Strength and Injury Prevention
Injury prevention has long been a topic of interest to researchers as injuries cost the medical system billions of dollars each year and cost individuals precious time or athletic seasons. The most commonly researched symptom is tight muscles. Tight muscles are more likely to be injured during intense exercise, however stretching rarely has been shown to decrease injury rates. This has made some very intelligent researchers ask a couple very important questions; Why are the muscles tight? And why wasn’t the stretching intervention effective?
First, as it turns out there are 2 different forms of muscle tightness. There is the tightness that comes from tissues being too short. This is treated with static stretching. A note on static stretching, for it to be effective at increasing tissue length, it needs to be held for a minimum of 30 seconds and you need a total of 5 minutes of stretching on that specific tissue in a week. The other kind of tightness is neurogenic tightness. This is tightness that comes from the central nervous system (brain and spinal cord) creating more tension in the system. This can come from a multitude of different things. One of the drivers can be weakness. When the body is too weak in a direction or plane of motion (the body thinks in motion not muscles), it will create tightness to prevent you from going in that motion that it cannot control. This can clinically be seen as weakness. Researchers have identified some minimum strength marks that when we see individuals drift below them, injury rates increase. Now this is not a guaranteed predictor of an injury, but it does give us insight on who is more likely to be injured and gives us actionable steps on what to do to prevent it.
In the knee, they have found that injuries often occur when the body struggles to control motion of turning in and the knee traveling in (internal rotation and adduction). Individuals should be able to generate 20% of their body weight in internal rotation and 35% of their body weight in holding their leg out to the side. An important note is that most traditional lifts used in strength training programs do not hit these movements. Squats, deadlifts, power clean all are fantastic exercises for creating strength in the forward/backward plane but do relatively little for the side to side plane, which is where most injuries occur. A proper strength training program should include single leg and staggered stance exercises to challenge the side to side strength and control of the hips.
In the shoulder, they found that a shoulder internal/external rotation ratio was a good predictor of whether or not an athlete was going to sustain a shoulder injury. To calculate this ratio you divide external rotation strength by internal rotation strength. The ideal ratio is .75 to 1.0. Anything under .75 and the athlete was much more likely to sustain an injury that led to lost playing time. This highlights another aspect of strength which is symmetry. Your training program should lead to strength gains in all planes and all motions on both sides of the body. This is especially important if you are an athlete that plays a one sided sport (anything throwing) or that is rotational.
Strength of the foot has been shown to predict injuries of the lower body as a whole, including injuries of the foot and ankle. An individual should be able to generate 10-20% of their body weight with their big toe and 7-15% with their lesser toes. This has also been shown to predict and prevent falls in the elderly as toe strength allows an individual to maintain their balance easier.
The main takeaways from this body of research is first, be strong on both sides of your body. Second, make sure that strength is in all planes of motion of all your joints. If you have symmetrical and balanced strength, you will already be miles ahead of your competitors. In our next post, we will address the neuromotor coordination aspect of movement and injuries.
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William D Bandy and others, The Effect of Time and Frequency of Static Stretching on Flexibility of the Hamstring Muscles, Physical Therapy, Volume 77, Issue 10, 1 October 1997, Pages 1090–1096,
Thomas, Ewan, et al. “The Relation between Stretching Typology and Stretching Duration: The Effects on Range of Motion.” International Journal of Sports Medicine, vol. 39, no. 04, 2018, pp. 243–254, https://doi.org/10.1055/s-0044-101146.
Møller M, Nielsen R, Attermann J, et al. Handball load and shoulder injury rate: a 31-week cohort study of 679 elite youth handball players. Br J Sports Med. 2017;51:231-237.
