Energy Zones in Swimming
Genadijus Sokolovas, Ph.D., Director of Physiology, USA Swimming
Energy Categories have been around for many decades and the current system adopted
by USA Swimming has been in use for almost 15 years. During that period we’ve gone
from a handful of coaches using the system to an increased number of our coaches using
the system. Although this is a positive trend, last year we conducted a poll among
coaches to gauge the level of use and interest in this area. The result was a mixed bag.
Although it showed that a large percentage of coaches used some form of energy
categories, not all coaches used the USA system. When Dr. Sokolovas joined USA
Swimming he was very used to using the European version, (Zone 1 to V) and this in
itself has inundated many coaches with another system or way of designing or
evaluating/gauging swimmer workloads.
Granted all systems do essentially the same thing, the basic difference is the number of
individual categories recognized within the energy continuum. Although we approach
these in a way that makes them look like individual zones or areas, we should all
remember that there are no solid boundaries between categories and everything is very
grey versus being black and white.
With this in mind we came up with a new version/interpretation that encompasses many
elements that are intrinsic to a combination of the old version and the current European
system. It can be seen as something that is simple with few categories (4), or something
more complex with the same number of categories as recognized in the current system
(7). We have structured it in a way that evolves 7 categories out of the simpler 4, and
allows coaches who prefer a simple approach to still compare and communicate with
coaches who prefer 7. It also gives introductory coaches an easier starting point, and
allows them to increase the number of categories when they are comfortable within the
basic system.
It is our hope that all coaches in this country will adopt this system as the only system
they use, (7 or 4) and as we migrate towards Internet based tracking and training
volume systems, having a universally recognized system in place will streamline the
process of data gathering. This will eventually lead to the utilization of this source of
knowledge as a foundation for future athlete development. The charts iincluded later in
this article to explain the modifications make it easier for coaches to share a common
language.
Why Are Energy Zones Important For Swimmers?
The importance of energy zones in swimming is based on the existence of several
different pathways to recycle energy in the muscle cells during exercise. The main
pathways of energy recycling are non-aerobic metabolism (creatine phosphate),
anaerobic metabolism (anaerobic glycolysis), and aerobic metabolism. Metabolism is the
process of storing and releasing the energy. Energy for the body is stored in different
forms and pathways are used to convert these forms into accessible energy that an
athlete can use to perform work. There are no "borders" to energy pathways in a body.
At any given time, several pathways, not just one, may be engaged in energy production
but dominance of an energy source depends on the duration and intensity of the exercise.
Usually workload is broken into several energy "zones" based on the duration and
intensity of the training. Energy "zones" allow athletes and coaches to develop a specific
pathway of energy recycling and to quantify, track, and plan the physiological adaptations
desired for their specific event.
There are several reasons for understanding energy zones in swimming:
1. Swimming sets of different duration and intensity are supported by energy from
different sources. During high intensity short-term swimming bouts, most energy
is recycled through the anaerobic pathway. It is a fast and non-oxidative way for
energy recycling. During low intensity long-term swimming, bouts the energy is
recycled mostly aerobically using oxygen. This way is slow but more efficient than
the anaerobic way.
2. Improvement of one energy system does not influence another one. When
athletes swim long distances they develop mostly aerobic energy sources. High
intensity swimming develops the anaerobic energy sources. Different swimming
events require the training of different energy pathways.
3. The same swimming set can be swum in different energy zones. For example,
swimmers can swim sets with higher or lower intensities. This will recruit different
pathways of energy recycling.
4. The preparation of competitive swimmers requires evaluation of individual
swimming intensities in each energy zone. The same swimming intensity or even
heart rate affects the energy recycling pathways differently when athletes are at
different stages of the season (i.e., detrained or at peak performances).
Adaptation in athletes to the same swimming intensity depends on their current
condition, types of muscle fibers, training history, and other factors. Therefore it is
important to test athletes during a season and select appropriate swimming
intensities (heart rate) to train different energy zones.
Energy Forms In The Body
Adenosine Triphosphate (ATP) is
the only source of potential
chemical energy in the body. It
consists of one molecule of
protein (adenosine) and three
molecules of phosphate. Muscle
cells always contain free ATP,
which reduces to ADP (adenosine
diphosphate) and releases the
energy during the first few
seconds of work (figure 1).
Decomposition of ATP into ADP
releases the energy and
phosphoric acid, which increases
the acid environment in the
muscles. Then other energy storage forms are used to recycle ADP back to ATP through
different pathways.
Energy forms in the body include:
Adenosine Triphosphate (ATP)
Creatine Phosphate (CP)
Glycogen (glucose)
Fats
Proteins
Working capacity in athletes depends more on the rate of recycling ATP (from CP,
glycogen, fats and proteins) than on the amount of ATP. With training, ATP-CP increases
less than 20%, while working capacity (swimming velocity) increases more dramatically.
Pathways of Energy Metabolism
There are three main pathways of energy metabolism:
1. Creatine Phosphate (immediate non-oxidative way of energy recycling)
2. Anaerobic Metabolism (anaerobic-glycolitic non-oxidative way of energy recycling)
3. Aerobic Metabolism (oxidative way of energy recycling)
Metabolism of Creatine Phosphate is the process of recycling ATP from CP. CP is stored in
muscle cells. It very rapidly recycles ATP from ADP. Usually after 2-3 seconds of high
intensity work, free ATP stores in muscle cells are depleted. Then CP phosphate is
involved to recycle ATP. After 10-15 seconds of high intensity work the rate of recycling
ATP from CP is slowed down. Creatine Phosphate has very high power, low capacity, and
low efficiency.
Examples of swimming sets and distances to develop creatine phosphate metabolism:
diving and turns, short distances (10-25 M/Y) with maximum intensity, swimming sets
with short distance and long rest interval (i.e., 4-6 x 12.5 M/Y, 2-4 x 25 M/Y with rest
interval 1-3 min.).
Anaerobic Metabolism (Anaerobic-Glycolitic) is the non-oxidative process of recycling of
ATP from glycogen. Glycogen is stored in the muscle cells. Glycogen fairly rapidly recycles
ATP, but it is slower than from CP. Anaerobic metabolism produces lactate. It is the main
energy system for exercise bouts of 30 sec until 3 min. When distances are longer,
aerobic metabolism predominates. Anaerobic metabolism has high power, middle
capacity, and low efficiency.
Examples of swimming sets and distances that develop anaerobic metabolism: distances
of 50 to 300 M/Y, high intensity swimming sets with short rest interval (i.e., 6-16 x 25
M/Y, 4-8 x 50 M/Y, 2-4 x 100 M/Y, 2 x 200 M/Y with rest interval 20-30 sec etc.).
Aerobic Metabolism is the oxidative process of recycling ATP primarily from glycogen. It is
a slow process of recycling ATP. Glycogen for aerobic metabolism is stored in muscle,
liver, and blood. Fats and proteins can be involved in aerobic metabolism also, but this
process is very slow (long distance swimming).
Aerobic metabolism is the main energy system for distances longer than 4 min. The
longer distance, the more energy derived from aerobic metabolism. Aerobic metabolism
takes place in a small intracellular organelle called mitochondria. Aerobic metabolism has
low power, high capacity, and high efficiency.
Examples of swimming sets and distances that develop aerobic metabolism: distances of
2000 M/Y and longer, low and middle intensity swimming sets with short rest interval
(i.e., 20 and more x 100 M/Y, 10 and more x 200 M/Y, 7 and more x 300 M/Y, 5 and
more x 400 M/Y etc.).
Energy Zones (Categories) In Swimming
Based on the physiological responses of athletes to different intensities, workload volume
can be divided into the several energy zones in swimming. There are several
classifications of workload. Below are the energy zone charts with sample sets.
Conclusions About Energy Zones
All energy zones are relative. There are no borders between energy zones. However, each
zone has a primary pathway for energy recycling. Understanding energy zones is helpful
in classifying swimming sets and developing particular pathways for energy recycling.
