption, aspirin use, and statin use. However, in the complete multivariate model, which included body fat, older ages (P = 0.047), greater trunk fat masses (P < 0.001), any oral HRT use (P < 0.001), and unopposed oral estrogen use (P = 0.012) were the sole independent predictors of higher serum CRP levels. The complete multivariate model accounted for 58% of the variance in serum CRP. We conclude that the association between higher physical activity and lower serum CRP levels is dependent on the lower body fat of the more active women, yet independent of oral HRT use. Future intervention trials should determine whether diet- and exercise-related reductions in body fat may be effective ways to diminish the proinflammatory effects of oral HRT in postmenopausal women.

Gains in hip bone mass from high-impact training are maintained: a randomized controlled trial in children.

OBJECTIVES: We previously reported significant gains in hip and spine bone mass after 7 months of high-impact training in 89 prepubertal children. Our aim in this investigation was to evaluate the bone response to 7 months of "detraining" in this cohort of children. STUDY DESIGN: Seventy-four boys and girls (n = 37 jumpers, n = 37 controls) from the original cohort completed follow-up testing. Bone mineral content (BMC; g) and bone area (BA; cm(2)) of the left proximal femoral neck and lumbar spine (L(1-4)) were assessed by dual-energy x-ray absorptiometry. In addition, anthropometric characteristics, Tanner staging, physical activity, and average dietary calcium intake were assessed. RESULTS: Over 14 months, jumpers maintained 4% greater femoral neck BMC and 4% greater femoral neck BA (P <.05 and P <.01, respectively) than controls. Group differences did not persist at the lumbar spine. CONCLUSION: Gains in both BMC and BA at the femoral neck from high-impact jumping were retained after an equivalent period of detraining. We conclude that this simple exercise may be useful in promoting bone growth at the hip and, thus, enhance peak bone mass.

Seasonal interaction of serum vitamin D concentration and bone density in alpacas.

OBJECTIVE: To evaluate temporal changes in bone mineral density associated with seasonal variation in serum vitamin D, calcium, and phosphorus concentrations in alpacas. ANIMALS: 5 healthy mature neutered male alpacas. PROCEDURE: Metacarpal bone mineral density was measured at 4 times during a year. Each time alpacas were weighed, blood was collected for determination of serum calcium, phosphorus, and vitamin D concentrations, and samples of feed were analyzed for nutrient content. Vitamin D status was determined by use of an assay that measured serum 25-hydroxycalciferol concentration. Effects of changes in serum vitamin D, calcium, and phosphorus concentration and body weight with season on bone mineral density were determined. RESULTS: Bone mineral density, body weight, and serum vitamin D and phosphorus concentrations varied with season. Bone mineral density, serum vitamin D concentration, and body weight also varied among individual alpacas. Serum vitamin D concentration was lower in January than the previous October and increased from May to the following September. The decrease in bone mineral density lagged behind the decrease in serum vitamin D concentration and was lower in May, compared with the previous October. Body weight was lower in May than the previous October or following September. Solar radiation was highest in July and lowest in December. CONCLUSIONS AND CLINICAL RELEVANCE: Seasonal changes in bone mineral density are associated with changes in serum vitamin D concentrations in alpacas. Changes in bone mineral density associated with a decline in serum vitamin D concentration may predispose some alpacas to developing fractures minimal trauma.