Nutrition for Endurance Rides.

Let's review the physiology.

I. THE SOURCE OF MUSCLE ENERGY (what to eat)

Percent VO2max (%VO2max) is the easiest way to express measure your level of exertion. Both glucose and fats are utilized to produce ATP at moderate levels of exertion (50% VO2max) but as exertion increases this ratio shifts toward glucose. And at >100% VO2max only glycogen can be used in the muscle for energy (ATP) production.

What keeps the muscle cell from using fat for high level exercise? It is assumed to be from bottlenecks, or rate limiting steps, in the intracellular metabolism of fat into ATP. The maximum rate at which our cells can produce ATP from fat (to provide energy for exercise) is about one-third the rate of ATP formation from glucose. The net effect is that fat alone as an exercise energy source sets an upper limit for maximal performance at ~ 65% VO2max.

With training you can modify the ratio of fat ATP to glycogen ATP used at any specified endurance pace (and extend your riding time before you bonk) BUT you cannot increase the %VO2max that can be achieved from fat alone (about 65% VO2max).

For those interested, the science of fat metabolism is covered in more detail in this paper, and the relationship of glycogen to fat calories as VO2max increases is nicely summarized in this graph. You will notice that the total calories from fat metabolism - stored muscle triglycerides and free fatty acids (FFA) extracted from the blood - remains relatively constant as exercise measured by VO2max increases. And extra caloric needs are met almost entirely from muscle glycogen or blood glucose.

II. WHEN TO EAT (rule of 4's)

Four days prior to the ride. Maintain a diet with enough carbohydrate Calories to cover those used on your rides. You should be tapering your training, so 9 gm carbohydrate/kg BW/day (600 grams/day) should be more than adequate.

Four hours prior to the event. This will be topping off the tank, so to speak. Carbohydrate Calories will have been digested, absorbed, and to a great degree metabolized into glycogen stores before you get on the bike. How big a meal? A 300 gm (1000 Calorie) complex carbohydrate meal (rice, pancakes) will minimize rapid absorption with an insulin spike. A high Caloric density glucose polymer sports drink is another option.

Four minutes before the ride. You are just getting on the bike and want to have some Calories starting their way through the digestive system. But not enough to just sit in your stomach, You are not worried about simple sugars leading to an insulin spike. A candy bar works well.

During the ride. The focus should be on regular carbohydrate replacement starting immediately as you begin the ride. Aim for 60 gram of carbohydrate per hour, liquid preferred (i.e. sports drink), 10% concentration optimal (equivalent to a cola drink), with a drink every 10 - 15 minutes to minimize fullness.

Four hours post ride. Take advantage of this interval for restocking of muscle glycogen. Start immediately, high carbohydrate, for 3 to 4 hours.

III. TRAINING INCREASES STORED GLYCOGEN

Less appreciated is that training also increases total body glycogen stores. These 2 training benefits then work together to improve your endurance riding. More "fuel" (glycogen) as well as a more efficient use of those precious carbohydrate calories.

Glycogen facts:

• Your body has limited glycogen stores but an almost unlimited amount of fat. Glycogen limits the duration of high %VO2max activity.
• 20% of our glycogen is stored in the liver and 80% in the muscles - where it is readily accessible by the exercising muscle.
• Endurance training increases the amount of stored glycogen. The data:
  • Subjects were compared to themselves. Muscle glycogen content was analyzed both before and then after 10 weeks of endurance training.
  • Post ride, all study participants maintained a high carbohydrate diet (10 g CHO/kg body wt/day) with a diet composition of 80% CHO, 7% fat, and 13% protein.
  • After endurance training, the participants could restore their depleted glycogen at a rate twice that of pre-training.
  • After training, total glycogen stores at 48 hours maxed out, on average, at 170 mmol/kg muscle compared to 95 mmol/kg pre training.
  The increased glycogen storage effect from training is in about the same as that seen with a more traditional glycogen depletion-glycogen loading regimen (carbo loading).

  It appears that the upper limits of human carbohydrate storage are in the range or 15 kg glycogen per kg body weight or approximately 1000 grams. This is almost twice the average 500 grams in those not training, and at 4 calories per gram equate to almost 5000 potential calories.

IV. CAN YOU OVERDO REPLACING GLYCOGEN STORES?

Let's review a few facts on dietary carbohydrates.

• The old teaching was "fat is bad and carbohydrates are good" to cut the risk of heart disease. We now know that high carbohydrate diets can actually increase the risks for obesity, high blood pressure, heart disease, and even cancer.
• All dietary carbohydrates are built up from single sugar molecules. Simple carbohydrates (table sugar for example) is composed of just two single sugar molecules (one glucose and one fructose). Complex carbohydrates are made from longer chains of multiple sugar molecules.
• To be absorbed (from the small intestine), all carbohydrates must first be broken down (digested) into single sugar molecules. Some complex carbohydrates are easily digested (wheat flour for instance) while others are not (fruit and vegetable fiber). A food's glycemic index measures the ease of digestion and absorption.
• Simple sugars (glucose, table sugar) are easily absorbed into the bloodstream and are often absorbed faster than they can be used in normal metabolism. This excess is shunted into fat (triglycerides) production to be stored for future needs. It is this sugar to fat conversion that is the likely culprit in the health risks of high carbohydrate diets.
• Complex carbohydrates or starches are more slowly broken down by digestive enzymes and in turn are more slowly absorbed. The rate of rise of the blood sugar after eating starches is less (their glycemic index is lower) and is spread over a longer period of time. The post eating blood sugar spike is less severe, less insulin is released, sugar calories are absorbed over a longer period of time, and the body now has more time to use them to fuel normal metabolism instead of fat production.

Your goal should be to eat just enough extra carbs (beyond your normal diet) to replace the Calories expended that day on the bike. How many Calories do you expend on a ride? There are a number of formulas floating around the internet. (Here is one on CPTIPS).

• 5 mph = 7 Cal/mile or 37 Cal/hr
• 10 mph = 13 Cal/mile or 133 Cal/hr
• 15 mph = 23 Cal/mile or 349 Cal/hr
• 20 mph = 37 Cal/mile or 742 Cal/hr

If 1 gram of carbohydrates yields 4 calories of energy, and we trim that 30 calories per mile to 28, a reasonable upper limit for replacement is 7 grams of carbohydrate per mile ridden. So log your mileage, multiply by 7, and you have a ballpark figure as a goal for your day's carbohydrate replacement after a ride - remember to subtract calories from snacking and gels taken while riding.

An easy way to check if you are in replacement balance is to weigh yourself every morning. Assuming you have been staying hydrated, a stable weight will show you are on track.

Is there a better time to replace those carbs? The rate of replacement of glycogen stores is highest in the hour or two after exercising, so an immediate post exercise soda or high starch snack makes sense, and try to plan your big meal of the day in those few hours after riding.

V. HOW ABOUT CARBOHYDRATE LOADING?

It was estimated that the full 3 day program of carbohydrate loading might increase the time to exhaustion (without the use of oral supplements while exercising) by 20%.

But the glycogen depletion phase was onerous and led to the next iteration, carboloading 2.0 with an elimination of the depletion phase while retaining the high carbohydrate diet. This modification was estimated to provide 90% of the benefits of the full depletion-repletion program while avoiding the digestive turmoil that carbohydrate depletion can produce.

Now we have evidence that suggests an adequate carbohydrate diet while endurance training maximizes glycogen reserves with the storage effect in the same range (1000 grams) as that obtained by a more traditional glycogen depletion-glycogen loading regimen. Add in the fact that any excess dietary carbohydrates (beyond those stored in the muscles and liver) are converted directly into fat, and carbo loading loses its appeal. There are no clear advantages versus the hassle of changing your diet before an event.

Thus we arrive at the strategy currently in favor - maintaining the high carbohydrate training diet, maximizing glycogen stores by cutting back training workloads for the three days before an endurance ride or event, and supplementing stored glycogen with oral carbohydrate replacement while exercising to extend the time to depletion.

And for shorter periods of exercise, remember that there is enough glycogen stored in the muscles to support 2 hours of vigorous cycling (which I'll define as cycling at greater than 70 to 80 % VO2max) without supplements.

VI. USE GLYCOGEN SPARING SNACKS, DRINKS, AND GELS WHILE RIDING.

If you will be on the bike for more than 2 hours, you should use oral carbohydrates to extend your glycogen stores. A reasonable target for these energy drink/energy bar supplements is 1 gm CHO per kg body weight per hour (in the range of 60 grams of carbohydrate or 200 to 300 Calories per hour).

As a rule of thumb, the higher the level of intensity of the ride (closer to your VO2max), the more simple (single sugar) carbohydrates you should use. On longer rides and at lower levels of exertion, snacks with complex carbohydrates and a higher fat content can be added as alternatives.

You should start your oral supplements as you start the ride - don't wait until you are beginning to bonk (thinking about food is a great clue) - and then take some Calories every 15 - 20 minutes.

Here are some on the bike snack ideas.

VII. CONTINUOUS GLUCOSE MONITORING - CAN IT HELP PLAN ON-THE-BIKE REPLACEMENT?

For diabetics, who have a much less resilient glucose metabolism, it is essential to monitor blood glucose levels to avoid life threatening low levels (hypoglycemia). Up until 2021, the only option was finger sticks. Now the technology of continuous glucose monitoring is ride changing for them.

For the ultra endurance athlete, continuous monitoring also has a role. This paper reveals how varied the metabolism in 2 highly trained athletes can be. Now there is a sure fired way to avoid poor performance from low blood sugars.

But for most of us, the rule of thumb approach to estimating replacement needs and then maintaining regular oral supplements is more than enough. If you guess wrong on the low side, you bonk and change your nutrition for the next outing. If you err on the high side having overestimated your needs, there is little if any harm done as long as you are exercising. So continuous monitoring becomes just a high tech reminder (like an alarm on your digital watch) to keep you on your scheduled replacement gels and drinks.

Like all tech, we tend to assume infallibility. The following two anecdotes suggest that performance is not just about blood glucose levels suggesting that if you are start chasing the numbers you may be fooling yourself. This is akin to training with heart rate monitors rather than perceived exertion where a mindless focus on the numbers actually has more risks than just listening to your body.

1. "Supersapiens gives you a Glucose Score from 1 to 100 for every workout. When the number is higher, it means you were able to maintain and control your glucose levels during exercise. When it is low, you may need to re-evaluate your fueling strategy to make sure that glucose availability isn't impeding your ability to perform. But again, it is not a strict measure of energy. You can have a low score and feel great or a high score and perform poorly. There are many factors that affect performance."

2. "the levels aren't always perfectly in sync with what you're feeling. Sometimes I'd feel draggy toward the end of a ride and see my glucose falling in real time. Other times, the sensations in my legs—heavy or light—didn't match the glucose readings, again, because there's more to performance than blood sugar."

Bottom line? A sound nutrition plan based on the science of exercise physiology and nutrition will be just as effective as a glucose monitor for the vast majority of riders. Get in touch with the signals from your body, there are no short cuts.

SUMMARY POINTS

• Glucose is the preferred energy source for moderate level, endurance activity.
• Glucose is the only energy source for activities at and above 100% VO2max
• If you want to preserve internal glycogen stores (limited) for an endurance ride by maximizing the use of fat reserve calories (large) you can either
  • ride slower OR
  • supplement glycogen stores with snacks while riding.
• Use the rule of 4's to time your carbohydrate intake for an endurance ride.
• Training increases the potential to store muscle glycogen, the preferred energy source for high level aerobic activity.
  • You can maximize this potential by eating a diet high in carbohydrate calories while training.
• The endurance training benefits (riding longer at a given level of exertion or %VO2max) are derived from the combination of decreasing the ratio of carbohydrates versus fat calories used to support muscle contraction as well as increasing available total carbohydrate calories (glycogen).
• It takes 7 grams of carbohydrates per mile ridden to replenish glycogen stores.
• Dietary carbohydrates should be complex while simple sugars are best for a boost while riding.
• Take advantage of the 1 or 2 hours post ride to maximize the rate of glycogen replenishment.
• If you are eating a carbohydrate replacement diet while training, carbohydrate loading is not necessary.
• For planned rides of more than 2 hours you will need carbohydrate supplements. Start at the time you start the ride, and eat something every 15 minutes.