Nikki A. Jeacocke

Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis

•  A single bolus of ∼20 g of protein after a bout of resistance exercise provides a maximal anabolic stimulus during the early post‐exercise recovery period (∼5 h), but the effect of various protein feeding strategies on skeletal muscle protein synthesis during an extended recovery period (12 h) is unknown. •  We compared three different patterns of ingestion of 80 g of protein during 12 h recovery after resistance exercise and the associated anabolic response in human skeletal muscle. Protein was ingested in 10, 20 or 40 g feedings using a pulsed, intermediate or bolus ingestion regimen, respectively. •  Our results indicate that repeated ingestion of 20 g of protein was superior for stimulating muscle protein synthesis during the 12 h experimental period. •  The three dietary treatments induced differential phosphorylation of signalling proteins and changes in mRNA abundance. •  This study shows that the distribution of protein intake is an important variable to promote attainment and maintenance of peak muscle mass.

Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling

We determined the effects of varying daily carbohydrate intake by providing or withholding carbohydrate during daily training on endurance performance, whole body rates of substrate oxidation, and selected mitochondrial enzymes. Sixteen endurance-trained cyclists or triathletes were pair matched and randomly allocated to either a high-carbohydrate group (High group; n = 8) or an energy-matched low-carbohydrate group (Low group; n = 8) for 28 days. Immediately before study commencement and during the final 5 days, subjects undertook a 5-day test block in which they completed an exercise trial consisting of a 100 min of steady-state cycling (100SS) followed by a 7-kJ/kg time trial on two occasions separated by 72 h. In a counterbalanced design, subjects consumed either water (water trial) or a 10% glucose solution (glucose trial) throughout the exercise trial. A muscle biopsy was taken from the vastus lateralis muscle on day 1 of the first test block, and rates of substrate oxidation were determined throughout 100SS. Training induced a marked increase in maximal citrate synthase activity after the intervention in the High group (27 vs. 34 micromol x g(-1) x min(-1), P < 0.001). Tracer-derived estimates of exogenous glucose oxidation during 100SS in the glucose trial increased from 54.6 to 63.6 g (P < 0.01) in the High group with no change in the Low group. Cycling performance improved by approximately 6% after training. We conclude that altering total daily carbohydrate intake by providing or withholding carbohydrate during daily training in trained athletes results in differences in selected metabolic adaptations to exercise, including the oxidation of exogenous carbohydrate. However, these metabolic changes do not alter the training-induced magnitude of increase in exercise performance.

Effects of lowering body temperature via hyperhydration, with and without glycerol ingestion and practical precooling on cycling time trial performance in hot and humid conditions.

BackgroundHypohydration and hyperthermia are factors that may contribute to fatigue and impairment of endurance performance. The purpose of this study was to investigate the effectiveness of combining glycerol hyperhydration and an established precooling technique on cycling time trial performance in hot environmental conditions.MethodsTwelve well-trained male cyclists performed three 46.4-km laboratory-based cycling trials that included two climbs, under hot and humid environmental conditions (33.3 ± 1.1°C; 50 ± 6% r.h.). Subjects were required to hyperhydrate with 25 g.kg-1 body mass (BM) of a 4°C beverage containing 6% carbohydrate (CON) 2.5 h prior to the time trial. On two occasions, subjects were also exposed to an established precooling technique (PC) 60 min prior to the time trial, involving 14 g.kg-1 BM ice slurry ingestion and applied iced towels over 30 min. During one PC trial, 1.2 g.kg-1 BM glycerol was added to the hyperhydration beverage in a double-blind fashion (PC+G). Statistics used in this study involve the combination of traditional probability statistics and a magnitude-based inference approach.ResultsHyperhydration resulted in large reductions (−0.6 to −0.7°C) in rectal temperature. The addition of glycerol to this solution also lowered urine output (330 ml, 10%). Precooling induced further small (−0.3°C) to moderate (−0.4°C) reductions in rectal temperature with PC and PC+G treatments, respectively, when compared with CON (0.0°C, P<0.05). Overall, PC+G failed to achieve a clear change in cycling performance over CON, but PC showed a possible 2% (30 s, P=0.02) improvement in performance time on climb 2 compared to CON. This improvement was attributed to subjects’ lower perception of effort reported over the first 10 km of the trial, despite no clear performance change during this time. No differences were detected in any other physiological measurements throughout the time trial.ConclusionsDespite increasing fluid intake and reducing core temperature, performance and thermoregulatory benefits of a hyperhydration strategy with and without the addition of glycerol, plus practical precooling, were not superior to hyperhydration alone. Further research is warranted to further refine preparation strategies for athletes competing in thermally stressful events to optimize health and maximize performance outcomes.

Manipulation of Muscle Creatine and Glycogen Changes DXA Estimates of Body Composition.

Standardizing a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. Purpose We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. Method Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n = 9) (20 g·d−1 for 5 d loading; 3 g·d−1 maintenance) or placebo (n = 9) with crossover application of glycogen loading (12 v 6 g·kg−1 BM per day for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. Results Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0% ± 0.7% and 2.0% ± 0.9%) and leg lean mass (3.1% ± 1.8% and 2.6% ± 1.0%) respectively. A substantial decrease in leg lean mass was observed after the glycogen depleting condition (−1.4% ± 1.6%). Total body water showed substantial increases after glycogen loading (2.3% ± 2.3%), creatine loading (1.4% ± 1.9%) and the combined treatment (2.3% ± 1.1%). Conclusions Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.Standardising a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. PURPOSE We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. METHOD Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n=9) (20 g/d for 5 d loading; 3 g/d maintenance) or placebo (n=9) with crossover application of glycogen loading (12 v 6 g/kg BM/d for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. RESULTS Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0 ± 0.7 % and 2.0 ± 0.9 %) and leg lean mass (3.1 ± 1.8 %and 2.6 ± 1.0 %) respectively. A substantial decrease in leg lean mass was observed following the glycogen depleting condition (-1.4 ± 1.6 %). Total body water showed substantial increases following glycogen loading (2.3 ± 2.3 %), creatine loading (1.4 ± 1.9 %) and the combined treatment (2.3 ± 1.1 %). CONCLUSIONS Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.

Manipulation of Muscle Creatine and Glycogen Changes Dual X-ray Absorptiometry Estimates of Body Composition

Standardizing a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. Purpose We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. Method Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n = 9) (20 g·d−1 for 5 d loading; 3 g·d−1 maintenance) or placebo (n = 9) with crossover application of glycogen loading (12 v 6 g·kg−1 BM per day for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. Results Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0% ± 0.7% and 2.0% ± 0.9%) and leg lean mass (3.1% ± 1.8% and 2.6% ± 1.0%) respectively. A substantial decrease in leg lean mass was observed after the glycogen depleting condition (−1.4% ± 1.6%). Total body water showed substantial increases after glycogen loading (2.3% ± 2.3%), creatine loading (1.4% ± 1.9%) and the combined treatment (2.3% ± 1.1%). Conclusions Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.Standardising a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. PURPOSE We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. METHOD Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n=9) (20 g/d for 5 d loading; 3 g/d maintenance) or placebo (n=9) with crossover application of glycogen loading (12 v 6 g/kg BM/d for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. RESULTS Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0 ± 0.7 % and 2.0 ± 0.9 %) and leg lean mass (3.1 ± 1.8 %and 2.6 ± 1.0 %) respectively. A substantial decrease in leg lean mass was observed following the glycogen depleting condition (-1.4 ± 1.6 %). Total body water showed substantial increases following glycogen loading (2.3 ± 2.3 %), creatine loading (1.4 ± 1.9 %) and the combined treatment (2.3 ± 1.1 %). CONCLUSIONS Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.

Effects of Creatine and Carbohydrate Loading on Cycling Time Trial Performance

Introduction Creatine (Cr) and carbohydrate loadings are dietary strategies used to enhance exercise capacity. This study examined the metabolic and performance effects of a combined CR and CHO loading regiment on time trial (TT) cycling bouts. Methods Eighteen well-trained (~65 mL·kg−1·min−1 V˙O2peak) men completed three performance trials (PT) that comprised a 120-km cycling TT interspersed with alternating 1- and 4-km sprints (six sprints each) performed every 10 km followed by an inclined ride to fatigue (~90% V˙O2peak). Subjects were pair matched into either CR-loaded (20 g·d−1 for 5 d + 3 g·d−1 for 9 d) or placebo (PLA) groups (n = 9) after the completion of PT1. All subjects undertook a crossover application of the carbohydrate interventions, consuming either moderate (6 g·kg−1 body mass (BM) per day; MOD) or CHO-loaded (12 g·kg−1 BM·d−1; LOAD) diets before PT2 and PT3. Muscle biopsies were taken before PT1, 18 h after PT1, and before both PT2 and PT3. Results No significant differences in overall TT or inclined ride times were observed between intervention groups. PLA + LOAD improved power above baseline (P < 0.05) during the final 1-km sprint, whereas CR + MOD and CR + LOAD improved power (P < 0.05) during the final 4-km sprint. Greater power was achieved with MOD and LOAD compared with baseline with PLA (P < 0.05). CR increased pre-PT BM compared with PLA (+1.54% vs +0.99% from baseline). CR + LOAD facilitated greater [total CR] (P < 0.05 vs baseline) and muscle [glycogen] (P < 0.01 vs baseline and MOD) compared with PLA + LOAD. Mechanistic target of rapamycin decreased from baseline after glycogen depletion (~30%; P < 0.05). Conclusions Power output in the closing sprints of exhaustive TT cycling increased with CR ingestion despite a CR-mediated increase in weight. CR cosupplemented with carbohydrates may therefore be beneficial strategy for late-stage breakaway moments in endurance events.

Manipulation of Muscle Creatine and Glycogen Changes DXA Estimates of Body Composition [accepted manuscript]

Standardizing a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. Purpose We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. Method Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n = 9) (20 g·d−1 for 5 d loading; 3 g·d−1 maintenance) or placebo (n = 9) with crossover application of glycogen loading (12 v 6 g·kg−1 BM per day for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. Results Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0% ± 0.7% and 2.0% ± 0.9%) and leg lean mass (3.1% ± 1.8% and 2.6% ± 1.0%) respectively. A substantial decrease in leg lean mass was observed after the glycogen depleting condition (−1.4% ± 1.6%). Total body water showed substantial increases after glycogen loading (2.3% ± 2.3%), creatine loading (1.4% ± 1.9%) and the combined treatment (2.3% ± 1.1%). Conclusions Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.Standardising a dual x-ray absorptiometry (DXA) protocol is thought to provide a reliable measurement of body composition. PURPOSE We investigated the effects of manipulating muscle glycogen and creatine content independently and additively on DXA estimates of lean mass. METHOD Eighteen well-trained male cyclists undertook a parallel group application of creatine loading (n=9) (20 g/d for 5 d loading; 3 g/d maintenance) or placebo (n=9) with crossover application of glycogen loading (12 v 6 g/kg BM/d for 48 h) as part of a larger study involving a glycogen-depleting exercise protocol. Body composition, total body water, muscle glycogen and creatine content were assessed via DXA, bioelectrical impedance spectroscopy and standard biopsy techniques. Changes in the mean were assessed using the following effect-size scale: >0.2 small, >0.6, moderate, >1.2 large and compared with the threshold for the smallest worthwhile effect of the treatment. RESULTS Glycogen loading, both with and without creatine loading, resulted in substantial increases in estimates of lean body mass (mean ± SD; 3.0 ± 0.7 % and 2.0 ± 0.9 %) and leg lean mass (3.1 ± 1.8 %and 2.6 ± 1.0 %) respectively. A substantial decrease in leg lean mass was observed following the glycogen depleting condition (-1.4 ± 1.6 %). Total body water showed substantial increases following glycogen loading (2.3 ± 2.3 %), creatine loading (1.4 ± 1.9 %) and the combined treatment (2.3 ± 1.1 %). CONCLUSIONS Changes in muscle metabolites and water content alter DXA estimates of lean mass during periods in which minimal change in muscle protein mass is likely. This information needs to be considered in interpreting the results of DXA-derived estimates of body composition in athletes.