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

                                      Time sec


    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)




***************Follow Up


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

8yr olds.



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.