Tour of California 2008
Once again, Dr. Gabe Mirkin gives us valuable evidence-based recommendations for nutrition and competition. Here's his blog reposted with permission.
Sugar and Caffeine for Competition
By Dr. Gabe Mirkin
The limiting factor to how fast you can move during a race
is the amount of oxygen that you can take in and use. Since sugar
requires less oxygen than fat to power your muscles, you want to
get as much sugar into your muscles as quickly as possible.
Anything that increases the amount of sugar that can be absorbed
from your intestines into your bloodstream will help you ride or
run faster and longer.
Sugar is carried across your intestinal tract into your
bloodstream by special protein transporter molecules. Glucose
has its own specific transporter protein and so does another
sugar, fructose. So your muscles use 165 percent as much sugar
when you take in glucose and fructose, compared to taking in only
glucose. To put it another way, when you take in drinks that
contain only glucose, your muscles can absorb and use only one
gram sugar per minute, compared to 1.75 grams per minute when
you take a drink that contains both glucose and fructose (Current
Opinion in Clinical Nutrition and Metabolic Care, July 2010).
Furthermore, adding caffeine to a drink can increase
absorption of sugar into the bloodstream by as much as 26
percent (Journal of Applied Physiology, June 2006).
The most effective drinks for endurance competition
therefore may be those that contain glucose, fructose and
caffeine, such as are found in many carbonated drinks. These
drinks are safe during exercise because contracting muscles can
prevent a high rise in blood sugar levels by drawing sugar from
the bloodstream without needing insulin. However, when you are
not exercising, these drinks can cause very high rises in blood
sugar, increasing risk for obesity and diabetes.
To learn more about Dr. Mirkin and to read this blog on his website, please visit: www.drmirkin.com
Many athletes experience muscle cramps during exercise. Cramps were once thought to be due to mineral deficiencies or dehydration. Dr. Gabe Mirkin (www.drmirkin.com) reviewed research that gives us another possible cause of muscle cramps during exercise below.
Dr. Gabe Mirkin's Fitness and Health E-Zine
January 16, 2011
Special Issue: Muscle Cramps in Exercisers
Muscle cramps are common during very intense exercise
and occur far less often during less-intense training, because
the most common cause of muscle cramps in exercisers is muscle
damage from all-out pressure on the muscles.
CAUSE: MUSCLE DAMAGE
The leading theory is that most cases of muscle cramps in
serious exercisers and athletes are caused by an exaggerated
"stretch reflex". When you stretch a muscle, it pulls on its tendon.
Stretch reflex nerves in that tendon send a message back to the
spinal cord (not the brain), and then the "stretch reflex" in the
spinal cord sends a message along nerves from the spine to
cause the muscle to contract. During sustained extreme pressure
on the muscles, the muscle retains its contraction to form a cramp.
A study from South Africa showed that the most likely cause is
muscle fatigue or tearing of the muscle itself (Medicine & Science
in Sports & Exercise, July 2005).
If this is true, muscle cramps during endurance events can
be prevented by slowing down when you feel excessive soreness
in one muscle group or straining in a muscle. Of course,
competitive athletes will not do this, and they pay for it with
The researchers studied triathletes and found that most
of the time, the muscles cramps were not caused by dehydration,
thyroid disease, blocked blood flow, nerve damage, or mineral
abnormalities of calcium, sodium, magnesium or potassium. The
athletes with cramps had normal electrolytes, and did not lose
more fluid during exercise than those who did not suffer cramps.
The researchers showed that the most likely cause is muscle
fatigue or tearing of the muscle itself. Electromyograph (EMG)
studies at one to five minutes showed markedly elevated electrical
activity of the nerves controlling the cramped muscles. A review
of the scientific literature shows the most common cause of muscle
cramps appears to be muscle damage (Journal of the American
Academy of Orthopaedic Surgeons, July 2007).
WHAT TO DO WHEN A CRAMP STRIKES
Almost all racers who experience exercise- associated
muscle cramps do not suffer from disease and can usually prevent
cramps by slowing down when one muscle group starts to feel
tight or excessive soreness. You do this by switching pressure
from the cramped leg to the uncramped one. A bicycle racer
moves most of his pressure to the pedal of the uncramped leg.
A runner shortens the stride of the cramped leg. Continuing to
put pressure on the cramped muscle can rupture the muscle.
DEHYDRATION AND LACK OF MINERALS LESS COMMON
Some cramps are caused by low mineral or fluid levels
(The Japanese Journal of Clinical Pathology, November 2007).
However, for the vast majority of people who suffer exercise-
associated muscle cramps, blood levels of sodium, potassium,
calcium and magnesium are normal. Research in athletes after they
ran in 52-mile races showed that the runners who suffered cramps
had the same level of dehydration and blood mineral levels as
those who did not get muscle cramps.
LACK OF SALT
The most common mineral cause of muscle cramps in
exercisers is lack of salt, according to a report from the
University of Oklahoma (Sports Medicine, April-May 2007). The
authors cite studies of tennis and football players, showing that
crampers tend to be salty sweaters; and of triathletes, where those
who cramp lost more salt during a race than their peers who did not
cramp. They found that intravenous saline can reverse cramping, and
that more salt in the diet or in sports drinks can help to prevent
For many years I have recommended eating salted peanuts or
other salty foods during heavy exercise, but other doctors believe
that extra salt may raise blood pressure. If this is a concern for
you, get a wrist cuff monitor and check your blood pressure every
day. You are likely to find that your blood pressure goes down,
not up, with regular exercise even when you add salt.
Nobody has shown consistent benefit from any of the most
common treatments: multivitamin pills; mineral pills with calcium,
zinc, magnesium, salt and/or potassium; massage or chiropractic
manipulation; drinking large amounts of water; dietary
manipulations; or bio-mechanical stretching and strengthening.
NON-CAUSES IN SERIOUS EXERCISERS
Known medical causes of muscle cramps are extremely
rare. If you suffer from recurrent muscle cramps, you may need
special tests for pinched nerves, Parkinson's disease, low thyroid,
diabetes, narrowed arteries from arteriosclerosis, low blood
mineral levels, metabolic diseases that cause muscle damage, or
side effects of drugs used for high cholesterol, high blood
pressure or diabetes, diuretics, oral contraceptives or alcohol
(Neurology 2010; 74: 691-96).
Quinine should not be used because it can damage blood
cells. Some studies show that gabapentin (an anticonvulsant),
diltiazem ( a blood pressure medication), or B-complex vitamins
may help to relieve muscle cramps in some people (Journal of
Clinical Pharmacology, 1998;38:1151)
Before a cramp develops, you will probably feel the
muscle pulling and tightening. If you slow down, the pulling
lessens, but if you continue to push the pace, the muscle goes
into a sustained cramp and you have to stop exercising to work
the cramp out. Further evidence that muscle damage is the cause
of the cramp is that the muscle often hurts for hours or days
You may be able to prevent cramps by exercising more
frequently but less intensely and for shorter periods of time,
but most racers do not want to do this.
There is some evidence that taking sugared drinks or
foods during prolonged exercise helps to maintain endurance and
muscle integrity which helps to prevent cramps. Take a source of
sugar every 30 minutes or so during vigorous workouts or races,
and back off if you feel a group of muscles pulling or tightening
LACK OF VITAMIN D
A leading cause of muscle damage, soreness and slow-
healing injuries in athletes is lack of vitamin D. If you suffer
frequent cramping and your muscles feel sore or you keep on
being injured when you exercise, get a blood test called D3. If it
is below 75 nmol/L, your problems may be caused by lack of vitamin
D and be cured by getting some sunshine or taking at least 2000
IU each day of the very inexpensive vitamin D3.
OCCASIONAL CRAMPS NOT HARMFUL
Most racers and serious exercisers accept that occasional cramps
will occur and cause no long-term harm.
Athlete Seminar Series: What you don't know about pronation.
Please join us for a presentation on WHAT happens, WHEN, and WHERE during running as it pertains to pronation of the foot.
: Tuesday, January 25 7:15PM
: Innersport 1250 Addison St. Suite 102, Berkeley, CA 947o2 510.883.1126 www.innersport.com
Why Soft Tissue Injuries Occur
Research has shown that up to 80% of runners are injured every year with most injuries being at the knee. (Van Gent et al., Clin J Sport Med. 2009.) Majority of these injuries are due to soft tissue overload. Other factors include flexibility, range of motion, strength, alignment, shoes, surface, etc. Soft tissue includes structures such as muscles, tendons, and ligaments. The body and soft tissue structures will adapt as long as the applied stress is not greater than it's capacity to adapt.
The Running Clinic has defined Load and Frequency below.
Load on a tissue is function of the forces applied in:
Frequency of stress is quantified as:
- Number of repetitions or time of stimulation
- The time between repetitions
- Number of workouts per week.
Each of our tissues has a minimum and maximum threshold.
There is a minimum threshold to meet in order for the body to adapt. Think of training for a marathon. We can't go from zero to 26 miles in a day. We have to train 3-4 months gradually for our bodies to adapt over time to running 26.2 miles. Stress (load and frequency) on soft tissues encourages remodeling which leads to adaptation, strength, and endurance. The Running Clinic terms the zone below this line as the "Un-Adaptation" zone.
Our soft tissues have a maximum threshold of stress applied for adaptation. We go over that threshold, we can no longer adapt, our soft tissues become overloaded, and we therefore suffer from injuries. The Running Clinic addresses the zone above this line as the "Mis-Adaptation Zone."
This leaves us with the "Adaptation Zone" or a safe zone, between the minimum threshold and the maximum threshold. This is the zone in which we would like to train in order to advance in performance and stay injury-free.
We Are Only as Strong as Our Weakest Link
Since we have two lower limbs and we are running equally on both sides, why does one side get injured?
It's simple. One limb's soft tissue has a lower Maximum Threshold. This is where your sports medicine practitioner enters into the picture. Factors that influence a change in the Maximum Threshold:
- Previous injury to tissue
- Flexibility discrepancies
- Strength discrepancies
- Scar tissue build-up
- Joint restrictions in extremities and spine
- Instability in joints and kinetic chain
- Motor control
- Occupation and self-care activities
Environmental factors such as shoes, surface, and terrain will also affect the maximum threshold.
Listen to your body!
How do we know we are going over the maximum threshold?
The Running Clinic has determined a simple way to determine when you are going over the maximum threshold line in training. They believe the body will tell you:
- Pain DURING exercise
- Pain remains 30 minutes AFTER exercise
- Increase in morning stiffness day after exercise
Bringing it all together
What does this mean for the injured runner?
- We must train between the minimum and maximum threshold OF OUR WEAKEST LINK to continue to improve and adapt without further injury
- If we want to raise the maximum threshold of a soft tissue, remove the weak link by seeking treatment
- If we want to continue to adapt, we must meet the minimum threshold without going over the maximum threshold
- Pain during or 30 minutes after exercise, or morning stiffness is a good indicator we are going over the maximum threshold
Dr. Greaux specializes in video analysis and biomechanics of running, cycling, and golf. She has been in private practice for 10 years in Berkeley and now has another office in Walnut Creek. Dr. Greaux is now starting a new online video analysis business, www.pressplayanalysis.com. Feel free to comment using the fields below to ask Dr. Jess a question or make a comment regarding this blog.