Download Acids

400 m running, Acids & Bases
(The production of lactic acid and its
subsequent neutralisation to ensure a stable pH
level in muscles)
The 400 metres
The 400 m, an event which can trace its heritage back to the Ancient
Olympic Games of 724 BC, is widely recognised as one of the most
physically demanding single athletics races.
It is considered to be so demanding because the energy system (anaerobic
glycolysis) employed by athletes for sprinting normally only provides energy
for 30 to 40 s, a few seconds fewer than it normally takes to complete the
distance.
The 400 metres
Lactate is an unfortunate by-product of anaerobic glycolysis and acids
and bases will be explored in the following slides through this link to
sport. Lactate itself is not an acid, but it is closely related to the
substance lactic acid (which you may have heard sports men and
women talk about) and for the purpose of this module they will be
considered to be the same for simplification.
Energy provision in the body
The body has three main processes in replenishing ATP stores – the
energy needed for cells to work and subsequently for muscles to
contract.
The demand for ATP will determine which process is used by the body.
The processes are:
ATP PC
Anaerobic glycolysis
Aerobic glycolysis
Energy provision in the body (ATP PC,
anaerobic and aerobic glycolysis)
ATP PC – creates ATP quickly but only lasts 6-10 s.
This energy system would commonly be
used for sudden and very fast muscle
contractions needed in very explosive
power events such as the 100 m sprint,
high jump and long jump.
Energy provision in the body –
Anaerobic glycolysis
Anaerobic glycolysis – no oxygen required but only lasts for 30-40 s.
An unfortunate by-product of anaerobic glycolysis is lactic acid, which
must be removed from muscle cells to ensure continued function.
This can be done by providing oxygen to the
muscle cells after the anaerobic glycolysis process
with a cool-down exercise, keeping welloxygenated blood circulating to these muscle cells.
Energy provision in the body –
Aerobic glycolysis
Aerobic glycolysis is the most efficient, but slowest, energy provision
process, and requires oxygen.
With this process glucose is fully broken down into water and
carbon dioxide, which can be removed from the muscle cells easily by
the blood.
Acids and bases
Acids
An acid is a proton, or H+, donor,
i.e. it will donate a hydrogen ion to
another compound.
Lactate, in its acidic form, is lactic acid. It is a H+ donor, which makes
it an acid, hence its name.
Acids and bases
Bases
A base is a proton, or H+, acceptor,
commonly an OH- ion, i.e. it is a
compound which will accept the H+
ions from an acid.
pH – the measurement of
acidity levels
 The pH scale is used to measure whether a solution is acidic or a
base.
 Pure water at 25 oC has a concentration of H+ ions equal to that of
OH- ions and this is defined as neutral on the pH scale with a value
of 7.0.
 Acids have a higher concentration of H+ ions than OH- ions and so
have a pH value of less than 7.0.
 Bases have a lower concentration of H+ ions than OH- ions so have
a pH value of more than 7.0.
Changing pH levels in muscle
+
cells due to build up of H ions
The normal pH level of muscle cells is 7.1, but this
reduce to 6.5 with the build up of free H+ ions
released through the hydrolysation of ATP. The
increase of intramuscular lactate concentration also
produces an increase in H+ ions.
The acidic pH level of 6.5 can impair muscle contraction
and stimulate nerve endings in the muscles, resulting in
the sensation of pain.
Balancing of pH levels in muscle
cells (Lactate removal)
The body will neutralise (return to its natural state) the pH level of its
muscle cells in two ways – by removing lactic acid, or more accurately
lactate, or preventing the build up of it in the first place.
Lactate is removed from the local muscle cells, either by being
dispersed by the blood to less concentrated areas of the body, or by
being taken by the blood to the liver, where it is converted back into
glucose.
Balancing of pH levels in muscle cells
(Prevention of lactate production or
accumulation)
Lactate can be prevented from being produced by employing an energy
system such as aerobic glycolyis, which does not result in the
production of lactate.
NB: When insufficient oxygen is available lactate is produced
Balancing of pH levels in muscle cells
(Prevention of lactate production or
accumulation continued)
The accumulation of lactate can also be prevented by ensuring a rapid
& continuous supply of oxygen reaches the muscle cells after
anaerobic glycolysis has taken place.
The oxygen breaks down the lactate to pyruvate, which can be used to
fuel a separate energy cycle. A cool-down can help oxygenated blood
to reach the required muscle cells quickly.
Worksheet answers – Q1 & 2
1. What is the energy system employed by the body that
produces lactic acid as a by-product?
The energy system that produces lactic acid as a by-product is
anaerobic glycolysis.
2. Define the terms acid and base.
An acid is: An acid is a proton or hydrogen ion (H+) donator.
A base is: A base is a hydrogen ion (H+) acceptor, most commonly
a hydroxide ion (OH-).
Worksheet answers - Q3
3. What is the scale used to measure acidity? What value is
considered to be neutral on this scale and how is this neutral value
determined?
The scale used to measure acidity is known as the pH scale. The
value 7.0 on this scale is considered to be neutral. This is determined
by the fact that at 25 oC pure water has a concentration of H+ ions
equal to that of OH- ions and has a value of 7.0 on the pH scale.
Worksheet answers – Q4
4. The pH value of a muscle cell under normal conditions is 7.1.
This can drop to a pH value of 6.5 if extensive amounts of
anaerobic glycolysis has taken place. If this happens would the
muscle cell be experiencing acidic or alkaline conditions? (Explain your
answer).
If the muscle cell pH value dropped to 6.5 on the scale the muscle
cell would be experiencing acidic conditions. This is because any value
under the neutral value of 7.0 on the pH scale is considered to be
acidic.