Investigating the effects of Gynostemma pentaphyllum supplementation on muscle in Males

The investigational product is a commercially available capsule-form herbal medicine containing Gynostemma pentaphyllum (G. pentaphyllum) extract (ActivAMP). The daily dose will be 450mg across 2 capsules daily. The aim of this study is to examine the effect of supplementation with G. pentaphyllum for 4 weeks on muscle AMPK activity. Since AMPK is involved in energy supply and performance, and its activity is also altered following exercise, participants following supplementation will undertake aerobic exercise performance trials. Muscle samples will be collected by a Trained Medical Doctor at different times during the steady state exercise to allow measurement of changes in AMPK activity during exercise. As AMPK also alters glucose uptake in muscle, we will also measure glucose uptake by the muscle. Blood and muscle samples will be collected following the supplementation period. The effects of the supplementation or placebo on aerobic exercise performance using two different measures including a steady state and time to fatigue test (TtE) and a 20km time trial using a double blind randomised cross-over study design will be undertaken. Participants will undertake a graded exercise test (GXT) to determine their maximal aerobic exercise capacity, which will be used to set the exercise intensities for the steady state submaximal exercise (SS) and TtE tests. They will then undertake a familiarisation of the TtE and TT within a week of the GXT. Two weeks following the familiarisation testing the participants will start supplementing with either placebo or the supplement (randomised and double blinded) for 28 days and then undertake the SS+TtE followed by the TT separated by two days (thus 30 days supplementation). The participant will then have a four week washout period before repeating the supplementation and exercise testing regimen with the treatment not used in the first trial. The measures to assess the endurance exercise performance are time to complete the TT, work done and power outputs in the TT, while time to fatigue will be determined during the TtE. All exercise completed on a stationary bike. Supplementation 2 weeks after the familiarisation TT participants will be provided with 60 capsules of either placebo or the active supplement. They will be asked to consume 2 capsules each day with their morning meal. Adherence monitored via capsule return. Dietary intake will be fully controlled (all foods provided) 3 days prior to the initial GXT for the week prior to each SS+TtE through to after the TT test. Energy requirements for each participant will be estimated using the Harris Benedict equation and adjusted for physical activity level such that an energy balanced diet is consumed that meets the Australian guide to Healthy Eating. Diets will be designed by a qualified dietitian. Activity will be monitored throughout the intervention to ensure a standardisation of overall activity levels via the use of accelerometers at baseline and during weeks 1 and 4 of the interventions for a one week period. SS+TtE: Participants will undertake 60 min of SS exercise on a stationary bike, after which they will have 5 min of active recovery (30 W) and then perform the TtE test which will be completed at a power output of 50% between that of the ventilatory threshold and the VO2 peak until voluntary exhaustion. Muscle: Muscle biopsies will be taken at rest, 30mins into the SS exercise and at the conclusion of the 60 min SS test (6 biopsies per person) by a trained medical professional. Muscle samples will be measured by the Oxygraph O2k high-resolution respirometer (Oroboros Instruments, Innsbruck, Austria) via a substrate, uncoupler, inhibitor titration (SUIT) protocol. Frozen muscle samples will be used for the determination of AMPK activity, gene expression and protein abundance of key metabolic pathways. Tracer infusion on SS+TtE day: The glucose tracer will commence 30 minutes after the resting biopsy has been taken. Syringe pumps will be used to infuse the [6,6-2H]-glucose. The solution will be infused at 0.2 ml.min-1(12 ml.hr-1). A bolus dose of glucose tracer (54 µmol.kg-1) will be given via the catheter prior to the initiation of the continuous constant infusion (0.62 µmol.kg-1.min-1) which will commence two hours prior to exercise and cease upon completion of exercise. Blood sampling: Blood will be collected prior to exercise and during the SS exercise tests for standard markers of metabolism and glucose tracer analysis and at start and conclusion of TtE test. Resting samples will also be collected for subsequent analysis (basic subject characteristics (glucose, cholesterol, triglycerides etc) as well as potentially other markers of metabolism and AMPK signalling (ie. leptin, adiponectin etc). Two days following the SS+TtE day, participants will, after an overnight fast, undertake a 20 km TT on a velotron™ cycle ergometer. Following this 20 km TT participants will undertake a 4 week washout period.