Pace makes the race?
Back in the late 70's and early 80's I was doing research on animal
locomotion, physiology, and sports training techniques while doing my
graduate work in engineering. At that time my hobby was breeding, training,
and racing sled dogs ( before geting involved with horses).
The following is an engineers approach to modeling the energy supply
that impact on the running of a race (pace).
Most of the research info was on humans with some on horses.
Energy Source When Available
Phosphate First 15-20 sec., stored in the muscles,Energy required to
run a 220 yd run for humans or 1/4 mile horse,
the recovery time is 1-2 min after an event
This is the energy used at the start and used
in the stretch for the final kick. Sometime a
a horse can be pressured during the race and
use his remaining reserves.
(Note: Quarter horse races could be done with heats)
Do they do this??
Glycogen Major energy source after phosphate and before
full oxygenation (VO max). Stored in the muscles
as carbohydrates with a max value of 2000-3000
calories in humans. During this stage the respiratory
system is increasing base on the demand level.
During this process lactic acid is produced.
The level of lactic acid generated is based on
the difference between demand and what part oxygenation
is covering and the time of the event. The time
threshold appears at 45-60 sec for full out events.
The threshold varies based on animal condition.
After 60 sec is when the respiratory system is
starting to provide the major part of the energy
from oxygenation of the carbohydrates. A human
runner will use about 100 cal/mile, which is
one reason marathon runner hit the wall at 21
miles unless they carbohydrate load. The respiratory
system will peak from 4-10 min based on conditioning.
Note: When a horse bleeds in a race a significant
loss in performance will occur after the 50 sec.
point in the race.
Note: lactic acid ~ oxygen debt
What does the above have to do with pace?
Each horse has different levels of phosphate, glycogen, and VOmax. At
the start each horse will use phosphate as the energy for the 1st 1/8 mi.
or more depending on the horses running style or jockey. If a jockey is
urging a horse harder at the start to get position there might not be
any phosphate for the stretch run. Once the phosphate are used up the
horse will have to slow down so that the energy can be replace via oxygenation.
Sometimes a horse reserves will be depleted during the middle portion
of the race because of pace or jockey positioning. After the start of
the race the second energy sources (glycogen) will come into play.
One of the by products of glycogen metabolism is the lactic acid. Each
horse depending on conditioning will be able to handle different levels
of lactic acid in the blood. The level of lactic acid is a function
of the demand work load and how much of the demand is being handled
from oxygen. For example: Work Load=40 lbs. Oxygen=20 lbs Glycogen=20 lbs
Faster lactic acid build up
Later in the race: Work Load= 35 lbs Oxygen=30 lbs. Glycogen =5 lbs
As I mentioned earlier the respiratory system will start to supply the
energy thru oxygenation in the later part of the race. Respiratory
system starts after a time lag of 15-20 sec and builds up exponentially
(Oxy=VOmax*(1-e^(-time/tau)) tau - time constant for respiratory system)
until VOmax is reached (4-10 min). Thus most racing is run at levels
where the horse will not get to VOmax.
The time to VOmax is a function of many factors:heart
and lung capacity , resistance within the respiratory system (from nostrils
to lungs), capability of the lungs to process the oxygen, and other
Other factors which impact performance: percent fast to slow muscle
fibers, shortening velocity of the muscles, conformation, etc.
Force| \ <- Demand work load curve for race --|
Level| \ |
| \________ v
| . --------------- _____________________
| .<- Phosphate ^ .........
| . Diff. Glycogen- --> v . <-Oxygen curve --^
0 10 20 30 40 50 60 70 80
Conclusion: If a horse can conserve phosphates at the start of
the race and control pace he will have reserve phosphate for the stretch
run. Control pace - maintain race pace at a level such that lactic
acid is below limit and have phosphate in reserve.
Start of race:0-20 sec Demand = phos + gly
Middle of race:20-60 sec Demand = gly + Oxy(% of VOmax) + phos (reserve)
End of race: 60-72 sec Demand = gly + Oxy(higher % of VOmax) + phos
Phosphate can be used any time during the race and once depleted
the horse has to slow down to recover. If the lactic acid level is
hit during the race the horse will also have to slow down to recover.
Routes have a lower demand at the start (more reserve phosphates) and
oxygenation becomes more important because of the longer race.
The above is a simplified explanation about how different energy sources
impact on the running of a race and why pace (demand work level) becomes
important. All of the above is my own interpretation of the literature
I collected in the late 70's and early 80's.
(See Scientic America, Mar 1972 Vol 226, No.3, "The sources of Muscular
Energy", by Rodolfo Margaria)
I would like to thank everyone for the positive response to my post
on pace and energy used. My post has brought up some question which
I will answer the best I can.
Some of the following will come from"Acta vet scand. 1974, 15 287-309"
"Fiber composition, enzyme activity and concentration of metabolites
and electrolytes in muscles of standardbred horses" by Arne Lindholm
and Karin Piehl, Stockholm, Sweden
"The Physiological and Biochemical response of standardbred horse to
exercise of varing speed and duration" Arne Lindholm and Bengt Saltin
Phosphate or called creatine phosphate are stored in the muscles and
can be recovered within minutes after and event. Concentration levels
range from 12.2-23.4 mmol/kg wet muscle from young horses (0-1yr) up
Glycogen concentration levels:
0-1 yr 1-2 2-3 3-4 4-5 5-8
95 98 107 110 122 126 mmol/kg wet muscle
Glycogen can be replace after a couple of hours depending on the level
and duration of the work load.
The Swedish study show that after maximum trotting, glycogen stores
had been refilled within 48 hrs.
Also, in the study they found that work interval of 400 meters were
to short for generating significant levels of lactate in the blood or
muscles. The study conducted 6- 400 m heats with muscles biopsies and
blood samples taken after each heat. Samples were taken within 20 sec
and 2 min after the heat. A 5 min rest before next heat. The study also conduct heats at 700m, 1000m, and 2000m heats.
Interval training techniques have shown that work efforts of 10 sec
with rest periods of 30 sec can maintain lactic acid level constant.
Muscle samples of the gluteus medius muscle show three 3 major categories,
slow twitch (ST), fast twitch and high oxidative (FTH), and fast twitch
(FT). FTH percentage increase with age and training level.
Conclusion: The energy stores in the muscles can be replace within a
short time after a race. However, other factors will prevent or hamper
running the horse without a couple of days rest. After any maximum
work effort the muscle and bones will need time to remodel and adapt
to the work load demand. If you look at any training program 4-5 days
are need between maximum work efforts. Most race horses will only work
every 5 days with the first work after a race at 7-9 days. Most horses
are usually given the next 1-2 days off from training after a race.