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.