Joyner, Michael

Background: Hypoxia challenges the regulation of arterial oxygenation (SaO 2 ), eliciting a compensatory increase in ventilation ([Formula: see text]E) to preserve blood-gas homeostasis. However, the ability to maintain blood-gas homeostasis during hypoxic exercise may differ between sexes due to differences in chemoreflex drive and the mechanical capacity to augment ventilation. The purpose of this study was to evaluate sex differences in ventilatory and blood-gas responses to progressive hypoxia during moderate walking exercise. Specifically, we asked whether females would be more susceptible to hypoxemia. We hypothesized that females would exhibit a smaller ventilatory response and a less steep ventilatory CO 2 -response (Δ[Formula: see text]E/ΔPaCO 2 ) compared with males, resulting in a greater reduction in SaO 2 during progressive hypoxia. Methods: Twenty-six physically active adults (15M: age 35.3±9.4; [Formula: see text]O 2 max 54.3±15.5 mL/kg/min, 11F: age 36.2±9.0; [Formula: see text]O 2 max 44.6±5.2 mL/kg/min) were studies during two visits. Visit 1: we determined the participants’ maximal oxygen uptake ([Formula: see text]O 2 max) during an incremental treadmill test. Visit 2: participants walked at ~50% of their [Formula: see text]O 2 max while we reduced the fraction of inspired oxygen (FiO 2 ) progressively every 5 minutes (0.21, 0.19, 0.17, 0.15, 0.13, 0.12, 0.11). Arterial blood samples were collected from a brachial artery catheter during the final 30 seconds of each stage; cardiometabolic and ventilatory data were averaged over the final minute of each stage. The test ended when peripheral oxygen saturation (SpO 2 ) fell below 70%. Because 0.13 FiO 2 was the lowest stage completed by all participants, Δ responses were calculated from 0.21 to 0.13 FiO 2 . Independent t-tests compared Δ responses between sexes; data are mean±SD, significance was set at p < 0.05. Results: There was no significant difference in ΔSaO 2 between sexes across hypoxia (M: −22.0±3.7%; F: −22.8±5.5%; p = 0.89). Males had higher arterial oxygen content (CaO 2 ) than females across all stages (M: 20.6±1.2 to 16.0±1.4 mL O 2 ·dL -1 ; F: 18.5±1.1 to 13.8±2.0 mL O 2 ·dL -1 ), but the ΔCaO 2 during hypoxia was not significantly different between sexes (M: −4.6±0.7; F: −4.7±1.4 mL O 2 ·dL -1 ; p = 0.86). Similarly, there was no significant difference in the change in arterial CO 2 (ΔPaCO 2 ) between sexes (M: −5.8±1.5 mmHg; F: −6.5±3.6 mmHg, p = 0.51). In contrast, males exhibited a significantly greater increase in ventilation (Δ[Formula: see text]E: +13.9±4.2 L·min -1 ) than females (+8.6±2.7 L·min -1 ; p = 0.003). Consequently, the ventilatory CO 2 -response (Δ[Formula: see text]E/ΔPaCO 2 ) was steeper in males (−2.46±0.66 L·min -1 ·mmHg -1 ) compared with females (−1.57±0.68 L·min -1 ·mmHg -1 ; p = 0.004). However, when Δ[Formula: see text]E was expressed relative to maximal ventilatory capacity (%[Formula: see text]Emax), there was no sex difference (M: 8.8±2.6% vs F: 8.3±2.8%; p = 0.68). Conclusion: Females were not more susceptible to hypoxemia than males; both sexes showed comparable reductions in SaO 2 during moderate exercise in progressive hypoxia. Reductions in PaCO 2 were also similar, indicating comparable ventilatory drive. Although males exhibited a larger absolute increase in [Formula: see text]E and a steeper ventilatory CO 2 -response, this difference disappeared when Δ[Formula: see text]E was expressed relative to %[Formula: see text]Emax. These findings indicate that apparent sex differences in ventilation during hypoxia largely reflect differences in ventilatory capacity rather than true differences in oxygenation or ventilatory drive. Taken together, these findings challenge the assumption that females are inherently more susceptible to hypoxemia or have a lower ventilatory drive than males during moderate hypoxic exercise. Funding: NIH T32 DK007352, UL1 TR002377 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: During hypoxic exercise, oxygen transport becomes increasingly challenged as oxygen availability decreases. As the inspired oxygen fraction (FiO 2 ) decreases, peripheral oxygen saturation (SpO 2 ) gradually declines, then drops rapidly upon reaching the steepest point of the sigmoidal shaped, oxyhemoglobin dissociation curve. This reduction in FiO 2 creates a distinct SpO 2 “breakpoint,” which likely represents the threshold at which compensatory mechanisms, such as increases in ventilation and cardiac output, can no longer maintain arterial oxygenation. Several physiological factors may modulate this breakpoint, including hemoglobin concentration, blood volume, and ventilatory capacity. This study aimed to determine the SpO 2 breakpoint during steady-state, submaximal, hypoxic exercise and examine whether factors like sex, age, and fitness level influence the SpO 2 breakpoint. We hypothesized that SpO 2 breakpoints would differ by sex, age, and fitness level, with earlier breakpoints visible in females, older adults, and those with higher aerobic fitness. Methods: Twenty-six physically active adults (15M: age 35±9 yrs, [Formula: see text]O 2 max 54.3±15.5 mL/kg/min, 11F: age 38±10 yrs, [Formula: see text]O 2 max 44.6±5.2 mL/kg/min) participated in a two-day study. Day one: participants performed a treadmill [Formula: see text]O 2 max test. Day two: participants walked at a steady state of ~50% of their [Formula: see text]O 2 max, for 40 minutes, while FiO 2 was progressively reduced every 5 minutes in a stepwise fashion (0.25, 0.21, 0.19, 0.17, 0.15, 0.13, 0.12, 0.11). The test was terminated when SpO 2 dropped below 70%. SpO 2 was measured continuously using a clinical-grade oximeter. Analysis was performed in RStudio by first determining each participant’s individual SpO 2 vs time breakpoint. Male and Female breakpoints were compared to assess sex-based differences. To evaluate whether SpO 2 breakpoint timing differed by age or fitness level, participants were then divided into tertiles for each variable. Age tertiles were derived from the sample distribution of chronological age, and fitness tertiles were defined using [Formula: see text]O 2 max (L/min). Mean breakpoint times were compared between the highest and lowest tertiles for both age and fitness. Mean SpO 2 breakpoints were compared between groups using independent sample t-tests. Significance was set to p< 0.05. Results: The overall mean breakpoint occurred at an SpO 2 of 90.7±2.8% during the 0.17 FiO 2 stage. No significant sex differences were observed in breakpoint SpO 2 and timing (M: SpO 2 = 90.7±2.7%, time = 18.6 min; F: SpO 2 = 90.7±3.0%, time = 17.7 min; p = 0.961). Age did not significantly influence breakpoint (younger tertile [21-30 yrs] SpO 2 = 91.0±2.4%, time = 18.4 min; older tertile [41-60 yrs] SpO 2 = 91.1±2.4%, time = 17.2 min, p = 0.953). Additionally, fitness level showed no significant difference on breakpoint (low fitness [1.91-3.01 L/min]: SpO 2 = 90.3±3.1%, time = 17.8 min; high fitness [4.38-5.25 L/min]: SpO 2 = 90.4±2.9%, time = 19.2 min; p = 0.992). Conclusion: During a hypoxic, steady state walking exercise, at ~50% [Formula: see text]O 2 max, we observed no difference in the peripheral oxygen saturation breakpoint, across sex, age, and fitness level. This may suggest that moderate exercise in hypoxia does not sufficiently challenge the cardiopulmonary system for individual variations in oxygen transport to influence the breakpoint. These findings imply that the SpO 2 breakpoint, during hypoxic exercise, may represent a physiological marker of the upper limit for maintaining oxygen saturation in healthy adults. Applying this protocol to identify SpO 2 breakpoints may offer insights for improving pharmacological interventions and our understanding of clinical populations with impaired oxygen transport. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Sex hormone concentrations, particularly testosterone, are primary determinants of sex-based differences in athletic and sports performance, and this relationship may inform fair competition and participation for athletes. This article describes the sex-based dichotomy in testosterone and the implications for sex-based differences in individual sports performance, including factors that relate to athletic performance for transgender individuals, and areas of future investigation.

Abstract Lifestyle interventions are pivotal for successful management of type 2 diabetes (T2D), however, the proportion of people with T2D adhering to physical activity advice has not been thoroughly studied. The purpose of this systematic review was to summarise the evidence on adherence to exercise or physical activity components in lifestyle interventions in those with T2D. We searched MEDLINE EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Scopus on 12 November 2019. Eligible studies enrolled adults with T2D and reported the proportion of adherence to lifestyle interventions as a primary or secondary outcome. We included 11 studies (nine randomised controlled trials (RCTs) enrolling 1717 patients and two nonrandomised studies enrolling 62 patients). Only one of the studies had low risk of bias. The proportion of participants adhering to physical activity varied from 32% to 100% with a median of 58%. Adherence was higher in interventions using supervised training and lowest in interventions using remote coaching and the adherence rate in observational studies was higher compared to RCTs (92% vs. 55%; p < 0.01). Study duration, risk of bias, or participants' sex, were not associated with adherence to physical activity. The proportion of those with T2D adhering to physical activity interventions for T2D varies widely and most of the included studies had a high risk of bias. These findings have important implications for planning and power analysis of future trials and when counselling patients about lifestyle interventions including physical activity or exercise components.

AbstractBackgroundRapid gastric emptying, increased food intake, and alterations in gastrointestinal hormones are associated with obesity. The effect of regular physical activity (PA) on food intake, gastric emptying (GE), gastric accommodation, and gastrointestinal (GI) hormones in adults with obesity remains unclear. Our aim was to compare, at time of presentation, weight trends, eating behavior, GE, and GI hormone levels among individuals with obesity who engage in regular PA compared to those who do not.MethodsIn 270 participants with obesity, we performed validated measurements of GI phenotypes: GE of solids and liquids, gastric volume (GV) during fasting and after consumption of 200 mL Ensure®, satiety by kcal intake (T‐kcal) during a buffet meal, satiation (volume to fullness [VTF] and maximal tolerated volume [MTV]) of a liquid nutrient, and plasma levels of fasting and postprandial GLP‐1, PYY, CCK, and ghrelin. Physical Activity Stages of Change Questionnaire was used to assess whether participants were regularly PA or not.Key resultsPA was associated with lower BMI (Δ 2.01 kg/m2, P = .001) and body weight (Δ 4.42 kg, P = .0278). GE of solids (T‐50% Δ 7.54 min, P = .021) and liquids (T‐50% Δ 2.99 min, P = .029%) was significantly more rapid in physically active participants. PA was also associated with relatively higher postprandial ghrelin AUC (Δ 10.4 pg/mL, P = .015). There was no significant difference in postprandial satiation, satiety, GV, or other GI hormones (CCK, PYY, or GLP‐1) between groups.Conclusions & InferencesPhysical activity is associated with lower BMI, but faster GE and higher postprandial ghrelin levels, two factors that are also associated with obesity.

Objectives: The Ice Hockey Summit III provided updated scientific evidence on concussions in hockey to inform these 5 objectives: (1) describe sport related concussion (SRC) epidemiology; (2) classify prevention strategies; (3) define objective, diagnostic tests; (4) identify treatment; and (5) integrate science and clinical care into prioritized action plans and policy. Methods: Our action plan evolved from 40 scientific presentations. The 155 attendees (physicians, athletic trainers, physical therapists, nurses, neuropsychologists, scientists, engineers, coaches, and officials) voted to prioritize these action items in the final Summit session. Results: To (1) establish a national and international hockey database for SRCs at all levels; (2) eliminate body checking in Bantam youth hockey games; (3) expand a behavior modification program (Fair Play) to all youth hockey levels; (4) enforce game ejection penalties for fighting in Junior A and professional hockey leagues; (5) establish objective tests to diagnose concussion at point of care; and (6) mandate baseline testing to improve concussion diagnosis for all age groups. Conclusions: Expedient implementation of the Summit III prioritized action items is necessary to reduce the risk, severity, and consequences of concussion in the sport of ice hockey.