Biomedical subjects

K M Winters

Publications and source records attributed to K M Winters.

4 recordsLinked to original sources

PubMed2000

Body composition predicts bone mineral density and balance in premenopausal women.

Low bone mineral density (BMD) and poor stability both contribute to increased risk of fractures associated with a fall. Our aim in this cross-sectional study was to determine the anthropometric and/or performance variables that best predicted BMD and stability in women. BMD, body composition, muscle strength, muscle power, and dynamic stability were evaluated in 61 women (age 40 +/- 4 years; % body fat 27% +/- 5%). In correlation analyses, BMD at all sites was significantly related to height, lean mass, strength, and leg power (r2 = 0.25-0.49). Significant inverse relationships were found between all independent variables and dynamic stability (r2 = 0.23-0.52). In stepwise regression, lean mass independently predicted BMD at the femoral neck (R2 = 0.20), total hip (R2 = 0.24), and whole body (R2 = 0.17), whereas hip abductor torque predicted 23% of the variance in trochanter BMD and added 6% to the variance in total hip BMD. Leg power was the only predictor of spine BMD (R2 = 0.14). Fat and lean mass both independently predicted poor performance on postural stability, with fat mass contributing 31% of the total variance (R2 = 0.38). In conclusion, we found lean mass to be a robust predictor of BMD in premenopausal women. Furthermore, both hip abductor torque and leg power independently predicted BMD at clinically relevant fracture sites (hip and spine). The finding that higher fat mass contributes to the majority of the variance in poor stability indicates that greater fat mass may compromise stability and, thus, increase fall risk in heavier individuals.

Absorptiometry, Photon↗

PubMed2000

Long-term exercise using weighted vests prevents hip bone loss in postmenopausal women.

BACKGROUND: Bone mineral density (BMD) is a primary risk factor for hip fracture. We studied the effect of long-term weighted vest plus jumping exercise on hip BMD in postmenopausal women as a strategy for reducing hip fracture risk. METHODS: Eighteen postmenopausal women (age = 64.1 +/- 1.6 years at baseline, 69.9 +/- 1.6 years at post-testing) who had participated in a 9-month exercise intervention volunteered for the long-term trial. Nine of the original group engaged in weighted vest plus jumping exercise three times per week for 32 weeks of the year over a period of 5 years. Nine of the original controls were active but not enrolled in the exercise program. BMD of the proximal femur was assessed by dual energy x-ray absorptiometry at baseline and after 5 years. RESULTS: At baseline, groups were similar for age, weight, height, years past menopause, and BMD of the femoral neck, trochanter, and total hip. At follow-up, differences in BMD at all regions of the hip were higher in exercisers than controls. For exercisers, changes in BMD were + 1.54% +/- 2.37%, -0.24% +/- 1.02%, and -0.82% +/- 1.04% (means + SE) at the femoral neck, trochanter, and total hip, respectively; controls decreased at all sites (-4.43% +/- 0.93%. 3.43% +/- 1.09%, and -3.80% +/- 1.03%, respectively). CONCLUSIONS: A 5-year program of weighted vest plus jumping exercise maintains hip BMD by preventing significant bone loss in older postmenopausal women. Furthermore, this particular program appears to promote long-term adherence and compliance, as evidenced by the commitment of the exercisers for more than 5 years.

Absorptiometry, Photon↗

PubMed2000

Detraining reverses positive effects of exercise on the musculoskeletal system in premenopausal women.

We studied the effects of a 6-month withdrawal of exercise after 12 months of progressive impact (jump) plus lower body resistance training on risk factors for hip fracture in premenopausal women (age, 30-45 years). Twenty-nine women completed the 12-month training and detraining programs and were compared with 22 matched controls. Bone mineral density (BMD) at the greater trochanter, femoral neck, lumbar spine, and whole body and body composition (% body fat) were measured by dual energy X-ray absorptiometry (DXA; Hologic QDR-1000/W). Knee extensor and hip abductor strength were assessed via isokinetic dynamometry (Kin-Com 500H); maximum leg power was tested using a Wingate Anaerobic Power test; and dynamic postural stability was measured on a stabilimeter (Biodex). All measurements were conducted at baseline, 12 months and 18 months with an additional midtraining measurement of BMD. Exercisers trained three times per week in a program of 100 jumps and 100 repetitions of resistance exercises at each session. Intensity was increased using weighted vests to final values of 10% and 13% of body weight (BW) for jump and resistance exercises, respectively. Differences between groups from training were analyzed by repeated measures analysis of covariance (ANCOVA), adjusted for baseline values. Detraining effects were analyzed by comparing the changes from training with the changes from detraining using repeated measures analysis of variance (ANOVA). Baseline values were not significantly different between exercisers and controls. Percent change over the training period was significantly greater in the exercise group than in the control group at the greater trochanter (2.7 +/- 2.5% vs. 0.8 +/- 0.8%, respectively; p < 0.01) and approached significance at the femoral neck (1.2 +/- 3.2% vs. -0.3 +/- 1.9%, respectively; p = 0.06). Significant improvements also were observed in exercisers versus controls for strength and power with exercisers increasing 13-15% above controls, whereas stability was not different between groups. After 6 months of detraining, BMD and muscle strength and power decreased significantly toward baseline values, whereas control values did not change. We conclude that the positive benefits of impact plus resistance training on the musculoskeletal system in premenopausal women reverse when training is withdrawn. Therefore, continued training, perhaps at a reduced frequency and intensity, is required to maintain the musculoskeletal benefit from exercise that may lower fracture risk in later life.

Adult↗

PubMed1996

Bone density and cyclic ovarian function in trained runners and active controls.

This study was conducted to determine whether rigorous exercise training adversely affects ovarian hormone levels and bone health in cyclically menstruating trained runners. Ovarian hormones, bone mineral density (BMD), body composition, 3-d diet records, 3-d estimated energy expenditure, and menstrual histories were evaluated in 10 trained collegiate runners and 10 moderately active controls. The trained runners had lower total body calcium per kg of soft lean tissue measured by DEXA (P = 0.045). Half of the trained runners had experienced stress fractures compared with only one of the moderately active controls. The trained runners' lumbar (L2-L4) BMD (1.178 g.cm-2) was not significantly different from that of the active controls (1.283 g.cm-2) (P = 0.074) but, for all subjects combined, there wasa significant inverse relation between L2-L4 BMD and distance run per week (P = 0.036). Further, adding age, body weight, percent body fat, daily energy intake, and daily calcium intake to a stepwise multiple regression analysis did not significantly improve predictive precision. The trained runners consumed nearly twice the amount of calcium (1089 mg.d-1 vs 641 mg.d-1, respectively; P = 0.036), while intake of other nutrients did not differ significantly between groups. Urinary estrone conjugates (E1C) were lower in the trained runners during the early follicular phase (P = 0.028), while pregnanediol-3-glucuronide (PdG) was not significantly different between groups during the luteal phase (P = 0.213). Thus, it appears that lower estrogen production, especially during the early follicular phase, and not progesterone, is associated with lower whole body calcium per kg of soft lean tissue and, probably, L2-L4 BMD. Results of this study also suggest that regular menstrual cycles do not imply normal ovarian hormone function in young women who are engaged in either recreational or competitive running.

Bone Density↗