Ultrasound therapy does nothing to help an injured skeletal muscle heal any faster, according to a new study conducted in rats.
Although ultrasound is one of the most frequently prescribed treatments for one of the most common sport and athletic injuries – skeletal muscle contusions – there's really no good scientific evidence showing that it treats injured muscles effectively, said Steven Devor, the study's lead author and an assistant professor of sport and exercise sciences at Ohio State University.
"Because the injured muscle feels better after ultrasound treatment, an athlete may be tempted to get back in the game before the skeletal muscle injury is really healed. This puts him at risk for more significant re-injury if the muscle isn't completely healed."
Devor and his colleagues used ultrasound to treat contusion injuries inflicted on rats' gastrocnemius muscles – the main muscle in the calf.
Ultrasound treatment didn't hasten healing at all, even when compared to injured muscles that weren't treated with ultrasound.
"It didn't make one bit of difference in the time it took the treated and non-treated calf muscles to heal," Devor said. "Millions of people receive ultrasound treatment every year for muscle injuries, with insurance companies usually covering the cost."
Ultrasound treatments can cost around $50 per 15-minute session.
The study appears in a recent issue of the International Journal of Sports Medicine.
The researchers dropped small weights – about six ounces – onto the gastrocnemius muscles of rats' right and left hind limbs. The impact created a contusion in each muscle.
"The injury is similar to what might happen to a field hockey player if she was struck in the calf with a hockey stick," Devor said.
The researchers treated one hind limb on each rat with ultrasound daily for seven days for five minutes per session. Ultrasound waves were transmitted through a small wand that was rubbed along the rats' limbs. The other limb, used as the control, was left to recover on its own. Rats were sacrificed at various points during the two-month study so that the researchers could evaluate how each gastrocnemius muscle was healing.
The researchers compared a variety of markers in the muscle tissue from the ultrasound treated and non-treated legs of each rat, including muscle mass, protein concentration and muscle fiber cross-section. Cross-section simply refers to the amount of force a muscle can exert – the greater the cross-section a muscle possesses, the more force it can produce.
A comparison of these markers led the researchers to conclude that the muscles treated with ultrasound healed at the same rate as the muscles that were left to heal naturally.
While Devor doesn't discount that ultrasound treatment may feel good, he worries that treating a sports-related muscle injury with ultrasound may give an athlete a false sense of security.
"Because the injured muscle feels better after ultrasound treatment, an athlete may be tempted to get back in the game before the skeletal muscle injury is really healed," Devor said. "This puts him at risk for more significant re-injury if the muscle isn't completely healed.
"I'm supportive of the placebo effect – massaging an injury may make the person feel better," he continued. "But in this case, ultrasound treatment didn't have any physiological effect. Medical practitioners who administer this treatment regularly need to ask more questions about its effectiveness in treating injured skeletal muscle."
The results from this study may readily translate to human muscular injuries, as the structure of skeletal muscle tissue is the same across species.
"Our skeletal muscle tissue is the same as what's in a rat, dog, cat, etc.," Devor said. "The difference is that the tissue is exposed to diverse hormonal environments."
He and his colleagues are continuing to study ultrasound therapy – they're currently looking at the effect that different types of ultrasound have on skeletal muscle contusion injuries.
In the meantime, Devor's best advice is that injured athletes let muscles heal as Mother Nature intended – on their own time.
This study was supported by a seed grant from Ohio State.
Devor conducted this work with Ohio State colleagues Timothy Kirby, an associate professor of sport and exercise sciences; Mark Merrick, an assistant professor with the School of Allied Medical Professions; and Linda Wilkin, a graduate student.