Plasma triglyceride concentrations are rapidly reduced following individual bouts of endurance exercise in women.

It is known that chronic endurance training leads to improvements in the lipoprotein profile, but less is known about changes that occur during postexercise recovery acutely. We analyzed triglyceride (TG), cholesterol classes and apolipoproteins in samples collected before, during and after individual moderate- and hard-intensity exercise sessions in men and women that were isoenergetic between intensities. Young healthy men (n = 9) and young healthy women (n = 9) were studied under three different conditions with diet unchanged between trials: (1) before, during and 3 h after 90 min of exercise at 45% VO(2)peak (E45); (2) before, during and 3 h after 60 min of exercise at 65% VO(2)peak (E65), and (3) in a time-matched sedentary control trial (C). At baseline, high-density lipoprotein cholesterol (HDL-C) was higher in women than men (P < 0.05). In men and in women, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), HDL-C, apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), and LDL peak particle size were unaltered by exercise either during exertion or after 3 h of recovery. In women, but not in men, average plasma TG was significantly reduced below C at 3 h postexercise by approximately 15% in E45 and 25% in E65 (P < 0.05) with no significant difference between exercise intensities. In summary, plasma TG concentration rapidly declines following exercise in women, but not in men. These results demonstrate an important mechanism by which each individual exercise session may incrementally reduce the risk for cardiovascular disease (CVD) in women.

Training improves the response in glucose flux to exercise in postmenopausal women.

We examined the effects of endurance training on parameters of glucose flux during rest and exercise in postmenopausal women. Ten sedentary, but healthy women (55 +/- 1 yr) completed 12 wk of endurance exercise training on a cycle ergometer [5 days/wk, 1 h/day, 65% peak oxygen consumption (Vo(2peak))]. Flux rates were determined by primed continuous infusion of [6,6-(2)H]glucose (D(2)-glucose) during 90 min of rest and 60 min of cycle ergometer exercise during one pretraining exercise trial [65% Vo(2peak) (PRE)] and two posttraining exercise trials [the power output that elicited 65% pretraining Vo(2peak) (ABT) and 65% posttraining Vo(2peak) (RLT)]. Training increased Vo(2peak) by 16.3 +/- 3.9% (P < 0.05). Epinephrine and glucagon were lower during ABT and lactate was lower during ABT and RLT (P < 0.05), but the apparent insulin response was unchanged. Whole body glucose rate of appearance decreased posttraining during exercise at a given power output (4.58 +/- 0.39 mg.kg(-1).min(-1) during ABT compared with 5.21 +/- 0.48 mg.kg(-1).min(-1) PRE, P < 0.05), but not at the same relative workload (5.85 +/- 0.36 mg.kg(-1).min(-1)). Training resulted in a 35% increase in glucose MCR during exercise at the same relative intensity (7.16 +/- 0.42 ml.kg(-1).min(-1) during RLT compared with 5.28 +/- 0.42 ml.kg(-1).min(-1) PRE, P < 0.05). Changes in parameters of glucose kinetics during exercise were accomplished without changes in dietary composition, body weight, or body composition. We conclude that despite changes in the hormonal milieu that occur at menopause, endurance training results in a similar magnitude in training-induced alterations of glucose flux as seen previously in younger women.

Validation of Pre-operative Templating for Total Disc Replacement Surgery.

OBJECTIVES: This was an analytic retrospective observational study. The aims were (1) to validate patient-specific templating process by comparing postoperative range of motion (ROM) with that predicted by the model, (2) to retrospectively determine the ideal implant size, height, configuration, and location to evaluate if the ROM achieved could have been improved, and (3) to correlate postoperative ROM and clinical outcome. BACKGROUND: Previous research revealed that after total disc replacement surgery, 34% of patients with less than 5° of postoperative ROM developed adjacent segment disease. The match between patient anatomy (size, facet orientation, disc height) and implant parameters are likely to affect postoperative ROM and clinical outcomes. METHODS: Seventeen consecutive patients were implanted with 22 ProDisc-L devices between 2008 and 2015. Three-dimensional finite element (FE) models of the implanted segment were constructed from preoperative computed tomography scans and virtually implanted with the ProDisc-L implant. ROM was determined with the endpoints of facet impingement in flexion and implant contact in extension. FE templating was used to determine the optimal implant size and location. ROM was then measured directly from flexion and extension radiographs and compared to predicted ROM. Pre and postoperative Oswestry Disability Index (ODI) data were used to correlate ROM with clinical outcomes. RESULTS: No significant difference was found between the actual and predicted ROM. The computational templating procedure identified an optimal ROM that was significantly greater than actual ROM. The ROM in our cohort could have been improved by an average of 1.2° or 12% had a different implant size or position been used. CONCLUSIONS: FE analyses accurately predicted ROM in this cohort and can facilitate selection of the optimal implant size and location that we believe will increase the chance of achieving clinical success with the application of this technology.

Statistical shape modeling characterizes three-dimensional shape and alignment variability in the lumbar spine.

The mechanics of the lumbar spine are heavily dependent on the underlying anatomy. Anatomical measures are used to assess the progression of pathologies related to low back pain and to screen patients for surgical treatment options. To describe anatomical norms and pathological differences for the population, statistical shape modeling, which uses full three-dimensional representations of bone morphology and relative alignment, can capture intersubject variability and enable comparative evaluations of subject to population. Accordingly, the objective of this study was to develop a comprehensive set of three-dimensional statistical models to characterize anatomical variability in the lumbar spine, by specifically describing the shape of individual vertebrae, and shape and alignment of the entire lumbar spine (L1-S1), with a focus on the L4-L5 and L5-S1 functional spinal units (FSU). Using CT scans for a cohort of 52 patients, lumbar spine geometries were registered to a template to establish correspondence and a principal component analysis identified the primary modes of variation. Scaling was the most prevalent mode of variation for all models. Subsequent modes of the statistical shape models of the individual bones characterized shape variation within the processes. Subsequent modes of variation for the FSU and entire spine models described alignment changes associated with disc height and lordosis. Quantification of anatomical variation in the spine with statistical models can inform implant design and sizing, assist clinicians in diagnosing pathologies, screen patients for treatment options, and support pre-operative planning.

Stand-alone Anterior Lumbar Interbody, Transforaminal Lumbar Interbody, and Anterior/Posterior Fusion: Analysis of Fusion Outcomes and Costs.

Fusion outcomes and costs of stand-alone anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF) in association with posterior fusion, and anterior/posterior (A/P) fusion were compared using clinical, radiographic, and billing data. Adult patients with symptomatic 1- or 2-level degenerative disk disease in isolation or in association with a grade 1 or 2 degenerative or lytic spondylolisthesis and canal and/or foraminal stenosis who underwent elective stand-alone ALIF, TLIF, or A/P fusion were compared. The analysis focused primarily on fusion rates and costs and secondarily on radiographic and clinical parameters. One hundred six patients at least 2 years beyond surgery (ALIF, 53; TLIF, 17; A/P fusion, 36) were reviewed. Demographics were similar except for age, with the ALIF group being younger (mean, 37.8 years) than the other groups (TLIF, 53.1 years; A/P fusion, 48.2 years). There were no differences between the groups in fusion rates or outcomes as assessed by the Numeric Rating Scale. Compared with the other 2 groups, the ALIF group had a significantly shorter operative time, less blood loss, and a shorter stay (P<.0001). Evaluation of radiographic parameters revealed significant differences regarding disk angle (P<.001), disk height (P<.0001), and pelvic tilt (P=.001) favoring ALIF and A/P fusion over TLIF. Stand-alone ALIF should be considered in the management of patients with 1- or 2-level lumbar degenerative disk disease for which the pathology can be addressed adequately via this approach. [Orthopedics. 2018; 41(5):e655-e662.].

Retention of intravenously infused [13C]bicarbonate is transiently increased during recovery from hard exercise.

The effects of exercise on energy substrate metabolism persist into the postexercise recovery period. We sought to derive bicarbonate retention factors (k) to correct for carbon tracer oxidized, but retained from pulmonary excretion before, during, and after exercise. Ten men and nine women received a primed-continuous infusion of [(13)C]bicarbonate (sodium salt) under three different conditions: 1) before, during, and 3 h after 90 min of exercise at 45% peak oxygen consumption (Vo(2peak)); 2) before, during, and 3 h after 60 min of exercise at 65% Vo(2peak); and 3) during a time-matched resting control trial, with breath samples collected for determination of (13)CO(2) excretion rates. Throughout the resting control trial, k was stable and averaged 0.83 in men and women. During exercise, average k in men was 0.93 at 45% Vo(2peak) and 0.94 at 65% Vo(2peak), and in women k was 0.91 at 45% Vo(2peak) and 0.92 at 65% Vo(2peak), with no significant differences between intensities or sexes. After exercise at 45% Vo(2peak), k returned rapidly to control values in men and women, but following exercise at 65% Vo(2peak), k was significantly less than control at 30 and 60 min postexercise in men (0.74 and 0.72, respectively, P < 0.05) and women (0.75 and 0.76, respectively, P < 0.05) with no significant postexercise differences between men and women. We conclude that bicarbonate/CO(2) retention is transiently increased in men and women for the first hour of postexercise recovery following endurance exercise bouts of hard but not moderate intensity.

Changes in ventilatory threshold at high altitude: effect of antioxidants.

PURPOSE: To investigate the effects of prolonged hypoxia and antioxidant supplementation on ventilatory threshold (VT) during high-altitude (HA) exposure (4300 m). METHODS: Sixteen physically fit males (25 +/- 5 yr; 77.8 +/- 8.5 kg) performed an incremental test to maximal exertion on a cycle ergometer at sea level (SL). Subjects were then matched on VO2peak, ventilatory chemosensitivity, and body mass and assigned to either a placebo (PL) or antioxidant (AO) supplement group in a randomized, double-blind manner. PL or AO (12 mg of beta-carotene, 180 mg of alpha-tocopherol acetate, 500 mg of ascorbic acid, 100 mug of selenium, and 30 mg of zinc daily) were taken 21 d prior to and for 14 d at HA. During HA, subjects participated in an exercise program designed to achieve an energy deficit of approximately 1400 kcal.d(-1). VT was reassessed on the second and ninth days at HA (HA2, HA9). RESULTS: Peak power output (Wpeak) and VO2peak decreased (28%) in both groups upon acute altitude exposure (HA2) and were unchanged with acclimatization and exercise (HA9). Power output at VT (WVT) decreased from SL to HA2 by 41% in PL, but only 32% in AO (P < 0.05). WVT increased in PL only during acclimatization (P < 0.05) and matched AO at HA9. Similar results were found when VT was expressed in terms of % Wpeak and % VO2peak. CONCLUSIONS: VT decreases upon acute HA exposure but improves with acclimatization. Prior AO supplementation improves VT upon acute, but not chronic altitude exposure.

Cytokine responses at high altitude: effects of exercise and antioxidants at 4300 m.

PURPOSE: This study tested the hypothesis that antioxidant supplementation would attenuate plasma cytokine (IL-6, tumor necrosis factor (TNF)-alpha), and C-reactive protein (CRP) concentrations at rest and in response to exercise at 4300-m elevation. METHODS: A total of 17 recreationally trained men were matched and assigned to an antioxidant (N = 9) or placebo (N = 8) group in a double-blinded fashion. At sea level (SL), energy expenditure was controlled and subjects were weight stable. Then, 3 wk before and throughout high altitude (HA), an antioxidant supplement (10,000 IU beta-carotene, 200 IU alpha-tocopherol acetate, 250 mg ascorbic acid, 50 microg selenium, 15 mg zinc) or placebo was given twice daily. At HA, energy expenditure increased approximately 750 kcal.d(-1) and energy intake decreased approximately 550 kcal.d, resulting in a caloric deficit of approximately 1200-1500 kcal.d(-1). At SL and HA day 1 (HA1) and day HA13, subjects exercised at 55% of VO2peak until they expended approximately 1500 kcal. Blood samples were taken at rest, end of exercise, and 2, 4, and 20 h after exercise. RESULTS: No differences were seen between groups in plasma IL-6, CRP, or TNF-alpha at rest or in response to exercise. For both groups, plasma IL-6 concentration was significantly higher at the end of exercise, 2, 4, and 20 h after exercise at HA1 compared with SL and HA13. Plasma CRP concentration was significantly elevated 20 h postexercise for both groups on HA1 compared to SL and HA13. TNF-alpha did not differ at rest or in response to exercise. CONCLUSION: Plasma IL-6 and CRP concentrations were elevated following exercise at high altitude on day 1, and antioxidant supplementation did not attenuate the rise in plasma IL-6 and CRP concentrations associated with hypoxia, exercise, and caloric deficit.

Patient-Specific Templating of Lumbar Total Disk Replacement to Restore Normal Anatomy and Function.

The purpose of this study was to develop a tool to determine optimal placement and size for total disk replacements (TDRs) to improve patient outcomes of pain and function. The authors developed a statistical shape model to determine the anatomical variables that influence the placement, function, and outcome of lumbar TDR. A patient-specific finite element analysis model has been developed that is now used prospectively to identify patients suitable for TDR and to create a surgical template to facilitate implant placement to optimize range of motion and clinical outcomes. Patient factors and surgical techniques that determine success regarding function and pain are discussed in this article.

Lipid oxidation in fit young adults during postexercise recovery.

To evaluate the hypothesis that lipid oxidation predominates in postexercise recovery, we examined healthy men (n = 6; age = 21.2 +/- 0.6 yr) and women (n = 6; age = 22.8 +/- 2.1 yr) during and after two exercise tasks [89 min at 45% and 60 min at 65% of peak rate of oxygen consumption (V(O2 peak))] as well as a time-matched resting control trial (Con). Exercise bouts were matched for energy expenditure. Respiratory exchange ratios (RER) during exercise at 65% V(O2 peak) for both men and women (0.95 +/- 0.01 and 0.93 +/- 0.02) were significantly higher than 45% V(O2 peak) (0.89 +/- 0.01 and 0.86 +/- 0.02) and Con trials (0.86 +/- 0.01 and 0.86 +/- 0.02, respectively). During recovery, for men RER values were 0.78 +/- 0.01 and 0.76 +/- 0.01 after 45% and 65% exercise, respectively. For women, values were 0.79 +/- 0.01 and 0.78 +/- 0.01. These were significantly lower than during both the preexercise resting period and the corresponding no-exercise Con period (0.82 +/- 0.01 and 0.83 +/- 0.01, mean RER for men and women, respectively). Hence, the contribution of lipid oxidation to energy supply increased significantly during recovery compared with preexercise levels, and it was greater after exercise than during the time-matched, no-exercise Con period. It is concluded that, although carbohydrate is the major fuel source during moderate- to high-intensity exercise, 1) there is substantial postexercise lipid oxidation; and 2) lipid oxidation is the same during postexercise recovery whether the relative power output is 45% or 65% of V(O2 peak) when energy expenditure of exercise is matched.

Hematological and acid-base changes in men during prolonged exercise with and without sodium-lactate infusion.

An emerging technique used for the study of metabolic regulation is the elevation of lactate concentration with a sodium-lactate infusion, the lactate clamp (LC). However, hematological and acid-base properties affected by the infusion of hypertonic solutions containing the osmotically active strong ions sodium (Na(+)) and lactate (Lac(-)) are a concern for clinical and research applications of LC. In the present study, we characterized the hematological and plasma acid-base changes during rest and prolonged, light- to moderate-intensity (55% Vo(2 peak)) exercise with and without LC. During the control (Con) trial, subjects were administered an isotonic, isovolumetric saline infusion. During LC, plasma lactate concentration ([Lac(-)]) was elevated to 4 meq/l during rest and to 4-7 meq/l during exercise. During LC at rest, there were rapid and transient changes in plasma, erythrocyte, and blood volumes. LC resulted in decreased plasma [H(+)] (from 39.6 to 29.6 neq/l) at the end of exercise while plasma [HCO(3)(-)] increased from 26 to 32.9 meq/l. Increased plasma strong ion difference [SID], due to increased [Na(+)], was the primary contributor to decreased [H(+)] and increased [HCO(3)(-)]. A decrease in plasma total weak acid concentration also contributed to these changes, whereas Pco(2) contributed little. The infusion of hypertonic LC caused only minor volume, acid-base, and CO(2) storage responses. We conclude that an LC infusion is appropriate for studies of metabolic regulation.

Antioxidant supplementation does not attenuate oxidative stress at high altitude.

INTRODUCTION: Hypobaric hypoxia and heightened metabolic rate increase free radical production. PURPOSE: We tested the hypothesis that antioxidant supplementation would reduce oxidative stress associated with increased energy expenditure (negative energy balance) at high altitude (HA 4300 m). METHODS: For 12 d at sea level (SL), 18 active men were fed a weight-stabilizing diet. Testing included fasting blood and 24-h urine samples to assess antioxidant status [plasma alpha-tocopherol, beta-carotene, lipid hydroperoxides (LPO), and urinary 8-hydroxydeoxyguanosine (8-OHdG)] and a prolonged submaximal (55% Vo2peak) oxidative stress index test (OSI) to evaluate exercise-induced oxidative stress (plasma LPO, whole blood reduced and oxidized glutathione, glutathione peroxidase, and urinary 8-OHdG). Subjects were then matched and randomly assigned to either a placebo or antioxidant supplement group for a double-blinded trial. Supplementation (20,000 IU of beta-carotene, 400 IU alpha-tocopherol acetate, 500 mg ascorbic acid, 100 microg selenium, and 30 mg zinc, or placebo) was begun 3 wk prior to and throughout a 14-d HA intervention. At HA, subjects' daily energy intake and expenditure were adjusted to achieve a caloric deficit of approximately 1400 kcal. Fasting blood and 24-h urine samples were collected throughout HA and the OSI test was repeated on HA day 1 and day 13. RESULTS: Resting LPO concentrations increased and urinary 8-OHdG concentrations decreased over HA with no effect of supplementation. Prolonged submaximal exercise was not associated with increased concentrations of oxidative stress markers at SL or HA. CONCLUSIONS: Antioxidant supplementation did not significantly affect markers of oxidative stress associated with increased energy expenditure at HA.

Gluconeogenesis and hepatic glycogenolysis during exercise at the lactate threshold.

Because the maintenance of glycemia is essential during prolonged exercise, we examined the effects of endurance training, exercise intensity, and plasma lactate concentration ([lactate]) on gluconeogenesis (GNG) and hepatic glycogenolysis (GLY) in fasted men exercising at, and just below, the lactate threshold (LT), where GNG precursor lactate availability is high. Twelve healthy men (6 untrained, 6 trained) completed 60 min of constant-load exercise at power outputs corresponding to their individual LT. Trained subjects completed two additional 60-min sessions of constant-load exercise: one at 10% below the LT workload (LT-10%), and the other with a lactate clamp (LT-10%+LC) to match the [lactate] of the LT trial. Flux rates were determined by primed continuous infusion of [6,6-(2)H(2)]glucose, [3-(13)C]lactate, and [(13)C]bicarbonate tracers during 90 min of rest and 60 min of cycling. Exercise at LT corresponded to 67.6 ± 1.3 and 74.8 ± 1.7% peak O(2) consumption in the untrained and trained subjects, respectively (P < 0.05). Relative exercise intensity was matched between the untrained group at LT and the trained group at LT-10%, and [lactate] during exercise was matched in the LT and LT-10%+LC trials via exogenous lactate infusion. Glucose kinetics (rate of appearance, rate of disposal, and metabolic clearance rate) were augmented with the lactate clamp. GNG was decreased in the trained subjects exercising at LT and LT-10% compared with the untrained subjects, but increasing [lactate] in the LT-10%+LC trial significantly increased GNG (4.4 ± 0.9 mg·kg(-1)·min(-1)) compared with its corresponding control (1.7 ± 0.4 mg·kg(-1)·min(-1), P < 0.05). Hepatic GLY was higher in the trained than untrained subjects, but not significantly different across conditions. We conclude that GNG plays an essential role in maintaining total glucose production during exercise in fasted men, regardless of training state. However, endurance training increases the ability to achieve a higher relative exercise intensity and absolute power output at the LT without a significant decrease in GNG. Furthermore, raising systemic precursor substrate availability increases GNG during exercise, but not at rest.

Lactate kinetics at the lactate threshold in trained and untrained men.

To understand the meaning of the lactate threshold (LT) and to test the hypothesis that endurance training augments lactate kinetics [i.e., rates of appearance and disposal (Ra and Rd, respectively, mg·kg(-1)·min(-1)) and metabolic clearance rate (MCR, ml·kg(-1)·min(-1))], we studied six untrained (UT) and six trained (T) subjects during 60-min exercise bouts at power outputs (PO) eliciting the LT. Trained subjects performed two additional exercise bouts at a PO 10% lower (LT-10%), one of which involved a lactate clamp (LC) to match blood lactate concentration ([lactate]b) to that achieved during the LT trial. At LT, lactate Ra was higher in T (24.1 ± 2.7) than in UT (14.6 ± 2.4; P < 0.05) subjects, but Ra was not different between UT and T when relative exercise intensities were matched (UT-LT vs. T-LT-10%, 67% Vo2max). At LT, MCR in T (62.5 ± 5.0) subjects was 34% higher than in UT (46.5 ± 7.0; P < 0.05), and a reduction in PO resulted in a significant increase in MCR by 46% (LT-10%, 91.5 ± 14.9, P < 0.05). At matched relative exercise intensities (67% Vo2max), MCR in T subjects was 97% higher than in UT (P < 0.05). During the LC trial, MCR in T subjects was 64% higher than in UT (P < 0.05), in whom %Vo2max and [lactate]b were similar. We conclude that 1) lactate MCR reaches an apex below the LT, 2) LT corresponds to a limitation in MCR, and 3) endurance training augments capacities for lactate production, disposal and clearance.

Cyclic hypobaric hypoxia improves markers of glucose metabolism in middle-aged men.

UNLABELLED: Chronic hypoxia increases dependence on glucose in men and increases insulin sensitivity in men and women. Cyclic Variations in Altitude Conditioning (CVAC) is a novel technology that provides exposure to rapidly fluctuating cyclic hypobaric hypoxia (CHH). PURPOSE: To test the hypothesis that markers of glucose metabolism would change with CVAC CHH, two groups of middle-aged men were exposed to 10 weeks (40 min/day, 3 day/week) of either CHH or sham (SH) sessions. METHODS: CHH subjects (age: 48 ± 6, weight: 86 ± 12 kg, BMI: 27.1 ± 3, n=11) experienced cyclic pressures simulating altitudes ranging from sea level to 3048 m (week 1) and progressing to 6096 m (by week 5 through week 10). SH subjects (age: 50 ± 4, weight: 89 ± 15 kg, BMI: 27.5 ± 3, n=10) were exposed to slowly-fluctuating pressures up to 607 m (all subjects blinded to elevation). Physical function and blood markers of glucose metabolism were measured at baseline, 3, 6, and 10 weeks. RESULTS: Two CHH subjects were dropped from analysis for failure to progress past 3048 m (CHH: n=9). Weight and physical activity remained stable for both groups. There was a group-by-time interaction in fasting glucose (CHH: 96 ± 9 to 91 ± 7 mg/dL, SH: 94 ± 7 to 97 ± 9 mg/dL, p<0.05). Reduction in plasma glucose response to oral glucose tolerance test [area under the curve] was greater in CHH compared to SH after 10 weeks of exposure (p<0.03). Neither group experienced changes in fasting insulin, insulin response during the OGTT, or changes in a timed walk test. CONCLUSION: Ten weeks of CVAC CHH exposure improves markers of glucose metabolism in middle-aged men at risk for metabolic syndrome.

Direct and indirect lactate oxidation in trained and untrained men.

Lactate has been shown to be an important oxidative fuel. We aimed to quantify the total lactate oxidation rate (Rox) and its direct vs. indirect (glucose that is gluconeogenically derived from lactate and subsequently oxidized) components (mg·kg(-1)·min(-1)) during rest and exercise in humans. We also investigated the effects of endurance training, exercise intensity, and blood lactate concentration ([lactate]b) on direct and indirect lactate oxidation. Six untrained (UT) and six trained (T) men completed 60 min of constant load exercise at power outputs corresponding to their lactate threshold (LT). T subjects completed two additional 60-min sessions of constant load exercise at 10% below the LT workload (LT-10%), one of which included a lactate clamp (LC; LT-10%+LC). Rox was higher at LT in T [22.7 ± 2.9, 75% peak oxygen consumption (Vo2peak)] compared with UT (13.4 ± 2.5, 68% Vo2peak, P < 0.05). Increasing [lactate]b (LT-10%+LC, 67% Vo2peak) significantly increased lactate Rox (27.9 ± 3.0) compared with its corresponding LT-10% control (15.9 ± 2.2, P < 0.05). Direct and indirect Rox increased significantly from rest to exercise, and their relative partitioning remained constant in all trials but differed between T and UT: direct oxidation comprised 75% of total lactate oxidation in UT and 90% in T, suggesting the presence of training-induced adaptations. Partitioning of total carbohydrate (CHO) use showed that subjects derived one-third of CHO energy from blood lactate, and exogenous lactate infusion increased lactate oxidation significantly, causing a glycogen-sparing effect in exercising muscle.

Effects of endurance training on cardiorespiratory fitness and substrate partitioning in postmenopausal women.

We examined the effect of endurance training on energy substrate partitioning during rest and exercise in postmenopausal women. Ten healthy sedentary (55 +/- 1 years old) subjects completed 12 weeks of endurance exercise training on a cycle ergometer (5 d/wk, 1 h/d, 65% peak oxygen consumption [Vo(2)peak]). Whole-body energy substrate oxidation was determined by indirect calorimetry during 90 minutes of rest and 60 minutes of cycle ergometer exercise. Subjects were studied at 65% Vo(2)peak before training and after training at the same absolute exercise intensity (same absolute workload as 65% of pretraining Vo(2)peak) and same relative exercise intensity (65% of posttraining Vo(2)peak). After training, Vo(2)peak increased by 16.3% +/- 3.9% and resting heart rate decreased by 4 beats per minute (P < .05). During exercise at same absolute intensity, mean arterial pressure decreased by 8 mm Hg (P < .05), heart rate decreased by 19 beats per minute (P < .05), energy derived from carbohydrate decreased by 9.6%, and the energy derived from lipid increased by 9.2% (P < .05). Lactate concentration was lower at the same absolute and relative exercise intensities (P < .05). Changes in substrate partitioning during exercise were accomplished without changes in dietary composition, body weight, or body composition. We conclude that endurance training in healthy postmenopausal women who remain in energy balance results in many of the classic cardiopulmonary training effects, decreases the reliance on carbohydrate, and increases lipid oxidation during a given submaximal exercise task without a reduction in body weight.

Glucoregulation is more precise in women than in men during postexercise recovery.

BACKGROUND: The regulation of glycemia is challenged in healthy men and women after exercise bouts of substantial energy expenditure. OBJECTIVE: We determined rates of glucose appearance (Ra), disappearance (Rd), and metabolic clearance (MCR) before, during, and after isoenergetic moderate and hard-intensity exercise. DESIGN: Ten men and 8 women received primed-continuous infusion of [6,6-(2)H(2)]glucose tracer to measure glucose kinetics. Participants were studied under 3 different conditions with diet unchanged between trials: 1) before, during, and 3 h after 90 min of exercise at 45% of peak oxygen consumption (VO(2)peak; E45); 2) before, during, and 3 h after 60 min of exercise at 65% VO(2)peak (E65), and 3) in a time-matched sedentary control trial. RESULTS: In men and women, Ra, Rd, and MCR increased above the control trial during exercise and were higher in E65 than in E45 (P < 0.05). Average Ra, Rd, and MCR remained elevated above the control over 3 h of postexercise recovery in men after exercise in E45 and E65 (P < 0.05), and blood glucose concentrations were depressed below the control during recovery (P < 0.05). Glucose concentrations were not depressed in women during 3 h of postexercise recovery, and in contrast with that in men, average Ra and Rd did not remain significantly elevated during postexercise recovery in women, although MCR did remain elevated in E65 (P < 0.05). CONCLUSIONS: After exercise bouts, women are better able to maintain glucose concentrations at sedentary control levels, thus not requiring the counter-regulation of glucose production that is seen in men and requiring less accentuation of lipid metabolism.

Substantial working muscle glycerol turnover during two-legged cycle ergometry.

We combined tracer and arteriovenous (a-v) balance techniques to evaluate the effects of exercise and endurance training on leg triacylglyceride turnover as assessed by glycerol exchange. Measurements on an exercising leg were taken to be a surrogate for working skeletal muscle. Eight men completed 9 wk of endurance training [5 days/wk, 1 h/day, 75% peak oxygen consumption (Vo(2peak))], with leg glycerol turnover determined during two pretraining trials [45 and 65% Vo(2peak) (45% Pre and 65% Pre, respectively)] and two posttraining trials [65% of pretraining Vo(2peak) (ABT) and 65% of posttraining Vo(2peak) (RLT)] using [(2)H(5)]glycerol infusion, femoral a-v sampling, and measurement of leg blood flow. Endurance training increased Vo(2peak) by 15% (45.2 +/- 1.2 to 52.0 +/- 1.8 mlxkg(-1)xmin(-1), P < 0.05). At rest, there was tracer-measured leg glycerol uptake (41 +/- 8 and 52 +/- 15 micromol/min for pre- and posttraining, respectively) even in the presence of small, but significant, net leg glycerol release (-68 +/- 19 and -50 +/- 13 micromol/min, respectively; P < 0.05 vs. zero). Furthermore, while there was no significant net leg glycerol exchange during any of the exercise bouts, there was substantial tracer-measured leg glycerol turnover during exercise (i.e., simultaneous leg muscle uptake and leg release) (uptake, release: 45% Pre, 194 +/- 41, 214 +/- 33; 65% Pre, 217 +/- 79, 201 +/- 84; ABT, 275 +/- 76, 312 +/- 87; RLT, 282 +/- 83, 424 +/- 75 micromol/min; all P < 0.05 vs. corresponding rest). Leg glycerol turnover was unaffected by exercise intensity or endurance training. In summary, simultaneous leg glycerol uptake and release (indicative of leg triacylglyceride turnover) occurs despite small or negligible net leg glycerol exchange, and furthermore, leg glycerol turnover can be substantially augmented during exercise.