David R. Lamb, Ph.D.
Exercise Physiology Laboratory
Sport and Exercise Science Faculty
The Ohio State University
Columbus, OH
Chairman, Gatorade Sports Science Institute
KEY POINTS
1. For most sports, the top competitor is generally the one
who can appropriately sustain the greatest power output to overcome
resistance or drag.
2. It is not sufficient for championship performance to simply
have the ability to produce great power. The champion must be
able to sustain power output in an efficient and skillful manner
for the duration of the competition.
3. During maximal exercise lasting a few seconds, the anaerobic
breakdown of phosphocreatine and glycogen in muscles can provide
energy at rates many times greater than can be supplied by the
aerobic breakdown of carbohydrate and fat. However, this high
rate of anaerobic energy production cannot be sustained for more
than about 20 seconds.
4. For exercise lasting more than a few minutes, an athlete
who has a high lactate threshold, that is, one who can produce
a large amount of energy aerobically without a major accumulation
of lactic acid in the blood, will be better able to sustain a
higher rate of energy expenditure than will a competitor who
has a lower lactate threshold.
5. A high level of mechanical efficiency, which is the ratio
of the mechanical power output to the total energy expended to
produce that power, is vital if an athlete is to make the most
of his or her sustainable rate of energy expenditure. Mechanical
efficiency depends upon the extent to which the athlete can recruit
slow-twitch muscle fibers, which are more efficient at converting
chemical energy into muscle contraction than are fast-twitch
fibers.
6. Neuromuscular skill is also critical to mechanical efficiency
because the more skillful athlete will activate only those muscle
fibers required to produce the appropriate movements. Extraneous
muscle contractions require more energy expenditure but do not
contribute to effective power output.
INTRODUCTION
The criterion for success in many sports, including those involving
running, swimming, bicycling, speed skating, rowing, and cross-country
skiing, is simply the time required to propel the athlete's body
(and essential equipment such as a bicycle, rowing shell, or
skis) for a given distance. In the case of Olympic weightlifting
and power lifting, success is determined by how much weight can
be lifted in the appropriate movements, whereas a wrestler is
judged by the degree of physical control over the opponent. These
sports are quite different in terms of the patterns of muscle
recruitment, the force and power produced, and the equipment
used; nevertheless, success in all of these seemingly diverse
sports depends on a complicated application of a simple principle--the
champion is the athlete best able to reduce the resistance or
drag that must be overcome in competition and best able to sustain
an efficient power output to overcome that resistance or drag
(Figure 1)(Coyle et al., 1994). This review provides an analysis
of the major factors that contribute to an athlete's ability
to produce power appropriately to overcome resistance or drag
and a number of important applied principles designed to help
trainers, coaches, physiologists, and others assist athletes
in achieving their goals in sport.
Figure 1. mode; of the interrelationship of major factors determining
sport performance. Performance is determined by how effectively
the athlete can sustain sufficient power output to overcome various
types of resistance or drag, depending on the sport event. Sustainable
power output depends on the rate of energy expenditure that can
be sustained throughout the event and the efficiency with which
that energy can be converted into mechanical power. Depending
on the sport event, sustainable energy expenditure will be a
function of the ability to sustain the production of energy by
anaerobic and/or aerobic means. Mechanical efficiency is dependent
on muscle efficiency, i.e., the efficiency with which muscles
convert the energy stored in carbohydrate and fat into muscle
shortening, and the neuromuscular skill with which the athlete
performs the event, i.e., the degree to which the athlete has
learned to recruit only those motor units required to produce
maximal power output in a skillful way.
RESISTANCE AND DRAG: EXAMPLES IN SPORT
Examples of resistance in sport include the mass of a barbell
in Olympic lifting or power lifting, the muscular efforts of
an opponent in wrestling or judo that are used to offset the
movements of a competitor, and the effect of gravity on resisting
a marathon runner's ability to move up a hill. A lifter who can
sustain adequate power output long enough to correctly lift a
greater weight than a competitor will beat that competitor. Likewise,
a competitor in wrestling or judo who can sustain power sufficient
to overcome the resistance provided by the opponent throughout
the match will be the winner.
Drag is a special case of resistance in which the friction of
air or water around a competitor retards forward motion. Obvious
examples of drag are the adverse effects of a headwind on the
forward velocity of a competitive cyclist and the retarding effects
of water drag on the efforts of a swimmer to move quickly ahead.
In cycling on a flat course at speeds greater than 13 km/h (8
mph), most of the resistance to the power generated by a bicyclist
is created by the air through which the cyclist's body moves;
relatively little bicycling power is lost to friction of the
moving components of the bicycle or to the rolling resistance
of the contact between the tire and road (Kale, 1991). It is
also important to realize that the air drag increases as the
square of the velocity of the moving object, i.e., if speed is
doubled, the drag increases by four-fold (Kale, 1991).
Air drag offers great resistance in any sport requiring the
athlete to move at relatively high velocities; such sports include
speed skating--30-40 km/h (19-25 mph) at distances of 0.5-10
km (3-6 mi)--and sprint running--25-35 km/h (15-22 mph) at distances
of 100-400 m. In fact, the air creates so much resistance in
speed skating that the skaters must assume a tightly crouched
posture to reduce their frontal areas exposed to air. Although
this posture reduces leg power, it reduces air drag to an even
greater extent and thus produces higher skating velocities. Swimmers
move at relatively low velocities because they encounter large
drag forces from the water as well as from the turbulence at
the surface of the water. This drag encountered by a swimmer
is not simply a function of body mass, but also of the geometry
of the body as it moves through the water.
It is obvious that in events such as bicycling, speed skating,
and possibly sprint running, each of which requires the athlete
to move through the air at high speeds, the ultimate race time
will be determined by the power generated relative to the air
resistance. The same is true for the swimmer who must overcome
the drag of the water at lower speeds. The main point is that
the race velocity in these sports is a function of power production
relative to the drag encountered at racing speeds. Therefore,
velocity (performance) can be increased by improving power output
and/or by reducing drag.
REDUCING RESISTANCE AND DRAG
In some sports, such as Olympic lifting, power lifting, and
the shot put, the very nature of the competition makes it impossible
to reduce resistance. If a competitive lifter chooses a low resistance--a
lightweight barbell, that athlete is unlikely to win the competition.
Likewise, the rules do not allow a shot putter to choose a lightweight
shot. However, there are methods that can be used in many sports
to reduce resistance or drag. Here are a few examples:
Use Skillful Technique. Competitors in wrestling, judo, rugby,
American football, and other "contact" sports can reduce
the resistance applied by opponents by skillful misdirection
movements that trick the opponents into resisting in the wrong
direction. These techniques are learned through many years of
practice under the instruction of skillful coaches.
Use Aerodynamic and Hydrodynamic Equipment and Body Postures.
In some sports, effective techniques have been employed to reduce
resistance and drag in air and water. The designs of golf balls
and javelins have become more aerodynamic over the years, and
the resulting reductions in air drag have improved the flight
characteristics of both. In cycling, riders wear aerodynamic
helmets and skintight clothing and assume crouch positions over
the handle bars ("aero bars") to minimize wind resistance.
In swimming, body position in the water and stroke mechanics
are optimized by careful study of underwater videos so that the
swimmer reduces water drag as much as possible. Also, engineers
have successfully modified the designs of rowing shells, canoes,
kayaks, sailboats, oars, and paddles to minimize water drag in
competitive events.
Reduce Body Mass. Athletes should carefully consider whether
they can effectively reduce resistance or drag by reducing body
weight. For pole vaulters, high jumpers, long jumpers, and triple
jumpers, gravity is the principal resistance that must be overcome,
and body weight is responsible for nearly all of this effect
of gravity. Therefore, if these athletes can reduce their body
weights without equivalent reductions in their abilities to skillfully
generate muscular power, their performances should improve. Of
course, if the body weight loss leads to a serious loss of muscular
power, performance may well be worsened, not improved. Competing
at an effectively low body weight is also critical for distance
runners, endurance cyclists, and cross-country skiers. In these
sports, the resistance of gravity is a crucial factor in determining
performance; in addition, at the higher velocities of cycling,
air drag is a major type of resistance that must be overcome,
and a smaller frontal body surface area can reduce that resistance.
Weight reduction is not so much of an issue in swimming because
the body mass is buoyed up by being immersed in water. However,
to the extent that reductions in body weight help reduce water
drag, weight loss could be of benefit in swimming, too. Differences
in swimmers' individual body builds could play a significant
role in determining whether or not weight loss improves swim
performance. For example, weight loss may be quite ineffective
in a swimmer who already presents a small frontal area and who
tends to lose weight mostly in the thighs. However, if a swimmer
has exceptionally large shoulders and a large chest, and if the
mass of these areas can be reduced effectively through a weight
loss program, such an approach could shave time off that swimmer's
personal records.
PROVIDING EFFICIENT SUSTAINED POWER OUTPUT TO OVERCOME RESISTANCE
AND DRAG
Power is the ability to apply force through a distance quickly.
In other words, power can be thought of as a combination of strength
and speed. Interestingly, the sport of power lifting is misnamed
because only strength, not speed, is required to be successful;
as long as the barbell is moved appropriately, time is of no
importance. On the other hand, a person could have exceptionally
strong leg muscles and be a pitiful high jumper, sprinter, or
long jumper if that strength could not be brought to bear quickly.
Unfortunately, absolute maximal muscular power can be sustained
for only a fraction of a second. Thus, assuming equal resistance
or drag, the champion in a sport event will not necessarily be
the competitor who can produce the greatest maximal power, but
instead will be the one who can sustain the greatest power output
to overcome the resistance or drag for the duration of the event.
This duration may be only a second or two, such as in power lifting,
or many hours, such as in an Ironman triathlon.
The ability to sustain a high power output to efficiently overcome
resistance or drag involves two major factors--the ability to
sustain energy production by the muscles and the ability to apply
that muscular energy efficiently to overcome resistance or drag.
SUSTAINING ENERGY PRODUCTION BY THE MUSCLES
When energy requirements are extremely high, such as during
a sprint in track or swimming or during an Olympic weightlifting
event, most of the muscular energy is supplied by two fuels,
phosphocreatine (PCr) and glycogen, that are stored in small
amounts in the muscles. Because these two fuels can be broken
down for energy without the use of oxygen, this is known as anaerobic
(without air) energy production. Aerobic energy production occurs
at a much slower rate as fats and carbohydrates are broken down
with the aid of oxygen in the muscles.
Sustainable Energy Expenditure in Brief, High-Power Events
Brief, high-power activities such as weightlifting and sprinting
rely largely on the anaerobic breakdown of PCr and muscle glycogen
for energy. When estimates of anaerobic energy production are
coupled with simultaneous measurements of aerobic energy production,
the approximate relative contributions of these two energy sources
during various phases of exercise lasting from 0-180 s are as
shown in Table 1. It is clear from the table that the percentage
anaerobic contribution to energy production falls off rapidly
as the exercise duration increases.
Both PCr degradation and anaerobic glycolysis are activated
instantaneously at the onset of high-intensity exercise. Measurements
of PCr and lactate from muscle biopsies taken following as little
as 1-10 s of electrical stimulation (Hultman & Sjoholm, 1983)
and after sprint cycling (Boobis et al., 1982; Gaitanos et al.,
1993; Jacobs et al., 1983) confirm the rapid breakdown of PCr
and rapid accumulation of lactate. At the onset of less intense
exercise, a similar instantaneous activation of both PCr degradation
and anaerobic glycolysis occurs but at a much slower rate because
the mismatch between energy demand and aerobic supply is reduced
during submaximal exertion.
Rate of Anaerobic Energy Production During Exercise
The rate of anaerobic energy provision is critical to success
in sports that require the development and short-term maintenance
of high power outputs. World-class power lifters and weightlifters
can produce power outputs that are 10-20 times that required
to elicit the maximal rate of aerobic energy provision, which
is estimated by the maximal rate at which the athlete can consume
oxygen (VO2max). However, such high power outputs can be maintained
for only a fraction of a second. Sprinters can achieve power
outputs that are 3-5 times the power output that elicits VO2max,
but they can sustain that power output for only about 10 s. However,
power output over a 30-40 s sprint can still be sustained at
twice the power output at VO2max. Estimates of the rates of anaerobic
provision of energy have been calculated from biochemical changes
in muscles following intense exercise lasting from 1.3 to 200
s (Spriet, 1994). These studies used non-elite athletes who performed
sprint cycling, sprint running, or repeated knee extensions or
who underwent electrical stimulation of their muscles. The highest
measured rates for energy production from PCr and anaerobic glycolysis
during various types of exercise lasting from 1.3-10 s were each
approximately 250-500% of the estimated maximal rate of energy
provision from aerobic metabolism. In other studies of sprint
cycling for 6-10 s, energy production rates from PCr and anaerobic
glycolysis combined were about 400-750% of that during maximal aerobic
metabolism (Boobis et al., 1982; Jacobs et al., 1983).
The anaerobic energy provision rates decrease when averaged
over longer periods of time. In studies that examined intense
exercise for 30 s, the average energy provision rate from PCr
was about 70-100% of that from maximal aerobic metabolism; anaerobic
glycolysis provided energy at a rate estimated to be 220-330%
of that from maximal aerobic metabolism (Spriet, 1994). The large
decrease in energy produced from PCr when averaged over 30 s,
as compared to less than 10 s, indicates that the PCr store becomes
depleted between 10 and 30 s of intense exercise. Thus, for maximal
exertion lasting longer than about 30 s, it appears that only
glycolysis can provide for further anaerobic energy production.
Anaerobic Energy Production During Intermittent High-Power
Exercise
Many athletes repeatedly engage in bursts of high-intensity
exercise with varying amounts of recovery time between exercise
bouts. Examples include a wide receiver in American football,
a basketball player in repeated fast break situations, or a swimmer
or track athlete during interval training. Most of the energy
for short bouts of high-intensity exercise is derived from anaerobic
sources; therefore, the ability to recover during rest periods
is essential for success in this type of activity. Many studies
have examined the performance effects of intermittent high intensity
exercise, but few have examined the anaerobic metabolism associated
with this type of metabolic stress. Examples of the exercise
models that have been studied and provided some conclusions include:
10 bouts of sprint cycling, each lasting 6 s with rest periods
of 30 s; four bouts of sprint cycling for 30 s with 4-min rest
periods; and two bouts of knee extension exercise to exhaustion
in 3 min with 10-60 min of recovery (Bangsbo et al., 1992; Gaitanos
et al., 1993; McCartney et al., 1986). Muscle biopsy measurements
demonstrated that PCr was decreased by approximately 50% after
6 s and by 75-80% during longer sprints. The PCr is quickly resynthesized
during recovery, reaching 50% of rest values by 30-60 s and about
80% by 2-4 min. With repeated sprinting, energy production from
anaerobic glycolysis is progressively more difficult to achieve.
Presumably, the accumulation of lactic acid in the active muscles
plays a major role in the inability to continue producing energy
by anaerobic glycolysis. Therefore, after repeated bursts of
exercise, PCr is the only potential anaerobic energy source that
can be relied upon. However, as described above, it is essential
that adequate rest be provided in between intermittent exercise
bouts to allow PCr stores to be replenished in the muscles.
Sustained Aerobic Energy Production
The maximal rate of aerobic energy production (VO2max) can be
sustained for only about 8-10 min by elite athletes. In events
lasting longer than 8-10 min, the best competitor among those
with similar values for VO2max is usually the one who can sustain
aerobic energy production at the greatest proportion of his or
her maximal rate, that is, at the greatest percentage of the
VO2max. This in turn is largely dependent on the extent to which
the athlete can produce energy aerobically at a high rate without
accumulating a large amount of lactic acid in the blood. In other
words, the athlete who produces a large amount of lactic acid
at a given speed of running, swimming, or cycling cannot continue
to perform at that pace for as long as the athlete who does not
accumulate as much lactic acid. An athlete who has the ability
to exercise at a high intensity before blood lactic acid begins
to accumulate is said to have a high lactate threshold (Coyle
et al., 1988; Holloszy & Coyle, 1984). An athlete's lactate
threshold seems to be a better indicator of endurance performance
lasting 30 min to 4 h than does the VO2max (Coyle et al., 1988,
1991).
This is because the lactate threshold is a better index of the
athlete's ability to sustain a high rate of energy expenditure
for the duration of the competition.
Role of Nutrition in Determining Sustainable Energy Production
Two nutrients, carbohydrate and water, are the dietary constituents
that have repeatedly been shown to be most important for optimizing
endurance performance. Muscles obviously cannot produce energy
without fuels derived from nutrients obtained in the diet, and
carbohydrate is an obligatory fuel for high-caliber sport performance.
It is well established that dietary carbohydrate consumption
before, during, and after exercise can make an important contribution
to performance. Carbohydrate consumption acts primarily by increasing
the body's stores of glycogen in muscles and in the liver before
exercise and by increasing the availability of glucose for use
by the muscles during exercise (Coggan & Swanson, 1992; Costill & Hargreaves,
1992; Coyle, 1991; Williams, 1993). Fluid intake during prolonged
exercise is also required to counteract the debilitating effects
of exercise and heat on cardiovascular function and on body temperature
regulation. When dehydration reduces blood volume, oxygen delivery
to the muscles by the blood can be compromised, and this reduces
the ability of the muscles to produce energy aerobically. Dehydration
also compromises the ability of the body to regulate its temperature,
resulting in eventual lethargy and potential heat illness, both
of which adversely affect the athlete's ability to sustain a
high rate of energy production. Carbohydrate-electrolyte beverages
are advocated as the most effective way to supply both carbohydrate
and fluid to the body during exercise (Coggan & Swanson,
1992; Gisolfi & Duchman, 1992).
IMPROVING THE ABILITY TO SUSTAIN ENERGY PRODUCTION AT A HIGH
RATE
Here are some ways that athletes may be able to improve their
abilities to sustain high rates of energy production so they
can sustain greater power output to overcome resistance and drag:
At the onset of a training season, the athlete should establish
a solid aerobic training foundation by training at relatively
low intensities for long durations. This will help develop a
greater blood volume, an improved ability of the heart to pump
blood, and better networks of capillaries in the trained muscles.
These cardiovascular adaptations will lead to an improved delivery
of oxygen to the muscles and an enhanced ability of the muscles
to sustain high rates of aerobic energy production.
For the bulk of the athlete's training, the specific muscle
groups involved in the competitive event should be overloaded,
and the athlete should train at a pace or intensity similar to
that used in competition (Hickson, 1977, 1985). Such training
can lead to improved stores of glycogen and PCr in the trained
muscles so that greater energy reserves will be present in the
muscles before competition begins. Furthermore, metabolic adaptations
to this type of training are likely to enhance the ability of
the muscles to utilize fat for energy and to spare muscle glycogen,
resulting in less lactic acid production and less accumulation
of lactic acid in the blood at a given pace or intensity (Holloszy & Coyle,
1984). This means that the athlete's lactate threshold will be
increased so that aerobic energy production can be sustained
longer at a greater rate than was possible before training.
During high intensity, anaerobic interval training, the duration
of recovery intervals should be sufficient--usually between 30
s and 4 min--to allow the muscles to replenish most of the PCr
depleted in the previous exercise interval. If these recovery
intervals are too brief, the supply of PCr in the exercising
muscles will be inadequate to provide energy anaerobically at
a high rate (Gaitanos et al., 1993; McCartney et al., 1986).
This means that the athlete will be forced to exercise at a lower
intensity (slower pace) and that inappropriate muscle groups
may be recruited to accomplish subsequent exercise intervals.
If these events occur, the athlete will be learning incorrect
movement patterns during training that may adversely affect competitive
performance.
The athlete should receive adequate rest--approximately 24 h--between
exhaustive training sessions to allow for total replenishment
of depleted glycogen stores in the muscles prior to the next
training session (Coyle, 1991). Otherwise, the quality of the
next training session may be compromised because the athlete's
muscles will be easily depleted of one of their main fuels. In
addition, training intensity and duration should be gradually
reduced during the week before a competitive event so that the
athlete's energy reserves are fully loaded before competition.
The athlete should drink plenty of fluids before, during, and
after exercise to avoid becoming dehydrated. Dehydration can
lead to a diminished ability to deliver oxygen to the muscles,
heat cramps, heat exhaustion, and even heat stroke, all of which
can impair muscular energy production.
On a daily basis, the athlete should consume a diet high in
carbohydrate, about 8 g of carbohydrate per kilogram of body
weight (4 g/lb). This will ensure that the muscles can store
extra glycogen and may help sustain energy production during
competition.
Preliminary evidence suggests that dietary creatine supplementation
may increase PCr stores in muscles (Dalsom et al., 1995) and
perhaps improve performance in events such as fastbreak basketball
that require repeated brief exertions. The extent to which creatine
supplementation proves to be useful in actual sport settings
remains to be seen.
During prolonged exercise, the athlete should consume carbohydrate-electrolyte
drinks containing approximately 6% carbohydrate (glucose, sucrose,
or maltodextrins) and a small amount of sodium to help maintain
an adequate carbohydrate energy supply to the muscles and to
minimize dehydration. Volumes of 150-250 mL (5-8 oz) should be
consumed every 15-20 min to replace most, if not all, of the
sweat lost by the athlete during exercise (Montain & Coyle,
1992).
MECHANICAL EFFICIENCY: A MAJOR DETERMINANT OF EFFECTIVE POWER
OUTPUT
Mechanical efficiency for a sporting event is the ratio of the
mechanical power output to the total energy expended to produce
that power. Typically, both power output and energy expenditure
are expressed in watts (W), and the ratio is expressed as a percentage.
For example, if a cyclist expends energy at the rate equivalent
to 5 L of oxygen per minute (1745 W) to produce 400 W of power
on a bicycle ergometer, the mechanical efficiency would be (400/1745)
100 = 23%. Two of the principal factors that determine the mechanical
efficiency of an athlete in a sport event are 1) the efficiency
with which the active muscles convert the chemical energy stored
in carbohydrate and fat to the mechanical energy required to
shorten the contractile elements in the muscles, and 2) the neuromuscular
skill with which the athlete performs the event.
Role of Muscle Efficiency in Determining Mechanical Efficiency
Muscle efficiency has two components, the first of which is
the efficiency with which chemical energy from carbohydrate and
fat is converted to adenosine triphosphate (ATP), the only form
of chemical energy that can power muscle contraction. The process
of ATP synthesis is about 40% efficient, i.e., 40% of the metabolic
energy in carbohydrate and fat is transferred into ATP synthesis,
whereas 60% of the energy is lost as heat (Kushmerick, 1983;
Kushmerick & Davies, 1969). This efficiency of ATP synthesis
is fairly constant among individuals.
The second component of muscle efficiency, i.e., the efficiency
with which the energy released during ATP hydrolysis is converted
to muscle fiber shortening, is more variable than is the efficiency
of converting stored fuels to ATP. The efficiency of ATP hydrolysis
is dependent on the velocities of muscle contraction (Goldspink,
1978; Kushmerick & Davies, 1969). A peak efficiency of approximately
60% or more can be elicited from myofilaments contracting at
one- third of maximal velocity; i.e., the velocity of peak efficiency
(Kushmerick, 1983; Kushmerick & Davies, 1969). Thus, slow-twitch
muscle fibers obviously have slower velocities of peak efficiency
than do fast-twitch fibers (Fitts et al., 1989).
Mechanical efficiency when cycling at 80 rpm is directly related
to the percentage of slow- twitch muscle fibers in the vastus
lateralis muscles (Coyle et al., 1992). It seems that when cycling
at this cadence, the velocity of muscle fiber shortening in the
vastus lateralis is close to one-third maximal velocity of the
slow-twitch fibers (Coyle et al., 1992). This makes slow-twitch
muscle fibers substantially more efficient than fast-twitch muscle
fibers at converting ATP into muscular power when cycling at
80 rpm (Coyle et al., 1992; Goldspink, 1978).
Muscle fiber type has a large effect on mechanical efficiency,
which in turn has a large influence on sustainable power output
as measured during a 60-min bout of cycling in a homogeneous
group of cyclists (Horowitz et al., 1994). The cyclists in this
study were paired and divided into two groups based upon the
percentage (i.e., above or below 56%) of slow-twitch muscle fibers
in their vastus lateralis muscles. One group possessed a normal
distribution of fiber types, with an average of 48% slow twitch
fibers. The other group had 72% slow-twitch fibers on average.
These two groups were identical in VO2 max as well as in the
VO2 maintained during the ride. Therefore, they possessed the
same aerobic energy expenditure potential for this type of task.
However, the cyclists with a high percentage of slow-twitch fibers
displayed significantly higher mechanical efficiencies and were
therefore able to sustain a 9% greater power output (342 W vs.
315 W) during the 60-min ride. Clearly, endurance cycling performance
is heavily influenced by mechanical efficiency, which in turn
appears to be dependent on the rider's muscle fiber type profile
and the efficiency of ATP hydrolysis by the muscle.
Role of Neuromuscular Skill in Determining Mechanical Efficiency
No matter how efficiently one can transform chemical energy
into mechanical energy in a given muscle fiber, the overall mechanical
efficiency in a sports event will be poor if the athlete is poorly
skilled. A good example of the importance of skill is the contrast
in the freestyle swimming performances of novice and elite swimmers.
The novice may produce a great deal of power, but because the
swimmer is so unskillful, the power output is misdirected so
that lots of thrashing about occurs with little forward velocity.
The elite swimmer, on the other hand, has learned to swim rapidly
and gracefully, using only those muscle fibers required to execute
the stroke effectively. Neuromuscular skill obviously plays a
greater role in determining the mechanical efficiency for some
sports, e.g., swimming and wrestling, than it does for others,
e.g., running and power lifting, but even small differences in
skill can have a major impact on performance in any sport at
the elite level.
IMPROVING THE ATHLETE'S ABILITY TO PROVIDE POWER OUTPUT IN
AN EFFICIENT MANNER
There is little that the athlete can do to improve muscle efficiency
because the chemical efficiency of converting fuels to ATP and
the proportion of slow-twitch fibers involved in various movements
are largely determined by heredity. An exception may be that
athletes over many months of training may learn to recruit more
of the efficient slow-twitch muscle fibers and fewer of the less
efficient fast-twitch fibers. In addition, there are three important
steps that can be taken to improve the skill with which power
output is applied.
The athlete should obtain the technical advice of competent
coaches who can explain how movement patterns should be altered
to become more skillful. Often the coach can rely upon personal
experience and observation to make critical improvements in an
athlete's technique.
Video analysis of the athlete's performance can provide clues
about changes in movement patterns that can be made to improve
efficiency. The assistance of a sport biomechanist or a coach
well-educated in biomechanics could be important in this phase
of the athlete's preparation.
The athlete must repeat the appropriate movement patterns in
a skillful manner many thousands of times during practice so
the nervous system learns to perform the movement correctly every
time throughout the entire duration of competition. There is
no substitute for skillful repetition of muscular activities
to ensure that such activities are likely to remain skillful
in the heat of competition.
SUMMARY
For most competitive sports, improving the performance of an
athlete can be accomplished by reducing the resistance or drag
that must be overcome or by increasing the athlete's ability
to sustain a high power output to overcome that resistance or
drag. Reducing air resistance or water drag typically involves
improving body position in the air or water by minimizing the
frontal surface area of the athlete that is exposed to the air
or water. Sometimes the apparel or equipment used in the sport,
e.g., helmets, swimwear, bicycles, and rowing shells, can be
made more aerodynamic or hydrodynamic to reduce resistance or
drag.
Increasing sustainable power output requires that the athlete
undergo a carefully designed training program that will improve
the athlete's abilities to: 1) produce metabolic energy by both
aerobic and anaerobic means, 2) sustain aerobic energy production
at high levels before lactic acid accumulates excessively in
the blood, 3) recruit more of the efficient slow-twitch muscle
fibers at exercise intensities used in competition, and 4) become
more skillful by recruiting fewer non- essential muscle fibers
during competition. Careful attention to maintaining a sufficient
intake of fluids and carbohydrate before, during, and after strenuous
competition and training sessions is also important.
Although it is apparent that some uniquely gifted athletes are
able to win consistently even when their approaches to training
are obviously not optimal for reducing resistance or drag and
for enhancing their sustainable power outputs, it is clear that
such athletes cannot achieve their full potentials in sport without
addressing these two basic principles.
* This article was adapted from "Introduction to Physiology
and Nutrition for Competitive Sport," by E.F. Coyle, L.
Spriet, S. Gregg, and P. Clarkson, which appeared in D.R. Lamb,
H.G. Knuttgen, and R. Murray (eds.), Perspectives in Exercise
Science and Sports Medicine, Vol. 7: Physiology and Nutrition
for Competitive Sport. Carmel, IN: Cooper Publishing Group, 1994,
pp. xv-xxxix. The author is especially grateful to Edward Coyle,
Ph.D. and Lawrence Spriet, Ph.D. who contributed much of the
text for this article.
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