We determined the effects of "periodized nutrition" on skeletal muscle and whole body responses to a bout of prolonged exercise the following morning. Seven cyclists completed two trials receiving isoenergetic diets differing in the timing of ingestion: they consumed either 8 g/kg body mass (BM) of carbohydrate (CHO) before undertaking an evening session of high-intensity training (HIT) and slept without eating (FASTED), or consumed 4 g/kg BM of CHO before HIT, then 4 g/kg BM of CHO before sleeping (FED). The next morning subjects completed 2 h of cycling (120SS) while overnight fasted. Muscle biopsies were taken on day 1 (D1) before and 2 h after HIT and on day 2 (D2) pre-, post-, and 4 h after 120SS. Muscle [glycogen] was higher in FED at all times post-HIT (P < 0.001). The cycling bouts increased PGC1α mRNA and PDK4 mRNA (P < 0.01) in both trials, with PDK4 mRNA being elevated to a greater extent in FASTED (P < 0.05). Resting phosphorylation of AMPK(Thr172), p38MAPK(Thr180/Tyr182), and p-ACC(Ser79) (D2) was greater in FASTED (P < 0.05). Fat oxidation during 120SS was higher in FASTED (P = 0.01), coinciding with increases in ACC(Ser79) and CPT1 as well as mRNA expression of CD36 and FABP3 (P < 0.05). Methylation on the gene promoter for COX4I1 and FABP3 increased 4 h after 120SS in both trials, whereas methylation of the PPARδ promoter increased only in FASTED. We provide evidence for shifts in DNA methylation that correspond with inverse changes in transcription for metabolically adaptive genes, although delaying postexercise feeding failed to augment markers of mitochondrial biogenesis.
Inhibition of nitric oxide synthase (NOS) significantly attenuates the increase in skeletal muscle glucose uptake during contraction/exercise, and a greater attenuation is observed in individuals with Type 2 diabetes compared with healthy individuals. Therefore, NO appears to play an important role in mediating muscle glucose uptake during contraction. In this study, we investigated the involvement of neuronal NOSμ (nNOSμ), the main NOS isoform activated during contraction, on skeletal muscle glucose uptake during ex vivo contraction. Extensor digitorum longus muscles were isolated from nNOSμ(-/-) and nNOSμ(+/+) mice. Muscles were contracted ex vivo in a temperature-controlled (30°C) organ bath with or without the presence of the NOS inhibitor N(G)-monomethyl-l-arginine (L-NMMA) and the NOS substrate L-arginine. Glucose uptake was determined by radioactive tracers. Skeletal muscle glucose uptake increased approximately fourfold during contraction in muscles from both nNOSμ(-/-) and nNOSμ(+/+) mice. L-NMMA significantly attenuated the increase in muscle glucose uptake during contraction in both genotypes. This attenuation was reversed by L-arginine, suggesting that L-NMMA attenuated the increase in muscle glucose uptake during contraction by inhibiting NOS and not via a nonspecific effect of the inhibitor. Low levels of NOS activity (~4%) were detected in muscles from nNOSμ(-/-) mice, and there was no evidence of compensation from other NOS isoform or AMP-activated protein kinase which is also involved in mediating muscle glucose uptake during contraction. These results indicate that NO regulates skeletal muscle glucose uptake during ex vivo contraction independently of nNOSμ.
Both the quantity and quality of pre-exercise carbohydrate (CHO) meals have been shown to improve endurance performance. However, their role in attenuating central fatigue (CF) is inconclusive. The use of neurophysiological techniques, such as voluntary activation (VA) and the central activation ratio (CAR), alongside maximum voluntary contraction (MVC) and sustained MVC (sMVC) can provide information on CF. Hence, the objective of this study was to investigate the effects of isocaloric pre-exercise meals: 1) a high versus low quantity of CHO and 2) a high quantity of CHO with a high versus low glycemic index (GI) on MVC, VA, and CAR following a 90-min run. The high and low quantity of CHO was 1.5 and 0.8 g/kg body wt, respectively, and high and low GI was ~75 and ~40, respectively. Blood insulin, serotonin, tryptophan, and gaseous exchange were also measured. High CHO preserved sMVC, VA, CAR, and serotonin postrunning with greater CHO oxidation and insulin response, whereas in low CHO, greater reductions in sMVC, VA, and CAR were accompanied by higher serotonin and fat oxidation with lower insulin response. These observations indicate central involvements. Meanwhile, high GI CHO better preserved force (sMVC), CAR, and tryptophan with greater CHO oxidation and insulin response compared with low GI. The findings of this study suggest that pre-exercise meals with varying quantity and quality of CHO can have an effect on CF, where greater CHO oxidation and insulin response found in both high CHO and high GI lead to attenuation of CF. NEW & NOTEWORTHY This paper examined the effects of carbohydrate interventions (high and low: quantity and quality wise) on central activity during prolonged exercise using mainly neurophysiological techniques along with gaseous exchange and blood insulin, serotonin, and tryptophan data.
Measurement error(s) of exercise tests for women are severely lacking in the literature. The purpose of this investigation was to 1) determine whether ovulatory status or ambient environment were moderating variables when completing a 30-min self-paced work trial and 2) provide test-retest norms specific to athletic women. A retrospective analysis of three heat stress studies was completed using 33 female participants (31 ± 9 yr, 54 ± 10 mL·min-1·kg-1) that yielded 130 separate trials. Participants were classified as ovulatory (n = 19), anovulatory (n = 4), and oral contraceptive pill users (n = 10). Participants completed trials ∼2 wk apart in their (quasi-) early follicular and midluteal phases in two of moderate (1.3 ± 0.1 kPa, 20.5 ± 0.5°C, 18 trials), warm-dry (2.2 ± 0.2 kPa, 34.1 ± 0.2°C, 46 trials), or warm-humid (3.4 ± 0.1 kPa, 30.2 ± 1.1°C, 66 trials) environments. We quantified reliability using limits of agreement, intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Test-retest reliability was high, clinically valid (ICC = 0.90, P < 0.01), and acceptable with a mean CV of 4.7%, SEM of 3.8 kJ (2.1 W), and reliable bias of -2.1 kJ (-1.2 W). The various ovulatory status and contrasting ambient conditions had no appreciable effect on reliability. These results indicate that athletic women can perform 30-min self-paced work trials ∼2 wk apart with an acceptable and low variability irrespective of their hormonal status or heat-stressful environments.NEW & NOTEWORTHY This study highlights that aerobically trained women perform 30-min self-paced work trials ∼2 wk apart with acceptably low variability and their hormonal/ovulatory status and the introduction of greater ambient heat and humidity do not moderate this measurement error.
Chronic pain is a pervasive health problem and is associated with tremendous socioeconomic costs. However, current pain treatments are often ineffective due, in part, to the multi-factorial nature of pain. Mild hypohydration was shown to increase experimental pain sensitivity in men, but whether this also occurs in women has not been examined. Fluctuations in ovarian hormones (i.e., 17ß-oestradiol and progesterone) throughout the menstrual cycle may influence a woman's pain sensitivity, as well as hydration levels, suggesting possible interactions between hypohydration and menstrual phase on pain. We investigated the effects of mild hypohydration (HYPO, 24 hr of fluid restriction) on ischaemic pain sensitivity in 14 eumenorrheic women during the early follicular (EF) and mid-luteal (ML) phases of their menstrual cycle. We also examined whether acute water ingestion could reverse the negative effects of hypohydration. Elevated serum osmolality, plasma copeptin, and urine specific gravity indicated mild hypohydration. Compared to euhydration, HYPO reduced pain tolerance (by 34 ± 46 s; P = 0.02, ηp2 = 0.37) and increased ratings of pain intensity (by 0.7 ± 0.7 cm; P = 0.004; ηp2 = 0.55) and unpleasantness (by 0.7 ± 0.9 cm; P = 0.02; ηp2 = 0.40); these results were not influenced by menstrual phase. Water ingestion reduced thirst perception (Visual Analogue Scale, by 2.3 ± 0.9 cm; P < 0.001, ηp2 = 0.88) but did not reduce pain sensitivity. Therefore, hypohydration increases pain sensitivity in women with no influence of menstrual phase.
Although complex in nature, a number of metabolites have been implicated in the onset of exercise-induced fatigue. The purpose of this study was to identify changes in the plasma metabolome and specifically, to identify candidate metabolites associated with the onset of fatigue during prolonged cycling. Eighteen healthy and recreationally active men (mean ± SD; age: 24.7 ± 4.8 yr; mass 67.1 ± 6.1 kg; body mass index: 22.8 ± 2.2; peak oxygen uptake: 40.9 ± 6.1 ml·kg-1·min-1) were recruited to this study. Participants performed a prolonged cycling time-to-exhaustion (TTE) test at an intensity corresponding to a fixed blood lactate concentration (3 mmol/l). Plasma samples collected at 10 min of exercise, before fatigue (last sample before fatigue <10 min before fatigue), immediately after fatigue (point of exhaustion), and 20 min after fatigue were assessed using a liquid chromatography-mass spectrometry-based metabolomic approach. Eighty metabolites were putatively identified, with 68 metabolites demonstrating a significant change during the cycling task (duration: ~80.9 ± 13.6 min). A clear multivariate structure in the data was revealed, with the first principal component (36% total variance) describing a continuous increase in metabolite concentration throughout the TTE trial and recovery, whereas the second principal component (14% total variance) showed an increase in metabolite concentration followed by a recovery trajectory, peaking at the point of fatigue. Six clusters of correlated metabolites demonstrating unique metabolite trajectories were identified, including significant separation in the metabolome between prefatigue and postfatigue time points. In accordance with our hypothesis, free-fatty acids and tryptophan contributed to differences in the plasma metabolome at fatigue.NEW & NOTEWORTHY Metabolites have long been implicated in the onset of fatigue. This study applied a metabolomic approach to track 80 plasma-borne metabolites during a cycle to fatigue task. Of these, 68 metabolites demonstrated significant change, with the plasma metabolome at fatigue being clearly distinguishable from other time points. Six unique clusters of metabolites were identified, and free fatty acids were strongly associated with fatigue onset therein lending support to the central fatigue hypothesis.