Practice is the defining method for improving virtually every athletic trait, and flexibility is no exception. Much like training regularly with heavy weights makes you stronger, spending time at or near the limits of your range of motion will develop flexibility. It should be evident, then, that any tool that allows you to practice with a slightly larger range of motion will promote greater flexibility gains in the long run. In a recent study in the Journal of Strength and Conditioning Research, the use of ice was examined as a way to improve flexibility.
The reason why cryotherapy, or the use of ice as treatment, works for improving flexibility is a bit confusing. The accepted theory is the reverse of what you might think. Essentially the cold will cause vasodilation, or the widening of your blood vessels. Vasodilation allows for greater blood flow and higher temperature inside the muscle. This has a soothing effect on the musculature, which in turn reduces its resistance to being stretched.
Anyone who has ever used ice to treat an injury or to improve recovery may think this odd. Ice is generally used to lower tissue temperature and induce vasoconstriction (the opposite of vasodilation), which inhibits swelling. Swelling is the enemy of injury repair and exercise recovery. But for flexibility, ice is used for the opposite effect. If you’ve studied biology, you will know that this is the standard reaction of the body to external cold: to reduce blood flow to the superficial (near the surface) blood vessels, while increasing blood flow underneath to prevent heat loss.
In this study the researchers focused on the hamstrings. This group of muscles is large enough that the cold from cryotherapy can’t penetrate the whole muscle. This creates a steep temperature gradient, meaning that the muscle near the surface is much cooler than the muscle deep down. The deeper muscle then experiences increased blood flow, and theoretically, the muscle’s resistance against stretching is reduced. In fact, the researchers rejected anyone with too much leg fat, which could interfere with this gradient effect.
The researchers were also interested to see if different applications of icewould also have different effects. They used both crushed ice in a bag, which is a therapeutic standard, and the same crushed ice with water. Water conducts the warmth of the body away faster than air and ice alone. The researchers hypothesized that the combination of water and ice would yield superior flexibility benefits.
To test flexibility, the researchers used a slightly different type of PNF stretching than you may have heard about. If you’re not already familiar with it, PNF stretchingtypically utilizes an effect called autogenic inhibition, which is a fancy way of saying it makes the muscle you’re stretching tired. You stretch a muscle like the hamstrings and then periodically flex the hamstrings as well. In this study they used standard PNF, but followed it by a contraction of the hip flexors, which is intended to create a further inhibition of the hamstring muscles.
There was no substantial difference between the two types of ice, but the ice was definitely effective at improving flexibility. In fact, the ice alone increased flexibility by about six angular degrees before the stretching even began. Stretching alone improved flexibility by ten degrees, but stretching and ice together (both kinds of ice therapy) improved flexibility by about fourteen degrees.
There was a small, insignificant trend for the wetted ice to work better, but essentially there’s a big point of diminishing returns somewhere around plain old ice in a bag. However, icing large muscles prior to flexibility sessions is a tool coaches and athletes should be employing where flexibility is a concern.
References:
1. Chelsea Larsen, et. al., “Effects of Crushed Ice and Wetted Ice on Hamstring Flexibility After PNF Stretching,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000340
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