Energy Source with Aerobic Training ~50-60% of energy during continuous exercise at 70% maximal oxygen capacity is derived from carbohydrates Remainder mainly from fatty acid oxidation Greater proportion from fat as intensity Energy derived from fat with aerobic training muscle TG utilized for energy Prevents glycogen depletion Coyle E et al. Am J Physiol. 1997.
Low Energy Intake Muscle Mass Bone density Menstrual Dysfunction Fatigue, Injury, Illness Inability to recover between workouts and from injury If weight loss is the goal, should take place in the off-season, not during the competitive season
Weight Loss in Competitive Season Loss of lean mass strength and endurance Impaired immune, endocrine and musculoskeletal function Resting Metabolic Rate Poor Micronutrient Intake Iron deficiency a major concern, especially with female athletes oxygen carrying capacity, critical for endurance athletes Burke LM et al. J Sports Sci. 2006.
Iron Deficiency Plasma volume expansion occurs with training ~300 mL for recreational runners Up to 1L for endurance athletes Hemolysis with exercise foot strike hemolysis for runners GI Bleeding Up to 1/4 of marathoners visceral blood flow, promoting ischemic damage LES pressure Needs estimated to be 70% greater Zoller and Vogel. Nutrition. 2004.
Carbohydrate Intake Muscle glycogen stores of a trained athlete are adequate to fuel exercise up to 60-90 minutes Fatigue or work capacity with prolonged continuous exercise or high intensity intermittent exercise of 60 minutes or greater Depletion of glycogen stores
Carbohydrate for Weight Training Muscle glycogen most likely not depleted Possible with sessions of high intensity lasting longer than an hour May be an issue for athletes doing cardio and weight lifting Muscle protein synthesis is maximized with addition of carbohydrate
Carbohydrate Loading Previous Protocol 3 days of low carbohydrate diet + training Deplete stores 3 days of high carbohydrate diet + tapered training or rest Current Protocol Found that 24-36 hours of rest and a high carbohydrate diet is sufficient to increase muscle glycogen stores
High Carbohydrate Diet 8-12 g/kg/day For a 70 kg person, 2240-3360 kcal of carbohydate per day 60-70% of kcal as CHO for 5000 kcal diet Okay for an elite athlete Pretty difficult for casual athlete or someone who restricts intake Aim for lower end of range Not a good idea to overeat just to maximize glycogen
Overall Carbohydrate Recommendations Casual Athlete: 50-55% of kcals 60-70% for 1-2 days before competition Endurance Athlete 60-65% of intake Protein will most likely be adequate given high caloric intake ~20% fat High fat diet will displace necessary carbohydrate
Carbohydrates during exercise Improves performance for exercise lasting longer than 90 minutes Intake greater than 1.5g/min lead to oxidation of exogenous glucose above 1.0g/min Alternative fuel source to muscle glycogen, preventing depletion Recommendation is 0.7g/kg body weight per hour Shown to improve performance 70 kg person: 49g/hr 8 oz Gatorade has 14 g carbohydrate ~28 oz (3.5 cups) an hour Jentjens RL et al. Metabolism. 2005.
2 Timing of Carbohydrate Ingestion TABLE 2. Total work and physiological responses during, and plasma lactate at the end of, 15-min performance ride following 2 h of exercise at 70+/- 1% [spacing dot above]VO2 peak with ingestion of a sweet placebo throughout exercise (CON), 7% carbohydrate throughout exercise (CHO-7), or a sweet placebo for the first 90 min followed by 21% carbohydrate (CHO-0/21). McConnell G et al. MSSE. 1996.
Recommendations During Exercise Consume carbohydrates spaced out every 15-20 minutes 6-8% carbohydrate, primarily glucose More concentrated source or fructose may slow gastric emptying or cause GI distress ~3-4 cups/hr
Postexercise Carbohydrates Delaying carbohydrate intake for 2 hours after exercise reduces maximal glycogen repletion 24 hours postexercise Recommendations: 1.0-1.5g/kg carbohydrate every 2 hours for up to 6 hours postexercise 70 g person: 70-105 g every 2 hours Simple if time meal after exercise Not critical if resting next day and diet provides adequate carbohydrate Ivy JL et al. J Appl Physiol. 1988.
Postexercise Carbohydrates Sample 50 gram carbohydrate choices for the foundation of a meal or snack: -Wheaties, 2 cups -Nature Valley Granola Bar, 2 packets (4 bars) -Thomas Bagel, 1 (3.5 oz) -Banana, 2 medium -Orange juice, 16 ounces -Apple, 2 medium -Raisins, 1/2 cup -Pepperidge Farm multi-grain bread, 2.5 slices -Baked potato, 1 large (6.5 ounces) -Pasta, 1 cup cooked -Rice, 1 cup cooked -Fig Newtons, 5 -Flavored Yogurt + 3 graham cracker squares
Carbohydrate Quality? Low GI recovery diet seemed to increase fat utilization during 90 minute cycling bout at 70% VO2 max No sparing of glycogen Needs more research Stevenson EJ et al. Am J Physiol Endocrinol Metab. 2009.
Hydration Loss of 2% of body weight impairs performance Within 4 hours of exercise: 5-7 ml/kg 70 kg: ~12-16 ounces During exercise Sweat rates vary depend on person, weather conditions, and intensity of exercise 0.3-2.4 L/h Fluid intake should be adjusted accordingly
Fluid Recommendations Adjust based on conditions Plan Ahead! Longer than 60-90 minutes: sodium aids in fluid retention (sports drinks) Fluid balance is hard during exercise Sweat rates may be greater than gastric emptying 8% carbohydrate or less Postexercise: 16-24 oz for every pound of weight lost With food: sodium sources
Tips for Performance Test out diets around training Get used to drinking fluids with longer sessions Meal timing and types of foods before competition should be tested in training Plan! Not bringing enough food Delaying consumption prior to next workout
Protein Needs Generally met in the typical Western diet Exceptions may be vegetarians or athletes who severely restrict their intake Current RDA (0.8 g/kg) is most likely adequate for most noncompetitive athletes
Protein and Endurance Athletes Nitrogen balance studies estimate needs at 1.2-1.4 g/kg per day oxidation for fuel with exercise Main concern is adequate energy intake to ensure protein sparing Will ensure that other fuels are oxidized, sparing amino acids for protein synthesis Phillips SM et al. Int J Sports Nutr Exer Metab. 2007. Tipton KD and Witard OC. Clin Sports Med. 2007.
Protein and Resistance Exercise Extra protein and energy required for muscle growth Range from 1.2-1.7g/kg per day Once again, usually being met, especially in resistance training population Needs are highest with initiation of training, where most size gain occurs Trained individuals more efficient in protein use Phillips SM et al. Int J Sports Nutr Exer Metab. 2007.
Protein Quality Cuthbertson et al. and Phillips et al. ~8.5-10g of EAAs maximally stimulates protein synthesis Comes out to ~20-25 g of protein sources of high biological value ~40% EAAs ~20-25 oz milk, 3 ounces meat, fish or poultry, ~4 eggs Cuthbertson DK et al. FASEB J. 2005. Phillips SM et al. Int J Sports Nutr Exer Metab. 2007.
Protein Synthesis in Response to Exercise Phillips SM. Nutrition. 2004.
Muscle protein synthesis and breakdown Phillips SM. Nutrition. 2004.
Protein Intake for Strength Athletes ~1.33 g/kg per day for Nitrogen Balance Phillips SM. Nutrition. 2004.
Nitrogen Balance Adequate to assess prevention of deficiency, but not for maximizing gains with resistance exercise Positive balance necessary for extra amino acids for muscle growth Problems with measurement Higher than possible balances with excessive protein intake Calculation of loss is hard to estimate
Recommendations Based on Research for Strength Athletes Protein intake for strength athletes will most likely be appropriate when energy needs are met Adequate energy intake is most often the limiting factor and area that demands more attention for muscle strength gain
Protein Consumption Around a Workout Essential amino acids (EAA) stimulate muscle protein synthesis 6 g EAA shown to be just as effective as 40 g for muscle protein synthesis stimulation postexercise No effect from nonessential amino acids
Amino Acid Infusion Acutely stimulates muscle protein synthesis Starts to fall back to baseline ~2 hours after infusion Substrate needs for synthesis met Enzymes for amino acid oxidation are upregulated in response to greater circulating concentrations Bohe J et al. J Physiol. 2001.
Importance of carbohydrate Insulin suppresses protein breakdown After resistance training, carbohydrate alone can reduce muscle protein breakdown No effect on muscle protein synthesis Combination of protein and carbohydrate around exercise would be most beneficial Milk? Amino acids for synthesis, carbohydrate to stimulate insulin, thus inhibiting breakdown Borsheim E. et al. J Appl. Physiol. 2004.
Ubiquitin Pathway Major pathway for protein breakdown Insulin reduces Ubiquitin mRNA ATP dependent process by fasting
High Protein Intake Not shown to detrimentally affect kidney function Difficult to link high protein intake with negative health outcomes Of course it exacerbates existing kidney disease Does it affect performance? Yes if you are an endurance athlete or engage in repeated high intensity exercise ~8 g/kg Carbohydrate is considered optimal; tough to reach if overeating protein Phillips et al. Int J Sports Nutr Exerc Metab. 2007.