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by Dr. Stacy Sims
August 17, 2015
WOMEN'S CYCLING BROUGHT TO YOU BY ORBEA
We consider it a major coup to have landed Dr. Stacy T. Sims, MSc, PhD, as a monthly columnist for Ella CyclingTips. Sims has contributed to the environmental exercise physiology and sports nutrition field for more than 15 years as both an athlete and a scientist. The chief research officer/co-founder of Osmo Hydration, Dr. Sims served an exercise physiologist and nutrition scientist in the human performance lab at Stanford University from 2007-2012 where she specialised in sex differences of environmental and nutritional considerations for recovery and performance. Her personal interest in sex differences and performance has been the precedence of her academic and consulting career, always looking at true physiology to apply innovative solutions in the sport nutrition world.
Not only an elite athlete herself, Dr. Sims has extensive experience working with athletes at all levels: from beginning recreational athletes to the Olympians and Tour de France-caliber cyclists. In 2012 she left her full time academic position at Stanfard to become a mum, launch a start up (Osmo Hydration ) and start her own consultancy practice – all to disseminate science into real world applications for athletes, coaches, educators, and colleagues.
Future topics from Dr. Sims will cover: the menstrual cycle and menstrual dysfunction, what menopause and perimenopause means to the female athlete, why popular diets often don’t work for women, how hormones affect hydration recommendations and why GI distress is more common in women than men. If there’s other topics of interest you’d like to see Dr. Sims tackle, feel free to let us know in the comments section
I’ll let you in on a little secret. My career is based upon one question: “Why?”. As a female athlete, I was always given training, nutrition and recovery information based on science, but that science was always from a population of 18-20 year old college-aged males. Until the 1980’s, it was widely assumed that the physiological responses to exercise did not truly differ between men and women. This explains why all the training, nutrition, recovery schedules I’ve seen, and for the most part still exist, are recommendations that have been generalised to women – without really questioning if this direct transfer was viable.
So as an athlete, I began to ask “Why?” in response to what I was observing and experiencing. Why did women have less heat tolerance when they were just about to have their period? Why did my female crew teammates recover less quickly than the guys after a heavy intense workout? Why does it seem harder for women to “lean up” when following the same advice as their age- and fitness-matched male counterparts? These are just some general questions, but throughout my career I have always asked: Why is this different for me and my athletic female friends and clients?
There are many angles to address here, but I want to specifically focus on the physiology and nutritional aspects of recovery. Regardless of gender, if you don’t recover, you won’t achieve your performance potential. In this vein, I want to give as much correct information to all you women (and the male coaches!) so you can start recovering properly.
First, let’s look at the differences of fuel utilisation during exercise, which may help explain why women need a bit less carbohydrate per hour than men. This allows us to create specific recovery nutrition guidelines for women.
Estrogen decreases the reliance on liver glycogen, increases the use of fat and decreases amino acid breakdown during exercise. These fuel responses have been attributed to a sex difference between catecholamine responses during exercise. Men release a larger amount of catecholamines at a given moderate-high intensity exercise load than women who have similar training status. This glycogen sparing, increased fat use is even greater during the high hormone phase (luteal phase) of the menstrual cycle when estrogen is at its highest concentrations.
How does this translate to every day practical use? Women have a greater capacity for burning fat and sparing glycogen (both in the liver and the muscle) in the high hormone phase. To maintain the capacity to hit intensities, women should look to stay on top of carbohydrate intake during exercise (e.g using glucose tablets before each high intensity interval), but during the low hormone phase, women can afford to ingest less exogenous carbohydrate than her age and fitness matched male counterpart (think: 45-55 grams per hour as opposed to the 65-80 grams per hour).
So does this mean women need to eat more fat? Actually, no. As long as a women’s current intake is approximately 30 percent of her daily caloric intake, adding fat is not necessary. When fat intake is 10-20 percent upping intake of “good” fats will ensure rapid restoration of fuel to muscles.
Researchers have looked at the recovery phase in men and women. Although women metabolise and use more fatty acids during prolonged exercise and have greater fat stores than men, women have a greater ability to maintain energy substrate stores during exercise and during recovery. Three hours post-exercise, men still have higher rates of blood glucose fluctuations and lower glycogen stores, whereas women are relatively close to the pre-exercise state (side note- this also contributes to the harder-to-get-lean factor many women face as they have less of a window of elevated metabolic state and fatty acid use at rest; this is something I’ll discuss in detail in a future column).
It is well known that carbohydrate is the predominant energy used for continuous endurance events with fat oxidation playing an increasingly important role over two hours; however amino acids (from circulation and muscle protein breakdown) can provide up to 10 percent of total energy during endurance exercise. The use of amino acids can be increased during higher intensity, longer duration exercise, but also if there is low glycogen availability and/or a habitually high-protein dietary strategy.
Women oxidise less protein and leucine than men even though there is no sex difference in the muscle enzyme that controls the intramuscular use of branch-chained amino acids. Although endurance exercise does lower the activity of the enzyme responsible for amino acid use, female endurance athletes run the risk of being in a negative leucine balance. During the high hormone phase of the menstrual cycle, progesterone (or a lower estrogen to progesterone ratio) increases the use of protein during exercise. This phase difference is important to note for recovery. Amino acids are key to immune function as well as muscle adaptations to stress.
In men, mixed muscle and myofibrillar protein synthesis rates are enhanced post-exercise with a small ingestion of protein of around 10 grams of protein, but further enhanced after the ingestion of approximately 20 grams protein. Greater quantities (up to 40 grams), do not increase synthesis rates, but increase amino acid oxidation and urea production.
In women, estrogen inhibits muscle protein synthesis, progesterone enhances muscle breakdown and a sex difference (of hepatic origin) exists in amino acid oxidation. With these additional factors, research findings indicate muscle protein synthesis is enhanced in women post-exercise with the ingestion of approximately 30 grams of protein. The leucine content is the contender here. Muscle protein synthesis is reliant on tissue-leucine concentration, and the effects of estrogen on protein synthesis inhibit the oxidation of leucine within the muscle.
Dietary proteins differ in their amino acid composition as well as rates of digestion and absorption – all which have measureable effects on post-exercise muscle protein synthesis and whole body protein synthesis. The Essential Amino Acid (EAA) content of the protein, in particular the leucine content, can dramatically affect muscle protein synthesis. For example, compared with casein and soy sources of protein, whey protein has distinct anabolic characteristics (and anti-inflammatory properties) which result in a greater synthesis of muscle protein both at rest and after exercise. When the overnight fast is taken into consideration, casein provided before sleep is absorbed more rapidly than casein provided during the day, increasing rates of muscle protein synthesis by approximately 22 percent as compared to a placebo and 10 percent as compared to whey.
Plasma volume is the watery component of blood that reduces the thickness of the blood and allows blood to flow quickly to working tissues. When we begin to sweat, it is the plasma volume that is lost first because this is the fluid that helps make up the sweat. We sweat to remove heat.
As women, we have an elevation of our resting core temperature in the luteal phase of the natural menstrual cycle and in the last 15 days of oral contraceptive pill (OCP) due to elevated progesterone concentrations. The increased progesterone stimulates the phrenic nerve, increasing respiration, and it also acts to increase sweat production later than in the low hormone times of the menstrual cycle. So, with elevated progesterone, there is a natural re-setting of the baseline body temperature by as much as 0.3 -0.5 °Celsius. Coupled with an increased time to sweat during the luteal (high hormone) phase, it can be seen that athletic performance is compromised in the luteal phase due to higher body temperature and less ability to get rid of the heat.
What’s more is that high estrogen and progesterone act on the kidney’s hormones to reduce plasma volume, a drop of up to eight percent from ovulation to the mid-luteal phase, and this fluid goes between the cells. This causes the bloating often associated with PMS. In general, during the luteal phase and the high hormone phase of the menstrual cycle, women are less able to cope with the heat and have a reduced ability to sweat to remove the heat from deep inside the body.
Before training: in the 90 minutes leading up to your training session, you need to drink as much as comfortable (~500 millilitres) of low-carbohydrate fluid and/or eat watery fruit and vegetables (salted tomatoes or salted watermelon). This is also good time to use a sodium-based fluid load drink (look for a sodium citrate + sodium bicarbonate mix rather than sodium chloride) to maximise body fluid and sodium stores.
During training: Similar to baseline needs, what you drink during your ride depends on several factors including temperature, environment, time of day, intensity of training, sex differences. It is important to go into a race or training situation hydrated. Remember it is much easier to come back from a low sugar ‘bonk’ (a few minutes after a bit of food) than it is to come back from dehydration (several hours for the kidneys and hormones to kick in for fluid balance)! Your fluid intake during training should allow you to maintain power towards the end of your ride. I recommend drinking a “functional hydration” (three-four percent carbohydrate beverage/three-four grams carbohydrate per 100ml) and basing your initial fluid needs on drinking to thirst.
Keep in mind here, drinking to thirst is not THE answer, you must start your session hydrated, then use thirst as a guide for the first three or four hours. Don’t become too thirsty (not drinking then all of a sudden needing to gulp copious fluid; instead sip sip, nibble nibble). If you are concerned that drinking to thirst is not optimal for you, the most recent scientific consortium guidelines recommend not exceeding 800ml/hour in temperate conditions and not to exceed 900ml/hour for hotter and/or more intense rides. Remember this is based on generalised guidelines. The best way to tap into what you specially need is to objectively measure your hydration status using pee sticks.
After Training: After you exercise, as a general rule, you need to slowly rehydrate over the course of 2-3 hours. Don’t gulp fluid. This is counterproductive for rehydration. Instead consume a combination of an protein-based drink (the amino acids help with rehydration) and watery foods for optimal rehydration and recovery
There are several key points presented here that you can take aboard and apply to your training, racing and recovery.
1. Women have greater fat stores and access fat to a greater degree during exercise, sparing liver glycogen, but during the high hormone phase of the menstrual cycle, this carbohydrate sparing mechanism can work against intensity and performance. In this phase, have extra quick hits of sugar in the form of glucose tablets, jelly beans or energy chews to maximise your interval sessions, racing and other high intensity events.
2. Women don’t oxidise as many branch-chained amino acids during exercise as men, but in the high hormone phase of the menstrual cycle, there is a greater reliance on protein during exercise (and at rest). Ideally, post exercise ingestion should comprise around 20-30 grams of high-quality protein within 30 minutes of exercise. Any delay compromises tissue leucine concentration, and enhances muscle tissue breakdown. Equally important is consuming subsequent doses of approximately 20 grams of protein across the day. Meal content should be around 0.25g/kg with one last dose of protein before bed. This strategy will support muscle adaptation, body fat loss (with negative energy balance) and lean mass preservation.
3. The post-exercise recovery phase: three hours post-exercise, a woman’s metabolism is pretty close to pre-exercise/baseline levels, so the two-hour recovery window after the first of a 2x day exercise session needs to be carefully planned in order to restore the muscles’ fuel stores
4. The quick return to baseline metabolism also contributes to the reduced ability to “lean up” in women. Again, women need to take advantage of the two-hour window to promote body composition change and glycogen/fat store recovery.