Cardiovascular fitness and physical activity in children with and without impaired glucose tolerance.

OBJECTIVE: To examine differences in cardiovascular fitness (VO(2max)) and physical activity levels in overweight Hispanic children with normal glucose tolerance (NGT) vs impaired glucose tolerance (IGT). PARTICIPANTS: A total of 173 overweight (BMI percentile 97.0 +/- 3.1) Hispanic children ages 8-13 years with a family history of type 2 diabetes. METHODS: VO(2max) was measured via a maximal effort treadmill test and open circuit spirometry. Physical activity was determined by questionnaire. Glucose tolerance was established by a 2-h oral glucose challenge (1.75 g of glucose/kg body weight). IGT was defined from an oral glucose tolerance test as a 2-h plasma glucose level > or =140 and <200 mg/dl. RESULTS: IGT was detected in 46 of the 173 participants (approximately 27%); no cases of type 2 diabetes were identified. No significant differences were found between youth with NGT and those with IGT in absolute VO(2max) (2.2 +/- 0.6 vs 2.1 +/- 0.5 l/min), VO(2max) adjusted for gender, age, and body composition (2.2 +/- 0.2 vs 2.1 +/- 0.2 l/min), or recreational physical activity levels (8.7 +/- 8.2 vs 6.9 +/- 6.2 h/week). CONCLUSION: Overweight Hispanic youth with IGT exhibit similar levels of VO(2max) and physical activity compared to their NGT counterparts. Longitudinal analyses are necessary to determine whether fitness/activity measures contribute significantly to diabetes risk over time in this group.

Patellofemoral joint kinetics during squatting in collegiate women athletes.

OBJECTIVE: To characterize the biomechanics of the patellofemoral joint during squatting in collegiate women athletes. DESIGN: Repeated measures experimental design. BACKGROUND: Although squatting exercises are required components of most intercollegiate resistance-training programs and are commonly performed during rehabilitation, the effects of various squatting depths on patellofemoral joint stress have not been quantified. METHODS: Anthropometric data, three-dimensional knee kinematics, and ground reaction forces were used to calculate the knee extensor moment (inverse dynamics approach) in five intercollegiate female athletes during squatting exercise at three different depths (approximately 70 degrees, 90 degrees and 110 degrees of knee flexion). A biomechanical model of the patellofemoral joint was used to quantify the patellofemoral joint reaction force and patellofemoral joint stress during each trial. RESULTS: Peak knee extensor moment, patellofemoral joint reaction force and patellofemoral joint stress did not vary significantly between the three squatting trials. CONCLUSIONS: Squatting from 70 degrees to 110 degrees of knee flexion had little effect on patellofemoral joint kinetics. The relative constancy of the patellofemoral joint reaction force and joint stress appeared to be related to a consistent knee extensor moment produced across the three squatting depths. RELEVANCE: The results of this study do not support the premise that squatting to 110 degrees places greater stress on the patellofemoral joint than squatting to 70 degrees. These findings may have implications with respect to the safe design of athletic training regimens and rehabilitation programs.

Knee strength and lower- and higher-intensity functional performance in older adults.

PURPOSE: This study characterizes the linear relations among knee strength, work capacity, and lower- and higher-intensity measures of functional performance in ambulatory, high-functioning older adults. METHODS: Sixty-two seniors (average age = 73.4 +/- 7.3 yr) participated in the study. Isokinetic measures included the peak flexion/extension torque produced during five continuous repetitions and the total flexion/extension work performed during 20 repetitions (60 degrees x s(-1)). Functional measures included lower-intensity tests (timed 8-foot and 50-foot walking tests at the participants' "normal" pace, and a standing reach task) and higher-intensity tests (a timed 50-foot "brisk" walk, timed chair stands, and a timed stair climb). RESULTS: Isokinetic strength and work capacity measures explained between 41% and 54% of the variance in the higher-intensity functional models and only between 31% and 33% of the variance in the lower-intensity models. The strength of the associations, approximated by the beta coefficients of the strength and work terms, was also greater for the higher-intensity functional tasks. CONCLUSIONS: Further research is warranted to determine whether exercises that increase knee strength and work capacity, improve brisk walking, stair climbing, and chair standing capabilities in older adults.

A randomized trial of weighted vest use in ambulatory older adults: strength, performance, and quality of life outcomes.

BACKGROUND: Lower extremity weakness is a major risk factor for falls and hip fractures. Aging muscle is capable of responding to strengthening techniques. Strategies for providing accessible, inexpensive, safe, and effective strengthening programs for older adults are needed. OBJECTIVE: To evaluate whether use of a weighted vest improved strength, physical performance, markers of bone turnover, or health-related quality of life. DESIGN: A 27-week randomized, controlled, unmasked clinical trial. The primary outcome was peak isokinetic knee extensor strength at follow-up, adjusted for baseline strength. SETTING: Home-based program. PARTICIPANTS: A total of 62 women and men, mean age 74 years. INTERVENTIONS: Subjects were randomized to: no vest (n = 21), 3% body weight (BW) vest (n = 19), or 5% BW vest (n = 22). The vest is a nylon garment with pockets that are loaded with adjustable weights. The vest was prescribed for 2 hours daily, 4 days per week. No specific physical activities were mandated. MEASUREMENTS: All measures were made at baseline and 27 weeks. These included: knee strength and endurance by isokinetic dynamometer; timed physical performance tests; serum osteocalcin and urinary N-telopeptides; and health-related quality of life scales. RESULTS: Follow-up values of muscular strength and endurance, physical performance, bone turnover markers, and health-related quality of life did not differ by treatment assignment. The final study visit was attended by 19 (90%), 15 (80%), and 20 (91%) of the control, 3%, and 5% groups, respectively. Three permanent discontinuations of vest use occurred. CONCLUSIONS: Weighted vest use did not result in improvement in multiple domains of strength and function and did not affect bone turnover markers. We conclude that the training stimulus afforded by the vest (at the dosage tested) was below the required amount to produce strength gains or bone stimulation.

Adaptations of immature trabecular bone to exercise and augmented dietary protein.

Exercise and diet synergistically influence bone, but it remains unclear whether augmenting dietary protein intake during moderate exercise has a beneficial or negative effect on immature bone mechanical integrity. Thus, we examined lumbar vertebral bodies (L6) and femoral necks (FN) in trained and untrained rats fed either a recommended protein (15%) or higher protein (30%) diet. Male Wistar rats (8 wk old) were assigned to one of two exercise groups (high protein exercise [HPE], recommended protein exercise [RPE], run 3 d.wk-1 on a motor-driven treadmill at approximately 80% of their maximum oxygen capacity) or to one of two sedentary caged-control groups (high protein control [HPC], recommended protein control [RPC]. After 8 wk, in the HPE group, FN maximum normal stress was significantly greater than all other groups, and FN maximum load and energy at maximum load (per unit body mass) were significantly greater than the sedentary control groups. L6 stress at the proportional limit and initial-maximum stress did not differ among groups, but L6 percent ash was significantly greater in the HPE and RPC groups. Thus, coupling high dietary protein with moderate exercise can produce positive effects on immature rat femoral neck mechanical properties and structure.

Long-term, high-fat-sucrose diet alters rat femoral neck and vertebral morphology, bone mineral content, and mechanical properties.

Short-term exposure to diets high in fat and sucrose can induce hyperinsulinemia, affect calcium and magnesium metabolism, and alter bone mineralization and mechanical properties. The current study focused on the morphological and structural changes that result from long-term exposure to a high-fat sucrose (HFS) diet. Inbred, female Fischer 344 rats were assigned randomly to a low-fat, complex-carbohydrate (LFCC) diet group or a HFS diet for 24 months. At the end of the 2 years, each femoral neck (FN) was tested to failure in cantilever-bending, the sixth lumbar vertebra (L6) was tested in compression, and geometrical characteristics of the bones were determined. Although the HFS rats were significantly fatter and heavier than the LFCC rats, the HFS L6 had a significantly smaller average cross-sectional area. When L6 structural properties were normalised with respect to body mass, the HFS L6 had significantly lower loads, energies, and stiffnesses. The HFS L6 stress and strain energy density values were also significantly less than the LFCC L6. Compared to the LFCC FN, the HFS FN had a smaller cortical shell and larger trabecular core. The HFS FN also had significantly lower mass-normalised loads, energies, and stiffnesses. These results suggest that a long-term HFS diet has a significant adverse effect on rat bone morphology and mechanics.

Adaptations of immature trabecular bone to moderate exercise: geometrical, biochemical, and biomechanical correlates.

Strenuous endurance exercise can adversely affect the mechanical integrity of immature bone, but it is unclear whether a more moderate exercise regimen would have a positive effect. Thus, to investigate the response of immature trabecular bone to moderate exercise, we randomly assigned female Sprague-Dawley rats (8 weeks old) to either a basal-control, exercise, or age-matched control group. The basal-control rats were killed at 8 weeks of age, while the other two groups were killed at 18 weeks of age. Between 8 and 18 weeks, one group remained sedentary, while another group was trained progressively on a motor-driven treadmill at a moderate level of intensity. Rat femoral necks (FN) were tested in cantilever bending to failure, and the sixth lumbar vertebral bodies (L6) were compressed to 50% of their initial height. Both tissues were analyzed for calcium, hydroxyproline, and collagen-crosslinking concentrations, and for changes in geometry. The adrenal mass per unit body mass was significantly greater in the exercised group, compared to the age-matched controls. L6 calcium content, compressional stress, and elastic modulus were significantly less in the exercise group as compared to the age-matched control group. Nonreducible collagen crosslinks (hydroxylysylpyridinoline [HP] and lysylpyridinoline [LP]) were significantly greater in the older exercise and age-matched control L6 and FN. In the weightbearing FN--but not L6--the LP concentration of the exercise group was significantly greater than the age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet-related changes in mechanical properties of rat vertebrae.

High fat and sucrose (HFS) diets may induce glucose intolerance, alter calcium metabolism, and lead to deficits in bone mineralization, development, and mechanical properties. To determine the mechanical and structural consequences of a HFS diet on rapidly growing vertebrae, female Sprague-Dawley rats (8 wk) were assigned randomly (2:1) either to a control group (n = 20) fed a low-fat complex-carbohydrate diet or an experimental group (n = 10) fed a HFS diet for 10-12 wk. The sixth lumbar vertebral body (L6) was isolated from the pedicles, morphological measures were taken, and compression was tested at a fast strain rate, while immersed in a warmed (37 degrees C) isotonic physiological buffer solution. No significant difference in body mass existed between HFS and control groups; nevertheless, HFS L6 cross-sectional areas, lengths, and volumes were significantly smaller than controls. The HFS L6 also had significantly lower mechanical properties, including initial maximum load, energy at initial maximum load, and strain energy density at initial maximum load. Diets high in sucrose and fat content have been associated with changes in calcium metabolism, and the results of the current study suggest that in immature vertebrae, a HFS diet may adversely affect vertebral body mechanical integrity and strength.

Structural and mechanical adaptations of immature trabecular bone to strenuous exercise.

Effects of strenuous exercise on immature bone were examined in two clinically important regions, femoral neck (FN) and lumbar vertebra (L6). Female Sprague-Dawley rats (n = 20, 8 wk of age, 150-170 g) were exercised progressively 5 days/wk for approximately 1 h/day for 10 wk at 75-80% of maximum oxygen capacity on a motor-driven treadmill. Caged age-matched rats served as controls (n = 20). Rat FNs were tested in cantilever bending, and vertebral bodies were compressed to 50% of their initial height at a fast strain rate. In response to the strenuous exercise, the relative area of the FN trabecular core increased significantly at the expense of the cortical shell. With that structural change, the exercised FN had significantly less energy to proportional limit than controls. The FN material properties (normal stresses at proportional limit and maximum) were significantly diminished after 10 wk of strenuous exercise. At the same time, no differences were found in vertebral geometry or structural and material properties. In the immature rate, the differential responses of the FN vs. L6 may relate to load history rather than a general systemic response to the strenuous exercise.

Interactive effects of nutrition, environment, and rat-strain on cortical and vertebral bone geometry and biomechanics.

Because of differences between rodent experiments on USSR and USA spaceflights, the present experiment was designed to generate comparative data about the sensitivity of cortical (humerus) and vertebral (T7) bones to cage environment, diet, and rat-strain differences. For 2 weeks (48-62 d), male Taconic-Sprague-Dawley and Czechoslovakian-Wistar rats were maintained in flight-simulation cages (1 rat/cage = USA, 10 rats/cage = USSR) and fed either USSR or USA diets. All rats increased (greater than 60%) their body mass during the two weeks, and there were no differences among humeral lengths for the different groups. Rats in USSR cages had significantly larger total and medullary cross-sectional areas for the humerus, and the cross-sectional areas of T7 of Taconic rats were greater than the Czech rats. USSR caging resulted in significantly enhanced structural and material properties in rat humeri, while the USA diet produced significantly greater humeral maximum and failure loads. The flexural rigidity of the Czech-rat humeri was significantly greater than the Taconic rats. Humeri from Czech rats on the USA diet had significantly greater material properties in the elastic-loading region than did Taconic rats on the USSR diet. Further, the humeral failure loads of Taconic rats on the USSR diet were more adversely affected by USA cages than were the Czech rats on the USSR diet. In T7 vertebrae, no significant structural differences were found among the groups, but material properties were influenced by all three factors; generally, the combination of factors that produced the significantly greater T7 material properties was: USSR caging, USSR diet, and the Czech strain of rat.

Spaceflight effects on biomechanical and biochemical properties of rat vertebrae.

The biomechanical and biochemical responses of lumbar vertebral bodies during a 12.5-day spaceflight (Cosmos 1887 biosatellite) were determined for rapidly growing rats (90-day-old, Czechoslovakian-Wistar). By use of age-matched vivarium controls (normal cage environment) and synchronous controls (simulated flight conditions), as well as a basal control group (killed before lift-off on the 1st day of flight), the combined influences of growth and space-flight could be examined. Centra of the sixth lumbar vertebrae (L6) were compressed to 50% strain at a fast strain rate while immersed in physiological buffer (37 degrees C). The body masses of vivarium and synchronous controls were significantly heavier than either the flight or basal controls. The flight group had an L6 vertebral body compressional stiffness that was 39% less than the vivarium controls, 47% less than the synchronous control, and 16% less than the basal controls. In addition, the average initial maximum load of the flight L6 was 22% less than vivarium controls and 18% less than the synchronous controls, whereas the linear compressional load of the flight group averaged 34% less than the vivarium and 25% less than the synchronous groups. The structural properties of the vertebrae from the 12.5-day-younger basal group closely resembled the flight vertebrae. Calcium, phosphorous, and hydroxyproline concentrations were not significantly different among the groups. Nevertheless, the lack of strength and stiffness development in spaceflight, coupled with a smaller proportion of mature hydroxypyridinoline cross-links, suggested that the 12.5 days of spaceflight slowed the maturation of trabecular bone in the vertebral bodies of rapidly growing rats.

Biomechanical and biochemical changes in lumbar vertebrae of rapidly growing rats.

Although growth-related biochemical, morphological, and biomechanical properties of rat cortical bone have been investigated, similar properties of immature rat vertebral bone have not been well characterized. Information about these properties is necessary, however, for comparative analyses of rat vertebral bone adaptation. Thus a method was developed to characterize growth-related differences in immature rat vertebral bone. The centra of sixth lumbar vertebrae (L6) of 44-day-old and 54-day-old male Sprague-Dawley rats were compressed to 50% of their initial height at a 50%/s strain rate while immersed in a potassium phosphate buffer solution (pH 7.4, 37 degrees C). Structural and material properties for the 54-day-old group that were significantly greater than those for the 44-day-old group included load, stress, and energy at the proportional limit; initial maximum load and stress; and load and energy at 50% strain. The structural stiffness of L6, as well as its elastic modulus, was significantly greater in the older animals. The calcium concentrations and calcium-to-collagen ratios in 54-day-old vertebrae were significantly greater than in younger animals. These results indicated that the specimen preparation and testing protocol developed for rat vertebrae produced reliable biomechanical results, even with the relatively small size of rat vertebrae bodies, and that the quantity and quality of the matrix of immature rat vertebral bone changed significantly during this period of rapid growth. Our test protocol will be useful for investigating the responses of rat vertebral bone to exercise, disease, and spaceflight.