Today, I will address the factors
that are responsible for the muscle soreness felt during and
immediately after exercise. The likely causes for
muscles cramps and spasms. And the muscle soreness and stiffness
experienced 8 to 48 hours after exercise, known as delayed onset muscle soreness. As the type of muscle contraction is
frequently the culprit in the various forms of muscle sores, let's click and
review these contractions. An isometric contraction is defined as
no change in the length of the muscle while tension is being developed. In a concentric contraction the muscle
shortens during tension development. Lastly, with eccentric contractions
the muscle is actually lengthening while tension is being developed. Let's begin with the muscle soreness felt
during and immediately after exercise. Symptoms include localized pain and
a burning sensation. The pain and discomfort generally disappear within
minutes after the exercise bout has ended. The primary cause of this type of
soreness is from a sustained or prolonged isometric contraction. During a strong isometric contraction,
the tension created by the muscle causes the blood vessels delivering oxygen
and fuel to the muscles to collapse. If this contraction is held or prolonged,
blood flow to the muscle can be shut down, resulting in a reduction
of oxygen delivery. As a result the muscles must rely on
anaerobic pathways for ATP production. The metabolic end products from these
pathways accumulate in the muscle leading to acidosis. The muscles contain pain receptors that
are sensitive to this increase in acidity, thuus producing the localized pain and
burning sensation experienced. As soon as the isometric contraction
is ended blood flow increases thereby flushing out the acid generating
metabolites and the pain quickly subsides. An example of immediate muscle
soreness is shown here. When sustaining a calf raise, the tension
in the muscles causes the venus and arterial blood vessels
in the calf to collapse. If held for more than several seconds, this will lead to acidosis in
the muscles and the burning sensation. Another good example is the burning you
feel in the lower part of your quadriceps muscles just above the knee joint when
engaged in a long downhill ski run. In both examples the pain from
the sustained isometric contraction rapidly subsides when the muscles are
relaxed and blood flow returns to normal. Next, let's examine the potential
causes of muscle cramps. These involuntary, intense muscle
spasms can be extremely painful, and occur during or
immediately following competition. While the exact causes responsible for muscle cramps are not fully understood,
two likely theories have emerged. The first theory proposes that
muscle cramps are a result of electrolyte imbalances associated
with excessive sweating, dehydration, and
exercising in hot environments. These electrolyte imbalances such as
with sodium, can make the neuromuscular junction more excitable, leading to
spontaneous intense muscle contractions. Ingestion of fluids and
salt solutions, along with massage and ice packs may assist in recovery. The second theory relates to
altered neuromuscular control. Basically abnormal sentry activity
from the muscle spindles and the Golgi tendon organ triggers the motor neuron to
fire involuntarily, resulting in cramping. This would explain why passive stretching
is the most effective treatment for relieving cramps. The stretching of the Golgi tendon organ
can inhibit motor neuron activity. The remainder of this video will focus
on the muscle soreness, weakness, and stiffness experienced 8 to
48 hours after exercise known as Delayed Onset Muscle Soreness. We have all experienced
this type of soreness, which is extremely common when
performing a novel type of exercise, or if you are just getting back into
exercising after a long absence. There is a big misconception that
the cause of this delayed onset muscle soreness is the result of lactic
acid production during exercise. This is unequivocally false. There is no absolutely no evidence
that lactic acid is the cause of this delayed onset muscle soreness. In fact, as shown here,
after intense exercise, blood lactate levels quickly return to pre-exercise
level, long before soreness sets in. The well accepted cause of
delayed onset muscle soreness are eccentric muscle contractions,
which are a component of most activities. For example,
after completing a biceps curl, the biceps are lengthening while the weight is
being lowered before the next curl. Or when running downhill, the quadriceps are lengthening to resist
gravity to prevent you from falling. During an eccentric contraction,
fewer fibers are recruited for an equivalent power output. This place is a greater
force per muscle fiber area compared to other types of contractions. As a result of this greater mechanical
stress placed upon the muscles, micro tears and
localized muscle damage can occur. This muscle damage will
eventually lead to inflammation, weakness, tenderness, and pain. There is clear evidence that this
type of muscle damage occurs during activities that involve
eccentric contractions. Large intramuscular proteins
such as creatine kinase, myoglobin, and lactate dehydrogenase
are found to leak into the blood. These large enzymes and
proteins could only leak into the blood if there was significant damage
to the muscle cell membranes. Which normally keep these
compounds trapped in the muscle. In the example shown here, blood creatine
kinase levels were measured in subjects before and up to 72 hours after
45 minutes of downhill running. Blood creatine kinase levels were
immediately elevated post-exercise. Indicating that a single bout of
exercise induce muscle damage. Similar results are found for
both myoglobin and lactate dehydrogenase. Definitive evidence of muscle damage
is observed when muscle biopsies are taken from the leg before and
after down hill running. A resting muscle sample taken prior
to downhill running is shown here. Notice the sarcomeres and
z lines are perfectly aligned. However immediately after a single
bout of downhill running, the biopsy clearly shows muscle damage
referred to as z line streaming. These damaged sarcomeres
will never return to normal. Instead, the body's immune
system will degrade and remove these damaged sarcomeres. This process results in inflammation,
tenderness, and localized pain. Over time, newly formed healthy
sarcomeres will replace the damaged ones. Not surprisingly the muscle damage
from eccentric contractions will result in muscle weakness which can
persist up to one week post exercise. The timeline for delayed onset
muscle soreness is shown here. As stated earlier, the muscle soreness and damage generally occurs when performing
novel or unaccustomed exercise. However, after you have recovered
from the initial soreness, subsequent battles of the exact same
exercise yield only minor symptoms. Thus, you do not continue to get
sore every time you lift weights or run down hill. While the mechanisms responsible for this
protective effect from the initial bout of muscle soreness remain unclear,
likely causes relate to formation of new healthier sarcomeres and
improved integrity. In summary, the soreness that
you experience during exercise generally results from the inclusion
of blood flow to muscles caused by a prolonged
isometric contraction. This produces localized acidosis which
can cause pain and burning sensations. Muscle cramps can be caused by
both electrolyte imbalances as well as abnormal
neuromuscular signaling. Delayed-onset muscle soreness is caused
by the eccentric contractions during unaccustomed exercise directly
resulting in muscle damage.
