Measuring Blood Flow and Muscle Stiffness for Performance and Injury Prevention

For decades, the benefits of stretching, when, how often and how much, have been grist for the debate mill. Some exercise scientists think stretching is a total waste of time, some think it is beneficial when done in a specific context, and some feel it is critical to optimal performance and recovery, and should be an integral part of any training, warmup and recovery routine.

Regular static stretching gives your joints a broader range of motion and added mobility, but to be useful for athletic performance, mobility needs to be balanced with stability. Static stretching performed prior to a competition or intense exercise can reduce muscle stiffness and increase blood flow to the muscles and tendons, to potentially enhance performance and reduce the risk of injury.

The question is when to stretch, and for how long?

Elasticity is a fundamental property of muscle tissue. It allows muscles to elongate in response to force loads and then return to their original length. The elastic property of muscle facilitates contraction and protects muscles from injury. Muscle elasticity allows elastic energy to be stored and released from muscles and tendons during physical activity.

Muscle stiffness can be defined as the resistance of muscle tissue to a change in length, and can be calculated as change in force divided by a corresponding change in length, when the change in length comes from an external force or from external load. Stiff muscles can inhibit joint mobility and are vulnerable to ruptures when imposed forces exceed the muscle’s resistance to change in length.

Increased blood flow to the muscles warms them up and infuses muscle cells with oxygen, lowering their resistance to length change. Well-trained muscles are highly vascular, with substantially more capillaries, giving oxygenated blood greater access to muscle cells.

Warming up the muscles and stretching them before intense physical activity is thought to help improve performance and prevent injury, but the jury is still out on when is the best time to stretch prior to exercise, and how long static stretches should be held.

In a recent study (Caliskan et al., 2019), researchers wanted to know whether the length of time a static stretch is held would affect blood flow and muscle stiffness in the rectus femoris (thigh muscle) of adolescent male athletes.

The experiment:

In a recent study (Caliskan et al., 2019), researchers wanted to know whether the length of time a static stretch is held would affect blood flow and muscle stiffness in the rectus femoris (thigh muscle) of adolescent male athletes.

• Participants were 20 young male athletes with an average age of 14.5 years.
• Subjects were assigned to one of two groups: 2 min and 5 min
• The first group held a static stretch of their rectus femoris muscle for 2 minutes, and the second group held their stretch for 5 minutes
• Measurements for muscle stiffness were taken using shear wave elastography (SWE), and blood flow was measured using superior microvascular imaging (SMI), both pre- and post-stretch for both groups

The results:

• There was no significant change in muscle stiffness between pre- and post-stretch measurements in the 2 min group, while the 5 min group was significantly less stiff post-stretch compared to pre-stretch
• Post-stretch blood flow increased significantly in both groups compared to pre-stretch

The conclusion:

• Both SWE and SMI provide reliable quantitative data for measuring muscle stiffness and blood flow, respectively
• The researchers recommended 5 minutes of static stretching for rehab, but only 2 minutes for pre-exercise warmup
• They recommended 5 minutes of static stretching for post-exercise cool-down and recovery

However…

Despite the potential benefits cited by Caliskan et al., another meta-analysis of studies (Simic et al., 2012) concluded that static stretching prior to exercise has negative effects on maximal muscle strength and explosive muscular performance.

The debate goes on!

There are multiple field tests for flexibility and joint range of motion that have been used for decades to assess muscle stiffness, but they are mostly observational, or provide only primitive and imprecise tools for measurement.

More recently, technology has given us new tools to accurately measure muscle stiffness and blood flow using sonoelastography and superior microvascular imaging, underpinned by high resolution ultrasonography. These tools give us quantitative metrics that help us diagnose and treat injured muscles and tendons.

• Shear wave elastography (SWE), aka sonoelastography, uses diagnostic ultrasound to estimate soft tissue elasticity and stiffness. It is based on the premise that when compressed, soft and elastic tissue produces greater displacement (has more “give”) than stiff and rigid tissues.
• Superior microvascular imaging (SMI) also uses ultrasound imaging to visualize blood flow in low velocity and small diameter blood vessels. SMI suppresses noise from motion artifacts, enabling it to detect weaker signals that indicate blood flow in small vessels, which implies healing.

At NYDNRehab, we use both SWE and SMI to diagnose, rehabilitate and monitor the progress of healing muscle and tendon tissue. These tools have proven invaluable for gauging when an injured athlete is fully ready to return to play. They also help us determine if our physical therapy and chiropractic treatment protocols are effective in facilitating the healing process.

Having the ability to precisely and accurately quantify human movement and recovery has been a game-changer in the world of physical therapy and rehabilitation. Our Manhattan clinic features some of the most technologically advanced equipment found under one roof in the United States, for diagnosis, rehabilitation and performance enhancement.

Whether you are a top athlete, or just want to move like one, contact NYCNRehab today for the best physical therapy and chiropractic treatment in NYC. And be sure to ask about our TeleHealth services for people on the go.