Errors in Dual Energy X-Ray Absorptiometry Estimation of Body Composition Induced by Hypohydration

Dual energy X-ray absorptiometry (DXA) is a popular tool to determine body composition (BC) in athletes, and is used for analysis of fat-free soft tissue mass (FFST) or fat mass (FM) gain/loss in response to exercise or nutritional interventions. The aim of the present study was to assess the effect of exercise-heat stress induced hypohydration (HYP, >2% of body mass (BM) loss) vs. maintenance of euhydration (EUH) on DXA estimates of BC, sum of skinfolds (SF), and impedance (Berk et al.) measurements in athletes. Competitive athletes (23 males and 15 females) recorded morning nude BM for 7 days prior to the first main trial. Measurements on the first trial day were conducted in a EUH condition, and again after exercise-heat stress induced HYP. On the second trial day, fluid and electrolyte losses were replaced during exercise using a sports drink. A reduction in total BM (1.6±0.4 kg; 2.3±0.4% HYP) and total LM (1.3±0.4 kg), mainly from trunk (1.1±0.5 kg), was observed using DXA when participants were HYP, reflecting the sweat loss. Estimated fat percent increased (0.3±0.3%), however, total FM did not change (0.1±0.2 kg). SF and IMP declined with HYP (losses of 1.5±2.9% and 1.6±3% respectively) suggesting FM loss. When EUH was maintained there were no significant changes in BM, DXA estimates, or SF values pre to post exercise, but IMP still declined. We conclude that use of DXA for LM assessment in athletes must ensure a EUH state, particularly when considering changes associated with nutritional or exercise interventions

Fluid and electrolyte balance considerations for female athletes

This review explores the effects of oestrogen and progesterone fluctuations across the menstrual cycle on fluid and electrolyte balance. The review aims to provide information on this topic for the exercising female but also for researchers working in this field. Beginning with a basic introduction to fluid and electrolyte balance, the review goes on to describe how oestrogen and progesterone have independent and integrated roles to play in the regulation of fluid and electrolyte balance. Despite evidence that oestrogen can influence the osmotic threshold for arginine vasopressin release, and that progesterone can influence aldosterone production, these actions do not appear to influence fluid retention, plasma volume changes at rest and during exercise, or electrolyte losses. However, the large inter-individual variations in hormonal fluctuations throughout the menstrual cycle may mean that specific individuals with high fluctuations could experience disturbances in their fluid and electrolyte balance. During phases of oestrogen dominance (e.g. late-follicular phase) heat dissipation is promoted, while progesterone dominance (e.g. mid-luteal phase) promotes heat conservation with overall higher basal body temperature. However, these responses do not consistently lead to any change in observed sweat rates, heat-stress, or dehydration during exercise. Finally, the literature does not support any difference in fluid retention during post-exercise rehydration periods conducted at different menstrual cycle phases. Although these mean responses largely reveal no effects on fluid and electrolyte balance, further research is required particularly in those individuals who experience high hormonal fluctuations, and greater exploration of oestrogen to progesterone interactions is warranted

A randomised trial to assess fluid and electrolyte balance responses following ingestion of different beverages in young and older men

Background Older adults are susceptible to dehydration and fluid overload due to a reduced ability to maintain homeostatic control of fluid and electrolyte balance. Purpose To assess fluid and electrolyte balance responses in young and older men following ingestion of commonly consumed beverages differing in composition. Methods 12 young and 11 older men were recruited. Euhydrated body mass was recorded. Participants consumed 1L (250 ml every 15 min) of water, fruit juice, a sports drink or low-fat milk in a randomized cross-over design. Urine and blood samples were obtained before and after the drinking period and every hour thereafter for 3-h. Samples were used to determine osmolality, electrolytes (Na+ and K+), water clearance, and glomerular filtration rate. Results Free water clearance was significantly higher in Young than Older at 1 and 2 h after the ingestion of W and S (p<0.05). Net Na+ and K+ balance were not different between Young and Older (p=0.91 and p=0.65) adults, respectively. At 3 h Na+ balance was negative after ingesting water and fruit juice, but neutral after sport drink and milk. Net K+ balance was neutral at 3 h after ingesting milk, but negative after water, fruit juice and sport drink. Conclusions Milk was retained longer than other beverages in Young, but not in Older, despite similar net electrolyte balance responses. Older had higher fluid retention in the first 2 h after the ingestion of all beverages, except for milk when compared to Young, indicating an age-related loss of ability to regulate fluid balance under current study conditions

Effect of Drinking Rate on the Retention of Water or Milk Following Exercise-Induced Dehydration

This study investigated the effect of drinking rate on fluid retention of milk and water following exercise-induced dehydration. In Part A, 12 male participants lost 1.9% ± 0.3% body mass through cycle exercise on four occasions. Following exercise, plain water or low-fat milk equal to the volume of sweat lost during exercise was provided. Beverages were ingested over 30 or 90 min, resulting in four beverage treatments: water 30 min, water 90 min, milk 30 min, and milk 90 min. In Part B, 12 participants (nine males and three females) lost 2.0% ± 0.3% body mass through cycle exercise on four occasions. Following exercise, plain water equal to the volume of sweat lost during exercise was provided. Water was ingested over 15 min (DR15), 45 min (DR45), or 90 min (DR90), with either DR15 or DR45 repeated. In both trials, nude body mass, urine volume, urine specific gravity and osmolality, plasma osmolality, and subjective ratings of gastrointestinal symptoms were obtained preexercise and every hour for 3 hr after the onset of drinking. In Part A, no effect of drinking rate was observed on the proportion of fluid retained, but milk retention was greater (p

Effects of vitamin D supplementation on maximal strength and power in athletes: a systematic review and meta-analysis of randomized controlled trials

BackgroundVitamin D is thought to be a powerful modulator of skeletal muscle physiology. However, available data on the effects of vitamin D supplementation on muscle function in athletes are limited and with mixed results. This meta-analysis therefore, aimed to quantitatively summarize the up-to-date literature assessing the effects of vitamin D supplementation on muscle strength and power in athletes.MethodsSport Discus, PubMed, Cochrane Library and Web of Science were searched to identify randomized controlled trials (RCTs) that used one-repetition maximum (1RM) tests to assess maximal strength, and vertical jump to assess muscle power in athletes. The Cochrane Risk of Bias tool was used to evaluate the included RCTs for sources of bias. The standardized mean difference (SMD) was used as the effect size, interpreted together with its 95% confidence intervals (CI). The effect sizes were calculated on the changes from baseline between vitamin D and placebo groups for maximal strength results by upper body and lower body, and for power results.ResultsEleven RCTs involving 436 athletes were included. The results indicated that if baseline serum 25(OH)D concentration was &lt; 75 nmol/L, the treatment had a small effect on upper body muscle strength [SMD 0.25, 95% CI: (−0.44, 0.95), p = 0.47] and on lower body muscle strength [SMD 0.26, 95% CI: (−0.13, 0.65), p = 0.19]; if the baseline serum 25(OH)D concentration was ≥ 75 nmol/L, the treatment had a trivial effect on muscle power [SMD 0.15, 95% CI: (−0.42, 0.72), p = 0.61].DiscussionThis meta-analysis demonstrated that there is not a statistically significant effect of vitamin D supplementation on improving maximum strength and power, but highlights that further research is required addressing the key limitations in previous studies before definitive conclusions can be made

Skinfold thickness in elite male professional football players: changes across 3 seasons including a COVID-19 lockdown period

This study investigates variations in skinfold thickness in a European professional football team within and across multiple seasons, including before and after COVID-19 restrictions. Skinfold thickness was measured in 49 male players on 32 occasions across three seasons (2018/19, 2019/20 and 2020/21). Intra- and inter-seasonal trends were examined by comparing values for the sum of eight skinfolds (sum8) at key time points using linear mixed models. In each season, the largest differences in sum8 occurred after the preseason period. These differences ranged from a mean difference (Mdiff) of −11.0 mm (p < 0.001) in 2018/19 to −4.8 mm (p < 0.001) in 2020/21. Increases in sum8 occurred after each off-season; however, the increase after the off-season before the 2020/21 season (which included the COVID-19 lockdown period) was the lowest in magnitude and was not statistically significant (Mdiff = 2.9 mm, p = 0.06). Changes occurring in sum8 between the start and end of the competitive season did not follow a consistent pattern and were generally smaller in magnitude than the changes between other seasonal time points. Despite the notable heterogeneity in sum8 between players, changes within players generally followed a similar pattern between the different seasonal timepoints. In summary, changes in skinfold thickness were predominantly related to off-season and ‘preparation for competition’ periods. Increases in skinfold thickness can be mitigated during extended remote training periods with appropriate training and nutritional strategies

Long-chain n-3 polyunsaturated fatty acid ingestion for the stimulation of muscle protein synthesis in healthy older adults

This review aims to critically evaluate the efficacy of long-chain ո-3 polyunsaturated fatty acid (ո-3 PUFA) ingestion in modulating muscle protein synthesis (MPS), with application to maintaining skeletal muscle mass, strength and function into later life. Ageing is associated with a gradual decline in muscle mass, specifically atrophy of type II fibres, that is exacerbated by periods of (in)voluntary muscle disuse. At the metabolic level, in otherwise healthy older adults, muscle atrophy is underpinned by anabolic resistance which describes the impaired MPS response to nonpharmacological anabolic stimuli, namely physical activity/exercise and amino acid provision. Accumulating evidence implicates a mechanistic role for n-3 PUFA in upregulating MPS under stimulated conditions (postprandial state or following exercise) via incorporation of eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) into the skeletal muscle phospholipid membrane. In some instances, these changes in MPS with chronic ո-3 PUFA ingestion have translated into clinically relevant improvements in muscle mass, strength and function; an observation evidently more prevalent in healthy older women than men. This apparent sexual dimorphism in the adaptive response of skeletal muscle metabolism to EPA and DHA ingestion may be related to a greater propensity for females to incorporate ո-3 PUFA into human tissue and/or the larger dose of ingested ո-3 PUFA when expressed relative to body mass or lean body mass. Future experimental studies are warranted to characterise the optimal dosing and duration of ո-3 PUFA ingestion in order to prescribe tailored recommendations regarding n-3 PUFA nutrition for healthy musculoskeletal ageing into later life

Hill Runner's Physiology, Performance and Nutrition: A Descriptive Study

Objectives: The aim of this descriptive study was to characterise anthropometric variables, aerobic capacity, running performance and energy intake and expenditure of hill runners in free-living conditions, and to investigate the relationship between age, anthropometric variables, aerobic capacity and running performance. Methods: Twenty-eight hill runners participated in this study (17 males and 11 females; aged 18–65 years). Body fat percentage estimate, sum of eight skinfolds (triceps, subscapular, biceps, iliac crest, supraspinale, abdominal, front thigh and medial calf) and maximal oxygen capacity (VO2max) were assessed in a laboratory setting. Participants also completed a timed hill run (Dumyat Hill, Scotland, ascent: 420 m, distance: 8 km) while wearing a portable gas analyzer to assess oxygen consumption (VO2). Energy intake and energy expenditure were assessed in free-living conditions over three consecutive days different from the testing days through self-reported food diaries and accelerometers. Results: VO2max assessed in the lab (51.2 ± 7.6 ml·min−1·kg−1) showed a weak negative relationship with age [rs(23) = −0.38, p = 0.08]. Neither body fat percentage (median 12.4; IQR 10.1–17.1) nor the sum of skinfolds (median 81.8; IQR 62.4–97.8 mm) correlated with age [rs(28) = 0.001, p = 0.10 and 26 rs(28) = −0.02, p = 0.94, respectively]. The observed intensity of the hill run was 89 ± 6% of the age predicted maximum heart rate and 87 ± 9% of the VO2max observed in the lab. Hill running performance correlated with VO2max [r(21) = 0.76, p < 0.001], age [rs(26) = −0.44, p = 0.02] and with estimated body fat percentage and sum of skinfolds [rs(26) = −0.66, p < 0.001 and rs(26) = −0.49, p = 0.01, respectively]. Energy intake negatively correlated with age [rs(26) = −0.43, p = 0.03], with the overall energy intake being significantly lower than the total energy expenditure (2273 ± 550 vs. 2879 ± 510 kcal·day−1; p < 0.001; d = 1.05). Conclusion: This study demonstrated that hill running performance is positively associated with greater aerobic capacity and negatively associated with increases in adiposity and age. Further, the study highlights that hill runners are at risk of negative energy balance

Assessing the Validity of Front-of-Pack Nutrition Labels for Evaluating the Healthiness of Mediterranean Food Choices: A Global Comparison

In response to growing public health concerns, governments worldwide have implemented various nutrition labelling schemes to promote healthier eating habits. This study aimed to assess the consistency and effectiveness of these labels in an out-of-home context, specifically focusing on restaurant, hospitality, and institutional food service settings. In total, 178 different dishes from Spain were analysed using labels from the Mazocco method, the UK's traffic light system, the Health Star Rating (Australia), Nutri-Score (France), multiple traffic lights (Ecuador), and warning labels (Chile and Uruguay). The results demonstrated a generally low level of agreement among these labels (K < 0.40), indicating notable variability and a lack of consensus, which could hinder consumers' ability to make informed food choices in out-of-home settings. Nutri-Score classified the highest number of dishes as unhealthy (38%). This study underscores the need for an easy-to-understand labelling system tailored to each country's culinary and socio-cultural contexts to improve consumer decision-making in various dining environments. Future research should focus on developing and testing qualitative methods to more accurately gauge the nutritional quality of cooked dishes in diverse out-of-home settings, thereby enhancing public health outcomes. By addressing the specific needs of the home, restaurants, hospitality, and institutional food services, tailored labelling schemes could significantly improve consumers' ability to make healthier food choices

Assessing the Validity of Front-of-Pack Nutrition Labels for Evaluating the Healthiness of Mediterranean Food Choices: A Global Comparison

In response to growing public health concerns, governments worldwide have implemented various nutrition labelling schemes to promote healthier eating habits. This study aimed to assess the consistency and effectiveness of these labels in an out-of-home context, specifically focusing on restaurant, hospitality, and institutional food service settings. In total, 178 different dishes from Spain were analysed using labels from the Mazocco method, the UK's traffic light system, the Health Star Rating (Australia), Nutri-Score (France), multiple traffic lights (Ecuador), and warning labels (Chile and Uruguay). The results demonstrated a generally low level of agreement among these labels (K < 0.40), indicating notable variability and a lack of consensus, which could hinder consumers' ability to make informed food choices in out-of-home settings. Nutri-Score classified the highest number of dishes as unhealthy (38%). This study underscores the need for an easy-to-understand labelling system tailored to each country's culinary and socio-cultural contexts to improve consumer decision-making in various dining environments. Future research should focus on developing and testing qualitative methods to more accurately gauge the nutritional quality of cooked dishes in diverse out-of-home settings, thereby enhancing public health outcomes. By addressing the specific needs of the home, restaurants, hospitality, and institutional food services, tailored labelling schemes could significantly improve consumers' ability to make healthier food choices