Effect of Menstrual Cycle Phase and Hormonal Contraceptives on Resting Metabolic Rate and Body Composition.

The cyclical changes in sex hormones across the menstrual cycle (MC) are associated with various biological changes that may alter resting metabolic rate (RMR) and body composition estimates. Hormonal contraceptive (HC) use must also be considered given their impact on endogenous sex hormone concentrations and synchronous exogenous profiles. The purpose of this study was to determine if RMR and dual-energy X-ray absorptiometry body composition estimates change across the MC and differ compared with HC users. This was accomplished during a 5-week training camp involving naturally cycling athletes (n = 11) and HC users (n = 7 subdermal progestin implant, n = 4 combined monophasic oral contraceptive pill, n = 1 injection) from the National Rugby League Indigenous Women's Academy. MC phase was retrospectively confirmed via serum estradiol and progesterone concentrations and a positive ovulation test. HC users had serum estradiol and progesterone concentrations assessed at the time point of testing. Results were analyzed using general linear mixed model. There was no effect of MC phase on absolute RMR (p = .877), relative RMR (p = .957), or dual-energy X-ray absorptiometry body composition estimates (p > .05). There was no effect of HC use on absolute RMR (p = .069), relative RMR (p = .679), or fat mass estimates (p = .766), but HC users had a greater fat-free mass and lean body mass than naturally cycling athletes (p = .028). Our findings suggest that RMR and dual-energy X-ray absorptiometry body composition estimates do not significantly differ due to changes in sex hormones in a group of athletes, and measurements can be compared between MC phases or with HC usage without variations in sex hormones causing additional noise.

Female Athlete Representation and Dietary Control Methods Among Studies Assessing Chronic Carbohydrate Approaches to Support Training.

The aim of this audit was to assess the representation of female athletes, dietary control methods, and gold standard female methodology that underpins the current guidelines for chronic carbohydrate (CHO) intake strategies for athlete daily training diets. Using a standardized audit, 281 studies were identified that examined high versus moderate CHO, periodized CHO availability, and/or low CHO, high fat diets. There were 3,735 total participants across these studies with only ∼16% of participants being women. Few studies utilized a design that specifically considered females, with only 16 studies (∼6%) including a female-only cohort and six studies (∼2%) with a sex-based comparison in their statistical procedure, in comparison to the 217 studies (∼77%) including a male-only cohort. Most studies (∼72%) did not provide sufficient information to define the menstrual status of participants, and of the 18 studies that did, optimal methodology for control of ovarian hormones was only noted in one study. While ∼40% of male-only studies provided all food and beverages to participants, only ∼20% of studies with a female-specific design used this approach for dietary control. Most studies did not implement strategies to ensure compliance to dietary interventions and/or control energy intake during dietary interventions. The literature that has contributed to the current guidelines for daily CHO intake is lacking in research that is specific to, or adequately addresses, the female athlete. Redressing this imbalance is of high priority to ensure that the female athlete receives evidence-based recommendations that consider her specific needs.

Fueling the Female Athlete: Auditing Her Representation in Studies of Acute Carbohydrate Intake for Exercise.

PURPOSE: The aim of this audit was to assess the representation of female athletes within the literature that has led to current guidelines for carbohydrate (CHO) intake in the acute periods surrounding exercise and the quality of this research. METHODS: We conducted a standardized audit of research assessing CHO loading protocols, CHO mouth rinse, and CHO intake before, during, and after exercise. RESULTS: A total of 937 studies were identified in this audit. There were a total of 11,202 participants across these studies, with only ~11% being women. Most studies involved male-only cohorts (~79%), with a mere 38 studies (~4%) involving female-only cohorts and 14 studies (~2%) including a methodological design for comparison of sex-based responses. The frequent use of incorrect terminology surrounding menstrual status and the failure of most studies (~69%) to provide sufficient information on the menstrual status of participants suggests incomplete understanding and concern for female-specific considerations among researchers. Of the 197 studies that included women, only 13 (~7%) provided evidence of acceptable methodological control of ovarian hormones, and no study met all best-practice recommendations. Of these 13 studies, only half also provided sufficient information regarding the athletic caliber of participants. The topics that received such scrutiny were CHO loading protocols and CHO intake during exercise. CONCLUSIONS: The literature that underpins the current guidelines for CHO intake in the acute periods around exercise is lacking in high-quality research that can contribute knowledge specific to the female athlete and sex-based differences. New research that considers ovarian hormones and sex-based differences is needed to ensure that the recommendations for acute CHO fueling provided to female athletes are evidence based.

Markers of Low Energy Availability in Overreached Athletes: A Systematic Review and Meta-analysis.

BACKGROUND: Overreaching is the transient reduction in performance that occurs following training overload and is driven by an imbalance between stress and recovery. Low energy availability (LEA) may drive underperformance by compounding training stress; however, this has yet to be investigated systematically. OBJECTIVE: The aim of this study was to quantify changes in markers of LEA in athletes who demonstrated underperformance, and exercise performance in athletes with markers of LEA. METHODS: Studies using a ≥ 2-week training block with maintained or increased training loads that measured exercise performance and markers of LEA were identified using a systematic search following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Changes from pre- to post-training were analyzed for (1) markers of LEA in underperforming athletes and (2) performance in athletes with ≥ 2 markers of LEA. RESULTS: From 56 identified studies, 14 separate groups of athletes demonstrated underperformance, with 50% also displaying ≥ 2 markers of LEA post-training. Eleven groups demonstrated ≥ 2 markers of LEA independent of underperformance and 37 had no performance reduction or ≥ 2 markers of LEA. In underperforming athletes, fat mass (d = - 0.29, 95% confidence interval [CI] - 0.54 to - 0.04; p = 0.02), resting metabolic rate (d = - 0.63, 95% CI - 1.22 to - 0.05; p = 0.03), and leptin (d = - 0.72, 95% CI - 1.08 to - 0.35; p < 0.0001) were decreased, whereas body mass (d = - 0.04, 95% CI - 0.21 to 0.14; p = 0.70), cortisol (d = - 0.06, 95% CI - 0.35 to 0.23; p = 0.68), insulin (d = - 0.12, 95% CI - 0.43 to 0.19; p = 0.46), and testosterone (d = - 0.31, 95% CI - 0.69 to 0.08; p = 0.12) were unaltered. In athletes with ≥ 2 LEA markers, performance was unaffected (d = 0.09, 95% CI - 0.30 to 0.49; p = 0.6), and the high heterogeneity in performance outcomes (I2 = 84.86%) could not be explained by the performance tests used or the length of the training block. CONCLUSION: Underperforming athletes may present with markers of LEA, but overreaching is also observed in the absence of LEA. The lack of a specific effect and high variability of outcomes with LEA on performance suggests that LEA is not obligatory for underperformance.

Blood flow restriction and stimulated muscle contractions do not improve metabolic or vascular outcomes following glucose ingestion in young, active individuals.

Glucose ingestion and absorption into the bloodstream can challenge glycemic regulation and vascular endothelial function. Muscular contractions in exercise promote a return to homeostasis by increasing glucose uptake and blood flow. Similarly, muscle hypoxia supports glycemic regulation by increasing glucose oxidation. Blood flow restriction (BFR) induces muscle hypoxia during occlusion and reactive hyperemia upon release. Thus, in the absence of exercise, electric muscle stimulation (EMS) and BFR may offer circulatory and glucoregulatory improvements. In 13 healthy, active participants (27 ± 3 yr, 7 females), we tracked post-glucose (oral 100 g) glycemic, cardiometabolic, and vascular function measures over 120 min following four interventions: 1) BFR, 2) EMS, 3) BFR + EMS, or 4) control. BFR was applied at 2-min intervals for 30 min (70% occlusion), and EMS was continuous for 30 min (maximum-tolerable intensity). Glycemic and insulinemic responses did not differ between interventions (partial η2 = 0.11-0.15, P = 0.2), however, only BFR + EMS demonstrated cyclic effects on oxygen consumption, carbohydrate oxidation, muscle oxygenation, heart rate, and blood pressure (all P < 0.01). Endothelial function was reduced 60 min post-glucose ingestion across interventions and recovered by 120 min (5.9 ± 2.6% vs 8.4 ± 2.7%; P < 0.001). Estimated microvascular function was not meaningfully different. Leg blood flow increased during EMS and BFR + EMS (+656 ± 519 mL·min-1, +433 ± 510 mL·min-1; P < 0.001); however, only remained elevated following BFR intervention 90 min post-glucose (+94 ± 94 mL·min-1; P = 0.02). Superimposition of EMS onto cyclic BFR did not preferentially improve post-glucose metabolic or vascular function among young, active participants. Cyclic BFR increased blood flow delivery 60 min beyond intervention, and BFR + EMS selectively increased carbohydrate usage and reduced muscle oxygenation warranting future clinical assessments.NEW & NOTEWORTHY Glucose ingestion challenges glycemic and vascular function. Exercise effectively counteracts these impairments, but is not always feasible. Blood flow restriction (BFR) and electric muscle stimulation (EMS) passively generate muscle hypoxia and contractions mimicking aspects of exercise. We tested BFR, EMS, and BFR + EMS in young, active participants post-glucose. No significant primary glycemic or vascular outcomes are observed. Cyclic BFR increased leg blood flow while BFR + EMS activated greater carbohydrate oxidation and lowered muscle oxygenation warranting future consideration.

Examining the Relationship between Exercise Dependence, Disordered Eating, and Low Energy Availability.

Both dietary and exercise behaviors need to be considered when examining underlying causes of low energy availability (LEA). The study assessed if exercise dependence is independently related to the risk of LEA with consideration of disordered eating and athlete calibre. Via survey response, female (n = 642) and male (n = 257) athletes were categorized by risk of: disordered eating, exercise dependence, disordered eating and exercise dependence, or if not presenting with disordered eating or exercise dependence as controls. Compared to female controls, the likelihood of being at risk of LEA was 2.5 times for female athletes with disordered eating and >5.5 times with combined disordered eating and exercise dependence. Male athletes with disordered eating, with or without exercise dependence, were more likely to report signs and symptoms compared to male controls-including suppression of morning erections (OR = 3.4; p < 0.0001), increased gas and bloating (OR = 4.0-5.2; p < 0.002) and were more likely to report a previous bone stress fracture (OR = 2.4; p = 0.01) and ≥22 missed training days due to overload injuries (OR = 5.7; p = 0.02). For both males and females, in the absence of disordered eating, athletes with exercise dependence were not at an increased risk of LEA or associated health outcomes. Compared to recreational athletes, female and male international caliber and male national calibre athletes were less likely to be classified with disordered eating.

A Review of Nonpharmacological Strategies in the Treatment of Relative Energy Deficiency in Sport.

Relative energy deficiency in sport (RED-S) can result in negative health and performance outcomes in both male and female athletes. The underlying etiology of RED-S is low energy availability (LEA), which occurs when there is insufficient dietary energy intake to meet exercise energy expenditure, corrected for fat-free mass, leaving inadequate energy available to ensure homeostasis and adequate energy turnover (optimize normal bodily functions to positively impact health), but also optimizing recovery, training adaptations, and performance. As such, treatment of RED-S involves increasing energy intake and/or decreasing exercise energy expenditure to address the underlying LEA. Clinically, however, the time burden and methodological errors associated with the quantification of energy intake, exercise energy expenditure, and fat-free mass to assess energy availability in free-living conditions make it difficult for the practitioner to implement in everyday practice. Furthermore, interpretation is complicated by the lack of validated energy availability thresholds, which can result in compromised health and performance outcomes in male and female athletes across various stages of maturation, ethnic races, and different types of sports. This narrative review focuses on pragmatic nonpharmacological strategies in the treatment of RED-S, featuring factors such as low carbohydrate availability, within-day prolonged periods of LEA, insufficient intake of bone-building nutrients, lack of mechanical bone stress, and/or psychogenic stress. This includes the implementation of strategies that address exacerbating factors of LEA, as well as novel treatment methods and underlying mechanisms of action, while highlighting areas of further research.