Bioelectrical Impedance Vector Analysis (BIVA) for Assessment of Hydration Status: A Comparison between Endurance and Strength University Athletes

INTRODUCTION

Athletic performance is greatly impacted by hydration status. The combination of several techniques is recommended to accurately measure water losses and gains.

AIM

The aim of this study is to assess the validity of bioelectrical impedance vector analysis (BIVA) as a tool for measuring hydration status in endurance and strength athletes.

METHODS

A total of 148 athletes were evaluated on one experimental day, pre- and post-training. Urine samples were collected and analyzed for color and specific gravity. Body weight changes were measured, sweat rate was calculated, and BIVA was performed. Reference ellipses were plotted using data of 200 healthy non-athletic individuals.

RESULTS

A moderate significant agreement was noted between raw bioelectrical values and urine specific gravity (USG) (p > 0.05). The sensitivity of classic BIVA in detecting minor changes in hydration status is confirmed both graphically and statistically. R/h and Z statistically significantly decreased post-training. Male athletes exhibited a specific BIA vector distribution compared to the reference population and were slightly more hydrated than female athletes.

CONCLUSIONS

BIVA validation may be an essential step to allow its use among university students to assess dehydration in a non-invasive, practical, and inexpensive way.

Blood, Sweat, and Tears: Implications for Hydration Testing in Combat Sports-Investigating Body Mass Loss and Biomarker Changes

Combat sports athletes often undergo rapid body mass loss (BML), which presents health risks. Hydration testing has been proposed as a possible solution to reduce or eliminate rapid BML. However, combat sports athletes may exhibit distinct physiological characteristics due to repeated exposure to BML. Thus, traditional and emerging hydration biomarkers should be investigated to determine their potential suitability for field use in this cohort. This study examined whether BML can explain changes in serum and urine osmolality (SosmΔ, UosmΔ), tear osmolarity (TosmΔ), hematocrit (HctΔ), and urine-specific gravity (USGΔ) after mild-moderate passive dehydration. Biomarker reliability was also assessed across two trials. Fifteen male and female combat sports athletes (age: 26.3 ± 5.3 years, body mass: 67.7 ± 9.9 kg) underwent a sauna protocol twice (5-28 days apart) aiming for 4% BML. The average BML in Trials 1 and 2 was 3.0 ± 0.7%. Regression analysis revealed that BML explained HctΔ (R2 = 0.22, p = 0.009) but not SosmΔ (R2 = 0.11, p = 0.079) or other biomarkers. Intraclass correlation coefficients (ICCs) were significant for all biomarkers except TosmΔ (ICC = 0.06, p = 0.37) and post-Tosm (ICC = 0.04, p = 0.42); post-Hct performed best (ICC = 0.82, p < 0.001). Contingency tables with post-Sosm (295 mOsm/kg) and post-USG (1.020) cutoffs revealed an 80% true negative rate (TNR) and a 62% true positive rate (TPR). Increasing the Sosm cutoff to 301 mOsm/kg decreased the TNR to 52% but increased the TPR to 83%. Although blood parameters were most sensitive to BML, they could only explain 11%-22% of biomarker variation. The typical USG cutoff misclassified 42% of athletes postdehydration, and reliability was generally poor-moderate. Alternative strategies should be pursued to manage rapid BML in combat sports.

Sex Differences in Hydration Biomarkers and Test-Retest Reliability Following Passive Dehydration

This study investigated (a) differences between males and females for changes in serum, tear, and urine osmolality, hematocrit, and urine specific gravity following acute passive dehydration and (b) assessed the reliability of these biomarkers separately for each sex. Fifteen males (age: 26.3 ± 3.5 years, body mass: 76 ± 7 kg) and 15 females (age: 28.8 ± 6.4 years, body mass: 63 ± 7 kg) completed a sauna protocol twice (5-28 days apart), aiming for 4% body mass loss (BML). Urine, blood, and tear markers were collected pre- and postdehydration, and change scores were calculated. Male BML was significantly greater than that of females in Trial 1 (3.53% ± 0.55% vs. 2.53% ± 0.43%, p < .001) and Trial 2 (3.36% ± 0.66% vs. 2.53% ± 0.44%, p = .01). Despite significant differences in BML, change in hematocrit was the only change marker that displayed a significant difference in Trial 1 (males: 3% ± 1%, females: 2% ± 1%, p = .004) and Trial 2 (males: 3% ± 1%, females: 1% ± 1%, p = .008). Regression analysis showed a significant effect for sex (male) predicting change in hematocrit (β = 0.8, p = .032) and change in serum osmolality (β = -3.3, p = .005) when controlling for BML but not for urinary or tear measures. The intraclass correlation coefficients for females (ICC 2, 1) were highest for change in urine specific gravity (ICC = .62, p = .006) and lowest for change in tear osmolarity (ICC = -.14, p = .689), whereas for males, it was posthematocrit (ICC = .65, p = .003) and post tear osmolarity (ICC = .18, p = .256). Generally, biomarkers showed lower test-retest reliability in males compared with females but, overall, were classified as poor-moderate in both sexes. These findings suggest that the response and reliability of hydration biomarkers are sex specific and highlight the importance of accounting for BML differences.

A systematic review of hot weather impacts on infant feeding practices in low-and middle-income countries

BACKGROUND

Increased rates of exclusive breastfeeding could significantly improve infant survival in low- and middle-income countries. There is a concern that increased hot weather due to climate change may increase rates of supplemental feeding due to infants requiring fluids, or the perception that infants are dehydrated.

OBJECTIVE

To understand how hot weather conditions may impact infant feeding practices by identifying and appraising evidence that exclusively breastfed infants can maintain hydration levels under hot weather conditions, and by examining available literature on infant feeding practices in hot weather.

METHODS

Systematic review of published studies that met inclusion criteria in MEDLINE, EMBASE, Global Health and Web of Science databases. The quality of included studies was appraised against predetermined criteria and relevant data extracted to produce a narrative synthesis of results.

RESULTS

Eighteen studies were identified. There is no evidence among studies of infant hydration that infants under the age of 6months require supplementary food or fluids in hot weather conditions. In some settings, healthcare providers and relatives continue to advise water supplementation in hot weather or during the warm seasons. Cultural practices, socio-economic status, and other locally specific factors also affect infant feeding practices and may be affected by weather and seasonal changes themselves.

CONCLUSION

Interventions to discourage water/other fluid supplementation in breastfeeding infants below 6 months are needed, especially in low-middle income countries. Families and healthcare providers should be advised that exclusive breastfeeding (EBF) is recommended even in hot conditions.

Reviewing the current methods of assessing hydration in athletes

Background

Despite a substantial body of research, no clear best practice guidelines exist for the assessment of hydration in athletes. Body water is stored in and shifted between different sites throughout the body complicating hydration assessment. This review seeks to highlight the unique strengths and limitations of various hydration assessment methods described in the literature as well as providing best practice guidelines.

Main body

There is a plethora of methods that range in validity and reliability, including complicated and invasive methods (i.e. neutron activation analysis and stable isotope dilution), to moderately invasive blood, urine and salivary variables, progressing to non-invasive metrics such as tear osmolality, body mass, bioimpedance analysis, and sensation of thirst. Any single assessment of hydration status is problematic. Instead, the recommended approach is to use a combination, which have complementary strengths, which increase accuracy and validity. If methods such as salivary variables, urine colour, vital signs and sensation of thirst are utilised in isolation, great care must be taken due to their lack of sensitivity, reliability and/or accuracy. Detailed assessments such as neutron activation and stable isotope dilution analysis are highly accurate but expensive, with significant time delays due to data analysis providing little potential for immediate action. While alternative variables such as hormonal and electrolyte concentration, bioimpedance and tear osmolality require further research to determine their validity and reliability before inclusion into any test battery.

Conclusion

To improve best practice additional comprehensive research is required to further the scientific understanding of evaluating hydration status.

The Current State of Weight-Cutting in Combat Sports-Weight-Cutting in Combat Sports

In combat sports, athletes are divided into categories based on gender and body mass. Athletes attempt to compete against a lighter opponent by losing body mass prior to being weighed (i.e., 'weight-cutting'). The purpose of this narrative review was to explore the current body of literature on weight-cutting and outline gaps for further research. Methods of weight-loss include energy intake restriction, total body fluid reduction and pseudo extreme/abusive medical practice (e.g., diuretics). The influence of weight-cutting on performance is unclear, with studies suggesting a negative or no effect. However, larger weight-cuts (~5% of body mass in <24 h) do impair repeat-effort performance. It is unclear if the benefit from competing against a smaller opponent outweighs the observed reduction in physical capacity. Many mechanisms have been proposed for the observed reductions in performance, ranging from reduced glycogen availability to increased perceptions of fatigue. Athletes undertaking weight-cutting may be able to utilise strategies around glycogen, total body water and electrolyte replenishment to prepare for competition. Despite substantial discussion on managing weight-cutting in combat sports, no clear solution has been offered. Given the prevalence of weight-cutting, it is important to develop a deeper understanding of such practices so appropriate advice can be given.

Effects of Rapid Weight Loss on Balance and Reaction Time in Elite Judo Athletes

Balance, reaction time, and strength are key factors affecting judo performance. Although ample research has been done examining potential strength changes caused by weight loss prior to competition, changes in balance and reaction time have been overlooked.

PURPOSE

To examine the effects of rapid and progressive weight loss (RWL and PWL) on balance, reaction time, and strength in a group of elite judo athletes.

METHODS

A total of 38 female and male judo athletes (age = 20.6 [2.6] y) completed balance, reaction-time, and strength assessments 1 wk prior to an official weigh-in (pretest) and immediately after the weigh-in (posttest). The athletes were divided into 3 groups, 1 control group who maintained regular training and eating habits, 1 experimental group who engaged in PWL (<3% reductions in body mass), and a second experimental group who used RWL techniques (>3% reductions in body mass).

RESULTS

The RWL group showed significant decreases (P < .05) in balance performance (ellipse area: 4.83 [0.87] vs 6.31 [1.39] mm2 with eyes closed; mean mediolateral velocity: 2.07 [0.2] vs 2.52 [0.45] mm·s-1 with eyes closed; and mean anteroposterior velocity: 2.25 [0.20] vs 2.51 [0.32] mm·s-1 with eyes open and 2.44 [0.26] vs 3.06 [0.56] mm·s-1 with eyes closed) and reaction time (0.38 [0.04] vs 0.42 [0.06] s) with no changes in strength from pretesting to posttesting. The athletes in the PWL and control groups maintained performance in all variables.

CONCLUSION

These findings demonstrate negative effects on perceptual motor-skill performance in judo athletes engaging in RWL strategies prior to competition.

Reliability of Urinary Dehydration Markers in Elite Youth Boxers

PURPOSE

To determine the reliability and diagnostic accuracy of noninvasive urinary dehydration markers in field-based settings on a day-to-day basis in elite adolescent amateur boxers.

METHODS

Sixty-nine urine samples were collected daily from 23 athletes (17.3 ± 1.9 y) during their weight-stable phase and analyzed by field and laboratory measures of hydration status. Urine osmolality (U_OSM), urine specific gravity (U_SG), total protein content (T_PC), and body-mass stability were evaluated to determine fluid balance and hydration status. Overall macronutrient and water intake were determined using dietary records. According to their anthropometric characteristics, athletes were assigned into 2 groups: lightweight (L_WB) and heavyweight (H_WB) boxers.

RESULTS

Data presented on U_OSM demonstrated a uniform increment by 11.2% ± 12.8% (L_WB) and 19.9% ± 22.7% (H_WB) (P < .001) over the course of the study, even during the weight-stable phase (body mass, ICC = .99) and ad libitum fluid intake (42 ± 4 mL · kg^-1 · d^-1). The intraclass correlation coefficients (ICCs) ranged from .52 to .55 for U_SG and .38 to .52 for U_OSM, further indicating inconsistency of the urinary dehydration markers. Poor correlations were found between U_SG and T_PC metabolites (r = .27, P = .211).

CONCLUSIONS

Urinary dehydration markers (both U_SG and U_OSM) exhibit high variability and seem to be unreliable diagnostic tools to track actual body-weight loss in real-life settings. The ad libitum fluid intake was apparently inadequate to match acute fluid loss during and after intense preparation. The applicability of a single-time-point hydration-status assessment concept may preclude accurate assessment of actual body-weight deficits in youth boxers.