The aim of the study was to investigate the pre- and during-race nutritional intake of cyclists competing in a 210-km 1-day ultraendurance cycle race. Forty-five endurancetrained male cyclists participated in this dietary survey and completed a 3-day dietary record. Mean reported carbohydrate (CHO) intake over the 3 days before the race (5.6 ± 1.7 g/kg) was below the recommended guidelines of 7–10 g/kg. Although 57% of participants indicated that they CHO loaded 1–3 days before the race, only 23% of these participants achieved CHO intakes of ≥7 g/kg over the 3-day period before the race, demonstrating a discrepancy between perceived and actual intakes of CHO. Most participants indicated the use of CHO supplements before (84%) and during (98%) the race and achieved a CHO intake of 63 ± 23 g/hr during the race. Although most cyclists failed to meet recommended prerace CHO intakes, most achieved the recommended CHO intakes during the race.
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Julia H. Goedecke, Virginia R. Clark, Timothy D. Noakes, and Estelle V. Lambert
The aims of the study were to determine if medium-chain triacylglycerol (MCT), ingested in combination with carbohydrate (CHO), would alter substrate metabolism and improve simulated competitive ultra-endurance cycling performance. Eight endurance-trained cyclists took part in this randomized, single-blind crossover study. On two separate occasions, subjects cycled for 270 min at 50% of peak power output, interspersed with four 75 kJ sprints at 60 min intervals, followed immediately by a 200 kJ time-trial. One hour prior to the exercise trials, subjects ingested either 75 g of CHO or 32 g of MCT, and then ingested 200 mL of a 10% CHO (wt/vol) solution or a 4.3% MCT + 10% CHO (wt/vol) solution every 20 min during the CHO and MCT trials, respectively. During the constant-load phases of the 270 min exercise trial, VO2, RER, and heart rate were measured at 30 min intervals and gastrointestinal (GI) symptoms were recorded. There was no difference in VO2 or RER between the MCT and CHO trials (P = 0.40). Hourly sprint (P = 0.03 for trial x time interaction) and time-trial times (14:30 ± 0.58 vs. 12:36 ± 1:6, respectively, P < 0.001) were slower in the MCT than the CHO trial. Half the subjects experienced GI symptoms with MCT ingestion. In conclusion, MCTs ingested prior to exercise and co-ingested with CHO during exercise did not alter substrate metabolism and significantly compromised sprint performance during prolonged ultra-endurance cycling exercise.
Estelle V. Lambert, Julia H. Goedecke, Charl van Zyl, Kim Murphy, John A. Hawley, Steven C. Dennis, and Timothy D. Noakes
We examined the effects of a high-fat diet (HFD-CHO) versus a habitual diet, prior to carbohydrate (CHO)-loading on fuel metabolism and cycling time-trial (TT) performance. Five endurance-trained cyclists participated in two 14-day randomized cross-over trials during which subjects consumed either a HFD (>65% MJ from fat) or their habitual diet (CTL) (30 ± 5% MJ from fat) for 10 day, before ingesting a high-CHO diet (CHO-loading, CHO > 70% MJ) for 3 days. Trials consisted of a 150-min cycle at 70% of peak oxygen uptake (V̇O2peak), followed immediately by a 20-km TT. One hour before each trial, cyclists ingested 400 ml of a 3.44% medium-chain triacylglycerol (MCT) solution, and during the trial, ingested 600 ml/hour of a 10% 14C-glucose + 3.44% MCT solution. The dietary treatments did not alter the subjects’ weight, body fat, or lipid profile. There were also no changes in circulating glucose, lactate, free fatty acid (FFA), and β-hydroxybutyrate concentrations during exercise. However, mean serum glycerol concentrations were significantly higher (p < .01) in the HFD-CHO trial. The HFD-CHO diet increased total fat oxidation and reduced total CHO oxidation but did not alter plasma glucose oxidation during exercise. By contrast, the estimated rates of muscle glycogen and lactate oxidation were lower after the HFD-CHO diet. The HFD-CHO treatment was also associated with improved TT times (29.5 ± 2.9 min vs. 30.9 ± 3.4 min for HFD-CHO and CTL-CHO, p < .05). High-fat feeding for 10 days prior to CHO-loading was associated with an increased reliance on fat, a decreased reliance on muscle glycogen, and improved time trial performance after prolonged exercise.
Julia H. Goedecke, Richard Elmer, Steven C. Dennis, Ingrid Schloss, Timothy D. Noakes, and Estelle V. Lambert
The effects of ingesting different amounts of medium-chain triacylglycerol (MCT) and carbohydrate (CHO) on gastric symptoms, fuel metabolism, and exercise performance were measured in 9 endurance-trained cyclists. Participants, 2 hr after a standardized lunch, cycled for 2 hr at 63% of peak oxygen consumption and then performed a simulated 40-km time trial (T trial). During the rides, participants ingested either 10% 14C-glucose (GLU), 10% 14C-GLU + 1.72%MCT(LO-MCT), or 10% l4C-GLU + 3.44%MCT(HI-MCT) solutions: 400 ml at the start of exercise and then 100 ml every lOmin.MCTingestiondid not affect gastrointestinal symptoms. It only raised serum free fatty acid (FFA) and ß-hydroxybutyrate concentrations. Higher FFA and ß-hydroxybutyrate concentrations with MCT ingestion did not affect fuel oxidation or T-trial performance. The high CHO content of the pretrial lunch increased starting plasma insulin levels, which may have promoted CHO oxidation despite elevated circulating FFA concentrations with MCT ingestion.
Amy E. Mendham, Julia H. Goedecke, Melony C. Fortuin-de Smidt, Lindokuhle Phiri, Louise Clamp, Jeroen Swart, Gosia Lipinska, and Dale E. Rae
Background: Improving sleep quality and reducing depressive symptoms may be target mechanisms for intervention-based research aimed at reducing cardiometabolic risk in low-income communities. This study assessed the effects of exercise training on depressive symptoms and sleep in obese women for a low socioeconomic community. The secondary aim explored associations between changes in depressive symptoms and sleep with changes in cardiorespiratory fitness and cardiometabolic risk factors. Methods: Participants were randomized into exercise (n = 20) or control (n = 15) groups. The exercise group completed 12 weeks of combined resistance and aerobic training (40–60 min, 4 d/wk), and the control group maintained habitual diet and activity. Preintervention and postintervention testing included questionnaires on symptoms of depression, psychological distress, and sleep quality. Sedentary time, peak oxygen consumption, body mass index, and insulin sensitivity were measured objectively. Sleep duration (accelerometry) was assessed at preintervention and weeks 4, 8, and 12. Results: Exercise training reduced depressive symptoms (P = .002) and improved sleep quality (P < .001) and sleep efficiency (P = .005). Reduced depressive symptoms were associated with improved peak oxygen consumption (rho = −.600, P < .001), and improved sleep quality correlated with reduced sedentary time (rho = .415, P = .018). Conclusion: These results highlight the potential for community-based exercise interventions to simultaneously address multiple comorbidities in a low-income setting.
Amy E. Mendham, Julia H. Goedecke, Nyuyki Clement Kufe, Melikhaya Soboyisi, Antonia Smith, Kate Westgate, Soren Brage, and Lisa K. Micklesfield
Background : We first explored the associations between physical behaviors and total and regional adiposity. Second, we examined how reallocating time in different physical behaviors was associated with total body fat mass in men and women from a low-income South African setting. Methods : This cross-sectional study included a sample of 692 participants (384 men and 308 women) aged 41–72 years. Physical behaviors were measured using integrated hip and thigh accelerometry to estimate total movement volume and time spent in sleeping, sitting/lying, standing, light physical activity, and moderate to vigorous physical activity (MVPA). Total body fat mass and regional adiposity were measured using dual-energy X-ray absorptiometry. Results : The associations between total movement volume and measures of regional obesity were mediated by total body adiposity. In men, reallocating 30 minutes of sitting/lying to 30 minutes of MVPA was associated with 1.0% lower fat mass. In women, reallocation of 30 minutes of sitting/lying to MVPA and 30 minutes of standing to MVPA were associated with a 0.3% and 1.4% lower fat mass, respectively. Conclusions : Although the association between physical behaviors and fat mass differed between men and women, the overall public health message is similar; reallocating sedentary time to MVPA is associated with a reduction in fat mass in both men and women.