Perhaps in your own experience, you've found that a negative-split performance helped you achieve a faster average time in swimming, cycling or running than did a bust-your-gut from the get-go strategy. Why does it work this way?
Illustrated by Lucy and Ethel
Those of you that watch old "I Love Lucy" reruns on cable or perhaps were around in at a time to watch when it was a new show might remember a story of Lucy and Ethel working in a chocolate factory. Lucy and Ethel did a fine job of boxing chocolates when the production line was at a manageable speed.
As the production line increased to speeds beyond what Lucy and Ethel were able to manage, Lucy tried to manage the abundance of chocolates by stuffing them into her mouth and everywhere else. This strategy worked for only a short time before chocolates ended up strewn around the room. The pace was too fast and the whole place ended up in a mess.
Our bodies work similar to Lucy's production line in that we can maintain a given pace for a certain length of time, whether the speed is anaerobic or aerobic. Pace, or speed, and heart rate are non-invasive tools to estimate when our bodies are producing greater amounts of energy anaerobically and when energy is produced primarily by aerobic means.
Metabolic acidosis
Anaerobic efforts, or very high speeds, are maintained for short periods of time for several reasons; including the main source of fuel for this type of effort is carbohydrate instead of oxygen, fat and carbohydrate (aerobic effort.) In our case when the speed of the production line (our pace), becomes excessive, lactic acid, a byproduct of anaerobic metabolism, begins to build up in the tissues. This is called metabolic acidosis.
The problem with metabolic acidosis is that it inhibits optimal enzyme functioning. The enzymes involved in fuel breakdown operate best within a very narrow range of acidity. So, excessive acidity actually inhibits the enzyme reactions necessary for fuel metabolism. Speedy and efficient fuel delivery to working cells is obviously necessary for optimal performance. If your system cannot access fuel, it's forced to slow down.
A second problem with excessive acid is it destabilizes cell membranes allowing critical enzymes to leak into the blood stream or into the interstitial fluid (the fluid between the cells.) The cell walls are literally damaged and again you are forced to slow down.
A third problem that occurs with an acidic cell is excessive ions or electrolytes within the cell create a water balance problem. Too many electrolytes within the cell, compared to surrounding blood and extracellular fluid, cause the cell to take on water (swelling) in an attempt to restore the fluid/electrolyte balance.
In addition to the cellular issues created by a searing pace, other factors contribute. These issues also lead to a forced decrease in pace. Some of the factors listed are more of an issue with longer races, however the factors include:
- Energy depletion
- Increased viscosity of connective tissues and muscles -- possibly created by dehydration and/or cellular swelling
- Although this is still being studied, theories include that problems are created due to a reduction in neurotransmitter chemicals that link nerve cells with muscle cells. This may be due to the association between the metabolic processes and the associated neurological processes. So, energy transfer and neurological coordination are not as precise.
Summary
In summary, if the production of acid builds to excessive levels creating metabolic acidosis, there's damage to the cell walls, fuel delivery to the cells is suboptimal and the cells take on water to bring balance back to the system. In addition to acidosis, there can be neuromuscular affects and perhaps dehydration and viscosity issues.
A negative-split strategy utilizing heart rate and pace as tools for time-trial-type events, such as non-drafting triathlon, helps us manage the production and elimination of acid within our cells. Like Lucy, we want the fastest pace that allows us to go the distance without having to slow down, or stop, due to a system overload.
Because triathlon involves three sports, overall race intensity must be considered in addition to the intensity within each sport. You can negative-slit each sport within the race and in the best case, finish the entire event stronger and faster than you began.