Muscle Glycogen Assessment and Relationship with Body Hydration Status: A Narrative Review

Compositional Aspects of Beverages Designed to Promote Hydration Before, During, and After Exercise: Concepts Revisited

Hypohydration can impair aerobic performance and deteriorate cognitive function during exercise. To minimize hypohydration, athletes are recommended to commence exercise at least euhydrated, ingest fluids containing sodium during long-duration and/or high-intensity exercise to prevent body mass loss over 2% and maintain elevated plasma osmolality, and rapidly restore and retain fluid and electrolyte homeostasis before a second exercise session. To achieve these goals, the compositions of the fluids consumed are key; however, it remains unclear what can be considered an optimal formulation for a hydration beverage in different settings. While carbohydrate-electrolyte solutions such as sports drinks have been extensively explored as a source of carbohydrates to meet fuel demands during intense and long-duration exercise, these formulas might not be ideal in situations where fluid and electrolyte balance is impaired, such as practicing exercise in the heat. Alternately, hypotonic compositions consisting of moderate to high levels of electrolytes (i.e., ≥45 mmol/L), mainly sodium, combined with low amounts of carbohydrates (i.e., <6%) might be useful to accelerate intestinal water absorption, maintain plasma volume and osmolality during exercise, and improve fluid retention during recovery. Future studies should compare hypotonic formulas and sports drinks in different exercise settings, evaluating different levels of sodium and/or other electrolytes, blends of carbohydrates, and novel ingredients for addressing hydration and rehydration before, during, and after exercise.

Ultrasound-based evaluation of loss of lean mass in patients with burns: A prospective longitudinal study

OBJECTIVES

To evaluate the loss of lean mass in patients with burns using ultrasonography of the quadriceps muscle of the thigh.

METHODS

A prospective longitudinal study was conducted using ultrasound of the quadriceps muscle of the thigh to assess the change in thickness in millimeters on days 1, 3 and 7 after study enrollment in 45 patients with burns who were admitted to a burn center (BTC) of a university hospital between April 2020 and September 2021. Patients burns on the thighs, which made it difficult to undertake examinations, were excluded. Depending on where they were admitted, patients were divided into ward and intensive care unit (ICU) patients. ICU patients were considered to have more severe injuries. The general data collected included age, sex, weight, height, area of body surface burn, burn degree and etiology, and airway injury. The data collected for all patients during hospitalization at the BTC were as follows: existence of chronic illness, requirement for mechanical ventilation, Simplified Acute Physiology Score 3 (SAPS 3) and Sequential Organ Failure Assessment (SOFA) on the first day of hospitalization in an intensive care bed in the burn treatment unit (BTU), health-related infection, feeding route, length of hospital stay, and time spent in the BTU.

RESULTS

Loss of muscle thickness was observed in all patients between days 1 and 7. The median thickness for all patients on day 1 was 24.50 mm (ITQ 21.22-30.85) and on day 7 it was 18.80 (ITQ 16.07-23.62), with P = 0.0001. The variation in thigh quadricep muscle thickness between day 1 and day 3, a median of - 2.80 mm (ITQ - 3.52-2.02) was obtained for patients on the ward and - 2.50 mm (ITQ - 3.92 to - 1.47) for ICU patients. Between day 3 and day 7, the variation was - 2.55 mm (ITQ - 4.55 to - 1.25) for ward patients and - 2.10 mm (ITQ - 3.12 to - 1.15) for ICU patients. The median thickness variation assessed between day 1 and day 7 was - 4.95 mm (ITQ - 8.25 to - 3.70) for patients on the ward and - 4.40 mm (ITQ - 7, 35 to - 2.90) for ICU patients. A correlation was observed between the variation in muscle thickness in the interval between day 1 to day 3 and age (P = 0.035).

CONCLUSIONS

Muscle loss occurred early and rapidly within the first seven days of hospitalization, reflecting the impact of burn injury on nutritional risk. An association was observed between muscle thickness loss and age, but no association was observed with the extent of burn, length of hospital stay, occurrence of health-related infections or mortality. These findings suggest the importance of monitoring muscle loss in these patients in planning nutritional therapy, early mobilization, and prevention of complications.

Day-to-day variability in euvolemic body mass

Short-term variability in body mass is a common, everyday phenomenon; however, data on body mass variability are scarce. While the physiological variability of body mass is negligible in healthy individuals, it could have implications for therapy in patients with impaired volume homeostasis, for example, patients with kidney failure undergoing kidney replacement therapy. We analyzed a long-term dataset comprising 9521 days of standardized body mass measurements from one healthy male individual and assessed the variability in body mass as a positive or negative relative difference in body mass measured on subsequent days. The average and median relative differences were zero, with a standard deviation (SD) of 0.53% for the one-day interval, increasing to 0.69% for the 7-day interval, and this variability was constant throughout the observation period. A body mass variability of approximately 0.6% (±450 mL in a 75-kg patient) should be taken into consideration when weight-dependent treatment prescriptions, e.g. the ultrafiltration rates in patients on hemodialysis, are being set. Consequently, a "soft target weight", considering the longitudinal variation of volume markers, such as body mass, might improve treatment quality.

Hydration, Hyperthermia, Glycogen, and Recovery: Crucial Factors in Exercise Performance-A Systematic Review and Meta-Analysis

Hyperthermia accelerates dehydration and can lead to a glycolysis malfunction. Therefore, to deeply understand the relationship between dehydration and hyperthermia during exercise, as well as in the recovery time, there might be important factors to improve athletic performance. A systematic review was carried out in different databases using the words "hydration" OR "dehydration" AND "glycogen" OR "glycogenesis" OR "glycogenolysis" AND "muscle" OR "muscle metabolism" OR "cardiovascular system" and adding them to the "topic section" in Web of Science, to "Title/Abstract" in PubMed and to "Abstract" in SPORTDiscus. A total of 18 studies were included in the review and 13 in the meta-analysis. The free statistical software Jamovi was used to run the meta-analysis (version 1.6.15). A total sample of 158 people was included in the qualitative analysis, with a mean age of 23.5 years. Ten studies compared muscle glycogen content after hydration vs. remaining dehydrated (SMD -4.77 to 3.71, positive 80% of estimates, \hat{\mu} = 0.79 (95% CI: -0.54 to 2.12), z = 1.17, p = 0.24, Q-test (Q(9) = 66.38, p < 0.0001, tau2 = 4.14, I2 = 91.88%). Four studies examined the effect of temperature on postexercise muscle glycogen content (SMD -3.14 to -0.63, 100% of estimates being negative, \hat{\mu} = -1.52 (95% CI: -2.52 to -0.53), (z = -3.00, p = 0.003, Q-test (Q(3) = 8.40, p = 0.038, tau2 = 0.68, I2 = 66.81%). In conclusion, both hyperthermia and dehydration may contribute to elevated glycogenolysis during exercise and poor glycogen resynthesis during recovery. Although core and muscle hyperthermia are the key factors in glycogen impairments, they are also directly related to dehydration.