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Cycling: Physiology And Training
Irvin E. FariaHuman Performance Laboratory
California State University, SacramentoSacramento, CA 95819
USA
This paper examines the sport of cycling as approached
from the perspectives of history, physiology, biochemistry,
ergometry, biomechanics, aerodynamics, and training. The
physiological and anatomical determinants of cycling are
briefly explored. Aerodynamics of cycling is considered with
particular reference to the rider, equipment and bicycle.
Finally, the impact of training methods on acute and chronic
physiological responses are examined.
HISTORICAL EVENTS
The concept of the bicycle dates back to 2300 BC, when in
China, and later Egypt and India, the bicycle was envisioned.
Count Médé de Sivrac of France, in 1790, built 2 wheels linked
by a narrow wooden bride which was driven by alternate pushes
of the feet on the ground. Baron Karl Friedrich Von Drais, in
1816, added a steering device to the hobby horse-like machine.
Two years later Von Drais, riding this primitive bicycle,
established the first world cycling record. He covered the
distance between Beaune and Dijon at the speed of 9 miles per
hour.
MacMillan, an Englishman, connected 2 rods to the axle of
the rear wheel of the hobby horse-like bicycle. Through
piston movements, onto the rods, the rider using short foot
thrusts turned the bicycle wheels. A few years later
Lallement, in 1855, attached pedals to the front wheel of the
machine which became known as the "boneshaker". This was the
first attempt to apply the concept of gearing to the bicycle
by increasing the diameter of the drive wheel. This wheel
ratio concept was then applied to the "ordinary" or "penny
farthing" bicycle. The penny farthing bicycle was
characterized by a very large diameter front wheel of
approximately 60 inches.
By 1867, the bicycle was constructed of steel tubing and
wheels with iron rims causing it to weigh 110.25 pounds. The
stronger construction allow greater speeds which, in 1869,
stimulated an interest in racing. The first race took place
in France in 1869 covering a distance of 20.4 miles. The
winner, Letourd, cycled the distance in 3 hours and 9 minutes,
for an average speed of 6.46 miles per hour. In the quest
for greater speed, by 1878 the use of wooden rims, tangential
spokes, and a frame built of tubes reduced the bicycle weight
to 66 pounds.
In the late 1880s the watchmaker, Guilmét, conceived the
idea of attaching a metal chain to the bicycle's rear wheel.
2
This chain resulted in the multiplication of turns on the
drive wheel, thus eliminating the need for the exaggerated
high front wheel. Four years later, in 1884, the diamond
frame was built by the Englishman Thomas Huber. The first
gear change system was employed in the 1932 world road racing
championships. Binda and Bertoni, two Italian cyclists, using
the new gearing system, won first and second place.
While the bicycle remained the primary means of rapid
transportation in third world countries, it became a toy for
children in the industrialized world. Following World War II,
use of the bicycle gave way to automobile. In general, little
attention was directed toward bicycle technology. In the
early 1950s industrialization provided large populations with
leisure time to invest in hobbies and sport interests.
Consequently, the use of bicycle regained popularity. Energy
was directed toward building a better bicycle for general
leisure time use and for racing. The goal was and remains
that of enhancing human movement efficiency.
Through improved design and the use of alloys for frame
and components cycling economy was greatly enhanced. For
example, the unaided walking person consumes about 0.75
kilocalories (kcal) per kilometer. When riding a bicycle,
however, the energy consumption for a given distance is
roughly 0.15 kcal.km-1. Each year streamlined aerodynamically adapted bicycles continue to reach higher speeds. Modern
bicycle technology proceeds contribute to the both the leisure
cyclist and racing enthusiast.
3
The sport of bicycling attracts more world wide
participation, from commuter to sport tourists and serious
racer, than any other exercise modality. Ironperson triathlon
events and mountain trail cycling have more recently
contributed to the flourishing interest in bicycling.
The physiological and biomechanical aspects of bicycling
have been investigated for nearly nine decades. New materials
for the construction of lighter, more durable and streamlined
bicycles and components coupled with modern technology
portends the prospect of constructing a bicycle that affords
cyclists of a given county the "competitive edge" in
international competition. Until the past decade, little was
known or written about how the cyclist applied forces to the
pedals or drive train. Dr. Peter Cavanagh, of the
biomechanics laboratory, at Pennsylvania State University was
among the first biomechanical engineers to study such forces.
His work, along with the many other scientists who followed,
revolutionized the sport of cycling. Like Dr. Cavanagh, Dr.
Chester Kyle, one of the founders of the International Human
Powered Vehicle Association, an aerodynamics expert, pioneered
the design of aerodynamic bicycles. His untiring efforts
influenced radical change in bicycle frame and component
design as well as body apparel of the cyclist.
High-speed cameras, strain gauges, digitizing computers,
dynamometers, and wind tunnels are employed in an attempt to
catch the elusive component of successful cycling. Exercise
physiologists, biomechanists, and psychologists continue the
4
search to identify the variable (s) which will, when
controlled, shave a few thousandths of a second from a rider's
time on the track and road. Most have come to recognize and
accept the fact that to optimize cycling performance the still
elusive factor and the most dependent variable lies in the
human power component. For the elite cyclist, championship
success rests on the human qualities of physiologic capacity
and mental toughness.
Metabolic Cost Of Cycling
The cyclist's energy expenditure is measured by the
oxygen consumed and expressed in liters of oxygen consumed per
minute of exercise and translated into a kilocalorie (Kcal)
cost value. Per liter of oxygen consumed the approximate
calorific transformation equals 5 kilocalories. The following
is an example calculation of cycling energy expenditure.
• Assume a 150 lb (68 kg) cyclist works at 80% of maximal
oxygen consumption of 70 ml.kg-1.min-1 (milliliters per kg body weight per minute) for four hours.
• The energy expenditure would be: 56 ml.kg-1.min-1 x 0.85 = 47.60 ml.kg-1.min-1 x 68 kg = 3236.80 ml.min-1.
• Converting to liters and Kcal then: 3.24 L.min-1 x 5
kcal = 16.2 kcal.min-1.
5
• The total energy expenditure becomes: 16.2 kcal.min-1 x
240 minutes (4 hr x 60 min) = 3888.0 kcal or 972.0
kcal.h-1. (Note: 0.85 represents the thermal
equivalent of oxygen for non-protein respiratory
quotient, including percent Kcal and grams derived from
approximately 50% carbohydrate and 50% fat.)
A MET, an acronym that stands for "Metabolic Equivalent
T" which is equal to 3.5 ml.kg-1.min-1 serves as a convenient expression of energy expenditure at rest. For the above
example an equivalent MET cost is (56 ml.kg-1.min-1 ÷ 3.5 ml.kg-1.min-1) 16 METs.min-1 or 16 times rest. This energy cost is equal to running on the flat at 10.5 mph or at
approximately a six minute mile pace.
In order to cycle at speeds common to road racing, the
endurance cyclist must increase the rate of muscular energy
production by more than 20 times rest. The elite racing
cyclist is capable of using 30.7 kcal.min-1 at 25 mph at a gross energy use efficiency of approximately 19% to 29%.
Figure 1 presents the relationship between cycling speed and
Kcal cost.
Oxygen Cost and Cycling Economy
Maximal oxygen consumption (.O2max) is defined as the
highest amount of oxygen an individual can use during physical
work while breathing air at sea level. Oxygen consumed during
6
cycling consists of three components: (1) that necessary to
maintain the body in position on the bicycle and for the
physiological maintenance work; (2) that required to move the
legs at zero load through the prescribed pattern of movement;
and, (3) that necessary to overcome the resistive load.
A moderately high oxygen consumption capacity is required
for successful competition at the national and international
level. Figure 2 summarizes the mean maximal oxygen
consumption values of several national cycling team members.
It can be observed that even elite cyclists vary considerably
in their maximal oxygen consumption values. Although
important, maximal oxygen consumption is not the final
variable for successful endurance performance. The submaximal
oxygen consumption per unit body weight (.O2 submax) required
to perform a given task (i. e., cycling a certain speed) is
equally crucial for success. It is considered a measure of
the cyclist's cycling economy.
Economy is defined as the submaximal oxygen use per unit
of body weight required to perform a given task. Economy
then, is the physiological criterion for "efficient"
performance. Conceptually economy of work is a very useful
measure for the evaluation of cyclist's ability to sustain a
high intensity of effort for a given time period.
Two factors influence cycling economy: (1) the cyclist's
maximal capacity to consume oxygen as reflected by the .O2max,
and (2) the maximal level for steady rate cycling as indicated
by the cycling intensity at the lactate threshold (TLA). The
7
oxygen use at the TLA is expressed as percent of .O2max. The
TLA represents the point at which lactic acid is produced at a
greater rate than it can be metabolized.
The cyclist who has the highest .O2max plus the highest
LAT plus the highest cycling economy plus the greatest ability
to tolerate metabolic acidosis has the leading potential for
winning. The combination of hereditary endowment and training
emphasis determine which of these variables will prevail.
Indices Of Cycling Potential
The cyclist's ability to perform at the highest potential
appears to depend on five factors: (1) .O2 at blood lactate
threshold (L.min-1), r2 = 0.86; (2) percent of slow-twitch oxidative muscle fibers, r2 = 0.91; 2) calf circumference, r2
= 0.92; (3) mid-thigh circumference, r2 = 0.95; and (4) muscle
myoglobin concentration, r2 = 0.97. The five factors which
best predict time-trial performance include: (1) average
absolute work rate for 1 hour performance, r2 = 0.78; (2)
muscle capillary density (capillaries per mm2) r2 = 0.94; (3)
muscle PFK (Phosphofructosekinase) activity, r2 = 0.97; (4)
lean body weight, r2 = 0.98; and, (5) .O2max at lactate
threshold (1.min-1), r2 = 0.99. Elite-national class cyclists are capable of cycling at
90 ±1% .O2max for 1 hour. Factors which distinguishes the
elite class from the "good-cyclist", include the %.O2 at the
LAT and a higher absolute .O2 at LAT
8
(l.min-1). The LAT may, therefore, be an effective criterion
for predicting performance. Muscle fiber type plus specific
enzyme presence contribute to the latter abilities. A high
muscle capillary density contributes to augmented lactate
removal from the muscle.
The reliability and validity of heart rate monitors has
made it possible to carefully structure a scientific training
program. Knowing the heart rate will allow the prediction,
with reasonable accuracy, of the oxygen cost of a given
cycling effort. Heart rate and oxygen consumption tend to be
linearly related throughout a large portion of the aerobic
range. Figure 3 illustrates this relationship of percent of
maximal heart rate to percent of maximal oxygen consumption.
Because this relationship is known the exercise heart rate can
be used to
estimate oxygen consumption and TLA during road cycling.
If only an estimation of the cyclist's aerobic power is
of concern a cycle ergometer may be employed. When gas
analysis is not possible the following formula is used to
estimate the oxygen consumption from cycle ergometer exercise
data.
.O2(ml.min-1)={( x )+(3.5 ml.kg-1.min-1 x kg (BW)}
Where: = the last minute of work performed on the ergometer.
POWER OUTPUT
9
The term force effectiveness is often used in cycling to
quantify the relationship between the force "applied" (Fr) by
the rider and the force "used" (Fe) in propulsion (force
applied perpendicular to the crank). Force effectiveness is
expressed by: Force effectiveness = Fe ÷ Fr
Direct measurement of these quantities using a force
measuring pedal has shown that the index of effectiveness
during the propulsive phase of cycling in elite riders is only
76%. This fact suggests that 24% of the applied force, during
cycling, is used to deform the cranks and other parts of the
bicycle. Thus, the conventional method of applying force to
common bicycle transmission is an inefficient process.
However, increased force effectiveness has not been found to
account for higher power output . Rather high power output is
attributed to higher peak vertical forces and torque during
the cycling downstroke. The standard cycling position,
compared to prone and supine, is clearly superior for power
development. Elite compared to "good-class" cyclist have been
shown to generate more power by producing higher peak vertical
forces and crank torque during the down-stroke. This greater
magnitude of vertical force results in more work per
revolution. In terms of equal RPM, this means a larger power
output. Therefore, it might be concluded that effective
vertical force is essential for superior performance. The
latter, however, is not necessarily the case. It has been
observed that the larger the proportion of the resultant force
applied to the pedal does not necessarily create propulsive
10
torque. Clearly then a measure of cycling effectiveness
cannot be based solely on the orientation of applied pedal
forces.
Cyclists may reduce the negative torque during the
upstroke by pulling up on the pedal. However, at high power
outputs, increased peak torque during the downstroke is more
responsible for increased power output than is reduced
negative torque during the upstroke.
Pursuit cyclists have registered power outputs ranging
from 331 to 449 watts with cadences between 103 and 126 rev
min-1. Competitive cyclists can maintain a power output of
more than 300 watts for one hour (0.4 horsepower). Eddy
Merckx, one of the world's greatest cyclists, has registered
the highest power output of 440 watts (0.6 horsepower) for
one hour.
Muscle Fiber Recruitment
Successful cycling performance may be a matter of cycling
technique including ineffective use of muscle fiber
recruitment. Fiber recruitment is influenced by contractual
needs and fiber type availability. Genetic as well as
training influence muscle fiber type.
Human skeletal muscles differ widely in their speed of
contraction, fatigue threshold, and response to different
rates of stimulation. Three distinct fiber types have been
identified. Slow-twitch oxidative (SO) fibers (Type I)
11
possess a greater quantity of mitochondria and contain
correspondingly greater amounts of Krebs Cycle and electron
transport system enzymes than other identified fibers. When
oxygen is provided, these fibers have a great potential to
produce adenosine triphosphate (ATP). Slow-twitch oxidative
fibers have a greater ability for fatty acid and ketone body
utilization than do less oxidative fibers. In contrast, fast-
twitch glycolytic (FG) fibers (Type IIa), possess high
myofibrillar ATPase and have a lesser oxidative potential but
exhibit greater anaerobic capacity to produce ATP than the SO
fibers. The FG fibers rely heavily on carbohydrates in the
form of glycogen as a substrate. Fast-twitch oxidative-
glycolytic (FOG) fibers (Type IIb) are considered to be
intermediate in character because their fast contraction
ability is combined with a moderately well developed potential
for both aerobic and anaerobic energy transfer.
Trained cyclists display a wide range of muscle fiber
types which compose their knee extensor muscles. Type SO
fibers have been shown to occupy 32 to 76 percent of road
racing cyclist's knee extensor muscles. The vastus lateralis,
one of the knee extensors, of the majority of racing cyclist
is high in SO fibers. Type FG fibers comprise the next largest
portion of the remaining fibers while FOG fibers are fewest in
number.
Increased years training and racing possibly has an
influence on the percentage of SO fibers in the vastus
lateralis and other major cycling muscles. Long term chronic
12
overloading of these muscles possibly enhances the presence of
SO fibers. Endurance athletes possess a higher percentage of
SO fibers in their trained muscles yet a normal percentage of
SO fibers in their untrained muscles. Figure 4 presents a
comparison of muscle fiber type between competitive, elite,
and untrained cyclists. Leg muscles of world-class sprint
cyclists, however, may show a predominance of FOG and FG
fibers. While a high percentage of one fiber type may suggest
potential for a specific mode of cycling, fiber type dominance
has not been shown to a determinant of success.
Pedaling Efficiency
Optimal pedal rates selected by different cyclists are
often a factor of cycling experience and skill level. Racing
cyclists tend to acquire the skill to ride at a cadence above
90 rev.min-1, whereas, recreational or novice cyclists tend to prefer lower pedal rates. The highly skilled cyclists
working at a constant power output (75% .O2max) at varying
pedal rates of approximately 70, 95 and 126 rev.min-1 are most economical with a preferred range of 80 to 120 rev min-1. At
80% of .O2max the most economical pedaling rate has been shown
to be slightly below 90 rpm. It has been suggest that
pedaling at 90-100 rpm may minimize peripheral forces and
therefore peripheral muscle fatigue even though such a rate
may result in a higher oxygen uptake.
13
Among the variables that affect pedaling efficiency,
pedaling rate is the most sensitive, followed by the crank arm
length, seat tube angle, seat height and longitudinal foot
position on the pedal. Seat tube angle decreases as the
cyclist size increases. A decreased tube angle shifts the hip
axis backward relative to the crank axis. Consequently, the
taller cyclist, with larger leg segments, will benefit from
shifting to a more rearward position. Conversely, the
shorter cyclist whose leg segments are smaller will benefit
from shifting to a forward position. Longitudinal foot
position increases with the cyclists size. Taller cyclists
will benefit from placing their foot further back on the
pedal. The seat angle should be adjusted to the cyclist to
realize minimum joint moments.
At a 120 rpm the duration of a crank cycle is 500
milliseconds (ms); half of the crank cycle lasts 250 ms.
Coincidentally the duration of twitch response of the
quadriceps muscle is about 250 ms. The relaxation time of
the quadriceps muscle after electrical stimulation is 103 ms.
When pedaling at 120 rpm the relaxation time represents a
crank rotation of 72 degrees. The inability of the muscle to
contract and relax more rapidly could explain why the force
continues further into the crank cycle than is desirable.
The forces applied to the pedals become less optimally
directed as the pedaling rate is increased. The average for
the effectiveness index, the ratio of the force applied
perpendicular to the crank arm to the force applied to the
14
pedals, decreases from 0.5 to 0.35 as the pedaling rate is
changed from 40 to 90 rpm at a power output producing 60% of
.O2max. The relationship that exists between the velocity
(speed) of muscle shortening and the tension it is able to
generate is an important constraint, or limiting factor in the
performance of rapid pedaling rates. Racing cyclists
typically spin at about 90 rev min-1 in cruising situations.
The tension a muscle is able to exert decreases as the speed
of muscle shortening increases. According to the force-
velocity relationship, the force that a muscle can exert is
inversely related to the speed of shortening. Thus, the
possible limitation set by the force-velocity relationship is
noteworthy when trying to apply large forces to rapidly
turning bicycle pedals.
Speed of limb movement has a marked effect on the gross
efficiency of work output. Efficiencies of 19.6% to 28.8%
have been reported in the literature. At high power output a
decrease in efficiency is not evident when pedal rate is
increased while holding power output constant. There appears
to be a significant advantage in employing a high pedaling
rate at high power output. Even at a pedal rate of 130 rev
min-1 a 22% gross efficiency has been observed.
Peak muscular efficiency generally occurs at a velocity
of approximately one-third of the maximal shortening velocity
in both SO fibers and FG fibers. SO fibers have been shown
to work most efficiently at a shortening velocity of about one
fiber length per second. A knee extension at 200° per second
15
requires the vastus lateralis muscle to shorten at about 90 mm
per second. The average muscle fiber length in the vastus
lateralis is about 72 mm, therefore a fiber shortening at 90
mm per second would be equal to approximately 1.2 fiber
lengths per second.
When pedaling at 80 rpm the knee extension velocity is
approximately 200° per second which is the velocity of peak
efficiency in SO fibers. Therefore, the 80 rpm pedaling speed
is close to the estimated peak efficiency in SO fibers. FG
fibers of endurance athletes are at their velocity of peak
efficiency when contracting at approximately 3 fiber lengths
per second. It has been predicted that efficiency is
approximately two-fold higher in SO compared with FG fibers
when cycling at 80 rpm. This thesis is supported by the
observation that SO muscle fibers are 2-3 times more efficient
than FG fibers. It should be made clear, however, that during
pedaling at high rpms almost all fibers, regardless of type
are recruited and share in the force generating effort. The
percent of SO fibers involved appears to relate positively to
a desired pedaling of 80 rpm.
Shoe and Pedal Merits
Cycling shoe design reflects the nature of forces applied
by the cyclists to the pedal-crank system of the bicycle.
Efficient pedaling action is a circular motion with a
repeating pattern of force application. The magnitude of the
16
force and the angle at which the force is applied vary
continuously throughout the pedal-crank rotation.
Crank rotation is dependent upon forces applied
perpendicular to the crank. At the bottom of the stroke the
total force is quite large, however, it is applied almost
parallel to the crank arm representing wasted force. At 90
degrees after top dead center (TDC) the force is applied
approximately perpendicular to the crank. At this point the
effective component is much larger. When the force is not
perpendicular to the crank, it is wasted. Pedal-crank
motion throughout the second 180 degrees of rotation often
results in force applied opposite to the desired direction.
During this "recovery phase" the goal is to introduce as much
positive effective force as possible. That is, to retain the
propulsive phase as long as possible. To do so, requires that
shoe and pedal design as well as cycling technique be given
special attention. Not only must the shoe ensure comfort and
safety but its interface between the cyclist's foot and
bicycle pedal provide effective transmission of force.
Negative peak torque represents lifting the foot during
the recovery phase by the opposite pedal. Experienced
cyclists do not significantly pull up on the pedal during the
upstroke. Rather, the larger peak torque observed during high
power output is attributable to recruitment of a larger
quantity of leg muscle per crank revolution.
While pushing down onto the pedal the major pressures
occur in the forefoot. The primary load bearing areas are
17
first metatarsal head region and the hallux. During steady
speed cycling, the most important interaction of the pedal
with the foot occur at the first metatarsal head, the lesser
metatarsal heads and the hallux.
Positive peak torque occurs within the range of 90° to
110° of the power phase of pedaling. A posterior foot
position instead of an anterior position decreases the
dorsiflexing ankle load moment and increases the gluteus
medius and rectus femoris activity. At the same time, there
is a decrease in soleus muscle activity but the hip and knee
moments are not changed.
CRANK LENGTH
Crank lengths between 165-180- mm at 2.5 mm increments
result in different energy costs. Cost function increases
with body size because a taller cyclist requires greater
kinematic joint moments than others to move the crank due to
the increased mass. Also, the moments of inertia of the
larger lower limb segments increase the cost. Optimal crank
arm lengths are seen to increase with increased body size. A
taller rider requires a longer crank arm than a shorter or
average cyclist. As the crank arm length increases, cadence
decreases as the rider's size increases. The longer crank
length requires low pedal forces resulting in a decrease in
static moments. Yet, a longer crank arm demands more motion
18
from leg segments. Thus, crank arm length and pedaling rate
effects are opposite.
Muscle Recruitment
Electromyographic (EMG) studies have been used to
identify the specific muscle involvement during the power and
recovery phase of pedaling. For a review of muscle
involvement see Faria and Cavanagh, 1978. The muscles which
are employed in cycling include the rectus femoris, vastus
lateralis and medialis, semimembranosus, biceps femoris,
tibialis anterior, gluteus maximus and gastrocnemius. The
illiopsoas like the rectus femoris, is partly responsible for
the motion of the leg during the recovery phase of the pedal
path. The vastus medialis and lateralis of the quadriceps
group extend the knee. The rectus femoris , part of the
quadriceps group, crosses both the hip and knee joints. Thus,
it both flexes the hip and extends the knee. The biceps
femoris long head, part of the hamstring group, crosses the
two joints, and by doing so serves to extend the hip and flex
the knee. The semimembranosus also crosses two joints, the
hip and knee, thereby it functions to both extend the hip and
flex the knee.
Lying in front of the knee joint is a small, flat and
triangular shape bone, the patella or knee cap which slides
along in a groove at the end of the femur. The efficiency of
the knee extensors is radically improved by the presence of
19
the patella. These muscles, the one-joint vasti group and the
two-joint rectus femoris, together make up the quadriceps;
all of these muscles terminate in the same tendon, which may
be felt just above the knee cap when tensing the quadriceps.
The patella increases the turning effect of the quadriceps by
moving the line of action of their force further from the
center of rotation of the joint.
Muscle activity is seen to increase with increased pedal
speed. However, there is a lack of increase in the gastroc
activity at higher pedal loads. The lack of a marked decrease
throughout the maximum activity regions in quadriceps is seen
at lower pedal loads. It is clear that the onset of muscle
activity for all muscles in the quadriceps group occurs well
before 0° or TDC. The rectus femoris begins its activity
close to the middle of the recovery phase (200° to TDC) only
to terminate contraction at about 120-130°. Its greatest
activity is observed from just prior to TDC, which is greater
than 50% maximum, for a brief period between 30° before TDC to
30 after. The onset of activity of the vasti appears later
than that of the rectus femoris. Both vasti muscles exhibit
greatest activity between 340° and 100°. At about 40-50°
later than the rectus femoris the vasti muscles turn on.
Quadriceps group activity terminates at about the same angle.
The biceps femoris region of greatest activity is between 80°
and bottom dead center (BDC). While the greatest activity for
the other hamstring occurs in the region from 60° to 240°.
20
The gluteus maximus is active from TDC to about 130°.
This activity is within the region of the power stroke (25-
160°). It greatest activity (>50%) has been observed between
10° and 110°. This represents the power stroke when the hip
is being extended. Just after TDC the biceps femoris and
semimembranosus exhibit the largest region of activity to the
middle of the recovery phase. In the lower leg, the tibialis
anterior muscle is active in the second half of the recovery
phase from about 280° to just past TDC. At about 30° the
gastrocnemius begins to contract and terminates at about 270°.
Activity of the gastrocnemius begins a few degrees after
termination of the tibialis anterior. Gastrocnemius activity
terminates a few degrees prior to the onset of the tibialis
anterior. It is interesting to observe that the gastrocnemius,
a knee flexor, active when the quadriceps are extending the
knee (45° to 110°) quadriceps and hamstrings. Consequently,
there is little co-contraction of agonist/antagonist muscles.
From TDC to 90° the active muscles include the gluteus
maximus, the muscles of the quadriceps group, and
gastrocnemius. From 90° to 270° the active muscles are
limited to the gastrocnemius and the hamstrings. Active
muscles from 270° to TDC include the tibialis anterior and
rectus femoris.
During pedaling, the hip and knee are very different in
their actions. Hip movement is extensor. Knee movement is
first extensor and then flexor. There appears to be dominance
of knee extensors over hip extensors in the first quadrant of
21
the pedal revolution. In the second quadrant of pedal
revolution substantial reduction of knee extensor activity is
observed. Muscle activity during pedaling is characterized
by little co-contraction of agonist/antagonist muscles. This
is especially true for the gastrocnemius/tibialis anterior and
at the ankle and hamstrings/quadriceps at the knee. If the
knee extensor muscles were to develop moments in excess of the
flexor moment generated at the knee by the two joint extensors
it would created an extremely uneconomical metabolic event.
Saddle Height
The saddle height should be 97% to 100% of trochanteric
leg length and 109% of the symphysis pubis height. Trochanter
length is the distance measured from the greater trochanter to
the floor with the subject standing straight-legged on bare
feet. Seat height is the distance from the top of the seat to
the top surface of the pedal platform, measured along the seat
tube with the crank arm in the down position but parallel to
the seat tube. These heights result in the most efficient use
of available energy. A lower seat results in greater
quadriceps force and thus higher muscle activity.
Aerodynamics Of Cycling
Air resistance is the major retarding force affecting
cycling. Wind forces of just 10 miles per hour begin to
significantly load the racing cyclist. A cyclist traveling at
22
20 mph typically displaces approximately 1,000 pounds of air
per minute. At that speed about 70 percent of the power
consumption is due to the air's resistance to the rider and 30
percent to the air's resistance to the bicycle. However, if
the cyclist bends the elbows and crouches with the torso
nearly parallel to the ground, the wind resistance is lowered
by approximately 20 percent. When a rider assumes a position
of hands on center of upper handlebars, chin resting on the
hands, and the crank parallel to ground, the wind resistance
is lowered by about 28 percent.
A bicycle moving through still air leaves a trial of
moving air, and loses the energy taken to set this air in
motion. Drag is the force that transfers this energy from the
bicycle to the air. Drag is very costly, for example, at 10
mph, 50 percent of a cyclist's energy goes into cutting
through the air; at 30 mph, 90 percent of energy is spent over
coming drag.
The rough-edged shape of the human body is an ideal model for
generating drag. The cyclist and bicycle are affected by two
forms of aerodynamic drag: First, when the flow of air fails
to follow the contours of the moving body, pressure drag is
created. When air is separated of from the body the
distribution of air pressure is changed. This separation
occurs toward the rear of the body. The air pressure at that
location becomes lower than it is on the forward surface,
resulting in drag. Second, skin-friction drag results from
the viscosity of the air. Friction is caused by the layer of
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air immediately next to the body. Projecting objects from the
bicycle frame or cyclist, cause airflow to separate from the
surfaces. Newly created low-pressure regions form behind the
projections result in pressure drag. However, air flows
smoothly around a streamlined shape closing in behind as the
body passes.
Head winds, tail winds, and crosswinds significantly
influence both aerodynamic drag and the power requirements.
For example, a cyclist traveling at 18 mph in still air must
increase the power output by 100 percent to maintain that
speed against a head wind of 10 mph. This change in power
output is best accomplished through changing gears. A tail
wind makes the bicycle go faster. A pure tail wind or head
wind will speed up or slow down the rider slightly more than
half the wind speeds. A rider going 20 mph with a 10 mph tail
wind is capable of traveling about 26 mph. A 10 mph head wind
will slow the same rider to about 14 mph. Overall, wind will
speed up or slow down a bicycle by about half the wind speed.
Though when drafting in the wake of another rider the power
requirements of the drafting rider are reduced by about 30
percent, tandem riders use 20 percent less power per rider
than two separate cyclists.
Aerodynamic drag increases as the square of the
velocity. Power is proportional to the product of the drag
force and velocity, so that the power needed to drive an
object through the air increases as the cube of the velocity.
Therefore, a small increase in speed requires an enormous
24
increase in power. The rider who suddenly doubles power
output, while traveling at 20 mph, will increase speed to only
26 mph. The point is that high speeds require extremely high
aerodynamic efficiency.
Four methods are effective in decreasing the wind
resistance of bicycling: 1) Reduce the frontal area of the
rider and bicycle; 2) Improve airflow around the shoe by
eliminating straps and toe clips. A drag decrease of about
0.08 pounds at 30 mph results from a cleaner shoe profile.
Spandex shoe cover reduces drag by 0.12 pound. With
particular streamlined shoes, drag may be reduced from 0.25 to
0.40 pounds. 3) Reduce air turbulence of the bicycle parts.
Aero tubing reacts better in cross wind than standard tubing.
Smaller wheels, fewer spokes, narrower tires, narrow hubs,
aero rims, covered wheels and aero spokes all lower drag; and,
4) Streamline the accessories. Even an inefficiently
streamlined water bottle adds almost 0.2 pounds of drag at 30
mph to the bicycle system. Sheathed cable adds about 0.03
pound per foot of drag if it is crossed to the wind. Bare
wire adds much less. A faired wheel has a much lower drag,
about one-quarter that of the plain wheel. Clothing can
significantly affect drag. A one-piece, full-length suit of
Lycra Spandex material with an aero hood will reduce overall
wind drag by about 11 percent. A streamlined helmet reduces
drag by 7%. From a practical view point, a 0.02 pound
decrease will lower the time for a 4000-meter pursuit by about
0.3 seconds. The maximum drag decrease possible, using
25
traditional equipment as standard, is about 1 pound at 30 mph.
A 1 pound decrease will result in 13 seconds faster for 4000
meters.
When riding in groups, cyclists behind consume less
energy by being partially shielded from the wind. Therefore,
the use of pace lines becomes an important race tactic. Even
touring cyclists of equal ability riding in a group can travel
from 1 mph to 3 mph faster than any lone rider. Cyclists
traveling in the wake or "slipstream" of those in front may
lower their wind resistance significantly. This is
accomplished by taking advantage of an artificial tail wind.
That is, the air is already moving forward when they reach it.
For example, two cyclists in a pace line at 24 mph, the front
cyclist consumes the same energy as if riding alone. However,
the cyclist following requires about 33% less power output.
At this speed, reduction in wind resistance is about 38%.
However, since rolling resistance is unaffected by
slipstreaming, the decrease in external power required is
smaller (33%).
The closer one cyclist follows another, the greater the
drag reduction. The total wind resistance decline averages
44% for 1.7 m between riders or a zero wheel gap, and only
about 27% average for 3.7 m between riders on a 2 m wheel gap.
Implications For Training
Lactate Threshold Training
26
The production of force by muscles used for cycling is
dependent upon a steady supply of energy. The form of energy
used for all the muscles' operations is the compound produced
inside the fibers, adenosine triphosphate (ATP). Possible
sources of ATP include the ATP stored in the muscles, that
produced from the aerobic breakdown of carbohydrates and fats,
and ATP produced anaerobically from muscle glycogen. Because
the quantity of ATP stored in the muscle is limited, enough
for three to five seconds of maximum effort, it must be
continuously manufactured.
Carbohydrates, fats, and protein, when broken down,
provide the energy bound into the ATP molecule. Within the
muscle cells special structures called mitochondria use
foodstuffs and oxygen (aerobic production) to produce large
amounts of ATP. The muscle can also produce ATP without
oxygen (anaerobic production), however, this method is
inefficient and limited for exercise of 20 to 60 seconds.
In order to speed the rate of energy production,
aerobically and anaerobically, the muscle cell employs
specialized proteins called enzymes. High intensity cycling
raises the muscle's lactic-acid level. Lactic acid is a
strong acid that ionizes and releases hydrogen ions. These
hydrogen ions can exert a powerful effect on other molecules
due to their small size and positive charge. Hydrogen ions
attach to molecules thereby altering the molecule's original
size and shape. The altered size and shape disrupts the
normal function of the molecule (enzyme) and therefore
27
negatively influences normal metabolism of the cell.
Increased intramuscular hydrogen ion concentration can impair
exercise performance by reducing the muscle cell's ability to
produce ATP by inhibiting key enzymes involved in both
anaerobic and aerobic production of ATP. The hydrogen ions
released by lactic acid block the breakdown of glucose. Also,
hydrogen ions compete with calcium ions for binding sites on
the muscle's contracting units, thereby hindering the
contractile process.
High lactic-acid levels, however, can be a good sign
because it indicates the capability of producing a lot of
energy "anaerobically" and the potential for high speed
cycling is excellent. If not controlled, however, the
increased muscle cell acidity has the potential to eventually
reduce muscle contraction resulting in fatigue. The muscle
and blood acidity level is expressed numerically in units of
"pH" which represents the concentration of hydrogen ion. The
pH of body fluids must be regulated (i.e., normal arterial
blood pH = 7.40± .02) in order to maintain homeostasis. Heavy
exercise can present a serious challenge to hydrogen ion
control systems due to lactic acid production. During high
intensity exercise acids accumulate inside the muscles which
can drop the pH to 6.9, then to 6.8 or even 6.6 during which
the muscle is unable to produce energy or contract
effectively. These acid-induced slow downs are avoidable if
the buffering capacity of the muscle is sufficiently high. A
buffer resists pH change by removing hydrogen ions when the
28
hydrogen ion concentration increases, and releasing hydrogen
ions when hydrogen ion concentration falls. The ability of
buffers to resist pH change rests on the individual buffers
ability to act as a buffer and the concentration of the buffer
present. The greater the concentration of a particular
buffer, the more effective the buffer may be in preventing pH
change. As the body's buffering capacity is improved the
ability to sustain a punishing sprint pace the last 400 to 800
meters to the finish will be enriched.
The training necessary to improve buffering is called
lactic-acid (LAT) training and is unique and different from
that used to enhance the lactate-threshold. The purpose of LAT
is to promote a "tolerance" for lactic acid or the ability to
continue to cycle fast even though the muscle cells increase
their production of acid. The goal is to gain the ability to
produce some lactic acid without suffering from large drops in
muscle pH. This tolerance enhances the ability to suddenly
sprint for a "breakaway" without suffering the consequences
sudden fatigue.
The principle of LAT training is to cycle for a short
period of time, raising the muscle-lactate level and lowering
muscle pH. The muscles are then allowed to recover for a
brief period of time followed by a repeat of high intensity
cycling. This sequence is repeated several times during a
training session. LAT results in enhanced buffering capacity
through the increase in the muscle cells creatine phosphate, a
high-energy compound which is also a buffer, and the
29
augmentation of special buffering proteins inside the muscles.
The muscles' ability to produce bicarbonate, an effective
buffer, is enhanced as is the muscle cells' ability to diffuse
lactate acid into the blood. LAT training will also result
in an increase in concentrations of phosphofructokinase, a key
muscle enzyme involved in anaerobic energy production.
Three LAT protocols appear to be effective: 1) 60-second
work intervals at close to top speed, with 2.5 minutes of
recovery between intervals; 2) 90-second work intervals at
close to maximal intensity, with 4 minutes of recovery; 3)
120-second near-top-speed intervals, with 5 minutes of
recovery between each. It is important not to extend the work
interval beyond two minutes. A longer work interval lowers
the intensity leading to a lower lactic-acid production, small
reduction in muscle pH, and an attenuated stimulus to enhance
buffering capability. Equally important is the recovery
interval. In general, the recovery interval should be about
two to three times as long as the work periods in order to
allow enough recovery so that work intervals remain at a very
high intensity. Four to 12 minutes of near-maximal cycling
per LAT training session is recommended. This time includes
only the work interval and not the recovery period. A
training session, for variety, may include a mix of 60-, 90-,
and 120-second LAT intervals.
Since LAT is so intense no more than one LAT session per
week is recommended and only after a solid mileage base has
been established. LAT should not be included during tapering
30
periods. Moderate quantities of LAT will help road cyclists
cope with race surges in intensity, accelerations during
longer racers, and sprints to the finish.
LAT training is ideal for the track racer, however, for
endurance cyclists, especially whose muscles are mainly
composed of slow-twitch muscle fibers, LAT should be limited.
There is a limited amount of energy and fuel available for
muscle use which may be channeled into improving buffering
capacity and anaerobic power. The resources for maximally
enhancing aerobic power, aerobic structure and enzymes could
then be reduced. Therefore, too much LAT performed by the
endurance athlete might reduce cycling economy.
Hill training sessions enhance both economy and .O2max.
The type of hill training which increases economy is quite
different from the inclined workouts which bolster the aerobic
qualities of the quadriceps. Both long, gently sloping hills
at 8 to 10 percent grade, and those of 20% or more incline
should be included in training. The hills may vary in length
from 200 meters to several miles. The ideal site is a six- or
seven-mile course with nonstop undulations of the flat-ground
portion no more than 25-30 percent of the total cycling.
A method of establishing intensity during the hill
sessions is to train at a pace that feels about as hard as
when cycling at anaerobic threshold speed, even though the
actual pace will be slower. Alternatively, the heart rate,
which should be about 85-87 percent of maximum during the last
two-thirds of the session (85% of maximum corresponds with 76-
31
percent .O2max intensity). The first few climbs should not be
excessively fast, rather intense to the level that each
successive climb may be equally intense. The goal is to train
at steady-state intensity. Six weeks of hill training can
increase the concentrations of enzymes in the quad muscles by
approximately 10 percent. An alternative to this steady-
intensity hill training is to alternate two minutes of hard
cycling at a pace that feels like a race pace or faster with
two minutes of easy cycling, and continue this pattern for
five to six miles. Over a period of several weeks, gradually
reduce the length of each easy-cycling period to only one
minute.
To enhance economy choose a fairly steep, 300- to 800-
meter hill, and surge up the incline at close to full speed on
every other repetition. Coast down the hill after each ascent
and then circle until rested enough to charge up the slope
again. A minimum of three of these type of training sessions
per month is suggested.
Recent evidence from the Netherlands suggests that two
weeks of super high-intensity training can be very rewarding.
The protocol is to, during two weeks, increase the total
training time 5 hours per week and the quantity of high-speed
interval training 7 hours per week. The overall intensity
training should represent 63% of the total workout time. The
intense intervals should be carried out at 90-100 percent
.O2max (93-100 percent of maximal heart rate), with one-to
three-minute work and rest intervals and five to 30 work
32
intervals per training session. Following the two weeks of
super intense training expect to experience negative feelings
of tiredness. However, two weeks after the over training
sessions have ended new performance peaks may be expected.
Expected modifications include increase in maximal power, less
lactic acid during top-speed cycling, and about a 4 percent
improvement in performance.
Aerobic Training
Aerobic conditioning should represent the bulk of the
road cyclists' training. The concept employed is sizable
volumes of continuous, long-distance cycling at below race
pace. The pace should allow conversation while cycling.
Training sessions may last 2 hours or more.
Aerobic conditioning is typically performed at 60% to 75%
of maximal oxygen uptake (.O2max) pace. This pace is equal to
a training heart rate of approximately 70% to 80% of heart
rate reserve, i.e., [(Max HR - Rest HR) x (.75) + (Rest
HR)]. Cycling slower than 60% of .O2max pace results in little
measurable aerobic improvement. Cycling faster than 75%
.O2max pace may causes excessive glycolytic (anaerobic)
activity.
The focus of aerobic training is the engagement, as much
as possible, of fatty acid metabolism. Short rides of 10 to
20 miles and longer rides from 30 to 60 miles are recommended.
The goal of this training is to improve oxidative capabilities
in cardiac and skeletal muscle cells.
33
The purpose of this training is to increase the quantity
of stored fuels (carbohydrates and fatty acids) as well as the
number and size of mitochondria in the stimulated muscle
cells. Through increasing blood volume and capillary density
in trained muscles improved oxygen delivery and carbon dioxide
removal results.
This form of aerobic training will stimulate primarily
the slow- twitch skeletal muscle motor units. In response to
training, during a ride fewer motor units are required to
maintain a given pace while those activated do not need to
work as hard as before for the same given maximum work output.
Their training response is reflected in their ability to work
at a given submaximal intensity with less fatigue. The result
is improved cycling economy because less muscle activity is
required and thus less oxygen consumption is required in
producing movement.
The benefits of aerobic training include: 1) An increase
in oxidative and glycolytic enzymes in working muscles; 2)
Activation of additional slow twitch muscle fibers that were
not stimulated by less intense training; and, 3) A small
increase in blood buffering capacity.
Anaerobic Threshold Training
Anaerobic threshold training is aimed at raising the
anaerobic threshold. In addition, it serves to train those
muscles involved in high pedal rates. Effective
34
aerobic/anaerobic conditioning requires a pace range from just
slower than road race pace to a pace just beyond
lactate/ventilatory threshold (Tvent). To be effective this
pace or work intensity is beyond that which blood lactic acid
begins to accumulate at an increasing rate. Training at a
pace slightly faster than the Tvent level optimally stimulates
those physiological mechanisms responsible for the anaerobic
threshold enhancement. The reward is ability to sustain a
faster pace for a longer period of time.
Exercise physiology laboratories are equipped necessary
to measure an individual's anaerobic threshold (AT). Once the
AT is determined the oxygen uptake value at the AT is divided
by the maximal oxygen uptake in order to determine the percent
relationship. For the trained endurance cyclist, the AT .O2
should be at least 80% the .O2max.
The heart rate at the AT may be used as a guide for
training intensity. An effective training protocol is to
cycle at the AT HR for anywhere from 15 to 30 minutes. The
training heart rate should represent between 80-90% of the
.O2max. An example training session would be a 20 minute ride
at the AT HR followed by a mile recovery and a 15-min ride at
the AT HR. This faster paced training should be sustained for
a period long enough to initiate physiological adaptation, yet
not so long that needless training discomfort occurs. Cycling
intervals of 4 to 10 minutes are also very beneficial. The
key to success in aerobic/anaerobic interval training is to
manipulate the rest intervals so that repeated work intervals
35
are performed at racing speed with rests of only 30 to 45
seconds. Limit this type of training to 2 or 3 times per
week.
It is difficult and impractical to measure oxygen uptake
during training, however, it is important to know at what
percentage of maximum oxygen uptake training intensity
represents. Intensity monitoring can be accomplished with the
use of a heart rate monitor or simply counting the pulse while
cycling. An effective method used to establish the training
intensity is the application of the relation between percent
.O2max and percent max heart rate. Figure 3 shows that in
order to train at 85% .O2max the corresponding intensity is 90%
heart rate max. For example, if an individual with a maximum
heart rate of 195 beats.min-1 wished to train at 85% of .O2max the training heart rate would equal approximately 176
beats.min-1.Tapering for Competition
Most athletes know that the optimal way to taper for
competition is to reduce dramatically the intensity and
duration of training sessions and consume plenty of
carbohydrates and liquid. Proper tapering periods relieve
fatigue and enhance certain performance-related variables,
such as lactate-threshold and cycling speed. An investigation
of several tapering protocols reveals that a six-day tapering
procedure produces impressive results. The six-day tapering
protocol is the following: Day 1- 40 minutes of exercise;
36
Day 2 - complete rest; Day 3 - 40 minutes of exercise; Day 4
- 20 minutes of exercise; Day 5 - 20 minutes of exercise; Day
5 - 20 minutes of exercise; Day 6 - complete rest. The
intensity of training during the taper should be maintained at
the same exertion level utilized during the regular training.
Thus, only the volume of training is reduced between 60-70
percent during tapering.
Through following this tapering protocol several
advantages can be realized. Lactate threshold may be higher
than it has been prior to the taper, muscle-enzymes
concentrations remain high, muscle glycogen stores are
significantly enhanced. The implications for the six-day
taper are clear: First, it is an effective way to improve
lactate threshold. Second, tapering periods may be
effectively used during regular training. For example, a one-
week tapering period might follow each six-week training
period in order to realize the benefits of the taper.
Finally, prior to race day not only is a sense of physical
recovery evident but lactate threshold is higher, muscle
glycogen is higher, and muscle enzyme levels remain high all
of which will enhance overall performance capacity.
References
1. Burke, E. R., I.E. Faria, and J.A. White, Cycling. In:
Physiology of Sports (Ed.) Reilly, T., Secher, N., Snell, P.
and Williams, C. New York: E. & F. N. Spon, 1990.
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2. Coyle, E. F., M. E. Feltner, S. A. Kautz,, M. T. Hamilton,,
S. J. Montain,, A. M. Baylor,, L. D. Abraham,, and G. W.
Petrek, Physiological and biomechanical factors associated
with elite endurance cycling performance. Med. Sci. Sports
Exerc., 23:93-107, 1991.
3. Davis, R., M. and Hull. Measurement of pedal loading in
bicycling: II. Analysis and Results. J. Biomechanics
14:857-872, 1981.
4. Faria, I.E. Applied Physiology of Cycling. Sports Med.
1:187-204, 1984.
5. Faria, I.E. Energy Expenditure, Aerodynamics and Medical
Problems in Cycling - An Update. Sports Med. 14:43-63,
1992.
6. Faria, I.E., and P. R. Cavanagh, The Physiology and
Biomechanics of Cycling. New York: John Wiley and Sons,
1978.
7. Garnevale, T. G. and G. A. Gaesser, Effects of pedaling
speed on the power-duration relationship for high-intensity
exercise. Med. Sci. Sports Exerc., 23:242-246, 1991.
8. Kyle, C. R. The Mechanics and Aerodynamics of Cycling, In:
Burke, E. R. (Ed), Medical and Scientific Aspects of
Cycling, Champaign, IL: Human Kinetics Books, 1988, pp. 235-
251.
9. Lafortune, M. and P. Cavanagh, Effectiveness and efficiency
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10. Patterson, R. P. and M. I. Moreno, Bicycle pedaling
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Cambridge, MA.: MIT Press, 1982.
39
FIGURE LEGENDS
Figure 1 - The relationship between cycling speed and
kilocalorie cost per minute.
Figure 2 - Summary of the mean maximal oxygen consumption
values (ml.kg-1.min-1) of several national and international
cycling team members.
Figure 3 - The relationship between the percent of maximal
heart rate (beats per minute) and percent of maximal oxygen
consumption. Five example points are plotted.
Figure 4 - The variability of percent of slow-twitch oxidative
(SO), fast-twitch glycolytic (FG) and fast-twitch oxidative
glycolytic (FOG) thigh muscle fiber types found for
competitive and elite road cyclists and untrained riders.
40