Relation between resting spleen volume and apnea-induced increases in hemoglobin mass.

Introduction: Indigenous populations renowned for apneic diving have comparatively large spleen volumes. It has been proposed that a larger spleen translates to heightened apnea-induced splenic contraction and elevations in circulating hemoglobin mass (Hbmass), which, in theory, improves O2 carrying and/or CO2/pH buffering capacities. However, the relation between resting spleen volume and apnea- induced increases in Hbmass is unknown. Therefore, we tested the hypothesis that resting spleen volume is positively related to apnea-induced increases in total Hbmass. Methods: Fourteen healthy adults (six women; 29 ± 5 years) completed a two-minute carbon monoxide rebreathe procedure to measure pre-apneas Hbmass and blood volume. Spleen length, width, and thickness were measured pre-and post-five maximal apneas via ultrasound. Spleen volume was calculated via the Pilström equation (test-retest CV:2 ± 2%). Hemoglobin concentration ([Hb]; g/dl) and hematocrit (%) were measured pre- and post-apneas via capillary blood samples. Post-apneas Hbmass was estimated as post-apnea [Hb] x pre-apnea blood volume. Data are presented as mean ± SD. Results: Spleen volume decreased from pre- (247 ± 95 mL) to post- (200 ± 82 mL, p<0.01) apneas. [Hb] (14.6 ± 1.2 vs. 14.9 ± 1.2 g/dL, p<0.01), hematocrit (44 ± 3 vs. 45 ± 3%, p=0.04), and Hbmass (1025 ± 322 vs. 1046 ± 339 g, p=0.03) increased from pre- to post-apneas. Pre-apneas spleen volume was unrelated to post-apneas increases in Hbmass (r=-0.02, p=0.47). O2 (+28 ± 31 mL, p<0.01) and CO2 (+31 ± 35 mL, p<0.01) carrying capacities increased post-apneas. Conclusion: Larger spleen volume is not associated with a greater rise in apneas-induced increases in Hbmass in non-apnea-trained healthy adults.

Acute moderate normobaric hypoxia does not modify circulating thyroid hormone concentrations induced by 1 h of head-out cold-water immersion.

This study tested the hypothesis that acute moderate normobaric hypoxia augments circulating thyroid hormone concentrations during and following 1 h of cold head-out water immersion (HOWI), compared with when cold HOWI is completed during normobaric normoxia. In a randomized crossover single-blind design, 12 healthy adults (27 ± 2 yr, 2 women) completed 1 h of cold (22.0 ± 0.1°C) HOWI breathing either normobaric normoxia ([Formula: see text] = 0.21) or normobaric hypoxia ([Formula: see text] = 0.14). Free and total thyroxine (T3) and triiodothyronine (T4), and thyroid-stimulating hormone (TSH) concentrations were measured in venous blood samples obtained before (baseline), during (15-, 30-, and 60 min), and 15 min following HOWI (post-), and were corrected for changes in plasma volume. Arterial oxyhemoglobin saturation and core (rectal) temperature were measured continuously. Arterial oxyhemoglobin saturation was lower during hypoxia (90 ± 3%) compared with normoxia (98 ± 1%, P < 0.001). Core temperature fell from baseline (normoxia: 37.2 ± 0.4°C, hypoxia: 37.2 ± 0.4°C) to post-cold HOWI (normoxia: 36.4 ± 0.5°C, hypoxia: 36.3 ± 0.5°C, P < 0.001) in both conditions but did not change differently between conditions (condition × time: P = 0.552). Circulating TSH, total T3, free T4, total T3, and free T4 concentrations demonstrated significant main effects of time (all P ≤ 0.024), but these changes did not differ between normoxic and hypoxic conditions (condition × time: all P ≥ 0.163). These data indicate that acute moderate normobaric hypoxia does not modify the circulating thyroid hormone response during 1 h of cold HOWI.NEW & NOTEWORTHY Acute head-out cold (22°C) water immersion (HOWI) decreased core temperature and increased thermogenesis. This thermogenic response was paralleled by the activation of the hypothalamic-pituitary-thyroid axis, as evidenced by changes in thyroid hormones. However, cold HOWI in combination with moderate normobaric hypoxia did not modify the thermogenic nor the circulating thyroid hormone response. This finding suggests that hypoxia-induced alterations in thyroid hormone concentrations are unlikely to acutely contribute to adaptations resulting from repeated cold-water exposures.

"Living High-Training Low" for Olympic Medal Performance: What Have We Learned 25 Years After Implementation?

BACKGROUND: Altitude training is often regarded as an indispensable tool for the success of elite endurance athletes. Historically, altitude training emerged as a key strategy to prepare for the 1968 Olympics, held at 2300 m in Mexico City, and was limited to the "Live High-Train High" method for endurance athletes aiming for performance gains through improved oxygen transport. This "classical" intervention was modified in 1997 by the "Live High-Train Low" (LHTL) model wherein athletes supplemented acclimatization to chronic hypoxia with high-intensity training at low altitude. PURPOSE: This review discusses important considerations for successful implementation of LHTL camps in elite athletes based on experiences, both published and unpublished, of the authors. APPROACH: The originality of our approach is to discuss 10 key "lessons learned," since the seminal work by Levine and Stray-Gundersen was published in 1997, and focusing on (1) optimal dose, (2) individual responses, (3) iron status, (4) training-load monitoring, (5) wellness and well-being monitoring, (6) timing of the intervention, (7) use of natural versus simulated hypoxia, (8) robustness of adaptative mechanisms versus performance benefits, (9) application for a broad range of athletes, and (10) combination of methods. Successful LHTL strategies implemented by Team USA athletes for podium performance at Olympic Games and/or World Championships are presented. CONCLUSIONS: The evolution of the LHTL model represents an essential framework for sport science, in which field-driven questions about performance led to critical scientific investigation and subsequent practical implementation of a unique approach to altitude training.

Fluid balance during physical work in the heat is not modified by the menstrual cycle when fluids are freely available.

We tested the hypothesis that women may be more at risk of becoming dehydrated during physical work in the heat in the early follicular phase (EF), compared with the late follicular (LF) and mid-luteal (ML) phases of the menstrual cycle when allowed free access to drink. Twelve healthy, eumenorrheic, unacclimated women (26 ± 5 yr) completed three trials (EF, LF, and ML phases) involving 4 h of exposure to 33.8 ± 0.8 °C, 54 ± 1% relative humidity. Each hour, participants walked on a treadmill for 30 min at a rate of metabolic heat production of 338 ± 9 W. Participants drank a cool, flavor-preferred non-caloric sport drink ad libitum. Nude body weight was measured pre- and post-exposure, and percent changes in body weight loss were interpreted as an index of changes in total body water. Total fluid intake and urine output were measured and sweat rate was estimated from changes in body mass corrected for fluid intake and urine output. Fluid intake was not different between phases (EF: 1,609 ± 919 mL; LF: 1,902 ± 799 mL; ML: 1,913 ± 671; P = 0.202). Total urine output (P = 0.543) nor sweat rate (P = 0.907) differed between phases. Percent changes in body mass were not different between phases (EF: -0.5 ± 0.9%; LF: -0.3 ± 0.9%; ML: -0.3 ± 0.7%; P = 0.417). This study demonstrates that the normal hormonal fluctuations that occur throughout the menstrual cycle do not alter fluid balance during physical work in the heat.NEW & NOTEWORTHY The effect of the menstrual cycle on fluid balance during physical work in the heat when fluids are freely available is unknown. This study demonstrates that fluid balance is not modified in women across three distinct phases of the menstrual cycle during physical work in the heat These results indicate that when women have free access to cool fluid during physical work in the heat, they respond similarly across all three phases to maintain fluid homeostasis across the menstrual cycle.

Increased spleen volume provoked by temperate head-out-of-water immersion.

This study tested the hypotheses that 1) spleen volume increases during head-out-of-water immersion (HOWI) and returns to pre-HOWI values postdiuresis, and 2) the magnitude of apnea-induced spleen contraction increases when preapnea spleen volume is elevated. Spleen volume was measured before and after a set of five apneas in 12 healthy adults (28 ± 5 yr, 3 females) before, during (at 30 and 150 min), and 20 min after temperate temperature (36 ± 1°C) HOWI. At each time point, spleen length, width, and thickness were measured via ultrasound, and spleen volume was calculated using the Pilström equation. Compared with pre-HOWI (276 ± 88 mL), spleen volume was elevated at 30 (353 ± 94 mL, P < 0.01) and 150 (322 ± 87 mL, P < 0.01) min of HOWI but returned to pre-HOWI volume at post-HOWI (281 ± 90 mL, P = 0.58). Spleen volume decreased from pre- to postapnea bouts at each time point (P < 0.01). The magnitude of reduction in spleen volume from pre- to postapneas was elevated at 30 min of HOWI (-69 ± 24 mL) compared with pre-HOWI (-52 ± 20 mL, P = 0.04) but did not differ from pre-HOWI at 150 min of HOWI (-54 ± 16 mL, P = 0.99) and post-HOWI (-50 ± 18 mL, P = 0.87). Thus, spleen volume is increased throughout 180 min of HOWI, and whereas apnea-induced spleen contraction is augmented after 30 min of HOWI, the magnitude of spleen contraction is unaffected by HOWI thereafter.

Dyspnea Is Attenuated by Auditory Distraction via Music with Headphones during Exercise in Healthy Individuals.

PURPOSE: This study aimed to determine whether listening to music through headphones (a) affects the sensory (breathing intensity [BI]) and/or affective (breathing unpleasantness [BU]) components of dyspnea during exercise at different intensities and (b) affects exercise performance. METHODS: Twenty-two recreationally active individuals (24 ± 3 yr, 10 women) performed two 5-min constant loads (10% below/above gas exchange threshold [GET]) and an 8-km cycling time trial with ambient laboratory noise or self-selected music in a randomized crossover design. BI, BU, and ventilation ( V̇E ) were measured at each minute of the constant loads and every 2 km of the time trial. Ratios of BU/ V̇E and BI/ V̇E were used to examine the gain in dyspnea during the time trial. RESULTS: In the 10% below GET trial, BU was reduced in the first ( P = 0.03) and final ( P = 0.04) minutes. In the 10% above GET trial, BU and BI were reduced with music ( P < 0.05). During the time trial with music, BU/ V̇E was significantly attenuated by 9%-13% ( P < 0.05) despite a greater heart rate and self-selected power output ( P < 0.05). CONCLUSIONS: Music through headphones mitigated the sensation of dyspnea and changed the accretion of dyspnea per unit increase in V̇E leading to a higher self-selected workload during self-paced exercise. The dyspnea-reducing intervention of self-selected music may improve exercise tolerance and performance and promote adherence to regular aerobic exercise.

High Intraindividual Variability in the Response of Serum Erythropoietin to Multiple Simulated Altitude Exposures.

Baranauskas, Marissa N., Timothy J. Fulton, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, and Robert F. Chapman. High intraindividual variability in the response of serum erythropoietin to multiple simulated altitude exposures. High Alt Med Biol. 23:85-89, 2022. Purpose: To evaluate within-subject variability in the serum erythropoietin (EPO) response to multiple simulated altitude exposures. Methods: Seven physically active men and women (age 27 ± 3 years, body mass index = 24.6 ± 4.0 kg/m2) were exposed to normobaric hypoxia (fraction of inspired oxygen [FiO2] = 0.14) for 12 hours on three separate occasions. Serum EPO concentrations were measured before exposure (0 hour), after 6 hours, and after 12 hours in hypoxia. The EPO response to hypoxia was calculated as percent change from 0 to 12 hours (ΔEPO0-12). Results: Exposure time had a significant effect on EPO (p < 0.001) with concentrations increasing 3.2 ± 1.3 mIU/ml from 0 to 6 hours (p = 0.034) and 4.7 ± 1.2 mIU/ml from 0 to 12 hours (p = 0.001). Group mean ΔEPO0-12 remained unchanged (p = 0.688) between the three exposures; however, there was considerable intraindividual variability in EPO responses. The intrasubject coefficient of variation for ΔEPO0-12 was 61% ± 28% (range: 17%-103%) with intrasubject associations ranging r = 0.052 to r = 0.651 between repeated exposures. Conclusions: Athletes who routinely supplement training with simulated altitude methods (e.g., hypoxic tents) should expect inconsistent EPO responses to intermittent exposures lasting ≤12 hours.

Nedocromil sodium and diphenhydramine HCl ameliorate exercise-induced arterial hypoxemia in highly trained athletes.

INTRODUCTION: Exercise-induced arterial hypoxemia (EIAH) has been observed in highly trained endurance athletes during near maximal exercise, which may be influenced by a histamine-mediated inflammatory response at the pulmonary capillary-alveolar membrane. In order to test this hypothesis, we examined whether the mast cell stabilizer nedocromil sodium (NS) and H1 -receptor antagonist diphenhydramine HCL (DH) would ameliorate EIAH and mitigate the drop in arterial oxyhemoglobin saturation (Sa O2 ) during intensive exercise. METHODS: Seven highly trained male cross country runners (age, 21 ± 2 years; V̇O2max , 74.7 ± 3.5 ml·kg-1 ·min-1 ) participated in the study. All subjects completed a maximal exercise treadmill test to exhaustion, followed by three 5-min constant-load exercise bouts at 70%, 80%, and 90% V̇O2max . Prior to testing, subjects received either placebo (PL), NS, or DH. RESULTS: Compared to PL, there was a significant treatment effect on Sa O2 (p < 0.001) for both NS and DH during both constant-load exercise and at V̇O2max . Post hoc tests revealed Sa O2  values, compared to PL, were significantly higher at V̇O2max and during DH trials and higher with NS at constant-load intensities except at 70% (p = 0.13). CONCLUSION: The findings provide further evidence that histamine contributes directly or indirectly to the development of EIAH during intense exercise in highly trained athletes.

A Narrative Analysis of the Progression in the Top 100 Marathon, Half-Marathon, and 10-km Road Race Times from 2001 to 2019.

PURPOSE: This study aimed to characterize and describe finishing time trends of the fastest 100 performers in the men's and women's marathon, half-marathon, and road 10-km each year from 2001 to 2019 and assess the underlying basis for recent performance improvements. METHODS: The top 100 performers for each sex, event, and year were partitioned into four arbitrary ranking groups: 1-10, 11-25, 26-50, and 51-100. The percent improvement in mean performance time for each year beyond 2001 was calculated for each ranking group, event, and sex. Multiple linear regression was also used to determine improvement trend for each ranking group, both sexes, and all events for each 3-yr period between Olympic years. RESULTS: In total, 11,400 performances in the marathon, half-marathon, and 10-km road races from 2001 to 2019 were analyzed. The 3-yr period preceding the original date of the Tokyo Olympics (2017-2019) accounted for 44% and 35% of the overall improvement in marathon time from 2001 to 2019 for women and men, respectively. The years 2017-2019 featured the largest average improvement of any 3-yr period and was the only period where nearly every ranking group in every event for both sexes improved. CONCLUSIONS: The results suggest that recent world record performances are a result of overall circumstances affecting road racing (e.g., shoe technology) rather than the outstanding physiology of individual top runners, per se.

World Championship and Olympic Games Experience Influences Future Medal Performance in Track-and-Field Athletes.

Some track-and-field national governing bodies send athletes to World Championship and Olympic Games (WC/OG) to gain experience that may positively impact future success, even though athletes may not be expected to place high or medal. However, it is unclear if this strategy is advantageous for future medal attainment. PURPOSE: To determine if participation and/or advancement at a track-and-field athlete's first WC/OG influences the odds of future medaling. METHODS: Performances of US track-and-field athletes who made their first WC/OG team during 2000-2013 were tracked through 2016 to stratify athletes into categories. Athletes who medaled on their first team or never made a subsequent team (ie, no experience) were compared with athletes who did not medal on their first team but made subsequent teams (ie, experience). The experience group was further divided into athletes who advanced or did not advance out of the initial round at their first competition for a secondary analysis. Odds ratios (ORs) were calculated using logistic regression to measure the association between experience level and medaling. RESULTS: A significant OR was obtained for advanced versus did not advance (OR = 2.29, 95% confidence interval, 1.07-4.89, P = .03), but not for experience versus no experience (OR = 1.04, 95% confidence interval, 0.60-1.78, P = .91) group. CONCLUSIONS: Advancing out of the initial round of competition during an athlete's first WC/OG competition is associated with increased odds of future medaling. National governing bodies should consider this "experience threshold" during team selection processes.

Variation in Heart-Rate Profile During a Prolonged, Submaximal Swim Bout.

PURPOSE: To describe the heart-rate (HR) response during a prolonged, submaximal, multirepetition swimming bout (ie, typical early-season swimming training), as there is currently little or no literature on this topic. METHODS: A total of 12 collegiate swimmers were instructed to complete sixty 91.4-m (100-yd) freestyle repetitions at their fastest sustainable pace, allowing between 5 and 10 seconds of rest between repetitions. Each swimmer was outfitted with a cardiotachometer, which monitored HR throughout the trial. Completion time (CT) was also recorded for each repetition. Individual means of HR and CT were calculated, and linear mixed models were used to determine the trend across repetitions and between- and within-subject SD for HR and CT. RESULTS: The mean (SD) value for HR was 167.8 (10.8) beats per minute (bpm), for CT was 68.7 (4.1) seconds, and for percentage of best time was 71.2% (4.5%). There was no change (Δ rep 55-6) in HR (-0.1 bpm; 95% confidence interval, -6.8 to 6.6 bpm; P = .97), whereas CT increased (3.0 s; 95% confidence interval, 1.5-4.4 s; P = .001). The between-subjects SD (95% confidence interval) for HR was 12.6 (8.4-19.3 bpm) and for CT was 4.6 (3.1-7.0 s). The within-subject SDs for HR and CT were 4.0 (3.8-4.3 bpm) and 0.9 (0.8-0.95 s), respectively. CONCLUSIONS: The inherent individual variability between swimmers in HR during training suggests that coaches carefully consider the common practice of prescribing workout intensity using rigid HR zones.

Influence of Zinc on the Acute Changes in Erythropoietin and Proinflammatory Cytokines with Hypoxia.

Baranauskas, Marissa N., Joseph Powell, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, Hunter L. Paris, and Robert F. Chapman. Influence of zinc on the acute changes in erythropoietin and proinflammatory cytokines with hypoxia. High Alt Med Biol. 22: 148-156, 2021. Background: Considerable, unexplained, interindividual variability characterizes the erythropoietin (EPO) response to hypoxia, which can impact hematological acclimatization for individuals sojourning to altitude. Zinc supplementation has the potential to alter EPO by attenuating increases in inflammation and oxidative stress. Yet, the application of such an intervention has not been evaluated in humans. In this proof-of-concept study, we aimed to evaluate the EPO and inflammatory responses to acute hypoxia in human participants following chronic zinc supplementation. Methods: Nine physically active participants (men n = 5, women n = 4, age 28 ± 4 years, height 176 ± 11 cm, mass 77 ± 21 kg) were exposed to 12 hours of normobaric hypoxia simulating an altitude of 3,000 m (FiO2 = 0.14) before and after 8 weeks of supplementation with 40 mg/day of elemental zinc from picolinate. Blood samples for subsequent analysis of serum zinc, EPO, superoxide dismutase (extracellular superoxide dismutase [EC-SOD]), C-reactive protein (CRP), and proinflammatory cytokines were obtained pre- and postsupplementation and exposure to hypoxia. Results: After zinc supplementation, EPO increased by 64.9 ± 36.0% (mean ± standard deviation) following 12 hours of hypoxia, but this response was not different from presupplementation (70.8 ± 46.1%). Considerable interindividual (range: -1% to +208%) variability was apparent in the acute EPO response. While most markers of inflammation did not change with hypoxia, interleukin-6 concentrations increased from 1.17 ± 0.05 to 1.97 ± 0.32 pg/ml during the final 6 hours. The acute EPO response at 12 hours was not related to changes in serum zinc, EC-SOD, CRP, or proinflammatory cytokines. Conclusions: Zinc supplementation does not influence the acute EPO or inflammatory response with short-term exposure to moderate levels of normobaric hypoxia (3,000 m) in apparently healthy young adults.

Heat Versus Altitude Training for Endurance Performance at Sea Level.

Environmental stressors, such as heat or altitude, elicit dissimilar physiological adaptations to endurance training programs. Whether these differences (i.e., increased hemoglobin mass vs plasma volume) differentially influence performance is debated. We review data in support of our novel hypothesis, which proposes altitude as the preferred environmental training stimulus for elite endurance athletes preparing to compete in temperate, sea-level climates (5°C-18°C).

Ventilatory Responsiveness during Exercise and Performance Impairment in Acute Hypoxia.

INTRODUCTION: An adequate increase in minute ventilation to defend arterial oxyhemoglobin saturation (SpO2) during hypoxic exercise is commonly viewed as an important factor contributing to large inter-individual variations in the degree of exercise performance impairment in hypoxia. Although the hypoxic ventilatory response (HVR) could provide insight into the underpinnings of such impairments, it is typically measured at rest under isocapnic conditions. Thus, we aimed to determine whether 1) HVR at rest and during exercise are similar and 2) exercise HVR is related to the degree of impairment in cycling time trial (TT) performance from normoxia to acute hypoxia (∆TT). METHODS: Sixteen endurance-trained men (V˙O2peak, 62.5 ± 5.8 mL·kg-1·min-1) performed two poikilocapnic HVR tests: one during seated rest (HVRREST) and another during submaximal cycling (HVREX). On two separate visits, subjects (n = 12) performed a 10-km cycling TT while breathing either room air (FiO2 = 0.21) or hypoxic gas mixture (FiO2 = 0.16) in a randomized order. RESULTS: HVREX was significantly (P < 0.001) greater than HVRREST (1.52 ± 0.47 and 0.22 ± 0.13 L·min-1·%SpO2-1, respectively), and these measures were not correlated (r = -0.16, P = 0.57). ∆TT was not correlated with HVRREST (P = 0.70) or HVREX (P = 0.54), but differences in ventilation and end-tidal CO2 between hypoxic and normoxic TT and the ventilatory equivalent for CO2 during normoxic TT explained ~85% of the variance in performance impairment in acute hypoxia (P < 0.01). CONCLUSION: We conclude that 1) HVR is not an appropriate measure to predict the exercise ventilatory response or performance impairments in acute hypoxia and 2) an adequate and metabolically matched increase in exercise ventilation, but not the gain in the ventilatory response to hypoxia, is essential for mitigating hypoxia-induced impairments in endurance cycling performance.

Respiratory Muscle Fatigue Alters Cycling Performance and Locomotor Muscle Fatigue.

PURPOSE: This study aimed to determine if preexisting respiratory muscle fatigue (RMF) alters motoneuronal output, locomotor muscle fatigue, and cycling performance. METHODS: Eight trained male cyclists performed 5-km cycling time trials after a resistive breathing task that induced RMF and under control conditions (CON). Motoneuronal output was estimated using vastus lateralis surface electromyography, and locomotor muscle fatigue was quantified as the change in potentiated quadriceps twitch force from preexercise to postexercise. RESULTS: Time to complete the time trial was 1.9% ± 0.9% longer in RMF compared with CON (P < 0.001). Estimated motoneuronal output was lower in RMF compared with CON during 1 km (45% ± 11% vs 53% ± 13%, P = 0.004) and 2 km (45% ± 14% vs 51% ± 14%, P = 0.008), but was not different thereafter. Ventilation was lower in RMF compared with CON during 1 km (114 ± 19 vs 135 ± 24 L·min, P = 0.003) and 2 km (136 ± 23 vs 152 ± 31 L·min, P = 0.009); however, ratings of dyspnea were similar. After the 5-km time trial, locomotor muscle fatigue was attenuated in RMF compared with CON (-22% ± 6%, vs -28% ± 7%, P = 0.02). CONCLUSIONS: Alterations to dyspnea for a given ventilation seem to have constrained power output during cycling exercise, thereby limiting the development of locomotor muscle fatigue. These findings indicate that the respiratory system is an integral component in a global feedback loop that regulates exercise performance and the development of locomotor muscle fatigue.

Attentional focus does not impact locomotor-respiratory coupling in trained runners.

PURPOSE: The purpose of this study was to explore relationships between attentional strategies and LRC, running economy, perceived exertion, and dyspnea. METHODS: 25 endurance-trained males ([Formula: see text]O2max = 68.2 ± 4.7 mL kg-1 min-1) ran for 5 min each at two different submaximal speeds, during which LRC and oxygen consumption ([Formula: see text]O2) were measured. The degree of LRC was calculated as the percentage of breaths occurring during the same decile of the step cycle. Attentional focus was assessed at the end of exercise using an Attentional Focusing Questionnaire, with subscales for association, dissociation, and distress. RESULTS: We found no significant relationships between attentional focus measures and LRC. However, dissociation scores were positively correlated with [Formula: see text]O2 (r = 0.404), as well as  %[Formula: see text]O2max (r = 0.474), at the slower running speed. Distress scores were the only attentional focus subscale related to perceived exertion and dyspnea (r = 0.378 to 0.654). CONCLUSION: These findings suggest attentional focus is not driving the high levels of LRC seen in trained endurance athletes but may relate to running economy and perceptual responses.

Serum ferritin distribution in elite athletes.

OBJECTIVES: It is not uncommon for athletes to be diagnosed with iron deficiency, yet there remains uncertainty whether the prevalence of suboptimal iron status in elite athletes differs from the normal population or warrants routine screening. The purpose of this study is to describe the distribution of serum ferritin (SF) in a cohort of elite athletes. DESIGN: Retrospective cohort study. METHODS: Electronic health records of 1085 elite adult athletes (570 women, 515 men) from 2012-2017 were examined retrospectively. SF values were compared to published normal population data. The proportion of athletes meeting criterion values for iron deficiency or initiation of treatment was examined. RESULTS: SF distributions in male athletes were significantly lower than normal males aged 20 to <24yrs. (χ2 28.8, p<0.001) and aged 24 to <28yrs. (χ2 91.9, p<0.001). SF status was similar in female athletes and normal women aged 20 to <24yrs. (χ2 9.5, p>0.05) or aged 24 to <28yrs. (χ2 11.5, p>0.05). Using 35ng/ml as the criterion value for stage one iron deficiency, 15% of male athletes and 52% of female athletes displayed suboptimal iron status. CONCLUSIONS: Male athletes have a significantly lower population distribution of SF values as compared to normative data on healthy males, with 15% of male athletes having suboptimal SF status. The distribution of SF values in elite female athletes did not differ from population values, however approximately half women athletes were iron deficient. These data suggest that iron screening should be considered in both male and female athlete populations.

"Train-High Sleep-Low" Dietary Periodization Does Not Alter Ventilatory Strategies During Cycling Exercise.

Objective: The purpose of this study was to investigate the effects of "train-high sleep-low" (THSL) dietary periodization on ventilatory strategies during cycling exercise at submaximal and maximal intensities.Method: In a randomized crossover design, 8 trained men [age (mean ± SEM) = 28 ± 1 y; peak oxygen uptake = 56.8 ± 2.4 mL kg-1 min-1] completed two glycogen-depleting protocols on a cycle ergometer on separate days, with the cycling followed by a low carbohydrate (CHO) meal and beverages containing either no additional CHO (THSL) or beverages containing 1.2 g kg-1 CHO [traditional CHO replacement (TRAD)]. The following morning, participants completed 4 minutes of cycling below (Stage 1), at (Stage 2), and above (Stage 3) gas exchange threshold, followed by a 5-km time trial.Results: Timetrial performance was significantly faster in TRAD compared to THSL (8.7 ± 0.3 minutes and 9.0 ± 0.3 minutes, respectively; p = 0.02). No differences in ventilation, tidal volume, or carbon dioxide production occurred between conditions at any exercise intensity (p > 0.05). During Stage 1, oxygen uptake was 37.9 ± 1.5 mL kg-1 min-1 in the TRAD condition and 39.6 ± 1.8 mL kg-1 min-1 in THSL (p = 0.05). During Stage 2, VO2 was 44.6 ± 1.7 mL kg-1 min-1 in the TRAD condition and 47.0 ± 1.9 mL kg-1 min-1 in THSL (p = 0.07). No change in operating lung volume was detected between dietary conditions (p > 0.05).Conclusions: THSL impairs performance following the dietary intervention, but this occurs with no alteration of ventilatory measures.

Iron insufficiency diminishes the erythropoietic response to moderate altitude exposure.

The effects of iron stores and supplementation on erythropoietic responses to moderate altitude in endurance athletes were examined. In a retrospective study, red cell compartment volume (RCV) responses to 4 wk at 2,500 m were assessed in athletes with low (n = 9, ≤20 and ≤30 ng/mL for women and men, respectively) and normal (n = 10) serum ferritin levels ([Ferritin]) without iron supplementation. In a subsequent prospective study, the same responses were assessed in athletes (n = 26) with a protocol designed to provide sufficient iron before and during identical altitude exposure. The responses to a 4-wk training camp at sea level were assessed in another group of athletes (n = 13) as controls. RCV and maximal oxygen uptake (V̇o2max) were determined at sea level before and after intervention. In the retrospective study, athletes with low [Ferritin] did not increase RCV (27.0 ± 2.9 to 27.5 ± 3.8 mL/kg, mean ± SD, P = 0.65) or V̇o2max (60.2 ± 7.2 to 62.2 ± 7.5 mL·kg-1·min-1, P = 0.23) after 4 wk at altitude, whereas athletes with normal [Ferritin] increased both (RCV: 27.3 ± 3.1 to 29.8 ± 2.4 mL/kg, P = 0.002; V̇o2max: 62.0 ± 3.1 to 66.2 ± 3.7 mL·kg-1·min-1, P = 0.003). In the prospective study, iron supplementation normalized low [Ferritin] observed in athletes exposed to altitude (n = 14) and sea level (n = 6) before the altitude/sea-level camp and maintained [Ferritin] within normal range in all athletes during the camp. RCV and V̇o2max increased in the altitude group but remained unchanged in the sea-level group. Finally, the increase in RCV correlated with the increase in V̇o2max [(r = 0.368, 95% confidence interval (CI): 0.059-0.612, P = 0.022]. Thus, iron deficiency in athletes restrains erythropoiesis to altitude exposure and may preclude improvement in sea-level athletic performance.NEW & NOTEWORTHY Hypoxic exposure increases iron requirements and utilization for erythropoiesis in athletes. This study clearly demonstrates that iron deficiency in athletes inhibits accelerated erythropoiesis to a sojourn to moderate high altitude and may preclude a potential improvement in sea-level athletic performance with altitude training. Iron replacement therapy before and during altitude exposure is important to maximize performance gains after altitude training in endurance athletes.