What Causes Our Muscles To Fatigue?
just 40 minutes into your regular gym session, steadily
training away on the cross trainer. Normally you love the cross trainer,
you could go for hours on this machine … well perhaps one hour. However,
today your legs are burning, you feel like your heart is ready to burst
and you are probably going to cough up a lung at any stage. You taper the
intensity right back, but unfortunately your legs still seem to be giving
way on you. Why are you so tired? Are you not as fit as you thought you
were? This poses the question in your mind … what causes your muscles to
fatigue on you?
There are a range of different reasons that our muscles fatigue, and a
combination of these may be the reason for your muscles fatiguing during
exercise of a medium to long duration. Traditionally carbohydrate
depletion (glycogen) and dehydration have been seen as the key reasons
contributing to fatigue … however there are other reasons
that may be
When you exercise, especially in a warmer environment, your muscles
generate heat, which is carried by your blood to the surface of your skin
via capillaries. Your body needs to cool itself … so to counter this heat
your sweat glands release sweat in order to cool both the surface of your
skin as well as the blood underneath. This process is an important
temperature regulation mechanism. However the down side is that with this
loss of fluid through sweating your body becomes dehydrated.
If you body becomes dehydrated this will affect your exercise
performance. Even mild dehydration, as little as 2% of your body weight,
has been shown to impair your athletic performance.
So what can we do about it? As most of you will know, to maintain the
optimal fluid levels, or at least to aspire towards them, we must replace
the fluid loss we incur by consuming the appropriate amount of liquid
before, during and after exercise. However, water is not necessarily the
best option if you are looking to rehydrate, or maintain hydration, during
your exercise bouts… A beverage containing glucose and sodium is most
effective during longer exercise sessions. Most sports drinks in store
these days will contain these two agents in the most appropriate
quantities for quick absorption.
So what is the take home message? In a nut shell … keep your fluid levels
up and you will decrease the risk, or lessen the impact of dehydration
In warmer environments, or with more intense exercise,
overheating can also be a risk factor contributing to fatigue. However,
generally this is something that endurance trained athletes are more at
risk of during exercise than the regular gym goer. Remember Craig
Barrett, the 50km walker at the Commonwealth games a few years back? …
overheating, combined with severe dehydration can have an enormous effect
on physical performance.
Again, drinking correct fluids (as this aids in cooling the body) and
avoiding training during the heat of the day should suffice for the most
of us in reducing the risk of overheating… The gym is normally air
of Muscle Fuels
Along with Dehydration, depletion of muscle fuels or glycogen
depletion can play a large part in fatiguing exercise performance.
Glucose is the main fuel source for your muscles in short term intensive
exercise lasting longer than 10 seconds and less than 3 minutes, and is
provided by a process called anaerobic glycolysis (the breakdown of
glycogen to glucose).
Exercise performed at a lower intensity and for a longer duration is also
reliant on glycogen, as well as a couple of other energy resources, such
as fatty acids and amino acids. It has been shown in various studies that
depletion of glycogen can reduce performance in short, medium and longer
To reduce the likelihood of fatigue due to glycogen depletion it is
especially important to ensure that pre exercise glycogen levels are high,
and also that
glycogen is replaced sufficiently.
A substantial meal rich in carbohydrates (eg pasta) eaten 2-3 hours prior
to longer exercise sessions, and a small carbohydrate snack eaten up to an
hour before exercising should ensure that your glycogen levels are fully
saturated. After exercise, a combination of carbohydrate, protein and
sufficient fluids are required at regular intervals to ensure you recover
fully from your exercise. The first hour is most important in your
recovery process … if you fail to re fuel you will probably feel it in
your next session!
The take home message …. Don’t go off to do your gym workout hungry, or
having not eaten. Otherwise you are bound to feel flat and
Recent research has indicated that mental fatigue, sometimes referred to
as central fatigue, can be a cause of impaired physical performance during
exercise. While this will not affect your muscles directly, as it results
from impaired function of the central nervous system, it can reduce your
capacity to perform. The onset of central fatigue is seemingly related to
a correlation between certain amino acid levels in the brain, and it has
been shown that supplementation of branched chain amino acids can improve
performance in sports and endurance events.
Take home message… a bit more research required here … but it may not be
that you are just lazy when you cut your exercise session short! It could
be due to central fatigue! But lets not use this as an excuse to cut
every session short!
exercise intensity that you perform at also has a large impact on the
level and onset of fatigue your muscles and body feel. If you are
exercising at a level that is too intense … and your aerobic system can
not supply the required energy … you will start to work the
system. The lactic acid system is capable of releasing energy without the
requirement for oxygen. However, if you are exercising at a level which
is above your lactate threshold
(level at which you begin to start working anaerobically)
… your exercise performance will become limited by the lactate build up
and the associated acidity of your muscles (due to increased Hydrogen Ion
levels in the muscles).
Sounds a bit
complicated I know, but
I am sure
you have all experienced the ‘burn’ in your muscles whether
during a game of soccer, rugby or some other pursuit.
Make sure that you are exercising at the appropriate intensity for your
current fitness level. Always warm up slowly before undertaking any
intensive exercise. If you are unsure about the intensity you should be
performing interval or tempo training consult your fitness instructor, or
have them perform a fitness test on you.
Lose The Beer Belly
you have just looked at the calendar and it is August already ... only a
few months until summer kicks in. Where did I put my Speedos?
Where did this beer belly come from?
Have you been doing nothing over the winter period? Or perhaps you
training just isn't working? Do you want to lose the beer belly so
you can get back in your togs over summer? The time to start is
Remember ... spot weight reduction doesn't work ... (ie you can't just
lose weight around your stomach), and no matter how many sit ups you do no
ones going to see a six pack until you lose the weight from the stomach
So what to do then?
1. Increase your cardio
The first place to start is to look at your cardio. If you are doing
nothing lets try top start off with 3-4 visits a week to the gym for 30
minutes or so of continuous exercise, exercise that maintains your
heart rate at an elevated level for a continuous period. Get started
burning those calories! If you are looking for a gym to attend
click here to
search for one in your area. To view some of the profiled gyms
2. Mix up intensity and duration
Have you been going to the gym religiously, 4 days a week, doing the same
session day after day... but still can't get the results that you desire?
It is time to mix things up ... break out of the habit ... if you keep
doing things the same you will get the same result. Try playing with
the intensity and duration of your sessions. Perhaps one longer
session per week of over an hour. Or include an interval session on
the bike where you do high intensity bursts of5 times 5 minutes.
If you are lost for ideas... it may be time to talk to your gym staff, or
even a personal trainer for some motivation.
Click here to
search the personal trainers listed in your area.
3. Take it down
One of the most important things that you can do is to write
down the training that you are doing. Often it feels as if you are
training hard and regularly, then when you look at your completed workouts
you have had two good weeks, a week and a half off, one good week, another
slack one ... you get the idea!
Write down your training ... what you aspire to do, and what you actually
do ... then you can analyse where you may be falling down ... you will
also find that it motivates you to train more regularly!
Good luck with your weight loss training ... and roll on Summer!