By Lisa Marshall
Iñigo San Millán, PhD.
(December 2015) What do a post-race marathoner and a car accident victim lying in the intensive care unit have in common?
to extreme stress, both have depleted their muscles of the glycogen, or
sugar (glucose), necessary to fuel energy and stave off further injury
and illness. As a result, both have also begun to eat away at their own
“Your body doesn’t know whether you’re running a marathon
or recovering from an accident. The metabolic and physiological
response is pretty much identical” explains Iñigo San Millán, PhD, an
assistant professor in the CU School of Medicine’s Department of
Physical Medicine and Rehabilitation. “The body is fighting for survival
and when it runs out of glycogen, the muscle eats itself to feed
Replenish those muscles the right amount at the right
time, and they can bounce back well. But overfeed them or, worse, let
them starve and the consequences can be grave. The challenge for
coaches, and for physicians grappling with the endemic problem of
muscle-wasting in the ICU: It’s nearly impossible to know just how much
muscle glycogen a person has at any given time.
That is, until now.
have basically developed a gas gauge” for glycogen levels, explains San
Millán, describing a new, patented technology, MuscleSound, he believes
could revolutionize nutrition and exercise advice for everyone from
critical care patients to NFL players to everyday athletes.
in 2010 by San Millán and colleague John Hill, DO, a professor in the
Department of Family Medicine, MuscleSound uses ultrasound technology to
provide—for the first time ever—real-time, non-invasive measurements of
glycogen levels in muscle tissue. Previously, the only way to measure
such levels was via a painful muscle biopsy or a costly and complicated
With this new technology, a technician moves a painless
probe across large muscles in the leg or arm, emitting sound waves that
bounce off the water that inevitably accompanies glycogen, indicating
its presence. On a nearby computer screen, an image of the muscle
appears: Dark regions indicate glycogen-loaded muscles; white spots
signal a shortfall. Within 15 seconds, a computer algorithm spits out a
glycogen score, from zero to 90, which doctors or coaches can use to
Hill and San Millán invented and patented the
technology in 2010 and now market it under the name MuscleSound. Today, a
few NCAA teams, including the University of Colorado Buffaloes, the
Dallas Mavericks professional basketball team, and the Colorado Rockies
professional baseball team use it.
But some believe its most profound potential lies in helping to improve outcomes for critically ill patients.
era of guessing at caloric needs with equations must end,” says Paul
Wischmeyer, MD, director of nutrition therapy services for the CU
School of Medicine and a vocal advocate for improving ICU recovery rates
nationwide. “There is a lot that we could do with this technology.”
Getting nutrition right in the ICU
the marathon runner and ICU patient have much in common
physiologically, they differ in one key way. After crossing the finish
line, the runner can go home, rest, and eat up. The ICU patient,
metabolically speaking, keeps running.
“The body has not evolved
to survive these types of injuries, so it doesn’t know when to turn off
this response,” explains Wischmeyer, noting that critically ill patients
can remain hyper-metabolic for days, or in the case of burn victims up
to two years after the initial trauma. “Being in the ICU is like
continuously running multiple marathons.”
Wischmeyer, Hill and San
Millán recently used this novel technology to test glycogen levels of
nine ICU patients, including cancer patients, burn, and accident victims
who had been in one day to five weeks.
The results were even more
dramatic than they’d suspected. Six out of nine patients had a score of
zero (meaning they had no detectable glycogen in their muscles). The
other three scored 5 to 15, far less than the 50 to 70 a health person
might score, or even the 15 to 25 an elite athlete might score
post-competition. Some patients had lost all glycogen in their muscles
within just 24 hours of admission.
That matters because, with
glycogen gone, the body starts eating muscle. And the less lean muscle
mass a patient has, the poorer the chance of surviving the ICU, notes
Even if the patient does survive, it’s hard to gain
back lost muscle. And prolonged muscle-wasting, or cachexia, can lead to
lasting or even permanent health problems. Studies show 60 percent to
80 percent of ICU survivors suffer functional impairment or
“ICU-acquired weakness” post-discharge. Some can never pick up their children or do their favorite sports again, says Wischmeyer.
as ICU providers have to ask the question, ‘Are we creating survivors
or are we creating victims?’” he says. “It’s critical that we get it
right while they are still hospitalized with us.”
This novel ultrasound technology could potentially help them get it right.
initial study findings, presented at the International Symposium of
Critical Care and Emergency Medicine in Brussels in March, demonstrate
its power as a research tool, says San Millán. He has long suspected
that severe glycogen depletion was to blame for muscle-wasting in the
ICU and that some patients aren’t getting enough calories via their
“Now,” he says, “we have some data to prove it.”
if ICU clinicians could measure muscle glycogen daily, physicians could
better calibrate a patient’s nutrition and time any changes
appropriately. There comes a time when the muscles move past the acute
shock stage, begin to take up glycogen again, have the capacity to
rebuild, and more aggressive feeding and physical therapy might become
“If we intervene with a lot of calories too soon, we
are fighting the body’s needed response and that can cause its own
problems,” Wischmeyer says. “We have never been able to know when that
transition happens. It’s measurable now.”
envisions a day when bedside muscle-glycogen testing could be used
alongside ultrasound lean body mass testing to determine if, or when, an
ICU patient might need anti-catabolic drugs (like beta-blockers) or
anabolic agents (like oxandrolone) to boost muscle growth.
In the meantime, San Millán has already started using this ultrasound technology for a very different purpose.
times a week, dozens of CU Buffs football players file into his office
at the new CU Sports Medicine and Performance Center in Boulder to
determine just how much, or how little, fuel they have in their muscles,
and what they should do about it.
If glycogen levels look low, which can leave a player
vulnerable to muscle injury, the players advised to lay off. If they
look high, they might be advised to eat less to avoid weight gain. The
system he and other sports medicine specialists use today is the size of
a laptop and costs in the tens of thousands of dollars. But San Millán
foresees an affordable, cellphone-sized device on the market for
recreational runners and cyclists.
“It would enable them to dial in nutrition and workload in a way that hasn’t been possible before.”