Endogenous Opioids and Exercise-Related Hypoalgesia: Modern Models, Measurement, and Mechanisms of Action.

This chapter will focus on the role exercise appears to have on activation and modulating factors within the central nervous system related to endogenous like opioids and its possible contribution to exercise-induced hypoalgesia. The implications for the exercise-mediated alterations of CNS activation factors related to opioids, specifically endorphins and enkephalins, will be presented. In this update, we discuss utilization of new technology and methods to monitor mechanisms of opioid involvement to suggest their contribution with exercise mediated hypoalgesia as well as their relationships to alterations of perceptions of pain and mood. Several special populations were included to suggest that not all individuals will respond to the exercise by mediating hypoalgesia. Factors that may confound the current understanding and suggestions from the recent literature will be presented as well as suggestions for future investigations.

The effects of separate and simultaneous upper and lower body cycling on cardiorespiratory responses in young men.

BACKGROUND: The aim of the present study was to examine the relative cardiorespiratory and perceptual responses to upper body ergometry, lower body ergometry, and combined upper and lower body ergometry at increasing exercising intensities. METHODS: Eight healthy males between 19 and 30 years of age completed three exercise sessions over seven days that included graded leg ergometry, arm ergometry, and combined arm and leg ergometry in counterbalanced fashion. During leg-only and arm-only sessions, participants exercised at workloads of 0, 32, 64, and 95 W. The combined session involved simultaneous arm and leg ergometry at 0, 32, 64, and 95 W, thus eliciting double the total power output of arm-only and leg-only sessions. RESULTS: At all workloads, oxygen consumption and minute ventilation responses were greater during combined arm and leg exercise than during leg-only or arm-only exercise. However, the pattern of changes in heart rate, systolic blood pressure, rate pressure product, and rating of perceived exertion (RPE) were similar in response to arm-only and combined upper and lower body exercise, despite combined exercise involving double the workload. These cardiorespiratory and perceptual responses were significantly lower during leg-only only exercise. CONCLUSIONS: The results of the study add to limited research comparing physiological and perceptual responses to upper, lower, and combined upper and lower body exercise. The findings highlight heightened cardiorespiratory and perceptual responses to upper body exercise alone or in combination with lower body exercise. Training that combines upper and lower body may create higher power output and elicit greater caloric expenditure while eliciting similar cardiovascular responses as upper body only exercise at moderate and higher intensities.

The effects of peripheral hormone responses to exercise on adult hippocampal neurogenesis.

Over the last decade, a considerable amount of new data have revealed the beneficial effects of exercise on hippocampal neurogenesis and the maintenance or improvement of cognitive function. Investigations with animal models, as well as human studies, have yielded novel understanding of the mechanisms through which endocrine signaling can stimulate neurogenesis, as well as the effects of exercise on acute and/or chronic levels of these circulating hormones. Considering the effects of aging on the decline of specific endocrine factors that affect brain health, insights in this area of research are particularly important. In this review, we discuss how different forms of exercise influence the peripheral production of specific endocrine factors, with particular emphasis on brain-derived neurotrophic factor, growth hormone, insulin-like growth factor-1, ghrelin, estrogen, testosterone, irisin, vascular endothelial growth factor, erythropoietin, and cortisol. We also describe mechanisms through which these endocrine responses to exercise induce cellular changes that increase hippocampal neurogenesis and improve cognitive function.

Relative energy deficiency in sports (RED-S): elucidation of endocrine changes affecting the health of males and females.

The purpose of this review is to present a different perspective of the relative energy deficiency syndrome, to improve understanding of associated endocrine alterations, and to highlight the need for further research in this area. The term "female athlete triad" was coined over 25 years ago to describe three interrelated components: disordered eating, menstrual dysfunction, and low bone mass. The syndrome's etiology is attributed to energy intake deficiency relative to energy expenditure required for health, function, and daily living. Recently, it became clear that there was a need to broaden the term, as the disorder is not an issue of only three interrelated problems but of a whole spectrum of insults resulting from low energy availability (LEA; i.e., insufficient energy availability to cover basic physiological demands) that can potentially affect any exerciser, irrespective of gender. The new model, termed relative energy deficiency in sport (RED-S), has received greater scrutiny in sports medicine due to its effects on both health and performance in athletes of both sexes. RED-S results from low-energy diets (intentional or unintentional) and/or excessive exercise. Energy deficiency reduces hypothalamic pulsatile release of gonadotropin-releasing hormone, this impairing anterior pituitary release of gonadotropins. In women, reduced FSH and LH pulsatility produces hypoestrogenism, causing functional hypothalamic amenorrhea and decreased bone mass. In men, it reduces testosterone and negatively affects bone health. Moreover, LEA alters other hormonal pathways, causing physiological consequences, such as alteration of the thyroid hormone signaling pathways, leptin levels, carbohydrate metabolism, the growth hormone/insulin-like growth factor-1 axis, and sympathetic/parasympathetic tone. This review explains and clarifies the effects of RED-S in both sexes.

Five Weeks of Aquatic-Calisthenic High Intensity Interval Training Improves Cardiorespiratory Fitness and Body Composition in Sedentary Young Adults.

Aquatic exercise may be better tolerated by sedentary, overweight individuals than land-based exercise. The purpose of the present study was to determine the effects of five weeks of aquatic high-intensity interval training (AHIIT) using standard calisthenic pool exercises, on cardiorespiratory fitness and body composition in sedentary young adults. Eleven college-age participants (9 women, 2 men) completed 15 exercise sessions that included three sessions per week for five weeks. Each session consisted of a five-minute warm-up period, 25 minutes of exercise, and a five-minute cool down. A training progression based upon standard progression principals from a pilot study was implemented. The exercises consisted of 25 exercise intervals lasting 10-30 seconds in duration, utilizing combinations of 8-12 different exercises. Twenty-two standard aquatic upper body, lower body, and full body aerobic exercises, most of which utilized aquatic dumbbells or hand paddles, were performed in an AHIIT protocol during each exercise session. Reductions in body composition (32.6 to 30.6% fat), submaximal (169 to 165 b·min-1) and peak heart rate (199 to 192 b·min-1), submaximal VO2 (21.7 to 19.3 ml·kg-1·min-1 and peak VO2 (30.5 to 31.95 ml·kg-1·min-1) occurred from pre- to post-program. This is the first study to determine the effectiveness of standard aquatic calisthenic exercises used in an AHIIT protocol. Improvements in cardiorespiratory fitness and exercise economy as well as body composition were observed in these sedentary individuals.

A Hydrothermally Processed Maize Starch and Its Effects on Blood Glucose Levels During High-Intensity Interval Exercise.

Hetrick, MM, Naquin, MR, Gillan, WW, Williams, BM, and Kraemer, RR. A hydrothermally processed maize starch and its effects on blood glucose levels during high-intensity interval exercise. J Strength Cond Res 32(1): 3-12, 2018-A hydrothermally processed maize starch (HPMS) has been shown to blunt initial blood glucose and insulin response during endurance activity at 70% maximal oxygen uptake (V[Combining Dot Above]O2max). High-intensity interval training (HIIT) is a form of exercise that has many health benefits although it is only performed for short periods of time with interspersed rest periods. The purpose of this study was to compare the blood glucose and associated metabolic stress responses to a sprint interval cycling (SIC) exercise protocol (a form of HIIT) with and without an HPMS in a healthy population. Fourteen subjects completed a total of 4 sessions: a preliminary session, an SIC session with HPMS, an SIC session without HPMS, and a control session in which only HPMS was ingested. Blood glucose, blood lactate, respiratory exchange ratio, oxygen consumption, and rating of perceived exertion responses were recorded during the sessions. There was a significant and progressive rise in blood glucose levels during each of the cycle sprints of both exercise sessions, but not a significant difference between treatment or nontreatment SIC sessions. This is the first study to determine blood glucose responses to SIC after each sprint interval and to report that ingestion of HPMS does not affect glucose responses to SIC. The findings provide some preliminary evidence suggesting subjects at risk for glucose excursions could use SIC to improve health through monitoring blood glucose concentrations during SIC and if necessary, modifying number, intensity, and duration of sprints completed.

Validity of Wearable Activity Monitors during Cycling and Resistance Exercise.

INTRODUCTION: The use of wearable activity monitors has seen rapid growth; however, the mode and intensity of exercise could affect the validity of heart rate (HR) and caloric (energy) expenditure (EE) readings. There is a lack of data regarding the validity of wearable activity monitors during graded cycling regimen and a standard resistance exercise. The present study determined the validity of eight monitors for HR compared with an ECG and seven monitors for EE compared with a metabolic analyzer during graded cycling and resistance exercise. METHODS: Fifty subjects (28 women, 22 men) completed separate trials of graded cycling and three sets of four resistance exercises at a 10-repetition-maximum load. Monitors included the following: Apple Watch Series 2, Fitbit Blaze, Fitbit Charge 2, Polar H7, Polar A360, Garmin Vivosmart HR, TomTom Touch, and Bose SoundSport Pulse (BSP) headphones. HR was recorded after each cycling intensity and after each resistance exercise set. EE was recorded after both protocols. Validity was established as having a mean absolute percent error (MAPE) value of ≤10%. RESULTS: The Polar H7 and BSP were valid during both exercise modes (cycling: MAPE = 6.87%, R = 0.79; resistance exercise: MAPE = 6.31%, R = 0.83). During cycling, the Apple Watch Series 2 revealed the greatest HR validity (MAPE = 4.14%, R = 0.80). The BSP revealed the greatest HR accuracy during resistance exercise (MAPE = 6.24%, R = 0.86). Across all devices, as exercise intensity increased, there was greater underestimation of HR. No device was valid for EE during cycling or resistance exercise. CONCLUSIONS: HR from wearable devices differed at different exercise intensities; EE estimates from wearable devices were inaccurate. Wearable devices are not medical devices, and users should be cautious when using these devices for monitoring physiological responses to exercise.

Attention-deficit/hyperactivity disorder medication does not alter exercise-induced hypoalgesia following an acute bout of dynamic circuit resistance exercise.

The primary goal of this study was to investigate the effects of attention-deficit/hyperactivity disorder (ADHD) medications on exercise-induced hypoalgesia (EIH), heart rate, and perceived exertion. Thirty college-age students (10 Controls, 10 ADHD diagnosis, and 10 ADHD diagnosis with medications) completed 2 sessions: 1) a maximal testing session and 2) an experimental session consisting of 3 consecutive dynamic resistance exercise circuits comprised of 12 repetitions of 9 exercises at 60% of 1-repetition maximum using a 1:1 work to rest ratio. All participants, regardless of condition (Controls vs. ADHD without medications vs. ADHD with medications), displayed EIH accompanied by an increase in blood lactate, heart rate, and perceived exertion for the duration of the exercise bout. Therefore, the effects of resistance exercise are not altered by ADHD diagnosis or psychostimulant medication use for ADHD. These findings are intriguing given the known ergogenic and hypoalgesic effects of caffeine, a less potent stimulant.

Exercise-induced hypoalgesia: Pain tolerance, preference and tolerance for exercise intensity, and physiological correlates following dynamic circuit resistance exercise.

Previous research has demonstrated significant decreases in pain perception in healthy individuals following both aerobic and upper body resistance exercise, but research on circuit training has been limited. The purpose of the study was to determine the effects of a strenuous bout of dynamic circuit resistance exercise on pain threshold and pain tolerance in conjunction with changes in blood lactate levels, heart rate (HR), and perceived exertion. A sample of 24 college-age students participated in 2 sessions: (1) a maximal strength testing session and (2) a circuit training bout of exercise that consisted of 3 sets of 12 repetitions with a 1:1 work to rest ratio at 60% one-repetition maximum (1-RM) predicted from a three-repetition maximum (3-RM) for 9 exercises. Participants exhibited increases in pain tolerance, blood lactate levels, HR and perceived exertion following resistance exercise. Preference for exercise intensity was positively correlated with lactate post exercise and tolerance for exercise intensity was positively correlated with pain tolerance and lactate post exercise. In conclusion, this is the first study to demonstrate increases in pain tolerance following a dynamic circuit resistance exercise protocol and disposition for exercise intensity may influence lactate and pain responses to circuit resistance exercise.

Comparison of Resistance Exercise Perceived Exertion and Muscle Activation at Varied Submaximal Durations, Loads, and Muscle Actions.

Hollander, DB, Worley, JR, Asoodeh, M, Wakesa, D, Magnuson, M, Dantzler, DK, Didier, JJ, and Kraemer, RR. Comparison of resistance exercise perceived exertion and muscle activation at varied submaximal durations, loads, and muscle actions. J Strength Cond Res 31(5): 1387-1394, 2017-Previous studies investigating muscle activation from dynamic, plate-loaded, concentric (CON) and eccentric (ECC) muscle contractions have not accounted for the greater absolute strength of ECC contractions. The purpose of the study was to determine the effect of different dynamic muscle contraction durations, loads, and contraction types (CON and ECC) on perceived exertion and muscle activation differences in 6 women (mean ± SD age, height, weight, body mass index 22.83 ± 2.56 years, 1.65 ± 0.261 m, 68.56 ± 2.72 kg, 25.26 ± 4.39 kg·m). The participants were recruited and trained to move weight at the appropriate duration (2, 3, 4, and 5 seconds) for leg extension using a displacement apparatus (sonic emitter, auditory) and a computer program (visual feedback of bar displacement). Concentric and ECC 1 repetition maximum (1RM) were determined for leg extension for the midrange 3-second duration. Thirty, 50, and 70% of either CON or ECC 1RM were loaded for the remainder of the sessions. Subjects were then assigned to complete trials in a counterbalanced fashion for load, contraction type, and contraction duration. Rating of perceived exertion (RPE) significantly increased in response to load (30, 50, and 70%) regardless of contraction type as did electromyography (EMG) root mean square amplitude. Greater time under tension significantly increased RPE regardless of contraction type during knee extension exercise. The EMG amplitude was less distinguishable between 2, 3, 4, and 5 seconds of contractions. The data highlight the effort sense distinctions made by women at submaximal exercise loads during knee extension. These findings should be used to develop effective resistance exercise protocols that facilitate positive perceptions and adherence resistance exercise loads, durations of contraction, and contraction type.

Effects of partial vascular occlusion on irisin responses to loaded muscle contractions.

The purpose of the study was to determine the effects of partial vascular occlusion on irisin responses. Eight males completed trials of light (30% 1-repetition maximum (1RM)) resistance exercise (single biceps curls and calf presses) with partial vascular occlusion (LRO), moderate resistance (70% 1RM) with no occlusion (MR), and occlusion only (OO). Blood was collected before, after, and 15 min after exercise. Changes in circulating irisin were more affected during LRO than MR and OO trials.

Plasma cell-free mitochondrial DNA declines in response to prolonged moderate aerobic exercise.

Increased plasma cell-free mitochondrial DNA (cf-mDNA), a damage-associated molecular pattern (DAMP) produced by cellular injury, contributes to neutrophil activation/inflammation in trauma patients and arises in cancer and autoimmunity. To further understand relationships between cf-mDNA released by tissue injury, inflammation, and health benefits of exercise, we examined cf-mDNA response to prolonged moderate aerobic exercise. Seven healthy moderately trained young men (age = 22.4 ± 1.2) completed a treadmill exercise trial for 90 min at 60% VO2 max and a resting control trial. Blood was sampled immediately prior to exercise (0 min = baseline), during (+18, +54 min), immediately after (+90 min), and after recovery (R40). Plasma was analyzed for cf-mDNA, IL-6, and lactate. A significant difference in cf-mDNA response was observed between exercise and control trials, with cf-mDNA levels reduced during exercise at +54 and +90 (with or without plasma volume shift correction). Declines in cf-mDNA were accompanied by increased lactate and followed by an increase in IL-6, suggesting a temporal association with muscle stress and inflammatory processes. Our novel finding of cf-mDNA decline with prolonged moderate treadmill exercise provides evidence for increased clearance from or reduced release of cf-mDNA into the blood with prolonged exercise. These studies contrast with previous investigations involving exhaustive short-term treadmill exercise, in which no change in cf-mDNA levels were reported, and contribute to our understanding of differences between exercise- and trauma-induced inflammation. We propose that transient declines in cf-mDNA may induce health benefits, by reducing systemic inflammation.

Comparison of Cardiorespiratory and Metabolic Responses in Kettlebell High-Intensity Interval Training Versus Sprint Interval Cycling.

The purpose of this study was to determine the effectiveness of a novel exercise protocol we developed for kettlebell high-intensity interval training (KB-HIIT) by comparing the cardiorespiratory and metabolic responses to a standard sprint interval cycling (SIC) exercise protocol. Eight men volunteered for the study and completed 2 preliminary sessions, followed by two 12-minute sessions of KB-HIIT and SIC in a counterbalanced fashion. In the KB-HITT session, 3 circuits of 4 exercises were performed using a Tabata regimen. In the SIC session, three 30-second sprints were performed, with 4 minutes of recovery in between the first 2 sprints and 2.5 minutes of recovery after the last sprint. A within-subjects' design over multiple time points was used to compare oxygen consumption (V[Combining Dot Above]O2), respiratory exchange ratio (RER), tidal volume (TV), breathing frequency (f), minute ventilation (VE), caloric expenditure rate (kcal·min), and heart rate (HR) between the exercise protocols. Additionally, total caloric expenditure was compared. A significant group effect, time effect, and group × time interaction were found for V[Combining Dot Above]O2, RER, and TV, with V[Combining Dot Above]O2 being higher and TV and RER being lower in the KB-HIIT compared with the SIC. Only a significant time effect and group × time interaction were found for f, VE, kcal·min, and HR. Additionally, total caloric expenditure was found to be significantly higher during the KB-HIIT. The results of this study suggest that KB-HIIT may be more attractive and sustainable than SIC and can be effective in stimulating cardiorespiratory and metabolic responses that could improve health and aerobic performance.

Endocrine alterations from concentric vs. eccentric muscle actions: a brief review.

Resistance exercise has a positive effect on many tissues, including heart, bone, skeletal muscle, and nervous tissue. Eccentric muscle actions offer a unique and a potentially beneficial form of exercise for maintaining and improving health. During resistance exercise, the effects of gravity, and mechanical properties of the sarcomere and connective tissue in skeletal muscle allow a greater muscle load during an eccentric (lengthening) muscle contraction than a concentric (shortening) muscle contraction. Consequently, older patients, patients with muscle or limb movement limitations or injuries, as well as cancer patients may be able to benefit from isolated eccentric muscle actions. There are specific physiological responses to eccentric muscle contractions. This review will describe the effects of different eccentric muscle contraction protocols on endocrine responses that could have positive effects on different tissues and recommend direction for future research.

Short bouts of high-intensity resistance-style training produce similar reductions in fasting blood glucose of diabetic offspring and controls.

Family history of diabetes (FH) is associated with impaired cardiometabolic function. Aerobic exercise improves insulin sensitivity, though resistance training studies on fasting glucose (FG) in FH are lacking. This study examined the effects of 7 weeks of high-intensity-resistance-focused training (HIRFT), including circuit, core, and plyometric resistance training on FG in FH and matched controls (CON). We hypothesized that HIRFT would reduce FG levels, with greater reductions in CON. Thirty-eight healthy men and women (23.5 ± 2 years; 171 ± 7.4 cm; 71 ± 14 kg) participated in 7 weeks of HIRFT including full-body, plyometric, and core resistance training on alternate days. Fasting glucose was analyzed before and after the 7-week training before and after workouts. One repetition maximum was calculated for bench press, squat, and deadlift before and after training. Body mass index and resting HR remained unchanged. Fasting glucose declined similarly between groups with training (-0.23 ± 0.08 vs. -0.20 ± 0.07 mmol·L, p < 0.01 for FH and CON, respectively), whereas strength increased (kg) (bench: 8.0 ± 1.8, squat: 19.4 ± 4.6, deadlift: 16.4 ± 3.6, overall mean percent increase: 38.9 ± 9.2, p < 0.001). Ten-minute postexercise glucose decreased (-0.65 mmol·L, p = 0.05) with training, with no differences between groups. Changes in FG and strength increase were inversely correlated (r = -0.519, p = 0.05). Strength increased equally between groups. Data indicate that HIRFT reduces FG concentrations similarly in FH and CON, making it effective for improving FG in FH.

Comparison of two-hand kettlebell exercise and graded treadmill walking: effectiveness as a stimulus for cardiorespiratory fitness.

Prevailing interest in the use of kettlebell (KB) exercises for rehabilitation and improvement of muscular strength has led to several recent studies, some suggesting that KB exercise may be useful for improvement of cardiorespiratory fitness. The purpose of this study was to determine whether KB exercise would produce similar cardiovascular stress to that of walking and thus provide an additional exercise mode for the improvement of cardiorespiratory fitness. It was hypothesized that a moderate-intensity, continuous KB protocol, would produce similar metabolic and cardiorespiratory responses as a brisk bout of graded treadmill (TM) walking, but greater rating of perceived exertion (RPE). Ten novice volunteers (5 men, 5 women) completed a preliminary session to determine body composition and VO2max and to familiarize participants with standardized KB exercise technique. Subsequently, they completed a 30-minute KB session that included 3 continuous 10-minute sets of 10 KB swings followed by 10 sumo deadlifts, with 3-minute rests between 10-minute exercise periods. The third session was a 30-minute TM regimen that began at the walking speed and 4% grade that matched the VO2 from the KB session and included 3-minute rest intervals after 10-minute TM exercise periods. VO2, respiratory exchange ratio, kcal·min, and blood pressure were similar for KB and moderate-intensity TM exercise, but RPE and heart rate were greater during KB exercise. Data indicate that a KB routine consisting of 2-hand swings and sumo deadlifts with 3-minute rest periods produces similar metabolic responses to those of a moderate-intensity TM walking protocol designed for the improvement of aerobic fitness.

No effect of menstrual cycle phase on glucose and glucoregulatory endocrine responses to prolonged exercise.

INTRODUCTION: Prolonged exercise requires increased utilization of blood glucose and adjustment of glucoregulatory hormones. Estrogen can reduce hepatic gluconeogenesis which could affect insulin concentrations. Amylin is co-secreted with insulin and controls influx of glucose into the blood. PURPOSE: To determine the effect of menstrual cycle stage on glucose, leptin, and pancreatic hormone responses to prolonged (90 min) exercise. METHODS: Five healthy, eumenorrheic women (24.6 ± 5.1 years; 67.4 ± 1 kg) were monitored for 3 months to determine menstrual cycle length. Subjects completed a preliminary session to determine exercise workloads and, in a fasted condition, completed two randomized 90-min treadmill exercise trials at 60 % VO2max during the early follicular (EFX) and mid-luteal phase (MLX) of their menstrual cycle. Blood samples were analyzed for glucose, insulin, C-peptide, amylin, glucagon, leptin, and cortisol concentrations at rest (-30 and 0 min), during exercise (18, 36, 54, 72, and 90 min) and after 20 min of recovery. RESULTS: No changes in amylin, leptin, or cortisol occurred for EFX and MLX trials. A significant (p < 0.05) time effect occurred for glucose, insulin, and glucagon with reduced insulin across the exercise trial and increases in glucose and glucagon later in the trial, but there were no differences between the EFX and MLX trials. CONCLUSIONS: Menstrual cycle stage does not affect glucose, insulin, C-peptide, amylin, glucagon, cortisol, and leptin responses to prolonged exercise; however, the exercise reduces insulin and increases glucose and glucagon concentrations. This is the first study to determine acute effects of exercise on amylin and other glucoregulatory hormone responses in women.

Metabolic dysfunction in diabetic offspring: deviations in metabolic flexibility.

UNLABELLED: In type 2 diabetes (T2D), insulin resistance is related to comorbidities, including high lipotoxicity, poor glucoregulation, and loss of metabolic flexibility. Controversy exists regarding whether reduced metabolic flexibility precedes insulin resistance or vice versa. PURPOSE: The purpose of this study was to determine whether a family history of T2D leads to metabolic inflexibility. METHODS: To examine potential loss of metabolic flexibility at early stages, we used a hooded metabolic cart to compare metabolic characteristics in people with T2D, family history of T2D (FH+), and controls (FH-) 1) at rest, 2) with passive stretching (PS) and recovery, and 3) with oral glucose load. Testing of 9 T2D, 11 FH+, and 9 FH- occurred after a 12-h fast under resting conditions. Expired gas and blood glucose (BG) were measured before and after each condition. RESULTS: PS lowered BG (P < 0.05) in FH- and FH+ (mean ± SD, -2.7 ± 5.9 and -5.8 ± 7.5 mg·mL(-1)) compared with T2D (-0.9 ± 7.7). CHO use (kcal·min(-1)) increased with PS in all groups (0.04 ± 0.18, 0.03 ± 0.26, and 0.22 ± 1.6 mg·mL(-1) in FH-, FH+, and T2D, respectively). For oral glucose load, different metabolic flexibility existed between FH- as well as FH+ (0.16 ± 0.07) as well as T2D (0.16 ± 0.07), with no difference between FH- and T2D. CONCLUSION: PS increases glycolytic activity without affecting BG in T2D, and reductions in metabolic flexibility exist in T2D and FH+ without glucoregulatory impairment in FH+, indicating early stage of mitochondrial dysfunction in FH+. Findings indicate PS is an important tool for assessing metabolic flexibility.

Estrogen mediation of hormone responses to exercise.

The roles of estrogens extend from the regulation of reproduction to other functions involved in control of metabolism, fluid balance, as well as gastrointestinal, lung, and brain function, with a strong effect on other hormones that subsequently alter the physiology of multiple tissues. As such, alteration of endogenous estrogens across the menstrual cycle, or from oral contraception and estrogen replacement therapy, can affect these tissues. Due to the important effects that estrogens have on different tissues, there are many investigations concerning the effects of a human estrogenic environment on endocrine responses to exercise. The following review will describe the consequences of varying estrogen levels on pituitary, adrenal, gonadal, and endocrine function, followed by discussion of the outcomes of different estrogen levels on endocrine tissues in response to exercise, problems encountered for interpretation of findings, and recommended direction for future research.