Isotonic contractions refer to a specific type of muscle
contraction, where the tension on the muscle remains the same, however, the
length of the muscle does not. Understanding isotonic contractions is important
for anyone who wants to increase their strength or tone up their muscles.
However, there are a number of misconception about isotonic contractions that
will be clarified below.
Isotonic Vs. Auxotonic Versus Isometric
You have most likely heard of the terms isotonic and
isometric, but you have may not have heard the term auxotonic. For a muscle
contraction to be truly isotonic according to the definition, it requires the
same tension on the muscle throughout the movement. In real life workouts this
is actually quite rare. As an exercise is undertaken (e.g. lifting a weight),
there is usually a slight fluctuation in speed as momentum shifts and joint
angles (and forces) change slightly to complete the exercise. We also need to
accelerate to overcome inertia at the start of a movement and decelerate toward
the end of a movement. In this case it is more likely to be auxotonic
contraction. During an auxotonic contraction the muscle may undergo increasing
or fluctuating tension (as it adjusts to changes in joint angles and momentum
shifts). Isometric contractions on the other hand occur when there is no change
in muscle length (i.e. the joint angle stays the same). Isometric contractions
are sometimes called 'static contractions' as the length of the muscle and
joint position does not really change.
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| Weight Lifting |
Concentric versus
eccentric during isotonic or auxotonic contractions
A concentric contraction occurs when the muscle exerts more
force than the resistance acting in the opposite direction. Consider the first
part of a barbell / bicep curl. As your biceps brachii (and the smaller elbow
flexors) contracts, it pulls your forearm (with the weight in your hand)
upward. At this point the force being exerted by your elbow is greater than the
force of gravity acting on the weight in your hand. Hence, the weight is being
lifted up. An important thing to note in this example of a concentric
contraction is that the length of your biceps is becoming shorter as complete
this phase of the bicep curl.
An eccentric contraction occurs when the muscle exerts less
force than the resistance acting in the opposite direction. Consider the second
part of a barbell / bicep curl. As you lower the weight back down (and extend
your elbow) the biceps brachii (and smaller elbow flexors) are still working to
slowly lower the weight back down (an prevent a sudden drop). As this point the
force being exerted by your elbow is less than the force of gravity acting on
the weight in your hand. During this eccentric contraction the length of your
biceps is becoming longer as you return to the starting
position.
Barbell Curl (Bicep Curl)
Most people would call this an isotonic exercise. Even with
the excellent technique used for each repetition, this is still not technically
isotonic an isotonic contraction. However, this doesn't really matter! When you
are planning or undertaking an exercise routine actually following through and
doing it is the key. Don't lose sleep over whether your contraction is
technically isotonic, its actually a good thing for your joints that these
exercise are auxotonic. The acceleration and deceleration that occurs at the
start and end of a movement actually help protect against joint injuries.
Dumbbell Bicep Curls
Dumbbell bicep curls are quite a straight forward exercise.
Nonetheless people often become too keen to try and lift the heaviest weight
possible, and can put themselves at risk of injury. When you are doing biceps
curls, ensure that you can complete the entire set without starting to do jerky
movements, or only start the movement with momentum (i.e. a bit of a swing at
the start of the concentric phase). If you want to push yourself to the limit,
it is perhaps better to do one arm at a time. That way as you get toward the
end of a set and are struggling to keep your good technique, you can just add a
feather touch from the other hand (sort of like self spotting) to finish the
set. This way you can challenge your biceps to a reasonable limit, and cause
desirable hypertrophy, while minimizing the risk of injury.
Incline Dumbbell Press
The incline dumbbell press is great for working your pecs
(targeting the clavicular portion of pectoralis major). In addition to the
pecs, the anterior deltoid and triceps also contribute to the movement. The
pecs work hardest in the early part of the exercise (while the adjustable dumbbells are
near the chest).
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| PowerBlock Adjustable Dumbbells |
Overhead Triceps Extension
As the name suggests, this exercise primarily targets your
triceps. In addition to your triceps, your shoulder stabilizers (both rotator
cuff and scapula stabilizers) will be working to counter the force of gravity
and torque generated by the exercise itself. However, if you are feeling a
pinching type feeling in your shoulder as you attempt this exercise, you should
cease the exercise and get it investigated by an appropriate health
professional. A sharping pinching, particularly at the front of your shoulder,
may well be indicative of shoulder impingement. As you raise your arm the gap
between your acromion (part of your shoulder blade) and the head of humerus
(upper arm bone) narrows and can pinch soft tissues (like tendons)! This tends
to feel like a sharp pinching feeling... don't 'push through' this, get it
checked out. However, if you don't feel a pinch, continue on as per your
intended plan for repetitions and sets.
Lying Hamstring Curl
Lying hamstring curls is one of those classics exercises
that people associate with isotonic contractions. Your hamstrings are made up
of three separate muscles (semitendinosus, semimembranosus and biceps femoris.
This exercise will work all of these muscles. Before you start, try to position
yourself with your knees in line with the machine pivot point. This can be
quite difficult on some poor quality equipment, or if you haven't made the
appropriate adjustments to suit your leg length.
