In Season Performance is Built in Off-Season Work

In Season Performance is Built in Off-Season Work, Part II Endurance Training

By Julie Young

In Part I of this series, we discussed the benefits of incorporating a well-developed strength program in to the transition season, a.k.a. “off-season,” to reach a higher peak performance, in season. In a year-round training program, we divide the year into phases, based on the individual’s athletic goals. To use a summer endurance athlete as an example, we consider fall, transition season. I think it is important for the athlete to understand that in-season performance is actually built and developed with investment in off-season work (and play). The image of the pyramid still applies, and the year-round phases help ensure that the foundation blocks of the pyramid’s base are in place, to support higher, in-season, peak performance.

Transition phase is characterized by general conditioning with focus on endurance base and strength training. Each consecutive phase becomes more specific to train the specific demands of the individual athlete’s specific goal event. It is valuable to understand that every phase has specific metabolic and physiologic objectives. We “stress,” with training, specific systems in order that they adapt and as a result become more resilient, efficient and durable. Each workout within the specific phase targets a specific physiologic and/or metabolic response. As an athlete, understanding the “why” of the workout fuels intention and motivation in the workout.

The key objective of transition season is to nurture mental and physical regeneration, and balance-out the training stress to rest account. While we diligently take dedicated rest days and more focused rest-recovery weeks at the end of a three- to four-week block, we still accrue more stress than recovery and rest over the competitive season.

During transition season capitalize on variety and take license with your endurance activities to mentally and physically mix it up. Be creative and use other modes of endurance base building to challenge your mind and body to move in different ways. Anything and everything goes, from hiking and backpacking to cross-country and back-country skiing. Treat your body to a variety of movement patterns. This hall-pass from a singular-sport focus will help you emerge from the “off-season” refreshed mentally and physically, and hungry to dig deeper when it counts.

As we mentioned in the last article, as the endurance base-building becomes more free-flowing this time of year, the focus, structure and purpose is placed on a well phased, endurance-specific strength program.

While some people seem to think, “If it does not hurt, then there is no benefit,” the less-stressful endurance work is actually the secret weapon to improved recovery, durability and higher in-season peak performance. Below are a few key points to the “why” of endurance training. Hopefully this brief explanation will help cure the temptation to chase Strava segments on endurance days.

Fuel Sources

First it is valuable to understand that each intensity level from a 10 sec sprint to a four-hour endurance ride or run, is fueled by a different fuel source. Adenosine triphosphate (ATP) is considered the energy currency of the cells. It is the primary molecule responsible for storing and transferring energy to the cells.

ATP is generated through either anaerobic or aerobic metabolism. Carbohydrates and fats are the two main substrates used to generate ATP production. While fats are mainly stored in adipose tissue and to a lesser extent in skeletal muscles, carbohydrates are stored in the form of glycogen, primarily in the skeletal muscles and to a lesser extent in the liver.

The exercise intensity and muscle recruitment required will determine which fuel substrate is used and energy system activated.

The majority of ATP is generated aerobically (approx. 55-75% of Vo2max, depending on individual fitness) utilizing primarily fats and to a lesser extent carbohydrates. Over the spectrum of increasing intensity, the ratio of fat to carbohydrate utilization adjusts with carbohydrates supplying a greater percentage of the fuel requirement at higher intensities. While fats are an abundant fuel source, the conversion to ATP is a slow, multi-step process. Carbohydrates and glycogen are limited resources, but quickly converted to ATP.

Muscle Fiber Types

We have two types of muscle fibers, Type I, a.k.a. slow twitch and Type II, a.k.a. fast twitch. Type II muscle fibers are further divided in to Type IIa and Type IIb. In an activity these muscle fibers are recruited on an as needed basis, in a sequential recruitment pattern. When the activity begins and is primarily slower and aerobic based, the Type I muscle fibers, rich in the ATP producing mitochondria, and efficient at utilizing fats for fuels, are recruited. As the intensity increases, Type IIa fibers, with less mitochondrial density, but a high aptitude for utilizing glucose kick in. And as intensity hits its peak, for example, in the final sprint, Type IIb fibers, with low mitochondrial density but high capacity to tap glucose, are recruited.

Why Endurance Training?

Endurance training develops mitochondrial and capillary density, as well as metabolic efficiency (using the right fuel for the right intensity), which support peak performance. Mitochondria are considered the powerhouse of the cell, they turn nutrients in to energy, i.e. ATP. Capillaries are key for delivering oxygen and nutrients to the cells and transporting waste products away. Metabolic efficiency is reliant both on training and nutrition (the topic of our next newsletter article). To become more efficient at metabolizing fats, we phase endurance training with the right nutritional choices. Metabolic efficiency improves our ability to use fats for fuels and preserves limited glycogen stores.

Endurance training also improves the body’s ability to clear lactate. Lactate is the by-product of cellular respiration when, in the lack of sufficient oxygen, glucose is used as fuel. Type I muscle fibers contain transporters to remove the lactate as well as transporters to help recycle lactate in to energy.

Improved metabolic efficiency as well as lactate clearance, shift the training zones to the “right.” This means running and riding faster, with improved efficiency and less “stress.”

Make the investment in the off-season to build a sturdy base on your pyramid, this will pay mental- and physical- dividends, in-season. Take advantage of variety and seize every opportunity to make your endurance days an adventure.

Stay tuned for Part III Improving Metabolic Efficiency