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Tuesday, January 11, 2011
Exercise Nutrient Interactions
Although many of us are aware that certain nutrients are essential for good performance and recovery from exercise it is often overlooked that by manipulating certain dietary components we can alter or even enhance adaptation to training. When we talk about 'nutrients' we are generally referring to the three macronutrients carbohydrate, fat and protein and more importantly how much we need of each to sustain a healthy body and promote adaptation. As endurance athletes we are mainly concerned with carbohydrate (CHO) and to a lesser extent fat (FAT) whereas anyone partaking in resistance training will preach all about protein and its benefits for muscle hypertrophy. In the past sports nutritionists have stressed the importance of a high CHO diet for athletes to be able to maintain high training intensities and also maximize performance. As many of us have experienced when our body becomes depleted of carbohydrate stores intensity suffers and performance declines. This can either be acutely at the end of a long training ride/run or race situation or after longer periods of a restricted CHO diet. As soon as muscle (and more importantly liver) glycogen stores are below optimal everything feels harder. So.... most of us pay attention to these nutrition guidelines and consume high CHO diets to maximize recovery but also eat bars/gels etc during prolonged exercise to avoid the dreaded 'Bonk' . Ok... Now for some science... If you've read my last post on training adaptation you will have noticed that the body adapts to physiological circumstances that cause cellular stress and sure enough running low on CHO stores is a major physiological stress!! There are a couple of studies that have very clearly shown that training with depleted muscle glycogen (glycogen is a stored form of glucose and glucose is a CHO) can actually magnify the training response. This has been termed as a 'train once daily vs train twice every second day' approach. In these studies subjects either trained once every day so that CHO stores could be replenished after each session (HIGH) or a second group trained twice every second day. This allows the group that trained twice every second day to perform the second exercise bout (usually ~2 hrs after the first) with reduced or low CHO stores (LOW). Both groups over a 3 wk period performed exactly then same amount of training but the LOW group performed 50% of training with reduced muscle glycogen. Amazingly after the 3 wk of training the LOW groups performance in a test of endurance and also several markers of skeletal muscle oxidative capacity were significantly improved compared to the HIGH group. So maybe we can now begin to recommend to athletes to undertake specific training sessions with reduced muscle glycogen and lay off those high CHO recovery meals.