THE THERAPY CORNER
Odds and Ends
One of the quirks of the
English language, that makes it a difficult one to learn as an adult, is the
fairly large number of words that have the same spelling but different
meanings, as well as different pronunciation in some cases.
Take the word eccentric,
for example; as an adjective (pronounced ik-'sen-trik),
it is most often used to describe an individual with an unusual or odd
personality. (E.g., a word employed by
nieces and nephews when talking about their uncle.)
When used in the context of muscle physiology,
however, the word eccentric (ee-'sen-trik)
refers to a specific type of contraction of skeletal muscle fibers –
specifically, those movements that result in a lengthening of a muscle while it
is contracting. An example of this would
be if you held a weight in your hand with your elbow bent and then lowered the
weight in a controlled manner to a table.
As your elbow is straightening, your biceps and other muscles are
contracting to control the movement, but they are getting longer at the same
time. (The opposite movement – the elbow
bending as you lift the weight up – is known as a concentric contraction. If
you held the weight in a fixed position, with no movement at the elbow, this
would be an isometric contraction.)
As we all know, repetitively
exercising a muscle will eventually result in fatigue of that muscle, whether
it is done concentrically or eccentrically.
The aftereffects of these two types of contractions differ,
however. Research has clearly shown that
eccentric contractions cause significantly higher levels of microtearing of
muscle fibers than either concentric or isometric contractions. Essentially, the muscle is injured to some
degree, which results in soreness that is felt within 24 hours, but peaks
between 48-72 hours, of the activity.
This is known in the exercise physiology world as DOMS (delayed-onset
muscle soreness).
Running is one activity that
places a certain degree of eccentric stress to the quadriceps muscles in particular. During the initial loading phase on the lower
extremity as the foot hits the ground, the knee is flexing approximately 30-40
degrees, before it reverses and straightens before the foot again leaves the
ground. While the knee is flexing, the
quads are contracting to control that bending movement, but they are
lengthening at the same time. As
described above, this is an eccentric contraction.
Biking, on the other hand,
utilizes the quad muscles in a concentric manner only, so the degree of DOMS is
considerably less than after running. I
always shake my head every Tour de France when commentators describe that race
as being equivalent to running a marathon almost every day for three weeks. I have done a few century (100 mile) bike
rides and I can tell you that, while I was plenty tired afterward and my quads
felt "dead" the next day, I didn't have to walk down stairs backwards
like I've had to after some tough marathons.
I could easily have gotten on the bike again the next day without being
in pain; I couldn't say the same for running the day after a marathon.
The degree of injury, and
subsequent DOMS, sustained as a result of eccentric exercise is dependent on a
couple of factors. First, as expected,
would be the intensity and duration of exercise. Anyone who has run a marathon will no doubt
have experienced the difference in DOMS of the quadriceps muscles felt after
that event compared to a 10k. Moreover,
those who have run a hilly marathon – especially a net-downhill marathon such
as
Millions of dollars are spent
every year by athletes seeking a "cure" for DOMS, or at least a
quicker recovery. Most popular are the plethora of creams and lotions that purport
to eliminate or at least reduce the pain of muscle soreness. These external analgesic substances are known
as counterirritants – they produce a heating sensation by chemically irritating
the skin, which has the effect of overriding pain signals sent to the
brain. While this may lower pain
perception, scientific studies of these products have shown that they have no
actual heating effect on the muscle tissue and do not actually produce any
change in the underlying cause of the soreness, which is the cellular damage
from eccentric exercise. The important
thing to realize from this information is that you may be causing yourself more
harm by using these products if they allow you to exercise by reducing your
pain level, in the same way that continuing to run on an injured leg after
taking pain medications may be counterproductive.
Massage, on the other hand,
may be effective in treating DOMS. I
have seen a few studies that produced favorable results indicating that massage
can reduce the subjective perception of pain from DOMS, while at the same time
not showing any significant change in muscle function or biochemical markers of
muscle damage. However, the experimental
design of these studies leaves something to be desired, in my opinion, so the
jury is still out on whether there really is a benefit from massage. Ultimately though, I don't think there is a
downside to this, so if you feel it helps, by all means go for it.
DOMS is not usually a
long-term "injury" in the same way tendinitis or a strain/sprain
might be, but it should still be respected in the same way when gauging when
and at what intensity you should return to running after a hard run or race
produces that level of pain. There is no
hard and fast rule on when that time might be, but I have always subscribed to
the notion that, if you have to walk down stairs backwards, it's too soon to
run.
Gabe Yankowitz, PT
Gabe is a
physical therapist practicing in Westvale and LaFayette. He has evaluated and treated