By Michelle Hanson MS, RD, LD

Addressing the nutrition needs of an athlete is actually quite a complicated topic. There is no one general formula that will work or that can be applied across all disciplines of sport. Developing a specific nutrition strategy for an individual takes months of trial and error to determine what strategy and specific nutrients work best. Timing of intake, type of energy consumed, and amount of energy consumed are all factors that can affect the nutrition needs of an athlete. More variation in nutrition needs comes from the different energy systems that are utilized in the body to allow one to participate in a certain event. For example: an athlete running the 400 meter race will rely on mainly his/her phosphocreatine system (PCr) to generate the energy needed. This is because the race is a short duration, high intensity effort that is most efficiently fueled by ATP from stored by phosphocreatine. On the flip side a marathon runner will rely mainly on his/her aerobic metabolism to generate the energy needed. This system utilizes oxygen (aerobic) to breakdown carbohydrate and fat for energy needs.

In the sport of triathlon, fueling properly can be quite a daunting task especially as one takes on the longer distance triathlons like half and full Ironman races. It is a complicated sport to develop a nutrition plan for because not only does the sport have a wide variety of distances that athletes take on, but it also has three different sports rolled into one “multi-sport.”

During triathlon our bodies mainly utilize carbohydrates for an immediate energy supply. Our body can utilize carbohydrates in two forms: the form circulating in our blood known as glucose and the form that is stored in our muscles and liver known as glycogen. Liver cells can store about 8% of its weight in glycogen and stores about 87-100 grams of carbohydrate (348-400 calories) and muscle cells can store about 3% of its weight in glycogen and 350 grams of carbohydrate (1,400 calories). The liver is responsible for stabilizing blood glucose levels when they drop within the body. It detects when glucose levels fall and it begins a process known as glycogenolysis, or the breakdown of glycogen. This process breaks down stored glycogen into usable glucose or “energy” for the body or in our case the triathlete. The glycogen stored in muscles is mainly used to provide energy to working muscles. The body relies mainly on circulating blood glucose for energy in triathlon, so when liver glycogen is depleted it therefore becomes crucial for the triathlete to consume exogenous forms of carbohydrate or nutrition.

For shorter distance triathlon, the athlete can rely on exogenous carbohydrates or carbohydrates that are ingested. For example: the body may get all that it needs from a pre-race meal during a shorter triathlon race. Typically, glycogen stores are enough to maintain athletic performance for about 90 minutes. But for longer races, such as a 70.3 or 140.6 the body relies on both exogenous and endogenous carbohydrate sources. Endogenous carbohydrate is the energy stored as glycogen. It is common knowledge that during longer distance triathlons that consumption of nutrition is critical not only for optimum performance, but also for completion of the distance itself. As a dietitian, I have frequently been asked the question: “do I need to consume any nutrition before, during or after the swim portion of my triathlon?” This is a question that many triathletes have pondered. Well, the answer depends on many factors. To determine an answer, one must first examine glycogen stores and depletion of them during the swim since we have already established that they are critical during longer distance triathlon.

There has been research to show that the more trained (or fit) the athlete is, the more efficient they are at utilizing their glycogen stores, thus the more time it takes for them to deplete their stores. Even more of a reason to go into a triathlon well-trained and adapted. Another critical factor affecting glycogen usage in the swim portion of a triathlon is the pre-race nutrition protocol. It is crucial for the triathlete to properly “fill-up” their stores. To do this he/she should consume about 7-13 grams of carbohydrate per gram of body weight for 2-3 days prior to the event. When the muscular glycogen stores are full the carbohydrate stored within can sustain the athlete for about 90 minutes. Usually after this time period the athlete will experience a drop in levels and will need to consume exogenous sources of energy. During lower intensity exercise (like a 70.3 or 140.6) the body utilizes more fat as an energy source. The percentage of fat usage goes up as the intensity of the exercise decreases. Thus making the percentage of carbohydrate vs. fat used during the swim portion very individual, depending on how much effort one is putting forward to complete the swim leg of the race. The more fit the individual, the less carbohydrate that needs to be expended to complete the swim portion of the race.

Another factor that can affect energy usage and performance during the swim portion of a triathlon is thermoregulation. Thermoregulation is defined as the body’s ability to maintain its internal body temperature despite external temperatures and/or other various factors. Maintaining an appropriate body temperature requires energy, thus burning additional calories. When applying this to triathlon of course race day conditions play a huge role in how much energy the body has to expend to regulate its core temperature. Temperature of the water and the air can affect how much energy is lost through thermoregulation. In colder conditions the body’s natural response is to: stop producing sweat, “goose bumps” appear which helps retain heat, capillaries under the skins surface shrink (reducing blood flow), and shivering may begin which increases heat production. In warmer conditions the body’s natural response is to get rid of heat: sweat is secreted, hair follicles relax to release heat, and blood flow increases in the capillary network. In either extreme extra energy is necessary to allow the body to adapt and regulate its core temperature in the environment. If a triathlete is racing in either of these conditions he/she must take the extra energy expenditure into consideration. This may come in either the pre-race meal or the post-swim to bike transition.

Nutrition guidelines surrounding the swim portion of a triathlon are dependent on many factors. In order to maximize performance during the swim one must take into account all of these various factors. The best way to determine your nutrition needs during the swim portion is to evaluate your individual needs, consider the distance of your race, and know what race day conditions will hold. Experimentation with your nutrition plan should never happen on race day. Practice during longer brick workouts to see if additional nutrition is necessary before, during, or after the swim to maximize your performance.

Michelle Hanson is a Registered Dietitian and former scholarship swimmer at LSU. She has competed in triathlon up to the Ironman distance. Michelle is a private swim coach for The Sport Factory.