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  • Author: Jenna B. Gillen x
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Brian J. Martin, Rachel B. Tan, Jenna B. Gillen, Michael E. Percival and Martin J. Gibala

Supplementation with green tea extract (GTE) in animals has been reported to induce numerous metabolic adaptations including increased fat oxidation during exercise and improved performance. However, data regarding the metabolic and physiological effects of GTE during exercise in humans are limited and equivocal.

Purpose:

To examine the effects of short-term GTE treatment on resting energy expenditure (REE), wholebody substrate utilization during exercise and time trial performance.

Methods:

Fifteen active men (24 ± 3 y; VO2peak = 48 ± 7 ml·kg·min−1; BMI = 26 ± 3 kg·m2(–1)) ingested GTE (3x per day = 1,000 mg/d) or placebo (PLA) for 2 day in a double-blind, crossover design (each separated by a 1 week wash-out period). REE was assessed in the fasted state. Subjects then ingested a standardized breakfast (~5.0 kcal·kg-1) and 90 min later performed a 60 min cycling bout at an intensity corresponding to individual maximal fat oxidation (44 ± 11% VO2peak), followed by a 250 kJ TT.

Results:

REE, whole-body oxygen consumption (VO2) and substrate oxidation rates during steady-state exercise were not different between treatments. However, mean heart rate (HR) was lower in GTE vs. PLA (115 ± 16 vs. 118 ± 17 beats·min−1; main effect, p = .049). Mixed venous blood [glycerol] was higher during rest and exercise after GTE vs. PLA (p = .006, main effect for treatment) but glucose, insulin and free-fatty acids were not different. Subsequent time trial performance was not different between treatments (GTE = 25:38 ± 5:32 vs. PLA = 26:08 ± 8:13 min; p = .75).

Conclusion:

GTE had minimal effects on whole-body substrate metabolism but significantly increased plasma glycerol and lowered heart rate during steady-state exercise, suggesting a potential increase in lipolysis and a cardiovascular effect that warrants further investigation.

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Andrew J.R. Cochran, Michael E. Percival, Sara Thompson, Jenna B. Gillen, Martin J. MacInnis, Murray A. Potter, Mark A. Tarnopolsky and Martin J. Gibala

Sprint interval training (SIT), repeated bouts of high-intensity exercise, improves skeletal muscle oxidative capacity and exercise performance. β-alanine (β-ALA) supplementation has been shown to enhance exercise performance, which led us to hypothesize that chronic β-ALA supplementation would augment work capacity during SIT and augment training-induced adaptations in skeletal muscle and performance. Twenty-four active but untrained men (23 ± 2 yr; VO2peak = 50 ± 6 mL·kg−1·min−1) ingested 3.2 g/day of β-ALA or a placebo (PLA) for a total of 10 weeks (n = 12 per group). Following 4 weeks of baseline supplementation, participants completed a 6-week SIT intervention. Each of 3 weekly sessions consisted of 4–6 Wingate tests, i.e., 30-s bouts of maximal cycling, interspersed with 4 min of recovery. Before and after the 6-week SIT program, participants completed a 250-kJ time trial and a repeated sprint test. Biopsies (v. lateralis) revealed that skeletal muscle carnosine content increased by 33% and 52%, respectively, after 4 and 10 weeks of β-ALA supplementation, but was unchanged in PLA. Total work performed during each training session was similar across treatments. SIT increased markers of mitochondrial content, including cytochome c oxidase (40%) and β-hydroxyacyl-CoA dehydrogenase maximal activities (19%), as well as VO2peak (9%), repeated-sprint capacity (5%), and 250-kJ time trial performance (13%), but there were no differences between treatments for any measure (p < .01, main effects for time; p > .05, interaction effects). The training stimulus may have overwhelmed any potential influence of β-ALA, or the supplementation protocol was insufficient to alter the variables to a detectable extent.

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Jenna B. Gillen, Jorn Trommelen, Floris C. Wardenaar, Naomi Y.J. Brinkmans, Joline J. Versteegen, Kristin L. Jonvik, Christoph Kapp, Jeanne de Vries, Joost J.G.C. van den Borne, Martin J. Gibala and Luc J.C. van Loon

Dietary protein intake should be optimized in all athletes to ensure proper recovery and enhance the skeletal muscle adaptive response to exercise training. In addition to total protein intake, the use of specific proteincontaining food sources and the distribution of protein throughout the day are relevant for optimizing protein intake in athletes. In the present study, we examined the daily intake and distribution of various proteincontaining food sources in a large cohort of strength, endurance and team-sport athletes. Well-trained male (n=327) and female (n=226) athletes completed multiple web-based 24-hr dietary recalls over a 2-4 wk period. Total energy intake, the contribution of animal- and plant-based proteins to daily protein intake, and protein intake at six eating moments were determined. Daily protein intake averaged 108±33 and 90±24 g in men and women, respectively, which corresponded to relative intakes of 1.5±0.4 and 1.4±0.4 g/kg. Dietary protein intake was correlated with total energy intake in strength (r=0.71, p <.001), endurance (r=0.79, p <.001) and team-sport (r=0.77, p <.001) athletes. Animal and plant-based sources of protein intake was 57% and 43%, respectively. The distribution of protein intake was 19% (19±8 g) at breakfast, 24% (25±13 g) at lunch and 38% (38±15 g) at dinner. Protein intake was below the recommended 20 g for 58% of athletes at breakfast, 36% at lunch and 8% at dinner. In summary, this survey of athletes revealed they habitually consume > 1.2 g protein/kg/d, but the distribution throughout the day may be suboptimal to maximize the skeletal muscle adaptive response to training.