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INTRODUCTION Although vitamin D is intimately involved in bone metabolism, the relationship between vitamin D status, as measured by serum total 25-hydroxyvitamin D [25(OH)D] concentration, and bone mineral density (BMD) is weak, particularly in non-White populations. Measurement of bioavailable 25(OH)D has been suggested as a better indicator of vitamin D status than total 25(OH)D concentration. To date, the bioavailable 25(OH)D biomarker has been explored minimally in athletic populations. The purpose of this study was to investigate the relationship between total and bioavailable 25(OH)D concentrations and BMD in collegiate athletes. METHODS NCAA Division 1 basketball and swimming athletes served as study participants (n = 53; 28 females, 25 males; 28 basketball players, 25 swimmers). All participants completed dual energy x-ray absorptiometry (DXA) scans for analysis of BMD, blood draws for vitamin D measures, and diet/lifestyle questionnaires. RESULTS Overall, total 25(OH)D was 80.0 + 13.9 nmol/L and bioavailable 25(OH)D was 6.0 ± 1.9 nmol/L. There was strong disagreement between total 25(OH)D and bioavailable 25(OH)D concentrations (κ = -0.299; r = -0.129) (p = 0.100); 53% of total participants and 77% of Black participants were classified differently (low vs. normal vitamin D status) based on total and bioavailable 25(OH)D criteria. Black participants had significantly lower total 25(OH)D and higher bioavailable 25(OH)D concentrations than White participants (59.5 vs. 102.5 nmol/L and 7.9 vs. 5.4 nmol/L, respectively) (p < 0.001). Total 25(OH)D and total BMD were not correlated, but bioavailable 25(OH)D and total BMD demonstrated a positive correlation (r = 0.618, p < 0.01). CONCLUSIONS These results suggest that bioavailable 25(OH)D concentration may be a better clinical measure of vitamin D status than total 25(OH)D in collegiate athletes as related to BMD, particularly in Black athletes. Further research on the utility of the bioavailable 25(OH)D biomarker in athletes is needed.

Background Human milk contains appetite-regulating hormones that may influence infant growth and obesity risk. Research aims We evaluated whether leptin, peptide tyrosine-tyrosine (PYY), glucagon-like peptide-1 (GLP-1), and ghrelin concentrations in human milk (1) changed during feeding (from foremilk to hindmilk) and during the first 6 months of infancy; (2) were explained by maternal factors; and (3) were associated with infant anthropometrics and growth. Methods Mother–infant dyads ( N = 22) participated. Samples of foremilk and hindmilk at 1 month postpartum were collected and analyzed for leptin, PYY, GLP-1, and ghrelin via radioimmunoassay and milkfat percentage estimated via creamatocrit. Samples were also collected in mothers ( n = 15) who breastfed through 6 months. Anthropometrics were obtained on all mother–infant dyads at 1 month and all infants at 6 months and 12 months. Results At 1 month, milk GLP-1 and milkfat concentration increased from foremilk to hindmilk ( p ≤ .05) while leptin and PYY concentrations remained stable during feeding. Milk hormone concentrations and milkfat tended to decline overtime, with lower leptin, PYY, and ghrelin at 6 months versus 1 month ( p < .05). At 1 month, milk leptin and milkfat content were associated with maternal markers of adiposity ( r = 0.49–0.78, p < .001); whereas, milk PYY was correlated with maternal serum PYY concentration ( r = 0.672, p = .001). Average 1-month milk concentrations of GLP-1 and leptin were negatively associated with weight-for-age z-scores at 6 months ( r = −0.46, p < .05) and 12 months ( r = −0.49, p < .05), respectively. Conclusion The content of certain appetite-regulating hormones in human milk may be influenced by maternal factors and play a role in infant growth; much needs to be learned about their role in the obesity protection of breastfed infants.

Purpose of Review: Sports nutrition guidelines typically state that athletes desiring weight gain follow a regimen that includes increasing energy intake by ~ 300–500 kcal/day with an emphasis on adequate protein and carbohydrate and judicious inclusion of energy-dense foods, in combination with rigorous resistance training. This regimen is thought to promote weekly gains of ~ 0.45 kg (1 lb), mostly as lean body mass (LBM). This review summarizes the evidence supporting these intentional weight gain regimens in athletes. Recent Findings: Although some research has been conducted in the past 5 years, research on intentional weight gain is lacking. Summary: Currently, available data suggests that weekly weight gain of 0.45 kg (1 lb), primarily as LBM, may be difficult for some athletes to achieve. Available evidence, however, suggests that commonly recommended strategies to promote calorie surplus, including consuming larger portions, incorporating energy-dense foods, and prioritizing liquid over solid foods, may prove helpful. Accepted version

This study evaluated the changes in bone mineral density (BMD) and serum lipids across the first postpartum year in lactating women compared to never-pregnant controls, and the influence of physical activity (PA). The study also explored whether N-telopeptides, pyridinoline, and deoxypyridinoline in urine serve as biomarkers of bone resorption. A cohort of 18 initially lactating postpartum women and 16 never pregnant controls were studied. BMD (dual energy X-ray absorptiometry), serum lipid profiles, and PA (Baecke PA Questionnaire) were assessed at baseline (4–6 weeks postpartum), 6 months, and 12 months. Postpartum women lost 5.2 ± 1.4 kg body weight and BMD decreased by 1.4% and 3.1% in the total body and dual-femur, respectively. Furthermore, BMDdid not show signs of rebound. Lipid profiles improved, with increases in high-density lipoprotein-cholesterol (HDL-C) and decreases in low-density lipoprotein cholesterol (LDL-C) and the cholesterol/HDL-C ratio at 12 months (vs. baseline). These changes were not influenced by lactation, but the fall the Cholesterol/HDL-C ratio was influenced by leisure-time (p = 0.051, time X group) and sport (p = 0.028, time effect) PA. The decrease in BMD from baseline to 12 months in total body and dual femur, however, was greater in those who continued to breastfeed for a full year compared to those who stopped at close to 6 months. Urinary markers of bone resorption, measured in a subset of participants, reflect BMD loss, particularly in the dual-femur, and may reflect changes bone resorption before observed changes in BMD. Results provide support that habitual postpartum PA may favorably influence changes in serum lipids but not necessarily BMD. The benefit of exercise and use of urinary biomarkers of bone deserves further exploration. Published version

Sports nutrition guidelines typically state that athletes desiring weight gain follow a regimen that includes increasing energy intake by ~ 300-500 kcal/day with an emphasis on adequate protein and carbohydrate and judicious inclusion of energy-dense foods, in combination with rigorous resistance training. This regimen is thought to promote weekly gains of ~ 0.45 kg (1 lb), mostly as lean body mass (LBM). This review summarizes the evidence supporting these intentional weight gain regimens in athletes.Although some research has been conducted in the past 5 years, research on intentional weight gain is lacking. Currently, available data suggests that weekly weight gain of 0.45 kg (1 lb), primarily as LBM, may be difficult for some athletes to achieve. Available evidence, however, suggests that commonly recommended strategies to promote calorie surplus, including consuming larger portions, incorporating energy-dense foods, and prioritizing liquid over solid foods, may prove helpful.

Low energy availability (EA) poses severe consequences to athlete performance and overall health. Suppressed resting metabolic rate (RMR) has been observed during periods of low EA. Thus, it has been suggested that the ratio of RMR measured via indirect calorimetry to predictive RMR using a standard predictive equation (RMR ratio) may be a useful assessment of EA in athletes. This review evaluated the use of RMR ratio as a surrogate marker for low EA in athletes and compared methodologies for measuring RMR ratio.Decreased RMR ratio in recent studies often correlates with signs of low EA; however, athletes with less severe cases of energy deficiency may not present with a low RMR ratio. Additionally, the methodology for RMR ratio measurements lacks standardization and varies in recent studies. Use of RMR ratio has promise as a complementary EA measurement when used in combination with other assessment tools.

Purpose This investigation had three purposes: (a) to evaluate changes in hydration biomarkers in response to a graded rehydration intervention (GRHI) following 3 days of water restriction (WR), (b) assess within-day variation in urine concentrations, and (c) quantify the volume of fluid needed to return to euhydration as demonstrated by change in Ucol. Methods 115 adult males and females were observed during 1 week of habitual fluid intake, 3 days of fluid restriction (1000 mL day−1), and a fourth day in which the sample was randomized into five different GRHI groups: no additional water, CON; additional 500 mL, G+0.50; additional 1000 mL, G+1.00; additional 1500 mL, G+1.50; additional 2250 mL, G+2.25. All urine was collected on 1 day of the baseline week, during the final 2 days of the WR, and during the day of GRHI, and evaluated for urine osmolality, color, and specific gravity. Results Following the GRHI, only G+1.50 and G+2.25 resulted in all urinary values being significantly different from CON. The mean volume of water increase was significantly greater for those whose Ucol changed from > 4 to

Background: The iodine status of the US population is considered adequate, but subpopulations remain at risk for iodine deficiency and a biomarker of individual iodine status has yet to be determined. The purpose of this study was to determine whether a 3 day titration diet, providing known quantities of iodized salt, is reflected in 24 h urinary iodine concentration (UIC), serum iodine, and thyroglobulin (Tg). Methods: A total of 10 participants (31.3 ± 4.0 years, 76.1 ± 6.3 kg) completed three, 3 day iodine titration diets (minimal iodine, US RDA, (United States Recommended Daily Allowance), and 3× RDA). The 24 h UIC, serum iodine, and Tg were measured following each diet. The 24 h UIC and an iodine-specific food frequency questionnaire (FFQ) were completed at baseline. Results: UIC increased an average of 19.3 μg/L for every gram of iodized salt consumed and was different from minimal to RDA (p = 0.001) and RDA to 3× RDA diets (p = 0.04). Serum iodine was different from RDA to 3× RDA (p = 0.006) whereas Tg was not responsive to diet. Baseline UIC was associated with iodine intake from milk (r = 0.688, p = 0.028) and fish/seafood (r = 0.646, p = 0.043). Conclusion: These results suggest that 24 h UIC and serum iodine may be reflective of individual iodine status and may serve as biomarkers of iodine status.

Older adults are frequently cited as an at-risk population for vitamin D deficiency that may in part be due to decreased cutaneous synthesis, a potentially important source of cholecalciferol (vitamin D3). Previous studies found that cutaneous D3 production declines with age, however, most studies have been conducted ex vivo or in the photobiology lab. The purpose of this study was to characterize the response of vitamin D metabolites following a 30-min bout of sun exposure (15-min each to the dorsal and ventral sides) at close to solar noon in younger and older adults. Methods: 30 healthy individuals with skin type II/III were recruited, a younger cohort, aged 20&ndash, 37 (n = 18) and an older cohort (n = 12), age 51&ndash, 69 years. Exposure was at outer limits of sensible sun exposure designed to enhance vitamin D synthesis without increasing risk of photo ageing and non-melanoma skin cancer. Serum D3 concentration was measured at baseline, 24, 48 and 72 h post-exposure. Serum 25(OH)D was measured at baseline and 72 h post-exposure plus 168 h post-exposure in the older cohort. Results: D3 increased in response to sun exposure (time effect, p = 0.002) with a trend for a difference in D3 between cohorts (time*group, p = 0.09). By regression modeling of continuous data, age accounted for 20% of the variation in D3 production. D3 production decreased by 13% per decade. Despite changes in D3, however, serum 25(OH)D did not change from baseline to 72 or 168 h post exposure (p &gt, 0.10). Conclusions: Serum D3 concentration increased significantly in response to outdoor sun exposure in younger and older adults. While ageing may dampen cutaneous synthesis, sunlight exposure is still a significant source of vitamin D3.

Thyroid disease is common in the general population, especially in women, and also may be prevalent among athletes. Autoimmune disorders are the most common cause of thyroid disorders in countries with iodine-fortification programs; however, thyroid dysfunction can be brought on by nutritional factors, including insufficient energy intake and iodine, selenium, iron, and vitamin D deficiency. Additionally, strenuous exercise may be associated with transient alterations in thyroid hormones. While the development of thyroid related disorders has the potential to impact health and peak performance, typical clinical manifestations are highly variable, lack specificity, and are frequently confused with other health problems. The assessment process should focus on anthropometric changes, biochemical tests (thyroid panel), personal and family history, examination for appropriate signs and symptoms, and diet and environmental assessment that includes adequacy of energy, iodine, iron, selenium, and vitamin D intake/status along with excess stress and exposure to environmental contaminants and dietary goitrogens.

Some dietary supplements are recommended to athletes based on data that supports improved exercise performance. Other dietary supplements are not ergogenic per se, but may improve health, adaptation to exercise, or recovery from injury, and so could help athletes to train and/or compete more effectively. In this review, we describe several dietary supplements that may improve health, exercise adaptation, or recovery. Creatine monohydrate may improve recovery from and adaptation to intense training, recovery from periods of injury with extreme inactivity, cognitive processing, and reduce severity of or enhance recovery from mild traumatic brain injury (mTBI). Omega 3-fatty acid supplementation may also reduce severity of or enhance recovery from mTBI. Replenishment of vitamin D insufficiency or deficiency will likely improve some aspects of immune, bone, and muscle health. Probiotic supplementation can reduce the incidence, duration, and severity of upper respiratory tract infection, which may indirectly improve training or competitive performance. Preliminary data show that gelatin and/or collagen may improve connective tissue health. Some anti-inflammatory supplements, such as curcumin or tart cherry juice, may reduce inflammation and possibly delayed onset muscle soreness (DOMS). Beta-hydroxy beta-methylbutyrate (HMB) does not consistently increase strength and/or lean mass or reduce markers of muscle damage, but more research on recovery from injury that includes periods of extreme inactivity is needed. Several dietary supplements, including creatine monohydrate, omega 3-fatty acids, vitamin D, probiotics, gelatin, and curcumin/tart cherry juice could help athletes train and/or compete more effectively.

Vitamin D is a unique vitamin with hormone actions. Synthesized cutaneously from UVB light or derived from the diet, vitamin D is essential for maintaining bone health and calcium homeostasis. Vitamin D is transported in the circulation bound to vitamin D-binding protein (DBP). The active form of vitamin D, 1,25(OH)2D, binds to the vitamin D receptor (VDR), a ligand-activated transcription factor, and this allows modulation of gene expression.

Background: Iodine deficiency is not seen as a public health concern in the US. However certain subpopulations may be vulnerable due to inadequate dietary sources. The purpose of the present study was to determine the dietary habits that influence iodine status in young adult men and women, and to evaluate the relationship between iodine status and thyroid function. Methods: 111 participants (31.6 &plusmn, 0.8 years, 173.2 &plusmn, 1.0 cm, 74.9 &plusmn, 1.7 kg) provided 24 h urine samples and completed an iodine-specific Food Frequency Questionnaire (FFQ) for assessment of urinary iodine content (UIC) as a marker of iodine status and habitual iodine intake, respectively. Serum Thyroid Stimulating Hormone (TSH) concentration was evaluated as a marker of thyroid function. Spearman correlational and regression analysis were performed to analyze the associations between iodine intake and iodine status, and iodine status and thyroid function. Results: 50.4% of participants had a 24 h UIC &lt, 100 &micro, g/L). Dairy (r = 0.391, p &lt, 0.000) and egg intake (r = 0.192, p = 0.044) were the best predictors of UIC, accounting for 19.7% of the variance (p &le, 0.0001). There was a significant correlation between UIC and serum TSH (r = 0.194, p &lt, 0.05) but TSH did not vary by iodine status category (F = 1.087, p = 0.372). Discussion: Total dairy and egg intake were the primary predictors of estimated iodine intake, as well as UIC. Iodized salt use was not a significant predictor, raising questions about the reliability of iodized salt recall. These data will be useful in directing public health and clinical assessment efforts in the US and other countries.

Some track-and-field athletes implement special diets aiming to improve health and/or performance. An evidence-based approach to any diet is recommended to minimize the risks associated with unnecessary dietary restriction, which may potentially do more harm than good. Four prevalent diets are reviewed in this study: (a) gluten-free; (b) low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP); (c) vegetarian; and (d) fasting diets. Recently, gluten-free diets and low FODMAP diets have emerged as novel regimes thought to improve gastrointestinal health and reduce the risk of exercise-associated gastrointestinal symptoms. No direct beneficial outcomes have been associated with avoiding gluten for clinically healthy athletes. Indirectly, a gluten-free diet is associated with other dietary changes, particularly FODMAP reduction, which may improve adverse gastrointestinal symptoms. Vegetarian diets can optimally support athletic demands. However, attention is required to ensure adequate energy and intake of specific nutrients that are less abundant or less well absorbed from plant sources. Finally, fasting is a long-standing concept that is undertaken on a voluntary and obligatory basis. Despite limited supporting research, voluntary fasting is a popular alternative to conventional diets perceptually offering health and body composition benefits. Strict obligatory fasting guidelines likely require the implementation of tailored nutrition strategies to help athletes cope with athletic demands. Overall, a multitude of factors influence adherence to special diets. Even when adherence to a special diet is a necessity, education and advice from an accredited dietitian/nutritionist are recommended for track-and-field athletes to optimize nutrition for health and performance.

Nutrition assessment is a necessary first step in advising athletes on dietary strategies that include dietary supplementation, and in evaluating the effectiveness of supplementation regimens. Although dietary assessment is the cornerstone component of the nutrition assessment process, it should be performed within the context of a complete assessment that includes collection/evaluation of anthropometric, biochemical, clinical, and environmental data. Collection of dietary intake data can be challenging, with the potential for significant error of validity and reliability, which include inherent errors of the collection methodology, coding of data by dietitians, estimation of nutrient composition using nutrient food tables and/or dietary software programs, and expression of data relative to reference standards including eating guidance systems, macronutrient guidelines for athletes, and recommended dietary allowances. Limitations in methodologies used to complete anthropometric assessment and biochemical analysis also exist, as reference norms for the athlete are not well established and practical and reliable biomarkers are not available for all nutrients. A clinical assessment collected from history information and the nutrition-focused physical exam may help identify overt nutrient deficiencies but may be unremarkable in the well-trained athlete. Assessment of potential food-drug interactions and environmental components further helps make appropriate dietary and supplement recommendations. Overall, the assessment process can help the athlete understand that supplement intake cannot make up for poor food choices and an inadequate diet, while a healthy diet helps ensure maximal benefit from supplementation. Establishment of reference norms specifically for well-trained athletes for the nutrition assessment process is a future research priority.

Understanding the dynamic nature of energy balance, and the interrelated and synergistic roles of diet and physical activity (PA) on body weight, will enable nutrition educators to be more effective in implementing obesity prevention education. Although most educators recognize that diet and PA are important for weight management, they may not fully understand their impact on energy flux and how diet alters energy expenditure and energy expenditure alters diet. Many nutrition educators have little training in exercise science; thus, they may not have the knowledge essential to understanding the benefits of PA for health or weight management beyond burning calories. This paper highlights the importance of advancing nutrition educators' understanding about PA, and its synergistic role with diet, and the value of incorporating a dynamic energy balance approach into obesity-prevention programs. Five key points are highlighted: (1) the concept of dynamic vs. static energy balance; (2) the role of PA in weight management; (3) the role of PA in appetite regulation; (4) the concept of energy flux; and (5) the integration of dynamic energy balance into obesity prevention programs. The rationale for the importance of understanding the physiological relationship between PA and diet for effective obesity prevention programming is also reviewed.

The study objective was to validate a food frequency and lifestyle questionnaire (FFLQ) to assess vitamin D intake and lifestyle factors affecting status. Methods: Data collected previously during the fall (n = 86), winter (n = 49), and spring (n = 67) in collegiate-athletes (Study 1) and in active adults (n = 123) (Study 2) were utilized. Study 1: Vitamin D intake and ultraviolet B exposure were estimated using the FFLQ and compared to serum 25(OH)D concentrations via simple correlation and linear regression modeling. Study 2: Vitamin D intake from food was estimated using FFLQ and compared to vitamin D intake reported in 7-Day food diaries via paired t-test and Bland&ndash, Altman analysis. Results: Study 1: Serum 25(OH)D was not associated with vitamin D intake from food, food plus supplements, or sun exposure, but was associated with tanning bed use (r = 0.39) in spring, supplement use in fall (r = 0.28), and BMI (body mass index) (r = &minus, 0.32 to &minus, 0.47) across all seasons. Serum 25(OH)D concentrations were explained by BMI, tanning bed use, and sun exposure in fall, (R = 0.42), BMI in winter (R = 0.32), and BMI and tanning bed use in spring (R = 0.52). Study 2: Estimated Vitamin D intake from food was 186.4 &plusmn, 125.7 via FFLQ and 148.5 &plusmn, 228.2 IU/day via food diary. There was no association between intake estimated by the two methodologies (r = 0.12, p &lt, 0.05). Conclusions: FFLQ-estimated vitamin D intake was not associated with serum 25(OH)D concentration or food-record-estimated vitamin D intake. Results highlight the difficulty of designing/utilizing intake methodologies for vitamin D, as its status is influenced by body size and both endogenous and exogenous (dietary) sources.

Objective: The presence of appetite hormones, namely glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and leptin in breast milk may be important in infant feeding regulation and infant growth. This study evaluated whether concentrations of GLP-1, PYY, and leptin change across a single feeding (from fore- to hindmilk), and are associated with maternal and infant anthropometrics. Design and Methods: Thirteen postpartum women (mean ± SD: 25.6 ± 4.5 years, 72.0 ± 11.9 kg) provided fore- and hindmilk samples 4-5 weeks after delivery and underwent measurements of body weight and composition by Dual X-ray Absorptiometry. GLP-1, PYY, and leptin concentrations were measured using radioimmunoassay, and milk fat content was determined by creamatocrit. Results: Concentration of GLP-1 and content of milk fat was higher in hindmilk than foremilk (P ≤ 0.05). PYY and leptin concentrations did not change between fore- and hindmilk. Both leptin concentration and milk fat content were correlated with indices of maternal adiposity, including body mass index (r = 0.65-0.85, P < 0.02), and fat mass (r = 0.65-0.84, P < 0.02). Hindmilk GLP-1 was correlated with infant weight gain from birth to 6 months (r = −0.67, P = 0.034). Conclusion: The presence of appetite hormones in breast milk may be important in infant appetite and growth regulation.

There is a high prevalence of vitamin D insufficiency and deficiency worldwide likely because of both limited sun-exposure and inadequate dietary intake. Meat, including pork, is not typically considered a dietary source of vitamin D, possibly because of management practices that raise pigs in confinement. This experiment determined the vitamin D content of loin and subcutaneous adipose tissue in sun-exposed finisher pigs. Two separate groups of pigs were used. The first group (28 white Landrace-Duroc) was assigned at random to either sunlight exposure (SUN) in spring and summer or confinement per standard practice (Control). The second (24 Yorkshire-Duroc-Landrace) underwent the same exposure protocol but was exposed in summer and fall or assigned to control (Control). A subsample of five SUN and four Control pigs, matched for weight and body condition score, was selected for slaughter from each group. Pigs (n = 10 SUN, n = 8 Control) had blood drawn for analysis of 25(OH)D3 concentration before/after sun exposure or control, and tissue samples were taken at slaughter for analysis of tissue vitamin D3 and 25(OH)D3 concentration. Three random samples from a single loin chop and surrounding adipose were collected and analyzed. Serum concentrations of 25(OH)D3 did not differ (P≥0.376) between treatments prior to sun exposure in either group, but was increased (time*treatment interaction, P

With the increasing popularity of Hatha yoga, it is important to understand the energy cost and METs of yoga practice within the context of the American College of Sports Medicine (ACSM) and the American Heart Association (AHA) physical activity guidelines.This systematic review evaluated the energy cost and metabolic intensity of yoga practice including yoga asanas (poses/postures) and pranayamas (breath exercises) measured by indirect calorimetry. The English-speaking literature was surveyed via PubMed using the general terms "yoga" and "energy expenditure" with no date limitations.Thirteen manuscripts were initially identified with an additional four located from review of manuscript references. Of the 17 studies, 10 evaluated the energy cost and METs of full yoga sessions or flow through Surya Namaskar (sun salutations), eight of individual asanas, and five of pranayamas. METs for yoga practice averaged 3.3 ± 1.6 (range = 1.83-7.4 METs) and 2.9 ± 0.8 METs when one outlier (i.e., 7.4 METs for Surya Namaskar) was omitted. METs for individual asanas averaged 2.2 ± 0.7 (range = 1.4-4.0 METs), whereas that of pranayamas was 1.3 ± 0.3. On the basis of ACSM/AHA classification, the intensity of most asanas and full yoga sessions ranged from light (less than 3 METs) to moderate aerobic intensity (3-6 METs), with the majority classified as light intensity.This review suggests that yoga is typically classified as a light-intensity physical activity. However, a few sequences/poses, including Surya Namaskar, meet the criteria for moderate- to vigorous-intensity activity. In accordance with the ACSM/AHA guidelines, the practice of asana sequences with MET intensities higher than three (i.e.,10 min) can be accumulated throughout the day and count toward daily recommendations for moderate- or vigorous-intensity physical activity.

In endurance-trained men, an acute bout of exercise is shown to suppress post-exercise appetite, yet limited research has examined this response in women. The purpose of this study was to investigate the effect of exercise intensity on appetite and gut hormone responses in endurance-trained women. Highly-trained women (n = 15, 18–40 years, 58.4 ± 6.4 kg, VO2MAX = 55.2 ± 4.3 mL/kg/min) completed isocaloric bouts (500 kcals or 2093 kJ) of moderate-intensity (MIE, 60% VO2MAX) and high-intensity (HIE, 85% VO2MAX) treadmill running at the same time of day, following a similar 48-h diet/exercise period, and at least 1-week apart. Blood was drawn pre-exercise (baseline), immediately post-exercise and every 20-min for the next 60-min. Plasma concentrations of acylated ghrelin, PYY3–36, GLP-1 and subjective appetite ratings via visual analog scale (VAS) were assessed at each time point. Acylated ghrelin decreased (p = 0.014) and PYY3–36 and GLP-1 increased (p = 0.036, p < 0.0001) immediately post-exercise, indicating appetite suppression. VAS ratings of hunger and desire to eat decreased immediately post-exercise (p = 0.0012, p = 0.0031, respectively), also indicating appetite suppression. There were no differences between exercise intensities for appetite hormones or VAS. Similar to males, post-exercise appetite regulatory hormones were altered toward suppression in highly-trained women and independent of energy cost of exercise. Results are important for female athletes striving to optimize nutrition for endurance performance.

Vitamin D deficiency is endemic in the general population; however, there is much to be learned about the vitamin D status of athletes. Purpose: The purposes of this study were to assess the prevalence of vitamin D insufficiency in collegiate athletes and to determine whether 25(OH)D concentrations are related to vitamin D intake, sun exposure, body composition, and risk for illness or athletic injury. Methods: 25(OH) vitamin D concentrations were measured in 41 athletes (18 men/23 women, 12 indoor/29 outdoor athletes) throughout the academic year. Dietary intake and lifestyle habits were assessed via questionnaire, bone density was measured by dual energy x-ray absorptiometry, and injury and illness were documented as part of routine care. Results: The 25(OH)D concentrations changed across time (P = 0.001) and averaged 49.0 ± 16.6, 30.5 ± 9.4, and 41.9 ± 14.6 ng·mL-1 (mean ± SD) in the fall, winter, and spring, respectively, and were higher in outdoor versus indoor athletes in the fall (P < 0.05). Using 40 ng·mL-1 as the cutoff for optimal status, 75.6%, 15.2%, and 36.0% of athletes had optimal status in the fall, winter, and spring, respectively. 25(OH)D concentrations were significantly (P < 0.05) correlated with multivitamin intake in the winter (r = 0.39) and tanning bed use in the spring (r = 0.48); however, status was otherwise not related to intake, lifestyle factors, or body composition. 25(OH)D concentrations in the spring (r = -0.40, P = 0.048) was correlated with frequency of illness. Conclusions: Our results suggest that collegiate athletes can maintain sufficient status during the fall and spring but would benefit from supplementation during the winter to prevent seasonal decreases in 25(OH)D concentrations. Results further suggest that insufficient vitamin D status may increase risk for frequent illness. Future research is needed to identify whether vitamin D status influences injury risk during athletic training or competition

Increased per capita consumption of sweeteners may be responsible in part for the rising prevalence of obesity in the United States. Recent studies suggest that consumption of honey is not associated with this same obesogenic effect and may have beneficial effects neuro on body weight. The purpose of this study was to evaluate whether the meal-induced responses of ghrelin and peptide YY(3-36) (PYY(3-36)) and/or meal-induced thermogenesis differ following a honey- versus a sucrose-containing meal.In a double-blind randomly assigned study, appetite hormones (ghrelin, PYY(3-36), leptin) and glycemic and thermic responses were evaluated following isoglucidic ∼450 kcal honey- or sucrose-containing breakfasts in 14 healthy, nonobese women (22 ± 3 y). Blood samples and hunger ratings were obtained at baseline and every 30 minutes for 240 minutes following the meal. Meal-induced thermogenesis was measured by indirect calorimetry. Ad libitum food intake was evaluated from a free-choice meal following the test meal.Honey consumption delayed the postprandial ghrelin response (p = 0.037), enhanced the total PYY (p = 0.007) response, and blunted the glucose response (p = 0.039) compared with consumption of the sucrose-containing meal. Meal-induced insulin response, hunger ratings, thermogenesis, and subsequent ad libitum food intake, however, did not differ (p0.10) between diet treatments.Alterations in meal-induced responses of ghrelin and PYY(3-36) but not meal-induced thermogenesis may be responsible in part for the potential "obesity protective" effect(s) of honey consumption. A blunted glycemic response may be beneficial for reducing glucose intolerance. Further research is required to determine if these findings hold true for obese individuals, for males, or with habitual consumption.

While it is well recognized that vitamin D is necessary for optimal bone health, emerging evidence is finding that adequate vitamin D intake reduces risk for conditions such as stress fracture, total body inflammation, infectious illness, and impaired muscle function. Studies in athletes have found that vitamin D status is variable and is dependent on outdoor training time (during peak sunlight), skin color, and geographic location. Although research has found that athletes generally do not meet the U.S. dietary reference intake for vitamin D, inadequate endogenous synthesis is the most probable reason for insufficient/deficient status. Given the recent findings, it is imperative that sports dietitians and physicians routinely assess vitamin D status and make recommendations to help athletes achieve a serum 25(OH)D concentration of >or=32 and preferably >or=40 ng.mL(-1). Further research is needed to determine the effect of vitamin D status on injury, training, and performance in athletes.

Intramyocellular and intrahepatic (IHL) lipids are significantly associated with insulin resistance in adults and adolescents and may represent an early marker for developing the metabolic syndrome or type 2 diabetes.During the pilot phase of a larger cross-sectional study, we used proton magnetic resonance spectroscopy ((1)H-MRS) to determine the feasibility of noninvasively evaluating IHL in 11 male (n = 4) and female (n = 7) prepubertal children using a standard clinical system and to determine whether IHL is correlated with adiposity, fasting insulin and glucose, and liver enzymes.Body mass index (BMI) (range, 13.4-32.4 kg/m(2)) and IHL stores (range, 0.07-3.2% relative to an oil phantom) were variable. IHL was correlated with body mass (r = 0.66, P = 0.037), BMI (r = 0.73, P = 0.016), percentage body fat (r = 0.73, P = 0.01, n = 10), waist circumference (r = 0.85, P = 0.016), and serum lactate dehydrogenase concentration (r = 0.77, P = 0.03) but was not significantly correlated with other markers of liver damage, including aspartate aminotransferase activity (r = 0.59, P = 0.09, n = 9) and alkaline phosphatase concentrations (r = 0.60, P = 0.087). IHL was also (P0.01) correlated with fasting insulin concentration (r = 0.85, P = 0.03, n = 6) and insulin resistance (r = 0.94, P = 0.006, n = 6), but these correlations were driven by the results for one child.These preliminary data suggest that (1)H-MRS obtained in a standard pediatric clinical environment may be used to determine IHL in healthy normal and overweight prepubertal youth. This noninvasive technique may prove useful in identifying early markers of the metabolic syndrome in at-risk youth.

Background: Epidemiologic studies suggest that childbearing is an important contributor to the development of obesity in many women and that breastfeeding may be protective. Ghrelin and peptide YY (PYY) are gut hormones involved in appetite regulation and energy homeostasis and are biological neuroendocrine signals that potentially affect body weight and adiposity. Objective: This study evaluated whether fasting or postprandial ghrelin or PYY is different between lactating and nonlactating postpartum women matched for age, body weight, and adiposity. Design: Ten postpartum lactating women (mean ± SD: 28.1 ± 4.9 y of age, 69.2 ± 11.3 kg, 35.4 ± 6.6% body fat) and 8 nonlactating women (28.8 ± 7.6 y of age, 75.6 ± 13.7 kg, 37.5 ± 6.5% body fat) at 4–5 wk postpartum underwent measurements of body weight, body composition, and ghrelin and PYY responses to a standardized meal (350 kcal). Seven never-pregnant women served as control subjects (29.7 ± 4.1 y of age, 60.4 ± 4.8 kg, 25.5 ± 2.0% body fat). Results: Ghrelin concentrations decreased, whereas PYY concentrations increased significantly (P < 0.05) in response to the meal, but fasting or meal-induced changes were not significantly different between lactating and nonlactating women. The fasting ghrelin concentration correlated with body mass index (r = −0.53, P < 0.05) and was significantly lower in postpartum than in control women (894.9 ± 247.7 compared with 1316.9 ± 241.0 pg/mL), even after adjustment for body mass index. Conclusions: Our data do not support the notion that ghrelin, PYY, or both are plausible neuroendocrine signals that influence body weight regulation during lactation. They suggest, however, that ghrelin may change with increased adiposity in the postpartum state and may potentially play a role in body weight regulation after child birth.

There is a debate over the independent effects of aerobic fitness and body fatness on mortality and disease risks.To determine whether a 25% energy deficit that produces equal change in body fatness leads to greater cardiometabolic benefits when aerobic exercise is included.Thirty-six overweight participants (16 males/20 females) (39 +/- 1 yr; 82 +/- 2 kg; body mass index = 27.8 +/- 0.3 kg x m2, mean +/- SEM) were randomized to one of three groups (n = 12 for each) for a 6-month intervention: control (CO, weight-maintenance diet), caloric restriction (CR, 25% reduction in energy intake), or caloric restriction plus aerobic exercise (CR + EX, 12.5% reduction in energy intake plus 12.5% increase in exercise energy expenditure). Food was provided during weeks 1-12 and 22-24. Changes in fat mass, visceral fat, VO2peak (graded treadmill test), muscular strength (isokinetic knee extension/flexion), blood lipids, blood pressure, and insulin sensitivity/secretion were compared.As expected, VO2peak was significantly improved after 6 months of intervention in CR + EX only (22 +/- 5% vs 7 +/- 5% in CR and -5 +/- 3% in CO), whereas isokinetic muscular strength did not change. There was no difference in the losses of weight, fat mass, or visceral fat and changes in systolic blood pressure (BP) between the intervention groups. However, only CR + EX had a significant decrease in diastolic BP (-5 +/- 3% vs -2 +/- 2% in CR and -1 +/- 2% in CO), in low-density lipoprotein (LDL) cholesterol (-13 +/- 4% vs -6 +/- 3% in CR and 2 +/- 4% in CO), and a significant increase in insulin sensitivity (66 +/- 22% vs 40 +/- 20% in CR and 1 +/- 11% in CO).Despite similar effect on fat losses, combining CR with exercise increased aerobic fitness in parallel with improved insulin sensitivity, LDL cholesterol, and diastolic BP. The results lend support for inclusion of an exercise component in weight loss programs to improve metabolic fitness.

To determine whether fasting and meal-induced appetite-regulating hormones are altered during lactation and associated with body weight retention after childbearing, we studied 24 exclusively breastfeeding women (BMI = 25.2 ± 3.6 kg/m2) at 4-5 weeks postpartum and 20 never-pregnant controls (BMI = 24.0 ± 3.1 kg/m2). Ghrelin, PYY, GLP-1, and appetite ratings were measured before/and 150 minutes after a standardized breakfast and 60 minutes after anad libitumlunch. Body weight/composition were measured at 6 and 12 months. Fasting and area under-the-curve responses for appetite-regulating hormones did not differ between lactating and control groups;ghrelinacyl, however, tended to track higher after the standardized breakfast in lactating women and was higher (p<0.05) after thead libitumlunch despite a 24% higher energy intake (p< 0.05). By 12 months, lactating women lost 5.3 ± 2.2 kg (n=18), whereas control women (n=15) remained weight stable (p=0.019); fifteen of the lactating women returned to within ±2.0 kg of prepregnancy weight but three retained >6.0 kg. The retainers had greater (p<0.05) postmeal ghrelin rebound responses following breakfast. Overall these studies do not support the hypothesis that appetite-regulating hormones are altered during lactation and associated with postpartum weight retention. Altered ghrelin responses, however, deserve further exploration.

Little is known concerning the contributions of oxidative phosphorylation (OxPhos), anaerobic glycolytic rate (AnGly), maximum creatine kinase (CK) activity, and metabolic economy (ME) on fatigue resistance. The purpose of this study was to model fatigue using muscle tissue metabolic measures during a maximal short-duration isometric contraction. Muscle metabolic function was measured with [31P]-magnetic resonance spectroscopy (MRS) in 54 premenopausal women (age: 33.8 ± 6.3 y) while they performed 100% isometric plantar flexions. Multiple regression analysis revealed that all metabolic variables were independent predictors of fatigue resistance after adjusting for maximum isometric force generated (R2= 0.56). ME accounted for the largest portion (36%) of overall shared variance. OxPhos accounted for the most shared variance of the three energy systems. These results support previous findings that OxPhos, AnGly, CK, and ME all contribute to fatigue resistance over a short duration. Additionally, the continued activity of CK at the end of 90 s of maximal exercise lends support to the concept of a CK shuttle facilitating energy transfer within the mitochondria.

The purposes of this study were to (a) determine whether structural differences in triceps surae muscle-tendon complex and walking economy exist between 14 African American and 19 Caucasian sedentary women and (b) determine whether muscle-tendon parameters are associated with walking economy. African American and Caucasian subjects were matched on body weight, height, and body composition. Muscle-tendon parameters were determined by magnetic resonance imaging and walking economy was evaluated at 4.8 km.h(-1). Medial gastrocnemius and total triceps surae muscle shape were different across ethnicity despite no ethnic differences in plantar flexion strength or in maximal cross-sectional area for any triceps surae muscles. African American women had shorter gastrocnemius muscles and longer tendons and performed walking more economically. Tendon length was the only variable related to walking economy. No ethnic differences were observed in walking economy after adjusting for tendon length. Data show gastrocnemius tendon length is related to level walking and longer gastrocnemius tendons may partly explain more economical walking in African American women. These preliminary findings indicate the structure of the muscle-tendon complex could be a factor partially accounting for reported ethnic differences in certain types of athletic-related performance.

An inverse relationship has been shown between running and cycling exercise economy and maximum oxygen uptake (VO2max). The purposes were: 1) determine the relationship between walking economy and VO2max; and 2) determine the relationship between muscle metabolic economy and muscle oxidative capacity and fiber type. Subjects were 77 premenopausal normal weight women. Walking economy (1/VO2max) was measured at 3 mph and VO2max during graded treadmill test. Muscle oxidative phosphorylation rate (OxPhos), and muscle metabolic economy (force/ATP) were measured in calf muscle using 31P MRS during isometric plantar flexion at 70 and 100% of maximum force, (HI) and (MI) respectively. Muscle fiber type and citrate synthase activity were determined in the lateral gastrocnemius. Significant inverse relationships (r from -0.28 to -0.74) were observed between oxidative metabolism measures and exercise economy (walking and muscle). Type IIa fiber distribution was inversely related to all measures of exercise economy (r from -0.51 to -0.64) and citrate synthase activity was inversely related to muscle metabolic economy at MI (r = -0.56). In addition, Type IIa fiber distribution and citrate synthase activity were positively related to VO2max and muscle OxPhos at HI and MI (r from 0.49 to 0.70). Type I fiber distribution was not related to any measure of exercise economy or oxidative capacity. Our results support the concept that exercise economy and oxidative capacity are inversely related. We have demonstrated this inverse relationship in women both by indirect calorimetry during walking and in muscle tissue by 31P MRS.

The purpose of this study was to determine whether muscle metabolic capacity was inversely related to age after adjusting for physical activity in sedentary premenopausal women. Eighty-three women (ages 23–47 yr) had their free-living, activity-related energy expenditure evaluated with doubly labeled water procedures, and room calorimeter determined sleeping energy expenditure. Maximum O2 uptake and strength were evaluated in all subjects, whereas 31P-magnetic resonance spectroscopy determined metabolic economy during maximal exercise, and muscle biopsy maximal enzyme activity was evaluated in subsets of the sample (48 and 18 subjects, respectively). Age was significantly related to whole body treadmill endurance time ( r = −0.32), plantar flexion strength ( r = −0.29), maximum O2 uptake ( r = −0.27),31P-magnetic resonance spectroscopy ADP recovery rate ( r = −0.44), and anaerobic glycolytic capacity ( r = −0.37), and muscle biopsy citrate synthase activity ( r = −0.48), glyceraldehyde-3-phosphate dehydrogenase ( r = −0.54), phosphofructokinase ( r = −0.62), and phosphorylase ( r = −0.58) activity even after adjusting for activity-related energy expenditure. These data suggest that, in sedentary premenopausal women, both oxidative and glycolytic muscle capacity decrease with age even when physical activity is taken into account.

Using a randomly assigned crossover design, we evaluated the change in intramyocellular lipid stores (IMCL) from baseline after a 2-h treadmill run [67% of maximal oxygen uptake (V˙o2 max)] and the recovery of IMCL in response to a postexercise very low-fat (10% of energy, LFAT) or moderate-fat (35% of energy, MFAT) recovery diet in seven female runners. IMCL was measured in soleus muscle by use of water-suppressed1H-NMR spectroscopic imaging before (baseline), after, and ∼22 h and 70 h after the run. IMCL fell by ∼25% ( P < 0.05) during the endurance run and was dependent on dietary fat content for postexercise recovery ( P = 0.038, diet × time interaction). Consumption of the MFAT recovery diet allowed IMCL stores to return to baseline by 22 h and to overshoot (vs. baseline) by 70 h postexercise. In contrast, consumption of the LFAT recovery diet did not allow IMCL stores to return to baseline even by 70 h after the endurance run ( P < 0.01 at 70 h). These results suggest that a certain quantity of dietary fat is required to replenish IMCL after endurance running.

HUNTER, G. R., R. L. WEINSIER, J. P. MCCARTHY, D. E. LARSON-MEYER, and B. R. NEWCOMER. Hemoglobin, muscle oxidative capacity, and V2max in African-American and Caucasian women. Med. Sci. Sports Exerc., Vol. 33, No. 10, 2001, pp. 1739–1743. Purpose: The purpose of this paper was to determine whether differences in hemoglobin (Hb) and muscle aerobic capacity exist between African-American (AA) and Caucasian (CA) premenopausal women and to determine whether Hb and aerobic capacity of the muscle are associated with the racial differences in maximum oxygen uptake (V2max). Methods: 43 AA and 46 CA sedentary premenopausal women were subjects. Percent body fat was determined by four-compartment model, leg lean tissue by dual energy x-ray absorptiometry, V2max during a graded exercise test, aerobic capacity of the calf muscle by 31P magnetic resonance spectroscopy, and serum Hb by the cyanide method. Results: AA women had reduced V2max (AA 29.3 ± 3.0 vs CA 33.6 ± 5.6 mL·kg−1 bdw−1·min, P < 0.01), reduced muscle aerobic capacity (AA 24.3 ± 5.8 vs CA 21.3 ± 4.8 s, P = 0.01, where lower values indicate higher aerobic capacity), and reduced Hb (AA 11.8 ± 1.3 vs CA 12.9 ± 0.8 g·dL−1, P < 0.01). The racial difference in V2max persisted whether the values were unadjusted or adjusted for fat-free mass or leg lean tissue. Multiple regression analysis revealed that both Hb and muscle aerobic capacity were related to V2max after adjusting for each other, race, and either fat-free mass or leg lean tissue. Being AA was associated with reduced V2max in mL O2·kg leg lean tissue−1.min−1 (zero-order simple Pearson-product correlation −0.60, P < 0.01). When multiple regression was used, the correlation between race and V2max decreased but persisted (−0.40

The relationships between in vivo (31)P magnetic resonance spectroscopy (MRS) and in vitro markers of oxidative capacity (mitochondrial function) were determined in 27 women with varying levels of physical fitness. Following 90-s isometric plantar flexion exercises, calf muscle mitochondrial function was determined from the phosphocreatine (PCr) recovery time constant, the adenosine diphosphate (ADP) recovery time constant, the rate of change of PCr during the initial 14 s of recovery, and the apparent maximum rate of oxidative adenosine triphosphate (ATP) synthesis (Q(max)). Muscle fiber type distribution (I, IIa, IIx), citrate synthase (CS) activity, and cytochrome c oxidase (COX) activity were determined from a biopsy sample of lateral gastrocnemius. MRS markers of mitochondrial function correlated moderately (P0.05) with the percentage of type IIa oxidative fibers (r = 0.41 to 0.66) and CS activity (r = 0.48 to 0.64), but only weakly with COX activity (r = 0.03 to 0.26, P0.05). These results support the use of MRS to determine mitochondrial function in vivo.

It is not known what causes the well-established inverse relationship between whole-body exercise economy and exercise intensity. The purpose of this study was to: (1) evaluate muscle exercise economy at 45%, 70%, and maximum isometric strength using 31P magnetic resonance spectroscopy (31P-MRS); and (2) determine the relationship between percent type II muscle fiber cross-section, whole-body exercise economy, and muscle exercise economy. Subjects included 32 premenopausal women. Muscle exercise economy was significantly different across the three exercise intensities (28.1 ± 10.4, 24.8 ± 8.2, and 20.2 ± 7.5 N/cm2 · mmol/L adenosine triphosphate [ATP] for the 45%, 70%, and maximum intensities, respectively). Percent type II muscle area was significantly related to whole-body metabolic economy during activities of daily living (r = −0.68) and 31P-MRS muscle metabolic economy during isometric plantar flexion (r = −0.53). These data suggest that skeletal muscle becomes less economical as force production increases, and that these decreases in metabolic economy may be related to increased dependence on inefficient type II muscle. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 654–661, 2001

The reliability, relation to whole-body maximal oxygen uptake (VO(2max)), and force-level sensitivity of (31)P MRS markers of mitochondrial function were studied in 39 normal-weight women. Following 90 s isometric plantar-flexion exercises at 45, 70 and 100% of maximum voluntary contraction, skeletal muscle mitochondrial function was determined from the phosphocreatine recovery time constant (TC(PCr)), the ADP recovery time constant (TC(ADP)), and the rate of change in PCr during the first 14 s of recovery (OxPhos). VO(2max) was measured on a treadmill. Test-retest measurements were obtained in a subset of seven women. Overall, TC(PCr), TC(ADP) and OxPhos were reproducible for all exercises (coefficients of variation = 2.3-19.3%). With increasing force-level, TC(PCr) was prolonged (29.0 +/- 8.2, 31.9 +/- 9.0 and 35.4 +/- 9.5 s), OxPhos was increased (0.159 +/- 0.081, 0.247 +/- 0.090 and 0.310 +/- 0.114), and TC(ADP) was shortened (22.4 +/- 7.9, 21.3 +/- 6.2, and 19.5 +/- 6.7; p < 0.01). All MRS markers of mitochondrial function were correlated with VO(2max) (r = 0.41-0.72; p < 0.05). These results suggest that measurements of TC(PCr), TC(ADP) and OxPhos yield reproducible results that correlate with whole-body VO(2max) and that vary in force-level sensitivity.

This study explored the link between vitamin D status and frequency of skin infections, inflammation, and injury in college wrestlers during an academic year. Methods: Serum 25-hydroxyvitamin D (25(OH)D) (n = 19), plasma cytokine (TNF-α, IL-6, IL-10) (n = 18) concentrations, and body weight/composition were measured and injury/illness/skin infection data were collected in fall, winter, and spring. Results: In the fall, 74% of wrestlers had vitamin D concentrations 0.05). Correlations between vitamin D status, cytokines, or frequency of illness, injury, or skin infections were not observed. Conclusions: A high prevalence of vitamin D insufficiency (

Insulin sensitivity is impaired and ectopic fat (accretion of lipids outside of typical adipose tissue depots) increased in obese adults and adolescents. It is unknown how early in life this occurs; thus, it is important to evaluate young children to identify potential factors leading to the development of metabolic syndrome. We examined an ethnically diverse cohort of healthy, exclusively prepubertal children (N = 123; F = 57, M = 66; age 8.04 ± 0.77 years) to examine differences in insulin sensitivity and ectopic and visceral fat deposition between obese and nonobese youth. Obesity was categorized by age- and sex-adjusted BMI z-scores (nonobese = z-score

Aging is associated with loss of endurance; however, aging is also associated with decreased fatigue during maximal isometric contractions. The aims of this study were to examine the relationship between age and walking endurance (WE) and maximal isometric fatigue (MIF) and to determine which metabolic/fitness components explain the expected age effects on WE and MIF. Subjects were 96 pre-menopausal women. Oxygen uptake (walking economy) was assessed during a 3-mph walk; aerobic capacity and WE by progressive treadmill test; knee extension strength by isometric contractions, MIF during a 90-s isometric plantar flexion (muscle metabolism measured by 31P MRS). Age was related to increased walking economy (low VO2, r = −0.19, P < 0.03) and muscle metabolic economy (force/ATP, 0.34, P = 0.01), and reduced MIF (−0.26, P < 0.03). However, age was associated with reduced WE (−0.28, P < 0.01). Multiple regression showed that muscle metabolic economy explained the age-related decrease in MIF (partial r for MIF and age −0.13, P = 0.35) whereas walking economy did not explain the age-related decrease in WE (partial r for WE and age −0.25, P < 0.02). Inclusion of VO2max and knee endurance strength accounted for the age-related decreased WE (partial r for WE and age = 0.03, P > 0.80). In premenopausal women, age is related to WE and MIF. In addition, these results support the hypothesis that age-related increases in metabolic economy may decrease MIF. However, decreased muscle strength and oxidative capacity are related to WE.

We have previously shown that Achilles tendon length is related to walking economy on the flat, presumably because of increased stretch-shortening cycle elastic energy savings. In addition, greater walking economy in African American (AA) women compared to European American (EA) women is explained by longer Achilles tendons in AA women. The purposes of this study were to determine whether economy while walking up a grade and during isometric plantar flexion, two tasks expected to produce proportionately less energy savings from elastic savings are different between AA and EA women. We evaluated walking economy at 4.8 km/h at 0 and 2.5% grade in 48 AA and 48 EA premenopausal women. Plantar flexor muscle metabolic economy (force/ATP) was also evaluated using (31) phosphate magnetic resonance spectroscopy ((31)P-MRS). AA women walked on the flat more economically (net VO(2), AA 8.3 and EA 8.9 ml kg(-1) min(-1), P = 0.04). No significant ethnic differences were observed while walking up a 2.5% grade or in (31)P-MRS determined plantar flexor muscle metabolic economy. These data support our previous study's suggestion that AA women are more economical while walking on the flat. On the other hand, in activities in which stretch-shortening cycle elastic energy savings would be expected to be reduced (grade walking and isometric force production), no differences in economy during grade walking or isometric force production were observed suggesting that biomechanical, i.e. stretch-shortening cycle elastic energy savings differences rather biochemical differences contribute to the better flat walking economy observed in AA women.