hello all this is dr alsup and in this video we will be discussing the types of contraction that
can occur in muscle and specifically we are going to focus on the types of phasic muscle contraction
or active contraction but we will touch on other types of contraction like reflexive or
tonic contractions because they do certainly play an important role in the musculoskeletal system
so there'll be two main types of the phasic contractions and isometric contraction which you
can see being illustrated here is one of these types and this is the contraction that i wager
most of us don't think about as much and the key to isometric contraction as in all contractions
is that there is force and muscle tension and this force is increased above the tonic or muscle tone
levels and energy is certainly being expended but what is unique to isotonic contraction
is that no movement occurs and the muscle length will remain the same this image makes it looks
like it changes just a little bit but it does which isn't true there'll be no change in terms of
length but you can see that there is no movement occurring with this type of contraction
the function of isometric contraction is mainly to
resist gravity or other antagonistic forces and is particularly important in postural muscles
the other major type of contraction is isotonic contraction
and um this is the type of muscle contraction where muscle does change in some form and length
and there is movement so those are kind of the two keys there's a change in length and there's a
change in movement or movement is occurring
the two major types of isotonic contraction are concentric and eccentric contractions
concentric contraction is um usually the type of contraction that we think of when
we're thinking of muscle contractions in fact when we talk about the individual muscles
and we start listing the actions of that muscle we are discussing
what actions occur when that muscle is concentrically contracting so this one
not that it's more important is just more of what we think of when we're thinking of contractions
with this type of contraction the muscle will shorten and that's kind of key so it's going to
the muscle will shorten in size and it will cause some form of movement particularly a
type of movement that will reduce the angle at a joint eccentric contraction is kind of the
opposite of that this is going to cause a muscle to lengthen lengthen is kind of the key here in
other words a muscle will have a controlled and kind of gradual relaxation while still exerting
an ever diminishing amount of force so you can see that it is kind of stretching in terms of
the muscle shape so stretching or lengthening and you can see that there is movement being caused
as i mentioned at the beginning there are other types of contraction reflexive contraction these
are not voluntarily controlled which is unique for skeletal muscle we know that because we
know that based on previous videos the skeletal muscle is supposed to be voluntarily controlled
but there are some exceptions to the rule and where some skeletal muscle will have reflexive
or more automatic contractions so for example the diaphragm or our main muscle of respiration
or inspiration excuse me is this a skeletal muscle and we typically aren't consciously contracting
that one so there will be some reflexive contraction associated with the diaphragm
tonic contraction is a very and i mean very slight contraction that does not produce
movement so this is um not going to be isometric contraction which doesn't produce movement
either it's going to be on an even smaller scale in terms of the the amount of tension
that occurs with the muscle and tonic contractions occur all the time in almost all muscles so even
when a muscle is relaxed there is a small often a noticeable amount of contraction actually
very often a noticeable amount of contraction and we call this muscle tone do i have that written
down yeah right here that's an important thing here so that's called muscle tone
functions of tonic contractions include stability of joints and maintenance of posture
and muscle tone can be loss it can be lost in nerve lesions or damage that result in muscle
paralysis or when an individual is unconscious all right so those are the main types of contraction
let's review a concept together question when a muscle stretches i.e muscle lengthening what type
of contraction is this so let's look at this question stem what are some of the keys here
well i see muscle stretches that's telling me something i think this is helpful ooh muscle
lengthening that's super health helpful which answer choice would you think best describes this
eccentric yes correct b is correct it is not concentric because muscles will shorten not
lengthen and isometric will have no change in shape same thing with tonic but tonic of course
is on a much smaller scale than the isometric with contraction so all that leaves is eccentric
or b as the correct answer excellent that was a lot of fun as always as you review this or any
other material please feel free to reach out with any questions and have a great rest of your day